Potassium niobate, KNbO 3 , (KN)-based ceramics were prepared by a modified conventional ceramic fabrication process to characterize their piezoelectric properties. The KN-MnCO 3 0.1 wt % (KN-Mn0.1) ceramic used in this study showed a high density ratio >96% and a high resistivity, , of about 10 13 Ácm without deliquescent properties. The shear mode of the KN-Mn0.1 ceramic showed excellent resonance and antiresonance characteristics with tiny spurious peaks upon optimization of the sample dimensions. The electromechanical coupling factor, k 15 , and piezoelectric strain constant, d 15 , of KN-Mn0.1 showed relatively large values of 0.55 and 207 pC/N, respectively. The shear-mode vibration of KN-based ceramics appears to be a very promising candidate for actuators and high-power applications.

No abstract

The complex impedance of a CuO/ZnO oxide semiconductor heterocontact was studied by applying a dc bias voltage in a mixture of CO or H2 (4000 ppm) in air between 250° and 400°C. The frequency dependence of reactance showed a minimum peak, and the absolute value of the reactance and the frequency giving the peak both changed in a different manner, depending on the presence of a reducing gas of either CO and H2, and also the dc bias. Sensing properties could be tuned to detect both CO and H2 gases in air or to detect only H2 gas in air, by selecting the measuring frequency and the applied dc bias at 400°C. Additional resistance and capacitance specific to the ambient gases were introduced to the interface impedance of the semiconductors, and then were estimated from impedance measurements. Tunable gas sensing was possible when the product of the resistance and the capacitance components in the interface had varying values, dependent on gas species and dc bias. This paper proposes this new method of tunable gas sensing that uses the complex impedance characteristics of a heterocontact. In addition, the mechanisms of the tuning function are discussed.

No abstract