Microstructure and electrical properties of (Sr, Cu) doped TiO₂ based varistors

Full text: The addition of different dopants affects the densification, mean grain size and electrical properties of TiO₂-based varistor ceramics. The microstructure and electrical properties are examined of the following systems (99-x)%TiO₂+1% SrO+x%CuO, where x=0.05, 0.15, 0.2 and 0.25 when doped with small quantities (0.05-0.2 at.%). The material was milled for 4 h in a ball mill. The resulting powders were pressed uniaxially under 150 MPa into pellets (10 mm diameter by 1.5 mm thickness). This was followed by sintering in a furnace at 1400°C for 1 h. The phases were identified by X-ray diffraction (XRD), the morphology of the pellets was characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy. The nonlinear coefficient (α) which was calculated from the characteristic current density curve (J) as a function of the applied electric field (E), was obtained with a high voltage source. This paper discusses the microstructural and electrical properties of (Sr, Cu) doped TiO₂ systems, demonstrating that some of these systems display electrical properties that allow for their use as low voltage varistor. Dopants such as SrO play a special role in the formation of barriers at the grain boundary and in the nonlinear behavior in TiO₂-based systems. (author)