Abstract: We have discovered advantageous substrates for III-V nitride semiconductors such as GaN. The substrate material is of the YbFe.sub.2 O.sub.4 or InFeO.sub.3 (ZnO).sub.n structure type and has general composition RAO.sub.3 (MO).sub.n, where R is one or more of Sc, In, Y and the lanthanides (atomic number 67-71); A is one or more of Fe(III), Ga, and Al; M is one or more of Mg, Mn, Fe(II), Co, Cu, Zn and Cd; and n is an integer.gtoreq.1, typically<9. Furthermore, the substrate material is selected to have a lattice constant that provides less than .+-.5% lattice mismatch with the III-V nitride semiconductor material that is to be deposited thereon. At least some of the substrate materials (e.g., ScMgAlO.sub.4) typically can be readily and relatively cheaply produced in single crystal form, are readily clearable on the basal plane, and do essentially not interact chemically with the III-V nitride under typical deposition conditions.

Abstract: Disclosed is an article that comprises a superconductor-insulator (s-i) layer structure. The superconductor material has nominal composition Ba.sub.1-x M.sub.x BiO.sub.3-y (M is K, Rb, or K and Rb, 0.35<x.ltorsim.0.5, 0<y.ltorsim.0.25). In some preferred embodiments the insulator is a Ba- and Bi containing oxide, exemplarily BaBi.sub.2 O.sub.4, Ba.sub.1-x M.sub.x BiO.sub.3 (0.ltoreq.x<0.35), or Ba.sub.1-x Bi.sub.1+x O.sub.3 (0.ltoreq.x.ltorsim.0.5). In other embodiments the insulator is an insulating oxide with the NaCl structure (e.g., Mg.sub.1-x Ca.sub.x O), an insulating perovskite (e.g., BaZrO.sub.3 ), an insulator with the K.sub.2 NiF.sub.4 structure (e.g., Ba.sub.2 PbO.sub.4), an insulating fluoride with the BaF.sub.2 structure (e.g., Ba.sub.1-x Sr.sub.x F.sub.2), or an insulating fluoride with the NaCl structure (e.g., LiF). Disclosed are also advantageous methods of making an article according to the invention.