FEATURES OF SIMULATION OF CHARACTERISTICS OF THERMOMETRIC MATERIAL Lu1-xZrxNiSb

The results of modeling the thermometric characteristics of the semiconductor solid solution Lu1-xZrxNiSb, which is a promising thermometric material for the manufacture of sensitive elements of thermoelectric and electro resistive thermocouples, are presented. Modeling of the electronic structure of Lu1-xZrxNiSb was performed by the Korringa-Kohn-Rostoker (KKR) method in the approximation of coherent potential and local density and by the full-potential method of linearized plane waves (FLAPW). KKR simulations were performed using the AkaiKKR software package in the local density approximation for the exchangecorrelation potential with parameterization Moruzzi, Janak, Williams in the semi-relativistic one taking into account the spin-orbit interaction. The implementation of the method in the Elk software package was used to perform FLAPW calculations. To check the limits of the existence of the thermometric material Lu1-xZrxNiSb, both methods were used to calculate the change in the values of the period of the unit cell a(x) in the range x=0–1.0. It is shown that there is an agreement between the change in the values of a(x) Lu1-xZrxNiSb calculated by the FLAPW method and the results of experimental studies. The obtained result indicates higher accuracy of modeling of structural parameters Lu1-xZrxNiSb by the FLAPW method in comparison with the KKR method. To study the possibility of obtaining thermometric material Lu1-xZrxNiSb and to establish the limits of its existence in the form of a continuous solid solution, modeling of thermodynamic characteristics in the approximation of harmonic oscillations of atoms within the theory of DFT density functional for a hypothetical solid solution Lu1-xZrxNiSb, x=0–1.0. The change in the values of the enthalpy of mixing ΔH and the total energy E Lu1-xZrxNiSb, x=0–1.0, allows us to state that the thermometric material exists in the form of a solid substitution solution in the concentration range x=0–0.20, stratification occurs (spinoidal phase decay) and thermometric material does not exist. To understand the mechanisms of electrical conductivity of the thermometric material Lu1-xZrxNiSb, the methods of entry of impurity Zr atoms into the matrix of the basic semiconductor p-LuNiSb and their occupation of different crystallographic positions, as well as the presence of vacancies in them, were investigated. For this purpose, its electronic structure was modeled for different variants of the spatial arrangement of atoms and the presence of vacancies in crystallographic positions. It is shown that the most acceptable results of experimental studies are the model of the electronic structure of p-LuNiSb, which assumes the presence of vacancies in the crystallographic positions of 4a Lu atoms (~0.005) and 4c Ni atoms (~0.04). In this model of the spatial arrangement of atoms and the presence of vacancies at positions 4a and 4c, the LuNiSb compound is a semiconductor of the hole-type conductivity, in which the Fermi level eF is located near the level of the valence band eV. The kinetic characteristics of the semiconductor thermometric material Lu1-xZrxNiSb, in particular, the temperature dependences of the resistivity ρ(T,x) and the thermopower coefficient α(T,x) are modeled. It is established that at the lowest concentrations of impurity atoms Zr the Fermi level eF Lu1-xZrxNiSb passes from the bandgap to the conduction band eС. This is indicated by the negative values of the thermopower coefficient α(T,x) and the metallic conductivity type Lu1-xZrxNiSb. This changes the type of main current carriers from holes to electrons.

Benchmarking Full-Potential Linearized Augmented Plane Wave (FLAPW) Method for Determination of Muon Stopping Sites in LiF

Muon stopping sites in Lithium Fluoride have been determined based on the minimum electrostatic potential calculation using density functional theory implemented in the full-potential linearized augmented planewave method. The isosurface of the electrostatic potential obtained in our calculation is similar to the calculation obtained by using pseudopotential-based plane wave (PPPW) method reported by Bernadini et al. [Physical Review B, 87 (2013) 115148]. This yields to the two possible muon sites inside the cage structure of Li-F forming tetrahedral coordination. One of the muon sites is located at the center of the tetrahedral while the other is at the equivalent site of the tetrahedral. In spite of the similar isosurface results, our global minimum is found at the center of the tetrahedral in contrast to the previous result obtained at the tetrahedral sites. The strategy to determine the muon possible sites based on the minimum of the total energy of the system will also be considered including the muon sites position between the two fluorine ions (F-).

Ca and S K-edge XANES of CaS calculated by different methods: influence of full potential, core hole and Eu doping

Ca and S K-edge spectra of CaS are calculated by the full-potential Green's function multiple-scattering method, by the FLAPW method and by the finite-difference method. All three techniques lead to similar spectra. Some differences remain close to the edge, both when comparing different calculations with each other and when comparing the calculations with earlier experimental data. Here it is found that using the full potential does not lead to significant improvement over the atomic spheres approximation and that the effect of the core hole can be limited to the photoabsorbing atom alone. Doping CaS with Eu will not affect the Ca and S K-edge XANES of CaS significantly but may give rise to a pre-edge structure not present for clean CaS.

Magnetic and Electronic Properties of LiVOPO4 and VOPO4 Cathodes

Magnetic and electronic properties of LiVOPO4 and VOPO4 cathodes have been studied using ab initio calculations, high temperature series expansions (HTSEs) calculations and Monte Carlo simulations (MCSs). Self-consistent ab initio calculations, based on Density Functional Theory approach (DFT) and using Full Potential Linear Augmented Plane Wave (FLAPW) method, were performed to investigate both electronic and magnetic properties of the LiVOPO4. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent V plans. Magnetic moments considered to lie along (010) axes are computed. Average equilibrium voltage over a full cycle ([Formula: see text]) of the LiVOPO4, battery have been estimated. Computed magnetic moments are used as input for HTSEs to compute other magnetic parameters using the mean field theory, MCSs and HTSEs. The obtained results by HTSEs and MCSs are comparable with experiments results.

Synthesis, Crystal Structure, Luminescence and Electronic Band Structure of K2BiZr(PO4)3 Phosphate Compound

The single crystals of langbeinite-related K2BiZr(PO4)3 have been obtained for the first time by spontaneous crystallization method from K-Zr-P-O-F molten system. The compound crystallizes in a space group P213 with cell parameter a = 10.30360 Å. The framework is built up from isolated Bi/ZrO6 octahedra connected together by PO4 units. For the two K+ cations two types of oxygen coordination numbers 9 and 12 are observed. The photoluminescence (PL) spectroscopy studies of K2BiZr(PO4)3 are carried out under the VUV synchrotron excitations. The electronic structure of K2BiZr(PO4)3 crystal is calculated by the FLAPW method. The PL spectra reveal two main components in the UV and visible spectral regions (peaking near 3.6 and 2.7 eV respectively). It is assumed that the <st1:address><st1:street>UV PL</st1:street></st1:address> component of K2BiZr(PO4)3 originates from transitions in ZrO6 polyhedra, while the visible one is related to Bi3+ ions in oxygen coordination.

Synthesis, Luminescence and Electronic Band Structure of Al(PO3)3 Crystals

The crystals of aluminium metaphosphate Al(PO3)3 are synthesized by flux method. The photoluminescence properties of Al(PO3)3 are studied under the vacuum ultra violet (VUV) synchrotron excitations. The electronic structure of Al(PO3)3 crystal is calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. The photoluminescence (PL) emission spectra of of aluminium metaphosphate reveal emission bands in the ultraviolet-blue and in the yellow-red spectral regions. Obtained results point to an active role of the electronic states of phosphate groups in the processes of intrinsic luminescence in Al(PO3)3 crystals.