MATERIALS FOR HTS-SHIELDED DIELECTRIC RESONATORS

The microwave properties of single crystalline LaAlO3, LSAT ((LaAlO3)( 0.3)-(Sr2AlTaO6)(0.7)), rutile (TiO2), and polycrystalline Al2O3 were investigated employing dielectric resonator techniques. LaAlO3 (epsilo n(r) = 23.7) exhibits a frequency dependent maximum of tan delta at ab out 70 K, which call be explained by defect dipole relaxation. This le ads to a variation of tan delta at 9 GHz and 77 K from 5.10(-6) to 2.1 0(-5), the lowest values were achieved with Verneuil grown crystals. L SAT (epsilon(r) = 22.8) exhibits an even more pronounced maximum with absolute values in the 10(-4) range. For rutile (epsilon(r) = 108) we measured a monotonous increase of tans with temperature, which can be explained by intrinsic losses due to phonons. The loss tangent of Ti-d oped polycrystalline, sintered Al2O3 was found to be only 4-10(-6) at 10 GHz and 77 K. Except LSAT the materials investigated so far provide a large potential for applications as dielectric resonators shielded by high temperature superconducting (HTS) films.