Low Loss Substrates for Microwave Applications and Sol-Gel Processing ofSuperconductors

摘要

This document is a final technical report of the research program entitled 'LowLoss Substrates for Microwave Applications and Sol-Gel Processing of Superconductors. Systematic studies on low K oxide substrate materials suitable for epitaxial deposition of high Tc superconducting (HTSC) yttrium barium cuprate (YBCO) films and their microwave applications have been extended to oxide materials with magnetoplumbite structure, such as LaMgAl11O19, NdGaMgAl10O19, CaGa6Al6O19, and CaGa12O19. The unique capabilities of a laser heated pedestal growth (LHPG) system have been utilized for test growth of candidate materials in single crystal fiber form to determine structure, thermal, and dielectric properties and to make positive identification of twin free systems. Dielectric properties, thermal expansion coefficients, melting temperatures and growth feasibility were tested. Through successful collaboration thorough tests on the compatibility of the SAT films as buffer layer in MgO/YBCO system have been performed. Excellent epitaxial YBCO films with Jc of 10(exp 6) A/cu cm were reproducibly obtained. Mechanisms relating the bonding nature and the order disorder in complex perovskite niobates and tantalates that governing the characteristics of their dielectric properties were studied through collaboration with the microprobe Raman spectroscopy groups. Work on the Shannon ion polarizability model for predicting dielectric permittivity in solids is being continued. Newly compiled normalized ion polarizabilities which take into consideration apparent bonding strengths improve the predictive capability considerably.