Based on electronic structure and atomic size considerations, nitrogen has been regarded as the most suitable impurity for p-type doping in ZnO. However, numerous experimental efforts by many different groups have not resulted in stable and reproducible p-type material, casting doubt on the efficacy of nitrogen as a shallow acceptor. Based on advanced first-principles calculations we find that nitrogen is actually a deep acceptor, with an exceedingly high ionization energy of 1.3 eV, and hence cannot lead to hole conductivity in ZnO. In light of this result, we reexamine prior experiments on nitrogen doping of ZnO.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-001476.pdf

Why nitrogen cannot lead to p-type conductivity in ZnO

Model metal/ceria and ceria/metal catalysts have been shown to be excellent systems for studying fundamental phenomena linked to the operation of technical catalysts. In the last fifteen years, many combinations of well-defined systems involving different kinds of metals and ceria have been prepared and characterized using the modern techniques of surface science. So far most of the catalytic studies have been centered on a few reactions: CO oxidation, the hydrogenation of CO2, and the production of hydrogen through the water–gas shift reaction and the reforming of methane or alcohols. Using model catalysts it has been possible to examine in detail correlations between the structural, electronic and catalytic properties of ceria–metal interfaces. In situ techniques (X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, infrared spectroscopy, scanning tunneling microscopy) have been combined to study the morphological changes under reaction conditions and investigate the evolution of active phases involved in the cleavage of C–O, C–H and C–C bonds. Several studies with model ceria catalysts have shown the importance of strong metal–support interactions. In general, a substantial body of knowledge has been acquired and concepts have been developed for a more rational approach to the design of novel technical catalysts containing ceria.

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Ceria-based model catalysts: fundamental studies on the importance of the metal–ceria interface in CO oxidation, the water–gas shift, CO2 hydrogenation, and methane and alcohol reforming

Nanoporous graphene as a reverse osmosis membrane: Recent insights from theory and simulation

The amorphous titanium dioxide (a-TiO2) has drawn attention recently due to the finding that it holds promise for coating conventional photoelectrodes for corrosion protection while still allowing the holes to transport to the surface. The mechanism of hole conductivity at a level much higher than the edge of the valence band is still a mystery. In this work, an amorphous TiO2 model is obtained from molecular dynamics employing the "melt-and-quench" technique. The electronic properties, polaronic states and the hole conduction mechanism in amorphous structure were investigated by means of density functional theory with Hubbard's energy correction (DFT + U) and compared to those in crystalline (rutile) TiO2. The formation energy of the oxygen vacancy was found to reduce significantly (by a few eV) upon amorphization. Our theoretical study suggested that the oxygen vacancies and their defect states provide hopping channels, which are comparable to experimental observations and could be responsible for hole conduction in the "leaky" TiO2 recently discovered for the photochemical water-splitting applications.

Oxygen vacancy and hole conduction in amorphous TiO2

Nanocomposites of selenium (Se) and ordered mesoporous silicon carbide-derived carbon (OM-SiC-CDC) are prepared for the first time and studied as cathodes for lithium-selenium (Li-Se) batteries. The higher concentration of Li salt in the electrolytes greatly improves Se utilization and cell cycle stability. Se-CDC shows significantly better performance characteristics than Se-activated carbon nanocomposites with similar physical properties. Se-CDC also exhibits better rate performance and cycle stability compared to similarly produced sulfur (S)–CDC for Li/S batteries.

Micro- and Mesoporous Carbide-Derived Carbon–Selenium Cathodes for High-Performance Lithium Selenium Batteries

The structural, magnetic and optical properties of Rh2MnAl and Rh2MnBi Heusler alloys have been studied through the full potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential was treated within the generalized gradient approximation (GGA). The effect of the magnetic ordering, i.e. ferromagnetic (FM) and antiferromangnetic (AFM) along [001] and [111] crystal axis on the dielectric functions is revealed. Our calculations show that the Kerr rotation and elipticity is enhanced within 0-8 eV energy range by the substitution of Al by semimet al. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhancement of the magneto-optical effects by bismuth in Heusler compound: A first-principle study

To better understand the electronic, structural, optical, and transport properties of the alkali metal-based nitridorhenate (Li 5 ReN 4 ), first-principles calculations were performed using the full potential linearized augmented plane wave (FP-LAPW) method within the generalised gradient approximation (GGA) framework. The ground-state properties were computed for an orthorhombic structure (Pmmn-59). Both the band structure and the total density of states were carried out. Based on the band structure, the Li 5 ReN 4 compound is a direct band semiconductor with a bandgap value of 2.68 eV. In addition, the optical properties were calculated, indicating that lithium nitridorhenate is a highly absorbent material. The effective masses of the electrons and holes were calculated. Also, we investigate the connection between exciton binding energy and band structure. Moreover, the exciton for Li 5 ReN 4 is a weak exciton of the Mott-Wannier type. Furthermore, the transport properties were investigated using the semi-classical Boltzmann theory as implemented in the BoltzTraP code. Owing to its semiconducting nature, the material has a high Seebeck coefficient (S) of 287 μV/K at 300 K. At 300 K and 400 K, the predicted thermoelectric figure of merit was 0.790 and 0.802. Each of these results shows that our compound is a strong choice for applications in photovoltaic, optoelectronic, and thermoelectrical devices. Additionally, based on the observation of thermoelectric figure of merit, the Li 5 ReN 4 compound is also suitable for waste heat regeneration or waste heat recovery process. The calculated charge density distribution of Li 5 ReN 4 along (011). 

R. D. Eithiraj

Papers

Enhancement of the magneto-optical effects by bismuth in Heusler compound: A first-principle study

Wannier-Mott excitons in alkali metal-based nitridorhenate: A DFT study

Exploring chemical bonding nature, weak exciton effect, electronic, optical and thermoelectric properties of NaReN2 via DFT computations

Structural, electronic, optical, and thermoelectric properties of Li2ZnCl4 based on density functional theory computations

Structural, Electronic, Optical and Thermoelectric Properties of Li2zncl4 Via Dft Computation