Evolution of electronic and crystal structure during room-temperature annealing of quenched REBa2Cu3O6+d, RE=Y, Nd

Abstract

The crystal structure parameters and the low-temperature magnetic moment of the HTSC cuprates YBa2Cu3O6+d, Y1-xCaxBa2Cu3O6+d, and Nd1+xBa2-xCu3O6+d, x = 0.2 are recorded after quenching them from the temperature of oxidative annealing. The subject of the present study is the aging effect, which results in an increase in the critical temperature Tc and a decrease in the c parameter of the crystal lattice for a while after the quenching. On the example of YBa2Cu3O6+d, it is shown that the oxygen content dependence of c undergoes the following changes with time: (1) there is an increase in the dependence slope with respect to the (6+d)-axis; (2) there is an increase in the dependence nonlinearity. The first type of changes is explained by an increase in the valence of copper ions in the CuOd planes that is accompanied by a decrease in their radius. The second type is explained by the electrostatic interaction of the CuO2 structural planes due to the accumulation on them electron holes. Calculation of the parameter c changes shows good quantitative agreement with the experimental data. The data obtained for the compounds Y1-xCaxBa2Cu3O6+d, and Nd1+xBa2-xCu3O6+d (the cases of the hole and electron doping of CuO2-planes) are discussed on the basis of the model representation developed by us for YBa2Cu3O6+d.