Structural and optical properties of BaTi2O5 thin films prepared by pulsed laser deposition at different substrate temperatures

BaTi₂O₅ thin films were prepared on MgO (1 0 0) substrates by pulsed laser deposition. The effect of substrate temperature (T_sub) on the structural and optical properties of the films, such as crystal phase, preferred orientation, crystallinity, surface morphology, optical transmittance and bandgap energy, was investigated. The preferred orientation of the films changed form (7 1 0) to (0 2 0) depending on T_sub, and the b-axis oriented BaTi₂O₅ thin film could be obtained at T_sub = 973–1023 K. The surface morphology of the films was different with changing T_sub, which showed a dense surface with an elongated granular texture at T_sub = 973–1023 K. The crystallinity and surface roughness increased at the elevated substrate temperatures. The as-deposited BaTi₂O₅ thin films were highly transparent with an optical transmittance of ～70%. The bandgap energy was found to decrease with increasing substrate temperature, from 3.76 eV for T_sub = 923 K to 3.56 eV for T_sub = 1023 K.