Abstract
The pressure dependence of octahedral distortions in rare-earth (R) orthochromites (RCrO3) has been studied using Raman scattering technique to probe the origin of the structural transition from orthorhombic Pnma to rhombohedral R3‾c phase in LaCrO3. The pressure-induced changes in the octahedral tilt modes demonstrate that tilt distortion is suppressed in LaCrO3 and is enhanced in the remaining members of the RCrO3 family. This crossover between the two opposite pressure behaviours occurs at a critical R-ion radius of 1.20 Å. We attempt to establish the relationship between this unusual crossover and compressibility at Cr- and R-sites by probing Raman phonon modes sensitive to the mean bond strength of Cr–O, and R–O, respectively. Finally, we study the bond length splitting of both CrO6 and RO12 polyhedra to ascertain the role of polyhedral self-distortion in determining the pressure dependent structural transition in the orthochromites.
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