Magnetic properties of 1D spin systems with compositional disorder of three-spin structural units

The exact diagonalization (ED) approach and Quantum Monte-Carlo (QMC) method were used for the study of the lowest energy states and low-temperature magnetic properties of some disordered 1D Heisenberg spin-1/2 systems formed by two types of three-spin structural units. For the system with a singlet ground state and the random distribution of structural units along the chain system, a significant decrease of the size of the intermediate magnetization plateau in comparison to the corresponding uniform spin system was found. For the “polyallyl” spin chain with a macroscopic value of the ground state spin, a transition to the singlet ground state due to the effect of compositional disorder was observed.

Nanoscale Engineering of Inorganic Composite Scintillation Materials

This review article considers the latest developments in the field of inorganic scintillation materials. Modern trends in the improvement of inorganic scintillation materials are based on engineering their features at the nanoscale level. The essential challenges to the fundamental steps of the technology of inorganic glass, glass ceramics, and ceramic scintillation materials are discussed. The advantage of co-precipitation over the solid-state synthesis of the raw material compositions, particularly those which include high vapor components is described. Methods to improve the scintillation parameters of the glass to the level of single crystals are considered. The move to crystalline systems with the compositional disorder to improve their scintillation properties is justified both theoretically and practically. A benefit of the implementation of the discussed matters into the technology of well-known glass and crystalline scintillation materials is demonstrated.

Probing Compositional Order in Atomic Columns: STEM Simulations Beyond the Virtual Crystal Approximation

Taking advantage of recent advances in parallel computing, we studied compositional disorder along metal–oxygen atomic columns in a complex Mo,V-oxide bronze using multislice frozen-phonon calculations. Commonly, the virtual crystal approximation (VCA) is used to model compositional disorder at crystallographic sites in a unit cell for a number of different theoretical and experimental techniques. In the VCA, a weighted linear sum of atomic properties is used to approximate the model structure. When using the VCA, the extracted V content of Mo,V–O columns from experimental high-angle annular dark-field (HAADF) images will be about half the V content estimated from simulations, considering the distinct cation ordering. This discrepancy is larger than the spread of HAADF signals of different configurational orders at a given V concentration, which can be up to 20%. Certain “isophilic” atomic arrangements along the column can be distinguished from more random ones using HAADF-STEM imaging. The trends and ratios of the simulated intensity spreads due to different compositional ordering along 11 M–O columns along the c-axis of the Mo,V oxide bronze qualitatively match those observed in experimental HAADF-STEM data. Instrumental and sample-based noise adds to the variability but does not significantly distort the relative ratios of column intensity variation. We observed that we only required seven random configurations to represent the intensity variations along columns.

Microhardness, phase transition, acoustic wave velocities and melting temperature of AlxGa1−xSb

The band structure of Al[Formula: see text]Ga[Formula: see text]Sb semiconducting ternary alloys and their related properties such as elastic constants, microhardness, transition pressure to the first phase, acoustic wave velocities and melting temperature have been investigated. The calculations are performed using a pseudopotential approach within the virtual crystal approximation which includes the effect of compositional disorder as an effective potential. Generally, our results are found to be in good accord with the experimental results. The composition dependence of all features of interest showed a monotonic behavior and suggests that the stiffness, hardness and structural stability becomes better in Al[Formula: see text]Ga[Formula: see text]Sb for higher Al concentrations. The bulk sound speeds and melting temperature are found to become larger when increasing the Al content.