title: Experimental and Theoretical Investigations on Structural and Vibrational Properties of Melilite-Type Sr2ZnGe2O7 at High Pressure and Delineation of a High-Pressure Monoclinic Phase.
abstract: 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 ∼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.
authors.affiliation: †Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India.
authors.forename: S Nagabhusan
authors.initials: SN
authors.lastname: Achary
authors.affiliation: ‡Departamento de Física Aplicada-ICMUV, MALTA Consolider Team, Universidad de Valencia, Edificio de Investigación, C/Dr. Moliner 50, 46100 Burjassot, Valencia, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: Errandonea
authors.affiliation: ‡Departamento de Física Aplicada-ICMUV, MALTA Consolider Team, Universidad de Valencia, Edificio de Investigación, C/Dr. Moliner 50, 46100 Burjassot, Valencia, Spain.|§Earth, Planetary and Space Sciences Department, University of California Los Angeles, 595 Charles Young Drive East, 951567, Los Angeles, United States.
authors.forename: David
authors.initials: D
authors.lastname: Santamaria-Perez
authors.forename: Oscar
authors.initials: O
authors.lastname: Gomis
authors.affiliation: †Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India.
authors.forename: Sadiqua J
authors.initials: SJ
authors.lastname: Patwe
authors.forename: Francisco Javier
authors.initials: FJ
authors.lastname: Manjón
authors.affiliation: #Departamento de Física, Instituto de Materiales y Nanotecnología, MALTA Consolider Team, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain.
authors.forename: Placida Rodríguez
authors.initials: PR
authors.lastname: Hernandez
authors.affiliation: #Departamento de Física, Instituto de Materiales y Nanotecnología, MALTA Consolider Team, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Muñoz
authors.affiliation: †Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India.
authors.forename: Avesh Kumar
authors.initials: AK
authors.lastname: Tyagi