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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]

Devices based on AlN generally require adherent and strong interfaces between AlN and other materials, whereas most metals are known to be nonwetting to AlN and form relatively weak interfaces with AlN. In this study, we selected four representative metals (Al, Cu, Ti, and Zr) to study the adhesion strength of the AlN/metal interfaces. Mathematical models were constructed between the adhesion strength and enthalpy of formation of Al–metal solid solutions, the surface energies of the metals, and the lattice mismatch between the metals and AlN, based on thermodynamic parameters calculated using density functional theory. It appears that the adhesion strength is mainly determined by the lattice mismatch, and is in no linear correlation with either the Al–metal solution's formation enthalpies or the metals’ surface energies. We also investigated the nucleation thermodynamics of the four metals on AlN substrates. It was found that Ti forms the strongest interface with AlN, and has the largest driving force for nucleation on AlN substrates among the four metals. [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]