Theoretical study of high-pressure phase stability of NaZr₂(PO₄)₃ via elastic constants and equation of state

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• 作者：Ravi Chinnappan ; B. K. Panigrahi
• 关键词：Lattice stability ; Born stability criteria ; Density functional theory calculations
• 刊名：Indian Journal of Physics
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：91
• 期：3
• 页码：277-286
• 全文大小：
• 刊物类别：Physics and Astronomy
• 刊物主题：Physics, general; Astrophysics and Astroparticles;
• 出版者：Springer India
• ISSN：0974-9845
• 卷排序：91

文摘

Phase stability of \(\mathrm {NaZr_2(PO_4)_3}\) has been studied through density functional theory calculations of elastic constants, equation of state and enthalpies. The changes in elastic constants as a function of pressure show that the ambient rhombohedral (R\(\bar{3}c\)) \(\mathrm {NaZr_2(PO_4)_3}\) becomes unstable above 8 GPa and this instability is driven by a softening of C\(_{44}\) elastic constant through one of the Born stability criteria. High-pressure equation-of-state and enthalpy calculations further show that the ambient rhombohedral (\(R\bar{3}c\)) structure transforms first into another rhombohedral (R3) phase and subsequently to LiZr\(_2\)(PO\(_4\))\(_3\)-type orthorhombic phase at pressures above 6 and 8 GPa respectively which are in agreement with a recent x-ray diffraction study. Analysis of interatomic distances show that LiZr\(_2\)(PO\(_4\))\(_3\)-type orthorhombic structure allows for shorter Na–O and Zr–P bonds at high pressures which appears to enable strong bonding and stability. Calculated formation enthalpy and bulk modulus of the ambient phase of \(\mathrm {NaZr_2(PO_4)_3}\) are found to be in reasonable agreement with the respective experimental values.