Iso-structural phase transition in pyrochlore iridates (Sm _{1-x}$Bi_x)₂Ir₂O₇(x= 0, 0.02, and 0.10): high-pressure...

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 (Sm_{1-x}Bi_x)₂Ir₂O₇(x= 0, 0.02, and 0.10). Our Raman and x-ray data suggest an iso-structural transition in Sm₂Ir₂O₇atPc∼ 11.2 GPa, associated with the rearrangement of IrO₆octahedra in the pyrochlore lattice. The transition pressure decreases to ∼10.2 and 9 GPa forx= 0.02 and 0.10, respectively. For all the samples, the linewidth of three phonons associated with Ir-O-Ir (A1gandE_g) and Ir-O (T2g4) vibrations show anomalous decrease up toPc, due to decrease in electron-phonon interaction.