Pressure-induced iso-structural phase transitions in pyrochlore iridates \(A_2\hbox {Ir}_2\hbox {O}_7\) (\(A\! \,=\,\)Pr, Gd, Dy and Er)

We investigated pressure-induced changes in pyrochlore iridates ( \(A_2\hbox {Ir}_2\hbox {O}_7\) $A_2{\text{Ir}}_2{\text{O}}_7$ , \(A=\) $A=$ 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 \(\hbox {IrO}_6\) ${\text{IrO}}_6$ octahedra in the pyrochlore lattice. Interestingly, the critical pressure ( \(P_\textrm{c}\) $P_{\text{c}}$ ) for this transition correlates inversely with the A-site cation radius, \(P_\textrm{c}\) $P_{\text{c}}$ decreased from \(\sim \) $\sim$ 10.8 GPa (Er, smallest cation) to \(\sim \) $\sim$ 7.5 GPa (Pr, largest cation). Additionally, the bulk modulus systematically decreases with increasing ionic radius of A-site across the \(A_2\hbox {Ir}_2\hbox {O}_7\) $A_2{\text{Ir}}_2{\text{O}}_7$ series. High-pressure Raman spectroscopy revealed anomalous decrease of the linewidth with increasing pressure for Ir–O ( \(T_{2g}^{4}\) $T_{2g}^4$ ) and Ir–O–Ir ( \(A_{1g}\) $A_{1g}$ and \(E_g\) $E_g$ ) vibrational modes, suggesting a suppression of electron–phonon coupling due to enhanced electronic bandwidth under pressure.