Combustion-synthesized ultrafine SrTiO3 nanocrystals with low-temperature sintering and multifunctional properties for LTCC applications

Nanocrystalline SrTiO3 was synthesized using a single-step modified combustion process, producing phase-pure perovskite powder suitable for low-temperature ceramic processing. Remarkably, the material achieved a high relative density of 99.2% at a sintering temperature of only 890 °C, without the use of any sintering additives. Structural analysis by X-ray diffraction confirmed a cubic perovskite phase with an average crystallite size of 16 nm, which was consistent with the TEM observations showing uniformly distributed nanoparticles with clear lattice fringes, indicating high crystallinity. XPS analysis verified the expected oxidation states of Ti4+ and Sr2+ and revealed oxygen-vacancy-related components in the O 1s spectrum, correlating well with the material's optical behavior. The optical band gap was determined to be 3.07 eV, and the strong blue photoluminescence emission originated from vacancy-induced defect states within the TiO6 octahedra. Thermal stability assessed through DTA–TGA showed no significant weight loss up to 900 °C, confirming robust thermochemical behavior. The sintered ceramics exhibited a dielectric constant of εᵣ ≈ 50, a loss factor of tan δ ≈ 0.3 at 5 MHz, and a low temperature coefficient of permittivity (TCK ≈ 0.505 ppm °/C). The combination of nanoscale features, excellent densification at reduced temperature, oxygen-vacancy-driven luminescence, and favorable dielectric properties highlights nanocrystalline SrTiO3 as a strong candidate for advanced LTCC (Low-Temperature Co-fired Ceramic) devices.