Vacancy engineering for high tetragonal BaTiO3 synthesized by solid-state approaches

Conventionally, tetragonality in BaTiO 3 powder is attributed to grain size, disregarding the role of Ba/Ti ratio. However, our study reveals a significant impact of Ba/Ti ratio on tetragonality in BaTiO 3 . With an increase in Ba/Ti ratio from 0.990 to 1.010, particle size remains around 200 nm. Tetragonality initially rises from 1.006 to a maximum of 1.0092 at Ba/Ti = 1.000, then decreases to 1.005. Lower tetragonality is associated with Ba or Ti vacancies, using density functional theory (DFT), we analyzed the electron density and lattice distinction in BaTiO 3 powders. Both Ba and Ti vacancies affect lattice distortion, the Ti vacancies leading to more significant lattice expansion and lower tetragonality than Ba vacancies. Using this powder, we fabricated high-density BaTiO 3 ceramics and multi-layer ceramics capacitors (MLCCs) with X7R temperature stability (−55 to 125 °C, ±15% coefficient) and excellent reliability. This strategy has broad implications for tetragonal BaTiO 3 nanopowders and MLCCs development.