Search

Low-index surfaces and morphologies of cobalt spinel (Co 3 O 4 ) are studied using density functional theory calculations. For each of the surfaces (100), (110), and (111), a set of terminations with different surface compositions and atomic structures are assessed to study their thermodynamic stability under different environmental conditions. Surface energies are calculated as functions of oxygen's chemical potential, which in turn is a function of temperature and partial pressure. We select seven typical shapes of cobalt oxide nanoparticles and compute their free energies of formation using the surface energies of all the surrounding facets. The results show that the shapes of octahedron and cuboctahedron have the lowest Gibbs free energies among the seven shapes for all the environmental conditions being explored. [ABSTRACT FROM AUTHOR]

• Multiple terminations of surfaces (10 1 ¯ 0) , (10 1 ¯ 1) , (11 2 ¯ 0) , and (0001) of Y(OH) 3 are established. • Effects of temperature and partial pressure of water and oxygen are included through first-principles thermodynamics. • The equilibrium morphology is of elongated hexagonal bipyramid enclosed by stoichiometric surfaces. Yttrium hydroxide Y(OH) 3 is an important precursor for yttrium oxides, and its morphologies are inherited by the yttrium oxides, thus affecting the products' properties and performance. Hydrothermally synthesized Y(OH) 3 particles are typically elongated hexagonal bipyramid, but thermodynamic parameters are inadequate for quantitative modeling of the morphology. We calculate surface energies and surface stresses of low-index orientations using density functional theory, and present a thermodynamic morphology model based on these parameters. We find that the thermodynamically stable surface terminations are always stoichiometric, and the surface energies are in the order of γ (10 1 ¯ 0) < γ (10 1 ¯ 1) < γ (11 2 ¯ 0) < γ (0001). The equilibrium morphology is of hexagonal prism capped by hexagonal pyramid enclosed by (10 1 ¯ 1) and (10 1 ¯ 0) surfaces. Because these terminations are stoichiometric, varying temperature or pressure is ineffective for modifying Y(OH) 3 particles' morphology, whereas surfactants should be used for this purpose in hydrothermal synthesis. Image, graphical abstract [ABSTRACT FROM AUTHOR]