Probing structural distortions in rare earth chromites using Indian synchrotron radiation source

Effect of R site ionic radius on the structural distortions in RCrO₃ (R: La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Y) rare earth perovskite chromites is investigated through synchrotron based X-ray diffraction technique. The said structural distortions are measured in the terms of CrO bond lengths, CrO₆ octahedral tilt, tolerance factor ( t) and RO₁₂ polyhedral distortion. It is observed that the lattice parameters (b and c), RO bond length, tolerance factor and Cr-O-Cr bond angle increases with increase in the radius of R site ion; whereas octahedral tilts (along [010] and [101]) and RO₁₂ polyhedral distortion decreases with increase in the radius of R site ion. Further it is observed that the radius of R site cation does not have significant effect on lattice parameter `a' and CrO bond length (hence on the distortion of CrO₆ octahedra). A comparison of the crystal structure parameters obtained using refinement of synchrotron powder X-ray data and that estimated theoretically using modern bond valence parameters (SPuDS) has been carried out. A one to one correlation between the experimental and theoretical results has been observed.