Dielectric properties of Ln(Mg _1/2 Ti _1/2 )O₃ as substrates for high-T_c superconductor thin films

Ln(Mg _1/2 Ti _1/2 )O₃ (Ln = Dy, La, Nd, Pr, Sm, Y) compositions have been prepared, and their pertinent properties for use as thin film substrates for YBa₂Cu₃O_x (YBCO) were measured. X-ray diffraction shows that Ln(Mg _1/2 Ti _1/2 )O₃ compositions have noncubic symmetry and the GdFeO₃-type structure. Dielectric constant measurements revealed values between 22 and 27, which are larger than those of the LnAlO₃ family. Quality factor (= 1/tan δ) of the ceramic specimens measured at room temperature was larger than 3000 at 10 GHz. Among the compounds, La(Mg _1/2 Ti _1/2 )O₃ exhibited the highest dielectric constant and the lowest dielectric loss. Chemical reaction was observed between Ln(Mg _1/2 Ti _1/2 )O₃ (Ln = Dy, Sm, Y) and YBCO after annealing a 1:1 mixture at 950°C. Considering dielectric and physical properties, La(Mg _1/2 Ti _1/2 )O₃ and Sm(Mg _1/2 Ti _1/2 )O₃ were determined to be suitable substrates for YBCO thin film used in microwave applications.