Experimental and Theoretical Investigations on Structural and Vibrational Properties of Melilite-Type Sr2ZnGe2O7 at High Pressure and Delineation of a High-Pressure Mo

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• 作者：S. Nagabhusan Achary ; Daniel Errandonea ; David Santamaria-Perez ; Oscar Gomis ; Sadiqua J. Patwe ; Francisco Javier Manj贸n ; Placida Rodr铆guez Hernandez ; Alfonso Mu帽oz ; Avesh Kumar Tyagi
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：July 6, 2015
• 年：2015
• 卷：54
• 期：13
• 页码：6594-6605
• 全文大小：556K
• ISSN：1520-510X

文摘

We report a combined experimental and theoretical study of melilite-type germanate, Sr₂ZnGe₂O₇, under compression. In situ high-pressure X-ray diffraction and Raman scattering measurements up to 22 GPa were complemented with first-principles theoretical calculations of structural and lattice dynamics properties. Our experiments show that the tetragonal structure of Sr₂ZnGe₂O₇ at ambient conditions transforms reversibly to a monoclinic phase above 12.2 GPa with 鈭?% volume drop at the phase transition pressure. Density functional calculations indicate the transition pressure at 鈭?3 GPa, which agrees well with the experimental value. The structure of the high-pressure monoclinic phase is closely related to the ambient pressure phase and results from a displacive-type phase transition. Equations of state of both tetragonal and monoclinic phases are reported. Both of the phases show anisotropic compressibility with a larger compressibility in the direction perpendicular to the [ZnGe₂O₇]^{2鈥?/sup> sheets than along the sheets. Raman-active phonons of both the tetragonal and monoclinic phases and their pressure dependences were also determined. Tentative assignments of the Raman modes of the tetragonal phase were discussed in the light of lattice dynamics calculations. A possible irreversible second phase transition to a highly disordered or amorphous state is detected in Raman scattering measurements above 21 GPa.}