Preparation and characterization of LaMn_0.5Co_0.5O₃–Ni_0.66Mn_2.34O₄ composite NTC ceramics

Negative temperature coefficient (NTC) thermistor materials based on (LaMn_0.5Co_0.5O₃)_x–(Ni_0.66Mn_2.34O₄)_1−x (0 ≤ x ≤ 0.5) composite ceramics, are fabricated by the conventional solid-state reaction method. The crystal structure, surface morphology and electrical properties of the composite ceramics are investigated and characterized by X-ray powders diffraction (XRD), scanning electron microscope (SEM), and Agilent digital multimeter, respectively. XRD results show that main phases of as-sintered ceramics are a cubic spinel structure Ni_0.66Mn_2.34O₄ phase and a rhombohedral perovskite structure LaMn_0.5Co_0.5O₃ phase. SEM images indicate that the grain size of the composite ceramics decreases with increasing the low-resistivity perovskite phase. The ρ ₂₅ and B value of the composite ceramics decreases with increasing x, and the B is still reasonably high in the range of 4000–3500 K when x ≤ 0.2. Meanwhile, the introduction of the perovskite phase leads to a decrease in the resistance drift, which the ΔR/R₀ is relatively low (0.26–1.8 %) after annealing at 125 °C for 600 h in air atmosphere. These findings exhibit that (LaMn_0.5Co_0.5O₃)_x–(Ni_0.66Mn_2.34O₄)_1−x (0 ≤ x ≤ 0.5) composite ceramics have a higher electrical stability in comparison with Ni_0.66Mn_2.34O₄ ceramics, are helpful for meeting demands for obtaining better stability and performance of NTC composites ceramics.