Origin of giant dielectric permittivity and localized polarons supported electrical conduction in CaCu3Ti4O12 for extreme environment energy storage applications

We have synthesized CaCu ₃ Ti ₄ O ₁₂ using a green synthesis route, employing an oxalate precursor obtained from a mixture of Averrhoa carambola (star fruit) fruit juice and aloe vera extract. The structural, microstructural, and ac electrical transport characteristics of this material were examined at high temperatures from 308 K to 773 K and in a wide frequency window of 100 Hz to 1 MHz. The Rietveld refinement of X-ray diffraction (XRD) and Raman spectroscopy demonstrates the single-phase body-centered cubic crystal structure with space group Im-3 and A _g and F _g vibrational modes due to rotations of TiO ₆ octahedral and Ti-O-Ti anti-stretching vibrations of CaCu ₃ Ti ₄ O ₁₂ . The fitted Nyquist plots (\(\:{Z}^{{\prime\:}}\text{v}\text{s}.\:Z{\prime\:}{\prime\:})\) at different temperatures exhibit the grain and grain boundary contributions, and the semicircles shrink at higher temperatures, which disclosed the negative temperature coefficient of resistance (NTCR) behavior. Both grain ( R _g ) and grain boundary resistance ( R _gb ) and capacitances (C _g , C _gb ) diminished with temperature, and their activation energy was estimated to be ~ 0.56 eV and ~ 0.84 eV, respectively. The ac electrical conductivity increases with frequency and temperature due to thermally activated charge carriers, and the frequency exponent ( n ) remains nearly constant at low temperature region (quantum mechanical tunneling model) and decreases after 573 K (correlated barrier hopping model). Their dc activation energy was determined to be 0.51 eV and 0.62 eV, respectively. High dielectric permittivity (\(\:{\epsilon\:}_{r}^{{\prime\:}}\)) ~ 9458 and low dielectric loss (\(\:\delta\:\)) ~ 0.308 were observed at 308 K and frequency 100 Hz, and both values increase with the evolution of temperatures and quantify a higher ability to store the electrical charges in an electric field. The dielectric relaxations at various temperatures are associated with the Maxwell-Wagner (MW) type polarization, and the distribution of relaxation behavior or Cole-Cole parameter (α) divulged a non-ideal Debye type broader and symmetric distribution with temperatures. The modulus spectra help us to comprehend the origin of the giant dielectric constant and strong interfacial polarization by highlighting the grain and grain boundary contributions. The high dielectric constant, low loss, and high temperature stability recommend its promising applications in several electronic, energy, and sensing applications.