Structural and transport properties of heteroepitaxial BaNbxTi1−xO3 (x = 0.05, 0.2) thin films

Heteroepitaxial BaNbxTi1−xO3 (x = 0.05, 0.2) thin films prepared on (100) MgO substrates have been studied by Micro-Raman spectroscopy, X-ray diffraction and electrical measurements. It is found that the BaNb0.05Ti0.95O3 thin film is at tetragonal phase while the BaNb0.2Ti0.8O3 thin film is at cubic phase. The measurement of temperature dependence of electrical resistivity shows that the BaNb0.05Ti0.95O3 thin film is a semiconductor from 570 to 170 K, but the BaNb0.2Ti0.8O3 thin film exhibits transitional conduction behavior between 570 and 78 K. Because of the two-dimensional compressive strain imposed on the film by the substrate, the phase transition characteristics for bulk BaTiO3 (i.e, cubic to tetragonal to orthorhombic to rhombohedral) are absent in the films over the temperature range of 78 to 550 K.