Dielectric and optical properties of substrates for high-temperature superconductor films

The dielectric constants ε of LaAlO3, NdGaCO3 and MgO substrates were measured using a dielectric filled resonant cavity. Precise values of ε were obtained for NdGaO3 and MgO. An inhomogeneous dielectric constant was observed for LaAlO3. Optical studies indicated that the extensive twinning in this material was the source of the inhomogeneity.