Strontium aluminum tantalum oxide and strontium aluminum niobium oxide as potential substrates for HTSC thin films

Single crystal fibers of A(B1_1/2B2_1/2)O₃ perovskites type with compositions Sr(Al_1/2Ta_1/2)O₃ (SAT) and Sr(Al_1/2Nb_1/2)O₃ (SAN) were grown successfully for the first time, using a laser-heated pedestal growth (LHPG) technique. Their crystallographic structures were found to be simple cubic perovskite with lattice parameters a = 3.8952 Å (SAT) and a = 3.8995 Å (SAN) that are close lattice matches to the YBCO superconductors. No structural phase transitions or twins have been found, and the average coefficients of the thermal expansion match well with the YBCO superconductor materials. We report that SAT is one of the most promising substrates to date for the epitaxial growth of HTSC thin films suitable for microwave device applications as it has low dielectric constants (K ∼ 11–12, at 100 Hz–10 GHz and 300 K) and low dielectric loss (∼4 × 10⁻⁵ at 10 kHz and 80 K), together with lattice parameter matching, thermal expansion matching, and chemical compatibility with the high T_c superconductors (YBCO).