Unusually Small Thermal Expansion of Ordered Perovskite Oxide CaCu₃Ru₄O with High Conductivity.

We measured the coefficient of thermal expansion (CTE) of conducting composite ceramics 30 vol.% CuO-mixed CaCu₃Ru₄O together with CaCu₃Ru₄O 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 CaCu₃Ru₄O (7⁻9 × 10/K) was as small as those of insulators such as CuO (9 × 10/K), alumina (8 × 10/K), and other insulating perovskite oxides. We propose that the thermal expansion of CaCu₃Ru₄O was suppressed by the Cu-O bond at the A-site due to the Jahn⁻Teller effect. This unusually small CTE of CaCu₃Ru₄O compared to other conducting oxides plays a vital role enabling successful coating of 30 vol.% CuO-mixed CaCu₃Ru₄O thick films on alumina substrates, as demonstrated in our previous study.