Structures and electric properties of cubic bismuth based pyrochlore thin films grown by pulsed laser deposition

Abstract

The effects of cation substitution on the structure, dielectric properties, tunability, and temperature dependence of (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) thin films were investigated. Four kinds of ceramic targets and thin films were prepared, which were (Bi1.5Zn0.1Ca0.4)(Zn0.5Nb1.5)O7 (BZNCa), (Bi1.5Zn0.5)(Nb0.5Ti1.5)O7 (BZNTi), (Bi1.5Sr0.5)(Sn1.5Nb0.5)O7 (BSSN) and (Bi1.5Sr0.5)(Zr1.5Nb0.5)O7 (BSZN). Thin films were deposited on Pt/TiO2/SiO2/Si(100) substrates at the substrate temperature of 650°C under an oxygen pressure of 10Pa by pulsed laser deposition. The resultant Bi-based thin films show a cubic pyrochlore structure. Meanwhile, the preferential orientation of the (111) plane is observed. Surface morphology features of the substituted thin films also show the difference. Compared with the pure BZN thin film, the dielectric constant of the BZNCa thin film slightly decreases. The temperature coefficient of capacitance (TCC) moves to the negative orientation TCC=−319ppm/°C. The dielectric constant of the BZNTi thin film significantly increases, reaching 229. At the same time, thin film still keeps the low loss tangent. However, the dielectric constants of the BSSN and BSZN thin films significantly decrease, dropping to 60 and 48, respectively. Furthermore the BSSN thin film exhibits the near zero temperature coefficient of +55ppm/°C. The BSZN thin film also shows the positive TCC value of +318ppm/°C. Moreover, BSSN and BSZN thin films show a near field independence (at low field).