Pressure-induced iso-structural phase transitions in pyrochloreiridates A2Ir2O7 (A = Pr, Gd, Dy and Er)

Abstract

We investigated pressure-induced changes in pyrochlore iridates (A(2)Ir(2)O(7), A = Pr, Gd, Dy and Er) using Raman spectroscopy and X-ray diffraction. All four compounds exhibited a pressure-driven isostructural transition associated with the rearrangement of IrO6 octahedra in the pyrochlore lattice. Interestingly, the critical pressure (P-c) for this transition correlates inversely with the A-site cation radius, P-c decreased from similar to 10.8 GPa (Er, smallest cation) to similar to 7.5 GPa (Pr, largest cation). Additionally, the bulk modulus systematically decreases with increasing ionic radius of A-site across the A(2)Ir(2)O(7) series. High-pressure Raman spectroscopy revealed anomalous decrease of the linewidth with increasing pressure for Ir-O (T-2g(4)) and Ir-O-Ir (A(1g) and E-g) vibrational modes, suggesting a suppression of electron-phonon coupling due to enhanced electronic bandwidth under pressure.