Enhancing photocatalytic properties of rutile TiO2 by codoping with N and metals e Ab initio study

Substitutional N to O and M to Ti (M = Pt, V, Sb) codoped rutile TiO2 was investigated using density functional theory (DFT) based calculations with both standard and hybrid exchange-correlation functionals. The band gaps calculated using generalized gradient approximation (GGA) exhibited narrowing compared to the pure rutile TiO2 in all the investigated cases. In contrast, the results obtained with hybrid exchange-correlation functional showed that there was no band gap narrowing, but doping induced localized states within the band gap just above the valence band, as well as below the conduction band for Pt doped TiO2. The presence of broad intermediate states (IS) in the band gap could enhance visible light absorption through a two step optical transition from the valence to the conduction band via the IS and at the same time lower recombination of the photogenerated charges

Magnetism in La2O3(Fe1-xMnx)2Se2 tuned by Fe/Mn ratio

We report the evolution of structural and magnetic properties in La2O3(Fe1-xMnx)2Se2. Heat capacity and bulk magnetization indicate an increased ferromagnetic component of the long-range magnetic order and possible increased degree of frustration. Atomic disorder on Fe(Mn) sites suppresses the temperature of the long-range order whereas intermediate alloys show a rich magnetic phase diagram.Comment: 7 pages, 7 figure

First principles calculations of tetragonal FeX X S, Se, Te Magnetism, hyperfine interaction, and bonding

Magnetic ground states, local crystallographic environment of Fe, and hyperfine interaction parameters in tetragonal FeX X S, Se, Te are investigated by means of density functional theory DFT calculations using augmented plane waves plus local orbitals APW lo method. We use several different mag netic configurations to evaluate the magnetic and electronic properties of this system, as well as the hyperfine interaction parameters at Fe lattice site. The results obtained for the ground state collinear anti ferromagnetic arrangement relatively well reproduce the quadruple splitting and isomer shifts from the available Mössbauer measurements. The Bader s atoms in molecule charge density analysis indicates bonding of closed shell type and a sizable charge transfer from Fe to X . The system properties are sensitive to the structural optimization of the position of the chalcogen atom with respect to the iron plan

Magnetic Properties and Electronic Structures of Compounds from Hf-Co Phase System

Magnetic measurements of molar susceptibilities as a function of temperature in the temperature range between 5 and 400 K were performed for the intermetallic compounds Hf2Co and HfCo2, using a SQUID magnetometer. The density of states at the Fermi level for Hf2Co was evaluated from the measured spin paramagnetic susceptibility. In addition, band structure calculations using the augmented plane waves plus local orbitals (APW+lo) method as implemented in the WIEN2k programme package for the two compounds were done. The obtained results were compared with the measured data

Magnetism of the Compounds in the Hf-Co Phase System

Magnetization M as a function of applied magnetic field H up to 50 kOe was measured at low temperature T = 5K, using an SQUID magnetometer, for HfCo2 and Hf2Co intermetallic compounds. Both samples showed paramagnetic behaviour with a weak ferromagnetic contribution due to impurities (0.01-0.001 wt%). The values of the mass susceptibilities χ were deduced from the measurements. In addition, calculations using full-potential linearized augmented plane wave (FP-LAPW) WIEN 97 programme package were done, in order to check their agreement with the experimental results

Local and electronic structure around Ga in CdTe: evidence of DX- and A-centers

The lattice relaxation around Ga in CdTe is investigated by means of extended X-ray absorption spectroscopy (EXAFS) and density functional theory (DFT) calculations using the linear augmented plane waves plus local orbitals (LAPW+lo) method. In addition to the substitutional position, the calculations are performed for DX- and A-centers of Ga in CdTe. The results of the calculations are in good agreement with the experimental data, as obtained from EXAFS and X-ray absorption near-edge structure (XANES). They allow the experimental identification of several defect structures in CdTe. In particular, direct experimental evidence for the existence of DX-centers in CdTe is provided, and for the first time the local bond lengths of this defect are measured directly.7th International Workshop on X-Ray Damage to Biological Crystalline Samples, Mar 14-16, 2012, Englan

Magnetic Properties, Mössbauer Effect and First Principle Calculations Study of Laves Phase HfFe2

The magnetic properties and hyperfine interaction parameters for Laves phase HfFe2 with C14 type structure are studied using SQUID magnetometer and Mossbauer measurement. The saturation magnetization, remanent magnetization, coercive field, magnetic moment per unit formula and the hyperfine magnetic field at Fe site are reported. In addition, a detailed theoretical study of the electronic structure and hyperfine magnetic fields of the two possible HfFe2 structures, C15 and C14, is presented. Using the full-potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN 97 package, the equilibrium volume, bulk moduli, magnetic moments and hyperfine magnetic fields for the two structures are calculated. The obtained results are compared with the measured data

SEM and XRD characterization of Ni Hf alloys at low Hf concentration

The alloying and phase formation in Ni Hf samples with 0.2 , 2 , and 5 at. Hf were studied by X ray diffraction XRD technique and scanning electron microscopy SEM . Both characterization methods, XRD and SEM, reveal the presence of the HfNi5 phase fee structure where the excess Ni atoms are present in the form of Ni or Ni rich segregations in the sample containing 5 at. Hf. The sample with 2 at. Hf is characterized by the presence of the two phases present in the 5 at. sample and by Hf atoms, which occupy substitutional lattice positions in the Ni lattice. Finally, in the third sample with 0.2 at. Hf, the Hf atoms mainly substitute the Ni atoms in the lattice. This analysis is being complemented with additional information on the local structure around Hf by extended X ray absorption fine structure spectroscopy EXAF

Hf dopands in gamma prime Ni3Al alloy

The Time Differential Perturbed Angular TDPAC measurements of nuclear quadrupole interactions NQIs at 181Ta ion probe in the polycrystalline intermetallic alloy c0 Ni3Al doped with 0.2 at. Hf were performed in the temperature range 78 1230K, in order to determine the lattice location of Hf atoms in the ordered c0 Ni3Al structure. The two NQIs obtained are discussed within the present L12 cubic structure and a tetragonal distortion of L12 to another two DO22 and L60 type structures. The first low frequency NQI at the site of the 181Ta ion probe after substitution of aluminum for hafnium in DO22 at ambient temperature, is vQ1 300 K 39 1 MHz with g1 0. The corresponding high frequency value on the second crystallographic site in L60, is vQ2 300 K 204 14 MHz with g2 0.47 11 . These two NQI s have different temperature behavior. The presence of both DO22 and L60 tetragonal distortions of the parent cubic L12 lattice, detected after adding 0.2 at. Hf, are with modulations to the lattice constant a with a ratio c a , 2.04 and 0.87, respectively. Ab initio calculations of electronic and structural properties and hyperfine parameters at the 181Ta ion probe of the c0 Ni3Al 0.2 at. Hf alloy were performed using the full potential augmented plane wave plus local orbital APW lo method as implemented in the WIEN2k code. The accuracy of the calculations and comparison with the experimental results enabled us to identify the observed hyperfine interactions and to infer the EFG sign that cannot be measured in conventional TDPAC measurement