Au Substitution Research Articles

Band gap engineering of Au doping and Au – N codoping into anatase TiO2 for enhancing the visible light photocatalytic performance

We investigate anatase TiO2 doping with Au to determine the change in the band gap energy and optoelectronic properties using experimental and theoretical analysis. The structural analysis using XRD patterns revealed that the synthesized materials primarily exhibited an anatase phase of TiO2, with no impurity peaks observed. However, as the concentration of Au increased, additional diffraction peaks corresponding to Au crystalline phases were detected, indicating successful doping. Furthermore, the crystallite size was found to decrease with increasing Au concentration. We observe that the band gap reduces through substitution of Au into the TiO2 lattice from 3.09 eV to 2.78 eV, demonstrating the feasibility of bandgap tuning of the TiO2 system. A redshift for Au doped TiO2 is observed from absorption spectroscopy and optical absorption intensity using hybrid density functional theory, facilitating visible light absorption, although with potential electron-hole recombination limitations. To enhance a visible light photocatalytic activity for water splitting, we extend our work to explore the impact of N and Au codoping into TiO2 lattice. It reveals that the combination between N and Au leads to a suitable reduction in the band gap width of pure TiO2. Interestingly, Au–N codoping may decrease the effect of photogenerated carriers, produce a new optical absorption feature in the visible region, and enhance the photocatalytic performance of TiO2. This codoping configuration is also a promising photocatalyst for the decomposition of water using visible light without inducing unoccupied states.

Influence of Golden Nanoparticles on the Incorporation of Eu2+ into BaI2 and Defect Concentration

Conjugated BaI2:Eu (5 at.%) nanocrystalline particles were synthesized, decorated with golden nanoparticles (GNP). GNP demonstrated some hydrophilic effect, leading to the BaI2·H2O phase creation. The Eu2+ luminescence intensity was reduced according to the GNP content. This was due to the decreased number of Eu2+ ions in the BaI2, most probably, arising from the Au substitution for Ba competing with Eu. Moreover, the decay time of luminescence was decreased upon GNP content. This was explained by the moderation of negative charge in the GNP, leading to the repulsion with an electron in the excited Eu2+.

Iridium and gold alloy beta gallium oxide expected to achieve p-type conductivity

The beta monoclinic gallium oxide (β-Ga2O3) is a wide-bandgap material with promising applications in high-power electronics, but bottleneck problem of p-type conductivity has become the biggest obstacle to device performance improvement. The effective p-type doping can be achieved in β-(Ir x Au y Ga1-x-y )2O3 alloys, promising to be synthesised in the laboratory, from an energy perspective. The β-(Ir x Ga1-x )2O3 exhibits an extended valence band with a maximum of 1.94 eV at the edge of the valence band. The location and bandwidth of the extended valence band can be changed with the Ir concentration. The Au substitution at the Ga(2) site actually creates a relatively shallow level, contrary to the expected deep acceptors. The 2p orbital of the O atom easily coupling with the doped atomic orbital to appear as a hole-polaronic state, while the higher energy of the Au-doped hole state avoids coupling with the valence band maximum of the host material. Theoretical feasibility of p-type doping of β-(Ir x Au y Ga1-x-y )2O3 is achieved.

Trace-element distribution and ore-forming processes in Au–Ag-rich hydrothermal chimneys and mounds in the TA25 West vent field of the Tonga Arc

We report detailed mineralogy and geochemistry of hydrothermal mounds and chimneys in the TA25 West vent field (TA25 WVF), a newly discovered magmatic–hydrothermal system in the Tonga (Tofua) arc. Chimney samples are classified as sulfate- or sulfide-rich, based on major sulfide, sulfosalt, and sulfate minerals. The former type represents a simple mineral assemblage of predominance of anhydrite/gypsum + barite + pyrite, whereas the sulfide-rich chimneys show three different stages of mineralization with decreasing fluid temperature: sphalerite–pyrite dominated stage I, sphalerite–sulfosalts dominated stage II, and stage III is dominated by seawater alteration. Mound samples are characterized by sulfide assemblages and paragenesis similar to those of sulfide-rich samples, but abundant chalcopyrite indicates a relatively high-temperature mineralization. The chimney and mound samples are enriched in Au (average 9.2 ppm), Ag (297 ppm), As (1897 ppm), Sb (689 ppm), Hg (157 ppm), and Se (34.6 ppm). LA–ICP–MS and FE–TEM studies indicate that most of these elements occur in sulfides or sulfosalts in solid solution, although some occur as nanoparticles. This is mainly controlled by the combined effects of fluid conditions (temperature and redox state) and influx of ambient seawater. Petrography and trace-element compositions of sulfides and/or sulfosalts suggest that most concentrations of Au and Ag in the TA25 WVF result from the precipitation and/or adsorption of Au–Ag-bearing nanoparticles on rapidly crystallized sulfides, the substitution of Au and Ag in sulfide and/or sulfosalt minerals, and the saturation of Ag in hydrothermal fluids during late, relatively low-temperature mineralization (< 150 °C). The maximum measured temperature (242 °C) of venting fluids and calculated formation temperatures of sphalerite (229–267 ℃) are below the boiling temperature of seawater at the depths (966–1096 m) of the TA25 WVF, suggesting fluid boiling had little effect on Au–Ag-rich mineralization in the TA25 WVF. The presence of enargite–tetrahedrite–tennantite assemblages, high concentrations of magma-derived elements (e.g., Au, Ag, As, Sb, Hg, and Se), low δ34S values (2.1 to 4.3‰) of sulfide minerals relative to the host rocks, and the distribution of CO2-rich hydrothermal plumes (500 to 1000 ppm) suggest that the TA25 WVF is a submarine hydrothermal system influenced by a magmatic contribution in an arc setting. Our results indicate that the magmatic contribution is most likely to play an important role in supplying various metals, including Au and Ag, to the TA25 WVF. Subsequently, the rapid crystallization of sulfides induced by abundant fluid-seawater mixing significantly contributes to the precipitation of Au–Ag-rich mineralization.

Noncovalent Synergy: Aurophilicity and Aryl Stacking in Bis(gold(I)aryl)-dmpm Complexes.

Bis(dimethylphosphino)methane (dmpm) was used as a ligand to synthesize four semi-supported dinuclear gold(I) complexes, dmpm(AuR)2 (R = Cl, C6H5, C6Cl5, and C6F5), which were studied concerning the synergistic effects of two weak noncovalent interactions: aurophilic and aryl-aryl stacking interactions. The chloro-substituted complex was synthesized by the ligand substitution of (tht)AuCl with dmpm and further functionalized by the reaction with PhMgBr or in situ-generated C6Cl5Li to afford the phenyl- and pentachlorophenyl-substituted compounds, respectively. The pentafluorophenyl-substituted gold complex was generated by the ligand substitution of (tht)Au(C6F5) with dmpm. All complexes were characterized by multinuclear NMR spectroscopy, CHN analyses, and X-ray diffraction experiments. Additionally, the basic photoluminescence properties of dmpm(AuCl)2, dmpm(AuC6Cl5)2, and dmpm(AuC6F5)2 were examined. The aggregation behavior of dmpm(AuC6F5)2 was further investigated by variable-temperature diffusion-ordered NMR spectroscopy experiments.

Enhancement of mechanical properties and shape memory effect of Ti–Cr–based alloys via Au and Cu modifications

The requirements for biomedical materials have been raised greatly due to the rapidly aging global population. Shape memory alloys (SMAs) are indeed promising materials for biomedical applications due to their controllable shape deformation via the manipulation of temperature and/or stress. This study investigated the enhancement of the fundamental mechanical properties and the shape memory effect (SME) in the Ti–Cr–based alloys via the modification of Au and Cu. The quaternary Ti–Cr–Au–Cu alloys were successfully manufactured by physical metallurgy methods and their phase constitutions, mechanical properties, SME, and superelastic (SE) behaviors have been investigated in this study. Cold–workability, which was enhanced by the introduction of the Au element, was elaborated by the phase constitutions of the alloys. The β–parent phase was stabilized to around body temperature by the introduction of the β–stabilizers of Cr, Au, and Cu, and the functionalities of the specimens were revealed at the operating temperature. Perfect SME at the shape recovery rate of 100% was practiced by the substitution of Au by Cu and the mechanical properties, such as strength and ductility, were also enhanced. Functional mappings of the fundamental mechanical properties, which could be a helpful tool for the investigations of the quaternary Ti–Cr–Au–Cu alloys, were constructed in this work.

Photodetectors for weak signal conditions from Au/Cu co-doped ZnO

Here, we have used a simple method for polyol synthesis, analysis, and testing of Au/Cu-doped ZnO Ultraviolet (UV) photodetectors (PD). Our results are reported and discussed by X-ray diffraction (XRD) to ensure that the manufactured samples show a hexagonal wurtzite ZnO structure. Transmission electron microscopy (TEM) confirmed the nanoparticle growth in the hexagonal sample on the surface, which is the key to improving the light response. Our prepared UV PD Au/Cu codoped ZnO showed a rapid time at a power density of 7.6 mW. the highest responsivity of R = 575 mA/W and sensitivity 103 obtained at 7.6 mW with an applied voltage of 1 V. Our results demonstrate the obvious substitution of Au and Cu in ZnO, thereby improving the UV-sensing light response.

Ultrathin Co films with Pt and Au covers—magnetic and structural properties driven by Ga+ ion irradiation

The X/Co 3 nm/Y (where X, Y = Au, Pt) trilayers with as deposited in-plane magnetization alignment were irradiated with 30 keV Ga+ ions in the wide range of ion fluence. The samples were investigated by means of complementary techniques: magneto-optical magnetometry and spectroscopy (in the photon energy range from 1.2 eV to 4.5 eV), magnetic force microscopy, positron annihilation spectroscopy, x-ray diffraction and reflectivity. Difference in miscibility of interface atoms is clearly manifested in various intermixing extent at Co/Pt and Co/Au interfaces and consequently in magnetic properties of the irradiated trilayers. Low irradiation fluence (∼1014 ions cm−2) leads to ∼1 nm interfaces broadening without visible surface etching for all samples, which is related with a distinct drop of magnetic anisotropy. However, the high irradiation fluence (∼5 × 1015 ions cm−2) results in enhanced interface broadening and significant surface etching (∼5 nm) partially removing also Co atoms. Tensile strains (up to 0.5%) were developed in the cover layers. The tensile strain, layers intermixing and the creation of Co–Pt(Au) alloys with different composition formed by irradiation are correlated with the increase of magnetic anisotropy. Moreover it was observed that substitution of Au instead of Pt (as a cap or buffer layer) results in substantial increase of perpendicular magnetic anisotropy. Maximal increase of magnetooptical parameters was observed for Pt/Co/Pt layer. Irradiation induced changes of concentration profiles are revealed using magnetooptical spectra, x-ray reflectivity spectra and simulations with use of binary collision approximation.

The structural, elastic, thermodynamic, and electronic properties of (Cu6-xAux)Sn5 (x = 0, 0.5, 1, 1.5, 2) intermetallic compounds

In this paper, the effects of substitution of Au for Cu on the structural, mechanical, thermodynamic, and electronic properties of Cu6Sn5 intermetallic compound (IMC) are studied based on first-principles calculations. The results manifest that doping Au in Cu6Sn5 IMC can form a thermodynamically more stable structure than the pure phase. It is also found that, with the increasing in Au concentration, the volume, anisotropic property, and ductility of Cu6Sn5 IMC increase. However, doping Au weakens the shear modulus, Young’s modulus, hardness, and Debye temperature of Cu6Sn5 IMC. The electronic density of states displays that the Au-doped Cu6Sn5 IMC has higher thermodynamic stability than the pure phase.

The influence of Au substitution and hydrostatic pressure on the phase transitions and magnetocaloric properties of MnCoGe alloys

In this work, the phase transitions and magnetocaloric properties of Mn1−xAuxCoGe (0≤x≤0.025) alloys were studied as a function of concentration x and applied hydrostatic pressure. The increasing substitution of Au for Mn results in the decrease of the first-order martensitic transition temperature, and this first-order martensitic transition was ultimately converted to a second-order magnetic transition when the Au substitution (x) reached 0.025. The magnitudes of the maximum magnetic entropy changes increased when the magnetic and structural transitions were coupled, which occurred for 0.005≤x≤0.020. The largest maximum magnetic entropy change for a field change of μ0ΔH=7 T was 33.1 J/kg K for the sample with x=0.020. Similar to the effect of Au substitution, the first-order martensitic transition temperature initially decreased, and then converted to second order, when the applied hydrostatic pressure reached a large enough value. Interestingly, both Au substitution and pressure application cause a volume reduction and, in both cases, the first-order martensitic transition temperature initially reduced and then converted to second-order. These results suggest two different methods of tuning the transition temperatures in these magnetocaloric materials. One can either apply hydrostatic pressure and temporarily adjust the transition temperatures or modify the composition chemically and permanently change the transition temperatures.

Effect of Au Doping on Elastic, Thermodynamic, and Electronic Properties of η-Cu6Sn5 Intermetallic

The effects of substitution of Au for Cu on the elastic, thermodynamic, and electronic properties of hexagonal η-Cu6Sn5 intermetallic compound (IMC) are investigated by first-principles calculations. The results show that Au atoms preferentially occupy Cu4 or Cu3 site to form η-Cu5Au1Sn5 or η-Cu4Au2Sn5 IMC, respectively. Doping Au in η-Cu6Sn5 IMC forms a more stable thermodynamic structure than pure phase. The ductility of η-Cu6Sn5 IMC increases after substitution of Au for Cu. However, doping Au weakens the Young’s modulus, shear modulus, hardness, and Debye temperature of η-Cu6Sn5 IMC. The results for the charge density difference, total density of states, and partial density of states show that doping Au atoms can stabilize the structure of η-Cu6Sn5 IMC.

Different Types of Ligand Exchange Induced by Au Substitution in a Maintained Nanocluster Template

Precisely regulating the ligand exchange on the nanocluster (NC) surface is challenging but important for fully understanding metal-ligand interactions and transformations. In this work, the homosilver nanocluster Ag40(TBBM)22(CH3COO)10 (Ag40) and its Au-substitution derivative AuAg39(TBBM)20(CH3COO)12 (AuAg39) have been synthesized and characterized by single-crystal X-ray crystallography (SC-XRD), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). By precisely controlling the template metal exchange progress, the intermediate product, namely, AuAg39(TBBM)21(CH3COO)11 (AuAg39-inter), was also obtained and then characterized by SC-XRD. These three nanoclusters possess a similar metallic framework, albeit some of the thiol ligands of Ag40 have been replaced by the introduced acetate ligands in both AuAg39-inter and AuAg39. Furthermore, Ag40 and AuAg39 NCs can serve as chiral amplifiers for testing the ee values of 2-chloropropionic acid, ibuprofen, naproxen, and isoleucine with high sensitivity.

Photodegradation of Methylene Blue Solution via Au Doped TiO2 Nanocomposite Catalysts Prepared Using Novel Photolysis Method

Gold doped TiO2 has been successfully synthesized via the photolysis method and is characterized by different techniques. NPs of gold doped TiO2 were utilized for the degradation of methylene blue as a material pigmentation pollutant. The substitution of Au on TiO2 surface was established via XRD, EDX, TEM, and FT-IR techniques. The TEM and SEM results appeared that the particles in the nano range and its size below 15nm. Without a catalyst, the degradation of dye under visible light in acid and nature medium gives humble results but good results at pH 11 while it gives excellent results at all conditions when using catalyst.

First-Principles Study of Substitution of Au for Ni in Ni3Sn4

First-principles calculations were performed to investigate the effects of substitution of Au for Ni on the structural, elastic, thermodynamic and electronic properties of Ni3Sn4. The calculated lattice constants for the pure phase are consistent with the reported values. Substitution of Au for Ni results in a stable␣thermodynamic structure. The bulk modulus, shear modulus, Young’s modulus, hardness and thermal conductivity are decreased and the relative brittleness is improved after substitution. A three-dimensional graphic representation of the anisotropy of Young’s modulus indicates that substitution of Au for Ni increases the anisotropy. All of the compound compositions examined are metallic and nonmagnetic. The electronic density of states manifests a conjoined peak between − 6 eV and − 4 eV hybridized by Au-d electrons and Sn-p electrons when the fraction of Au atom is above 14.29 at.% in Ni3Sn4.

Network Formation by Condensed Tetrahedral [Au3Al] Units in Na2Au3Al: Crystal and Electronic Structure, Spectroscopic Investigations, and Physical Properties of an Ordered Ternary Auride.

Na2Au3Al, the first experimentally prepared compound in the ternary Na-Au-Al system, crystallizes in the cubic crystal system with space group P4132 (a = 771.42(2) pm). It can be described as a P-centered ternary ordered variant of the F-centered Laves phase MgCu2 and is isostructural to Mo3Al2C. A phase width was found for the series Na2Au4-xAlx allowing a successive substitution of Au by Al. The primitive structure forms for x ≥ 0.5. Na2Au3Al is diamagnetic at room temperature but metallic in nature, as seen from susceptibility and electrical resistivity measurements. Band structure calculations and X-ray photoelectron spectroscopy confirm the metallic nature of the title compound as states are found at the Fermi level of the DOS, along with its "auride" character. 23Na and 27Al solid-state-NMR investigations show the existence of both a disordered (x = 0.5 and 0.75) and a fully ordered (x = 1.0) representative within this series. Both COHP and Bader charge analyses suggest the presence of strong Au-Al interactions forming an anionic [Au3Al]δ- network, with the Na cations occupying the cavities.

Candidate Elastic Quantum Critical Point in LaCu_{6-x}Au_{x}.

The structural properties of LaCu_{6-x}Au_{x} are studied using neutron diffraction, x-ray diffraction, and heat capacity measurements. The continuous orthorhombic-monoclinic structural phase transition in LaCu_{6} is suppressed linearly with Au substitution until a complete suppression of the structural phase transition occurs at the critical composition x_{c}=0.3. Heat capacity measurements at low temperatures indicate residual structural instability at x_{c}. The instability is ferroelastic in nature, with density functional theory calculations showing negligible coupling to electronic states near the Fermi level. The data and calculations presented here are consistent with the zero temperature termination of a continuous structural phase transition suggesting that the LaCu_{6-x}Au_{x} series hosts an elastic quantum critical point.

First-Principles Study of Substitution of Cu and Au for Ni in Ni3Sn2

The effects of substitution of Cu and Au for Ni on the mechanical, thermodynamic and electronic properties of two different Ni3Sn2 structures are investigated by first-principles calculations. Cu atom at Ni2 site and Au atom at Ni1 site of the η phase lead to the thermodynamic stable structure. For the λ phase, Au atom can only replace the Ni1 site. Substitution causes the decrease of the polycrystalline elastic modulus and the Debye temperature. The degree of anisotropy along Z axis decreases dramatically for η phase, but it increases along Y axis for λ phase after substitution. The Ni3Sn2-based intermetallics are all ductile; the η phase is more ductile than the λ phase. The electronic density of states manifest an energy gap appearing in η phase and the effective mass of the η phase is lower than λ phase.

Role of magnetism in superconductivity ofBaFe2As2: Study of5dAu-doped crystals

We investigate properties of BaFe2As2 (122) single crystals upon gold doping, which is the transition metal with the highest atomic weight. The Au substitution into the FeAs-planes of 122 crystal structure (Au-122) is only possible up to a small amount of ~3%. We find that 5d is more effective in reducing magnetism in 122 than its counter 3d Cu, and this relates to superconductivity. We provide evidence of short-range magnetic fluctuations and local-lattice inhomogeneities that may prevent strong percolative superconductivity in Ba(Fe1-xAux)2As2.

The Skaergaard PGE and Gold Deposit: the Result ofin situFractionation, Sulphide Saturation, and Magma Chamber-scale Precious Metal Redistribution by Immiscible Fe-rich Melt

The Skaergaard intrusion, Greenland, is the type locality for Skaergaard-type mineralizations. Mineralization levels are perfectly concordant with igneous layering, up to 5 m thick, internally fractionated, and contain crystallized sulphide droplets and precious metal alloys, sulphides, arsenides and telluride. Immiscible Cu-rich sulphide droplets, formed in a mush zone below the roof, scavenged precious metals. They were subsequently dissolved and transported to the floor in late-formed, immiscible, Fe-rich mush melts. Mineralized stratigraphic intervals of floor gabbro formed in ‘proto-macrolayers‘, owing to local sulphide saturation in melt concentrated between floating plagioclase and sinking clinopyroxene. The floor mineralization is divided into four stratigraphic sections. Formation of the Lower Platinum Group Element Mineralization (LPGEM) involved: (1) crystallization of the bulk liquid liquidus paragenesis and in situ fractionation; (2) sulphide saturation and formation of sulphide droplets in melt in the upper part of ‘proto-macrolayers‘. After further in situ fractionation, the following steps occurred: (3) the onset of silicate–silicate immiscibility and the consequent loss of buoyant and immiscible Si-rich melt; (4) dissolution of unprotected droplets of sulphide melt present in the Fe-rich mush melt; (5) compaction-driven upwards loss of residual mush melt enriched in, for example, Au. The LPGEM preserves upward increasing bulk Pd/Pt (∼6–13) owing to a continued supply of PGE and Au, with high Pd/Pt. The further development of the LPGEM ceased as the supply of precious metals to the floor waned. The Upper PGE Mineralization (UPGEM) subsequently formed from precious metals recycled in the floor. The UPGEM is characterized by increasing Au substitution in PGE phases, and a decrease in total PGE and Pd/Pt owing to upward fractionation in migrating mush melts and exhaustion of Pd and Pt. An upper Au-rich mineralization level (UAuM) was caused by late remobilization of Au and deposition on grain boundaries in fully crystallized gabbro. Cu concentrations (∼150 ppm) are not correlated with PGE and Au. Repeated Cu mineralization levels (CuM), attaining >1000 ppm, occur above the Au levels, caused by local mush layer sulphide saturation. PGE, Au and Cu distributions in the floor mineralization reflect sub-liquidus, but supra-solidus, processes and reactions in mushes at the roof, wall and floor. Constraints provided by a new model for the mineralization provide the basis for re-evaluation of the solidification processes in the Skaergaard intrusion. We have identified the importance of extensive in situ fractionation and intrusion-wide elemental redistributions in immiscible Fe- and Si-rich silicate melts. Our model characterizes the floor cumulates as bulk liquid orthocumulates containing an upwards-increasing proportion crystallized from Fe-rich, immiscible mush melt. The roof-rocks are complementary to the floor, with downwards increasing proportions crystallized from the conjugate Si-rich melt. Petrographic observations and the relative timing of crystallization support the hypothesis that crystallization was restricted to marginal mush zones. Bulk melt remaining in the magma chamber evolved not, as generally assumed, as a result of loss of crystals grown from the bulk melt, but as the consequence of mixing with recycled and evolved melt expelled from the mush by compaction. Redistribution of Fe in immiscible melts may be common to mafic intrusions and puts into question the validity of petrogenetic modelling of bulk liquids in mafic intrusions based only on consideration of floor cumulates.

Silver- and Zirconium-added ternary and quaternary TiAu based high temperature shape memory alloys

Low strength in B2 phase, incomplete shape memory effect and high cost of Au are obstacles for the use of Ti–50Au as a high temperature shape memory alloy. We investigated the effects of partial substitution of Ti with Zr and Au with Ag in Ti–Au on phase constitution, phase transformation, and high temperature thermo-mechanical and shape memory properties. Partial substitution of Ti with Zr in Ti–50Au and Ti–40Au–10Ag was found to improve the thermo-mechanical and shape memory effect. However, partial substitution of Au with Ag in Ti–50Au and Ti–50Au–10Zr was found to have negligible effects. Reasons for such different behavior of Zr- and Ag-added Ti–Au alloys are considered.