LATTICE PARAMETER CHANGE OF BaSrTiO_3 FILMS GROWN BY PULSED LASER DEPOSITION

摘要

Single phase Ba_(0.5)Sr_(0.5)TiO_3 films with three different thicknesses (40, 80, and 160 nm) have been deposited onto MgO substrates by pulsed laser deposition (PLD). The lattice parameters for the thin film have been measured using x-ray diffraction. The deposited films all show a significant tetragonal distortion. The in-plane lattice parameters for all film thickness are always larger than surface normal lattice parameters for as-deposited films. Films (80 and 160 nm) annealed at 900, 1100, and 1200 °C for 6 hours after deposition show reduced tetragonal distortion compared to as-deposited films. Further, tetragonal distortion of annealed films with thicknesses of 80 and 160 nm were reduced with decreasing annealing temperature from 1200 °C to 900 °C, while that with a thickness of 40 nm is increased with decreasing annealing temperature. This result indicates that the stress due to lattice mismatch and thermal expansion difference changes as a function of film thickness.