Incipient ferroelectric to a possible ferroelectric transition in Te⁴⁺ doped calcium copper titanate (CaCu₃Ti₄O₁₂) ceramics at low temperature as evidenced by Raman and dielectric spectroscopy

Abstract

Partial replacement of Ti⁴⁺ by Te⁴⁺ ions in calcium copper titanate lattice improved its dielectric behaviour mostly due to cubic-to-tetragonal structural transformation and associated distortion in TiO₆ octahedra. The relative permittivity values (23–30 x 10³) of Te⁴⁺ doped ceramics is more than thrice that of un-doped ceramics (8 x 10³) at 1 kHz. A decreasing trend in relative permittivity with increasing temperature (50–300 K) is observed for all the samples. Barrett’s formula, as a signature of incipient ferroelectricity, is invoked to rationalize the relative permittivity variation as a function of temperature. A systematic investigation supported by temperature dependent Raman studies reveal a possible ferroelectric transition in Te⁴⁺ doped ceramic samples below 120 K. The possible ferroelectric transition is attributed to the interactions between quasi-local vibrations associated with the micro-clusters comprising TiO₆ and TeO₆ structural units and indirect dipole-dipole interactions of off-center B–cations (Ti⁴⁺ and Te⁴⁺) in double perovskite lattice.