The present review describes mainly the history of SnO2-based voltage-dependent resistors, discusses the main characteristics of these polycrystalline semiconductor systems and includes a direct comparison with traditional ZnO-based voltage-dependent resistor systems to establish the differences and similarities, giving details of the basic physical principles involved with the non-ohmic properties in both polycrystalline systems. As an overview, the text also undertakes the main difficulties involved in processing SnO2- and ZnO-based non-ohmic systems, with an evaluation of the contribution of the dopants to the electronic properties and to the final microstructure and consequently to the system’s non-ohmic behavior. However, since there are at least two review texts regarding ZnO-based systems [Levinson, L. M., and Philipp, H. R. Ceramic Bulletin 1985;64:639; Clarke, D. R. Journal of American Ceramic Society 1999;82:485], the main focus of the present text is dedicated to the SnO2-based varistor systems, although the basic physical principles described in the text are universally useful in the context of dense polycrystalline devices. However, the readers must be careful of how the microstructure heterogeneity and grain-boundary chemistry are capable to interfere in the global electrical response for particular systems. New perspectives for applications, commercialization and degradation studies involving SnO2-based polycrystalline non-ohmic systems are also outlined, including recent technological developments. Finally, at the end of this review a brief section is particularly dedicated to the presentation and discussions about others emerging non-ohmic polycrystalline ceramic devices (particularly based on perovskite ceramics) which must be deeply studied in the years to come, specially because some of these systems present combined high dielectric and non-ohmic properties. From both scientific and technological point of view these perovskite systems are quite interesting.

SnO2, ZnO and related polycrystalline compound semiconductors: An overview and review on the voltage-dependent resistance (non-ohmic) feature

Properties of the perovskite ferroelectrics Na0.5Bi0.5TiO3 (NBT), K0.5Bi0.5TiO3 (KBT) and their solid solutions are reviewed. Consideration of the NBT behavior draws attention to phenomena of the ion ordering, coexistence of several phase regions within a crystal lattice, phase transition diffusion and to a quite new phenomenon: existence of the isotropization points (temperatures) in the AFE-phase-temperature interval. In the KBT the isotropic points are absent. NBT, KBT, and their solid solutions are considered as possible useful materials for technical (in particular, for piezoelectric) applications. There are also some other A0.5 +Bi0.5B4+O3 perovskites which are interesting for future research.

Ferroelectric Na0.5Bi0.5TiO3 and K0.5Bi0.5TiO3 Perovskites and Their Solid Solutions

A model is proposed here to explain how the chemical features of metal oxide varistors can alter their nonohmic physical behavior, based on nonohmic similarities in the electrical properties of ZnO- and SnO2-based varistors. The proposed model explains the electrical properties of ZnO- and SnO2-based varistors before and after thermal treatments in oxygen- and nitrogen-rich atmospheres, which cause similar changes in the nonohmic feature of these polycrystalline ceramics with greatly differing chemical compositions and microstructures. The model is based on the key role that oxygen plays in varistor grain boundaries, independently of the type of ceramic system (ZnO-, SnO2- or even SrTiO3-based varistors) involved.

Role of oxygen at the grain boundary of metal oxide varistors: A potential barrier formation mechanism

Electroceramic calcium copper titanates (CaCu3Ti4O12, CCTO), with high dielectric permittivities (e) of approximately 105 and 104, respectively, for single crystal and bulk materials, are produced for a number of well-established and emerging applications such as resonator, capacitor, and sensor. These applications take advantage of the unique properties achieved through the structure and properties of CCTO. This review comprehensively focuses on the primary processing routes, effect of impurity, dielectric permittivity, and deposition technique used for the processing of electroceramics along with their chemical composition and micro and nanostructures. Emphasis is given to versatile and basic approaches that allow one to control the microstructural features that ultimately determine the properties of the CCTO ceramic. Despite the intensive research in this area, none of the studies available in the literature provides all the possible relevant information about CCTO fabrication, structure, the factors influencing its dielectric properties, CCTO immobilization, and sensing applications.

/pdf/a-short-review-on-copper-calcium-titanate-ccto-n7mpsb6ecj.pdf

A Short Review on Copper Calcium Titanate (CCTO) Electroceramic: Synthesis, Dielectric Properties, Film Deposition, and Sensing Application

In this work, using a combination of a theoretical framework and atomistic calculations, we highlight the concept of “surface piezoelectricity,” which can be used to interpret the piezoelectricity of nanostructures. Focusing on three specific material systems (ZnO, SrTiO3, and BaTiO3), we discuss the renormalization of apparent piezoelectric behavior at small scales. In a rather interesting interplay of symmetry and surface effects, we show that nanostructures of certain non-piezoelectric materials may also exhibit piezoelectric behavior. Finally, for the case of ZnO, using a comparison with first principles calculations, we also comment on the fidelity of the widely used core–shell interatomic potentials to capture non-bulk electro-mechanical response.

/pdf/surface-piezoelectricity-size-effects-in-nanostructures-and-3ihect3lcc.pdf

Surface piezoelectricity: Size effects in nanostructures and the emergence of piezoelectricity in non-piezoelectric materials

Electrical properties of SnO 2 -ZnO-Nb 2 O 5 varistor system

The Sb2O3-doped TiO2 varistors were obtained by conventional ceramic processing. The 0.75 mol% Sb2O399.25 mol% TiO2 varistor has a nonlinear coefficient α = 7 and a minimum breakdown electrical field of 6 V/mm. The nonlinear electrical behaviour of TiO2Sb2O3 ceramics was explained by the introduction of defects in the crystal lattice that are responsible for the formation of Schottky potential barriers at grain boundaries.

https://iopscience.iop.org/article/10.1088/0256-307X/17/7/024/pdf

Nonlinear Electrical Behaviour of the TiO 2 ·Sb 2 O 3 System

The dielectric, piezoelectric, ferroelectric and pyroelectric properties of (Bi0.5Na0.5)1-xBaxTiO3 (x=0.00，0.04，0.06，0.08, 0.12) ceramics prepared by sol-gel method were investigated. It was found that all the samples in this experiment show improved piezoelectric properties,obtained by using this chemical method. For(Bi0.5Na0.5)0.94Ba0.06TiO3 ceramic, as its composition is near the morphotropic phase boundary (MPB), it shows the largest piezoelectric constant, d33=173×10-12C/N, which is about 40% improvement compared to the conventional processed ceramics in this system. In addition, from the ferroelectric and pyroelectric measurements, the remanent polarization Pr, coercive field Ec and depolarization temperature Td of the (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramic were found to be 25μC/cm2, 28kV/cm, and 80℃, respectively.

Enhanced piezoelectric properties of (Bi0.5Na0.5)1－xBax TiO3 lead-free ceramics by sol-gel method

We prepared bismuth sodium titanate (Bi0.5Na0.5TiO3) ultrafine powders by the sol-gel method. The dielectric properties of the pressed pellets and fired ceramics with different grain sizes as a function of temperature at various frequencies were studied. With decreasing grain size, the dielectric anomaly around 200°C increases, while the dielectric thermal hysteresis decreases. All the samples with grain sizes larger than 100 nm show dielectric peaks at temperature of about 350°C. The very little change in Tm observed down to the critical size indicates that Bi0.5Na0.5TiO3 is an order-disorder system above 200°C. In addition, the dielectric peak becomes lower with decreasing grain size and the ferroelectric critical size of Bi0.5Na0.5TiO3 was eventually determined to be about 100 nm according to the disappearance of dielectric peak.

http://iopscience.iop.org/article/10.1088/0256-307X/20/2/335/pdf

Grain-size effect on the dielectric properties of Bi0.5Na0.5TiO3

In order to understand well the different ferroelectric behaviour of quantum paraelectrics and ferroelectrics and the origin of the ferroelectricity of the solid solution KTa0.5Nb0.5O3(KTN), we calculated the electronic structure of CaTiO3, BaTiO3 and KTN by first principles calculation. From total energy analysis, it is shown that, with increasing cell volume, the crystals (CaTiO3, SrTiO3) will have a ferroelectric instability. For BaTiO3, the ferroelectricity will disappear as the cell volume is decreased. From the density of states analysis, it is shown that the hybridization between B d and O p is very important for the ferroelectric stability of ABO3 perovskite ferroelectrics. This is consistent with the analysis of band structure.

https://iopscience.iop.org/article/10.1088/1009-1963/11/7/313/pdf

Zhong Wei-Lie

Papers

Electrical properties of SnO 2 -ZnO-Nb 2 O 5 varistor system

Nonlinear Electrical Behaviour of the TiO 2 ·Sb 2 O 3 System

Enhanced piezoelectric properties of (Bi0.5Na0.5)1－xBax TiO3 lead-free ceramics by sol-gel method

Grain-size effect on the dielectric properties of Bi0.5Na0.5TiO3

First principles study on the ferroelectricity of the perovskite ABO3 ferroelectrics