Effect of piezoelectric vibration on electrical properties of YSZ film prepared by MOCVD
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Effect of piezoelectric vibration on electrical properties of YSZ film prepared by MOCVD Hiroshi Masumoto and Takashi Goto Institute for Materials Research, Tohoku University, Sendai 980-8577, JAPAN
ABSTRACT To improve electric properties of ion-conductors at low temperatures, ion-conducting/piezoelectric multifunctional film was prepared. Yttria-stabilized zirconia (YSZ) film as an ion-conducting film was deposited on a MgO substrate by metal-organic chemical vapor deposition (MOCVD). The significant [100] preferred orientation of cubic-YSZ single-phase film c ontaining 8 mol%Y2O3 was obtained at a deposition temperature of 973 K. The film consisted of fine grains of about 400 nm in diameter and had a columnar structure. It was capable of ionic conduction, as shown by the fact that a semicircle and a spike appeared at high and low frequencies, respectively, in the complex impedance measurement. The obtained YSZ thin film was placed on a multilayer piezoelectric actuator composed of seven sheets of a PZT (lead zirconate titanate) system. The effect of piezoelectric vibration on the electric properties of the ion-conducting film was investigated. The impedance value of the YSZ thin film decreased with increasing amplitude of piezoelectric vibration. The electrical conductivity of the YSZ thin film at 353 K, with an applied vibration frequency of 115 kHz and a voltage of 40 V, was about 2x10-4 Sm-1. The value of this conductivity was 103 times greater than that without vibration. Vibration by the actuator was thus suggested to improve the ionic conduction of the YSZ thin film.
INTRODUCTION Yttria-stabilized zirconia (YSZ) is characterized by excellent thermal and chemical stability, as well as by oxide ion conduction, and thus shows promise for use in oxide ion conducting devices such as oxide sensors and solid-oxide fuel cells. However, the ionic conductivity of YSZ at around room temperature is insufficient, and YSZ should be heated to about 700 K for sensor application [1]. To improve the sensitivity of YSZ sensors at low temperatures, electrodes h ave been developed [2,3] to modify the sensing mechanism [4-6] and to enhance the ionic conductivity of YSZ. It is well-known that the ionic conductivity of YSZ can be increased by doping with aliovalent elements [7]. The ionic conductivity of YSZ may also be increased by distorting the YSZ lattice. Suzuki et al. reported that the ionic conductivity of YSZ film increased with increasing lattice parameter based on the thermal expansion difference between substrates and YSZ films [8]. A piezoelectric actuator may be applicable for induction of distortion of the YSZ lattice, resulting in an increase in ionic conductivity of YSZ film. In the present study, YSZ film was prepared by metal-organic chemical vapor deposition (MOCVD), and this was placed on a multilayer piezoelectric PZT (lead zirconate titanate) actuator. The effect of piezoelectric vibration on the electric properties of the YSZ film was investigated.
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EXPERIMENTAL PROCEDURE Figure 1 is a sche
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