Li2CaP2O7 pyrophosphate ceramics with dual functionality: high-performance NTC thermistor behavior and giant dielectric permittivity

Abstract

Inorganic pyrophosphate-based materials are widely recognized for their diverse functional properties, positioning them as strong contenders for a range of advanced technological applications. In this work, the compound Li₂CaP₂O₇ was synthesized and examined using a cost-efficient solid-state reaction route. Comprehensive structural and microstructural investigations were carried out to confirm phase purity and assess morphological features. Electrical studies performed between 373 and 673 K revealed semiconducting behavior governed by thermally activated hopping, characterized by a thermistor constant β = 5554 K, an activation energy E_a = 0.49 eV (±0.01), and high temperature sensitivity (−4.0 to −1%/K⁻¹), together with an excellent stability factor (SF = 3.02), underscoring its suitability for high-temperature sensing applications. Analysis of the Nyquist plots using an appropriate equivalent-circuit model allowed the separation of grain and grain-boundary effects. Notably, Li₂CaP₂O₇ exhibited an extremely large dielectric permittivity, on the order of 10⁷ at low frequencies, along with low dielectric losses at higher frequencies. These features point to strong interfacial polarization consistent with the Maxwell–Wagner framework, and the material displays thermally activated, non-Debye-type relaxation dynamics. The interplay between charge transport and polarization mechanisms gives rise to the remarkable coexistence of NTC behavior and giant dielectric response. Altogether, these attributes establish Li₂CaP₂O₇ as a highly promising multifunctional material for integrated high-temperature sensing–capacitor devices and other advanced electronic systems.