Introduction: Half Heusler alloys are among the most studied materials because of their high performance as thermoelectric materials. In view of this, we present electronic and thermoelectric properties of RhTiP. In this work, DFT-GGA(PBEsol) was used to obtained lattice constant and electronic band structure and Elastic properties. Semi-classical Boltzmann theory was used to obtain the Seebeck coefficient, electrical conductivity, power factor, and electronic fitness function. The lattice constant of RhTiP is 5.69
Å
, and the band structure shows that RhTiP has an indirect bandgap of 0.83 eV. The Elastic properties predict the mechanical stability of RhTiP. The Seebeck coefficient of 368.23 ?V/K and power factor of 0.51 mW/m at 800 K are obtained from this calculation, Electronic Fitness Function of 1.13 is obtained at 800 K. From our results, it shows that RhTiP is a good thermoelectric material.
Introduction: Huge attention has been shifted to thermoelectric properties of half-Heusler compounds because of the ability of these compounds to convert heat into electricity. The calculations of thermoelectric properties of these compounds are necessitated by the search for alternatives to fossil fuel. This report presents ab initio calculations of electronic and thermoelectric properties of the most stable phase of hafnium–rhodium-based arsenic, antimony and bismuth (HfRhZ(Z = As, Sb and Bi)) half-Heusler compounds by density functional theory based on projector augmented wave pseudopotential method with Perdew–Burke–Ernzerhof generalized gradient approximation used for exchange–correlation functional. The properties calculated in this work are the equilibrium lattice constant, the density of states, band structures, Seebeck coefficients, electrical conductivity, power factor and electronic fitness function (EFF). EFF is calculated to overcome the problem of optimizing Seebeck coefficient and electrical conductivity because of inverse proportion relationship between Seebeck coefficient and electrical conductivity. The ? phase of these compounds is found to be most stable, and thus, electronic and thermoelectric properties of this phase are obtained for the p-type HfRhZ( Z = As, Sb and Bi). The p-type HfRhZ(Z = As, Sb and Bi) is a better thermoelectric material than the n-type HfRhZ(Z = As, Sb and Bi). The Seebeck coefficients of these compounds are 272.01 ?V/K, 555.75 ?V/K and 244.92 ?V/K for HfRhAs, HfRhSb and HfRhBi, respectively, and EFF of HfRhAs, HfRhSb and HfRhBi is 1.21×10?19W5/3ms?1/3K?2 at 1.75×1020cm?3, 1.55×10?19W5/3ms?1/3K?2 at 1.64×1020cm?3 and 1.07×10?19W5/3ms?1/3K?2 at 4.50×1020cm?3, respectively. The results obtained in this work show that HfRhSb and HfRhAs are better potential thermoelectric materials than some known high-performance thermoelectric materials.
Introduction: In this work, details density functional theory calculations were performed to obtain the electronic, elastic, phonon and thermodynamic properties of half-Heusler alloys HfNiX (X = Ge and Sn). The PBE functional as implemented in Projector augmented-wave (PAW) pseudopotentials was used for all the calculations. From our results, we reported the energy gap of 0.38 eV for HfNiSn and 0.61 eV for HfNiGe indicating the semiconductor property of these compounds. Also, the mechanical and elastical stabilities of these compounds were confirmed from the comparison of the elastic constants of these compounds with conditions for stabilities. Although the phonon dispersion curves for HfNiGe and HfNiSn are similar with splitting at the ? point, the shift in their frequency was as a result of the mass different in Ge and Sn. The phonon dispersion curve predicts the dynamically stabilities of these half-Heusler alloys. From the thermodynamic properties of these compounds, it was revealed that these compounds are soft at low temperature, but at a high temperature they tend to be hard materials. Our calculations showed that these two compounds are mechanically, elastically and dynamically stable as cubic half-Heusler alloys.
Introduction: Detailed first-principle calculations of properties in zinc blende quaternary alloy BxAlyIn1?x?yN at various concentrations are investigated using density functional theory (DFT) within virtual crystal approximation (VCA) implemented in alchemical mixing approximation. The calculated bandgaps show direct transitions at ?–? and indirect transitions at ?–X, which are opened by increasing boron concentration. The density of state (DOS) revealed upper valence band (VB1) domination by p-states atoms, while s-states dominate the lower valence band (VB2); also, the DOS shows the contribution of d-states to the conduction band. The first critical point in the dielectric constant ranges between 0.07–4.47 eV and is due to the first threshold optical transitions in the energy bandgap. Calculated static dielectric function (DF) ?1(0) is between 5.15 and 10.35, an indication that small energy bandgaps yield large static DFs. The present results indicate ZB-BxAlyIn1?x?yN alloys are suitable candidates of deep ultraviolet light emitting diodes (LEDs), laser diodes (LDs) and modern solar cell since the concentrations x and y make the bandgap and lattice constant of ZB-BxAlyIn1?x?yN quaternary alloys tunable to desirable values.
Introduction: We present first-principle calculations of structural, electronic, and optical properties of zinc-blende (z) BxAlyGa1-x-yN quaternary alloy, using alchemical mixing of plane-wave pseudopotentals method based on density functional theory (DFT). Generalized gradient approximation (GGA) is used to describe exchange–correlation potential coupled with the Perdew, Burk and Ernzerhof (PBE) flavour. The calculated structural properties, equilibrum lattice constant and bulk modulus are in excellent agreement with available theoretical and experimental data. The bandgaps obtained depend on alloying concentrations x and y. The bandgap and density of states (DOS) are in good agreement with available theoretical data. The optical spectra obtained are given in the energy range of 0–8?eV. The results obtained in this calculation indicate that BxAlyGa1-x-yN alloy is a desirable material for manufacturing of deep ultraviolet (UV) light emitting diodes (LEDs) and laser diodes (LDs).
Introduction: First principle calculations have been performed to obtain detailed electronic structure, optical functions and optical properties of BCC . Frequency dependent dielectric matrix was employed in the determination of imaginary part of the dielectric function from which the real part has been obtained through the use of Kramers–Kronig (KK) relations. The calculated optical constants of show an indirect band gap at 0.41 eV, while critical points are observed at 2.25, 2.94 and 5.93 eV. Other optical properties like optical conductivity, absorption coefficient and reflectivity were also determined.
Introduction: In Africa, we assessed the performance of all the three options of International Reference Ionosphere 2012, IRI-2012 (i.e. IRI-2001, IRI-2001COR and IRI-NeQuick), NeQuick-2 and IRI-Plas 2015 models prior to and during 2009 sudden stratospheric warming (SSW) event to predict equatorial ionization anomaly (EIA) crest locations and their magnitudes using total electron content (TEC) from experimental records of Global Positioning System (GPS). We confirmed that the IRI-Plas 2015 that appeared as the best compared to all of the models as regard prediction of the EIA crest locations in the northern hemisphere of Africa is due to discontinuities in the GPS data between ?8° N and 22° N. As regard the predictions of EIA crest magnitudes and the location of EIA crests in the southern hemisphere of Africa, they are not present in all the models. The NeQuick-2 model does not have the capability to predict either the EIA crest location in the northern or southern hemisphere. The SSW effect on the low latitude was able to modify a single EIA crest to pre-noon and post noon EIA crests in the northern hemisphere during the SSW peak phase and significantly reduced the GPS TEC magnitudes over the hemispheres as well. These SSW effects and delays of plasma transportation to higher latitudes in GPS TEC were absent in all the models. For future improvements of IRI-2012, NeQuick-2 and IRI-Plas 2015 models, SSW conditions should be included in order to characterize the effect of lower atmosphere on the ionosphere. The EIA trough modeling is only present in IRI-2001COR and IRI-2001NeQuick options. In the middle latitude, all the model could not predict the location of highest TEC magnitudes found at RBAY (Richardsbay, South Africa).