Physical properties of holmium promoted superconductivity in Nd-doped YBCO $HT_C$ -superconductors

Özet

Samples of the nominal composition $(Y_{0.5}Nd_{0.5-x}Ho_x)$ $Ba_2Cu_3O_{7-\delta}$, $0\leq x\leq 0.5$, have been prepared using the conventional solid state reaction. The effect of holmium and neodymium substitution on electrical resistivity, transition temperature $T_c$, lattice parameters, size of crystallite and grain size has been investigated. X-ray diffraction, electron micro-probe, scanning electron microscope and IR spectra, have been used in our investigation. The results show that the transition temperature $T_c$, electron-hole jump rate and lattice parameters (a, b) have minimum values at x = 0.2, while c increases to maximum at x = 0.2. The size of crystallite, the electrical resistivity and grain size are also maximum at x = 0.2. The real composition, molecular state and electronic state of the prepared samples are discussed.