Investigation of surface defects in BaTiO3 nanopowders studied by XPS and positron annihilation lifetime spectroscopy

[Display omitted] •New complementary method for studies of the surface defects in nanoparticles.•Experimental confirmation of the interrelations between defect structure and magnetism in BaTiO3 nanoparticles.•Charge compensation process and grain growth mechanism are essential for the nanoparticle magnetism. Defect structures of BaTiO3 nanoparticles annealed in the air and their correlation with magnetic properties have been studied. As main research techniques, complementary methods such as XPS and positron annihilation lifetime spectroscopy were used. It was found that low-temperature annealing creates additional oxygen vacancies in nanoparticles both inside and on the nanoparticle surface, and high-temperature annealing favors the reduction of Ti. These changes influence nanoparticle magnetism and occur due to the charge compensation process and grain growth mechanism. Performed studies show that complementary XPS and positron annihilation spectroscopy are the effective tools to determine nanoparticle surface defect structure, which can be used to fabricate new rare room-temperature multiferroics materials.