Preparation and Characterization of NTC NiMn_2O_4-La_(1-x)Ca_xMnO_3 (0≤x≤0.3) Composite Ceramics

摘要

Composite ceramics made of spinel structure NiMn_2O_4 and CaO-doped perovskite structure LaMnO_3 were prepared by a conventional solid state reaction and sintered at different temperatures. The XRD patterns have shown that the major phases presented in the sintered samples are NiMn_2O_4 compounds with the spinel structure, La_(1-x)Ca_xMnO_3 with the perovskite structure and NiO with a monoclinic structure. SEM images show that the density and grain size of the composite ceramics increases with sintered temperature increasing. The electrical resistivity of the composite ceramics at 25°C is found to change significantly depending on the CaO content, while the thermal constant B is still reasonably large in the range of 2400 to 3000 K. For the composition x = 0.1, the composite with a low electrical resistivity (ρ25°C=4.46Ω·cm) and moderate B value (B_(25/50)=2762K) was obtained. These composites could be applied as potential candidates for NTC thermistors in the suppression of the inrush current.