Фазовые переходы в фрустрированном кобальтите TmBaCo-=SUB=-4-=/SUB=-O-=SUB=-7-=/SUB=-

Abstract

For the first time, changes in lattice parameters (metrics) during a structural transition in stoichiometric cobalt TmBaCo4O7+x with x~ 0 (iodometric titration method) obtained by quenching from 900-950oC were investigated by direct X-ray method. It was found that during the structural transition TS~220-240 K, the Delta a/a parameter does not detect any features, parameters b and c experience jumps of different sign and different magnitude Delta b/b~3.5·10-3 and Delta c/c~-4.0·10-3, which leads to a jump in the volume of Delta V/V~ -0.5·10-3. The distortion value eo ~ -3.5·10-3 remains constant with increasing temperature and disappears abruptly during the transition.The distortion of the structure is accompanied by abnormal behavior of the Young's Delta E(T)/E0 module in the TS region. In the region of the expected magnetic phase transition of the cobalt subsystem, anomalies on the Young's modulus curve Delta E(T)/E0 were not detected, and a strong absorption peak at T~ 96 K on the internal friction dependence q-1(T) is, apparently, a sign of a developed short-range order.