A low-temperature specific heat study of giant dielectric constant materials

A low-temperature specific heat study has been performed on the insulating giant dielectric constant material CaCu₃Ti₄O₁₂ and two related compounds, Bi_2/3Cu₃Ti₄O ₁₂ and La_0.5Na_0.5Cu₃Ti ₄O₁₂, from 0.6 to 10 K. From analyzing the specific heat data in a very low-temperature range, 0.6-1.5 K, and moderately low-temperature range, 1.5-5 K, in addition to the expected Debye terms, we observed significant contributions originating from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice vibrations occurring at the grain boundaries and induced by local defects. Together with the findings on electronic and mechanical properties, a phenomenological model is proposed to explain the high dielectric constant behavior in both low and high frequency regions.