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Systematic first-principles calculations were performed to study the lattice dynamics of Yb14MnSb11 and hence to obtain a wide range of its thermodynamic properties at high temperatures. The calculated results were analyzed in terms of the lattice contribution and the electronic contribution, together with a comparison with a collection of experimental thermochemical data. At 0 K, the electronic density of states showed the typical feature of a p-type semiconductor—a small amount of unoccupied electronic states exclusively made of the major spin by a range of ∼0.6 eV above the Fermi energy. It showed that the Mn atom had a ferromagnetic spin moment of ∼4 μB. As a semiconductor, it was found that the electronic contribution to the heat capacity was substantial, with an electronic heat capacity coefficient of ∼0.0006 J/mole-atom/K2.

The steady state growth equation for a paraboloid of revolution and a parabolic cylinder, taking the interfacial energy into account, is revisited. Although the consideration of the interfacial energy was necessary, the growth equation was much more complicated than the original equation with a zero interfacial energy, since both the thermodynamics and kinetics of the growth are considered in one equation. In the present work, we take advantage of the development in computational thermodynamics and consider the thermodynamics and kinetics of the process in separate equations, but solve them simultaneously. A consistent framework to describe the phenomena and compare it with previous treatment of the interfacial energy will be presented.

This paper is concerned with the prediction of oxygen diffusivities in fcc nickel from first-principles calculations and large-scale atomic simulations. Considering only the interstitial octahedral to tetrahedral to octahedral minimum energy pathway for oxygen diffusion in fcc lattice, greatly underestimates the migration barrier and overestimates the diffusivities by several orders of magnitude. The results indicate that vacancies in the Ni-lattice significantly impact the migration barrier of oxygen in nickel. Incorporation of the effect of vacancies results in predicted diffusivities consistent with available experimental data. First-principles calculations show that at high temperatures the vacancy concentration is comparable to the oxygen solubility, and there is a strong binding energy and a redistribution of charge density between the oxygen atom and vacancy. Consequently, there is a strong attraction between the oxygen and vacancy in the Ni lattice, which impacts diffusion.

The variation of elastic properties, e.g., elastic constants, bulk modulus, and shear modulus of dilute Ni-base superalloys due to alloying elements (X's) and temperature, has been studied via first-principles calculations. Here, 26 alloying elements are considered: Al, Co, Cr, Cu, Fe, Hf, Ir, Mn, Mo, Nb, Os, Pd, Pt, Re, Rh, Ru, Sc, Si, Ta, Tc, Ti, V, W, Y, Zn, and Zr. It is found that (i) both the bulk and shear moduli of Ni-X decrease approximately linearly with increasing equilibrium volume, especially within each group of 3d, 4d, or 5d transition-metal alloying elements; (ii) all alloying elements considered herein increase the ratio of bulk to shear modulus (i.e., the ductility) and the elastic anisotropy of the Ni-X alloys; and (iii) the largest decrease of elastic properties of Ni is caused by alloying element Y. It is observed that the change of elastic properties of Ni due to various alloying elements is traceable from the distribution of (magnetization) charge density, for instance the spherical...

Exploration of longstanding issues in magnetic materials, for example the nature of Curie/Neel temperature and the Schottky anomaly of heat capacity, appeals to reliable models at finite temperatures. Based on first-principles calculations and partition function approach with the microstates being the collinear magnetic configurations, the magnetic thermodynamics of fcc Ni, including the heat capacity and the pressure-dependent Curie temperature, is predicted well and compared with the results from experiments and mean-field approach. As demonstrated in fcc Ni, it is found that the magnetic thermodynamics containing anomalies stems from the magnetic configurational entropy caused by the competition of various magnetic states.

The anisotropy of antiphase boundary (APB) energies in ordered L12–Ni3Al is studied, owing to its importance in understanding the anomalous flow behavior of this intermetallic compound. We report first-principle calculations for two types of APBs in the ordered compound: (001) and (111). The magnetic perturbations associated with these APBs are calculated as a function of supercell size to ensure that their periodic images are isolated both magnetically and elastically. The magnetic perturbation associated with the (111) APB is wider than that of the (001) APB. The fully relaxed, spin-polarized APB energies for (001) and (111) APBs are calculated to be 82 mJ/m2 and 177 mJ/m2, respectively. The resulting anisotropy ratio of σ(111)/σ(001)=2.16, which is significantly higher than previously reported values, suggests that cross-slip between (001) and (111) is highly favorable.

We applied phase-field approach to investigate both ferroelectric and antiferrodistortive transitions in (001) SrTiO3 epitaxial thin films that are strained biaxially. A domain/phase stability diagram of “misfit strain-temperature” was constructed for equibiaxially strained (001) SrTiO3 thin films, which exhibits significant differences from previous diagrams obtained using thermodynamic analysis of a single domain. For unequibiaxially strained (001) SrTiO3 thin films, “misfit strain-misfit strain” domain stability diagrams at several representative temperatures were obtained. The predicted phase transitions, domain stabilities, and domain structures in three different SrTiO3 thin films under either equibiaxial or unequibiaxial strains agree well with experimental observations.

The magnetic and electronic properties of postperovskite CaRuO3 are investigated by performing the first-principles calculation based on generalized gradient approximation plus parameter U method. A Mott–Hubbard insulating ground state with low spin Ru4+ is found, and the A-type antiferromagnetic (AFM) spin ordering is preferred. Ru4+ ions exhibit the spatially anisotropic exchange with the exchange in a-b plane weaker than that along c direction. The large Jahn–Teller distortion lowers the energy of dz2 orbital, leading to the stabilization of low spin Ru4+ and ferromagnetic (FM) orbital ordering. The transitions of metal-insulator and FM-AFM-FM depend on the Hubbard parameter U.

The properties of many electronic materials are governed by defect type, distribution, and concentration. In this paper, we demonstrate the influence of equilibrated nonstoichiometry on the ferroelectric properties of the perovskite BaTiO3. It is shown from measurements of the transition temperature, thermal hysteresis, latent heat, and transformation strain that the concentration of partial and/or full Schottky defects significantly alters the nature of the weak first-order transition between paraelectric and ferroelectric phases. The coefficients of a conventional 2-4-6 Ginzburg–Landau polynomial, determined from the measured transition parameters, were also found to vary as functions of the defect type and concentration. These results illustrate for the first time the strong sensitivity of the Landau coeffecients characterizing the properties of the monodomain ferroelectric state to nonstoichiometry involving partial Schottky disorder reactions in the perovskite-structured oxides. The strong dependence...

A single-domain thermodynamic theory is employed to predict the spontaneous polarizations of (001)c, (101)c, and (111)c oriented epitaxial BiFeO3 thin films grown on dissimilar substrates. The effects of various substrate-induced strains on the spontaneous polarization were studied. The dependences of the spontaneous polarization on film orientations and the types of substrate-induced strains were analyzed.

Various thermodynamic properties of MgO were studied using both ab initio phonon theory and the mean-field potential (MFP) approach. They include thermal pressure, thermal expansion, the 300K equation of state, and the shock Hugoniot. It is found that the results of ab initio phonon theory and the MFP approach agree with each other, except that ab initio phonon theory gave a poor description of the thermal pressure when temperature became relatively high.

A phase-field model for investigating the surface morphological evolution of a film is developed, taking into account the surface energies of film and substrate, the interfacial energy between the film and substrate, and the elastic energy associated with the lattice mismatch between the film and substrate. Using the lattice mismatch and the surface energies for the Ge∕Si heteroepitaxial system, the morphology of islands and the formation of a wetting layer are investigated using two-dimensional simulations. The results show that the wetting angle increases continuously with the increase in the lattice mismatch, and the surface angle of the island on wetting layer varies with the island size. It is demonstrated that the anisotropy of elastic interactions alone is not sufficient to cause surface angle discontinuity or faceting that is observed in experiments.