Enhanced structural, NTCR behavior and dielectric polarization in LiGaP2O7 pyrophosphate: implications for advanced technological applications

Abstract

Materials exhibiting negative temperature coefficient of resistance (NTCR) behavior and efficient ionic transport properties are of considerable interest for advanced dielectric and energy-storage applications. In this work, single-phase LiGaP₂O₇ pyrophosphate was successfully synthesized using a conventional solid-state reaction route. X-ray diffraction analysis confirmed the formation of a monoclinic structure with the space group P2₁, while scanning electron microscopy revealed a polycrystalline morphology with an average grain size of about 2.49 µm. The electrical and dielectric properties were investigated by impedance spectroscopy over a wide frequency range (0.1 Hz–1 MHz) and temperature interval (513–673 K). Nyquist plots demonstrated that the electrical response is mainly governed by grain boundary effects and were successfully fitted using an equivalent circuit based on parallel R//C//Q elements. The compound exhibited a pronounced NTCR behavior associated with a thermally activated hopping process. Dielectric investigations revealed a non-Debye relaxation behavior accompanied by strong frequency dispersion due to Maxwell–Wagner interfacial polarization. A high dielectric permittivity of approximately 6.32 × 10⁴ was obtained at low frequencies. Electric modulus and conductivity analyses indicated that long-range Li⁺ ion migration dominates the transport mechanism. The AC conduction mechanism follows the correlated barrier hopping (CBH) model in the temperature range of 513–593 K with an activation energy of about 0.72 eV, while at higher temperatures (613–673 K), the non-overlapping small polaron tunneling (NSPT) model becomes predominant with an activation energy close to 1.19 eV. These findings provide deeper insight into the dielectric relaxation and charge transport mechanisms of pyrophosphate materials and highlight LiGaP₂O₇ as a promising candidate for low-frequency dielectric devices, energy-storage systems, and NTC thermistor applications.