Dependence of BaMO₃ (M=Zr, Sn, Hf) Materials on Lattice Stress and T_c in BaMO₃-Doped SmBa₂Cu₃O_y Thin Films

Abstract

The dependence of BaMO₃ (BMO: M = Zr, Sn, Hf) materials on reducing critical temperature (T_c) and lattice stress in BMO-doped SmBa₂Cu₃O_y (SmBCO) films is investigated by comparing the T_c and c-axis length of BaZrO₃ (BZO)-, BaSnO₃ (BSO)- and BaHfO₃ (BHO)-doped SmBCO films with various BMO contents in this report. The T_c reduction rate against c-axis expansion was identical in all BMO-doped SmBCO films. It was revealed that the lattice stress on the SmBCO matrix in the BHO-doped SmBCO films was weaker than that in the BZO- and BSO-doped SmBCO films when comparing the SmBCO-BMO interfacial area dependence of the c-axis length of the SmBCO matrix. In addition, we confirmed that BHO was strongly strained by the SmBCO matrix as compared to BZO and BSO in SmBCO films. This is because the Young's modulus of BHO was smaller than that of BZO and BSO. We conclude that restraining c-axis expansion is effective for keeping T_c high, and the BMO material with a small Young's modulus can inhibit c-axis expansion.