Triggering Incipient Ferroelectricity in Calcium Copper Titanate (CaCu$_{3}$Ti$_{4}$O$_{12})$ ceramics through partial B-site substitution with Te$^{4+}$ ion.

Double perovskite structured dielectric ceramic CaCu$_{3}$Ti$_{4-}_{x}$Te$_{x}$O$_{12}$ (CCTTO) ($x \quad =$ 0, 0.05, 0.1, 0.15, 0.2) was fabricated from the powder obtained by conventional solid state synthetic route. The room temperature XRD patterns for the $x =$0, 0.05, 0.075 modified samples were confirmed to possess a single phase with cubic space group \textit{Im3 }by Rietveld refinement. But, the Rietveld refinement performed on XRD patterns recorded for the compositions corresponding to $x =$ 0.1, 0.15, 0.2 shows the coexistence of the cubic phase (space group \textit{Im3}; a $=$ 7.4065{\AA}) and tetragonal phase (space group \textit{I4/mcm}; a $=$ 7.369 {\AA} and c $=$ 6.967 {\AA}). The dielectric properties of these ceramics were studied over a wide frequency (40Hz--2MHz) and temperature range (30-400K). The Te$^{4+}$ doped samples (CCTTO) exhibited dielectric permittivity (?$_{r})$ value of \textasciitilde 23-33X10$^{3}$ which is more than twice that of undoped CCTO (\textasciitilde 11x10$^{3})$ at 1kHz. A decreasing trend in dielectric permittivity with increasing temperature, a signature of incipient ferroelectricity, was observed for all the samples. Barrett's formula was invoked to rationalize the dielectric permittivity variation as a function of temperature. The incipient ferroelectric behavior is correlated with soft phonon mode observed in temperature dependent Raman Spectroscopic studies. .