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Tailorable thermal expansion and hygroscopic properties of cerium-substituted Y2W3O12 ceramics
Journal of Alloys and Compounds 751 (2018) 49e55
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Tailorable thermal expansion and hygroscopic properties of ceriumsubstituted Y2W3O12 ceramics Hongfei Liu a, *, Weikang Sun a, Zhiping Zhang b, Min Zhou a, Xiangdong Meng a, Xianghua Zeng a a b
School of Physical Science and Technology, Yangzhou University, Yangzhou, 225002, PR China Department of Electrical and Mechanical Engineering, Guangling College, Yangzhou University, Yangzhou, 225009, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 February 2018 Received in revised form 5 April 2018 Accepted 7 April 2018 Available online 11 April 2018
A new series of cerium-substituted Y2W3O12 ceramics were first fabricated with the goal of tailoring the thermal expansion and reducing the hygroscopicity. Influence of cerium substitution on the structure, hygroscopicity and thermal expansion property of Y2W3O12 ceramics were investigated using XRD, FESEM, HRTEM, XPS, TGA and TMA. Results indicate that the Y3þ can partly be substituted by Ce3þ in Y23þ in Y2W3O12 by Ce3þ results in the crystal structure xCexW3O12 ceramics and increasing substitution of Y change from orthorhombic to monoclinic. Single-phase Y2-xCexW3O12 ceramics can be synthesized in the range of 0.0 x 0.25 with an orthorhombic Y2W3O12-type crystal structure and 1.0 < x 2.0 with monoclinic Ce2W3O12-type crystal structure, respectively. As the amount of substituted cerium increases, the hygroscopic phenomenon of Y2-xCexW3O12 is significantly promoted, meanwhile the coefficient of thermal expansion gradually decreases. The linear coefficient of thermal expansion of Y2-xCexW3O12 ceramics can be adjusted from 13.094 106 K1 to 2.327 106 K1 by changing the substituted amount of cerium. Moreover, Y0.25Ce1.75W3O12 does not absorb moisture in air and shows almost zero thermal expansion from 182 C to 700 C and its coefficient of thermal expansion is tested to be 0.820 106 K1. This low thermal expansion Y0.25Ce1.75W3O12 material may have great potential applications in manufacturing precision device in many fields. © 2018 Elsevier B.V. All rights reserved.
Keywords: Thermal expansion Solid-state reaction Tungstates Thermogravimetric analysis
1. Introduction As temperature rises, most solid materials will expand in nature. However, recently some materials have been found to show an opposite property. These materials shrink on heating and exhibit negative thermal expansion (NTE). NTE materials have attracted wide attention for their distinctive property and great application value. One of the applications is that the NTE materials can be mixed with the positive thermal expansion (PTE) materials, such as epoxy resin, metal and ceramics, to fabricate the composites with low or even zero coefficient of thermal expansion (CTE) [1e5]. Such functional materials will have a range of potential applications in microelectronic packaging and electronic, optical and hightemperature devices. The series of A2M3O12 materials, where A is trivalent transition
* Corresponding author. School of Physical Science and Technology, Yangzhou University, No. 180 Siwangting Road, Yangzhou, 225002, PR China. E-mail address: [email protected] (H. Liu). https://doi.org/10.1016/j.jallcom.2018.04.081 0925-8388/© 2018 Elsevier B.V. All rights reserved.
metal cations or lanthanide and M is W6þ or Mo6þ, have aroused much attention for the last two decades. In terms of thermal expansion property, A2W3O12 family is highly dependent on the type of A cation. When the A is a cation in the range from La to Eu, A2W3O12 materials crystallize in monoclinic structure at room temperature and show PTE. While A is a cation in the range from Ho to Lu, A2W3O12 materials will adopt an orthorhombic structure, which are highly hygroscopic in air and demonstrate a very intense NTE only after the loss of the hygroscopic water [6e12]. Furthermore, lager ionic radius of A cation leads to more negative thermal expansion in A2W3O12 family. Thereby the presence of a larger sized A cation, such as Y3þ, in the structure of A2M3O12 causes the most pronounced NTE over all known A2M3O12 phases. This NTE property may be either isotropic or anisotropic. Thus, some materials show NTE in all three crystallographic directions, whereas others show this behavior in only one or two directions [13e17]. More remarkably, Y2W3O12 exhibits NTE behavior along all three crystallographic directions, and consists of an open frame work with corner shared polyhedral [16,17]. NTE is
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Fig. 1. Room temperature XRD patterns for the obtained Y2-xCexW3O12 (0 x 2) ceramics (a) and the crystal structures of Y2-xCexW3O12 (b) monoclinic (space group:C2/c) and (c) orthorhombic (space group: Pnca) forms.
CTE of Y2-xCexW3O12 to be negative, near-zero and positive by changing the Y/Ce ration. The influence of substituted Ce3þ on the crystal structure, hygroscopicity and the CTE value of Y2-xCexW3O12 (0 x 2) ceramics was also studied. 2. Experimental
Fig. 2. Partial XRD patterns for Y2-xCexW3O12 (x ¼ 1, 1.5, 1.75, 2) ceramics.
Table 1 The unit cell parameters of Y2-xCexW3O12 (x ¼ 1, 1.5, 1.75 and 1) compounds as a function of composition. Y2-xCexW3O12
a (Å)
b (Å)
c (Å)
b ( )
V(Å3)
x¼2 x ¼ 1.75 x ¼ 1.5 x¼1
7.833 7.800 7.779 7.765
11.745 11.690 11.645 11.613
11.720 11.690 11.645 11.613
109.36 109.44 109.47 109.50
1007.62 995.68 985.28 978.97
attributed to the transverse thermal vibrations of bridging-O atoms of A-O-W linkages in their structure [6]. It has reported that partial substitution of the A-site cation may dramatically influence the CET of A2M3O12 [11,12,18,19]. Nonhygroscopic Ce2W3O12 crystallizes in monoclinic structure and exhibits PTE. In this work, an attempt has been made to prepare Y2xCexW3O12 solid solutions with controllable CET and overcome the hygroscopicity of Y2W3O12. Essentially, this work aims to adjust the
Analytically pure Y2O3, CeO2 and WO3 powders were used as raw materials to prepare Y2-xCexW3O12 (0 x 2) ceramics. All the raw materials were preheated at 500 C for 12 h and then weighed in accordance with the different stoichiometry. Powder mixture was co-milled for 12 h in alcohol and dried at 100 C. Subsequently, the mixtures were heated at 600 C for 6 h, followed by an intermediate grinding at room temperature and then pressed into pellets at 25 MPa. Finally, the pellets were heated at 950 C for 12 h in the furnace. Phase composition was characterized using a powder X-ray diffractometer (XRD, Shimadzu-7000) with CuKa incident radiation at 40 kV and 30 mA. The data was collected in the 2q angular range of 10 e60 with a scanning speed of 5 /min. The micromorphology of the specimen was studied using a scanning electron microscope (SEM, Hitachi S-4800). The microscopic observation and elemental mapping were also conducted using a FEI-Tecnai F30 S-TWIN high resolution transmission electron microscope (TEM) and an energy dispersive X-ray spectroscopy (EDX). The elemental electrovalence and compositions of the sample were carried out using a X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific ESCALAB250Xi). The hygroscopicity of the sample was measured using a thermogravimetric analyzer (TGA, Perkin-Elmer Pyris1) in the temperature range from room temperature to 300 C with a heating rate of 10 C/min. The thermal expansion behavior of the sample was characterized using a thermal mechanical analyzer (TMA, Seiko 6300), and the heating rate is 10 C/ min from room temperature to 700 C. 3. Results and discussion 3.1. Phase identification XRD patterns of Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2)
H. Liu et al. / Journal of Alloys and Compounds 751 (2018) 49e55
51
Fig. 3. (a) STEM image of a Y0.25Ce1.75W3O12 particle; (b)e(e) EDX composition maps for the elements of Ce, W, O and Y in the same Y0.25Ce1.75W3O12 particle; (f)e(g) TEM image of Y0.25Ce1.75W3O12 particle and part HRTEM image of Y0.25Ce1.75W3O12 particle acquired from the area marked by a square in image f; (h) EDX spectrum acquired from the area in image a.
samples as a function of composition x are shown in Fig. 1(a). When x is 0 and 0.25, the Y2-xCexW3O12 samples both crystallize in orthorhombic Y2W3O12-type structure with Pnca space group symmetry, and Fig. 1(c) shows their crystal structure. The broad diffraction peaks and low diffraction intensity in the XRD patterns of Y2-xCexW3O12 (x ¼ 0, 0.25) corroborates the presence of amorphous phase, which is in close agreement with the report that Y2W3O12 is hygroscopic at room temperature [16,17]. All diffraction peaks of Y2-xCexW3O12 (x ¼ 1, 1.5, 1.75, 2) can be indexed to the C2/c monoclinic structure of Ce2W3O12-type with JCPDS card number 31-0340, and the corresponding crystal structure is also given in Fig. 1(b). In the case of Y1Ce1W3O12, however, showed several weak peaks belonging to Y2W3O12, indicating that single phase of Ce2W3O12-type can only form in the range of 1 < x 2. Furthermore, it can be obviously observed from Fig. 2 that the diffraction peaks of (221), (132), (023), (040) crystalline planes for Y2xCexW3O12 (x ¼ 1, 1.5, 1.75, 2) gradually shift towards smaller 2q angles with the increase of x, indicating the expansion of lattice parameters. The unit-cell parameters and volumes of Y2-xCexW3O12
compounds (x ¼ 1, 1.5, 1.75 and 1) were calculated using the Topas software, which was shown in Table 1. As increasing amount of substituted cerium, the unit-cell parameters for a, b, c axis and volume all increase gradually, whereas the b decrease little by little. Mainly because the ionic radius of Ce3þ(1.034 Å) is larger than that of Y3þ (0.9 Å), which is consistent with Vegard's law [6]. However, in the case of 0.5 x 1, XRD patterns of Y2-xCexW3O12 display diffraction peaks belonging to both the above two phases. Some representative reflections of orthorhombic Y2W3O12 and monoclinic Ce2W3O12 are labeled in Fig. 1(a). These results suggest that solid solutions can be only formed in a finite composition range (0 x 0.25 and 1 < x 2), which can be ascribed to the relatively great difference in their structure between monoclinic Ce2W3O12 and orthorhombic Y2W3O12, and radii difference between Y3þ (0.9 Å) and Ce3þ (1.034 Å). Fig. 3 exhibits the TEM, scanning-mode TEM, high resolution TEM images of Y0.25Ce1.75W3O12 powder and the corresponding Y, Ce, W and O elemental maps. As shown in Fig. 3(a)-(e), all the elements homogeneously distributed over the surface of the
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ceramics as expected. 3.2. SEM analysis Scanning electron microscope (SEM) was conducted to examine the influence of Ce content on morphology. Fig. 5 shows the SEM cross-sectional micrographs of Y2W3O12, Ce2W3O12 and Y2xCexW3O12 ceramics with different x values. Y2W3O12 (Fig. 5 (a)) and Ce2W3O12 (Fig. 5 (g)) ceramics both comprised spherical-like grains with some pores and voids, however, Ce2W3O12 ceramics showed a denser morphology compared to Y2W3O12. The SEM photographs of Y2-xCexW3O12 (0 < x < 2) indicate that samples with 0.25 x 1 (Fig. 5 (b)-(d)) showed the similar microstructure to Y2W3O12 ceramics, while samples with 1.5 x 2 (Fig. 5 (e)-(f)) exhibited essentially the same fracture surface morphology as Ce2W3O12 ceramics. At x ¼ 0.25 and 0.5, the microstructure of Y2xCexW3O12 ceramics were lowly dense, when Ce content was increased to x ¼ 1, 1.5 and 1.75, it can be seen that the ceramic grains were developed and formed a more densified microstructure. In addition, SEM micrographs also show the dependence of the particle morphology on Ce content x. Indeed, as the cerium content increases, the uniformity of gain size and shape was improved for 0.25 x 1. However, no remarkable change was observed for samples with high Ce content (x ¼ 1.5, 1.75). 3.3. Thermogravimetric analysis
Fig. 4. XPS spectra of Ce 3d and Y 3d in Y0.25Ce1.75W3O12 ceramics.
observed Y0.25Ce1.75W3O12 particle, no impurity element was detected. In Fig. 3(f)-(g), the clear HRTEM lattice fringes indicate the highly crystalline nature of Y0.25Ce1.75W3O12 ceramics. The interplanar spacing was 0.326 nm, which is ascribed to the d-spacing of (221) planes of Y0.25Ce1.75W3O12. Fig. 3(h) shows the EDX spectrum acquired from Y0.25Ce1.75W3O12 particle in Fig. 3 (a), and the molar ratio of the Y: Ce is tested to be 1:7.09, which is in good agreement with the expected Y: Ce ratio in Y0.25Ce1.75W3O12. XPS was also used to characterize the valence states of Y and Ce ions presented in Y0.25Ce1.75W3O12 ceramics. Fig. 4 displays the XPS patterns of Ce 3d and Y 3d core levels in Y0.25Ce1.75W3O12. As shown in Fig. 4(a), the peak at 882.11 eV attributes to 3d5/2 with its satellite at 885.98 eV. Similarly, the peak appearing at 900.41 eV and its satellite at 904.38 eV corresponds to 3d3/2. Besides, no peaks were observed around 916 eV, confirming the Ce4þ is absent. These results indicate the Ce ion exhibits a þ3 valence state in Y0.25Ce1.75W3O12. In Fig. 4(b), the XPS pattern for Y 3d consists of two peaks at 158.11 eV for Y 3d5/2 and 160.16 eV for Y 3d3/2, which indicates that the Y ion also adopts a þ3 valence state in Y0.25Ce1.75W3O12. Combined with the above XRD and elemental mapping analysis, it can be concluded that the Ce3þ ions were successfully isovalently substituted by Y3þ ions in Y0.25Ce1.75W3O12
TG curves of Y2-xCexW3O12 (0 x 2) specimens are shown in Fig. 6. Obviously, a weight loss region was seen in the TG curves of Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1) specimens from 30 C to 97 C, attributing to the hygroscopicity of Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1) in air. Table 2 shows the weight loss, corresponding water loss temperature range and the calculated number of crystal water of Y2-xCexW3O12 specimens. The weight losses of the Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5 and 1) specimens are about 5.61%, 5.05%, 3.17% and 1.47%, respectively. The corresponding number of crystal water is calculated to be 3.04, 2.76, 1.72 and 0.81, which gradually decreases as increasing amount of substituted cerium. Futhermore, it can be found that the water molecules lost easier, as the upper limit of water loss temperature for Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1) samples decreases from 97 C to 76 C. The same hygroscopic phenomenon also has been observed in some other orthorhombic A2W3O12 (A ¼ Ho-Lu) compounds [7,11,12]. Indeed, the loose structure with pores and voids is inclined to absorb moisture. However, no obvious weight loss region exists in the TG curves of Y2-xCexW3O12 (x ¼ 1.5, 1.75, 2), indicating these specimens are nonhygroscopic. It can be found that the hygroscopic phenomenon of Y2-xCexW3O12 specimens are reduced with more Y3þ replaced by Ce3þ. 3.4. Thermal expansion property Fig. 7 displays the dilatometric curves of Y2-xCexW3O12 (0 x 2) ceramics below 700 C. The dilatometric curves for orthorhombic Y2W3O12 and monoclinic Ce2W3O12 ceramics are also provided for comparison. Monoclinic Ce2W3O12 ceramics show PTE over the whole testing temperature range, whereas orthorhombic Y2W3O12 ceramics expand with increasing temperature in the 23e154 C and then shrank upon further heating. All investigated Y2-xCexW3O12 (x ¼ 0.25, 0.5, 1) ceramics exhibited very similar TMA patterns to orthorhombic Y2W3O12. According to the above TG analysis, Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1) samples are
H. Liu et al. / Journal of Alloys and Compounds 751 (2018) 49e55
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Fig. 5. SEM images of the obtained Y2-xCexW3O12 (0 x 2) ceramics (a) Y2W3O12, (b) Y1.75Ce0.25W3O12, (c) Y1.5Ce0.5W3O12, (d) Y1Ce1W3O12, (e) Y0.5Ce1.5W3O12, (f) Y0.25Ce1.75W3O12, (g) Ce2W3O12.
hygroscopic. The initial expansion in the curves is mainly because the crystal water limits the transverse vibration of the bridge oxygen atom in Y-O-W linkages and hinders NTE behavior [16,17]. As temperature rises, the compounds lost their absorbed water molecules gradually, and NTE was only observed after complete removal of moistures. As for x ¼ 1.5, 1.75, the thermal expansion curves of Y2-xCexW3O12 ceramics also showed a small initial expansion. It is mainly due to the existence of pores and microcracks in ceramics, which may lead to thermal expansion hysteresis in the monoclinic tungstates [7]. Above analysis indicates that the thermal expansion behavior changes drastically by the introduction of Ce3þ into the crystal structure of Y2W3O12. Different thermal expansion behavior of Y2xCexW3O12 ceramics leads to a different variety in the CTE (see
Table 3). It can be found that NTE has a significant weakening from x ¼ 0 to x ¼ 2. As more Y3þ was replaced by Ce3þ, the magnitude of CTE of Y2-xCexW3O12 would become less negative and then become positive. The result suggests that the CTE of Y2-xCexW3O12 ceramics can be tailored in the range from 13.094 106 K1 to 2.327 106 K1 by controlling the substituted Ce3þ content. It is worthy to note that the obtained Y0.25Ce1.75W3O12 ceramics almost exhibits near-zero thermal expansion from 182 C to 700 C with an average linear CTE of 0.82 106 K1. 4. Conclusions A new series of Ce-substituted Y2-xCexW3O12 (0 x 2) ceramics were successfully fabricated by solid-state reaction
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H. Liu et al. / Journal of Alloys and Compounds 751 (2018) 49e55 Table 3 Average linear CTEs of Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2) ceramics.
Fig. 6. Thermogravimetric curves of Y2-xCexW3O12 samples (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2).
Table 2 Crystalline water number and corresponding water loss temperature range of compounds Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2). Y2-xCexW3O12$nH2O
Water loss temperature range ( C)
Weight loss
n (water molecules in the compounds)
x ¼ 0.00 x ¼ 0.25 x ¼ 0.50 x ¼ 1.00 x ¼ 1.50 x ¼ 1.75 x ¼ 2.00
30e97 30e91 30e82 30e76 / / /
5.61% 5.05% 3.17% 1.47% 0 0 0
3.04 2.76 1.72 0.81 0 0 0
technique. Single phase can be formed in the range of 0 x 0.25 and the Y2-xCexW3O12 ceramics crystallize in orthorhombic Y2W3O12-type structure. Meanwhile, when 1 < x 2, the Y2xCexW3O12 ceramics crystallize in monoclinic Ce2W3O12-type structure, whereas samples with 0.5 x 1 contain both of the above structures. TG analysis indicates Y2-xCexW3O12 (0 x 1)
Fig. 7. Dilatometric curves for Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2) ceramics.
Y2-xCexW3O12
Temperature range ( C)
a l ( 106K1)
x ¼ 0.00 x ¼ 0.25 x ¼ 0.50 x ¼ 1.00 x ¼ 1.50 x ¼ 1.75 x ¼ 2.00
154e700 159e700 171e700 138e700 109e700 182e700 23e700
13.094 11.399 9.590 3.758 1.787 0.820 2.327
ceramics are hygroscopic and the adsorbed moistures will be removed in the temperature range from 30 to 97 C. However, Y2xCexW3O12 (1 < x 2) ceramics are non-hygroscopic. The CTEs of the Y2-xCexW3O12 (0 x 2) specimens can be adjusted between 13.094 106 K1 and 2.327 106 K1 by tailoring the amount of substituted Ce cation. The Y0.25Ce1.75W3O12 ceramics exhibits very low NTE with an average linear CTE of 0.82 106 K1 from 182 C to 700 C. This non-hygroscopic and near-zero thermal expansion ceramics may have a wide range of applications in future. Acknowledgments We are grateful for the support of National Natural Science Foundation of China (No. 51602280 and No. 51102207), Qing Lan Project of Jiangsu Province, Guangling College of Yangzhou University Natural Science Research Foundation under grant No. ZKZD17001. References [1] S.E. Tallentire, F. Child, I. Fall, L. Vella-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 Zr1xSnxMo2O8, J. Am. Chem. Soc. 135 (2013) 12849e12856. [2] L.M. Sullivan, C.M. Lukehart, Zirconium tungstate (ZrW2O8)/polyimide nanocomposites exhibiting reduced coefficient of thermal expansion, Chem. Mater. 17 (2005) 2136e2141. [3] Q.Q. Liu, J. Yang, X.N. Cheng, G.S. Liang, X.J. Sun, Preparation and characterization of negative thermal expansion Sc2W3O12/Cu coreeshell composite, Ceram. Int. 38 (2012) 541e545. [4] J. Yang, Y.S. Yang, Q.Q. Liu, G.F. Xu, X.N. Cheng, Preparation of negative thermal expansion ZrW2O8 powders and its application in polyimide/ZrW2O8 composites, J. Mater. Sci. Technol. 26 (2010) 665e668. [5] N.A. Banek, H.I. Baiz, A. Latigo, C. Lind, Autohydration of nanosized cubic zirconium tungstate, J. Am. Chem. Soc. 132 (2010) 8278e8279. [6] P.M. Forster, A. Yokochi, A.W. Sleight, Enhanced negative thermal expansion in Lu2W3O12, Solid State Chem. 140 (1998) 157e158. [7] S. Sumithra, A.M. Umarji, Role of crystal structure on the thermal expansion of Ln2W3O12 (Ln ¼La, Nd, Dy, Y, Er and Yb), Solid State Sci. 6 (2004) 1313e1319. [8] P.S. Anjana, T. Joseph, M.T. Sebastian, Low temperature sintering and microwave dielectric properties of Ce2(WO4)3 ceramics, Ceram. Int. 36 (2010) 1535e1540. [9] S. Sumithra, A.M. Umarji, Negative thermal expansion in rare earth molybdates, Solid State Sci. 8 (2016) 1453e1458. [10] M.M. Wu, Y.Z. Cheng, J. Peng, X.L. Xiao, D.F. Chen, R. Kiyanagi, J.S. Fieramosca, S. Short, J. Jorgensen, Z.B. Hu, Synthesis of solid solution Er2-x CexW3O12 and studies of their thermal expansion behavior, Mater. Res. Bull. 42 (2007) 2090e2098. [11] H.F. Liu, W. Zhang, Z.P. Zhang, X.B. Chen, Synthesis and negative thermal expansion properties of solid solutions Yb2xLaxW3O12 (0x2), Ceram. Int. 38 (2012) 2951e2956. [12] Y.Z. Cheng, X.L. Xiao, X.F. Liu, M.M. Wu, J. Peng, Z.B. Hu, Study of the structures and thermal expansion properties of solid solutions Yb2-xDyxW3O12 (0x1.5 and1.8x2.0), Physica B 411 (2013) 173e177. [13] A.K.A. Pryde, K.D. Hammonds, M.T. Dove, V. Heine, J.D. Gale, M.C. Warren, Origin of the negative thermal expansion in ZrW2O8 and ZrV2O7, J. Phys. Condens. Matter 8 (1996) 10973e10982. [14] N.A. Banek, H.I. Baiz, A. Latigo, C. Lind, Autohydration of nanosized cubic zirconium tungstate, J. Am. Chem. Soc. 132 (2010) 8278e8279. [15] J.S.O. Evans, T.A. Mary, A.W. Sleight, Negative thermal expansion in Sc2(WO4)3, J. Solid State Chem. 137 (1998) 148e160. [16] D.A. Woodcock, P. Lightfoot, C. Ritter, Negative thermal expansion in
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Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Tailorable thermal expansion and hygroscopic properties of ceriumsubstituted Y2W3O12 ceramics Hongfei Liu a, *, Weikang Sun a, Zhiping Zhang b, Min Zhou a, Xiangdong Meng a, Xianghua Zeng a a b
School of Physical Science and Technology, Yangzhou University, Yangzhou, 225002, PR China Department of Electrical and Mechanical Engineering, Guangling College, Yangzhou University, Yangzhou, 225009, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 February 2018 Received in revised form 5 April 2018 Accepted 7 April 2018 Available online 11 April 2018
A new series of cerium-substituted Y2W3O12 ceramics were first fabricated with the goal of tailoring the thermal expansion and reducing the hygroscopicity. Influence of cerium substitution on the structure, hygroscopicity and thermal expansion property of Y2W3O12 ceramics were investigated using XRD, FESEM, HRTEM, XPS, TGA and TMA. Results indicate that the Y3þ can partly be substituted by Ce3þ in Y23þ in Y2W3O12 by Ce3þ results in the crystal structure xCexW3O12 ceramics and increasing substitution of Y change from orthorhombic to monoclinic. Single-phase Y2-xCexW3O12 ceramics can be synthesized in the range of 0.0 x 0.25 with an orthorhombic Y2W3O12-type crystal structure and 1.0 < x 2.0 with monoclinic Ce2W3O12-type crystal structure, respectively. As the amount of substituted cerium increases, the hygroscopic phenomenon of Y2-xCexW3O12 is significantly promoted, meanwhile the coefficient of thermal expansion gradually decreases. The linear coefficient of thermal expansion of Y2-xCexW3O12 ceramics can be adjusted from 13.094 106 K1 to 2.327 106 K1 by changing the substituted amount of cerium. Moreover, Y0.25Ce1.75W3O12 does not absorb moisture in air and shows almost zero thermal expansion from 182 C to 700 C and its coefficient of thermal expansion is tested to be 0.820 106 K1. This low thermal expansion Y0.25Ce1.75W3O12 material may have great potential applications in manufacturing precision device in many fields. © 2018 Elsevier B.V. All rights reserved.
Keywords: Thermal expansion Solid-state reaction Tungstates Thermogravimetric analysis
1. Introduction As temperature rises, most solid materials will expand in nature. However, recently some materials have been found to show an opposite property. These materials shrink on heating and exhibit negative thermal expansion (NTE). NTE materials have attracted wide attention for their distinctive property and great application value. One of the applications is that the NTE materials can be mixed with the positive thermal expansion (PTE) materials, such as epoxy resin, metal and ceramics, to fabricate the composites with low or even zero coefficient of thermal expansion (CTE) [1e5]. Such functional materials will have a range of potential applications in microelectronic packaging and electronic, optical and hightemperature devices. The series of A2M3O12 materials, where A is trivalent transition
* Corresponding author. School of Physical Science and Technology, Yangzhou University, No. 180 Siwangting Road, Yangzhou, 225002, PR China. E-mail address: [email protected] (H. Liu). https://doi.org/10.1016/j.jallcom.2018.04.081 0925-8388/© 2018 Elsevier B.V. All rights reserved.
metal cations or lanthanide and M is W6þ or Mo6þ, have aroused much attention for the last two decades. In terms of thermal expansion property, A2W3O12 family is highly dependent on the type of A cation. When the A is a cation in the range from La to Eu, A2W3O12 materials crystallize in monoclinic structure at room temperature and show PTE. While A is a cation in the range from Ho to Lu, A2W3O12 materials will adopt an orthorhombic structure, which are highly hygroscopic in air and demonstrate a very intense NTE only after the loss of the hygroscopic water [6e12]. Furthermore, lager ionic radius of A cation leads to more negative thermal expansion in A2W3O12 family. Thereby the presence of a larger sized A cation, such as Y3þ, in the structure of A2M3O12 causes the most pronounced NTE over all known A2M3O12 phases. This NTE property may be either isotropic or anisotropic. Thus, some materials show NTE in all three crystallographic directions, whereas others show this behavior in only one or two directions [13e17]. More remarkably, Y2W3O12 exhibits NTE behavior along all three crystallographic directions, and consists of an open frame work with corner shared polyhedral [16,17]. NTE is
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Fig. 1. Room temperature XRD patterns for the obtained Y2-xCexW3O12 (0 x 2) ceramics (a) and the crystal structures of Y2-xCexW3O12 (b) monoclinic (space group:C2/c) and (c) orthorhombic (space group: Pnca) forms.
CTE of Y2-xCexW3O12 to be negative, near-zero and positive by changing the Y/Ce ration. The influence of substituted Ce3þ on the crystal structure, hygroscopicity and the CTE value of Y2-xCexW3O12 (0 x 2) ceramics was also studied. 2. Experimental
Fig. 2. Partial XRD patterns for Y2-xCexW3O12 (x ¼ 1, 1.5, 1.75, 2) ceramics.
Table 1 The unit cell parameters of Y2-xCexW3O12 (x ¼ 1, 1.5, 1.75 and 1) compounds as a function of composition. Y2-xCexW3O12
a (Å)
b (Å)
c (Å)
b ( )
V(Å3)
x¼2 x ¼ 1.75 x ¼ 1.5 x¼1
7.833 7.800 7.779 7.765
11.745 11.690 11.645 11.613
11.720 11.690 11.645 11.613
109.36 109.44 109.47 109.50
1007.62 995.68 985.28 978.97
attributed to the transverse thermal vibrations of bridging-O atoms of A-O-W linkages in their structure [6]. It has reported that partial substitution of the A-site cation may dramatically influence the CET of A2M3O12 [11,12,18,19]. Nonhygroscopic Ce2W3O12 crystallizes in monoclinic structure and exhibits PTE. In this work, an attempt has been made to prepare Y2xCexW3O12 solid solutions with controllable CET and overcome the hygroscopicity of Y2W3O12. Essentially, this work aims to adjust the
Analytically pure Y2O3, CeO2 and WO3 powders were used as raw materials to prepare Y2-xCexW3O12 (0 x 2) ceramics. All the raw materials were preheated at 500 C for 12 h and then weighed in accordance with the different stoichiometry. Powder mixture was co-milled for 12 h in alcohol and dried at 100 C. Subsequently, the mixtures were heated at 600 C for 6 h, followed by an intermediate grinding at room temperature and then pressed into pellets at 25 MPa. Finally, the pellets were heated at 950 C for 12 h in the furnace. Phase composition was characterized using a powder X-ray diffractometer (XRD, Shimadzu-7000) with CuKa incident radiation at 40 kV and 30 mA. The data was collected in the 2q angular range of 10 e60 with a scanning speed of 5 /min. The micromorphology of the specimen was studied using a scanning electron microscope (SEM, Hitachi S-4800). The microscopic observation and elemental mapping were also conducted using a FEI-Tecnai F30 S-TWIN high resolution transmission electron microscope (TEM) and an energy dispersive X-ray spectroscopy (EDX). The elemental electrovalence and compositions of the sample were carried out using a X-ray photoelectron spectroscopy (XPS, Thermo Fisher Scientific ESCALAB250Xi). The hygroscopicity of the sample was measured using a thermogravimetric analyzer (TGA, Perkin-Elmer Pyris1) in the temperature range from room temperature to 300 C with a heating rate of 10 C/min. The thermal expansion behavior of the sample was characterized using a thermal mechanical analyzer (TMA, Seiko 6300), and the heating rate is 10 C/ min from room temperature to 700 C. 3. Results and discussion 3.1. Phase identification XRD patterns of Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2)
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Fig. 3. (a) STEM image of a Y0.25Ce1.75W3O12 particle; (b)e(e) EDX composition maps for the elements of Ce, W, O and Y in the same Y0.25Ce1.75W3O12 particle; (f)e(g) TEM image of Y0.25Ce1.75W3O12 particle and part HRTEM image of Y0.25Ce1.75W3O12 particle acquired from the area marked by a square in image f; (h) EDX spectrum acquired from the area in image a.
samples as a function of composition x are shown in Fig. 1(a). When x is 0 and 0.25, the Y2-xCexW3O12 samples both crystallize in orthorhombic Y2W3O12-type structure with Pnca space group symmetry, and Fig. 1(c) shows their crystal structure. The broad diffraction peaks and low diffraction intensity in the XRD patterns of Y2-xCexW3O12 (x ¼ 0, 0.25) corroborates the presence of amorphous phase, which is in close agreement with the report that Y2W3O12 is hygroscopic at room temperature [16,17]. All diffraction peaks of Y2-xCexW3O12 (x ¼ 1, 1.5, 1.75, 2) can be indexed to the C2/c monoclinic structure of Ce2W3O12-type with JCPDS card number 31-0340, and the corresponding crystal structure is also given in Fig. 1(b). In the case of Y1Ce1W3O12, however, showed several weak peaks belonging to Y2W3O12, indicating that single phase of Ce2W3O12-type can only form in the range of 1 < x 2. Furthermore, it can be obviously observed from Fig. 2 that the diffraction peaks of (221), (132), (023), (040) crystalline planes for Y2xCexW3O12 (x ¼ 1, 1.5, 1.75, 2) gradually shift towards smaller 2q angles with the increase of x, indicating the expansion of lattice parameters. The unit-cell parameters and volumes of Y2-xCexW3O12
compounds (x ¼ 1, 1.5, 1.75 and 1) were calculated using the Topas software, which was shown in Table 1. As increasing amount of substituted cerium, the unit-cell parameters for a, b, c axis and volume all increase gradually, whereas the b decrease little by little. Mainly because the ionic radius of Ce3þ(1.034 Å) is larger than that of Y3þ (0.9 Å), which is consistent with Vegard's law [6]. However, in the case of 0.5 x 1, XRD patterns of Y2-xCexW3O12 display diffraction peaks belonging to both the above two phases. Some representative reflections of orthorhombic Y2W3O12 and monoclinic Ce2W3O12 are labeled in Fig. 1(a). These results suggest that solid solutions can be only formed in a finite composition range (0 x 0.25 and 1 < x 2), which can be ascribed to the relatively great difference in their structure between monoclinic Ce2W3O12 and orthorhombic Y2W3O12, and radii difference between Y3þ (0.9 Å) and Ce3þ (1.034 Å). Fig. 3 exhibits the TEM, scanning-mode TEM, high resolution TEM images of Y0.25Ce1.75W3O12 powder and the corresponding Y, Ce, W and O elemental maps. As shown in Fig. 3(a)-(e), all the elements homogeneously distributed over the surface of the
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ceramics as expected. 3.2. SEM analysis Scanning electron microscope (SEM) was conducted to examine the influence of Ce content on morphology. Fig. 5 shows the SEM cross-sectional micrographs of Y2W3O12, Ce2W3O12 and Y2xCexW3O12 ceramics with different x values. Y2W3O12 (Fig. 5 (a)) and Ce2W3O12 (Fig. 5 (g)) ceramics both comprised spherical-like grains with some pores and voids, however, Ce2W3O12 ceramics showed a denser morphology compared to Y2W3O12. The SEM photographs of Y2-xCexW3O12 (0 < x < 2) indicate that samples with 0.25 x 1 (Fig. 5 (b)-(d)) showed the similar microstructure to Y2W3O12 ceramics, while samples with 1.5 x 2 (Fig. 5 (e)-(f)) exhibited essentially the same fracture surface morphology as Ce2W3O12 ceramics. At x ¼ 0.25 and 0.5, the microstructure of Y2xCexW3O12 ceramics were lowly dense, when Ce content was increased to x ¼ 1, 1.5 and 1.75, it can be seen that the ceramic grains were developed and formed a more densified microstructure. In addition, SEM micrographs also show the dependence of the particle morphology on Ce content x. Indeed, as the cerium content increases, the uniformity of gain size and shape was improved for 0.25 x 1. However, no remarkable change was observed for samples with high Ce content (x ¼ 1.5, 1.75). 3.3. Thermogravimetric analysis
Fig. 4. XPS spectra of Ce 3d and Y 3d in Y0.25Ce1.75W3O12 ceramics.
observed Y0.25Ce1.75W3O12 particle, no impurity element was detected. In Fig. 3(f)-(g), the clear HRTEM lattice fringes indicate the highly crystalline nature of Y0.25Ce1.75W3O12 ceramics. The interplanar spacing was 0.326 nm, which is ascribed to the d-spacing of (221) planes of Y0.25Ce1.75W3O12. Fig. 3(h) shows the EDX spectrum acquired from Y0.25Ce1.75W3O12 particle in Fig. 3 (a), and the molar ratio of the Y: Ce is tested to be 1:7.09, which is in good agreement with the expected Y: Ce ratio in Y0.25Ce1.75W3O12. XPS was also used to characterize the valence states of Y and Ce ions presented in Y0.25Ce1.75W3O12 ceramics. Fig. 4 displays the XPS patterns of Ce 3d and Y 3d core levels in Y0.25Ce1.75W3O12. As shown in Fig. 4(a), the peak at 882.11 eV attributes to 3d5/2 with its satellite at 885.98 eV. Similarly, the peak appearing at 900.41 eV and its satellite at 904.38 eV corresponds to 3d3/2. Besides, no peaks were observed around 916 eV, confirming the Ce4þ is absent. These results indicate the Ce ion exhibits a þ3 valence state in Y0.25Ce1.75W3O12. In Fig. 4(b), the XPS pattern for Y 3d consists of two peaks at 158.11 eV for Y 3d5/2 and 160.16 eV for Y 3d3/2, which indicates that the Y ion also adopts a þ3 valence state in Y0.25Ce1.75W3O12. Combined with the above XRD and elemental mapping analysis, it can be concluded that the Ce3þ ions were successfully isovalently substituted by Y3þ ions in Y0.25Ce1.75W3O12
TG curves of Y2-xCexW3O12 (0 x 2) specimens are shown in Fig. 6. Obviously, a weight loss region was seen in the TG curves of Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1) specimens from 30 C to 97 C, attributing to the hygroscopicity of Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1) in air. Table 2 shows the weight loss, corresponding water loss temperature range and the calculated number of crystal water of Y2-xCexW3O12 specimens. The weight losses of the Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5 and 1) specimens are about 5.61%, 5.05%, 3.17% and 1.47%, respectively. The corresponding number of crystal water is calculated to be 3.04, 2.76, 1.72 and 0.81, which gradually decreases as increasing amount of substituted cerium. Futhermore, it can be found that the water molecules lost easier, as the upper limit of water loss temperature for Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1) samples decreases from 97 C to 76 C. The same hygroscopic phenomenon also has been observed in some other orthorhombic A2W3O12 (A ¼ Ho-Lu) compounds [7,11,12]. Indeed, the loose structure with pores and voids is inclined to absorb moisture. However, no obvious weight loss region exists in the TG curves of Y2-xCexW3O12 (x ¼ 1.5, 1.75, 2), indicating these specimens are nonhygroscopic. It can be found that the hygroscopic phenomenon of Y2-xCexW3O12 specimens are reduced with more Y3þ replaced by Ce3þ. 3.4. Thermal expansion property Fig. 7 displays the dilatometric curves of Y2-xCexW3O12 (0 x 2) ceramics below 700 C. The dilatometric curves for orthorhombic Y2W3O12 and monoclinic Ce2W3O12 ceramics are also provided for comparison. Monoclinic Ce2W3O12 ceramics show PTE over the whole testing temperature range, whereas orthorhombic Y2W3O12 ceramics expand with increasing temperature in the 23e154 C and then shrank upon further heating. All investigated Y2-xCexW3O12 (x ¼ 0.25, 0.5, 1) ceramics exhibited very similar TMA patterns to orthorhombic Y2W3O12. According to the above TG analysis, Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1) samples are
H. Liu et al. / Journal of Alloys and Compounds 751 (2018) 49e55
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Fig. 5. SEM images of the obtained Y2-xCexW3O12 (0 x 2) ceramics (a) Y2W3O12, (b) Y1.75Ce0.25W3O12, (c) Y1.5Ce0.5W3O12, (d) Y1Ce1W3O12, (e) Y0.5Ce1.5W3O12, (f) Y0.25Ce1.75W3O12, (g) Ce2W3O12.
hygroscopic. The initial expansion in the curves is mainly because the crystal water limits the transverse vibration of the bridge oxygen atom in Y-O-W linkages and hinders NTE behavior [16,17]. As temperature rises, the compounds lost their absorbed water molecules gradually, and NTE was only observed after complete removal of moistures. As for x ¼ 1.5, 1.75, the thermal expansion curves of Y2-xCexW3O12 ceramics also showed a small initial expansion. It is mainly due to the existence of pores and microcracks in ceramics, which may lead to thermal expansion hysteresis in the monoclinic tungstates [7]. Above analysis indicates that the thermal expansion behavior changes drastically by the introduction of Ce3þ into the crystal structure of Y2W3O12. Different thermal expansion behavior of Y2xCexW3O12 ceramics leads to a different variety in the CTE (see
Table 3). It can be found that NTE has a significant weakening from x ¼ 0 to x ¼ 2. As more Y3þ was replaced by Ce3þ, the magnitude of CTE of Y2-xCexW3O12 would become less negative and then become positive. The result suggests that the CTE of Y2-xCexW3O12 ceramics can be tailored in the range from 13.094 106 K1 to 2.327 106 K1 by controlling the substituted Ce3þ content. It is worthy to note that the obtained Y0.25Ce1.75W3O12 ceramics almost exhibits near-zero thermal expansion from 182 C to 700 C with an average linear CTE of 0.82 106 K1. 4. Conclusions A new series of Ce-substituted Y2-xCexW3O12 (0 x 2) ceramics were successfully fabricated by solid-state reaction
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H. Liu et al. / Journal of Alloys and Compounds 751 (2018) 49e55 Table 3 Average linear CTEs of Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2) ceramics.
Fig. 6. Thermogravimetric curves of Y2-xCexW3O12 samples (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2).
Table 2 Crystalline water number and corresponding water loss temperature range of compounds Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2). Y2-xCexW3O12$nH2O
Water loss temperature range ( C)
Weight loss
n (water molecules in the compounds)
x ¼ 0.00 x ¼ 0.25 x ¼ 0.50 x ¼ 1.00 x ¼ 1.50 x ¼ 1.75 x ¼ 2.00
30e97 30e91 30e82 30e76 / / /
5.61% 5.05% 3.17% 1.47% 0 0 0
3.04 2.76 1.72 0.81 0 0 0
technique. Single phase can be formed in the range of 0 x 0.25 and the Y2-xCexW3O12 ceramics crystallize in orthorhombic Y2W3O12-type structure. Meanwhile, when 1 < x 2, the Y2xCexW3O12 ceramics crystallize in monoclinic Ce2W3O12-type structure, whereas samples with 0.5 x 1 contain both of the above structures. TG analysis indicates Y2-xCexW3O12 (0 x 1)
Fig. 7. Dilatometric curves for Y2-xCexW3O12 (x ¼ 0, 0.25, 0.5, 1, 1.5, 1.75, 2) ceramics.
Y2-xCexW3O12
Temperature range ( C)
a l ( 106K1)
x ¼ 0.00 x ¼ 0.25 x ¼ 0.50 x ¼ 1.00 x ¼ 1.50 x ¼ 1.75 x ¼ 2.00
154e700 159e700 171e700 138e700 109e700 182e700 23e700
13.094 11.399 9.590 3.758 1.787 0.820 2.327
ceramics are hygroscopic and the adsorbed moistures will be removed in the temperature range from 30 to 97 C. However, Y2xCexW3O12 (1 < x 2) ceramics are non-hygroscopic. The CTEs of the Y2-xCexW3O12 (0 x 2) specimens can be adjusted between 13.094 106 K1 and 2.327 106 K1 by tailoring the amount of substituted Ce cation. The Y0.25Ce1.75W3O12 ceramics exhibits very low NTE with an average linear CTE of 0.82 106 K1 from 182 C to 700 C. This non-hygroscopic and near-zero thermal expansion ceramics may have a wide range of applications in future. Acknowledgments We are grateful for the support of National Natural Science Foundation of China (No. 51602280 and No. 51102207), Qing Lan Project of Jiangsu Province, Guangling College of Yangzhou University Natural Science Research Foundation under grant No. ZKZD17001. References [1] S.E. Tallentire, F. Child, I. Fall, L. Vella-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 Zr1xSnxMo2O8, J. Am. Chem. Soc. 135 (2013) 12849e12856. [2] L.M. Sullivan, C.M. Lukehart, Zirconium tungstate (ZrW2O8)/polyimide nanocomposites exhibiting reduced coefficient of thermal expansion, Chem. Mater. 17 (2005) 2136e2141. [3] Q.Q. Liu, J. Yang, X.N. Cheng, G.S. Liang, X.J. Sun, Preparation and characterization of negative thermal expansion Sc2W3O12/Cu coreeshell composite, Ceram. Int. 38 (2012) 541e545. [4] J. Yang, Y.S. Yang, Q.Q. Liu, G.F. Xu, X.N. Cheng, Preparation of negative thermal expansion ZrW2O8 powders and its application in polyimide/ZrW2O8 composites, J. Mater. Sci. Technol. 26 (2010) 665e668. [5] N.A. Banek, H.I. Baiz, A. Latigo, C. Lind, Autohydration of nanosized cubic zirconium tungstate, J. Am. Chem. Soc. 132 (2010) 8278e8279. [6] P.M. Forster, A. Yokochi, A.W. Sleight, Enhanced negative thermal expansion in Lu2W3O12, Solid State Chem. 140 (1998) 157e158. [7] S. Sumithra, A.M. Umarji, Role of crystal structure on the thermal expansion of Ln2W3O12 (Ln ¼La, Nd, Dy, Y, Er and Yb), Solid State Sci. 6 (2004) 1313e1319. [8] P.S. Anjana, T. Joseph, M.T. Sebastian, Low temperature sintering and microwave dielectric properties of Ce2(WO4)3 ceramics, Ceram. Int. 36 (2010) 1535e1540. [9] S. Sumithra, A.M. Umarji, Negative thermal expansion in rare earth molybdates, Solid State Sci. 8 (2016) 1453e1458. [10] M.M. Wu, Y.Z. Cheng, J. Peng, X.L. Xiao, D.F. Chen, R. Kiyanagi, J.S. Fieramosca, S. Short, J. Jorgensen, Z.B. Hu, Synthesis of solid solution Er2-x CexW3O12 and studies of their thermal expansion behavior, Mater. Res. Bull. 42 (2007) 2090e2098. [11] H.F. Liu, W. Zhang, Z.P. Zhang, X.B. Chen, Synthesis and negative thermal expansion properties of solid solutions Yb2xLaxW3O12 (0x2), Ceram. Int. 38 (2012) 2951e2956. [12] Y.Z. Cheng, X.L. Xiao, X.F. Liu, M.M. Wu, J. Peng, Z.B. Hu, Study of the structures and thermal expansion properties of solid solutions Yb2-xDyxW3O12 (0x1.5 and1.8x2.0), Physica B 411 (2013) 173e177. [13] A.K.A. Pryde, K.D. Hammonds, M.T. Dove, V. Heine, J.D. Gale, M.C. Warren, Origin of the negative thermal expansion in ZrW2O8 and ZrV2O7, J. Phys. Condens. Matter 8 (1996) 10973e10982. [14] N.A. Banek, H.I. Baiz, A. Latigo, C. Lind, Autohydration of nanosized cubic zirconium tungstate, J. Am. Chem. Soc. 132 (2010) 8278e8279. [15] J.S.O. Evans, T.A. Mary, A.W. Sleight, Negative thermal expansion in Sc2(WO4)3, J. Solid State Chem. 137 (1998) 148e160. [16] D.A. Woodcock, P. Lightfoot, C. Ritter, Negative thermal expansion in
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