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Experimental and Theoretical Investigations on Structural and Vibrational Properties of Melilite-Type Sr2ZnGe2O7 at High Pressure and Delineation of a High-Pressure Monoclinic Phase
journal contribution
posted on 2015-07-06, 00:00 authored by S. Nagabhusan Achary, Daniel Errandonea, David Santamaria-Perez, Oscar Gomis, Sadiqua J. Patwe, Francisco
Javier Manjón, Placida Rodríguez Hernandez, Alfonso Muñoz, Avesh Kumar TyagiWe
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 ∼1% volume drop at the phase transition
pressure. Density functional calculations indicate the transition
pressure at ∼13 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– 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.