Local symmetry lowering in CdMn2O4 spinel

This work presents an atomic scale study of the electric field gradient (EFG) in the tetragonally distorted CdMn2O4 spinel manganite. The EFG temperature dependence at the Cd and Mn sites was followed via perturbed angular correlation measurements with the In-111 and Cd-111m probes, from 873 down to 12 K at Isolde-CERN. The results show that in the 12-600 K temperature range, a single Jahn-Teller distorted local phase exists. However above 100 K, a dynamic lattice distortion, evidenced by time dependent EFG fluctuations, sets in suggesting a structural instability. Above 600 K, a local MnO6 octahedra with relaxed Jahn-Teller distortions emerge and grow in the low temperature matrix, although no macroscopic tetragonal to cubic phase transition was observed. (C) 2014 AIP Publishing LLC.