Octahedra in the orthorhombic perovskite structure are not rigid. The bond-length splitting at an octahedral site can be described by two degenerate vibration modes, the orthorhombic Q₂ and the tetragonal Q₃. A polar plot of r=ρ=(Q₂²+Q₂²)1/2 and φ=tan^-1(Q₃/Q₂) has been made to map out the site distortion as a function of the rare-earth ionic size for three families, RFeO₃, RVO₃, and RMnO₃. The octahedral-site distortion deduced from RFeO₃ is found to be intrinsic to orthorhombic perovskites and to strongly bias orbital ordering and spin ordering in compounds that have the same structure.
No takes yet. Share an insight, caveat, or question.
Zhou et al. (2008) studied this question.
Synapse has enriched 5 related papers. Consider them for comparative context: