THERMAL-EXPANSION ANOMALIES IN REBA(2)CU(3)O(7-DELTA)

Results of theoretical and experimental study of the contribution of 4 f electrons to the coefficient of linear thermal expansion alpha(m)(T) for orthorhombic REBa(2)Cu(3)O(7-delta) are presented. Theoretically, alpha(m)(T) is treated in terms of the electric quadrupole moments of the 4f shell of the RE(3+) ions induced by the crystal field. Conside ring the available crystal field parameters we calculate the temperatu re dependence of alpha(m) for RE ions which form the REBa(2)Cu(3)O(7-d elta 6) structure. Experimentally, we have studied alpha(m)(T) of poly crystalline PrBa2Cu3O7-delta using strain gauges in the temperature ra nge 10-300 K. The latter compound was chosen with regard to its outsta nding features, lack of superconductivity in particular. The anomalies on alpha(m)(T) observed for PrBa2Cu3O7-delta as well as those availab le for a high-T-c superconductor DyBa2Cu3O7-delta at low temperatures compare well with the prediction of the theory.