Structural and electric properties of Bi2Zn2/3Nb4/3O7 thin films prepared by pulsed laser deposition

Abstract

Bi2Zn2/3Nb4/3O7 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 Bi2Zn2/3Nb4/3O7 thin films have been systematically investigated. Bi2Zn2/3Nb4/3O7 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 Bi2Zn2/3Nb4/3O7 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.