For the leaching experiments, 10 g of the classified BaTiO3 powder (grain size fraction 5–10 m; labeled in the following as BaTiO3 seeds) were suspended in 40 ml of the leaching medium in a teflon container. The leaching was performed in these containers either under conventional hydrothermal conditions (laboratory autoclave Berghoff HR 200) or under the influence of microwave radiation (microwave accelerated reaction system MARS 5 (CEM Corporation)) with stirring of the suspension by a magnetic stirrer.