Synthesis and Properties of BaPb₁₋ₓBiₓO₃ (BPBO) Epitaxial Thin Films on Lattice-Matched Substrates

BaPb₁₋ₓBiₓO₃ (BPBO) exhibits rich superconducting behavior that is strongly influenced by epitaxial strain and disorder. The lattice parameter of BPBO is approximately 4.29 Å, which leads to a large lattice mismatch with most commercially available substrates. Recently, BaZrO₃ bulk single crystals—with cubic symmetry and a closely matched lattice constant (≈ 2.3% mismatch)—have been developed, offering a promising new substrates platform for BPBO heteroepitaxy. We have grown epitaxial BPBO thin films on various substrates, including BaZrO₃, with different lattice mismatches using 90° off-axis sputtering. The smaller mismatch is expected to improve film quality and enhance superconductivity. Systematic variation of film thickness enables investigation of the superconductor–insulator transition and the correlation between disorder parameters and superconducting transition temperatures (T_c). Comparative studies on different substrates evaluate crystallinity, surface morphology, and critical thickness. The strain state and relaxation behavior are characterized via x-ray diffraction reciprocal space mapping. By integrating structural and transport measurements, this study aims to deepen the understanding of strain and disorder effects in BPBO thin films and to identify pathways for enhancing superconducting properties in oxide heterostructures.