Structural and electric properties of Bi₂Zn_2/3Nb _4/3O₇ thin films prepared by pulsed laser deposition

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited on Pt/TiO₂/SiO₂/Si(100) substrates under an oxygen pressure of 10 Pa by pulsed laser deposition. The substrate temperature varied from 500 ^°C to 750 ^°C. Effects of substrate temperature on the crystallinity, microstructure, and electric properties of Bi₂Zn_2/3Nb_4/3O₇ thin films have been systematically investigated. Bi₂Zn_2/3Nb _4/3O₇ thin films are amorphous in nature at a substrate temperature of 500 ^°C. With increase of substrate temperature to 550 ^°C, thin films begin to crystallize. At higher temperature of 750 ^°C, Bi₂O₃ phase can be detected in thin films. However, the crystallized thin films exhibit a cubic pyrochlore structure, not a monoclinic zirconolite structure, which is probably attributed by the composition deviation from the stoichiometric ratio. The resultant Bi₂Zn_2/3Nb_4/3O₇ thin films exhibit the character with high dielectric constant and low loss tangent. The dielectric constant gradually increases with the substrate temperature and reaches a maximum at 700 ^°C. The dielectric constant and loss tangent of the thin films deposited at 700 ^°C are 152 and 0.002 at 10 kHz, respectively. With further increase of substrate temperature to 750 ^°C, the dielectric constant decreases to 128. However, the tunability of the resultant thin films disappears, and the temperature coefficients are positive, which implies a more ordered structure in thin films.