The dependence of BaMO3 (BMO: M = Zr, Sn, Hf) materials on reducing critical temperature (Tc) and lattice stress in BMO-doped SmBa2Cu3Oy (SmBCO) films is investigated by comparing the Tc and c-axis length of BaZrO3 (BZO)-, BaSnO3 (BSO)- and BaHfO3 (BHO)-doped SmBCO films with various BMO contents in this report. The Tc 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 Tc high, and the BMO material with a small Young's modulus can inhibit c-axis expansion.
