Growth temperature dependence of crystal symmetry in Nb-doped BaTiO_3 thin films

摘要

Growth temperature effects on the microstructure of Nb-doped BaTiO_3 thin films of the composition BaTi_(0.98)Nb_(0.02)O_3 are studied using X-ray diffraction and transmission electron microscopy (TEM). Reciprocal space maps and electron diffraction patterns show that the α-axis lattice parameter increases and the c-axis parameter decreases with increasing growth temperature, indicating a decrease of tetragonality. Bright-field TEM images show low and high densities of threading defects in films grown at low and high temperatures, respectively. The observations are discussed in terms of a hindering of the cubic-to-tetragonal phase transition by a high defect density and a high unit cell volume.