THE TETRAGONAL-TO-ORTHORHOMBIC PHASE-TRANSITION IN RBA1F4 - AN X-RAY-SCATTERING STUDY

The tetragonal-to-orthorhombic phase transition in RbAlF4 at almost-equal-to 290 K has been investigated using x-ray scattering techniques. For temperatures above almost-equal-to 290 K, the wavevector dependence of the critical scattering at the X point was measured and was well described by an anisotropic Lorentzian, with no evidence for a second Lorentzian-squared component as has recently been reported close to the anti-ferrodistortive transition in several perovskites. The critical exponents describing the temperature dependence of the primary and secondary order parameters, inverse correlation length and static susceptibility were determined and found to be consistent with those expected for the isotropic n = 2, d = 3 model.