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Influence of tin substitution on negative thermal expansion of K2Zr2-xSnxP2SiO12 (x = 0 - 2) phosphosilicates ceramics
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Influence of tin substitution on negative thermal expansion of K2Zr2xSnxP2SiO12 (x = 0 - 2) phosphosilicates ceramics Daneshwaran Balaji, Triveni Rajashekhar Mandlimath, Sathasivam Pratheep Kumar∗ Materials Chemistry Research Laboratory, Department of Chemistry, KPR Institute of Engineering and Technology, Arasur, Coimbatore, 641407, Tamil Nadu, India
ARTICLE INFO
ABSTRACT
Keywords: Langbeinite phosphosilicates Powder XRD Negative thermal expansion Thermal analysis
In this research work, compounds of the chemical formula K2Zr2-xSnxP2SiO12 (x = 0, 0.5, 1, 1.5, 2) were synthesized by solution method and characterized by powder X-ray diffraction and spectroscopic techniques. Powder XRD analysis revealed that the phase formation temperature vary with the substitution of Sn4+ for Zr4+ at the octahedral site of langbeinite structure. The stretching and bending vibrational modes of PO43− and SiO44− tetrahedra were identified in the region of 407 cm−1 - 1094 cm−1. Thermogravimetric analysis proved that the compounds K2Zr2P2SiO12 and K2Sn2P2SiO12 were thermally stable up to 1000 °C and 650 °C, respectively. Interestingly, negative thermal expansion coefficient was observed for the solid solutions K2Zr2xSnxP2SiO12 (X = 0, 0.5, 1, 1.5, 2). The average thermal expansion coefficients of K2Zr2P2SiO12, K2Zr1.5Sn0.5P2SiO12, K2ZrSnP2SiO12, K2Zr0.5Sn1.5P2SiO12 and K2Sn2P2SiO12 in the temperature range 30 °C–600 °C were found to be −7.01 × 10−6/°C, −4.96 × 10−6/°C, −1.08 × 10−5/°C, −1.53 × 10−5/°C and −1.27 × 10−5/°C, respectively. Coefficient of thermal expansion was increased by the substitution of tin for zirconium. The increase was obvious up to 250 °C and stabilized after 300 °C. The ionic radii, bond strength, structural distortion, density and microstructures were considered to explain the variation in thermal expansion.
1. Introduction Development of Negative Thermal Expansion (NTE) material is turned out to be an ever increasing area of interest in the field of Science and Technology since the discovery of ZrW2O8 by Sleight et al. [1]. NTE ceramics show considerable significance in the fabrication of zero or low thermal expansion materials combined with positive thermal expansion materials [2]. In addition, these materials play an important role to enhance the properties such as thermal stability, thermal shock resistance, thermal conductivity, radiation resistance and structural stability [1–7] for cook top panels, electronic devices, nuclear and space technologies, automobile engines, modern equipment, telescopes, optoelectronics and high precision instruments [2,4,8]. Ceramics are identified as low, zero and NTE materials. For instance, ZrW2O8 shows an average volume expansion of −2.73 × 10−5 K−1 in the temperature range 0–300 K [9]. Low thermal expansive lithium aluminium silicate, Invar (Fe–Ni alloy) and super Invar (Fe–Ni – Co alloy) are reported in the literature [10,11]. AM2O7 (A = Ti, Zr, Hf; M = P, V) family members [12] and cyanide bridged materials Cd(CN)2 [13] exhibit high NTE. Similarly, zircon (αav = 4.2 × 10−6 K−1) and cordierite (αav = 1.4 × 10−6 K−1) ∗
ceramics are considered as low thermal expansion materials [14,15]. Recently, NTE coefficient for an orthorhombic HfMn(MoO4)3 is observed as −3.8 × 10−6 K−1 in the range of 400 K–700 K [16]. Among various existing low/zero thermal expansion ceramics, phosphates show much attention due to their structural feasibility in tailoring NTE materials and phase transformations [17–19]. Sodium Zirconium Phosphate (NaZr2(PO4)3 (NZP)) and its family members with rhombohedral structure and R-3c space group are extensively studied as low, zero and NTE materials [20,21]. The crystal structure consist of a framework [M2(XO4)3], in which MO6 octahedra is interconnected with XO4 tetrahedra by corner sharing oxygen atoms and creates interstitial positions for the occupation of heterovalent ions [22]. Phosphates such as AZr2(PO4)3 (A = Na, K, Rb, Cs), NaHf2(PO4)3, CsHf2(PO4)3, MX2(PO4)3 (M = Li, Na, K; X = Ti, Ge), A0.52+Zr2(PO4)3 (A = Ca, Sr, Cd, Ba), Sr0.5Hf2(PO4)3, Ca0.5Ti2(PO4)3, Sr0.5Ti2(PO4)3, Ca0.25Sr0.25Zr2(PO4)3 are explored as low and NTE ceramics [21,23–25]. Similarly, thermal expansion of NZP structure is studied with different ionic substitutions at XO4 site. LiZr2AsxP3-xO12, Na1+xZr2SixP3-xO12 solid solutions, CsZr2(AsO4)3, CsZr2(AsO4)1.5(PO4)1.5 and CsZr2(VO4)0.2(PO4)2.8 are identified as few examples for anionic substitutions at tetrahedral site of NZP structure, which exhibit low thermal expansion [26–30].
Corresponding author. E-mail addresses: [email protected], [email protected] (S.P. Kumar).
https://doi.org/10.1016/j.ceramint.2020.02.181 Received 16 October 2019; Received in revised form 13 February 2020; Accepted 17 February 2020 0272-8842/ © 2020 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Daneshwaran Balaji, Triveni Rajashekhar Mandlimath and Sathasivam Pratheep Kumar, Ceramics International, https://doi.org/10.1016/j.ceramint.2020.02.181
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Though the NZP structured ceramics are prominent in producing NTE materials, thermal expansion of similar type structures such as K2Mn2(SO4)3, Mg3Al2(SiO4)3 and Sc2(WO4)3 are also investigated in the literature [31–33]. K2Mn2(SO4)3, a member of langbeinite structure is known for its important properties like ferroelectric, magnetic, catalytic, luminescence, dielectric and phase transition [31,34–37]. The basic unit [M2(XO4)3] of NZP and langbeinite polymorph is formed by the corner sharing MO6 octahedra and XO4 tetrahedra. NZP and langbeinite have similar framework but different spatial packing [36]. Most of the phosphates and sulphates of langbeinites are crystallized in a high temperature cubic phase with the space group of P213. However, few of them are also crystallized in low temperature orthorhombic phase with P212121 space group. For instance, K2M2(SO4)3 (M = Mn, Ni, Zn, Mg, Co) [38–42], phosphate with trivalent lanthanides and tetravalent zirconium ion at the M22+ position of langbeinite structure is crystallized in cubic system at room temperature [43,44] whereas, the compounds such as K2Cd2(SO4)3, K2Ca2(SO4)3 and vanadates of the formula MBaCr2(VO4)3 (M = Li, Na or Ag) are crystallized in orthorhombic system at room temperature [45–47]. The difference in cubic and orthorhombic langbeinite structures is owing to the coordination of ‘K’ ion with respect to oxygen atoms [46,48]. In cubic structure, the ‘K’ ion is coordinated with nine nearest oxygen atoms, whereas, the orthorhombic structure consist of two different K–O environment: K(1) ion is surrounded by ten nearest oxygen atoms and K (2) ion by nine oxygen atoms. This disordered K–O coordination reflects a slight change in the interatomic distance, atomic positions and a distortion in the angle of metal octahedra [46,48]. Thermal expansion of langbeinites is not explored well in the literature. Nevertheless, thermal expansion of few high temperature cubic phosphates such as KPbMgTi(PO4)3, K5/3MgTi4/3(PO4)3 and K5/3MgZr4/ 3(PO4)3 is reported as isotropic expansion materials [49]. In general, thermal expansion is influenced by the size, nature and electronegativity of cations and occupancy of cationic position in the framework. Several isovalent and heterovalent substitutions in NZP structure are reported in the literature for the improvement of thermal expansion characteristics [8,50]. Owing to the crystal structure similarity of NZP and langbeinite, it is presumed that the langbeinite compounds would also yield low thermal expansion at low temperature orthorhombic phase. Recently, we have investigated and reported a series of rare earth substituted orthorhombic langbeinite phosphosilicates and their chemical durability for high level nuclear waste storage [51]. Phosphosilicates are of our particular interest due to their importance as ionic conductors [52], phosphors [53], bioactive materials [54], electrolytes and cathode materials for batteries [55]. Recently Wang et al. and Tallentire et al. have found that the thermal expansion of zirconium phosphate ceramic is reduced by the substitution of tin for zirconium and silicon for phosphorus [56,57]. Further, due to the transverse vibration of bridging oxygens, most of the orthorhombic phases exhibit low or NTE when compared to cubic and monoclinic phases [16,58]. Considering the above factors along with the structural feasibility and unavailability of zirconium and tin substituted langbeinite phosphosilicates, herein, we report the fabrication of novel zirconium and tin containing phosphosilicates with langbeinite structure. The phase stability, spectral analysis and thermal expansion of solid solutions are investigated.
Fig. 1. Flow chart: Synthesis of K2Zr2-xSnxP2SiO12 (X = 0, 0.5, 1, 1.5, 2).
H3PO4 and Si(C2H5)4 were accurately weighted and dissolved separately in double distilled water and ethanol, respectively. Metal solutions of potassium and tin or zirconyl chloride were mixed together. To the metallic mixture, phosphate and subsequently silicate solutions were added dropwise with constant stirring. During the addition of phosphate and silicate solutions, the clear solution turned into turbid and finally the formation of precipitate was observed. The slurry was then further stirred for 30 min to attain the homogeneity. After homogenization, the gelatinous mixture was dried at 80 °C for 24 h. The dried precursor was calcined at 300, 500, 600, 800 and 900 °C for 8 h at each stage with intermittent grinding. Flow chart of the synthetic route is given in Fig. 1. 2.2. Characterization Powder XRD patterns were obtained by Bruker, D8 Advance diffractometer with CuKα radiation at room temperature. Unit cell parameters were obtained by least-squares method. FTIR spectra were recorded by JASCO, FT-IR/4100 spectrometer using KBr pellet in the frequency range of 400–4000 cm−1. Raman spectra for the powder samples were obtained by Bruker RFS 27: FT-Raman spectrometer equipped with Nd:YAG laser at 1064 nm. Scanning Electron Microscope (SEM) FEI Quanta FEG 200 SEM EDAX was used to obtain the surface morphology of the compounds. Thermal analysis was tested by TA instruments model SDT Q600 in the temperature range RT – 1000 °C. 2.3. Thermal expansion Bulk thermal expansion of the compounds was measured by push rod dilatometer (VB Ceramics Consultants, India) from RT to 600 °C at a rate of 5 °C/min [59]. Dilatometer consists of quartz made push rod, sample holder and a compact furnace. Type K- thermocouple is attached with the sample holder to measure the accurate temperature which will be displayed in Nippon PID programmable digital temperature indicator cum controller. A spring loaded configuration Linear Variable Displacement Transducer (LVDT) with the displacement range ± 1 mm and the resolution 100 nm is attached to one end of the push rod to convert the dilation change into EMF signal. The other end of the push rod is connected to have a contact with the sample. For thermal expansion analysis, powder samples were pressed into pellet by hydraulic pellet press with dimension 2.5 mm × 10 mm and sintered at 600 °C/8 h. The sintered pellets were polished, measured and analyzed. Coefficient of thermal expansion and percentage expansion were
2. Experimental procedure 2.1. Synthesis K2Zr2-xSnxP2SiO12 (x = 0, 0.5, 1.0, 1.5, 2) were synthesized by simple solution method. (COOK)2.H2O (99.9% S.D. Fine, India), ZrOCl2.8H2O (99.5%, SRL Chemicals, India), SnCl4.5H2O (99%, Sigma Aldrich, India), H3PO4 (85%, S.D. Fine, India) and Si(C2H5)4 (98% Sigma Aldrich, India) were used as starting materials. Initially, stoichiometric amount of (COOK)2.H2O and ZrOCl2.8H2O, SnCl4.5H2O, 2
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determined by considering the following formula. % Expansion = ΔL/L x 100 Coefficient of Thermal Expansion = (ΔL/L) / (Tmax – Tmin) Where L is initial length, ΔL is change in length and (Tmax –Tmin) is the difference between maximum and initial temperature. Reproducibility of the results was confirmed by triplication of the experiment. 3. Results and discussion 3.1. Phase formation and structure analysis Figs. 2 and 3 represent the powder XRD patterns of K2Zr2P2SiO12 (KZP) and K2Sn2P2SiO12 (KSP), calcined at different temperatures. Fig. 2 shows that the phase formation temperature for KZP is 800 °C, beyond which the impurity phase K2Zr(PO4)2 is appeared. Fig. 3 proves that the formation of orthorhombic langbeinite is started after 300 °C and completed at 600 °C. When the temperature is increased from 600 °C to 800 °C, the evolution of secondary phase which corresponds to KSnO(PO4) (ICDD No: 80–0894) is observed and it becomes predominant at 900 °C. This observation authenticates that the K2Sn2P2SiO12 is stable up to 600 °C and KZP is more stable than KSP when compared to the phase forming temperature of both the powder patterns. The difference in phase forming temperature is attributed to the bonding nature of Zr–O and Sn–O. Subsequent to the phase formation analysis, the powder XRD patterns of pure phases are compiled and shown in Fig. 4. All the peaks in the XRD patterns are indexed based on the orthorhombic langbeinite K2Ca2(SO4)3 (ICDD No: 74–0404). In KSP phase, the extra peak at 2θ = 24.2° is assigned as (220). In spite of the large number of existing cubic langbeinites, the prepared phosphosilicates are crystallized in orthorhombic structure. Formation of orthorhombic structure can be explained based on the size of substituted ions. The ionic radii of S, P
Fig. 3. Powder XRD patterns of K2Sn2P2SiO12 calcined at(a) 300 °C (b) 500 °C (c) 600 °C (d) 800 °C and (e) 900 °C.
and V from [S3O12], [P3O12] and [V3O12] in tetrahedral coordination is 0.36, 0.51 and 1.07 Å respectively. Survey of langbeinite type compounds indicate that most of the sulphates and phosphates are crystallized in cubic structure. However, vanadates of the formula MBaCr2(VO4)3 (M = Li, Na or Ag) are crystallized in orthorhombic symmetry [48]. Thus, it is understood that the replacement of lighter anionic group ([S3O12]/[P3O12]) by a bulkier anionic group ([V3O12]) in langbeinite structure lead to the transformation of cubic to orthorhombic system. Further, when the room temperature structures of K2Mg2(SO4)3 and K2Ca2(SO4)3 are compared, it is noted that the presence of bigger Ca2+ ion results a symmetry reduction. In the current systems 1/3rd of ‘PO4’ tetrahedra are replaced by bigger ‘SiO4’ tetrahedra [60]. Therefore, it is understood that the average size of the tetrahedra influences the structure and results in orthorhombic symmetry of the compounds K2Zr2P2SiO12 and K2Sn2P2SiO12. Crystallographically, Speer and Salje demonstrated that the driving force behind the structural transformation is due to the slight rotation of SO4 tetrahedra [46]. Similarly, in the present work the formation of orthorhombic langbeinite structure could be due to the distortion of ‘PO4’ tetrahedra with the substitution of Si. When the powder XRD patterns of KZP and KSP are compared, a shift in the peak positions towards higher angle and intensity variation are noticed for KSP phase (Fig. 4b). Table 1 represents the unit cell parameters and cell volume of KZP and KSP calculated by least-squares refinement method. It is expected that the cell parameters and volume of KSP would result smaller values than the KZP phase due to the smaller ionic radius of Sn4+ (0.69 Å) than Zr4+ (0.72 Å) [60]. However, since the size difference is very small, ‘a’ parameter is stabilized without any change and ‘b’, ‘c’ parameters show the slight variation for KSP when compared to KZP. The minor change in lattice parameters indicate that the crystal lattice is flexible in accommodating the
Fig. 2. Powder XRD patterns of K2Zr2P2SiO12 calcined at (a) 300 °C (b) 500 °C (c) 600 °C (d) 800 °C and (e) 900 °C. 3
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Fig. 4. Powder XRD patterns of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12. Fig. 5. Powder XRD patterns of K2Zr2-xSnxP2SiO12 (a) x = 0, (b) x = 0.5, (c) x = 1.0, (d) x = 1.5 and (e) x = 2).
Table 1 Lattice parameter and cell volume of K2Zr2-xSnxP2SiO12 (x = 0–2). Compounds
X=0
X = 0.5
X=1
X = 1.5
X=2
Space group a, Å b, Å c, Å V, Å3
P212121 10.22 (5) 10.23 (9) 10.22 (3) 1070
P212121 10.20 (7) 10.28 (1) 10.17 (2) 1067
P212121 10.20 (3) 10.27 (4) 10.17 (3) 1066
P212121 10.20 (7) 10.28 (2) 10.15 (6) 1065
P212121 10.22 (5) 10.28 (4) 10.16 (1) 1068
simultaneous substitution of ions in octahedral and tetrahedral positions of three dimensional langbeinite structure. In order to find the effect of Sn4+ substitution for Zr4+, solid solutions of the formula K2Zr2-xSnxP2SiO12 (X = 0, 0.5, 1.0, 1.5, 2) were prepared and characterized by powder XRD. The XRD patterns of tin substituted phases are shown in Fig. 5. Interpretation of the results emphasize that the replacement of Zr4+ by Sn4+ led to a notable deviation in the peak positions and intensity. When X = 0.5, the peaks (111), (210) and (211) are absent, whereas, they started to appear from X = 1 and predominant for X = 2. In addition to the intensity variation, peak shift is also noticed. The calculated unit cell parameters of K2Zr2-xSnxP2SiO12 (x = 0, 0.5, 1.0, 1.5, 2) are compared in Table 1. The slight change in a, b, c parameters and cell volume is observed with the replacement of zirconium ion by tin. Further, a keen observation of Fig. 5d, reveals that the appearance of both broad and sharp peaks in the XRD pattern, which indicates the possibility of secondary phase formation. This led us to give more attention on the tin substituted phases. The analysis of Fig. 5b, c and 5d with the other possible phases shows that few peaks have close match with R-3c (Rhombohedral, ICDD: 48–1100) space group along with P212121 space group. The peaks are, when x = 0.5; 2θ = 40.51°, x = 1; 2θ = 13.90°, 18.97° and x = 1.5; 2θ = 13.99°, 19.15°, 20.61°, 23.49°, 30.68°.
Fig. 6. FT-IR spectra of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12.
3.2. FT-IR and Raman analysis The FT-IR spectra of KZP and KSP are depicted in Fig. 6. Stretching and bending vibrational modes of (P–O) and (Si–O) are observed in the region 407 cm−1 - 1094 cm−1. The IR assignments of phosphate and 4
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Table 2 FTIR and Raman assignments for K2Zr2P2SiO12 and K2Sn2P2SiO12. Assignments
K2Zr2P2SiO12 IR (cm
PO43−
SiO44−
v3 v1 v4 v2
(vas)
v3 v1 v4 v2
(vas)
(vs) (δas) (δs) (vs) (δas) (δs)
−1
K2Sn2P2SiO12 −1
)
Raman (cm
1094,1024
1172, 1051 916 627, 558 444
577, 559 460 887 790,500 440, 409
1020 745 444
)
IR (cm−1)
Raman (cm−1)
1045,1012 935 580, 560 479, 469
1180,1053 633, 588 453
877 779, 505 438, 407
1011 868 726 341
silicate groups are given in Table 2. Due to the overlapping of phosphate and silicate vibrational bands, a broad peak is noticed between 1012 and 1094 cm−1, which corresponds to the stretching bands of (P–O) and (Si–O) [51]. The peak broadness is high for KSP when compared to KZP. In addition to the broadness, the effect of tin substitution is apparent in the spectrum (Fig. 6b) by means of additional bands at 935 cm−1 and 469 cm−1. Further, a shift in both stretching and bending modes is observed in KSP. The red and blue shift in FTIR and Raman spectra could be attributed to the factors such as electronegativity, bond strength and the crystallinity of the material. Additionally, the lower electronegativity of Zr (1.33) compared to Sn (1.96) and the higher bond strength of Zr–O (0.671) than Sn–O (0.422) are also considered to be the responsible factors for the shift. Since langbeinite structure exists in different phases, Raman spectra of KZP and KSP were recorded to support the powder XRD results. For comparison, a known cubic langbeinite K2FeZrP3O12 (KFZP) was prepared and characterized. Raman spectra of KZP, KSP and KFZP are shown in Fig. 7. Though the Raman bands correspond to PO43− and SiO44− are assigned similar to the FTIR vibrational modes, interestingly a major difference is observed between the region 950 cm−1 and 1150 cm−1. As noted by Kreske and Devarajan, additional Raman bands are observed for the orthorhombic KZP and KSP when compared to the cubic KFZP [33]. A broad band at 1050 cm−1 is observed for KFZP, whereas, it is transformed into narrow and splitted as two bands at ~1020 and 1050 cm−1 for the orthorhombic KZP and KSP. The band splitting is apparently visible for the compound KSP. Similar to our results, the peak splitting in orthorhombic structure is also observed by Sakai et al. in their phase transition study on K2Mn2(SO4)3 [61]. Thus, the orthorhombic structure of KZP and KSP is
Fig. 8. TGA traces of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12.
further evidenced by the Raman spectra. The peak splitting in KZP and KSP could be attributed to the loss of symmetry due to the nonequivalent PO43− and SiO44− ions. 3.3. Thermal and SEM-EDAX study TGA curves of the calcined powders KZP and KSP are shown in Fig. 8 between 30 °C and 1000 °C. It is clear from the TGA traces that the compounds KZP and KSP are thermally stable up to 1000 °C and 650 °C, respectively. In case of KSP, the gradual weight loss up to 5 wt % is observed between 30 °C and 300 °C, which corresponds to the loss of adsorbed moisture content. Similarly, 13.5 wt % loss is noted in the range 650 °C–800 °C due to the decomposition of KSP and formation of KSnO(PO4). This is corroborated by the x-ray analysis. Compared to the powder XRD patterns of KSP calcined at 600 °C and 800 °C, it is apparent that the phase is decomposed and the secondary phase is evolved after 800 °C. Thus, the TGA curves and powder X-ray diffraction analysis of KSP confirmed that the weight loss observed above 650 °C is due to the decomposition of the compound. The lower and higher magnified scanning electron micrographs of both KZP and KSP are shown in Fig. 9. SEM image of KZP (Fig. 9 a) depicts that the particles are stacked by one another and there is no specified shape. In KSP, the existence of pores and cubic shaped particles are noticed along with the agglomeration. Quantitative elemental analysis (Wt. %) of both KZP and KSP, obtained by energy dispersive Xray analysis are compared with the theoretical Wt. % of the elements and given in Table 3. The experimental results indicate that the values are closely matching with the theoretical values. 3.4. Thermal expansion Figs. 10 and 11 represent the average thermal expansion and coefficient of thermal expansion (CTE) curves for KZP and KSP, respectively. Fig. 10 illustrates that the average thermal expansion of KZP and KSP increase sharply in a negative scale from 30 °C - 250 °C and gradually from 250 °C to 600 °C. Nevertheless, KSP exhibits a drastic increase up to 250 °C and gradual decrease in the range 250 °C–500 °C and stabilized after 500 °C. Effect of tin substitution on thermal expansion is apparent from the average CTEs. The average CTE of K2Zr2P2SiO12, K2Zr1.5Sn0.5P2SiO12, K2ZrSnP2SiO12, K2Zr0.5Sn1.5P2SiO12 and K2Sn2P2SiO12 between 30 °C and 600 °C are −7.01 × 10−6/°C, −4.96 × 10−6/°C, −1.08 × 10−5/°C, −1.53 × 10−5/°C, −1.27 × 10−5/°C respectively. Table 4 represents the average CTEs of K2Zr2-xSnxP2SiO12 (X = 0, 0.5, 1.0, 1.5, 2). It can be seen from Table 4 that, when x = 0.5, the CTE decreased slightly compared to x = 0 and increased gradually when x = 1 and 1.5. For the compound KSP, the
Fig. 7. Raman spectra of (a) K2FeZrP3O12 (b) K2Zr2P2SiO12 and (c) K2Sn2P2SiO12. 5
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Fig. 10. Average thermal expansion of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12. Fig. 9. SEM images of (a) K2Zr2P2SiO12and (b) K2Sn2P2SiO12. Inset shows higher magnified images. Table 3 Elemental analysis of KZP and KSP by EDX. Elements
Weight percentage K2Zr2P2SiO12
K Zr P Si a
K2Sn2P2SiO12
Theoritical
Experimentala
Theoritical
Experimentala
14.4 33.6 11.4 5.2
12.6 29.5 9.2 4.3
13.1 39.7 10.4 4.7
11.2 34.8 10.8 3.5
Average of three different spots.
average CTE is one magnitude higher than that of KZP and slightly lower than the composition where x = 1.5. Overall, a large expansion at lower temperature and smaller and linear expansion at higher temperature are observed for all the compositions. The absence of any sharp peaks during cooling indicates that there is no phase change occur in both KZP and KSP. The influence of tin substitution in CTE can be explained based on several factors such as the ionic radii, bond strength, thermal stress resistance, microstructure, porosity and density. (i) The initial dimensional expansion is attributed to the non-linear increase of instrument temperature as observed by Wang et al. for tin substituted NZP system [56]. (ii) The smaller ionic radius of Sn4+ (rSn = 0.69 Å) compared to Zr4+ (rZr = 0.72 Å) led to higher thermal expansion. This is in good
Fig. 11. Thermal expansion coefficient of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12.
agreement with the literature report [20]. It is presumed that the replacement of larger ZrO6 octahedra by a smaller SnO6 octahedra in a M2(XO4)3 fragment led to the contraction of crystal lattice and made the structure to more closely packed. Though the simultaneous substitution of Sn4+ for Zr4+ and Si4+ for P5+ is expected to stabilize the crystal lattice, the ionic size difference might have distorted the structural polyhedra by promoting the deformation of structure, which resulted a linear expansion. (iii) Tallentire et al., and Kutty et al., reported that the substitution of Sn for Zr could control the CTE due to the 6
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and experimental density and porosity of the 600 °C fired pellets are given in Table 5. The difference between theoretical and experimental density is due to the porosity of the sample. The SEM images of the sintered pellets are shown in Fig. 12. It is clearly visible from the image that KZP is more porous than KSP. The average pore size of KZP and KSP calculated from ImageJ software is 0.34 μm and 0.17 μm respectively. Thus based on the density and microstructure analysis, it is evident that the sample KZP is highly porous and less dense than the sample KSP. The SEM and density results corroborate the thermal expansion of KZP and KSP. KZP undergoes more contraction than KSP due to the higher porosity and lower density. The effect of porosity and density on thermal expansion have been reported by Wang et al. and Liu et al. [63,64]. Thus, the above factors combined together led to control negative expansion upon tin substitution.
Table 4 Coefficient of Thermal expansion (CTE) of K2Zr2-xSnxP2SiO12 (x = 0–2). K2Zr2-xSnxP2SiO12
CTE ( × 10−6/°C)
x x x x x
−7.01 −4.96 −0.108 −0.153 −0.127
= = = = =
0 0.5 1 1.5 2
Table 5 Density and porosity of KZP and KSP. Compounds
KZP KSP a b
Density (g/cm3)
Average Porosity (%)
Theoretical
Experimental
Theoreticala
Experimentalb
2.329 2.687
3.433 3.783
37.5 20.1
34.8 17.4
4. Conclusions Negative thermal expansion ceramics of the formula K2Zr2(x = 0, 0.5, 1, 1.5, 2) with langbeinite structure were successfully synthesized. Spectral analysis confirmed the phase formation, structure and compositions. Thermal expansion of zirconium phosphosilicates was controlled by the replacement of zirconium by tin in the octahedral site of langbeinite structure. Effect of tin was analyzed based on the ionic size, bond strength, porosity, density and microstructure. The results emphasize that KZP and tin substituted ceramics could be a good additive to develop challenging zero thermal expansion materials. A remarkable change in the average thermal expansion coefficient was observed by the substitution of tin (K2Sn2P2SiO12: 1.27 × 10−5/°C) for zirconium in KZP (K2Zr2P2SiO12 (−7.01 × 10−6/ °C). This indicate that tin is an important substituent for controlling the thermal expansivity of zirconium based compounds related to M2(XO4)3 structures. xSnxP2SiO12
Calculated from density and. Calculated from SEM image.
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments The authors are thankful to the Science and Engineering Research Board, Department of Science and Technology, India for the financial support (Grant No: EEQ/2017/000740). One of the authors S. Pratheep Kumar also thank Dr. G. Buvaneswari, Professor, VIT University, India for her valuable suggestions in finding novel phases. KPR Institute of Engineering and Technology is acknowledged for providing necessary facilities. References [1] A.W. Sleight, Compounds that contract on heating, Inorg. Chem. 37 (1998) 2854–2860, https://doi.org/10.1021/ic980253h. [2] J. Chen, L. Hu, J. Deng, X. Xing, Negative thermal expansion in functional materials, Chem. Soc. Rev. 44 (2015) 3522–3567, https://doi.org/10.1039/ C4CS00461B. [3] N. Anantharamulu, K. K Rao, G. Rambabu, V. B Kumar, V. Radha, M. Vithal, A wideranging review on Nasicon type materials, J. Mater. Sci. 46 (2011) 2821–2837, https://doi.org/10.1007/s10853-011-5302-5. [4] K. Kamali, T.R. Ravindran, N.V. C Shekar, K.K. Pandey, S.M. Sharma, Pressure induced phase transformations in NaZr2(PO4)3 studied by X-ray diffraction and Raman spectroscopy, J. Solid State Chem. 221 (2015) 285–290, https://doi.org/10. 1016/j.jssc.2014.10.017. [5] V.I. Petkov, E.A. Asabina, Thermophysical properties of NZP ceramics (A review), Glass Ceram. 61 (2004) 233–239, https://doi.org/10.1023/B:GLAC.0000048353. 42467.0a. [6] V.I. Petkov, E.A. Asabina, V. Loshkarev, M. Sukhanov, Systematic investigation of the strontium zirconium phosphate ceramic form for nuclear waste immobilization, J. Nucl. Mater. 471 (2016) 122–128, https://doi.org/10.1016/j.jnucmat.2016.01. 016.
Fig. 12. SEM images of sintered pellets (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12.
distortion of O–Sn–O and Sn–O–P bonds [57,62]. Similar to their observation, our results show higher CTE for KSP than KZP. (iv) In addition to the effect of ionic size and bond strength, microstructure, density and porosity of the fired pellets play a vital role in the bulk thermal expansion behaviour [63]. To corroborate the thermal expansion data, the surface morphology of KZP and KSP pellets was recorded and density was calculated by Archimedes principle. The theoretical 7
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D. Balaji, et al. [7] V.I. Petkov, Complex phosphates formed by metal cations in oxidation states I and IV, Russ. Chem. Rev. 81 (2012) 606–637, https://doi.org/10.1070/ RC2012v081n07ABEH004243. [8] V.I. Petkov, A.I. Orlova, Crystal-chemical approach to predicting the thermal expansion of compounds in the NZP Family, Inorg. Mater. 39 (2003) 1013–1023, https://doi.org/10.1023/A:1026074722220. [9] T.A. Mary, J.S.O. Evans, T. Vogt, A.W. Sleight, Negative thermal expansion from 0.3 to 1050 K in ZrW2O8, Sci 272 (1996) 90–92, https://doi.org/10.1126/science.272. 5258.90. [10] L. Xia, G. Wen, L. Song, X. Wang, The crystallization behavior and thermal expansion properties of eucryptite prepared by sol–gel route, Mater. Chem. Phys. 119 (2010) 495–498, https://doi.org/10.1016/j.matchemphy.2009.10.003. [11] T. Nagayama, T. Yamamoto, T. Nakamura, Thermal expansions and mechanical properties of electrodeposited Fe–Ni alloys in the Invar composition range, Electrochim. Acta 205 (2016) 178–187, https://doi.org/10.1016/j.electacta.2016. 04.089. [12] V. Korthuis, N. Khosrobvani, A.W. Sleight, N. Roberts, R. Dupree, W.W. Warren Jr., Negative thermal expansion and phase transitions in the ZrV2-xPxO7 series, Chem. Mater. 7 (1995) 412–417, https://doi.org/10.1021/cm00050a028. [13] A.E. Philips, A.L. Goodwin, G.J. Halder, P.D. Southon, C.J. Kepert, Nanoporosity and exceptional negative thermal expansion in single-network cadmium cyanide, Angew. Chem. Int. 47 (2008) 1396–1399, https://doi.org/10.1002/anie. 200704421. [14] I. Yanase, M. Miyagi, H. Kobayashi, Fabrication of zero-thermal-expansion ZrSiO4/ Y2W3O12 sintered body, J. Eur. Ceram. Soc. 29 (2009) 3129–3134, https://doi.org/ 10.1016/j.jeurceramsoc.2009.06.001. [15] A.M. Efremov, G. Bruno, B.R. Wheaton, Texture coefficients for the simulation of cordierite thermal expansion: a comparison of different approaches, J. Eur. Ceram. Soc. 31 (2011) 281–290, https://doi.org/10.1016/j.jeurceramsoc.2010.10.005. [16] Y. Liu, B. Yuan, Y. Cheng, E. Liang, X. Ge, H. Yuan, Y. Zhang, J. Guo, M. Chao, Phase transition and negative thermal expansion of HfMnMo3O12, Mater. Res. Bull. 99 (2018) 255–259, https://doi.org/10.1016/j.materresbull.2017.11.009. [17] Y. Liu, M.S. Molokeev, Q. Liu, Z. Xia, Crystal structure, phase transition and thermal expansion property of NaZr2(PO4)3-SrZr4(PO4)6 solid solutions, Inorg. Chem. Front. 5 (2018) 619–625, https://doi.org/10.1039/C7QI00782E. [18] J.S.O. Evans, Negative thermal expansion materials, Dalton Trans. (1999) 3317–3327, https://doi.org/10.1039/A904297K. [19] C. Thieme, C. Russel, Very high or close to zero thermal expansion by the variation of the Sr/Ba ratio in Ba1−xSrxZn2Si2O7 – solid solutions, Dalton Trans. 45 (2016) 4888–4895, https://doi.org/10.1039/C5DT04970A. [20] P. Oikonomou, C. Dedeloudis, C.J. Stournaras, C. Fitkos, [NZP], A new family of ceramics with low thermal expansion and tunable properties, J. Eur. Ceram. Soc. 27 (2007) 1253–1258, https://doi.org/10.1016/j.jeurceramsoc.2006.04.021. [21] K.V.G. Kutty, R. Asuvathraman, R. Sridharan, Thermal expansion studies on the sodium zirconium phosphate family of compounds A1/2M2(PO4)3: effect of interstitial and framework cations, J. Mater. Sci. 33 (1998) 4007–4013, https://doi.org/ 10.1023/A:1004661132398. [22] M. Barre, M.P.C. Lopez, F.L. Berre, J. Emery, E. Suard, J.L. Fourrquet, Room temperature crystal structure of La1/3Zr2(PO4)3, a NASICON-type compound, Chem. Mater. 17 (2005) 6605–6610, https://doi.org/10.1021/cm0515045. [23] V.I. Petkov, A.I. Orlova, G.N. Kazantsev, S.G. Samoilov, M.L. Spiridonova, Thermal expansion in the Zr and 1-, 2-valent complex phosphates of NaZr2(PO4)3 (NZP) structure, J. Therm. Anal. Calorim. 66 (2001) 623–632, https://doi.org/10.1023/ A:1013145807987. [24] S.Y. Limaye, A.K. Agrawal, R. Roy, Y. Mehrotra, Synthesis, sintering and thermal expansion of Cal-xSrxZr4P6O24 - an ultra-low thermal expansion ceramic system, J. Mater. Sci. 26 (1991) 93–98, https://doi.org/10.1007/BF00576037. [25] D.A. Woodcock, P. Lighfoot, R.I. Smith, Powder neutron diffraction studies of three low thermal expansion phases in the NZP family: K0.5Nb0.5Ti1.5(PO4)3, Ba0.5Ti2(PO4)3 and Ca0.25Sr0.25Zr2(PO4)3, J. Mater. Chem. 9 (1999) 2631–2636, https://doi.org/10.1039/A903489G. [26] D.O. Savinykh, S.A. Khainakov, A.I. Orlova, S. Garcia-Granda, New phosphatesulfates with NZP structure, Russ. J. Inorg. Chem. 63 (2018) 714–724, https://doi. org/10.1134/S0036023618060207. [27] W. Haizeng, P. Wenqin, Hydrothermal synthesis and characterization of NaZr2(AsO4)3, J. Mater. Chem. 3 (1993) 989, https://doi.org/10.1039/ JM9930300989. [28] V.I. Petkov, M.V. Sukhanov, A.S. Shipilov, V.S. Kurazhkovskaya, E.Y. Borovikova, I.Y. Pinus, A. Yaroslavtsev, Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4)x(PO4)3–x, Inorg. Mater. 50 (2014) 263–272, https://doi.org/10.1134/ S0020168514030091. [29] H.P. Hong, Crystal structures and crystal chemistry in the system Nal+xZr2SixP3xO12, Mater. Res. Bull. 11 (1976) 173–182, https://doi.org/10.1016/00255408(76)90073. [30] V.I. Petkov, A.S. Shipilov, M.V. Sukhanov, Thermal expansion of MZr2(AsO4)3 and MZr2(TO4)x(PO4)3-x (M = Li, Na, K, Rb, Cs; T = As, V), Inorg. Mater. 51 (2015) 1079–1085, https://doi.org/10.1134/S002016851510012X. [31] N. Yamada, Y. Chubachi, T. Ikeda, Optical and dielectric properties of K2Mn2(SO4)3, J. Phys. Soc. Jpn. 45 (1978) 1638–1644, https://doi.org/10.1143/JPSJ.45.1638. [32] T. Lauret, R. Jacques, R. Pascal, High-temperature thermal expansion and decomposition of garnets, Eur. J. Mineral 10 (1998) 7–16, https://doi.org/10.1127/ejm/ 10/1/0007. [33] M.T. Weller, P.F. Henry, C.C. Wilson, An analysis of the thermal motion in the negative thermal expansion material Sc2(WO4)3 using isotopes in neutron diffraction, J. Phys. Chem. B 104 (2000) 12224–12229, https://doi.org/10.1021/ jp0030037.
[34] S. Kreske, V. Devarajan, Vibrational spectra and phase transitions in ferroelectricferroelastic langbeinites: K2Mn2(SO4)3, (NH4)2Cd2(SO4)3 and Tl2Cd2(SO4)3, J. Phys. C Solid State Phys. 15 (1982) 7333, https://doi.org/10.1088/0022-3719/15/36/ 015. [35] H. Oelkrug, T. Bruckel, D. Hohlwein, A. Hoser, W. Prandl, The magnetic structure of the langbeinite K2Mn2(SO4)3, Phys. Chem. Miner. 16 (1988) 246–249, https://doi. org/10.1007/BF00220692. [36] A.I. Orolova, I.G. Trubach, V.S. Kurazhkovskaya, P. Pertierra, M.A. Salvado, S. Garcia-Granda, S.A. Khainakov, J.R. Garcia, Synthesis, characterization, and structural study of K2FeZrP3O12 with the langbeinite structure, J. Solid State Chem. 173 (2003) 314–318, https://doi.org/10.1016/S0022-4596(03)00101. [37] M.B. Gawanda, S.S. Deshpande, S.U. Sonavane, R.V. Jayaraman, A novel sol–gel synthesized catalyst for Friedel–Crafts benzoylation reaction under solvent-free conditions, J. Mol. Catal. Chem. 241 (2005) 151–155, https://doi.org/10.1016/j. molcat.2005.06.069. [38] I.A. Trussov, L.L. Driscoll, L.L. Male, M.L. Sanjunan, A. Orera, P.R. Slater, Synthesis and structures of sodium containing K2-xNaxMg2(SO4)3 langbeinite phases, J. Solid State Chem. 276 (2019) 37–46, https://doi.org/10.1016/j.jssc.2019.04.036. [39] L. Lander, G. Rousse, D. Batuk, C.V. Colin, D.A.D. Corte, J.-M. Tarascon, Synthesis, structure, and electrochemical properties of K-based sulfates K2M2(SO4)3 with M = Fe and Cu, Inorg. Chem. 56 (2017) 2013–2021, https://doi.org/10.1021/acs. inorgchem.6b02526. [40] V.S. Jayakumar, I.H. Joe, G. Aruldhas, IR and single crystal Raman spectra of langbeinities M2+Ni2(SO4)3 (M+ = NH4, K), Ferroelectrics 165 (1995) 307–318, https://doi.org/10.1080/00150199508228311. [41] C. Moriyoshi, K. Itoh, T. Hikita, Structural study of phase transition in K2Zn2(SO4)3 langbeinite, Physica B 219–220 (1996) 602–604, https://doi.org/10.1016/09214526(95)00825-X. [42] M.J. L. Percival E. Salje, Optical absorption spectroscopy of the P213-P212121 transformation in K2Co2(SO4)3 langbeinite, Phys. Chem. Miner. 16 (1989) 563–568, https://doi.org/10.1007/BF00202212. [43] I.V. Ogorodnyk, I.V. Zatovsky, V.N. Baumer, N.S. Slobodyanik, O.V. Shishkin, Synthesis and crystal structure of langbeinite related mixed-metal phosphates K1.822Nd0.822Zr1.178(PO4)3 and K2LuZr(PO4)3, Crys, Respir. Technol. 42 (2007) 1076–1081, https://doi.org/10.1002/crat.200710961. [44] I.G. Trubach, A.I. Beskrovnyi, A.I. Orlova, V.A. Orlova, V.S. Kurazhkovskaya, Synthesis and investigation of the new phosphates K2LnZr(PO4)3 (Ln = Ce–Yb, Y) with langbeinite structure, Crystallogr. Rep. 49 (2004) 614–618, https://doi.org/ 10.1134/1.1780625. [45] S.C. Abrahams, F. Lissade, J.L. Bernstein, Piezoelectric langbeinite type K2Cd2(SO4)3 structure at four temperatures below and one above the 432°K ferroelastic–paraelastic transition, J. Chem. Phys. 68 (1978) 1926–1935, https://doi. org/10.1063/1.435919. [46] D. Speer, E. Salje, Phase transitions in langbeinites I: crystal chemistry and structures of K-double sulfates of the langbeinite M2++ Type K2(SO4)3, M++ = Mg, Ni, Co, Zn, Ca, Phys. Chem. Miner. 13 (1986) 17–24, https://doi.org/10.1007/ BF00307309. [47] M.A. Nabar, D.S. Phanasgaonkar, Spectral studies of triple orthovanadates MICr2(VO4)3 having langbeinite structure, Spectrochim. Acta 37A (1981) 279–281, https://doi.org/10.1016/0584-8539(81)80175-4. [48] V.A. Zeeman, J. Zeeman, Die kristallstruktur von langbeinit, K2M2(SO4)3, Acta Crystallogr. 10 (1957) 409–413, https://doi.org/10.1107/S0365110X57001346. [49] V.I. Petkov, A.S. Shipilov, A.S. Dmitrienko, A.A. Alekseev, Characterization and controlling thermal expansion of materials with kosnarite- and langbeinite type structures, J. Ind. Eng. Chem. 57 (2018) 236–243, https://doi.org/10.1016/j.jiec. 2017.08.029. [50] D.M. Bykov, R.J.M. Konings, C. Apostolidis, A. Hen, E. Colineau, T. Wiss, P. Raison, Synthesis and investigation of neptunium zirconium phosphate, a member of the NZP family: crystal structure, thermal behaviour and Mossbauer spectroscopy studies, Dalton Trans. 46 (2017) 11626–11635, https://doi.org/10.1039/ C7DT02110K. [51] S. Pratheep Kumer, G. Buvaneswari, New rare earth langbeinite phosphosilicates KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) for lanthanide comprising nuclear waste storage, J. Alloys Compd. 657 (2016) 422–429, https://doi.org/10.1016/j. jallcom.2015.10.088. [52] Q. Ma, M. Guin, S. Naqash, C.L. Tsai, F. Tietz, O. Guillon, Scandium-substituted Na3Zr2(SiO4)2(PO4) prepared by a solution assisted solid-state reaction method as sodium-ion conductors, Chem. Mater. 28 (2016) 4821–4828, https://doi.org/10. 1021/acs.chemmater.6b02059. [53] M. Jiao, W. Lv, W. Lu, Q. Zhao, B. Shao, H. You, Optical properties and energy transfer of a novel KSrSc2(PO4)3: Ce3+/Eu2+/Tb3+ phosphor for white light emitting diodes, Dalton Trans. 44 (2015) 4080–4087, https://doi.org/10.1039/ C4DT03906H. [54] D. Carta, R.J. Newport, J.C. Knowles, M.E. Smith, P. Guerry, Sol–gel produced sodium calcium phosphosilicates for bioactive applications: synthesis and structural characterization, Mater. Chem. Phys. 130 (2011) 690–696, https://doi.org/10. 1016/j.matchemphys.2011.07.050. [55] K.B. Hueso, M. Armand, T. Rojo, High temperature sodium batteries: status, challenges and future trends, Energy Environ. Sci. 6 (2013) 734–749, https://doi.org/ 10.1039/C3EE24086J. [56] Y. Wang, Y. Zhou, N. Tong, Z. Han, F. Liu, Crystal structure, mechanical and thermophysical properties of Ca0.5Sr0.5Zr4-xSnxP6O24 ceramics, J. Alloys Compd. 748 (2019) 8–15, https://doi.org/10.1016/j.jallcom.2018.12.379. [57] S.E. Tallentire, F. Child, I. Fall, L.V. Zarb, I.R. Evans, M.G. Tucker, D.A. Keen, C. Wilson, J.S.O. Evans, Systematic and controllable negative, zero and positive thermal expansion in cubic Zr1–xSnxMo2O8, J. Am. Chem. Soc. 135 (2013)
8
Ceramics International xxx (xxxx) xxx–xxx
D. Balaji, et al. 12849–12856, https://doi.org/10.1021/ja4060564. [58] H. Liu, X. Wang, Z. Zhang, X. Chen, Synthesis and thermal expansion properties of Y2-xLaxMo3O12 (x = 0, 0.5, 2), Ceram. Int. 38 (2012) 6349–6352, https://doi.org/ 10.1016/j.ceramint.2012.05.006. [59] P.H. Kumar, V.K. Singh, P. Kumar, G. Yadav, R.K. Chaturvedi, Effect of Al2O3 on leucite based bioactive glass ceramic composite for dental veneering, Ceram. Int. 42 (2016) 3591–3597, https://doi.org/10.1016/j.ceramint.2015.11.022. [60] R.D. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Crystallogr. A32 (1976) 751–767, https://doi.org/10.1107/S0567739476001551. [61] A. Sakai, M. Kitoh, M. Negishi, K. Itoh, Micro-Raman scattering study of the phase transition of K2Mn2(SO4)3, Ferroelectrics 217 (1998) 99–103, https://doi.org/10.
1080/00150199808015026. [62] K.V.G. Kutty, A. Asuvathraman, C.K. Mathews, U.V. Varadaraju, Effect of variation in framework composition on the thermal expansivity of NZP phases, Mater. Res. Bull. 29 (1994) 1009–1016, https://doi.org/10.1016/0025-5408(94)90081-7. [63] Y. Wang, Y. Zhou, Y. Song, L. Yang, F. Liu, Mechanical and thermal expansion studies on Ca0.5Sr0.5Zr4-xTixP6O24 ceramics, Ceram. Int. 44 (2018) 16698–16702, https://doi.org/10.1016/j.ceramint.2018.06.097. [64] Q. Liu, J. Yang, X. Rong, X. Sun, X. Cheng, H. Tang, H. Li, Structural, negative thermal expansion and photocatalytic properties of ZrV2O7: a comparative study between fibers and powders, Mater. Char. 96 (2014) 63–70, https://doi.org/10. 1016/j.matchar.2014.07.001.
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Influence of tin substitution on negative thermal expansion of K2Zr2xSnxP2SiO12 (x = 0 - 2) phosphosilicates ceramics Daneshwaran Balaji, Triveni Rajashekhar Mandlimath, Sathasivam Pratheep Kumar∗ Materials Chemistry Research Laboratory, Department of Chemistry, KPR Institute of Engineering and Technology, Arasur, Coimbatore, 641407, Tamil Nadu, India
ARTICLE INFO
ABSTRACT
Keywords: Langbeinite phosphosilicates Powder XRD Negative thermal expansion Thermal analysis
In this research work, compounds of the chemical formula K2Zr2-xSnxP2SiO12 (x = 0, 0.5, 1, 1.5, 2) were synthesized by solution method and characterized by powder X-ray diffraction and spectroscopic techniques. Powder XRD analysis revealed that the phase formation temperature vary with the substitution of Sn4+ for Zr4+ at the octahedral site of langbeinite structure. The stretching and bending vibrational modes of PO43− and SiO44− tetrahedra were identified in the region of 407 cm−1 - 1094 cm−1. Thermogravimetric analysis proved that the compounds K2Zr2P2SiO12 and K2Sn2P2SiO12 were thermally stable up to 1000 °C and 650 °C, respectively. Interestingly, negative thermal expansion coefficient was observed for the solid solutions K2Zr2xSnxP2SiO12 (X = 0, 0.5, 1, 1.5, 2). The average thermal expansion coefficients of K2Zr2P2SiO12, K2Zr1.5Sn0.5P2SiO12, K2ZrSnP2SiO12, K2Zr0.5Sn1.5P2SiO12 and K2Sn2P2SiO12 in the temperature range 30 °C–600 °C were found to be −7.01 × 10−6/°C, −4.96 × 10−6/°C, −1.08 × 10−5/°C, −1.53 × 10−5/°C and −1.27 × 10−5/°C, respectively. Coefficient of thermal expansion was increased by the substitution of tin for zirconium. The increase was obvious up to 250 °C and stabilized after 300 °C. The ionic radii, bond strength, structural distortion, density and microstructures were considered to explain the variation in thermal expansion.
1. Introduction Development of Negative Thermal Expansion (NTE) material is turned out to be an ever increasing area of interest in the field of Science and Technology since the discovery of ZrW2O8 by Sleight et al. [1]. NTE ceramics show considerable significance in the fabrication of zero or low thermal expansion materials combined with positive thermal expansion materials [2]. In addition, these materials play an important role to enhance the properties such as thermal stability, thermal shock resistance, thermal conductivity, radiation resistance and structural stability [1–7] for cook top panels, electronic devices, nuclear and space technologies, automobile engines, modern equipment, telescopes, optoelectronics and high precision instruments [2,4,8]. Ceramics are identified as low, zero and NTE materials. For instance, ZrW2O8 shows an average volume expansion of −2.73 × 10−5 K−1 in the temperature range 0–300 K [9]. Low thermal expansive lithium aluminium silicate, Invar (Fe–Ni alloy) and super Invar (Fe–Ni – Co alloy) are reported in the literature [10,11]. AM2O7 (A = Ti, Zr, Hf; M = P, V) family members [12] and cyanide bridged materials Cd(CN)2 [13] exhibit high NTE. Similarly, zircon (αav = 4.2 × 10−6 K−1) and cordierite (αav = 1.4 × 10−6 K−1) ∗
ceramics are considered as low thermal expansion materials [14,15]. Recently, NTE coefficient for an orthorhombic HfMn(MoO4)3 is observed as −3.8 × 10−6 K−1 in the range of 400 K–700 K [16]. Among various existing low/zero thermal expansion ceramics, phosphates show much attention due to their structural feasibility in tailoring NTE materials and phase transformations [17–19]. Sodium Zirconium Phosphate (NaZr2(PO4)3 (NZP)) and its family members with rhombohedral structure and R-3c space group are extensively studied as low, zero and NTE materials [20,21]. The crystal structure consist of a framework [M2(XO4)3], in which MO6 octahedra is interconnected with XO4 tetrahedra by corner sharing oxygen atoms and creates interstitial positions for the occupation of heterovalent ions [22]. Phosphates such as AZr2(PO4)3 (A = Na, K, Rb, Cs), NaHf2(PO4)3, CsHf2(PO4)3, MX2(PO4)3 (M = Li, Na, K; X = Ti, Ge), A0.52+Zr2(PO4)3 (A = Ca, Sr, Cd, Ba), Sr0.5Hf2(PO4)3, Ca0.5Ti2(PO4)3, Sr0.5Ti2(PO4)3, Ca0.25Sr0.25Zr2(PO4)3 are explored as low and NTE ceramics [21,23–25]. Similarly, thermal expansion of NZP structure is studied with different ionic substitutions at XO4 site. LiZr2AsxP3-xO12, Na1+xZr2SixP3-xO12 solid solutions, CsZr2(AsO4)3, CsZr2(AsO4)1.5(PO4)1.5 and CsZr2(VO4)0.2(PO4)2.8 are identified as few examples for anionic substitutions at tetrahedral site of NZP structure, which exhibit low thermal expansion [26–30].
Corresponding author. E-mail addresses: [email protected], [email protected] (S.P. Kumar).
https://doi.org/10.1016/j.ceramint.2020.02.181 Received 16 October 2019; Received in revised form 13 February 2020; Accepted 17 February 2020 0272-8842/ © 2020 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Daneshwaran Balaji, Triveni Rajashekhar Mandlimath and Sathasivam Pratheep Kumar, Ceramics International, https://doi.org/10.1016/j.ceramint.2020.02.181
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Though the NZP structured ceramics are prominent in producing NTE materials, thermal expansion of similar type structures such as K2Mn2(SO4)3, Mg3Al2(SiO4)3 and Sc2(WO4)3 are also investigated in the literature [31–33]. K2Mn2(SO4)3, a member of langbeinite structure is known for its important properties like ferroelectric, magnetic, catalytic, luminescence, dielectric and phase transition [31,34–37]. The basic unit [M2(XO4)3] of NZP and langbeinite polymorph is formed by the corner sharing MO6 octahedra and XO4 tetrahedra. NZP and langbeinite have similar framework but different spatial packing [36]. Most of the phosphates and sulphates of langbeinites are crystallized in a high temperature cubic phase with the space group of P213. However, few of them are also crystallized in low temperature orthorhombic phase with P212121 space group. For instance, K2M2(SO4)3 (M = Mn, Ni, Zn, Mg, Co) [38–42], phosphate with trivalent lanthanides and tetravalent zirconium ion at the M22+ position of langbeinite structure is crystallized in cubic system at room temperature [43,44] whereas, the compounds such as K2Cd2(SO4)3, K2Ca2(SO4)3 and vanadates of the formula MBaCr2(VO4)3 (M = Li, Na or Ag) are crystallized in orthorhombic system at room temperature [45–47]. The difference in cubic and orthorhombic langbeinite structures is owing to the coordination of ‘K’ ion with respect to oxygen atoms [46,48]. In cubic structure, the ‘K’ ion is coordinated with nine nearest oxygen atoms, whereas, the orthorhombic structure consist of two different K–O environment: K(1) ion is surrounded by ten nearest oxygen atoms and K (2) ion by nine oxygen atoms. This disordered K–O coordination reflects a slight change in the interatomic distance, atomic positions and a distortion in the angle of metal octahedra [46,48]. Thermal expansion of langbeinites is not explored well in the literature. Nevertheless, thermal expansion of few high temperature cubic phosphates such as KPbMgTi(PO4)3, K5/3MgTi4/3(PO4)3 and K5/3MgZr4/ 3(PO4)3 is reported as isotropic expansion materials [49]. In general, thermal expansion is influenced by the size, nature and electronegativity of cations and occupancy of cationic position in the framework. Several isovalent and heterovalent substitutions in NZP structure are reported in the literature for the improvement of thermal expansion characteristics [8,50]. Owing to the crystal structure similarity of NZP and langbeinite, it is presumed that the langbeinite compounds would also yield low thermal expansion at low temperature orthorhombic phase. Recently, we have investigated and reported a series of rare earth substituted orthorhombic langbeinite phosphosilicates and their chemical durability for high level nuclear waste storage [51]. Phosphosilicates are of our particular interest due to their importance as ionic conductors [52], phosphors [53], bioactive materials [54], electrolytes and cathode materials for batteries [55]. Recently Wang et al. and Tallentire et al. have found that the thermal expansion of zirconium phosphate ceramic is reduced by the substitution of tin for zirconium and silicon for phosphorus [56,57]. Further, due to the transverse vibration of bridging oxygens, most of the orthorhombic phases exhibit low or NTE when compared to cubic and monoclinic phases [16,58]. Considering the above factors along with the structural feasibility and unavailability of zirconium and tin substituted langbeinite phosphosilicates, herein, we report the fabrication of novel zirconium and tin containing phosphosilicates with langbeinite structure. The phase stability, spectral analysis and thermal expansion of solid solutions are investigated.
Fig. 1. Flow chart: Synthesis of K2Zr2-xSnxP2SiO12 (X = 0, 0.5, 1, 1.5, 2).
H3PO4 and Si(C2H5)4 were accurately weighted and dissolved separately in double distilled water and ethanol, respectively. Metal solutions of potassium and tin or zirconyl chloride were mixed together. To the metallic mixture, phosphate and subsequently silicate solutions were added dropwise with constant stirring. During the addition of phosphate and silicate solutions, the clear solution turned into turbid and finally the formation of precipitate was observed. The slurry was then further stirred for 30 min to attain the homogeneity. After homogenization, the gelatinous mixture was dried at 80 °C for 24 h. The dried precursor was calcined at 300, 500, 600, 800 and 900 °C for 8 h at each stage with intermittent grinding. Flow chart of the synthetic route is given in Fig. 1. 2.2. Characterization Powder XRD patterns were obtained by Bruker, D8 Advance diffractometer with CuKα radiation at room temperature. Unit cell parameters were obtained by least-squares method. FTIR spectra were recorded by JASCO, FT-IR/4100 spectrometer using KBr pellet in the frequency range of 400–4000 cm−1. Raman spectra for the powder samples were obtained by Bruker RFS 27: FT-Raman spectrometer equipped with Nd:YAG laser at 1064 nm. Scanning Electron Microscope (SEM) FEI Quanta FEG 200 SEM EDAX was used to obtain the surface morphology of the compounds. Thermal analysis was tested by TA instruments model SDT Q600 in the temperature range RT – 1000 °C. 2.3. Thermal expansion Bulk thermal expansion of the compounds was measured by push rod dilatometer (VB Ceramics Consultants, India) from RT to 600 °C at a rate of 5 °C/min [59]. Dilatometer consists of quartz made push rod, sample holder and a compact furnace. Type K- thermocouple is attached with the sample holder to measure the accurate temperature which will be displayed in Nippon PID programmable digital temperature indicator cum controller. A spring loaded configuration Linear Variable Displacement Transducer (LVDT) with the displacement range ± 1 mm and the resolution 100 nm is attached to one end of the push rod to convert the dilation change into EMF signal. The other end of the push rod is connected to have a contact with the sample. For thermal expansion analysis, powder samples were pressed into pellet by hydraulic pellet press with dimension 2.5 mm × 10 mm and sintered at 600 °C/8 h. The sintered pellets were polished, measured and analyzed. Coefficient of thermal expansion and percentage expansion were
2. Experimental procedure 2.1. Synthesis K2Zr2-xSnxP2SiO12 (x = 0, 0.5, 1.0, 1.5, 2) were synthesized by simple solution method. (COOK)2.H2O (99.9% S.D. Fine, India), ZrOCl2.8H2O (99.5%, SRL Chemicals, India), SnCl4.5H2O (99%, Sigma Aldrich, India), H3PO4 (85%, S.D. Fine, India) and Si(C2H5)4 (98% Sigma Aldrich, India) were used as starting materials. Initially, stoichiometric amount of (COOK)2.H2O and ZrOCl2.8H2O, SnCl4.5H2O, 2
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determined by considering the following formula. % Expansion = ΔL/L x 100 Coefficient of Thermal Expansion = (ΔL/L) / (Tmax – Tmin) Where L is initial length, ΔL is change in length and (Tmax –Tmin) is the difference between maximum and initial temperature. Reproducibility of the results was confirmed by triplication of the experiment. 3. Results and discussion 3.1. Phase formation and structure analysis Figs. 2 and 3 represent the powder XRD patterns of K2Zr2P2SiO12 (KZP) and K2Sn2P2SiO12 (KSP), calcined at different temperatures. Fig. 2 shows that the phase formation temperature for KZP is 800 °C, beyond which the impurity phase K2Zr(PO4)2 is appeared. Fig. 3 proves that the formation of orthorhombic langbeinite is started after 300 °C and completed at 600 °C. When the temperature is increased from 600 °C to 800 °C, the evolution of secondary phase which corresponds to KSnO(PO4) (ICDD No: 80–0894) is observed and it becomes predominant at 900 °C. This observation authenticates that the K2Sn2P2SiO12 is stable up to 600 °C and KZP is more stable than KSP when compared to the phase forming temperature of both the powder patterns. The difference in phase forming temperature is attributed to the bonding nature of Zr–O and Sn–O. Subsequent to the phase formation analysis, the powder XRD patterns of pure phases are compiled and shown in Fig. 4. All the peaks in the XRD patterns are indexed based on the orthorhombic langbeinite K2Ca2(SO4)3 (ICDD No: 74–0404). In KSP phase, the extra peak at 2θ = 24.2° is assigned as (220). In spite of the large number of existing cubic langbeinites, the prepared phosphosilicates are crystallized in orthorhombic structure. Formation of orthorhombic structure can be explained based on the size of substituted ions. The ionic radii of S, P
Fig. 3. Powder XRD patterns of K2Sn2P2SiO12 calcined at(a) 300 °C (b) 500 °C (c) 600 °C (d) 800 °C and (e) 900 °C.
and V from [S3O12], [P3O12] and [V3O12] in tetrahedral coordination is 0.36, 0.51 and 1.07 Å respectively. Survey of langbeinite type compounds indicate that most of the sulphates and phosphates are crystallized in cubic structure. However, vanadates of the formula MBaCr2(VO4)3 (M = Li, Na or Ag) are crystallized in orthorhombic symmetry [48]. Thus, it is understood that the replacement of lighter anionic group ([S3O12]/[P3O12]) by a bulkier anionic group ([V3O12]) in langbeinite structure lead to the transformation of cubic to orthorhombic system. Further, when the room temperature structures of K2Mg2(SO4)3 and K2Ca2(SO4)3 are compared, it is noted that the presence of bigger Ca2+ ion results a symmetry reduction. In the current systems 1/3rd of ‘PO4’ tetrahedra are replaced by bigger ‘SiO4’ tetrahedra [60]. Therefore, it is understood that the average size of the tetrahedra influences the structure and results in orthorhombic symmetry of the compounds K2Zr2P2SiO12 and K2Sn2P2SiO12. Crystallographically, Speer and Salje demonstrated that the driving force behind the structural transformation is due to the slight rotation of SO4 tetrahedra [46]. Similarly, in the present work the formation of orthorhombic langbeinite structure could be due to the distortion of ‘PO4’ tetrahedra with the substitution of Si. When the powder XRD patterns of KZP and KSP are compared, a shift in the peak positions towards higher angle and intensity variation are noticed for KSP phase (Fig. 4b). Table 1 represents the unit cell parameters and cell volume of KZP and KSP calculated by least-squares refinement method. It is expected that the cell parameters and volume of KSP would result smaller values than the KZP phase due to the smaller ionic radius of Sn4+ (0.69 Å) than Zr4+ (0.72 Å) [60]. However, since the size difference is very small, ‘a’ parameter is stabilized without any change and ‘b’, ‘c’ parameters show the slight variation for KSP when compared to KZP. The minor change in lattice parameters indicate that the crystal lattice is flexible in accommodating the
Fig. 2. Powder XRD patterns of K2Zr2P2SiO12 calcined at (a) 300 °C (b) 500 °C (c) 600 °C (d) 800 °C and (e) 900 °C. 3
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Fig. 4. Powder XRD patterns of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12. Fig. 5. Powder XRD patterns of K2Zr2-xSnxP2SiO12 (a) x = 0, (b) x = 0.5, (c) x = 1.0, (d) x = 1.5 and (e) x = 2).
Table 1 Lattice parameter and cell volume of K2Zr2-xSnxP2SiO12 (x = 0–2). Compounds
X=0
X = 0.5
X=1
X = 1.5
X=2
Space group a, Å b, Å c, Å V, Å3
P212121 10.22 (5) 10.23 (9) 10.22 (3) 1070
P212121 10.20 (7) 10.28 (1) 10.17 (2) 1067
P212121 10.20 (3) 10.27 (4) 10.17 (3) 1066
P212121 10.20 (7) 10.28 (2) 10.15 (6) 1065
P212121 10.22 (5) 10.28 (4) 10.16 (1) 1068
simultaneous substitution of ions in octahedral and tetrahedral positions of three dimensional langbeinite structure. In order to find the effect of Sn4+ substitution for Zr4+, solid solutions of the formula K2Zr2-xSnxP2SiO12 (X = 0, 0.5, 1.0, 1.5, 2) were prepared and characterized by powder XRD. The XRD patterns of tin substituted phases are shown in Fig. 5. Interpretation of the results emphasize that the replacement of Zr4+ by Sn4+ led to a notable deviation in the peak positions and intensity. When X = 0.5, the peaks (111), (210) and (211) are absent, whereas, they started to appear from X = 1 and predominant for X = 2. In addition to the intensity variation, peak shift is also noticed. The calculated unit cell parameters of K2Zr2-xSnxP2SiO12 (x = 0, 0.5, 1.0, 1.5, 2) are compared in Table 1. The slight change in a, b, c parameters and cell volume is observed with the replacement of zirconium ion by tin. Further, a keen observation of Fig. 5d, reveals that the appearance of both broad and sharp peaks in the XRD pattern, which indicates the possibility of secondary phase formation. This led us to give more attention on the tin substituted phases. The analysis of Fig. 5b, c and 5d with the other possible phases shows that few peaks have close match with R-3c (Rhombohedral, ICDD: 48–1100) space group along with P212121 space group. The peaks are, when x = 0.5; 2θ = 40.51°, x = 1; 2θ = 13.90°, 18.97° and x = 1.5; 2θ = 13.99°, 19.15°, 20.61°, 23.49°, 30.68°.
Fig. 6. FT-IR spectra of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12.
3.2. FT-IR and Raman analysis The FT-IR spectra of KZP and KSP are depicted in Fig. 6. Stretching and bending vibrational modes of (P–O) and (Si–O) are observed in the region 407 cm−1 - 1094 cm−1. The IR assignments of phosphate and 4
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Table 2 FTIR and Raman assignments for K2Zr2P2SiO12 and K2Sn2P2SiO12. Assignments
K2Zr2P2SiO12 IR (cm
PO43−
SiO44−
v3 v1 v4 v2
(vas)
v3 v1 v4 v2
(vas)
(vs) (δas) (δs) (vs) (δas) (δs)
−1
K2Sn2P2SiO12 −1
)
Raman (cm
1094,1024
1172, 1051 916 627, 558 444
577, 559 460 887 790,500 440, 409
1020 745 444
)
IR (cm−1)
Raman (cm−1)
1045,1012 935 580, 560 479, 469
1180,1053 633, 588 453
877 779, 505 438, 407
1011 868 726 341
silicate groups are given in Table 2. Due to the overlapping of phosphate and silicate vibrational bands, a broad peak is noticed between 1012 and 1094 cm−1, which corresponds to the stretching bands of (P–O) and (Si–O) [51]. The peak broadness is high for KSP when compared to KZP. In addition to the broadness, the effect of tin substitution is apparent in the spectrum (Fig. 6b) by means of additional bands at 935 cm−1 and 469 cm−1. Further, a shift in both stretching and bending modes is observed in KSP. The red and blue shift in FTIR and Raman spectra could be attributed to the factors such as electronegativity, bond strength and the crystallinity of the material. Additionally, the lower electronegativity of Zr (1.33) compared to Sn (1.96) and the higher bond strength of Zr–O (0.671) than Sn–O (0.422) are also considered to be the responsible factors for the shift. Since langbeinite structure exists in different phases, Raman spectra of KZP and KSP were recorded to support the powder XRD results. For comparison, a known cubic langbeinite K2FeZrP3O12 (KFZP) was prepared and characterized. Raman spectra of KZP, KSP and KFZP are shown in Fig. 7. Though the Raman bands correspond to PO43− and SiO44− are assigned similar to the FTIR vibrational modes, interestingly a major difference is observed between the region 950 cm−1 and 1150 cm−1. As noted by Kreske and Devarajan, additional Raman bands are observed for the orthorhombic KZP and KSP when compared to the cubic KFZP [33]. A broad band at 1050 cm−1 is observed for KFZP, whereas, it is transformed into narrow and splitted as two bands at ~1020 and 1050 cm−1 for the orthorhombic KZP and KSP. The band splitting is apparently visible for the compound KSP. Similar to our results, the peak splitting in orthorhombic structure is also observed by Sakai et al. in their phase transition study on K2Mn2(SO4)3 [61]. Thus, the orthorhombic structure of KZP and KSP is
Fig. 8. TGA traces of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12.
further evidenced by the Raman spectra. The peak splitting in KZP and KSP could be attributed to the loss of symmetry due to the nonequivalent PO43− and SiO44− ions. 3.3. Thermal and SEM-EDAX study TGA curves of the calcined powders KZP and KSP are shown in Fig. 8 between 30 °C and 1000 °C. It is clear from the TGA traces that the compounds KZP and KSP are thermally stable up to 1000 °C and 650 °C, respectively. In case of KSP, the gradual weight loss up to 5 wt % is observed between 30 °C and 300 °C, which corresponds to the loss of adsorbed moisture content. Similarly, 13.5 wt % loss is noted in the range 650 °C–800 °C due to the decomposition of KSP and formation of KSnO(PO4). This is corroborated by the x-ray analysis. Compared to the powder XRD patterns of KSP calcined at 600 °C and 800 °C, it is apparent that the phase is decomposed and the secondary phase is evolved after 800 °C. Thus, the TGA curves and powder X-ray diffraction analysis of KSP confirmed that the weight loss observed above 650 °C is due to the decomposition of the compound. The lower and higher magnified scanning electron micrographs of both KZP and KSP are shown in Fig. 9. SEM image of KZP (Fig. 9 a) depicts that the particles are stacked by one another and there is no specified shape. In KSP, the existence of pores and cubic shaped particles are noticed along with the agglomeration. Quantitative elemental analysis (Wt. %) of both KZP and KSP, obtained by energy dispersive Xray analysis are compared with the theoretical Wt. % of the elements and given in Table 3. The experimental results indicate that the values are closely matching with the theoretical values. 3.4. Thermal expansion Figs. 10 and 11 represent the average thermal expansion and coefficient of thermal expansion (CTE) curves for KZP and KSP, respectively. Fig. 10 illustrates that the average thermal expansion of KZP and KSP increase sharply in a negative scale from 30 °C - 250 °C and gradually from 250 °C to 600 °C. Nevertheless, KSP exhibits a drastic increase up to 250 °C and gradual decrease in the range 250 °C–500 °C and stabilized after 500 °C. Effect of tin substitution on thermal expansion is apparent from the average CTEs. The average CTE of K2Zr2P2SiO12, K2Zr1.5Sn0.5P2SiO12, K2ZrSnP2SiO12, K2Zr0.5Sn1.5P2SiO12 and K2Sn2P2SiO12 between 30 °C and 600 °C are −7.01 × 10−6/°C, −4.96 × 10−6/°C, −1.08 × 10−5/°C, −1.53 × 10−5/°C, −1.27 × 10−5/°C respectively. Table 4 represents the average CTEs of K2Zr2-xSnxP2SiO12 (X = 0, 0.5, 1.0, 1.5, 2). It can be seen from Table 4 that, when x = 0.5, the CTE decreased slightly compared to x = 0 and increased gradually when x = 1 and 1.5. For the compound KSP, the
Fig. 7. Raman spectra of (a) K2FeZrP3O12 (b) K2Zr2P2SiO12 and (c) K2Sn2P2SiO12. 5
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Fig. 10. Average thermal expansion of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12. Fig. 9. SEM images of (a) K2Zr2P2SiO12and (b) K2Sn2P2SiO12. Inset shows higher magnified images. Table 3 Elemental analysis of KZP and KSP by EDX. Elements
Weight percentage K2Zr2P2SiO12
K Zr P Si a
K2Sn2P2SiO12
Theoritical
Experimentala
Theoritical
Experimentala
14.4 33.6 11.4 5.2
12.6 29.5 9.2 4.3
13.1 39.7 10.4 4.7
11.2 34.8 10.8 3.5
Average of three different spots.
average CTE is one magnitude higher than that of KZP and slightly lower than the composition where x = 1.5. Overall, a large expansion at lower temperature and smaller and linear expansion at higher temperature are observed for all the compositions. The absence of any sharp peaks during cooling indicates that there is no phase change occur in both KZP and KSP. The influence of tin substitution in CTE can be explained based on several factors such as the ionic radii, bond strength, thermal stress resistance, microstructure, porosity and density. (i) The initial dimensional expansion is attributed to the non-linear increase of instrument temperature as observed by Wang et al. for tin substituted NZP system [56]. (ii) The smaller ionic radius of Sn4+ (rSn = 0.69 Å) compared to Zr4+ (rZr = 0.72 Å) led to higher thermal expansion. This is in good
Fig. 11. Thermal expansion coefficient of (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12.
agreement with the literature report [20]. It is presumed that the replacement of larger ZrO6 octahedra by a smaller SnO6 octahedra in a M2(XO4)3 fragment led to the contraction of crystal lattice and made the structure to more closely packed. Though the simultaneous substitution of Sn4+ for Zr4+ and Si4+ for P5+ is expected to stabilize the crystal lattice, the ionic size difference might have distorted the structural polyhedra by promoting the deformation of structure, which resulted a linear expansion. (iii) Tallentire et al., and Kutty et al., reported that the substitution of Sn for Zr could control the CTE due to the 6
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and experimental density and porosity of the 600 °C fired pellets are given in Table 5. The difference between theoretical and experimental density is due to the porosity of the sample. The SEM images of the sintered pellets are shown in Fig. 12. It is clearly visible from the image that KZP is more porous than KSP. The average pore size of KZP and KSP calculated from ImageJ software is 0.34 μm and 0.17 μm respectively. Thus based on the density and microstructure analysis, it is evident that the sample KZP is highly porous and less dense than the sample KSP. The SEM and density results corroborate the thermal expansion of KZP and KSP. KZP undergoes more contraction than KSP due to the higher porosity and lower density. The effect of porosity and density on thermal expansion have been reported by Wang et al. and Liu et al. [63,64]. Thus, the above factors combined together led to control negative expansion upon tin substitution.
Table 4 Coefficient of Thermal expansion (CTE) of K2Zr2-xSnxP2SiO12 (x = 0–2). K2Zr2-xSnxP2SiO12
CTE ( × 10−6/°C)
x x x x x
−7.01 −4.96 −0.108 −0.153 −0.127
= = = = =
0 0.5 1 1.5 2
Table 5 Density and porosity of KZP and KSP. Compounds
KZP KSP a b
Density (g/cm3)
Average Porosity (%)
Theoretical
Experimental
Theoreticala
Experimentalb
2.329 2.687
3.433 3.783
37.5 20.1
34.8 17.4
4. Conclusions Negative thermal expansion ceramics of the formula K2Zr2(x = 0, 0.5, 1, 1.5, 2) with langbeinite structure were successfully synthesized. Spectral analysis confirmed the phase formation, structure and compositions. Thermal expansion of zirconium phosphosilicates was controlled by the replacement of zirconium by tin in the octahedral site of langbeinite structure. Effect of tin was analyzed based on the ionic size, bond strength, porosity, density and microstructure. The results emphasize that KZP and tin substituted ceramics could be a good additive to develop challenging zero thermal expansion materials. A remarkable change in the average thermal expansion coefficient was observed by the substitution of tin (K2Sn2P2SiO12: 1.27 × 10−5/°C) for zirconium in KZP (K2Zr2P2SiO12 (−7.01 × 10−6/ °C). This indicate that tin is an important substituent for controlling the thermal expansivity of zirconium based compounds related to M2(XO4)3 structures. xSnxP2SiO12
Calculated from density and. Calculated from SEM image.
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments The authors are thankful to the Science and Engineering Research Board, Department of Science and Technology, India for the financial support (Grant No: EEQ/2017/000740). One of the authors S. Pratheep Kumar also thank Dr. G. Buvaneswari, Professor, VIT University, India for her valuable suggestions in finding novel phases. KPR Institute of Engineering and Technology is acknowledged for providing necessary facilities. References [1] A.W. Sleight, Compounds that contract on heating, Inorg. Chem. 37 (1998) 2854–2860, https://doi.org/10.1021/ic980253h. [2] J. Chen, L. Hu, J. Deng, X. Xing, Negative thermal expansion in functional materials, Chem. Soc. Rev. 44 (2015) 3522–3567, https://doi.org/10.1039/ C4CS00461B. [3] N. Anantharamulu, K. K Rao, G. Rambabu, V. B Kumar, V. Radha, M. Vithal, A wideranging review on Nasicon type materials, J. Mater. Sci. 46 (2011) 2821–2837, https://doi.org/10.1007/s10853-011-5302-5. [4] K. Kamali, T.R. Ravindran, N.V. C Shekar, K.K. Pandey, S.M. Sharma, Pressure induced phase transformations in NaZr2(PO4)3 studied by X-ray diffraction and Raman spectroscopy, J. Solid State Chem. 221 (2015) 285–290, https://doi.org/10. 1016/j.jssc.2014.10.017. [5] V.I. Petkov, E.A. Asabina, Thermophysical properties of NZP ceramics (A review), Glass Ceram. 61 (2004) 233–239, https://doi.org/10.1023/B:GLAC.0000048353. 42467.0a. [6] V.I. Petkov, E.A. Asabina, V. Loshkarev, M. Sukhanov, Systematic investigation of the strontium zirconium phosphate ceramic form for nuclear waste immobilization, J. Nucl. Mater. 471 (2016) 122–128, https://doi.org/10.1016/j.jnucmat.2016.01. 016.
Fig. 12. SEM images of sintered pellets (a) K2Zr2P2SiO12 and (b) K2Sn2P2SiO12.
distortion of O–Sn–O and Sn–O–P bonds [57,62]. Similar to their observation, our results show higher CTE for KSP than KZP. (iv) In addition to the effect of ionic size and bond strength, microstructure, density and porosity of the fired pellets play a vital role in the bulk thermal expansion behaviour [63]. To corroborate the thermal expansion data, the surface morphology of KZP and KSP pellets was recorded and density was calculated by Archimedes principle. The theoretical 7
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D. Balaji, et al. [7] V.I. Petkov, Complex phosphates formed by metal cations in oxidation states I and IV, Russ. Chem. Rev. 81 (2012) 606–637, https://doi.org/10.1070/ RC2012v081n07ABEH004243. [8] V.I. Petkov, A.I. Orlova, Crystal-chemical approach to predicting the thermal expansion of compounds in the NZP Family, Inorg. Mater. 39 (2003) 1013–1023, https://doi.org/10.1023/A:1026074722220. [9] T.A. Mary, J.S.O. Evans, T. Vogt, A.W. Sleight, Negative thermal expansion from 0.3 to 1050 K in ZrW2O8, Sci 272 (1996) 90–92, https://doi.org/10.1126/science.272. 5258.90. [10] L. Xia, G. Wen, L. Song, X. Wang, The crystallization behavior and thermal expansion properties of eucryptite prepared by sol–gel route, Mater. Chem. Phys. 119 (2010) 495–498, https://doi.org/10.1016/j.matchemphy.2009.10.003. [11] T. Nagayama, T. Yamamoto, T. Nakamura, Thermal expansions and mechanical properties of electrodeposited Fe–Ni alloys in the Invar composition range, Electrochim. Acta 205 (2016) 178–187, https://doi.org/10.1016/j.electacta.2016. 04.089. [12] V. Korthuis, N. Khosrobvani, A.W. Sleight, N. Roberts, R. Dupree, W.W. Warren Jr., Negative thermal expansion and phase transitions in the ZrV2-xPxO7 series, Chem. Mater. 7 (1995) 412–417, https://doi.org/10.1021/cm00050a028. [13] A.E. Philips, A.L. Goodwin, G.J. Halder, P.D. Southon, C.J. Kepert, Nanoporosity and exceptional negative thermal expansion in single-network cadmium cyanide, Angew. Chem. Int. 47 (2008) 1396–1399, https://doi.org/10.1002/anie. 200704421. [14] I. Yanase, M. Miyagi, H. Kobayashi, Fabrication of zero-thermal-expansion ZrSiO4/ Y2W3O12 sintered body, J. Eur. Ceram. Soc. 29 (2009) 3129–3134, https://doi.org/ 10.1016/j.jeurceramsoc.2009.06.001. [15] A.M. Efremov, G. Bruno, B.R. Wheaton, Texture coefficients for the simulation of cordierite thermal expansion: a comparison of different approaches, J. Eur. Ceram. Soc. 31 (2011) 281–290, https://doi.org/10.1016/j.jeurceramsoc.2010.10.005. [16] Y. Liu, B. Yuan, Y. Cheng, E. Liang, X. Ge, H. Yuan, Y. Zhang, J. Guo, M. Chao, Phase transition and negative thermal expansion of HfMnMo3O12, Mater. Res. Bull. 99 (2018) 255–259, https://doi.org/10.1016/j.materresbull.2017.11.009. [17] Y. Liu, M.S. Molokeev, Q. Liu, Z. Xia, Crystal structure, phase transition and thermal expansion property of NaZr2(PO4)3-SrZr4(PO4)6 solid solutions, Inorg. Chem. Front. 5 (2018) 619–625, https://doi.org/10.1039/C7QI00782E. [18] J.S.O. Evans, Negative thermal expansion materials, Dalton Trans. (1999) 3317–3327, https://doi.org/10.1039/A904297K. [19] C. Thieme, C. Russel, Very high or close to zero thermal expansion by the variation of the Sr/Ba ratio in Ba1−xSrxZn2Si2O7 – solid solutions, Dalton Trans. 45 (2016) 4888–4895, https://doi.org/10.1039/C5DT04970A. [20] P. Oikonomou, C. Dedeloudis, C.J. Stournaras, C. Fitkos, [NZP], A new family of ceramics with low thermal expansion and tunable properties, J. Eur. Ceram. Soc. 27 (2007) 1253–1258, https://doi.org/10.1016/j.jeurceramsoc.2006.04.021. [21] K.V.G. Kutty, R. Asuvathraman, R. Sridharan, Thermal expansion studies on the sodium zirconium phosphate family of compounds A1/2M2(PO4)3: effect of interstitial and framework cations, J. Mater. Sci. 33 (1998) 4007–4013, https://doi.org/ 10.1023/A:1004661132398. [22] M. Barre, M.P.C. Lopez, F.L. Berre, J. Emery, E. Suard, J.L. Fourrquet, Room temperature crystal structure of La1/3Zr2(PO4)3, a NASICON-type compound, Chem. Mater. 17 (2005) 6605–6610, https://doi.org/10.1021/cm0515045. [23] V.I. Petkov, A.I. Orlova, G.N. Kazantsev, S.G. Samoilov, M.L. Spiridonova, Thermal expansion in the Zr and 1-, 2-valent complex phosphates of NaZr2(PO4)3 (NZP) structure, J. Therm. Anal. Calorim. 66 (2001) 623–632, https://doi.org/10.1023/ A:1013145807987. [24] S.Y. Limaye, A.K. Agrawal, R. Roy, Y. Mehrotra, Synthesis, sintering and thermal expansion of Cal-xSrxZr4P6O24 - an ultra-low thermal expansion ceramic system, J. Mater. Sci. 26 (1991) 93–98, https://doi.org/10.1007/BF00576037. [25] D.A. Woodcock, P. Lighfoot, R.I. Smith, Powder neutron diffraction studies of three low thermal expansion phases in the NZP family: K0.5Nb0.5Ti1.5(PO4)3, Ba0.5Ti2(PO4)3 and Ca0.25Sr0.25Zr2(PO4)3, J. Mater. Chem. 9 (1999) 2631–2636, https://doi.org/10.1039/A903489G. [26] D.O. Savinykh, S.A. Khainakov, A.I. Orlova, S. Garcia-Granda, New phosphatesulfates with NZP structure, Russ. J. Inorg. Chem. 63 (2018) 714–724, https://doi. org/10.1134/S0036023618060207. [27] W. Haizeng, P. Wenqin, Hydrothermal synthesis and characterization of NaZr2(AsO4)3, J. Mater. Chem. 3 (1993) 989, https://doi.org/10.1039/ JM9930300989. [28] V.I. Petkov, M.V. Sukhanov, A.S. Shipilov, V.S. Kurazhkovskaya, E.Y. Borovikova, I.Y. Pinus, A. Yaroslavtsev, Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4)x(PO4)3–x, Inorg. Mater. 50 (2014) 263–272, https://doi.org/10.1134/ S0020168514030091. [29] H.P. Hong, Crystal structures and crystal chemistry in the system Nal+xZr2SixP3xO12, Mater. Res. Bull. 11 (1976) 173–182, https://doi.org/10.1016/00255408(76)90073. [30] V.I. Petkov, A.S. Shipilov, M.V. Sukhanov, Thermal expansion of MZr2(AsO4)3 and MZr2(TO4)x(PO4)3-x (M = Li, Na, K, Rb, Cs; T = As, V), Inorg. Mater. 51 (2015) 1079–1085, https://doi.org/10.1134/S002016851510012X. [31] N. Yamada, Y. Chubachi, T. Ikeda, Optical and dielectric properties of K2Mn2(SO4)3, J. Phys. Soc. Jpn. 45 (1978) 1638–1644, https://doi.org/10.1143/JPSJ.45.1638. [32] T. Lauret, R. Jacques, R. Pascal, High-temperature thermal expansion and decomposition of garnets, Eur. J. Mineral 10 (1998) 7–16, https://doi.org/10.1127/ejm/ 10/1/0007. [33] M.T. Weller, P.F. Henry, C.C. Wilson, An analysis of the thermal motion in the negative thermal expansion material Sc2(WO4)3 using isotopes in neutron diffraction, J. Phys. Chem. B 104 (2000) 12224–12229, https://doi.org/10.1021/ jp0030037.
[34] S. Kreske, V. Devarajan, Vibrational spectra and phase transitions in ferroelectricferroelastic langbeinites: K2Mn2(SO4)3, (NH4)2Cd2(SO4)3 and Tl2Cd2(SO4)3, J. Phys. C Solid State Phys. 15 (1982) 7333, https://doi.org/10.1088/0022-3719/15/36/ 015. [35] H. Oelkrug, T. Bruckel, D. Hohlwein, A. Hoser, W. Prandl, The magnetic structure of the langbeinite K2Mn2(SO4)3, Phys. Chem. Miner. 16 (1988) 246–249, https://doi. org/10.1007/BF00220692. [36] A.I. Orolova, I.G. Trubach, V.S. Kurazhkovskaya, P. Pertierra, M.A. Salvado, S. Garcia-Granda, S.A. Khainakov, J.R. Garcia, Synthesis, characterization, and structural study of K2FeZrP3O12 with the langbeinite structure, J. Solid State Chem. 173 (2003) 314–318, https://doi.org/10.1016/S0022-4596(03)00101. [37] M.B. Gawanda, S.S. Deshpande, S.U. Sonavane, R.V. Jayaraman, A novel sol–gel synthesized catalyst for Friedel–Crafts benzoylation reaction under solvent-free conditions, J. Mol. Catal. Chem. 241 (2005) 151–155, https://doi.org/10.1016/j. molcat.2005.06.069. [38] I.A. Trussov, L.L. Driscoll, L.L. Male, M.L. Sanjunan, A. Orera, P.R. Slater, Synthesis and structures of sodium containing K2-xNaxMg2(SO4)3 langbeinite phases, J. Solid State Chem. 276 (2019) 37–46, https://doi.org/10.1016/j.jssc.2019.04.036. [39] L. Lander, G. Rousse, D. Batuk, C.V. Colin, D.A.D. Corte, J.-M. Tarascon, Synthesis, structure, and electrochemical properties of K-based sulfates K2M2(SO4)3 with M = Fe and Cu, Inorg. Chem. 56 (2017) 2013–2021, https://doi.org/10.1021/acs. inorgchem.6b02526. [40] V.S. Jayakumar, I.H. Joe, G. Aruldhas, IR and single crystal Raman spectra of langbeinities M2+Ni2(SO4)3 (M+ = NH4, K), Ferroelectrics 165 (1995) 307–318, https://doi.org/10.1080/00150199508228311. [41] C. Moriyoshi, K. Itoh, T. Hikita, Structural study of phase transition in K2Zn2(SO4)3 langbeinite, Physica B 219–220 (1996) 602–604, https://doi.org/10.1016/09214526(95)00825-X. [42] M.J. L. Percival E. Salje, Optical absorption spectroscopy of the P213-P212121 transformation in K2Co2(SO4)3 langbeinite, Phys. Chem. Miner. 16 (1989) 563–568, https://doi.org/10.1007/BF00202212. [43] I.V. Ogorodnyk, I.V. Zatovsky, V.N. Baumer, N.S. Slobodyanik, O.V. Shishkin, Synthesis and crystal structure of langbeinite related mixed-metal phosphates K1.822Nd0.822Zr1.178(PO4)3 and K2LuZr(PO4)3, Crys, Respir. Technol. 42 (2007) 1076–1081, https://doi.org/10.1002/crat.200710961. [44] I.G. Trubach, A.I. Beskrovnyi, A.I. Orlova, V.A. Orlova, V.S. Kurazhkovskaya, Synthesis and investigation of the new phosphates K2LnZr(PO4)3 (Ln = Ce–Yb, Y) with langbeinite structure, Crystallogr. Rep. 49 (2004) 614–618, https://doi.org/ 10.1134/1.1780625. [45] S.C. Abrahams, F. Lissade, J.L. Bernstein, Piezoelectric langbeinite type K2Cd2(SO4)3 structure at four temperatures below and one above the 432°K ferroelastic–paraelastic transition, J. Chem. Phys. 68 (1978) 1926–1935, https://doi. org/10.1063/1.435919. [46] D. Speer, E. Salje, Phase transitions in langbeinites I: crystal chemistry and structures of K-double sulfates of the langbeinite M2++ Type K2(SO4)3, M++ = Mg, Ni, Co, Zn, Ca, Phys. Chem. Miner. 13 (1986) 17–24, https://doi.org/10.1007/ BF00307309. [47] M.A. Nabar, D.S. Phanasgaonkar, Spectral studies of triple orthovanadates MICr2(VO4)3 having langbeinite structure, Spectrochim. Acta 37A (1981) 279–281, https://doi.org/10.1016/0584-8539(81)80175-4. [48] V.A. Zeeman, J. Zeeman, Die kristallstruktur von langbeinit, K2M2(SO4)3, Acta Crystallogr. 10 (1957) 409–413, https://doi.org/10.1107/S0365110X57001346. [49] V.I. Petkov, A.S. Shipilov, A.S. Dmitrienko, A.A. Alekseev, Characterization and controlling thermal expansion of materials with kosnarite- and langbeinite type structures, J. Ind. Eng. Chem. 57 (2018) 236–243, https://doi.org/10.1016/j.jiec. 2017.08.029. [50] D.M. Bykov, R.J.M. Konings, C. Apostolidis, A. Hen, E. Colineau, T. Wiss, P. Raison, Synthesis and investigation of neptunium zirconium phosphate, a member of the NZP family: crystal structure, thermal behaviour and Mossbauer spectroscopy studies, Dalton Trans. 46 (2017) 11626–11635, https://doi.org/10.1039/ C7DT02110K. [51] S. Pratheep Kumer, G. Buvaneswari, New rare earth langbeinite phosphosilicates KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) for lanthanide comprising nuclear waste storage, J. Alloys Compd. 657 (2016) 422–429, https://doi.org/10.1016/j. jallcom.2015.10.088. [52] Q. Ma, M. Guin, S. Naqash, C.L. Tsai, F. Tietz, O. Guillon, Scandium-substituted Na3Zr2(SiO4)2(PO4) prepared by a solution assisted solid-state reaction method as sodium-ion conductors, Chem. Mater. 28 (2016) 4821–4828, https://doi.org/10. 1021/acs.chemmater.6b02059. [53] M. Jiao, W. Lv, W. Lu, Q. Zhao, B. Shao, H. You, Optical properties and energy transfer of a novel KSrSc2(PO4)3: Ce3+/Eu2+/Tb3+ phosphor for white light emitting diodes, Dalton Trans. 44 (2015) 4080–4087, https://doi.org/10.1039/ C4DT03906H. [54] D. Carta, R.J. Newport, J.C. Knowles, M.E. Smith, P. Guerry, Sol–gel produced sodium calcium phosphosilicates for bioactive applications: synthesis and structural characterization, Mater. Chem. Phys. 130 (2011) 690–696, https://doi.org/10. 1016/j.matchemphys.2011.07.050. [55] K.B. Hueso, M. Armand, T. Rojo, High temperature sodium batteries: status, challenges and future trends, Energy Environ. Sci. 6 (2013) 734–749, https://doi.org/ 10.1039/C3EE24086J. [56] Y. Wang, Y. Zhou, N. Tong, Z. Han, F. Liu, Crystal structure, mechanical and thermophysical properties of Ca0.5Sr0.5Zr4-xSnxP6O24 ceramics, J. Alloys Compd. 748 (2019) 8–15, https://doi.org/10.1016/j.jallcom.2018.12.379. [57] S.E. Tallentire, F. Child, I. Fall, L.V. Zarb, I.R. Evans, M.G. Tucker, D.A. Keen, C. Wilson, J.S.O. Evans, Systematic and controllable negative, zero and positive thermal expansion in cubic Zr1–xSnxMo2O8, J. Am. Chem. Soc. 135 (2013)
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Ceramics International xxx (xxxx) xxx–xxx
D. Balaji, et al. 12849–12856, https://doi.org/10.1021/ja4060564. [58] H. Liu, X. Wang, Z. Zhang, X. Chen, Synthesis and thermal expansion properties of Y2-xLaxMo3O12 (x = 0, 0.5, 2), Ceram. Int. 38 (2012) 6349–6352, https://doi.org/ 10.1016/j.ceramint.2012.05.006. [59] P.H. Kumar, V.K. Singh, P. Kumar, G. Yadav, R.K. Chaturvedi, Effect of Al2O3 on leucite based bioactive glass ceramic composite for dental veneering, Ceram. Int. 42 (2016) 3591–3597, https://doi.org/10.1016/j.ceramint.2015.11.022. [60] R.D. Shannon, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides, Acta Crystallogr. A32 (1976) 751–767, https://doi.org/10.1107/S0567739476001551. [61] A. Sakai, M. Kitoh, M. Negishi, K. Itoh, Micro-Raman scattering study of the phase transition of K2Mn2(SO4)3, Ferroelectrics 217 (1998) 99–103, https://doi.org/10.
1080/00150199808015026. [62] K.V.G. Kutty, A. Asuvathraman, C.K. Mathews, U.V. Varadaraju, Effect of variation in framework composition on the thermal expansivity of NZP phases, Mater. Res. Bull. 29 (1994) 1009–1016, https://doi.org/10.1016/0025-5408(94)90081-7. [63] Y. Wang, Y. Zhou, Y. Song, L. Yang, F. Liu, Mechanical and thermal expansion studies on Ca0.5Sr0.5Zr4-xTixP6O24 ceramics, Ceram. Int. 44 (2018) 16698–16702, https://doi.org/10.1016/j.ceramint.2018.06.097. [64] Q. Liu, J. Yang, X. Rong, X. Sun, X. Cheng, H. Tang, H. Li, Structural, negative thermal expansion and photocatalytic properties of ZrV2O7: a comparative study between fibers and powders, Mater. Char. 96 (2014) 63–70, https://doi.org/10. 1016/j.matchar.2014.07.001.
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