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The application of materials with a perovskite structure has currently become one of the most promising approaches for the development of photovoltaic systems. A method for high-speed synthesis (under 15 minutes) of CaTiO3 perovskite — TiO2 rutile with the possibility of concurrent doping of the product has been developed. The density of electronic states, phase composition features, and resistivity of niobium-doped perovskite (CaTiO3 ) were investigated. The calculations of the density of electronic states for niobium-doped CaTiO3 have shown that at low concentrations of niobium, the samples exhibit conductivity characteristic of semiconductors. Since niobium has one more valence electron compared to titanium, as the niobium content increases, the Fermi level shifts to the band of free states. This shift of the Fermi level should lead to a change in the nature of the conductivity of doped crystals, eventually transitioning to metallic conductivity at high concentrations of niobium. Composite analysis (CaTiO3 + ТіО2 ) by X-ray diffraction has shown that the use of niobium as a doping element significantly accelerates the CaTiO3 synthesis reaction, and increases the perovskite concentration in the sample. The concentration of CaTiO3 in the sample the with niobium is 83% vol. at a temperature of 900 ºC and a synthesis time of 5 min, whereas when using a mixture without Nb, the content of perovskite will be only 58% vol. at a synthesis time of 12 min. X-ray phase analysis methods confirm the formation of a solid solution (doping) Ca (Ti,Nb)O3, resulting in the preparation of samples (CaTiO3 + ТіО2 ) with resistivity inherent to semiconductors. [ABSTRACT FROM AUTHOR]

We report data of band-structure calculations based on density functional theory (DFT) of ternary strontium lead bromide, SrPb3Br8, a prospective scintillation and optoelectronic material. Similar band-structure calculations are made also for the isostructural lead dibromide, PbBr2. The present DFT calculations reveal the similarity of the main electronic contributors to the valence-band region for both bromides. In particular, Br 4p states are the principal contributors to the upper portion of the valence band, while its bottom is dominated by Pb 6s states in SrPb3Br8 and PbBr2. However, the main contributors at the bottom of the conduction band are the unoccupied Br 4p and Pb 5p states in the case of SrPb3Br8 and PbBr2, respectively. Some substantial contributions of the electronic states associated with strontium atoms are detected in the central and upper portions of the valence band, while the unoccupied Sr d states at the bottom of the conduction band of SrPb3Br8. The calculations indicate that the SrPb3Br8 and PbBr2 bromides are indirect-gap semiconductors with band gaps of 3.05 eV and 3.14 eV, respectively. The theoretical data of band-structure calculations of SrPb3Br8 and PbBr2 are confirmed experimentally by measurements of the transmission spectra of these bromides. [ABSTRACT FROM AUTHOR]

This paper presents the results of a systematic study of the propagation of shock waves in porous samples of silicon carbide. Samples both with few pores (1-3) of different geometry and with a porosity from 9 to 17% were considered. A detailed discussion is presented of the microscopic mechanisms of fracture of the studied materials under action of shock wave impact. [ABSTRACT FROM AUTHOR]

The energy-band structure, density of states, electron density distribution, equation of state, and bulk moduli of three boron-nitride fulborenite crystals, i.e., B12N12 with diamond lattice and B24N24, B12N12 with simple cubic lattice, whose sites contain fulborene B12N12 and B24N24 molecules, are calculated for the first time using the full-potential linearized augmented plane wave method. The following hyperdiamond B12N12 parameters were obtained: the equilibrium lattice parameter a = 1.1191 nm, the B-N bond length a BN = 0.1405 nm, the number of atoms per unit cell Z = 192, the density ρ = 2.823 g/cm3, the bulk modulus B 0 = 658 GPa, and the band gap Δ E g = 3.05 eV. This is a previously unknown unique light superhard semiconductor faujasite with a recorded bulk modulus higher than that of diamond. There are reasons to assume that it is a E phase. The characteristics of B24N24 with simple cubic lattice are as follows: the equilibrium lattice parameter a = 0.7346 nm, the B-N bond length a BN = 0.1521 nm, the number of atoms per unit cell Z = 48, the density ρ = 2.495 g/cm3, the bulk modulus B 0 = 367 GPa, and the band gap Δ E g = 3.76 eV. This material is a heteropolar semiconductor or insulator with a bulk modulus comparable with that of cubic boron nitride, as well as a new boron-nitride zeolite with channel diameter of 0.46 nm. B12N12 with simple cubic lattice is a molecular semimetal. [ABSTRACT FROM AUTHOR]

Calculations were performed for the first time for the equation of state, the energetic band structure, and the densities of states for a novel allotropic modification of carbon that was synthesized previously and established recently to consist of the simple cubic lattice built from molecules C24 (SCF-C24 ) copolymerized by square faces, known previously as "cubic graphite." Volume dependence of total energy was shown to have the equilibrium minimum under an inter-carbon distance aCC =0.1550 nm, intermediate between diamond (0.1544 nm) and graphite (0.1421 nm). Band structure consisted of five bands with semiconducting band gap ∼1.9 eV. On the density-of-state curve the sharp peaks are pronounced as a peculiar feature of zero-dimensional fullerene molecules. In conclusion the SCF-C24 was shown to be the diamond-like, direct-band molecular semiconductor combining a nonpolarizability and porosity with its mechanical strength (bulk modulus B=308 GPa), chemical inertness, thermal stability, high thermal conductance, and compatibility in lattice parameter (0.5933 nm) with number of semiconductors. All of these point to the SCF-C24 as a high promising low-dielectric material (e < 5.7) for fast interconnectors and integrated circuits substrates in future nanoelectronics. [ABSTRACT FROM AUTHOR]