Temperature dependence of mechanical deformations in strontium titanate thin film on the sapphire substrate

Abstract

The temperature dependence of the dielectric constant (ε) of SrTiO₃ films on the various dielectric substrates differs radically from ε(T) dependence for bulk single crystal. This difference may be connected with temperature dependence of mechanical stress in the film. XRD measurements suggest the high mechanical deformation (u) of STO film unit cells at room temperature. But there is no experimental data about dependence u(T) nowadays. Present work is devoted to investigation of temperature and electric field dependencies of capacitance (C(U,T), C(Q,T)) of capacitor on the structure STO film/sapphire substrate. It is shown that derivative of inverse capacitance on the temperature is not constant and has a maximum at temperature about 200 K. Position of maximum is not influenced by charge (Q_i) on the capacitor. The mechanical deformations play the dominant role in the formation of maximum. The temperature behavior of macroscopic mechanical deformations in STO thin film on sapphire substrate is discussed.

Key Words:

• strontium titanate
• film
• dielectric permittivity
• stress.