Iso-structural phase transition in pyrochlore iridates (Sm1-xBix)2Ir2O7 (x = 0, 0.02, and 0.10): High-pressure Raman and X-ray diffraction studies.

Abstract

The pyrochlore iridates, A2Ir2O7, show a wide variety of structural, electronic, and magnetic properties controlled by the interplay of different exchange interactions, which can be tuned by external pressure. In this work, we report pressure-induced iso-structural phase transitions at ambient temperature using synchrotron-based X-ray diffraction (up to ∼ 20 GPa) and Raman-scattering measurements (up to ∼ 25 GPa) of the pyrochlore series (Sm1-xBix)2Ir2O7 (x = 0, 0.02, and 0.10). Our Raman and X-ray data suggest an iso-structural transition in Sm2Ir2O7 at Pc ∼ 11.2 GPa, associated with the rearrangement of IrO6 octahedra in the pyrochlore lattice. The transition pressure decreases to ∼ 10.2 and 9 GPa for x = 0.02 and 0.10, respectively. For all the samples, the linewidth of three phonons associated with Ir-O-Ir (A1g and Eg) and Ir-O (T24g ) vibrations show anomalous decrease up to Pc, due to decrease in electron-phonon interaction.