New negative temperature coefficient ceramics in ACu3Ti4O12 (A = Sr, La2/3, Ca, Y2/3) system

In this work, new ACu3Ti4O12 (A = Sr, La2/3, Ca, Y2/3) negative temperature coefficient (NTC) ceramics have been successfully fabricated by traditional solid-state reaction method. XRD analysis shows that the ACu3Ti4O12 ceramics are of the CaCu3Ti4O12 phase with body-centered cubic structure, suggesting that the change of A-site ion does not change the crystal structure. The scanning electron microscope image shows that the difference of A-site ion in ACu3Ti4O12 results in the different micromorphology. The X-ray photoelectron spectroscopy analysis further confirms the coexistence of Cu+/Cu2+ and/or Ti3+/Ti4+ in the compounds, which are one of the important factors for the electrical conductivity in ACu3Ti4O12 ceramics. Electrical performance analysis proves that the effect of grain size on resistivity is greater than that of the A-site ion species. The resistivity decreases with increasing temperature from 25 to 500 °C, indicative of NTC characteristics.