Lanthanide gallate perovskite-type substrates for epitaxial, high-Tc superconducting Ba2YCu3O7-δ films

Previous studies had indicated promising use of lanthanide gallate perovskite-type substrates for the deposition of epitaxial, high-T
c
superconducting Ba
2
YCu
3
O
7-δ
(BYCO) films. They were also found to have moderate dielectric constants (∼25 compared to ∼277 for SrTiO
3
). This study was undertaken to further explore the use of LaGaO
3
, NdGaO
3
, SrTiO
3
, MgO, and Y-stabilized ZrO
2
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 LaGaO
3
. Lattice mismatch strains were calculated for orthorhombic BYCO films on a number of substrates. NdGaO
3
was found to have the best lattice match with BYCO, and is now available twin-free.