Lanthanide gallate perovskite-type substrates for epitaxial, high-T_c superconducting Ba₂YCu₃O_7-δ films

Previous studies had indicated promising use of lanthanide gallate perovskite-type substrates for the deposition of epitaxial, high-Tc superconducting Ba2YCu3O7-δ (BYCO) films. They were also found to have moderate dielectric constants (approximately 25 compared to approximately 277 for SrTiO3). This study was undertaken to further explore the use of LaGaO3, NdGaO3, SrTiO3, MgO, and Y-stabilized ZrO2 substrates, prepared from single-crystal boules grown by several suppliers using the Czochralski method. Films were prepared by cylindrical magnetron sputtering and laser ablation. Substrate evaluations included measurement of dielectric constant and loss, thermal expansion, and mechanical hardness and toughness. In addition to their moderate dielectric constants, they were found to have satisfactory mechanical properties, except for the twinning tendency of LaGaO3. Lattice mismatch strains were calculated for orthorhombic BYCO films on a number of substrates. NdGaO3 was found to have the best lattice match with BYCO, and is now available twin-free.