title: Structural Stability and Anharmonicity of Pr2Ti2O7: Raman Spectroscopic and XRD Studies.
abstract: Herein we report results of pressure- and temperature-dependent Raman scattering studies on Pr2Ti2O7. Pressure-dependent studies performed up to 23 GPa suggest a reversible phase transition above 15 GPa with subtle changes. Temperature-dependent investigations performed in the range of 77-1073 K showed anomalous temperature dependence of some of the Raman modes. Temperature-dependent X-ray diffraction data indicated no structural transition but nonlinear expansion of unit-cell parameters with increasing temperature. With increasing temperature, the structure dilates anisotropically, and volume of coordination polyhedra around all the atoms expands. Also with increasing temperature the distortions in coordination polyhedra around all the atoms decrease, and appreciable decrease is observed in Pr(1)O10and Pr(3)O9units. The pressure evolution of Raman-mode frequencies was analyzed for both ambient as well as high-pressure phases, and mode Grüneisen parameters for ambient pressure phase were obtained. The temperature evolution of Raman-mode frequencies was analyzed to obtain the explicit and implicit anharmonic components, and it was found that some of the modes attributable to TiO6octahedra and PrOnpolyhedra have dominating explicit anharmonic component. Comparison of the structural data with the temperature dependence of Raman modes suggests that the anomalous behavior in Raman modes is due to phonon-phonon interaction.
authors.forename: Swayam
authors.initials: S
authors.lastname: Kesari
authors.forename: Nilesh P
authors.initials: NP
authors.lastname: Salke
authors.forename: Sadeque Jahedkhan
authors.initials: SJ
authors.lastname: Patwe
authors.forename: Srungarpu Nagabhusan
authors.initials: SN
authors.lastname: Achary
authors.affiliation: Indus Synchrotron Utilization Division, Raja Ramanna Centre for Advanced Technology , Indore 452013, India.
authors.forename: Anil K
authors.initials: AK
authors.lastname: Sinha
authors.forename: Pulya Umamaheswara
authors.initials: PU
authors.lastname: Sastry
authors.forename: Avesh Kumar
authors.initials: AK
authors.lastname: Tyagi
authors.forename: Rekha
authors.initials: R
authors.lastname: Rao