Paramagnetic electron centers in BaTiO3 nanoparticle powders

Abstract

Knowledge about the emergence and depletion of point defects in BaTiO₃ (BTO) nano-structures during materials processing is key to our understanding of their later activity as components in functional dielectric devices or as photocatalysts. In this electron paramagnetic resonance (EPR) study we investigated BaTiO₃ nanoparticle powders produced by flame spray pyrolysis (FSP) with powders of TiO₂ anatase nanocrystals of comparable size as reference system. Paramagnetic Ti³⁺ ions located at regular lattice sites and with well-defined EPR signatures were measured in vacuum annealed BaTiO₃ nanoparticles, which convert upon further annealing in the temperature range between 873 K and 1173 K from monocrystalline grains with an average size of d = 12 nm, BTO (873 K), to polycrystalline particles with d = 70 nm, BTO (1173 K). Whereas the starting material hosts predominantly polaron-type Ti³⁺ ions being surrounded by compressed O²⁻ ion octahedra, barium–oxygen divacancy complexes, , become susceptible to electron trapping in polycrystalline and tetragonal BTO (1173 K) particles after pre-annealing at temperatures T > 873 K. The insights obtained provide a base for the detection of local distortion effects, for the identification of charge trapping sites and for the elucidation of their impact on spontaneous polarization in BaTiO₃ nanoparticles as photocatalysts or dielectric components.