Thermal properties of a PrBa2Cu3O6+x ceramic with x=0.4 and 0.9

The low-temperature variations of the thermal expansion coefficient alpha(T ) of a PrBa2Cu3O6+x ceramic are reported for two oxygenation states (x = 0. 4 and 0.9). They show a peak at the ordering temperature of Pr deduced from the susceptibility chi(T) and the specific heat C-p(T), i.e. at T-N = 9.5 and 14.5 K, for x = 0.4 and 0.9, respectively. The deduced Gruneisen parame ter Gamma(eff) is rather large, show almost no anomaly at T-N, but a sharp increase below approximate to 5 K. The origin of these variations is discus sed in terms of magnetic behaviour of the Pr and Cu sublattices. (C) 2000 E lsevier Science B.V. All rights reserved.