Colossal permittivity and low losses in Ba1-xSrxTiO3-δ reduced nanoceramics

The oxalate route offers a controlled approach to synthesize pure Ba1-xSrxTiO3 (BST) (0 ≤ x ≤ 1) nanoparticles (ϕ ≈ 150 nm in diameter). Reduced BST dense nanoceramics were obtained by spark plasma sintering (SPS) and then annealed for a short time to reach colossal permittivity (ϵ′r = 105) with low dielectric losses (tan δ = 0.03) at 1 kHz and 300 K. The effects of Ba-Sr substitution on structural, microstructural and electrical properties were analyzed. Comprehensive analysis of the electrical properties indicates that polaron hopping, mediated by Ti3+ ions and oxygen vacancies is the main contributing mechanism to colossal permittivity in Ba-rich BST compounds. Substitution of Ba by Sr reduced the contribution of polaron hopping and led to a decrease of real and imaginary parts of permittivity, while preserving interfacial polarization and yielding better temperature stability. The lowest temperature coefficient of capacitance, or TCC (variation of capacitance between 310 K and 450 K) value, i.e., 44 ppm K−1, is obtained for SrTiO3.