MODIFIED MIXED-OXIDE PEROVSKITES 0.7SR(AL1/2B1/2)O-3-CENTER-DOT-0.3LAALO(3) AND 0.7SR(AL1/2B1/2)O-3-CENTER-DOT-0.3NDGAO(3) (B=TA5+ OR NB5+) FOR HIGH-T-C SUPERCONDUCTOR SUBSTRATE APPLICATIONS

Single-crystal fibres of modified strontium aluminium tantalum oxide (1 - x)Sr(Al1/2Ta1/2) O-3.xLaAlO(3)(SAT.LA) and (1 - x)Sr(Al1/2Ta1/2)O-3.xNdGaO(3)(SAT.NG), and modified strontium aluminum niobium oxide (1 - x)Sr(Al1/2Nb1/2)O-3.xNdGaO(3)(SAT.NG) and (1-x)Sr (Al1/2Nb1/2)O-3.xLaAlO(3) (SAN.LA) were grown using a laser-heated pedestal growth technique. 0.7SAT.0.3LA grows congruently and retains a twin free simple cubic perovskite structure (as the SAT) when cooled down to room temperature. 0.7SAT.0.3LA crystals have a moderate dielectric constant (kappa = 21.7) and low dielectric loss (tan delta = 7.5x10(-5)) at 10 kHz and 90 K. The reduction problem of Ta5+ is eliminated (which is common in the case of SAT growth). 0.7SAT.0.3NG and 0.7SAN.0.3NG have lower melting temperatures and crystal growth is easier. NdGaO3 addition to the SAT and SAN enhances the potential of SAT and SAN as large-area substrates for high-T-c superconductor growth. However, the dielectric constants increased from kappa similar or equal to 12 to kappa similar or equal to 16(0.7SAT.0.3NG) and from kappa similar to 18 to kappa similar to 23 (0.7SAN.0.3NG) as a result of NdGaO3 incorporation.