Enhanced breakdown field of xSrCu3Ti4O12/(1- x)CaCu₃Ti₄O₁₂ composite ceramics

xSrCu₃Ti₄O₁₂/(1-x)CaCu₃Ti₄O₁₂ (x=0.2, 0.4, 0.6, 0.8)composite ceramics were prepared by traditional solid-state method with sintering for 5 h at 1000oC. Breakdown fields of all the samples were greatly enhanced compared to CCTO ceramics, especially for samples of 0.4SrCu₃Ti₄O₁₂/ 0.6CaCu₃Ti₄O₁₂ and 0.6SrCu₃Ti₄O₁₂/0.4CaCu₃Ti₄O₁₂. SEM images displayed that round shape grains with size of 1μm were extensively existed in samples. Statistic of grain size distribution from SEM images proved that longer sintering time lead to larger average grain size. I-V measurement indicated that breakdown voltages of samples in both sintering conditions were highest when x=0.4 and lowest when x=0.8, in which highest value of breakdown voltages is 25 kV·cm^-1 for 0.4SrCu₃Ti₄O₁₂/0.6CaCu₃Ti₄O₁₂. In addition, it was found from C-V measurements that reduced donor density was responsible for the elevated barrier height while interface density remained almost constant.