Structural disorder has been known to suppress carrier concentration and carrier mobility in common covalent semiconductors, such as silicon, by orders of magnitude. This is expected from a reduced overlap of the electron clouds on neighboring orbitals and the formation of localized tail states near the band edges caused by local distortions and lack of periodicity in the amorphous phase. In striking contrast to the covalent semiconductors, wide-bandgap oxides of post-transition metals with ionic bonding not only allow for crystalline-like electron mobility upon amorphization, but also exhibit two orders of magnitude higher carrier concentration in the disordered phase as compared to the crystalline oxide. Here, the results of computationally intensive ab initio molecular dynamics simulations, comprehensive structural analysis, and accurate density-functional calculations reveal complex interplay between local distortions, coordination, and long-range bond morphology and help establish the microscopic origin of carrier generation and transport across the crystalline–amorphous transition in In2O3−x. Departing from traditional oxygen vacancy in crystalline oxides, the derived structural descriptors help categorize “defects” in disordered ionic oxides, quantify the degree of the associated electron localization and binding energy, and determine their role in the resulting electronic and optical properties. The results will be instrumental in the development of next-generation transparent amorphous semiconductors with a combination of properties not achievable in Si-based architectures.

The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe1−xCox)2B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit "hot spots" by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization due to these peculiar electronic mechanisms, which contrast starkly with those assumed in existing models.

Bulk Au-Fe alloys separate into Au-based fcc and Fe-based bcc phases, but L10 and L12 orderings were reported in single-phase Au-Fe nanoparticles. Motivated by these observations, we study the structural and ordering energetics in this alloy by combining density functional theory (DFT) calculations with effective Hamiltonian techniques: a cluster expansion with structural filters, and the configuration-dependent lattice deformation model. The phase separation tendency in Au-Fe persists even if the fcc-bcc decomposition is suppressed. The relative stability of disordered bcc and fcc phases observed in nanoparticles is reproduced, but the fully ordered L10 AuFe, L12 Au3Fe, and L12 AuFe3 structures are unstable in DFT. However, a tendency to form concentration waves at the corresponding [001] ordering vector is revealed in nearly-random alloys in a certain range of concentrations. This incipient ordering requires enrichment by Fe relative to the equiatomic composition, which may occur in the core of a nanoparticle due to the segregation of Au to the surface. Effects of magnetism on the chemical ordering are also discussed.

The frequencies of the phonon branches that correspond to the vibrations of the close packed atomic planes in bcc, fcc, and hcp crystals with short range interatomic interaction are shown to be described by a universal relationship, which only contains two parameters for each branch, for any polarization λ. These phonon branches correspond to the (ξ, ξ, 0) direction in bcc crystals, the (ξ, ξ, ξ) direction in fcc crystals, and the (0, 0, ξ) direction in hcp crystals. This universal relationship can only be violated by long range inter actions, namely, the interactions outside the sixth coordination shell in a bcc crystal, the fifth coordination shell in an fcc crystal, and the eleventh or tenth coordination shell in an hcp crystal. The effect of these long range interactions for each phonon branch can be quantitatively characterized by certain parameters Δ nλ , which are simply expressed in terms of the frequencies of three phonons of the branch. The values of these parameters are presented for all bcc, fcc, and hcp metals whose phonon spectra are measured. In most cases, the proposed relationships for the frequencies are found to be fulfilled accurate to several percent. In the cases where the Δ nλ parameters are not small, they can give substantial information on the type and scale of long range interaction effects in various metals.

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