Superconducting and Vickers hardness properties of ZnO‐added YBCO polycrystalline superconductors

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Abstract
The effects of ZnO addition on the microstructure and mechanical properties of the YBCO have been investigated through XRD, SEM, EDX, ac susceptibility measurements and the standard Vickers microhardness testing method. We have prepared the samples by a conventional solid‐state reaction method and used an additive method for the YBCO system (0, 0.5 and 1 wt% of ZnO). The orthorhombic strain Δ = (b – a)/(b + a) increases as the Zn content increases, where a and b are the relevant lattice parameters of the samples. The superconducting transition temperatures and hardness depend on the Zn content of the samples. The hardness is found to be load dependent. From the relation between applied load F and the square of the impression diagonal, d2, the true hardness, H0, and the dissipative portion of the indentation load F0, were derived from the slope and the intercept (at d2 = 0) of the straight line, respectively. The hardness was increased while the transition temperature decreased with the amount of ZnO addition to YBCO.