Effects of Ta2O5 on the microstructure and electrical properties of ZnO linear resistance ceramics

ZnO-Al2O3-MgO-TiO2-SiO2-Ta2O5 (ZnO-based) linear resistance ceramics with doping different molar percentages of Ta2O5 were prepared by a conventional ceramics method. Effects of Ta2O5 additives on the phase composition, microstructures, and electrical properties of ZnO-based linear resistive ceramics were investigated. The results show that doping Ta2O5 can refine the grains of the main crystalline phase ZnO and the secondary crystalline phase ZnAl2O4 in terms of microstructure, and also can reduce the grain boundary barrier and optimize the I-V characteristics in terms of electrical properties. In addition, the doping of Ta2O5 can improve the stability of the resistivity , and the impedance frequency indicates that the doping of Ta2O5 makes the sample suitable for high-frequency electric fields. The resistivity of the sample doped with 0.2 mol% Ta2O5 is 56.2 Ω·cm, and this sample has the best grain boundary barrier height, nonlinear coefficient and temperature coefficient of resistance of 0.054 eV, 1.04 and -3.48×10-3 / ℃，respectively.

Solid-phase crystallization of ultra-thin amorphous Ge layers on insulators

A simple method to form ultra-thin (< 20 nm) semiconductor layers with a higher mobility on a 3D-structured insulating surface is required for next-generation nanoelectronics. We have investigated the solid-phase crystallization of amorphous Ge layers with thicknesses of 10−80 nm on insulators of SiO2 and Si3N4. We found that decreasing the Ge thickness reduces the grain size and increases the grain boundary barrier height, causing the carrier mobility degradation. We examined two methods, known effective to enhance the grain size in the thicker Ge (>100 nm). As a result, a relatively high Hall hole mobility (59 cm2/Vs) has been achieved with a 20-nm-thick polycrystalline Ge layer on Si3N4, which is the highest value among the previously reported works.

AC Impedence Properties of Multifunction Ceramics ZrScMo2VO12

Alternating current (AC) impedance properties of negative expansion material ZrScMo2VO12 are studied with electrochemical impedance spectroscopy. The conductivity is measured as 2.49×10-4 Ohm-1cm-1K at 673 K and 4.15×10-4 Ohm-1cm-1K at 773 K. We have also elucidated that the conduction of ZrScMo2VO12 come from defects and the co-doping of N and P type in semiconductors. The Schottky defect and Frenkel defect in the material lead to O2- ion conduction, and co-doping leads to electron conduction. And the grain boundary barrier could limit the conduction of electron and hole. This work may be useful for the application exploration of ZrScMo2VO12 in fuel cell and corresponding energy conversion fields.

Noise Modeling in MOX Gas Sensors

In this paper, we propose a new model of adsorption–desorption (AD) noise in chemoresistive gas sensors by taking into account the polycrystalline structure of the sensing layer and the effect of the adsorbed molecule’s density fluctuation on the grain boundary barrier height. Using Wolkenstein’s isotherm, in the case of dissociative and non-dissociative chemisorption, combined with the electroneutrality, we derive an exact expression for power density spectrum (PDS) of the AD noise generated around one grain. We show that the AD noise generated in the overall sensing layer is a combination of multi-Lorentzian components. The parameters of each Lorentzian depend on the nature of the detected gas, the grain size, and the gas concentration. Moreover, we show that, according to the sensing layer microstructure (distribution of grain sizes in the sensing layer), this combination can lead to a [Formula: see text] spectrum, and in this case the noise level of the [Formula: see text] spectrum depends on the nature of the detected gas. The noise modeling presented in this paper confirms that noise spectroscopy is a useful tool for improving the gas sensor selectivity.

Simulation of the Electrical Properties of Semiconductive BaTiO3 Ceramic Varistors Using Continuum Theory

A continuum field model describing the electrical characteristics of polycrystalline semiconductors ceramics is suggested. Taking into account the continuum theory, a static differential equation about electron level on the base of Poisson equation is established. The one-dimensional quantitative calculation is carried out using the Runge-Kutta method. The results show that as the applied voltage increases, the grain boundary barrier in the nonlinear zone drop drastically. The nonlinear characteristics of high temperature paraelectric phase is larger than that of room temperature ferroelectric phase.