Effect of Bi2O3 additive on microstructure and non-lonear coefficient of ZnO varistor

Abstract

The varistor ZnO has been made by using raw materials: ZnO (E-Merck) and additive 0%, 2.5%, 5%, 7.5%, and 10% wt. Bi₂O₃. The important property of varistor ZnO is coefficient of non linear (α) and it can give influence correlation between current I and voltage V. The mixing process of raw materials was done by using magnetic stirrer and liquid acetone as media, and then was dried at 60°C, and also grinded until passing 400 meshes. Pellet was made by using pressing 50 MPa, and fired at 1050°C with holding time 2 hours. After firing, all samples are characterized, such as: measurement of coefficient of non linear (α), and observation of microstructure by using Scanning Electron Microscope (SEM). The results show that sample without additive has α less than 5 and this sample has not properties as varistor, but the highest value of α is 64 for sample with additive 7.5% Bi₂O₃. The result of photos SEM shows that the increase of percentage of additive Bi₂O₃ can influence of formation grain boundary and grain size. Where, value of coefficient of non linear (α) is depend on existing of grain boundary and thickness of grain boundary.