High temperature NTC ceramic resistors (ambient–1000 °C)

New temperature sensors operating from ambient to 1000 °C, stable in diesel exhaust gas, and cheap, are needed. Such components may be ceramics. The value of their electrical resistance versus temperature is classically expressed as R=a.exp(B/T). Compounds from the ternary diagram Y2O3–Mn2O3–Cr2O3 may permit the obtaining of such performances. We have synthesized some compositions by solid-state reaction. Dense ceramics sintered at 1600 °C are two-phased, compound of a Y2O3 phase and an orthorhombic perovskite YCr0.5Mn0.5O3 phase. Their resistivity at room temperature can be in the range 4 kΩ cm to 106 MΩ cm together with a B coefficient value of about 3600 K. Such ceramics can be used to make NTC resistors with a resistance value ranging from some hundreds kΩ at room temperature to some Ω at 1000 °C.