Iso-structural phase transition in pyrochlore iridates (Sm ₁₋ₓ$ Bix)₂Ir₂O₇ (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 at P c ∼ 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 ( A 1 g and E g ) and Ir–O ( T 2 g 4 ) vibrations show anomalous decrease up to P c , due to decrease in electron–phonon interaction.