Transactions of Nonferrous Metals Society of China
JOURNAL OF RAILWAY SCIENCE AND ENGINEERING
|Vol. 17 No. 6 December 2007|
（1. Department of Electronic Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China; 2. Key Laboratory of Ferroelectric and Piezoelectric Materials and Devices of Hubei Province, School of Physics and Electronic Technology, Hubei University, Wuhan 430062, China ）
Abstract:The green sheets with Ni paste as inner electrodes were sintered at 1 320 ℃ for 1 h under a N2/H2 mixing gas at an oxygen partial pressure p(O2)=10−8−10−12 MPa, and then reoxided at 900−1 000 ℃ to form multilayer positive temperature coefficient of resistance(PTCR). During the experiments, electronic characteristic effects of PTC with different thicknesses were contrasted. A certain extending of Ni diffusion is beneficial to the ohmic contact of multilayer PTCR but excessive diffusion is hamful to PTCR. The diffusion was studied by scanning electron microscopy(SEM) and energy-dispersive X-ray spectrometry(EDS). Inter-diffusion of element takes place along the Ni-BaTiO3 interface, especially Ni diffusion to BaTiO3 dominated the process. Furthermore, the degree of Ni diffusion is very severe as ceramic layers are very thin.
Key words: Ni; positive temperature coefficient of resistance; BaTiO3; diffusion