Varistors are the most efficient devices for the protection of power transmission lines and electronic devices against excessive transient surges. The current trends that require varistors with more functions have led to research to develop new ceramic varistor material and titanium dioxide (TiO 2 ) is the emerging new material. In this research nanosized TiO 2 was taken as the base materials to which a small amount of impurities was added as dopants for enhancing the properties. Ta 2 O 5 , WO 3, Bi 2 O 3 and Co 3 O 4 were used as dopants where the percentage of Bi 2 O 3 and Co 3 O 4 was fixed; 0.5% and 0.2% respectively. Samples were prepared with different weight percentages of dopants and sintered at a constant temperature of 1300˚C with 2 hour's holding time to observe the effect of these dopants on physical and mechanical properties of nanosized TiO 2 . Analysis was undertaken to evaluate the properties of the nanosized TiO 2 , such as green density, fired density, fired strength, axial and radial shrinkage. It was found that with the composition of 98.1% TiO 2 +0.7% Ta 2 O 5 +0.5% WO 3 +0.2%Co 3 O 4 +0.5%Bi 2 O 3 have a significant influence on the physical and mechanical properties, which is anticipated to improve the performance of varistor. With the improvement in the physical and mechanical properties of TiO 2 , the composite material has potential application in low voltage application devices.

Varistors are the electronic devices which are used in various industries to protect the electrical and electronic systems from sudden surges. In this research, the electrical properties of titanium dioxide (TiO 2 ) doped with tantalum pentoxide (Ta 2 O 5 ), tungsten trioxide (WO 3 ), cobalt oxide (Co 3 O 4 ), and bismuth oxide (Bi 2 O 3 ) and fired at different temperatures were investigated for low-voltage applications. The adequate amount of dopants at suitable sintering temperature had beneficial effect in improving the properties of TiO 2 . The relative density was found to be more than 97% of theoretical density when samples sintered between 1300°C and 1400°C for all composition compared to undoped samples. On the other hand, the addition of dopants enhanced hardness and compressive strength of varistor disks. The average grain size was also increased with the dopants system, making it suitable for low-voltage application. Furthermore, the current-voltage characteristic of the TiO 2 revealed a significantly high value of nonlinearity of 19.6. A high dielectric constant of 10 4 with minimum dissipation factor of 0.002852 at 1 kHz was also obtained, thereby making it suitable for low-voltage application.Based in part on the thesis submitted for Master's degree in Mechanical Engineering, Universiti Tenaga Nasional, Kajang, Selangor, 2014.

Titanium dioxide (TiO 2 ) varistors doped with tungsten oxide (WO 3 ) and bismuth oxide (Bi 2 O 3 ) were investigated. The microstructure and electrical characterization were studied, where the effects of different concentrations of WO 3 and a fixed amount of Bi 2 O 3 were investigated. TiO 2 based varistors have promising potential for the high performance development. The percentage of dopant was varied at various levels and the prepared samples were then characterized by evaluating IV relationships to determine the degree of non-linearity in the varistor. Evaluation was conducted based on non-linear coefficients, breakdown voltage and power loss. Microstructure analysis was also carried out using SEM. The average grain size was determined to find the relationship between microstructure and electrical properties. It was found that a molar concentration with 99.1%TiO 2 . 0.4%WO 3 . 0.5%Bi 2 O 3 yielded the best results in terms of electrical and microstructural properties. The addition of 0.5%Bi 2 O 3 and 0.4%WO 3 creates a relatively low clamping efficiency, higher non-linear coefficient, low breakdown voltage and less power loss.