Phase transitions and the temperature dependence of the dielectric properties in tetragonally strained barium strontium titanate films

The dielectric properties of sputter-deposited Ba1−xSrxTiO3 (BST) thin films on (001) MgO substrates with in-plane or out-of-plane tetragonal lattice structure distortions were characterized as a function of temperature. A temperature-dependent interpolation calibration technique was developed for increased efficiency of the microwave measurements. The BST films showed significant differences in the ferroelectric phase transition due to lattice distortions with a strong temperature dependence of the in-plane dielectric behavior for films under tensile strain and a weak temperature dependence for films under compressive strain. The experimental data agreed well with theoretical modeling of the BST film strain effect based on Devonshire’s theory.