Structure and Optical Characteristics of Barium–Strontium Niobate Films on Al₂O₃ Substrates

The structure and optical characteristics of thin films of relaxor ferroelectric Ba_0.5Sr_0.5Nb₂O₆ grown by RF sputtering in an oxygen atmosphere on an Al₂O₃ substrate (c cut) have been studied. X-ray diffraction analysis shows that Ba_0.5Sr_0.5Nb₂O₆ films are c-oriented and unit-cell parameter c is 3.948(1) Å. Ellipsometric measurements confirm that SBN-50 films are characterized by a natural growth direction, which coincides with the direction of the optical crystal axis. An analysis of ellipsometric results shows that there is no transition layer at the film/substrate interface; the damaged layer on the free film surface is 7.5 nm thick, and the volume filling factor is estimated to be 0.625.