Investigation of substitution for copper in YBCO in internal friction measurement

Internal friction (IF) was measured in the range of low frequency for undoped YBa2Cu3O7- delta (YBCO) and doped YBa2Cu3-xAlxOy (x=0.05, 0.2, YBCAO) oxides. Two IF peaks, located one above and one below 200 degrees C, were observed; these are due to the stress-induced diffusional redistribution of oxygen atoms between OA(1/2, 0, 0) and OB(0, 2/1, 0) sites in the basal planes for the respective orthorhombic and tetragonal phases. From the obvious difference in the IF behaviour especially in the peak height and the peak temperature, between the undoped and doped YBCO compounds subjected to vacuum annealing, it is certain that the doping Al3+ ions substitute for the Cu(1) in the basal planes. Also the IF experimental results show that the doping with Al results in a change in the order of the O-T phase transition for doped YBCAO.