Iso-structural phase transition in pyrochlore iridates (Sm _{1-x}$Bi x ) 2 Ir 2 O 7 ( x = 0, 0.02, and 0.10): high-pressure Raman and x-ray diffraction studies.

The pyrochlore iridates, A ₂ Ir ₂ O ₇ , 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 ) ₂ Ir ₂ O ₇ ( x = 0, 0.02, and 0.10). Our Raman and x-ray data suggest an iso-structural transition in Sm ₂ Ir ₂ O ₇ atPc∼ 11.2 GPa, associated with the rearrangement of IrO ₆ 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 (A1gand E _g ) and Ir-O (T2g4) vibrations show anomalous decrease up toPc, due to decrease in electron-phonon interaction.
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