Element Strategy Using Ru-Mn Substitution in CuO-CaCu3Ru4O12 Composite Ceramics with High Electrical Conductivity

CaCu3Ru4−xMnxO12 bulks with various substitution amounts x and sintering additive CuO (20 vol.%) were prepared, and the influence of x on the electrical conductivity in a wide temperature range (8–900 K) was investigated. Microstructural observations showed an enhancement of bulk densification upon Mn substitution. Although the resistivity increased with increasing x, the resistivity was as low as a few mΩcm even in the sample with x = 2.00, where half of Ru is substituted by Mn. This high conductivity despite the loss of Ru 4d conduction following the substitution is explained by the A-site (Cu2+) conduction in CaCu3Ru4−xMnxO12. The thermopower of CaCu3Ru4−xMnxO12 was found to be influenced by the substitution, and a sign inversion was observed in the substituted samples at low temperature. The partial substitution of Ru by Mn in CaCu3Ru4O12 enables the reduction of the materials cost while maintaining good electrical conductivity for applications as a conducting device component

Trial of an All-Ceramic SnO2 Gas Sensor Equipped with CaCu3Ru4O12 Heater and Electrode

We have constructed a gas sensor of SnO2 equipped with ceramic electrodes and a heater made of CaCu3Ru4O12, which demonstrated good device performance at high temperature. The CaCu3Ru4O12-based electrodes and heater were formed on Al2O3 substrates using a screen-printing process, which is cost-effective and suitable for mass-production. This all-ceramic device reached 600 °C at the lowest, and remained intact after one week of operation at 500 °C and rapid thermal cycling of 500 °C temperature changes within 10 s. We propose CaCu3Ru4O12 as a robust and reliable conducting material that can be a substitute for Pt in various devices

Unusually Small Thermal Expansion of Ordered Perovskite Oxide CaCu3Ru4O12 with High Conductivity

We measured the coefficient of thermal expansion (CTE) of conducting composite ceramics 30 vol.% CuO-mixed CaCu3Ru4O12 together with CaCu3Ru4O12 and CuO. Although conducting ceramics tend to show higher CTE values than insulators, and its CTE value does not match with other ceramic materials, the CTE of CaCu3Ru4O12 (7–9 × 10−6/K) was as small as those of insulators such as CuO (9 × 10−6/K), alumina (8 × 10−6/K), and other insulating perovskite oxides. We propose that the thermal expansion of CaCu3Ru4O12 was suppressed by the Cu-O bond at the A-site due to the Jahn–Teller effect. This unusually small CTE of CaCu3Ru4O12 compared to other conducting oxides plays a vital role enabling successful coating of 30 vol.% CuO-mixed CaCu3Ru4O12 thick films on alumina substrates, as demonstrated in our previous study