scholarly journals Antiferromagnetic Ordering and Transport Anomalies in Single-Crystalline CeAgAs2

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3865
Author(s):  
Maria Szlawska ◽  
Daniel Gnida ◽  
Piotr Ruszała ◽  
Maciej J. Winiarski ◽  
Małgorzata Samsel-Czekała ◽  
...  
Keyword(s):  
Electrical Transport ◽  
Electronic Band Structure ◽  
Chemical Vapor ◽  
Chemical Vapor Transport ◽  
Gap Formation ◽  
X Ray Diffraction ◽  
Electronic Band ◽  
Antiferromagnetic Ordering ◽  
Structure Calculations ◽  
Distinct Increase

Single crystals of the ternary cerium arsenide CeAgAs2 were grown by chemical vapor transport. They were studied by means of x-ray diffraction, magnetization, heat capacity and electrical transport measurements. The experimental research was supplemented with electronic band structure calculations. The compound was confirmed to order antiferromagnetically at the Néel temperature of 4.9 K and to undergo metamagnetic transition in a field of 0.5 T at 1.72 K. The electrical resistivity shows distinct increase at low temperatures, which origin is discussed in terms of pseudo-gap formation in the density of states at the Fermi level and quantum corrections to the resistivity in the presence of atom disorder due to crystal structure imperfections.

scholarly journals On the New Oxyarsenides Eu5Zn2As5O and Eu5Cd2As5O

Crystals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 475
Author(s):  
Gregory Darone ◽  
Sviatoslav Baranets ◽  
Svilen Bobev
Keyword(s):  
Electronic Band Structure ◽  
Charge Balance ◽  
X Ray Diffraction ◽  
Electronic Band ◽  
Cell Parameters ◽  
Pearson Symbol ◽  
Formal Charge ◽  
Valence Electrons ◽  
Metal Flux ◽  
Structure Calculations

The new quaternary phases Eu5Zn2As5O and Eu5Cd2As5O have been synthesized by metal flux reactions and their structures have been established through single-crystal X-ray diffraction. Both compounds crystallize in the centrosymmetric space group Cmcm (No. 63, Z = 4; Pearson symbol oC52), with unit cell parameters a = 4.3457(11) Å, b = 20.897(5) Å, c = 13.571(3) Å; and a = 4.4597(9) Å, b = 21.112(4) Å, c = 13.848(3) Å, for Eu5Zn2As5O and Eu5Cd2As5O, respectively. The crystal structures include one-dimensional double-strands of corner-shared MAs4 tetrahedra (M = Zn, Cd) and As–As bonds that connect the tetrahedra to form pentagonal channels. Four of the five Eu atoms fill the space between the pentagonal channels and one Eu atom is contained within the channels. An isolated oxide anion O2– is located in a tetrahedral hole formed by four Eu cations. Applying the valence rules and the Zintl concept to rationalize the chemical bonding in Eu5M2As5O (M = Zn, Cd) reveals that the valence electrons can be counted as follows: 5 × [Eu2+] + 2 × [M2+] + 3 × [As3–] + 2 × [As2–] + O2–, which suggests an electron-deficient configuration. The presumed h+ hole is confirmed by electronic band structure calculations, where a fully optimized bonding will be attained if an additional valence electron is added to move the Fermi level up to a narrow band gap (Eu5Zn2As5O) or pseudo-gap (Eu5Cd2As5O). In order to achieve such a formal charge balance, and hence, narrow-gap semiconducting behavior in Eu5M2As5O (M = Zn, Cd), europium is theorized to be in a mixed-valent Eu2+/ Eu3+ state.

scholarly journals Preparation, thermal stability and electrical transport properties of vaesite, NiS2

2019 ◽  
Author(s):  
Helena M Ferreira ◽  
Elsa B Lopes ◽  
José F Malta ◽  
Luís M Ferreira ◽  
Maria H Casimiro ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Electrical Transport ◽  
Hot Pressing ◽  
Density Functional ◽  
Single Phase ◽  
Electronic Band Structure ◽  
Electrical Transport Properties ◽  
Electronic Band ◽  
Metallic Behavior ◽  
Starting Point

Vaesite, a nickel chalcogenide with NiS2 formula, has been synthetized and studied by theoretical and experimental methods. NiS2 was prepared by solid-state reaction under vacuum and densified by hot-pressing, at different consolidation conditions. Dense single-phase pellets (relative densities >94%) were obtained, without significant lattice distortions for different hot-pressing conditions. The thermal stability of NiS2 was studied by thermogravimetric analysis. Both as-synthetized and hot-pressed NiS2 have a single phase nature, although some hot-pressed samples had traces of the sulfur deficient phase, Ni1-xS (<1%vol), due to the strong desulfurization at T > 340ºC. The electronic band structure and density of states were calculated by Density Functional Theory (DFT), indicating a metallic behavior. However, the electronic transport measurements showed p-type semiconductivity for bulk NiS2, verifying its characteristic behavior has a Mott insulator. The consolidation conditions strongly influence the electronic properties, with the best room-temperature Seebeck coefficient, electrical resistivity and power factor being 182µVK-1, 2257μΩm and 14.1µWK-2m-1, respectively, pointing this compound as a good starting point for a new family of thermoelectric materials.

Computational Analysis of Strain Effects on Electrical Transport Properties of Crystalline Nanocomposite Thin Films

2011 ◽  
Author(s):  
Hua Li ◽  
Gang Li
Keyword(s):  
Thin Films ◽  
Electrical Conductivity ◽  
Band Structure ◽  
Transport Properties ◽  
Electrical Transport ◽  
Electronic Band Structure ◽  
Electrical Transport Properties ◽  
Electronic Band ◽  
Strain Effects ◽  
Nanocomposite Thin Films

In this work, we model the strain effects on the electrical transport properties of Si/Ge nanocomposite thin films. We utilize a two-band k·p theory to calculate the variation of the electronic band structure as a function of externally applied strains. By using the modified electronic band structure, electrical conductivity of the Si/Ge nanocomposites is calculated through a self-consistent electron transport analysis, where a nonequilibrium Green’s function (NEGF) is coupled with the Poisson equation. The results show that both the tensile uniaxial and biaxial strains increase the electrical conductivity of Si/Ge nanocomposite. The effects are more evident in the biaxial strain cases.

Control of Valence States by a Codoping Method in P-Type GaN Materials

1997 ◽  
Vol 468 ◽  
Author(s):  
T. Yamamoto ◽  
H. Katayama-Yoshtoa
Keyword(s):  
Control Method ◽  
Electronic Band Structure ◽  
Ionic Charge ◽  
Electronic Band ◽  
Valence States ◽  
Madelung Energy ◽  
Valence Control ◽  
P Type ◽  
Structure Calculations ◽  
Codoping Method

ABSTRACTWe propose a new valence control method, the “codoping method (using both n- and p-type dopants at the same time)”, for the fabrication of low-resistivity p-type GaN crystals based on the ab-initio electronic band structure calculations. We have clarified that while doping of acceptor dopants, BeGa and MgGa, leads to destabilization of the ionic charge distributions in p-type GaN crystals, doping of Sica or ON give rise to p-type doped GaN with high doping levels due to a large decrease in the Madelung energy. The codoping of the n- and p-type dopants (the ratio of their concentrations is 1:2) leads to stabilization of the ionic charge distribution inp-type GaN crystals due to a decrease in the Madelung energy, to result in an increase in the net carrier densities.

Efficient Discovery of Optimal N-Layered TMDC Hetero-Structures

MRS Advances ◽  
2018 ◽  
Vol 3 (6-7) ◽  
pp. 397-402 ◽  
Author(s):  
Lindsay Bassman ◽  
Pankaj Rajak ◽  
Rajiv K. Kalia ◽  
Aiichiro Nakano ◽  
Fei Sha ◽  
...  
Keyword(s):  
Band Structure ◽  
Physical Properties ◽  
Band Gap ◽  
Electronic Band Structure ◽  
Transport Coefficients ◽  
Optimization Technique ◽  
Bayesian Optimization ◽  
Material Structure ◽  
Electronic Band ◽  
Structure Calculations

ABSTRACTVertical hetero-structures made from stacked monolayers of transition metal dichalcogenides (TMDC) are promising candidates for next-generation optoelectronic and thermoelectric devices. Identification of optimal layered materials for these applications requires the calculation of several physical properties, including electronic band structure and thermal transport coefficients. However, exhaustive screening of the material structure space using ab initio calculations is currently outside the bounds of existing computational resources. Furthermore, the functional form of how the physical properties relate to the structure is unknown, making gradient-based optimization unsuitable. Here, we present a model based on the Bayesian optimization technique to optimize layered TMDC hetero-structures, performing a minimal number of structure calculations. We use the electronic band gap and thermoelectric figure of merit as representative physical properties for optimization. The electronic band structure calculations were performed within the Materials Project framework, while thermoelectric properties were computed with BoltzTraP. With high probability, the Bayesian optimization process is able to discover the optimal hetero-structure after evaluation of only ∼20% of all possible 3-layered structures. In addition, we have used a Gaussian regression model to predict not only the band gap but also the valence band maximum and conduction band minimum energies as a function of the momentum.

Preparation of Plate-Like Bulk Beta Iron-Disilicide Crystals Using Metal to Semiconductor Phase Transition by Heat Treatment

2002 ◽  
Vol 749 ◽  
Author(s):  
Masato Osamura ◽  
Hidetaka Ishihara ◽  
Zhengxin Liu ◽  
Hisao Tanoue ◽  
Shirou. Sakuragi ◽  
...  
Keyword(s):  
Chemical Vapor ◽  
Chemical Vapor Transport ◽  
Annealing Duration ◽  
Bulk Crystals ◽  
X Ray Diffraction ◽  
X Ray ◽  
Flat Surfaces ◽  
The Matrix ◽  
The Mean ◽  
Micro Analysis

ABSTRACTPlate-like β-FeSi2 bulk crystals with size of 10×10 mm2 and thickness of 1 mm were fabricated by annealing CVT (chemical vapor transport)-grown plate-like α-Fe2Si5 at 800°C in Ar atmosphere. Before annealing, α-Fe2Si5 crystals were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM) to be single crystals with flat surfaces. XRD measurements of β-FeSi2 crystals subjected to annealing showed that they had a po lycrystalline structure. The mean Fe/Si co mposit ion rat io of β-FeSi2 crystal measured by energy dispersive x-ray spectroscopy (EDX) was 31/69 and it was the same as that of α-Fe2Si5 bulk crystal before annealing. SEM, Raman scattering and electron probe micro-analysis (EPMA) measurements identified that there existed small Si precipitates mixed in the matrix of β-FeSi2 crystals. At annealing temperature of 800°C, the plate-like β-FeSi2 bulk was obtained even the annealing duration time was as short as 5 hours.

Ab Initio Electronic Structure Studies of CuO Multiferroics

2012 ◽  
Vol 488-489 ◽  
pp. 129-132 ◽  
Author(s):  
C. Kanagaraj ◽  
Baskaran Natesan
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Metallic State ◽  
Magnetic Ground State ◽  
Electronic Band ◽  
Functional Theory ◽  
High Tc ◽  
Band Structure Calculations ◽  
Structure Calculations

We have performed detailed structural, electronic and magnetic properties of high - TC multiferroic CuO using first principles density functional theory. The total energy results revealed that AFM is the most stable magnetic ground state of CuO. The DOS and electronic band structure calculations show that in the absence of on-site Coulomb interaction (U), AFM structure of CuO heads to a metallic state. However, upon incorporating U in the calculations, a band gap of 1.2 eV is recovered. Furthermore, the Born effective charges calculated on Cu does not show any anomalous character.This suggests that the polarization seen in CuO could be attributed to the spin induced AFM ordering effect.

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