Additive-free low-temperature densification and dielectric behavior of combustion-derived nanocrystalline CaTiO₃ for LTCC applications

Abstract

Nanocrystalline calcium titanate (CaTiO₃) was synthesized via a modified single-step combustion route using citric acid as fuel, enabling additive-free processing. The combustion-derived powders exhibited high reactivity and nanoscale crystallinity (~18 nm), facilitating efficient densification at reduced temperature. Phase-pure orthorhombic CaTiO₃ was confirmed by X-ray diffraction and Rietveld refinement, while thermal analysis indicated complete phase formation below 600 °C. Near-theoretical density (~99.5%) was achieved at an optimized sintering temperature of 894 °C without sintering aids. Microstructural analysis revealed dense and uniform grain morphology, while optical studies indicated a direct band gap of ~3.4 eV with defect-related states confirmed by photoluminescence and Urbach energy analysis. The dielectric properties exhibited stable permittivity with low dielectric loss over a wide frequency and temperature range, governed by Maxwell–Wagner interfacial polarization and Koop’s model. The combination of additive-free densification, reduced sintering temperature, and favorable dielectric response highlights the potential of combustion-derived CaTiO₃ as a promising material for low-temperature co-fired ceramic (LTCC) substrates and high-frequency dielectric applications.