Unusually Small Thermal Expansion of Ordered Perovskite Oxide CaCu(3)Ru(4)O(12) with High Conductivity

We measured the coefficient of thermal expansion (CTE) of conducting composite ceramics 30 vol.% CuO-mixed CaCu(3)Ru(4)O(12) together with CaCu(3)Ru(4)O(12) 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 CaCu(3)Ru(4)O(12) (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 CaCu(3)Ru(4)O(12) was suppressed by the Cu-O bond at the A-site due to the Jahn–Teller effect. This unusually small CTE of CaCu(3)Ru(4)O(12) compared to other conducting oxides plays a vital role enabling successful coating of 30 vol.% CuO-mixed CaCu(3)Ru(4)O(12) thick films on alumina substrates, as demonstrated in our previous study.