Theoretical investigations on mechanical and thermal properties of MSiO 4 (M = Zr, Hf)
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In this contribution, the structural, mechanical, and thermal properties of MSiO4 have been investigated theoretically and the anisotropy of elastic properties has been discussed in detail. The heterogeneous bonding nature was revealed from density functional theory computations and chemical bond theory (CBT). The Young’s modulus and shear modulus of MSiO4 were anisotropic and the anisotropy on different planes was quite different. The thermal expansion coefficients of MSiO4 estimated from CBT were 5.1 106 and 4.4 106 K1 for ZrSiO4 and HfSiO4, respectively. These results were quite consistent with the experiments. The temperature dependent thermal conductivities of MSiO4 were estimated from Slack’s model, the minimum thermal conductivity was predicted to be 1.54 and 1.24 W m1 K1 for ZrSiO4 and HfSiO4, respectively. Our theoretical results show that MSiO4 are excellent thermal barrier materials with good tolerance to withstand the mechanical damage. I. INTRODUCTION
Contributing Editor: Gary L. Messing a) Address all correspondence to this author. e-mail: [email protected], [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-editor-manuscripts/ DOI: 10.1557/jmr.2015.172
of MSiO4 has been fully understood experimentally and theoretically.5–16 The high pressure phase transition of zircon is also a hot topic since the zircon–reidite transition is fast and occurs at ambient temperature, which is quite unusual in silicate minerals.17 Experimentally, the transition pressure ranged from 10 to 23 GPa for room temperature transitions, around 12 for high temperature transitions.17–19 Theoretically, Du et al. estimated a transition pressure of 11.6 GPa.11 The mechanical properties of MSiO4, which are important to the applications as refractory materials, are also studied. It was found that the bending strength of zircon ceramics could maintain up to 1000–1400 °C, depending on the purity of sintered body.20,21 Moreover, recently reported experiments revealed that MSiO4 are the main constitutions of oxidation products of Zr- and Hf-based ultrahigh temperature ceramics, especially under low oxygen partial pressure and simulated hypersonic flight conditions.22,23 The presence of high content of zircon phase could improve the oxidation resistance of the matrix. Despite the structure, phase stability and mechanical properties of zircon phase have been reported, the structure–property relationship, anisotropy in mechanical properties and thermal properties of MSiO4 (M 5 Zr, Hf) are still not fully understood. The thermal properties, especially the thermal conductivity–temperature relationship, are crucial to the applications as thermal barrier coating and solid state laser. In addition, mechanical anisotropy and the ability of withstanding external mechanical damages are the key factors need to be considered when using as structural components. Lacking of th
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