Effect of doping CaO in NiMn2O4-LaMnO3 composite NTC thermistors on microstructure and electrical properties

2^nd International Conference and Exhibition on Materials Science & Engineering

October 07-09, 2013 Hampton Inn Tropicana, Las Vegas, NV, USA

Huimin Zhang

Accepted Abstracts: J Material Sci

Abstract :

The negative temperature coefficient (NTC) thermistors (TRs) based on mixed transition-metal and rare earth metal manganite electroceramics have been widely used for temperature measurement, control, compensation and suppression of inrush current, due to their high stability and low cost. In general, NTC materials are spinel oxides, a high B value generally couples with high electrical resistivity and vice versa. However, some applications such as suppressing the inrush current require NTC materials with a low electrical resistivity (≤10 Ω?m) while possessing a large B (≥2600 K) and sufficient stability. General ways to design a new material are composite and doping. In principle, the material with low electrical resistivity and high B may be obtained through introducing a second phase with low electrical resistivity into a spinel oxide of high B. What?s more, the composite can make full use of favorable condition and promote complementarity in each component due to the adjustability of its multiplicity and binding form, and the outstanding and attractive properties that the single component couldn?t achieve may be obtained by complex method. Therefore, we propose and verify that the resistivity and B value can be adjusted to desired values by introducing LaMnO 3 doped by CaO into the spinel oxide NiMn 2 O 4 . The composite ceramics (NiMn 2 O 4 ) 0.50 (La 1-x Ca x MnO 3 ) 0.50 (0≤x≤0.3) consisting of spinel-structured NiMn 2 O 4 and perovskite- structured CaO-doped LaMnO 3 were prepared by classical solid state reaction. The obtained ρ25 , B 25/50 constants of the composite samples doped by CaO are in the range 0.234-8.61 Ω?m and 2600-2962 K, respectively, and the resistivity drift after aging at 125 °C for 500 h in air is relatively small (0.34% when x=0.3). The electrical conduction of the composite ceramics can be elaborated by the ions migration mechanism. Such ceramics could be used as potential candidates for NTC thermistors in suppression of inrush current.

Biography :

Huimin Zhang has completed the Ph.D. at the age of 23 years from Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences. She has been to University of Washington as a visiting scholar in 2011. When she came back to China, she has been working for ceramic material preparation and device fabrication as Associate Professor. Up to now, she has published more than 10 papers and 5 patents.