Colossal dielectric properties of Na1/3Ca1/3Sm1/3Cu3Ti4O12 ceramics: Computational and experimental investigations

Abstract

A modified sol−gel technique was used to synthesize a high dielectric ceramic, Na1/3Ca1/3Sm1/3Cu3Ti4O12. The crystal structure of this sintered ceramic matches the standard pattern of a body−centered cubic (bcc) system within the Im3 space group (JCPDS No. 75–2188). No impurity phases were observed. Interestingly, a high dielectric permittivity of ∼1.14–1.35 × 104 and a low loss tangent of ∼0.027–0.039 were achieved in this sintered Na1/3Ca1/3Sm1/3Cu3Ti4O12 ceramic. Our DFT calculations disclosed that substitution of Na+ ions at Cu2+ sites causes an observed excess Cu concentration. As a result, metastable insulating phases were formed at a relatively high sintering temperature. Additionally, our electron density calculations revealed that Na ions lose their electrons to Sm ions, whereas the oxidation states of Cu and Ti are unaltered. Our results show that Cu+ and Ti3+ were observed after introducing an oxygen vacancy into this lattice. Significantly different values of Rg, Rgb, and Eg, Egb support an internal barrier layer capacitor as the most likely origin of the giant dielectric properties of this ceramic. XPS results show mixed Cu+/Cu2+ and Ti3+/Ti4+ in all ceramics, suggesting that electron hopping between Cu+↔Cu2+ and Ti3+↔Ti4+ is the probable origin of the n−type semiconducting state inside the grains.