Nonlinearity and Microwave Losses in Cubic Strontium-Titanate

The complex dielectric constant of single-crystal strontium-titanate has been measured from 90^∘{} to 230^∘{}K at microwave frequencies. The real part of the dielectric constant consists of a large field-independent contribution which obeys a Curie-Weiss law over the entire range of measurement plus a smaller anisotropic field-dependent contribution. These results are shown to be in qualitative agreement with the theory of ferroelectricity in perovskite structures as proposed by Slater. The observed loss tangent consists of a contribution which is quadratic in an applied biasing field plus a field-independent contribution. The field-independent loss tangent goes through a minimum at about 170^∘{} with a much steeper slope on the low-temperature side of the minimum than on the high-temperature side. The origin of the behavior of the field-independent loss tangent is discussed.