Microwave dielectric and Raman scattering studies on bismuth zinc niobate thin films

Bismuth zinc niobate (Bi1.5Zn1.0Nb1.5O7) thin films were deposited on fused silica substrates by pulsed laser deposition. Its phase composition and microstructure were characterized by x-ray diffraction and atomic force microscopy. The as deposited films were amorphous and all of them were crystallized after a postdeposition annealing at 600 degrees C for 30 min in air. The crystallite size of the films was found to be varying between 31 and 60 nm with respect to the oxygen pressure in the deposition chamber. The films were found to be less oriented with the decreasing crystallite size. The films deposited under different oxygen pressures showed a microwave dielectric permittivity in between 98-124 and a loss tangent in between 0.005 and 0.007 over the X-band frequency range. From the Raman scattering data of the bulk and thin films, it was found that the Raman modes in thin films are relatively more intense and additional Raman modes were appearing in the films in the low frequency range, which reveal that the local symmetry in the films is different from that of the bulk. The variations in the microwave dielectric properties due to processing can be attributed to the change in the local symmetry of the film.