Enhanced thermoelectric properties of Zn-doped GaSb nanocomposites

In this work, Zn-doped GaSb nanocomposites (Ga_1−xZn_xSb, x = 0.002, 0.005, 0.01, and 0.015) have been synthesized via ball milling followed by hot pressing. It is shown that thermoelectric properties of the synthesized Ga_1−xZn_xSb nanocomposites vary with both the grain size and the Zn content. The grain boundaries formed in the nanocomposites not only scatter phonons and reduce thermal conductivity, but also trap charge carriers and reduce electrical conductivity. Zn doping is adopted to compensate for the trapping effect of grain boundaries on carrier transport in order to enhance the thermoelectric figure of merit, ZT, of Ga_1−xZn_xSb alloys. By optimizing the amount of Zn doping, the maximum ZT value was found to be 0.087 at 500 K for Ga_0.99Zn_0.01Sb nanocomposites, which is 51% higher than the reported value in the literature for bulk Ga_1−xZn_xSb alloys.

The maximum ZT value of Zn-doped GaSb nanocomposites was improved by 51% corresponding to the literature bulk value.     

Study of half metallicity,structural and mechanical properties in inverse Heusler alloy Mn2ZnSi(1−x)Gex and a superlattice

The electronic and magnetic properties of Mn₂ZnSi_(1−x)Ge_x (x = 0.0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, and 1.0) inverse Heusler alloys and Mn₂ZnSi/Mn₂ZnGe superlattice have been investigated using first-principles calculations. All these alloys are stable in the fcc magnetic phase and satisfies the mechanical and thermal stability conditions as determined from the elastic constants and negative formation energy. The spin-polarized electronic band structures and the density of states indicate half-metallicity with 100% spin polarization at the Fermi energy level for x = 0.0, 0.125, 0.25, 0.50, and 1.0, with the integral values of the total magnetic moments per formula unit at their equilibrium lattice constants, following the Slater–Pauling rule. The electronic properties and the magnetic moments are mostly contributed by two Mn atoms and are coupled anti-parallel to each other, making them ferrimagnetic in nature. The presence of the half-metallic bandgap with an antiparallel alignment of Mn atoms makes these Heusler alloys a potential candidate for spintronic applications.

The electronic and magnetic properties of Mn₂ZnSi_(1−x)Ge_x (x = 0.0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, and 1.0) inverse Heusler alloys and Mn₂ZnSi/Mn₂ZnGe superlattice have been investigated using first-principles calculations.     

Biomonitoring of 30 trace elements in urine of children and adults by ICP-MS

The paper provides physicians and clinical chemists with statistical data (concentration ranges, geometric mean values, selected percentiles, etc.) about 30 urinary trace elements in order to determine whether people have trace element deficiencies or have been exposed to higher elemental concentrations. Morning urine samples of 72 children and 87 adults from two geographical areas of Germany were collected and the elements Li, Be, V, Cr, Mn, Ni, Co, Cu, Zn, Ga, As, Se, Rb, Sr, Mo, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, Pt, Au, Pb, Tl, Bi and U were determined by inductively coupled plasma mass spectrometry (ICP-MS) with a new octopole based collision/reaction cell. The urine samples were analysed directly after a simple 1/5 (V/V) dilution with deionised water and nitric acid. Information on exposure conditions of all human subjects were collected by questionnaire-based interviews. The described concentration data down to the ng/l range are very useful for the formulation of reference values. For some elements either new data are described (e.g., for V, Ga, In, Bi, Rh, Mn) or differences to earlier studies were found (e.g., for Be, As). For other elements (e.g., Sb, Se, Mo, Ba, Cu, Zn, Li) our results are in good correlation with previous studies and also complemented with urinary trace element concentrations for children.     

Half-metallicity in new Heusler alloys Mn2ScZ (Z = Si,Ge, Sn)

Study of half-metallicity has been performed in a new series of Mn₂ScZ (Z = Si, Ge and Sn) full Heusler alloys using density functional theory with the calculation and implementation of a Hubbard correction term (U). Volume optimization in magnetic and non-magnetic phases for both the Cu₂MnAl and Hg₂CuTi type structures was done to predict the stable ground state configuration. The stability was determined by calculating their formation energy as well as from elastic constants under ambient conditions. A half-metal is predicted for Mn₂ScSi and Mn₂ScGe with a narrow band gap in the minority spin whereas Mn₂ScSn shows a metallic nature. The magnetic moments of Mn and Sc are coupled in opposite directions with different strengths indicating that the ferrimagnetic order and the total magnetic moment per formula unit for half-metals follows the Slater Pauling rule. And a strong effect was shown by the size of the Z element in the electronic and magnetic properties.

Study of half-metallicity has been performed in a new series of Mn₂ScZ (Z = Si, Ge and Sn) full Heusler alloys using density functional theory with the calculation and implementation of a Hubbard correction term (U).     

Enhanced thermoelectric properties of hydrothermally synthesized Bi0.88−xZnxSb0.12 nanoalloys below the semiconductor–semimetal transition temperature

Bi_0.88−xZn_xSb_0.12 alloys with x = 0.00, 0.05, 0.10, and 0.15 were prepared using hydrothermal synthesis in combination with evacuating-and-encapsulating sintering. The effects of partial Zn substitution for Bi and different sintering temperatures on the thermoelectric properties of Bi_0.88−xZn_xSb_0.12 alloys were investigated between 25 K and 425 K. Both the electrical conductivity and absolute thermopower are enhanced for the set of alloys sintered at 250 °C. The maximum power factor of 57.60 μW cm⁻¹ K⁻² is attained for the x = 0.05 alloy sintered at 250 °C. As compared with Zn-free Bi_0.88Sb_0.12, both the total thermal conductivity and lattice component are reduced upon Zn doping. Bipolar conduction is observed in both electronic and thermal transport. The maximum zT of 0.47 is attained at 275 K for the x = 0.05 alloy sintered at 250 °C.

The peak zT is attained for hydrothermally synthesized Bi_0.83Zn_0.05Sb_0.12 nanoalloy due to the significantly enhanced thermoelectric power factor and relatively low thermal conductivity.     

Charge-induced electromechanical actuation of Mo- and W-dichalcogenide monolayers

Using first-principle density functional calculations, we investigate electromechanical properties of two-dimensional MX₂ (M = Mo, W; X = S, Se, Te) monolayers with the 1H and 1T structures as a function of charge doping for both electron and hole doping. We find that by increasing the atomic number, Z_X, of X atoms (Z_S < Z_Se < Z_Te), the work density per cycle of the MX₂ monolayers are increased and decreased for the 1H and 1T structures, respectively. On the other hand, the work density per cycle of the WX₂ monolayers are higher than that of the MoX₂ monolayers for both the 1H and 1T structures. Therefore, WTe₂ and WS₂ monolayers for the 1H and 1T structures, respectively, have the best electromechanical performances in the MX₂ compounds. In addition, the MX₂ monolayers show a reversible strain up to 3%, which is higher than that of graphene (∼1%). Our results provide an important insight into the electromechanical properties of the MX₂ monolayers, which are useful for artificial muscles applications.

Using first-principle density functional calculations, we investigate electromechanical properties of two-dimensional MX₂ (M = Mo, W; X = S, Se, Te) monolayers with the 1H and 1T structures as a function of charge doping for both electron and hole doping.     

Improvement in the thermoelectric performance of highly reproducible n-type (Bi,Sb)2Se3 alloys by Cl-doping

(Bi,Sb)₂Se₃ alloys are promising alternatives to commercial n-type Bi₂(Te,Se)₃ ingots for low-mid temperature thermoelectric power generation due to their high thermoelectric conversion efficiency at elevated temperatures. Herein, we report the enhanced high-temperature thermoelectric performance of the polycrystalline Cl-doped Bi_2−xSb_xSe₃ (x = 0.8, 1.0) bulks and their sustainable thermal stability. Significant role of Cl substitution, characterized to enhance the power factor and reduce the thermal conductivity synergetically, is clearly elucidated. Cl-doping at Se-site of both Bi_1.2Sb_0.8Se₃ and BiSbSe₃ results in a high power factor by carrier generation and Hall mobility improvement while maintaining converged electronic band valleys. Furthermore, point defect phonon scattering originated from mass fluctuations formed at Cl-substituted Se-sites reduces the lattice thermal conductivity. Most importantly, spark plasma sintered Cl-doped Bi_2−xSb_xSe₃ bulks are thermally stable up to 700 K, and show a reproducible maximum thermoelectric figure of merit, zT, of 0.68 at 700 K.

Cl-doped Bi_2−xSb_xSe₃ bulks are thermally stable at below 700 K showing a reproducible maximum zT of ∼0.68 at 700 K.     

Element concentrations in urine of patients suffering from chronic arsenic poisoning

In order to know the element levels in the urine of patients with chronic arsenic poisoning caused by arsenic assimilated from burning coal via air and food, we investigated various elements in the urine of 16 patients with this disease and 16 controls living in the same county in Guizhou Province of China. Concentrations of 25 elements (Al, As, Ba, Be, Bi, Ca, Cd, Cr, Cu, Fe, Ga, Mg, Mn, Mo, Ni, P, Pb, Rb, Sb, Se, Sn, Sr, Ti, V and Zn) were determined by an inductively coupled plasma mass spectrometer or an inductively coupled plasma atomic emission spectrometer. The average concentrations of Cu, Ga and Sn as well as As in the patients were significantly higher, and those of Cr, Rb, Sr and Ti in the patients were significantly lower than the control values. Al, Ba, Mn, Ni and Se were under detection limit in the patients, though they could be detected in the controls. There were no positive correlations between the concentration of As and the concentrations of other elements, including Cu, Ga and Sn in the patients. The results of this study suggest that As from burning coal might influence the urinary excretion of some elements.     

Catalytically active nanosized Pd9Te4 (telluropalladinite) and PdTe (kotulskite) alloys: first precursor-architecture controlled synthesis using palladium complexes of organotellurium compounds as single source precursors

Several intermetallic binary phases of Pd–Te including Pd₃Te₂, PdTe, PdTe₂, Pd₉Te₄, Pd₃Te, Pd₂Te, Pd₂₀Te₇, Pd₈Te₃, Pd₇Te₂, Pd₇Te₃, Pd₄Te and Pd₁₇Te₄ are known, and negligible work (except few studies on PdTe) has been done on exploring applications of such phases and their fabrication at nanoscale. Hence, Pd(ii) complexes Pd(L1)Cl₂ and Pd(L2-H)Cl (L1): Ph–Te–CH₂–CH₂–NH₂ and L2: HO–2-C₆H₄–CH N–CH₂CH₂–Te–Ph were synthesized. Under similar thermolytic conditions, complex Pd(L1)Cl₂ with bidentate coordination mode of ligand provided nanostructures of Pd₉Te₄ (telluropalladinite) whereas Pd(L2-H)Cl with tridentate coordination mode of ligand yielded PdTe (kotulskite). Bimetallic alloy nanostructures possess high catalytic potential for Suzuki coupling of aryl chlorides, and reduction of 4-nitrophenol. They are also recyclable upto six reaction cycles in Suzuki coupling.

First precursor-architecture controlled synthesis of Pd₉Te₄ and PdTe nanostructures that have potential applications in Suzuki coupling of 4-chlorobenzaldehyde and catalytic reduction of 4-nitrophenol.     

Comprehensive DFT investigation of transition-metal-based new quaternary Heusler alloys CoNbMnZ (Z = Ge,Sn): compatible for spin-dependent and thermoelectric applications

The hunt for high spin polarization and efficient thermoelectric materials has endured for decades. In this paper, we have explored the structural, mechanical stability, magneto-electronic, and thermoelectric properties of two new quaternary Heusler alloys, CoNbMnZ (Z = Ge, Sn), using first-principles simulation methods. The alloys are stable, showing a Y₁-type phase and ferromagnetic nature. Based on a generalized gradient approximation method, the alloys exhibit metallic nature; upon employing a modified version of the Becke–Johnson potential, both alloys demonstrate half-metallic nature, with gaps of 0.43 and 0.45 eV, which is a precursor for high spin polarization in these alloys. The alloys also follow the necessary Slater–Pauling rule condition M_T = Z_T − 24 for half-metallicity and they have a total magnetic moment of 1 μ_B. Elastic parameters convey the mechanical stabilities of these alloys, with Debye temperatures of 518 K and 445 K. These materials act as anisotropic media with respect to longitudinal and transverse sound velocities. Possible energy efficiency and thermoelectric applications were scrutinized via computing Seebeck coefficients, electrical and electronic lattice thermal conductivities, and, lastly, power factors. The highest S values for Ge- and Sn-based alloys are 60.43 and 68.2 μV K⁻¹, respectively, and the highest power factors are 32 and 35 μW K⁻² cm⁻¹, respectively, suggesting potential efficient applications in thermoelectric power generation.

Possible d–d hybridization for characterizing the electronic profile of the materials.     

Atomic layer deposition and tellurization of Ge–Sb film for phase-change memory applications

We studied the atomic layer deposition (ALD) and the tellurization of Ge–Sb films to prepare conformal crystalline Ge–Sb–Te (GST) films and to achieve void-free gap filling for emerging phase-change memory applications. ALD Ge–Sb film was prepared by alternating exposures to GeCl₂-dioxane and Sb(SiEt₃)₃ precursors at 100 °C. The growth rate was 0.021 nm per cycle, and the composition ratio of Ge to Sb was approximately 2.2. We annealed the ALD Ge–Sb films with a pulsed feeding of di(tert-butyl)tellurium. The ALD Ge–Sb films turned into GST films by the tellurization annealing. When the tellurization temperature was raised to 190 °C or higher temperatures, the Raman peaks corresponding to Ge–Sb bond and amorphous Ge–Ge bond disappeared. The Raman peaks corresponding to Ge–Te and Sb–Te bonds were evolved at 200 °C or higher temperatures, resulting in the phase transition temperature of 123 °C. At 230 °C or higher temperatures, the entire film was fully tellurized to form a GST film having a relatively uniform composition of Ge₃Sb₂Te₆, and the carbon impurities in the as-deposited ALD Ge–Sb film were eliminated. As the tellurization temperature increases, the volume of the ALD film is expanded owing to the incorporation of tellurium, resulting in complete filling of a trench pattern by GST film after the tellurization at 230 °C.

We studied the atomic layer deposition (ALD) and the tellurization of Ge–Sb films to prepare conformal crystalline Ge–Sb–Te (GST) films and to achieve void-free gap filling for emerging phase-change memory applications.     

Enhanced room-temperature thermoelectric performance of p-type BiSbTe by reducing carrier concentration

Improving room-temperature thermoelectric performance of p-type (Bi,Sb)₂Te₃ is essential for its practical application. However, the usual doping or alloying methods increase the carrier concentration and result in enhanced thermoelectric properties at high temperatures but not room temperature. In this work, we find that Ti is a promising dopant to shift the optimum thermoelectric properties of p-type (Bi,Sb)₂Te₃ to room temperature by reducing its carrier concentration. p-type Bi_0.5Sb_1.5−xTi_xTe₃ samples with various Ti contents have been prepared using a simple melting method. The carrier concentration of Bi_0.5Sb_1.5−xTi_xTe₃ is reduced by partially replacing Sb with Ti, leading to not only a significantly increased Seebeck coefficient but also an improved power factor near room temperature. Moreover, the total thermal conductivity near room temperature also decreases owing to the combined effect of decreased electrical conductivity and an anisotropic microstructure. An optimal zT value of ∼1.2 is achieved near room temperature for the sample containing 6 at% Ti, and its average zT value below 150 °C increases to ∼1.1, demonstrating the great potential of this material for room-temperature thermoelectric devices.

Ti substitution leads to enhanced thermoelectric performance of p-type Bi_0.5Sb_1.5Te₃ due to carrier concentration regulation, alloy effect and anisotropic microstructure.     

Facile transmetallation of [SbIII(DOTA)]− renders it unsuitable for medical applications

The antimony(iii) complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) has been prepared and its exceptionally low stability observed. The Sb(iii) ion in Na[Sb(DOTA)]·4H₂O shows an approximately square antiprismatic coordination geometry that is close to superimposable to the Bi(iii) geometry in [Bi(DOTA)]⁻ in two phases containing this anion, Na[Bi(DOTA)]·4H₂O, [H₃O][Bi(DOTA)]·H₂O for which structures are also described. Interestingly, DOTA itself in [(H₆DOTA)]Cl₂·4H₂O·DMSO shows the same orientation of the N₄O₄ metal binding cavity reflecting the limited flexibility of DOTA in an octadentate coordination mode. In 8-coordinate complexes it can however accommodate M(iii) ions with r_ion spanning a relatively wide range from 87 pm (Sc(iii)) to 117 pm (Bi(iii)). The larger Bi³⁺ ion appears to be the best metal–ligand size match since [Bi(DOTA)]⁻ is associated with greater complex stability. In the solution state, [Sb(DOTA)]⁻ is extremely susceptible to transmetallation by trivalent ions (Sc(iii), Y(iii), Bi(iii)) and, significantly, even by biologically important divalent metal ions (Mg(ii), Ca(ii), Zn(ii)). In all cases just one equivalent is enough to displace most of the Sb(iii). [Sb(DOTA)]⁻ is resistant to hydrolysis; however, since biologically more abundant metal ions easily substitute the antimony, DOTA complexes will not be suitable for deployment for the delivery of the, so far unexploited, theranostic isotope pair ¹¹⁹Sb and ¹¹⁷Sb.

The antimony(iii) complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) has been prepared and its exceptionally low stability observed.     

First-principles investigation on the electronic structures of CdSexS1−x and simulation of CdTe solar cell with a CdSexS1−x window layer by SCAPS

The short-circuit current density (J_SC) of CdTe solar cells both in the short and long wavelength regions can be effectively enhanced by using CdS/CdSe as the composite window layer. CdS/CdSe composite layers would interdiffuse to form the CdSe_xS_1−x ternary layer during the high temperature deposition process of CdTe films. In this paper, the electronic properties of CdSe_xS_1−x (0 ≤ x ≤ 1) ternary alloys are investigated by first-principles calculation based on the density functional theory (DFT) and the performance of CdS/CdSe/CdTe devices are modeled by SCAPS to reveal why CdS/CdSe complex layers have good effects. The calculation results show that the position of the valence band of CdSe_xS_1−x moves towards the vacuum level as the doping concentration of Se increases and the band gap becomes narrow. According to device modeling, the highest conversion efficiency of 20.34% could be achieved through adjusting the conduction band offset (CBO) of theCdSe_xS_1−x/CdTe interface to about 0.11 eV while the Se concentration x approaches 0.75. Further investigations suggest a 50–120 nm thickness of CdSe_xS_1−x (x = 0.75) would obtain better device performance. It means that solar cells with a CdSe_xS_1−x/CdTe structure need a suitable Se content and thickness of CdSe_xS_1−x. These results can provide theoretical guidance for the design and fabrication of high efficiency CdTe solar cells.

The performance of CdS/CdSe/CdTe devices is related to the conduction band offset of CdSe_xS_1−x/CdTe layers on CdTe solar cells.     

Influence of low Bi contents on phase transformation properties of VO2 studied in a VO2:Bi thin film library

A thin-film materials library in the system V–Bi–O was fabricated by reactive co-sputtering. The composition of Bi relative to V was determined by Rutherford backscattering spectroscopy, ranging from 0.06 to 0.84 at% along the library. The VO₂ phase M1 was detected by X-ray diffraction over the whole library, however a second phase was observed in the microstructure of films with Bi contents > 0.29 at%. The second phase was determined by electron diffraction to be BiVO₄, which suggests that the solubility limit of Bi in VO₂ is only ∼0.29 at%. For Bi contents from 0.08 to 0.29 at%, the phase transformation temperatures of VO₂:Bi increase from 74.7 to 76.4 °C by 8 K per at% Bi. With X-ray photoemission spectroscopy, the oxidation state of Bi was determined to be 3+. The V⁵⁺/V⁴⁺ ratio increases with increasing Bi content from 0.10 to 0.84 at%. The similarly increasing tendency of the V⁵⁺/V⁴⁺ ratio and T_c with Bi content suggests that although the ionic radius of Bi³⁺ is much larger than that of V⁴⁺, the charge doping effect and the resulting V⁵⁺ are more prominent in regulating the phase transformation behavior of Bi-doped VO₂.

A VO₂:Bi thin-film library was fabricated by reactive co-sputtering. The phase transformation temperature of VO₂:Bi increases from 74.7 to 76.4 °C by 8 K/at% Bi in the range of 0.08–0.29 at% suggesting an effect of charge doping from Bi³⁺.     

Influence of Ch substitution on structural,electronic, and thermoelectric properties of layered oxychalcogenides (La0.5Bi0.5O)CuCh (Ch = S,Se, Te): a new insight from first principles

We study the structural, electronic, and thermoelectric properties of p-type layered oxychalcogenides (La_0.5Bi_0.5O)CuCh (Ch = S, Se, Te) from first principles. Ch substitution from S to Te enhances the local-symmetry distortions (LSDs) in CuCh₄ and OLa₂Bi₂ tetrahedra, where the LSD in OLa₂Bi₂ is more pronounced. The LSD in CuCh₄ tetrahedra comes from the possible pseudo-Jahn–Teller effect, indicated by the degeneracy-lifted t_2g and e_g states of Cu 3d¹⁰ orbital. The Ch substitution decreases bandgap from 0.529, 0.256 (Γ → 0.4Δ), to 0.094 eV (Z → 0.4Δ), for Ch = S, Se, Te, respectively, implying the increasing carrier concentration and electrical conductivity. The split-off energy at Z and Γ points are also increased by the substitution. The valence band shows deep O 2p states in the electron-confining [LaBiO₂]²⁺ layers, which is essential for thermoelectricity. (La_0.5Bi_0.5O)CuTe provides the largest thermoelectric power from the Seebeck coefficient and the carriers concentration, which mainly come from Te 5p_x/p_y, Cu 3d_zx, and Cu 3d_zy states. The valence band shows the partial hybridization of t_2g and Chp states, implied by the presence of nonbonding valence t_2g states. This study provides new insights, which predict experimental results and are essential for novel functional device applications.

Substituting Ch from S to Se to Te enhances local-symmetry distortion and thermoelectricity of (La_0.5Bi_0.5O)CuCh from first principles.     

Structural and electronic properties of hydrogenated GaBi and InBi honeycomb monolayers with point defects

First-principles calculations are carried out to systematically investigate the structural and electronic properties of point defects in hydrogenated GaBi and InBi monolayers, including vacancies, antisites and Stone–Wales (SW) defects. Our results imply that the perfect H₂-Ga(In)Bi is a semiconductor with a bandgap of 0.241 eV (0.265 eV) at the Γ point. The system turns into a metal by introducing a Ga(In) vacancy, substituting a Bi with a Ga(In) atom or substituting an In with a Bi atom. Other defect configurations can tune the bandgap value in the range from 0.09 eV to 0.3 eV. In particular, the exchange of neighboring Ga(In) and Bi increases the bandgap, meanwhile the spin splitting effect is preserved. All SW defects decrease the bandgap. The lowest formation energy of defects occurs when substituting a Ga(In) with a Bi atom and the values of SW defects vary from 0.98 eV to 1.77 eV.

Vacancies, antisites and Stone–Wales defects in H₂-Ga(In)Bi monolayer are investigated using first-principles calculations.     

The crystallization kinetics of Co doping on Ni–Mn–Sn magnetic shape memory alloy thin films

Co doping is an effective means to improve the performance of Ni–Mn–Sn alloy bulks and thin films. However, the Co doping effect on the crystallization process of the Ni–Mn–Sn alloy thin films is important but not clear. Therefore, we investigate the influence of Co doping on the crystallization kinetics for Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) magnetic shape memory alloy thin films by DSC analysis. For the non-isothermal process, each DSC curve has a single exothermic peak, which is asymmetrical. The crystallization peak temperatures and the activation energy of thin films both rise gradually with increasing Co content. Then, the activation energy of Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) thin films obtained by the Kissinger equation method is determined as 157.9 kJ mol⁻¹, 198.8 kJ mol⁻¹, 213 kJ mol⁻¹ and 253.6 kJ mol⁻¹, respectively. The local activation energy of thin films with different Co content show the different variation tendency. In the isothermal crystallization, the average of the Avrami exponent n for thin films of each Co content is approximately 1.5, suggesting that the mechanism of crystallization is two-dimensional diffusion-controlled growth for Ni₅₀Mn_37−xSn₁₃Co_x (x = 0, 0.5, 1.5, 4) thin films.

Co doping is an effective means to improve the performance of Ni–Mn–Sn alloy bulks and thin films.     

Electronic structure and thermoelectric properties of full Heusler compounds Ca2YZ (Y = Au,Hg; Z = As,Sb, Bi,Sn and Pb)

We investigate the transport properties of bulk Ca₂YZ (Y = Au, Hg; Z = As, Sb, Bi, Sn and Pb) by a combination method of first-principles and Boltzmann transport theory. The focus of this article is the systematic study of the thermoelectric properties under the effect of a spin–orbit coupling. The highest dimensionless figure of merit (ZT) of Ca₂AuAs at optimum carrier concentration are 1.23 at 700 K. Interestingly enough, for n-type Ca₂HgPb, the maximum ZT are close to each other from 500 K to 900 K and these values are close to 1, which suggests that semimetallic material can also be used as an excellent candidate for thermoelectric materials. From another viewpoint, at room temperature, the maximum PF for Ca₂YZ are greater than 3 mW m⁻¹ K⁻², which is very close to that of ∼3 mW m⁻¹ K⁻² for Bi₂Te₃ and ∼4 mW m⁻¹ K⁻² for Fe₂VAl. However, the room temperature theoretical κ_l of Ca₂YZ is only about 0.85–1.6 W m⁻¹ K⁻¹, which is comparing to 1.4 W m⁻¹ K⁻¹ for Bi₂Te₃ and remarkably lower than 28 W m⁻¹ K⁻¹ for Fe₂VAl at same temperature. So Ca₂YZ should be a new type of promising thermoelectric material at room temperature.

We investigate the transport properties of bulk Ca₂YZ (Y = Au, Hg; Z = As, Sb, Bi, Sn and Pb) by a combination method of first-principles and Boltzmann transport theory.     

Reaction induced robust PdxBiy/SiC catalyst for the gas phase oxidation of monopolistic alcohols

Reaction induced Pd_xBi_y/SiC catalysts exhibit excellent catalytic activity (92% conversion of benzyl alcohol and 98% selectivity of benzyl aldehyde) and stability (time on stream of 200 h) in the gas phase oxidation of alcohols at a low temperature of 240 °C due to the formation of Pd⁰–Bi₂O₃ species. TEM indicates that the agglomeration of the 5.8 nm nanoparticles is inhibited under the reaction conditions. The transformation from inactive PdO–Bi₂O₃ to active Pd⁰–Bi₂O₃ under the reaction conditions is confirmed elaborately by XRD and XPS.

Reaction induced Pd_xBi_y/SiC catalysts exhibit excellent catalytic activity and stability in the gas phase oxidation of monopolistic alcohols at a low temperature of 240 °C due to the formation of Pd⁰–Bi₂O₃ species.