Lattice variations in CaTiO3 cubes and cuboids and their use in photocatalytic benzimidazole formation

Abstract

CaTiO3 perovskite cubes with tunable sizes of 90 to 886 nm, as well as 156 and 725 nm cuboids, have been hydrothermally synthesized. Remarkably, despite their similar appearance, only cubes show a preferred orientation effect in X-ray diffraction (XRD) patterns. Peak positions also shift slightly with particle size and shape. Synchrotron XRD analysis reveals the presence of bulk and surface layer lattices with clearly shifted peaks. Unexpectedly, while a CaTiO3 cube presents (002) lattice fringes in transmission electron microscopy (TEM) images, a cuboid shows (001) lattice fringes. They also have discernably different lattice point patterns. These lattice features give rise to dissimilar dielectric constants and optical facet dependence. The cuboid crystals show stronger piezoelectric and ferroelectric responses than cubic particles do. Their surface properties differ completely with cuboidal particles being moderately active toward rhodamine B photodegradation, while cubes are inactive from floating above the dye solution with stirring. The CaTiO3 cuboids are more effective than cubes in photocatalyzing the formation of benzimidazole. This work demonstrates that interior lattice variations can significantly tune various materials properties, so detailed structural analysis is necessary to explain shape-related behaviors.