Investigation of the dielectric properties of materials obtained by substituting the Ca2+ ion in the compound CaCu3Ti4O12 with Na+ and Bi3+ ions

Abstract

This paper presents the results of an experimental investigation into the dielectric properties of NaCu₂.₅Ti₄.₅O₁₂, NaBi₁/₃Cu₃Ti₄O₁₂, and Bi₂/₃Cu₃Ti₄O₁₂ from the family CaCu₃Ti₄O₁₂ (CCTO). The study involved substituting the Ca²⁺ ion in CaCu₃Ti₄O₁₂ with Na⁺, Bi³⁺, and a combination of Na⁺ and Bi³⁺ ions. The impact of the valence state and ionic radius of the substituting ions on the dielectric properties of these materials was examined. X-ray phase analysis confirmed the stoichiometric correctness of the considered compounds. Temperature and frequency dependencies of the dielectric characteristics of the studied materials were presented. The importance of resonance phenomena, including observations of negative dielectric constant, was highlighted. At a measurement frequency of 1 MHz, graphical illustrations of the voltage dependence of dielectric constant for all samples were provided. Notably, the significant changes in dielectric constant values for Bi-containing materials within the voltage range of 100 mV to 1 V suggest their potential use as sensitive varicaps. Electron microscopic images of the structure of ceramic samples are presented which is important for understanding the studied dielectric properties.