Electronical and thermoelectric properties of half-Heusler ZrNiPb under pressure in bulk and nanosheet structures for energy conversion

The pressure dependence of structural,electronic and thermoelectric properties of half-Heusler ZrNiPb was investigated in the bulk and nanosheet structures.In order to obtain the accurate results,the full-potential(linearized) augmented plane-wave(FP(L)APW)calculations were performed with the Perdew-BurkeErnzerhof generalized gradient approximation(PBE-GGA)and modified Becke-Johnson(mBJ) plus spin-orbit coupling(SOC).Obtained band gap values are in close agreement with the experimental results(0.5 eV).The variations of the thermoelectric properties of the ZrNiPb were studied under different temperatures,carrier concentrations and the hydrostatic pressures.The results show that the hydrostatic pressure decreases the lattice constant value.The band structure calculations display that the band gap increases with pressure for the bulk state and it is 0 for the nanosheet of ZrNiPb [010].The highest value of figure of merit(ZT)=0.95 is found at 9.378 GPa at a carrier concentration of n=1 × 10~(18) cm~(-3) at 250 K for p-type of ZrNiPb.     

DFT research on activation of sphalerite

Activation of sphalerite ZnS, (Zn, Fe)S, (Zn, Cu)S were carried out using the density functional theory (DFT) method. The electronic structures and related properties of three kind of zinc sulfide compounds were investigated. In addition, the relation between electronic structure and flotation behavior was discussed. The results show that, ZnS has a broader band gap than (Zn,Cu)S and (Zn,Fe)S do, and it has low electrochemistry activity to react with flotation collectors to render the surface hydrophobic. When the Zn atom in ZnS is replaced by Cu atom,the band gap will be reduced, and the top valence band will be occupied by Cu 3d orbit, thus it is beneficial to the interaction between mineral surface and collector.     

Bonding Character and Formation Energy of Point Defects of He and Vacancy on （001） Surface of bcc Iron by First Principle Calculations

The structure and energy of He impurities and vacancy on (001) surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found: some of He atoms at surface atomic layers (SAL) relax into vacuum gap; some of surface He atoms at octahedral interstitial site relax into more stable tetrahedral interstitial site; some of surface He atoms still stay at tetrahedral interstitial site. The un-stability of the He atom at the surface system can be explained by deformation mechanism of charge densities and electronic densities of states. It is found that formation energy of the point defects from the topmost SAL to bulk-like atomic layer increase gradually, for example, the formation energies of a monovacancy at the first five topmost SALs are equal to 0.33, 1.56, 2.04, 2.02 and 2.11 eV, respectively. The magnetic moments of Fe atoms in the surface atomic layers are also calculated.     

Elastic and optical properties of zinc-blende CrSb and its effective mass

The elastic, optical, and effective mass properties of CrSb in zinc-blende（ZB） phase were investigated.The calculations were carried out using the full-potential linearized augmented plane wave plus local orbital according to the density functional theory. The results of elastic calculations by generalized gradient approximation and local density approximation approximations indicate that ZB CrSb is a ductile material and its Debye temperature is rather low. Band structure and density of state calculations introduce the ZB CrSb as a half-metal with spin polarization of100 %. In metal state, 16 th and 17 th bands cut off the Fermi level. Calculations study the effective mass, Fermi velocity,and Fermi surface at 16 th and 17 th bands. In continue,optical quantities such as dielectric function, energy loss function, and optical conductivity were investigated.     

Structural stability of intermetallic compounds of Mg-Al-Ca alloy

A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the energetic and electronic structures of intermetallic compounds of Mg-Al-Ca alloy, such as Al2Ca, Al4Ca and Mg2Ca. The negative formation heat, the cohesive energies and Gibbs energies of these compounds were estimated from the electronic structure calculations, and their structural stability was also analyzed. The results show that Al2Ca phase has the strongest alloying ability as well as the highest structural stability, next Al4Ca, finally Mg2Ca. After comparing the density of states of Al2Ca, Al4Ca and Mg2Ca phases, it is found that the highest structural stability of Al2Ca is attributed to an increase in the bonding electron numbers in lower energy range below Fermi level, which mainly originates from the contribution of valence electron numbers of Ca（s） and Ca（p） orbits, while the lowest structural stability of Mg2Ca is resulted from the least bonding electron numbers near Fermi level.     

STM and STS investigations of Ce-doped TiO2 nanoparticles

Ce-doped titanium oxide nanoparticles were investigated in the paper. The surface structures of undoped and Ce-doped TiO2 nanoparticles were observed by scanning tunneling microscopy （STM）. The experimental results of scanning tunneling spectroscopy （STS） show that the surface electronic structures of TiO2 nanoparticles are modified by introducing new electronic states in the surface band gap through cerium ion doping. The results are discussed in terms of the influence of doping concentration on the surface band gap of TiO2.     

Valence electron structure and hydrogen storage property of LaNi_-4Co

In the present study, two models of atom occupation in 4 Co were put forward and corresponding valence electron structures(VESs) of these two models were investigated according to empirical electron theory(EET) of solids and molecules. Results demonstrate that the VES-concerned hardness factor(FH) of LaNi4 Co is lower than that of LaNi5, so LaNi4 Co has lower hardness,higher plasticity and improved anti-pulverization ability. In the mean time, the difference of the equilibrium hydrogen pressure between LaNi4 Co and LaNi5 was analyzed in the electronic level. The analysis shows that the strength of the weakest bond net in octahedron lattice interstices of LaNi4 Co is much lower than that in LaNi5; consequently,LaNi4Co’s bond net easily deforms to accommodate hydrogen so that LaNi4 Co has lower equilibrium hydrogen pressure in comparison with LaNi5. The results can provide some theory guide on the design of hydrogen storage alloys.     

Effect of Deposition Potential on Synthesis,Structural,Morphological and Photoconductivity Response of Cu_2O Thin Films by Electrodeposition Technique

The present work describes the effect of deposition potentials on structural, morphological, optical, electrical and photoconductivity responses of cuprous oxide(Cu_2O) thin films deposited on fluorine-doped tin oxide glass substrate by employing electrodeposition technique. X-ray diffraction patterns reveal that the deposited films have a cubic structure grown along the preferential(111) growth orientation and crystallinity of the film deposited at. 0.4 V is improved compared to the films deposited at. 0.2,. 0.3 and. 0.5 V. Scanning electron microscopy displays that surface morphology of Cu_2O film has a well-defined three-sided pyramid-shaped grains which are uniformly distributed over the surface of the substrates and are significantly changed as a function of deposition potential. Raman and photoluminescence spectra manifest that the film deposited at. 0.4 V has a good crystal quality with higher acceptor concentration compared to other films. UV–visible analysis illustrates that the absorption of Cu_2O thin film deposited at. 0.4 V is notably higher compared to other films and the band gap of Cu_2O thin films decreases from 2.1 to 2.04 eV with an increase in deposition potential from. 0.2 to. 0.5 V.The frequency–temperature dependence of impedance analysis shows that the film deposited at. 0.4 V has a high conductivity.I – V measurements elucidate that the film deposited at. 0.4 V exhibits a good photoconductivity response compared to films deposited in other deposition potentials.     

SrCo0.7Fe0.2Nb0.1O3-δ perovskite stabilized by niobium for oxygen permeation

The effect of Nb doping on the oxygen permeation and stability of SrCo0.8Fe0.2O3-δ(SCFO)was investigated comprehensively.Cubic perovskite phase was formed in SrCo0.7Fe0.2Nb0.1O3-δ(SCFNO).The SCFNO with a thickness of 1 mm had a high level of oxygen permeation flux of 1.4 ml·min-1·cm-2 at 850 ℃ under air/He gradient.The bulk diffusion is the rate-limiting step in overall oxygen permeation mechanism for SCFNO when the thickness is higher than 1.0 mm.The partial substitution of Nb for Co suppresses the transition of oxygen vacancies order/disorder proven by DSC measurement and enhances the phase stability under low oxygen partial pressure.During long-term tests under low oxygen pressure,the SCFNO extibites structural stability and stable oxygen permeation.It is proved that substitution of Nb for Co is an effective way to improve the properties of SCFO.     

Effect of surface state properties of modified TiO2 powders on their photo—catalytic activity

With an attempt to investigate the effect of impurity and tungstem oxide on the recombination and separation of electron-hole pairs,and disclose the effect of surface state on the photo-catalytic activity of TiO2,an innovative photo-catalyst 3%WO3/0.5%Au^3 /AiO3 was prepared by means of sol-el method.The photo-oxidation efficiency of photo-catalyst was evaluated by conducting a set of experiments to photo-degraeds methylene blut(MB)in aqueous solution.The surface state properties were examined by means of surface photovoltage spectra(SPS)and electron-field-induced SPS(EFISPS).The experiments demonstrate that the strongest peak is attributed to electron excited from valence band to conduction band and the second strongest peak is attributed to electron excited from valence band to oxygen molecular for all samples,Electron is trapped by O2 absorbed on the surface of TiO2.And the surface state of O2^- forms.For(1%,3%)Au^3 /TiO2 sample,two new peaks that significantly present at 414nm and 400nm respectively should be attributable to gold impurity energy level.And for tungsten oxides doping samples,4 peaks that significantly present in the region of 500-800nm should be attributable to tungstem impurity energy level.The intensity of EFISPS decreases with increasing the content of gold ion or tungsten oxide when its content is no more than their optimal dosage.However,when the content of gold ion or tungsten oxide is more than their optimal dosage,impurity energy level becomes recombination center from separation center and the intensity of all peaks increases for them.     

Magnetocaloric effect of （Gd1-xCex）Co2 compounds in low magnetic fields

The phases in the compounds (Gd_1−x Ce _x )Co₂ with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 were investigated by X-ray diffraction, and the magnetocaloric effect for x = 0–0.4 was studied by magnetization measurements. The samples are almost single phase with a cubic MgCu₂-type structure for x = 0–0.5. The magnetization decreases with an increase in Ce content. There is almost no magnetic transition for x = 0.5 at 100–350 K. The Curie temperature (T _c) of the (Gd_1−x Ce _x )Co₂ compounds with x from 0.1 to 0.4 are 350, 344, 340, and 338 K respectively. The maximum magnetic entropy change is 2.34 J·kg⁻¹·K⁻¹ when x = 0.3. The results of Arrott plots show that the magnetic phase transition is second-order magnetic phase transition in these compounds.     

Formation of ferromagnetism in pseudobinary PrNi<Subscript>5 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (2.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 5) solid solutions

The structure and magnetic properties of the PrNi_{5 − x} Cu _x alloys have been studied in a composition range of 2.5 ≤ x ≤ 5. Single-phase solid solutions with a hexagonal structure of the CaCu₅ type have been shown to be realized within this composition range. It has been found that upon the introduction of nickel into the Van Vleck paramagnet PrCu₅ the ground state of the alloys with x ≤ 4.3 becomes ferromagnetic. All the compositions under study exhibit high magnetocrystalline anisotropy of the “easy-basal-plane” type. With allowance for the literature data available, a complete magnetic phase diagram of the PrNi_{5 − x} Cu _x system was constructed; it is characterized by two maxima in the compositional dependence of the Curie temperature. The earlier suggested model of the effect of local random crystal fields on the magnetic state of Pr³⁺ ions in alloys with low copper contents was shown to be applicable also for the explanation of magnetic properties of alloys with low nickel contents. The results of this study confirm the hypothesis about the determining role of local irregular crystal fields in the formation of the magnetic properties of the pseudobinary PrNi_{5 − x} Cu _x intermetallic compounds.     

Structure and Inter-Diffusion Coefficients of Liquid Na<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>K<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Alloys

Structure and atomic transport properties of liquid Na-K alloys are reported. Inter-diffusion coefficients of liquid Na _x K_1−x , alloys are calculated using scaling law proposed by Samanta et al. following Dzugutov which express the possible relationship between the excess entropy and diffusion coefficient. The interatomic interactions are described from the individual version of the electron-ion potential proposed by Fiolhais et al. The partial pair distribution functions and structure factors are calculated from the solution of Ornstein-Zernike integral equation with Rogers-Young closure. The evaluation with the composition of static structure and inter-diffusion properties are discussed.     

Effects of tungsten addition on tensile properties of a refractory Nb−18Si−10Ti−10Mo−<Emphasis Type="Italic">x</Emphasis>W (<Emphasis Type="Italic">x</Emphasis>=0,5, 10 and 15 mol.%)<Emphasis Type="Italic">in-situ</Emphasis> Composites at 1670 K

To investigate the effect of tungsten addition on mechanical properties, we prepared refractory (62−x)Nb−18Si−10Mo−10Ti−xW (x=0, 5, 10 and 15 mol.%)in-situ composites by the conventional arc-casting technique, and then explored the microstructure, hardness and elastic modulus at ambient temperature and tensile properties at 1670 K. The microstructure consists of relatively fine (Nb, Mo, W, Ti)₅Si₃ silicide and a Nb solid solution matrix, and the fine eutectic microstructure becomes predominant at a Si content of around 18 mol.%. The hardness of (Nb, Mo, W, Ti)₅Si₃ silicide in a W-free sample is 1680 GPa, and goes up to 1980 GPa in a W 15 mol.% sample. The hardness, however, of Nb solid solution does not exhibit a remarkable difference when the nominal W content is increased. The elastic modulus shows a similar tendency to the hardness. The optimum tensile properties of the composites investigated are achieved at W 5 mol.% sample, which exhibits a relatively good ultimate strength of 230 MPa and an excellent balance of yield strength of 215 MPa, and an elongation of 3.7%. The SEM fractography generally indicates a ductile fracture in the W-free sample, and a cleavage rupture in W-impregnated ones.     

Magnetic properties and structure of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi<Subscript>2</Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1.5)

Crystal structure, magnetization, coercive force, magnetic susceptibility, and anisotropic magnetostriction of nonstoichiometric rare-earth transition-metal intermetallic compounds TbNi₂Mn _x (0 ≤ x ≤ 1.5) have been studied. The samples with x ≤ 1 have an fcc structure, whereas TbNi₂Mn_1.25 has a rhombohedral structure of the PuNi₃ type. It has been found that the magnetic ordering temperature increases sharply when manganese is added. As the Mn concentration grows, the magnetization and the magnetostriction decrease monotonically, while the coercive force increases. The experimental data obtained have been interpreted on the assumption that a partial substitution of manganese for terbium in TbNi₂Mn _x leads to local distortions of the crystal field acting on Tb ions, to the appearance of a local uniaxial random anisotropy, and to the formation of a noncollinear magnetic structure in the terbium sublattice.     

Optical and magnetooptical properties of Heusler alloys <Emphasis Type="Italic">X</Emphasis>MnSb (<Emphasis Type="Italic">X</Emphasis> = Co,Pt)

The ellipsometry method (with photon energies ħω= 0.1–5.0 eV) has been used to study the optical properties of the CoMnSb phase with a structure of the L2₁ type. Infrared-absorption features indicating the existence of a pseudogap in the density of states at the Fermi level N(E _F) have been revealed. The transverse Kerr effect in CoMnSb and PtMnSb has been measured at photon energies ħω = 0.4–4.5 eV. It has been shown that the observed peaks of magnetooptical activity in CoMnSb are due to the off-diagonal component ɛ _ij of the tensor of the complex dielectric constant [^(e)]\hat \varepsilon. Spectral dependences of the magnetooptical effect δ _q quadratic in magnetization M have been studied for the first time for PtMnSb for the s and p polarizations of the light wave. In the region where a giant Kerr effect (ħω ∼ 1.7 eV) is observed in PtMnSb, a sharp increase in the δ _q effect has been revealed caused by the change in the diagonal component ɛ _ii of the tensor] of the dielectric constant in an external magnetic field. Based on the δ _q spectra for the p polarization of the light wave, additions have been calculated to the real and imaginary parts of the diagonal component of the [^(e)]\hat \varepsilon tensor in the magnetic field (Re(Δɛ _ij ) ^p and (Δɛ) _ij ) ^p , respectively). The spectrum of Im(Δε _ij ) ^p has been analyzed in terms of the existing concepts on the electron structure of PtMnSb.     

Structure and principal electrophysical properties of Ge<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>-Si<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

In the process of thermal treatment of deposited Ge_0.85Si_0.15 films, a number of peculiarities were found related to the character of their conductivity. The films of Ge_0.85Si_0.15 solid solutions are rather resistant to thermal quenching. It was shown experimentally that irradiation with electrons under an accelerating voltage enhances the crystallization in the films and lowers their electric conductivity.     

Obtaining ZrO<Subscript>2</Subscript> + CeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> + TiO<Subscript>2</Subscript>/Ti compositions by plasma-electrolytic oxidation of titanium and investigating their properties

Regularities of the effect produced by Ce₂(SO₄)₃ salt introduced in an aqueous electrolyte containing Zr(SO₄)₂ on the plasma-electrolytic formation of oxide coatings on titanium, their composition, and structure are studied. ZrO₂ + CeO _x + TiO₂ three-phase oxide coatings with a thickness about 10 μm are obtained. The coatings involve ZrO₂ cubic phase. The ZrO₂-to-TiO₂ phase ratio in the coatings can be controlled. The zirconium content in the coatings reaches 20 at %, while that of cerium is 3–5 at %. The surface layer (∼3-nm thick) contains Ce³⁺ (∼30%) and Ce⁴⁺ (∼70%). Pores in the surface part of coatings have diameters around or smaller than 1 μm and are regularly arranged. The obtained systems have a certain catalytic activity with respect to the oxidation of CO to CO₂ at temperatures above 400–450°C. The coatings are corrosion-resistant in chloride-containing environments. The thickness h of coatings depending on the charge Q supplied to the cell is described by the equation h = h ₀(Q/Q ₀) ⁿ , where n = 0.35 and h ₀ is the thickness of the coating formed at Q ₀ = 1 C/cm².     

Electrochemical characteristics of amorphous MgTixNi （x = 0,0.1, and 0.2） hydrogen storage alloys

MgTi _x Ni (x = 0, 0.1, and 0.2) alloys were successfully prepared by mechanical alloying (MA), and the influence of milling time on the electrochemical characteristics of the electrodes was discussed. MgTi _x Ni alloys after 90 h milling displayed the best electrochemical performance. The X-ray diffraction patterns showed that the alloy ball-milled for 90 h was amorphous with a widened diffraction peak. The charge-discharge tests indicated that these alloys had good electrochemical activation properties, and the MgTi_0.2Ni alloy electrode exhibited the best cycle performance. The initial discharge capacity of the MgTi_0.2Ni alloy reached up to 401.1 mAh·g⁻¹, and the retention rate of capacity was 31.0% after 30 cycles, much higher than that of MgNi (17.3%). The Tafel polarization curves revealed that Ti addition could enhance the anticorrosion performance of these alloys in alkali solution, which was responsible for the ameliorated cyclic stability of these alloy electrodes.     

Wetting of Sn-Zn-<Emphasis Type="Italic">x</Emphasis>In (<Emphasis Type="Italic">x</Emphasis> = 0.5, 1.0, 1.5 wt%) Alloys on Cu and Ni Substrates

Wetting angles of Sn-8.8Zn and Sn-8.8Zn-xIn alloys (x = 0.5, 1.0, 1.5 wt%) were studied with the sessile drop method. Wetting tests were carried out for 900 s in the presence of ORM0 flux at 493, 523, and 573 K on copper and at 523 K on nickel substrates, respectively. It was found that the addition of In to Sn-8.8Zn alloy improves its wetting on both substrates by reducing the value of apparent wetting angle. Also, with increasing temperature a decrease of wetting angle on copper is observed in the case of 0 and 1.5 wt% of In alloys. Solidified solder-substrate couples were cross-sectioned and examined with scanning electron microscopy coupled with electron dispersive X-ray analysis. Interlayers were found at the interface of solders with copper and nickel, and their compositions are close to Cu₅Zn₈ and Ni₅Zn₂₁ intermetallics, respectively. However, in the case of Sn-8.8Zn-1.5/Ni couple small scallops are observed instead of continuous interlayer.