Pressure driven structural phase transition in EuTaO 4 : experimental and first principles investigations.

In this article we report the synthesis, characterization and high pressure (HP) investigation on technologically important, rare earth orthotantalate, EuTaO 4 . Single phase polycrystalline sample of EuTaO 4 has been synthesized by solid state reaction method adopting monoclinic M'-type fergusonite phase with space group P 2/ c . Structural and vibrational properties of as synthesized compound are investigated using synchrotron based x-ray powder diffraction, and Raman spectroscopic techniques respectively. Both the techniques show presence of an isostructural, first order, reversible phase transition near 17 GPa. Bulk modulus obtained by fitting the experimental pressure volume data for low pressure and HP phase is 136.0(3) GPa and 162.8(21) GPa. HP phase is accompanied by an increase in coordination number around Ta atom from 6 to 8. First principles calculations under the frame work of density functional theory also predicts the isostructural phase transition and change in coordination around Ta atom, corroborating the experimental findings.