Study on Mn₃O₄ - La_1-xCa_xMnO₃ composite ceramics with high temperature coefficient of resistance in large temperature range

La_1-xCa_xMnO₃, as a candidate for thermal radiation detectors, has received more attention due to the quest for a higher temperature coefficient of resistance (TCR), however, the narrow high-TCR temperature range greatly limits its application in uncooled bolometer. In this paper, Mn₃O₄ - La_1-xCa_xMnO₃ (x = 0–0.33) composite ceramics were prepared using the sol-gel method. A suitable TCR was achieved over a wide temperature range, including room temperature, by adjusting the Ca content. As the Ca content decreased, the resistivity (ρ) of the composite gradually increased at 300 K, and the positive TCR (PTC) peak shifted to a lower temperature. However, the negative TCR (NTC) was enhanced over a wider temperature range. When x = 0.05, the maximal NTC was −3.2%·K⁻¹ within the range of 172 K–350 K and |TCR| > 2%·K⁻¹, spanning a large temperature range around 180 K, including room temperature. These results strongly indicate that the composite, such as Mn₃O₄ - La_1-xCa_xMnO₃, provides a new idea for uncooled bolometer/night vision.