Charge Separation in BaTiO3 Nanocrystals: Spontaneous Polarization Versus Point Defect Chemistry

The fate of photogenerated charges within ferroelectric metal oxides is key for photocatalytic applications. The authors study the contributions of i) tetragonal distortion, responsible for spontaneous polarization, and ii) point defects, on charge separation and recombination within BaTiO3 (BTO) nanocrystals of cubic and tetragonal structure. Electron paramagnetic resonance (EPR) in combination with O-2 photoadsorption experiments show that BTO nanocrystals annealed at 600 degrees C have a charge separation yield enhanced by a factor > 10 compared to TiO2 anatase nanocrystals of similar geometries. This demonstrates for the first time the beneficial effect of the BTO perovskite nanocrystal lattice on charge separation. Strikingly, charge separation is considerably hindered within BTO nanoparticles annealed >= 600 degrees C, due to the formation of Ba-O divacancies that act as charge recombination centers. The opposing interplay between tetragonal distortion and annealing-induced defect formation inside the lattice highlights the importance of defect engineering within perovskite nanoparticles.

Automated summary

The fate of photogenerated charges within ferroelectric metal oxides is studied, focusing on the contributions of tetragonal distortion and point defects on charge separation and recombination in BaTiO3 (BTO) nanocrystals. The results show that BTO nanocrystals have significantly enhanced charge separation compared to TiO2 anatase nanocrystals, highlighting the beneficial effect of the BTO perovskite nanocrystal lattice. However, charge separation is hindered within BTO nanoparticles with higher annealing temperatures due to the formation of Ba-O divacancies.