- Email: [email protected]
Solubility limit of Zn2+ in low thermal expansion ZrMgMo3O12 and its influence on phase transition temperature
Ceramics International xxx (xxxx) xxx–xxx
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Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Short communication
Solubility limit of Zn2+ in low thermal expansion ZrMgMo3O12 and its influence on phase transition temperature Alison Madrida, Patricia I. Pontónb, Flávio Garciac, Michel B. Johnsond, Mary Anne Whited,e, Bojan A. Marinkovica,∗ a
Department of Chemical and Materials Engineering, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), 22453-900, Rio de Janeiro, RJ, Brazil Department of Materials, Escuela Politécnica Nacional, 170525, Quito, Ecuador c Centro Brasileiro de Pesquisas Físicas (CBPF), 22290-180, Rio de Janeiro RJ, Brazil d Clean Technologies Research Institute, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada e Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada b
A R T I C LE I N FO
A B S T R A C T
Keywords: Negative thermal expansion A2M3O12 In situ XRPD Thermal shock resistance
Low thermal expansion in ABM3O12 phases, such as ZrMgMo3O12, have drawn significant attention due to their potencial applications as advanced ceramics with remarkable thermal shock resistance. Herein, we explored Zn2+ additions into ZrMgMo3O12 due to its potential to tune the coefficient of thermal expansion to even lower values. The influence of the solubility limit of Zn2+ in ZrMg1-xZnxMo3O12 on the temperature of the phase transition from the monoclinic to the orthrombic phase (x = 0.10; 0.30; 0.35 and 0.40) was thoroughly studied. X-ray powder diffraction (XRPD) confirmed the stability of the orthorhombic (Pna21) phase over a wide temperature range, for compositions up to x = 0.35, while for x = 0.40 the solubility limit of Zn2+ was exceeded and monoclinic ZnMoO4 appeared as a secondary phase. As the Zn2+ content increases, the transition temperature is shifted to higher temperatures, as demonstrated by XRPD and differential scanning calorimetry (DSC). The onset of the transition temperature for x = 0.10, 0.30 and 0.35 was 181, 240 and 253 K, respectively. All these values are well below room temperature, which is of paramount importance from a technological perspective. Thermogravimetric analysis shows that the as-synthesized phases are not hygroscopic.
1. Introduction Since the discovery of negative thermal expansion in the A2M3O12 family by Evans et al. [1], several others sub-families, such as ABM3O12 [2–13], ABM2XO12 [9,14–16] and A2MX2O12 [17–19] have been developed and considered for different applications, from light emission diodes (LED) to thermal shock resistance components. It is common for all these compounds to crystallize in monoclinic or orthorhombic crystal systems, although only orthorhombic phases demonstrate unusually low positive or negative thermal expansion. One of the peculiarities, and advantages, of these familes is the great chemical flexibility within the orthorhombic space groups Pbcn or Pna21, which permits tailoring the coefficient of thermal expansion (CTE) via the recently established non-empirical approach [7,20]. Since the phases from the ABM3O12 sub-family generally present low positive to low negative CTE values, these are potential candidates for the development of near zero thermal expansion materials and thermal shock resistance applications. Recently, Li et al. [13], decreased the CTE of HfMgMo3O12, a low
∗
positive thermal expansion phase (1.02x10-6 K-1), as reported by Marinkovic et al. [3], to near zero values (~3x10-7 K-1). They reached this reduction through the partial substitution of Mg2+ by the larger Zn2+ ion, within the HfMg1-xZnxMo3O12 system for x = 0.2 and 0.3, where the CTE was determined by XRPD over the temperature range between 350 and 573 K. This reduction of CTE by addition of Zn2+ fits the proposed theory [7,20] where larger cations in octahedral sites decrease interatomic forces within the octahedra and, therefore, permit and enhance polyhedra distortion, essential for the transversal motion of two-folded oxygen atoms. This mechanism causes shrinkage of ABM3O12 in the orthorhombic structure when heated. The same authors reported [13], additionally, reduction of the thermal anisotropy of the phases containing Zn2+ in comparison to pure HfMgMo3O12. This property benefits lower thermal stress and therefore enhances their application in thermal shock resistance components. However, the higher electronegativity of Zn2+ in comparison to Mg2+ (1.65 and 1.31 on the Pauling scale, respectively) causes an increase of the phase transition temperature, for the phases x = 0.4 and 0.5, to room and to
Corresponding author. E-mail address: [email protected] (B.A. Marinkovic).
https://doi.org/10.1016/j.ceramint.2019.09.252 Received 26 July 2019; Received in revised form 4 September 2019; Accepted 25 September 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Alison Madrid, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.09.252
Ceramics International xxx (xxxx) xxx–xxx
A. Madrid, et al.
Fig. 1. XRPD patterns of ZrMg1-xZnxMo3O12 system at room temperature for (a) x = 0.10, Rwp = 2.7 and goodness-of-fit (GoF) = 1.59; (b) x = 0.30, Rwp = 3.39 and GoF = 1.87; (c) x = 0.35, Rwp = 2.96 and GoF = 1.72 and (d) x = 0.40, Rwp = 3.36 and GoF = 1.83. Peak related to traces of hexagonal ZrMo2O8 system (P 31c ) is marked as *. Peaks of monoclinic ZnMoO4 system (C2/m) are marked as ▪.
above room temperatures, while for the composition x = 0.3 the phase transition is ~ 273 K. Also, Li et al. [13], noticed that the solubility of Zn2+ is limited to the compositions with x≤0.5. ZrMgMo3O12 is a near-zero thermal expansion phase between 298 K and 723 K, in accordance to Romao et al. [7] although Song et al. [6], evaluated its CTE, between 300 and 1000 K, at −3.73x10-6 K-1. Considering the CTE reported by Romao et al. of 1.7x10-7 K-1 (298 K-723 K), here we studied the solubility limit of Zn2+ in ZrMg1-xZnxMo3O12 and its influence on the transition temperature from monclinic to orthorhombic phase. An increase of transition temperature to higher than room temperature would negativly impact the applications of these materials. Lastly, hygroscopicity, another technologically important parameter, has been evaluated.
Panalytical X'Pert PRO (CuKα radiation, steps of 0.01° (2θ), 2 s per step) in the same (2θ) range used at room temperature and with a cooling rate of 10 K min-1 in air. All diffraction sets were refined by the Le Bail method, using Topas 4.2 software. Differential scanning calorimetry (DSC) analyses of the as-prepared phases were conducted in a TA Instruments Q200, equipped with a liquid N2 cooling head, under He purge gas (25 mL min-1), with a heating rate of 20 K min-1 over the temperature range from 98 to 323 K. Thermogravimetric analyses (TGA) were carried out in a PerkinElmer STA-6000, under a synthetic air flow (20 mL min-1), with a heating rate of 20 K min-1, in the range 298–873 K.
2. Experimental
3.1. Solubility limit of Zn2+ in ZrMg1-xZnxMo3O12
The synthesis of ZrMg1-xZnxMo3O12 (x = 0.10, 0.30, 0.35, 0.40 and 1) was carried out by a solid-state route, using ZnO (Sigma-Aldrich, 97%), MgO (Sigma-Aldrich, 97%), ZrO2 (Sigma-Aldrich, 99%) and MoO3 (Fluke, 98%) powders, pre-heated at 773 K for 1 h. These reagents, at stoichiometric ratios, were manually mixed in an agate mortar for 2 h. The mixture was uniaxially pressed into pellets by applying 98 MPa for 1 min. The green pellets were then calcined in air at 1073 K for 5 h. Room-temperature X-ray powder diffraction (XRPD) measurements of the ZrMg1-xZnxMo3O12 calcined powders were carried out in a Bruker D8 Discover diffractometer (CuKα radiation, steps of 0.02° (2θ), 2s per step) over a range of 10 ̶ 60° (2θ). In situ XRPD analyses below room temperatures (173, 213, 253 and 298 K) were performed in a
Room-temperature XRPD patterns of ZrMg1-xZnxMo3O12 for x = 0.1, 0.30, 0.35 and 0.40 (Fig. 1) were analyzed for phase identification. Le Bail adjustment revealed the formation of the orthorhombic (Pna21) phase for compositions up to x = 0.35, with only traces of hexagonal ZrMo2O8 (P 31c ), according to the Powder Diffraction File (PDF) 77–1784. The presence of ZrMo2O8 traces could be inherent to the synthesis route, due to manual mixing of four different oxide reactants. For x = 0.40, the solubility limit of Zn2+ was exceeded, and the monoclinic ZnMoO4 system (C2/m), PDF 01-087-6506, emerged as a secondary phase (Fig. 1 d). An attempt to synthesize ZrZnMo3O12 was not successful and its final product was a mixture of hexagonal ZrMo2O8 and monoclinic ZnMoO4 with a small amount of monoclinic MoO3, as observed by
3. Results and discussion
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Fig. 2. XRPD patterns of ZrMg1-xZnxMo3O12 system at room and below room temperatures for (a) x = 0.10; (b) x = 0.30 and (c) x = 0.35. The characteristic peak of monoclinic phase is indicated by the arrow.
Fig. 3. (a) DSC curves of ZrMg1-xZnxMo3O12 powders and (b) TGA curve of ZrMg0.9Zn0.1Mo3O12 (the same trend was observed for other compositions).
overlapped forming a characteristic broadened peak, the fingerprint of the monoclinic phase in this ceramic family, indicated with an arrow in Fig. 2. For x = 0.10, the transition temperature is not well defined from XRPD since at 173 K the system was close to the phase transformation temperature (see below for corroboration by DSC results) and possibly there is the co-existence of the orthorhombic and monoclinic phases. The transition temperature for x = 0.30 is between 213 and 253 K, while in the case of x = 0.35 it is between 253 and 298 K. As the Zn2+ content increases, the transition temperature is shifted to higher
XRPD (not shown). 3.2. Phase transition in ZrMg1-xZnxMo3O12 XRPD patterns at and below room temperature in the 2θ range of 20 ̶ 26° (Fig. 2) allowed insight into the phase transition temperatures in the ZrMg1-xZnxMo3O12 system. The two characteristic diffraction peaks of the orthorhombic phase appeared at 21.8° and 22.4° (2θ), while after the transition to monoclinic phase, at lower temperatures, these peaks 3
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temperature range.
temperatures. This experimental observation is in agreement with the model proposed by Evans et al. [1], which takes into the account the effective charges on oxygen anions and their correlation with the electronegativity of the cations present in A2M3O12 and related families. The model considers that more electronegative cations would reduce the effective oxygen anion charge and, consequently, induce secondary oxygen-to-oxygen attractive forces, leading to the stabilization of the denser monoclinic polymorphs. In fact, this kind of secondary oxygen-to-oxygen bonding is responsible for the existence of some peculiar molecular oxides, such as OsO4 and RuO4 [21]. Therefore, cations with higher electronegativity, in A2M3O12 and related families, increase the temperature stability range of the denser monoclinic polymorph up to very high temperatures (for example, in Fe2Mo3O12), while low electronegativity cations expand the temperature stability range of the less dense orthorhombic polymorph, and in few cases, such as Y2W3O12 and Y2Mo2O12, completely suppress the phase transition to the monoclinic phase. Accordingly, partial substitution of Mg2+, which is a less electronegative cation (1.31), by Zn2+, which is a higher electronegative cation (1.65), will decrease the effective charge of the oxygen cations and promote stabilization of secondary oxygen-to-oxygen bonds, thereby stabilizing the monoclinic polymorph over a wider temperature range. The monoclinic to orthorhombic phase transition was also confirmed, and more accurately determined, by the onset of the endothermic peak in DSC curves (Fig. 3a) for all the studied compositions. The transition onset temperatures for x = 0.10, 0.30 and 0.35 were 181, 240 and 253 K, respectively, higher than for the pure ZrMgMo3O12, found to be at 147 K by Romao et al., [7]. Additionally, in the case of x = 0.40, the onset of the transition temperature was determined to be 256 K, which suggests that the solubility limit would be higher than x = 0.35, but lower than x = 0.40. Although it could be expected that partial substitution of Mg2+ by larger Zn2+ would influence the hygroscopicity of the ZrMg1xZnxMo3O12 phases and make them more hydroscopic, TGA curves showed insignificant hygroscopicity (Fig. 3b). It is promising for technological purposes both that the temperatures of phase transitions for ZrMg1-xZnxMo3O12 (x≤0.5) have been maintained well below room temperature, and that the newly synthesized phases were not hygroscopic. The latter ensures that the intrinsic thermal expansion properties of the ZrMg1-xZnxMo3O12 materials are not influenced by the presence of water. However, the solubility limit of Zn2+ in ZrMg1-xZnxMo3O12 is more restrictive than for HfMg1xZnxMo3O12, and this property could restrain the tuning of CTE inside this system. The appearance of hexagonal ZrMo2O8, at low quantities, in all composition will not contribute additionally to NTE since this phase presents normal positive expansion, differently from the cubic ZrMo2O8 which exhibits NTE over a large temperature interval [22].
Acknowledgments This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil (CAPES) –Finance Code 001. B.A.M. is grateful to CNPq (National Council for Scientific and Technological Development) for a Research Productivity Grant and to CAPES-Print for financial support. M.A.W. acknowledges support of NSERC and the Facilities for Materials Characterization managed by the Clean Technology Research Institute at Dalhousie University. P.I.P. is grateful to Escuela Politécnica Nacional (Project PIE-EPN-PUC-RIO2018) and CAPES-Print. The authors are grateful to Centro Brasileiro de Pesquisas Físicas (CBPF) for low temperature XRPD measurements. References [1] J.S.O. Evans, T.A. Mary, A.W. Sleight, Negative thermal expansion in a large molybdate and tungstate family, J. Solid State Chem. 133 (1997) 580–583, https://doi. org/10.1126/science.275.5296.61. [2] T. Suzuki, A. Omote, Negative thermal expansion in (HfMg)(WO4)3, J. Am. Ceram. Soc. 87 (2004) 1365–1367, https://doi.org/10.1111/j.1151-2916.2004.tb07737.x. [3] B.A. Marinkovic, P.M. Jardim, M. Ari, R. R de Avillez, F.F. Ferreira, Low positive thermal expansion in HfMgMo3O12, Phys. Status Solidi B 245 (2008) 2514–2519, https://doi.org/10.1002/pssb.200880262. [4] T.I. Baiz, A.M. Gindhart, S.K. Kraemer, C. Lind, Synthesis of MgHf(WO4)3 and MgZr (WO4)3 using a non-hydrolytic sol-gel method, J. Sol. Gel Sci. Technol. 47 (2008) 128–130, https://doi.org/10.1007/s10971-008-1765-5. [5] K.J. Miller, M.B. Johnson, M.A. White, B.A. Marinkovic, Low-temperature investigations of the open-framework material HfMgMo3O12, Solid State Commun. 152 (2012) 1748–1752, https://doi.org/10.1016/j.ssc.2012.06.022. [6] W.B. Song, E.J. Liang, X.S. Liu, Z.Y. Li, B.H. Yuan, J.Q. Wang, A negative thermal expansion material of ZrMgMo3O12, Chin. Phys. Lett. 30 (2013) 126502, , https:// doi.org/10.1088/0256-307X/30/12/126502. [7] C.P. Romao, F.A. Perras, U. Werner-Zwanziger, J.A. Lussier, K.J. Miller, C.M. Calahoo, J.W. Zwanziger, M. Bieringer, B.A. Marinkovic, D.L. Bryce, M.A. White, Zero thermal expansion in ZrMgMo3O12: NMR crystallography reveals origins of thermoelastic properties, Chem. Mater. 27 (2015) 2633–2646, https:// doi.org/10.1021/acs.chemmater.5b00429. [8] Y.G. Cheng, Y.C. Mao, X.S. Liu, B.H. Yuan, M.J. Chao, E.J. Liang, Near-zero thermal expansion of In2(1-x)(HfMg)xMo3O12 with tailored phase transition, Chin. Phys. B 25 (2016), https://doi.org/10.1088/1674-1056/25/8/086501. [9] Y. Cheng, Y. Liang, Y. Mao, X. Ge, B. Yuan, J. Guo, M. Chao, E. Liang, A novel material of HfScW2PO12 with negative thermal expansion from 140 K to 1469 K and intense blue photoluminescence, Mater. Res. Bull. 85 (2017) 176–180, https://doi. org/10.1016/j.materresbull.2016.09.008. [10] T. Li, X.S. Liu, Y.G. Cheng, X.H. Ge, M.D. Zhang, H. Lian, Y. Zhang, E.J. Liang, Y.X. Li, Zero and controllable thermal expansion in HfMgMo3-xWxO12, Chin. Phys. B 26 (2017) 2–7, https://doi.org/10.1088/1674-1056/26/1/016501. [11] D. Chen, B. Yuan, Y. Cheng, X. Ge, Y. Jia, E. Liang, M. Chao, Phase transition and near-zero thermal expansion in ZrFeMo2VO12, Phys. Lett. A 380 (2016) 4070–4074, https://doi.org/10.1016/j.physleta.2016.10.009. [12] X.H. Ge, Y.C. Mao, L. Li, L.P. Li, N. Yuan, Y.G. Cheng, J. Guo, M.J. Chao, E.J. Liang, Phase transition and negative thermal expansion property of ZrMnMo3O12, Chin. Phys. Lett. 33 (2016) 046503, , https://doi.org/10.1088/0256-307X/33/4/ 046503. [13] S. Li, X. Ge, H. Yuan, D. Chen, J. Guo, R. Shen, M. Chao, E. Liang, Near-zero thermal expansion and phase transitions in HfMg1−xZnxMo3O12, Frontiers in Chemistry 6 (2018) 115, https://doi.org/10.3389/fchem.2018.00115. [14] X. Ge, Y. Mao, X. Liu, Y. Cheng, B. Yuan, E. Liang, Negative thermal expansion and broad band photoluminescence in a novel material of ZrScMo2VO12, Sci. Rep. 6 (2016) 24832, , https://doi.org/10.1038/srep24832. [15] N. Zhang, W. Zhou, M. Chao, Y. Mao, J. Guo, Y. Li, D. Feng, E. Liang, Negative thermal expansion, optical and electrical properties of HfMnMo2PO12-x, Ceram. Int. 41 (2015) 15170–15175, https://doi.org/10.1016/j.ceramint.2015.08.090. [16] D. Chen, B. Yuan, H. Yuan, X. Ge, J. Guo, E. Liang, M. Chao, Phase transition and thermal expansion properties of Cr1.5-xScxZr0.5Mo2.5V0.5O12, Ceram. Int. 44 (2018) 9609–9615, https://doi.org/10.1016/j.ceramint.2018.02.187. [17] M. Cetinkol, A.P. Wilkinson, Pressure dependence of negative thermal expansion in Zr2(WO4)(PO4)2, Solid State Commun. 149 (2009) 421–424, https://doi.org/10. 1016/j.ssc.2009.01.002. [18] T. Isobe, T. Umezome, Y. Kameshima, A. Nakajima, K. Okada, Preparation and properties of negative thermal expansion Zr2WP2O12 ceramics, Mater. Res. Bull. 44 (2009) 2045–2049, https://doi.org/10.1016/j.materresbull.2009.07.020. [19] M. Cetinkol, A.P. Wilkinson, P.L. Lee, Structural changes accompanying negative thermal expansion in Zr2(MoO4)(PO4)2, J. Solid State Chem. 182 (2009) 1304–1311, https://doi.org/10.1016/j.jssc.2009.02.029. [20] B.A. Marinkovic, M. Ari, R.R. de Avillez, F. Rizzo, F.F. Ferreira, K.J. Miller, M.B. Johnson, M.A. White, Correlation between AO6 polyhedral distortion and
4. Conclusions The Zn2+ solubility limit and phase transition temperature, two relevant parameters for tailoring CTE and determination of temperature stability range of orthorhombic structure, have been investigated for the new ZrMg1-xZnxMo3O12 system, with an aim to promote low and near-zero thermal expansion. The Zn2+ solubility limit in ZrMg1-xZnxMo3O12 restricts the homogeneous composition to x < 0.4, while ZrZnMo3O12 appears not to be a stable phase. The addition of Zn2+ from x = 0.1 to x = 0.35 elevated the monoclinic to orthorhombic transition temperature from 181 K to 253 K, while still keeping it far below room temperature. Hygroscopicity is not an issue for the ZrMg1-xZnxMo3O12 system and the thermal expansion is intrinsically controlled by the open-structure framework. It is anticipated, but yet to be confirmed by XRPD, that the addition of Zn2+ in the ZrMg1-xZnxMo3O12 system up to x = 0.35 might be sufficient to tune the CTE towards zero thermal expansion over a wide 4
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[22] E.J. Liang, Y. Liang, Y. Zhao, J. Liu, Y. Jiang, Low-frequency phonon modes and negative thermal expansion in A(MO4)2 (A= Zr ,Hf and M =W,Mo) by Raman and terahertz time-domain spectroscopy, J. Phys. Chem. 112 (2008) 12582–12587, https://doi.org/10.1021/jp805256d.
negative thermal expansion in orthorhombic Y2Mo3O12 and related materials, Chem. Mater. 21 (2009) 2886–2894, https://doi.org/10.1021/cm900650c. [21] L.P. Prisco, P.I. Pontón, W. Paraguassu, C.P. Romao, M.A. White, B.A. Marinkovic, Near-zero thermal expansion and phase transition in In0.5(ZrMg)0.75Mo3O12, J. Mater. Res. 31 (2016) 3240–3248, https://doi.org/10.1557/jmr.2016.329.
5
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Short communication
Solubility limit of Zn2+ in low thermal expansion ZrMgMo3O12 and its influence on phase transition temperature Alison Madrida, Patricia I. Pontónb, Flávio Garciac, Michel B. Johnsond, Mary Anne Whited,e, Bojan A. Marinkovica,∗ a
Department of Chemical and Materials Engineering, Pontifical Catholic University of Rio de Janeiro (PUC-Rio), 22453-900, Rio de Janeiro, RJ, Brazil Department of Materials, Escuela Politécnica Nacional, 170525, Quito, Ecuador c Centro Brasileiro de Pesquisas Físicas (CBPF), 22290-180, Rio de Janeiro RJ, Brazil d Clean Technologies Research Institute, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada e Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada b
A R T I C LE I N FO
A B S T R A C T
Keywords: Negative thermal expansion A2M3O12 In situ XRPD Thermal shock resistance
Low thermal expansion in ABM3O12 phases, such as ZrMgMo3O12, have drawn significant attention due to their potencial applications as advanced ceramics with remarkable thermal shock resistance. Herein, we explored Zn2+ additions into ZrMgMo3O12 due to its potential to tune the coefficient of thermal expansion to even lower values. The influence of the solubility limit of Zn2+ in ZrMg1-xZnxMo3O12 on the temperature of the phase transition from the monoclinic to the orthrombic phase (x = 0.10; 0.30; 0.35 and 0.40) was thoroughly studied. X-ray powder diffraction (XRPD) confirmed the stability of the orthorhombic (Pna21) phase over a wide temperature range, for compositions up to x = 0.35, while for x = 0.40 the solubility limit of Zn2+ was exceeded and monoclinic ZnMoO4 appeared as a secondary phase. As the Zn2+ content increases, the transition temperature is shifted to higher temperatures, as demonstrated by XRPD and differential scanning calorimetry (DSC). The onset of the transition temperature for x = 0.10, 0.30 and 0.35 was 181, 240 and 253 K, respectively. All these values are well below room temperature, which is of paramount importance from a technological perspective. Thermogravimetric analysis shows that the as-synthesized phases are not hygroscopic.
1. Introduction Since the discovery of negative thermal expansion in the A2M3O12 family by Evans et al. [1], several others sub-families, such as ABM3O12 [2–13], ABM2XO12 [9,14–16] and A2MX2O12 [17–19] have been developed and considered for different applications, from light emission diodes (LED) to thermal shock resistance components. It is common for all these compounds to crystallize in monoclinic or orthorhombic crystal systems, although only orthorhombic phases demonstrate unusually low positive or negative thermal expansion. One of the peculiarities, and advantages, of these familes is the great chemical flexibility within the orthorhombic space groups Pbcn or Pna21, which permits tailoring the coefficient of thermal expansion (CTE) via the recently established non-empirical approach [7,20]. Since the phases from the ABM3O12 sub-family generally present low positive to low negative CTE values, these are potential candidates for the development of near zero thermal expansion materials and thermal shock resistance applications. Recently, Li et al. [13], decreased the CTE of HfMgMo3O12, a low
∗
positive thermal expansion phase (1.02x10-6 K-1), as reported by Marinkovic et al. [3], to near zero values (~3x10-7 K-1). They reached this reduction through the partial substitution of Mg2+ by the larger Zn2+ ion, within the HfMg1-xZnxMo3O12 system for x = 0.2 and 0.3, where the CTE was determined by XRPD over the temperature range between 350 and 573 K. This reduction of CTE by addition of Zn2+ fits the proposed theory [7,20] where larger cations in octahedral sites decrease interatomic forces within the octahedra and, therefore, permit and enhance polyhedra distortion, essential for the transversal motion of two-folded oxygen atoms. This mechanism causes shrinkage of ABM3O12 in the orthorhombic structure when heated. The same authors reported [13], additionally, reduction of the thermal anisotropy of the phases containing Zn2+ in comparison to pure HfMgMo3O12. This property benefits lower thermal stress and therefore enhances their application in thermal shock resistance components. However, the higher electronegativity of Zn2+ in comparison to Mg2+ (1.65 and 1.31 on the Pauling scale, respectively) causes an increase of the phase transition temperature, for the phases x = 0.4 and 0.5, to room and to
Corresponding author. E-mail address: [email protected] (B.A. Marinkovic).
https://doi.org/10.1016/j.ceramint.2019.09.252 Received 26 July 2019; Received in revised form 4 September 2019; Accepted 25 September 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Alison Madrid, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.09.252
Ceramics International xxx (xxxx) xxx–xxx
A. Madrid, et al.
Fig. 1. XRPD patterns of ZrMg1-xZnxMo3O12 system at room temperature for (a) x = 0.10, Rwp = 2.7 and goodness-of-fit (GoF) = 1.59; (b) x = 0.30, Rwp = 3.39 and GoF = 1.87; (c) x = 0.35, Rwp = 2.96 and GoF = 1.72 and (d) x = 0.40, Rwp = 3.36 and GoF = 1.83. Peak related to traces of hexagonal ZrMo2O8 system (P 31c ) is marked as *. Peaks of monoclinic ZnMoO4 system (C2/m) are marked as ▪.
above room temperatures, while for the composition x = 0.3 the phase transition is ~ 273 K. Also, Li et al. [13], noticed that the solubility of Zn2+ is limited to the compositions with x≤0.5. ZrMgMo3O12 is a near-zero thermal expansion phase between 298 K and 723 K, in accordance to Romao et al. [7] although Song et al. [6], evaluated its CTE, between 300 and 1000 K, at −3.73x10-6 K-1. Considering the CTE reported by Romao et al. of 1.7x10-7 K-1 (298 K-723 K), here we studied the solubility limit of Zn2+ in ZrMg1-xZnxMo3O12 and its influence on the transition temperature from monclinic to orthorhombic phase. An increase of transition temperature to higher than room temperature would negativly impact the applications of these materials. Lastly, hygroscopicity, another technologically important parameter, has been evaluated.
Panalytical X'Pert PRO (CuKα radiation, steps of 0.01° (2θ), 2 s per step) in the same (2θ) range used at room temperature and with a cooling rate of 10 K min-1 in air. All diffraction sets were refined by the Le Bail method, using Topas 4.2 software. Differential scanning calorimetry (DSC) analyses of the as-prepared phases were conducted in a TA Instruments Q200, equipped with a liquid N2 cooling head, under He purge gas (25 mL min-1), with a heating rate of 20 K min-1 over the temperature range from 98 to 323 K. Thermogravimetric analyses (TGA) were carried out in a PerkinElmer STA-6000, under a synthetic air flow (20 mL min-1), with a heating rate of 20 K min-1, in the range 298–873 K.
2. Experimental
3.1. Solubility limit of Zn2+ in ZrMg1-xZnxMo3O12
The synthesis of ZrMg1-xZnxMo3O12 (x = 0.10, 0.30, 0.35, 0.40 and 1) was carried out by a solid-state route, using ZnO (Sigma-Aldrich, 97%), MgO (Sigma-Aldrich, 97%), ZrO2 (Sigma-Aldrich, 99%) and MoO3 (Fluke, 98%) powders, pre-heated at 773 K for 1 h. These reagents, at stoichiometric ratios, were manually mixed in an agate mortar for 2 h. The mixture was uniaxially pressed into pellets by applying 98 MPa for 1 min. The green pellets were then calcined in air at 1073 K for 5 h. Room-temperature X-ray powder diffraction (XRPD) measurements of the ZrMg1-xZnxMo3O12 calcined powders were carried out in a Bruker D8 Discover diffractometer (CuKα radiation, steps of 0.02° (2θ), 2s per step) over a range of 10 ̶ 60° (2θ). In situ XRPD analyses below room temperatures (173, 213, 253 and 298 K) were performed in a
Room-temperature XRPD patterns of ZrMg1-xZnxMo3O12 for x = 0.1, 0.30, 0.35 and 0.40 (Fig. 1) were analyzed for phase identification. Le Bail adjustment revealed the formation of the orthorhombic (Pna21) phase for compositions up to x = 0.35, with only traces of hexagonal ZrMo2O8 (P 31c ), according to the Powder Diffraction File (PDF) 77–1784. The presence of ZrMo2O8 traces could be inherent to the synthesis route, due to manual mixing of four different oxide reactants. For x = 0.40, the solubility limit of Zn2+ was exceeded, and the monoclinic ZnMoO4 system (C2/m), PDF 01-087-6506, emerged as a secondary phase (Fig. 1 d). An attempt to synthesize ZrZnMo3O12 was not successful and its final product was a mixture of hexagonal ZrMo2O8 and monoclinic ZnMoO4 with a small amount of monoclinic MoO3, as observed by
3. Results and discussion
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Fig. 2. XRPD patterns of ZrMg1-xZnxMo3O12 system at room and below room temperatures for (a) x = 0.10; (b) x = 0.30 and (c) x = 0.35. The characteristic peak of monoclinic phase is indicated by the arrow.
Fig. 3. (a) DSC curves of ZrMg1-xZnxMo3O12 powders and (b) TGA curve of ZrMg0.9Zn0.1Mo3O12 (the same trend was observed for other compositions).
overlapped forming a characteristic broadened peak, the fingerprint of the monoclinic phase in this ceramic family, indicated with an arrow in Fig. 2. For x = 0.10, the transition temperature is not well defined from XRPD since at 173 K the system was close to the phase transformation temperature (see below for corroboration by DSC results) and possibly there is the co-existence of the orthorhombic and monoclinic phases. The transition temperature for x = 0.30 is between 213 and 253 K, while in the case of x = 0.35 it is between 253 and 298 K. As the Zn2+ content increases, the transition temperature is shifted to higher
XRPD (not shown). 3.2. Phase transition in ZrMg1-xZnxMo3O12 XRPD patterns at and below room temperature in the 2θ range of 20 ̶ 26° (Fig. 2) allowed insight into the phase transition temperatures in the ZrMg1-xZnxMo3O12 system. The two characteristic diffraction peaks of the orthorhombic phase appeared at 21.8° and 22.4° (2θ), while after the transition to monoclinic phase, at lower temperatures, these peaks 3
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temperature range.
temperatures. This experimental observation is in agreement with the model proposed by Evans et al. [1], which takes into the account the effective charges on oxygen anions and their correlation with the electronegativity of the cations present in A2M3O12 and related families. The model considers that more electronegative cations would reduce the effective oxygen anion charge and, consequently, induce secondary oxygen-to-oxygen attractive forces, leading to the stabilization of the denser monoclinic polymorphs. In fact, this kind of secondary oxygen-to-oxygen bonding is responsible for the existence of some peculiar molecular oxides, such as OsO4 and RuO4 [21]. Therefore, cations with higher electronegativity, in A2M3O12 and related families, increase the temperature stability range of the denser monoclinic polymorph up to very high temperatures (for example, in Fe2Mo3O12), while low electronegativity cations expand the temperature stability range of the less dense orthorhombic polymorph, and in few cases, such as Y2W3O12 and Y2Mo2O12, completely suppress the phase transition to the monoclinic phase. Accordingly, partial substitution of Mg2+, which is a less electronegative cation (1.31), by Zn2+, which is a higher electronegative cation (1.65), will decrease the effective charge of the oxygen cations and promote stabilization of secondary oxygen-to-oxygen bonds, thereby stabilizing the monoclinic polymorph over a wider temperature range. The monoclinic to orthorhombic phase transition was also confirmed, and more accurately determined, by the onset of the endothermic peak in DSC curves (Fig. 3a) for all the studied compositions. The transition onset temperatures for x = 0.10, 0.30 and 0.35 were 181, 240 and 253 K, respectively, higher than for the pure ZrMgMo3O12, found to be at 147 K by Romao et al., [7]. Additionally, in the case of x = 0.40, the onset of the transition temperature was determined to be 256 K, which suggests that the solubility limit would be higher than x = 0.35, but lower than x = 0.40. Although it could be expected that partial substitution of Mg2+ by larger Zn2+ would influence the hygroscopicity of the ZrMg1xZnxMo3O12 phases and make them more hydroscopic, TGA curves showed insignificant hygroscopicity (Fig. 3b). It is promising for technological purposes both that the temperatures of phase transitions for ZrMg1-xZnxMo3O12 (x≤0.5) have been maintained well below room temperature, and that the newly synthesized phases were not hygroscopic. The latter ensures that the intrinsic thermal expansion properties of the ZrMg1-xZnxMo3O12 materials are not influenced by the presence of water. However, the solubility limit of Zn2+ in ZrMg1-xZnxMo3O12 is more restrictive than for HfMg1xZnxMo3O12, and this property could restrain the tuning of CTE inside this system. The appearance of hexagonal ZrMo2O8, at low quantities, in all composition will not contribute additionally to NTE since this phase presents normal positive expansion, differently from the cubic ZrMo2O8 which exhibits NTE over a large temperature interval [22].
Acknowledgments This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil (CAPES) –Finance Code 001. B.A.M. is grateful to CNPq (National Council for Scientific and Technological Development) for a Research Productivity Grant and to CAPES-Print for financial support. M.A.W. acknowledges support of NSERC and the Facilities for Materials Characterization managed by the Clean Technology Research Institute at Dalhousie University. P.I.P. is grateful to Escuela Politécnica Nacional (Project PIE-EPN-PUC-RIO2018) and CAPES-Print. The authors are grateful to Centro Brasileiro de Pesquisas Físicas (CBPF) for low temperature XRPD measurements. References [1] J.S.O. Evans, T.A. Mary, A.W. Sleight, Negative thermal expansion in a large molybdate and tungstate family, J. Solid State Chem. 133 (1997) 580–583, https://doi. org/10.1126/science.275.5296.61. [2] T. Suzuki, A. Omote, Negative thermal expansion in (HfMg)(WO4)3, J. Am. Ceram. 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4. Conclusions The Zn2+ solubility limit and phase transition temperature, two relevant parameters for tailoring CTE and determination of temperature stability range of orthorhombic structure, have been investigated for the new ZrMg1-xZnxMo3O12 system, with an aim to promote low and near-zero thermal expansion. The Zn2+ solubility limit in ZrMg1-xZnxMo3O12 restricts the homogeneous composition to x < 0.4, while ZrZnMo3O12 appears not to be a stable phase. The addition of Zn2+ from x = 0.1 to x = 0.35 elevated the monoclinic to orthorhombic transition temperature from 181 K to 253 K, while still keeping it far below room temperature. Hygroscopicity is not an issue for the ZrMg1-xZnxMo3O12 system and the thermal expansion is intrinsically controlled by the open-structure framework. It is anticipated, but yet to be confirmed by XRPD, that the addition of Zn2+ in the ZrMg1-xZnxMo3O12 system up to x = 0.35 might be sufficient to tune the CTE towards zero thermal expansion over a wide 4
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