| Summary: | In this paper, Li<sub>x</sub>Ca<sub>(1−x)</sub>Cu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub> (LCCTO) solid solutions were successfully synthesized. XRD diagrams showed that dopant acceptor Li<sup>+</sup> cations, in a concentration range of x = 0.01–0.10, were successfully merged into CCTO structure. It was found that doping with low concentrations of lithium (x < 0.05) inhibited grain growth during annealing; however, for x > 0.05, the grain growth process resumed. Permittivity and dielectric losses of obtained LCCTO ceramics were analyzed by the means of impedance spectroscopy in a frequency range from 10<sup>−1</sup> to 10<sup>6</sup> Hz. It was revealed that acceptor doping with lithium at an appropriate concentration of x = 0.05 allowed to obtain ceramics with a permittivity level of ε′ = 3 × 10<sup>4</sup> and low dielectric losses tanδ < 0.1 at 1 kHz. Further addition of lithium in a concentration range of x = 0.075–0.10 led to a sharp decline in permittivity and an increase in dielectric losses. It was discovered that lithium addition to CCTO ceramics drastically decreased grain boundary resistivity from 115 MΩ·cm to 5–40 MΩ·cm at x = 0.01–0.10. Using Havriliak–Negami equation, the relaxation times for grain dipoles and grain boundary dipoles were found to be ranging from 0.8 × 10<sup>−6</sup> to 1.7 × 10<sup>−6</sup> s and from 0.4 × 10<sup>−4</sup> to 7.1 × 10<sup>−4</sup> s, respectively. The developed materials can be used in the manufacture of Multilayer Ceramic Capacitors (MLCC) as a dielectric.
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