Hf-doping effect on phase composition and superconducting characteristics of yttrium ceramics

The possibility of synthesizing ceramics of the YBa2Cu3-xHfxO7-δ composition (0≤x≤2) is studies. The synthesis from oxides was performed using the standard ceramic technology with annealing for six hours at T=945 deg C. The samples obtained were used to carry out X-ray and magnetic measurements. The X-ray diffraction analysis shows that at Hf concentrations x≤0.2 samples contain the standard rhombic phase 1-2-3 and the green phase (not more than 10 %). On increasing the Hf contents in the samples, two new phases appear - BaHfO3 and Ba2HfO4, whose amount considerably increases with x growing. The superconducting transition temperature (measurements of dynamic magnetic susceptibility) lowers from 91 K (starting ceramic material) to 82.3 K (at x=1.0). At higher Hf concentrations no superconducting transition is registered in the samples