BaTiO₃ nanocube and assembly to ferroelectric supracrystals

New strategies for materials fabrication are of fundamental importance in the advancement of science and technology. Nanocrystals, especially with an anisotropic shape such as cubic, are candidates for building blocks for new bottom-up approaches to materials assembly, yielding a functional architecture. Such materials also receive attention because of their intrinsic size-dependent properties and resulting applications. Here, we report synthesis and characteristics of BaTiO₃ and SrTiO₃ nanocubes and the ordered assemblies as ferroelectric supracrystals. BaTiO₃ and SrTiO₃ nanocubes with narrow size distributions were obtained in an aqueous process. BaTiO₃ films made up of ordered nanocube assemblies were fabricated on various substrates by evaporation-induced self-assembly method. Regardless of the substrate, the nanocubes exhibited {100} orientations and a high degree of face-to-face ordering, which remained even after heat treatment at 850 °C. Piezoresponse force microscopy was carried out on the supracrsytal films to obtain plots of the d ₃₃ piezoelectric coefficient against the poling field, and ferroelectric hysteresis curves were shown.