A barrier model for ZnO varistors

Abstract

A model of current transport in ZnO varistors is proposed. The model is a modification of an earlier one suggested by Levine, with the major difference being the inclusion of a thin (?10 Å) ’’disordered’’ layer which separates the single-crystal ZnO grains. The proposed model is shown to be consistent with electrical and microstructural observations and can satisfactorily account for α’s in excess of 60. A technique for extracting the surface-state density Ns(E) and doping profiles from C-V and I-V data is described. It is also shown from the theory that the maximum α is approximately proportional to the grain voltage, a result that is in agreement with measurements on varistors made under a wide range of processing conditions. By calculating the I-V characteristic for different Ns(E) profiles, it is shown that Ns(E) largely determines this characteristic and that certain profiles are to be favored over others when processing conditions are considered.

Electrochemical heavy metal detection, photocatalytic, photoluminescence, biodiesel production and antibacterial activities of Ag–ZnO nanomaterial

“…1.The XRD pattern of pure ZnO( In the case of Ag-ZnO Nps the intensity of peak is reduced due to the formation of Ag nanoparticles on the surface of ZnO Nps [30] . A broad peak at 3434 cm -1 (stretching) and 1330cm -1 to 1670 cm -1 (bending) indicates the presence of hydroxyl residue which is due to atmospheric moisture [31,32].…”

Electrical degradation of double-Schottky barrier in ZnO varistors

“…32,33 However, the microscopic origins of DSB are still un-fully identified, 32 though various models have been proposed focusing on the conduction mechanism since the discovery of non-ohmic properties of ZnO varistors by Matsuoka, 34 including the successful description by Pike, Blatter and Greuter. 1,33,35,36 So far, the intergranular layer, 34 segregation of additives, 37,38 thin disordered layer, 39 oxygen-excess defects like chemisorbed oxygen or excess amount of oxygen, 40,41 native point defects such as zinc vacancy (V Zn ) and oxygen interstitial (O i ), 2,15,42 and certain complex defect composed of additives and native defects 43 have all been considered as the possible candidates for promoting the generation of acceptor-states. In effect, recent successes in performing first-principles calculations on ZnO materials to consider the grain boundary structure, 2,32 dopant segregation 44 and defect formation [43][44][45] have made it possible to understand the formation of acceptor state from atomic scale.…”

Characterization of Interface States in Degraded ZnO Varistors

“…[1][2][3][4][5] Also, several models have been proposed to explain the degradation phenomena. 2,6-9) Eda et al 7) reported that the degradation occurred due to a reduction of the barrier height caused by the migration of two types of the ions that exist in the intergranular or the depletion layers.…”