Study Of The Doped LaMnO₃ System NTC Material

LaMnO₃ is semiconductor ceramic with negative resistance-temperature characteristic and can be used as Negative Temperature Coefficient Resistor(NTCR). In this paper, a new NTCR material have been studied through doping in LaMnO₃. To increase the resistance valueρ25℃and improve the B value as well as to get good sintering ceramic elements, introduce different elements such as Fe, Ni, V, Ti, Ba, Sr, Cu was into A and B sites. Then the relationships between structure and electrical properties are discussed by aids of XRD, SEM etc. And the conducting mechanism of the NTC material with perovskite type structure was studied .First, Fe₂ O₃ ,NiCO₃ ,V₂O₅ and TiO₂ were doped in LaMnO₃ with different content. The systems such as LaMn_1-xFe x O₃ , LaMn_1-xNi_xO₃ , LaMn_1-xV_xO₃ ,LaMn_1-xTi_xO₃ (0.1≤x 0.4) were prepared by conventional solid-state reaction at 1200℃≤for 2h in air. The NTC character of such samples was researched. And it was found thatρ25℃and the B value increase obviously when Ti⁴⁺ substitutes Mn³⁺.Then the system(LaMn_0.6Ti_0.4O₃)with low resistivity, high B and good sintering way were selected to be doped with SrCO₃ , BaCO₃, CuO. The systems of La_1-xSrx Mn_0.6Ti_0.4O₃ ,La_1-xBa x Mn_0.6Ti_0.4O₃ (0.1≤x≤0.6),LaMn_0.6Ti_0.4-yCuy O₃ (0.05≤y 0.2) were prepared by conventional solid-state reaction. The resistivity of samples changed with the temperature was measured from 25℃≤to 300℃.The X-ray diffractograms (XRD) of the samples were recorded and the microstructure was observed by scanning electron microscope (SEM). It was found that theρ-T curves of all the samples matched NTC characteristic. A new NTCR material with low resistivity(180Ω·cm ), high sensitivity to temperature change(B=3270K) and high stability can be get. And the conducting mechanism of the NTC material was studied with the semiconductor carriers mechanism.