N. U. Nekrasova

Dept. of Electronics, St.-Petersburg Electrotechnical University, 5 Prof. Popov st., 197376, St. Petersburg, Russia

Introduction 
    The dielectric nonlinearity of ferroelectrics makes it possible to elaborate electrically tunable microwave devices and components. Ba_xSr_1-xTiO₃ (BSTO) is a typical ferroelectric material suitable for microwave application at room temperature [1]. 
    According to the theory of ferroelectricity, the temperature dependence of the dielectric permittivity ε(T) of a homogeneous BSTO sample obeys the Curie-Weiss law [2]. The measurements of BSTO planar capacitors revealed that the observed experimental temperature dependence ε(T) did not follow this law. In order to explain this anomalous behavior of the capacitance, it is supposed that the investigated BSTO films consist of layers with different phase transition temperatures, which correspond to the different barium concentration across the BSTO film profile.