Structures and dielectric properties of pyrochlore bismuth zinc niobate thin films with zinc compensation

摘要

Pyrochlore Bi_(1.5)Zn_(1.0)Nb_(1.5)O_7 (BZN) thin films deposited at 650 °C under an oxygen pressure of 10 Pa by pulsed laser deposition were characterized as a function of zinc amount. The zinc concentration in the thin films was varied using ceramic targets having 0-40 mol% excess zinc contents. The X-ray diffraction measurement shows that thin films have a cubic pyrochlore phase structure and a strong preferential orientation of (111) plane. The dielectric properties are investigated as functions of temperature and frequency. Dielectric constant and loss tangent of the thin films both slightly increase with the increase of Zn amount. The thin film with 40 mol% zinc exhibits a dielectric constant of 198 and a loss tangent of 0.004 at 10 kHz. The dielectric relaxation behavior has been studied by measuring the temperature dependence of dielectric properties. The characteristic temperatures (T_m) move to the high temperature with the increase of Zn and gradually approach that of BZN ceramic. Meanwhile, in a wide frequency and temperature range (1 kHz-1 MHz, -100-150 °C), the dielectric constant of the thin films almost keeps unchanged and shows a negative temperature coefficient. Leakage current density of the thin films with 20 mol% zinc is approximately three order magnitude lower than that of films with 0mol% zinc at 400kV/cm. The conduction of BZN thin films is controlled by the Schottky emission mechanism and the space-charge-limited current mechanism.