An endor investigation of the structural phase transition in RbCdF₃:Mn⁺⁺

Abstract

The perovskite RbCdF₃ shows a structural phase transition from cubic to tetragonal symmetry at Tc = 124 K. The transition is characterized by a rotation of the CdF₆ octahedra around one of their fourfold axes; the rotational angle is taken as the order parameter of the transition. In crystals doped with Mn⁺⁺ as a probe, the superhyperfine (shf) interactions between the probe and the nearest neighbour fluorines could be measured by electron nuclear double resonance (ENDOR) as a function of temperature up to Tc. From the data the local rotational angle of the MnF6-octahedra was inferred. Furthermore, at low temperature (T=20 K), the shf interactions with the second fluorine shell and the first Cd⁺⁺ neighbours could be determined. The results show an appreciable influence of the lattice distortion around the impurity on the rotational angles of the surrounding octrahedra, which reaches out at least to the second shell of fluorines.