Small Amount Of Au Research Articles

Au-Ru alloy nanofibers as a highly stable and active bifunctional electrocatalyst for acidic water splitting

Bimetallic AuRu alloy nanofibers (NFs) with Au:Ru atomic ratios of 7.5:92.5 are constructed and characterized as a bifunctional electrocatalyst for electrochemical overall water splitting (OWS) of both oxygen (OER) and hydrogen evolution reaction (HER). First, composite NFs consisting of RuO2 fibrous mainframes adorned with tiny Au nanoparticles are synthesized by electrospinning and calcination. The following heat treatment of these composite NFs under H2 gas flowing induces the reduction of RuO2 mainframes to metallic Ru within which Au atoms are dispersed to form homogeneous AuRu alloy NFs regardless of their immiscibility. The OWS activities of prepared AuRu alloy NFs are investigated in 0.5 M H2SO4 aqueous solution; and compared to those of RuO2, Ru, Au, and commercial catalysts, M/C (20 wt% metal loading on Vulcan XC-72 with M = Pt, Ru and Ir). In particular, AuRu alloy NFs show outstanding activity for OER: the lowest overpotential at 10 mA cm−2 and the smallest Tafel slope among the tested catalysts. Of great importance, AuRu alloy NFs also present an excellent long-term stability in a sharp contrast to easily deteriorated Ru-based catalysts (e.g., Ru NFs and Ru/C). AuRu alloy NFs also exhibit good HER activity and stability better than most of tested materials. In a two-electrode system, AuRu NFs ∣∣ AuRu NFs is confirmed to have a lower overpotential for OWS than Ir/C ∣∣ Pt/C, a commercial standard. The OWS performance of AuRu alloy NFs is superior to those of Ru-based bifunctional catalysts found in the literature. HER at AuRu alloy is further studied with density functional theory calculation. The current study reveals Ru alloyed with a small amount of Au having a robust nanofibrous morphology improves the electroactivity and stability for both OER and HER in acidic environments. Given that stable bifunctional catalysts for acidic water splitting have been rarely reported, AuRu alloy NFs exhibit an outstanding feasibility as a practical electrocatalyst for overall water splitting with the high activity and stability.

Suppression of hysteresis in absorption of hydrogen by a Pd-Au alloy.

Hydrogen absorption by Pd exhibits hysteresis loops (provided the temperature is not too high) and represents one of the classical examples of first-order phase transitions in metals. Experiments indicate that addition of even a small amount of Au is able to suppress hysteresis. From this perspective, we analyze the energetics of hydrogen in a Pd-Au alloy by using extensive density-functional-theory (DFT) calculations. The dependence of the hydrogen binding energy on the number (n) of Au atoms forming an adsorption site is found to be appreciably nonlinear. With the DFT input for statistical calculations, we reproduce special features of the hydrogen absorption isotherms and explain the rapid decrease of the corresponding critical temperature with increasing Au fraction. The key factor here is that the phase transition is related primarily to absorption in sites formed only by Pd. With increasing Au amount, the fraction of such sites rapidly decreases, the distance between H atoms located there becomes on average larger, the interaction between them becomes weaker, and accordingly the driving force for the phase transition decreases. It is of interest that all these effects can be illustrated by taking only the configurations with n≤2 into account. This means that in the context under consideration the fine details of the dependence of the hydrogen binding energy on n are in fact not too important.

Enhancement of the Thermoelectric Performance of Si-Ge Nanocomposites Containing a Small Amount of Au and Optimization of Boron Doping

In the present work, Si65-xGe31Au4Bx (x = 1, 2, 3, and 4) nanocomposites were synthesized by ball milling and spark plasma sintering to investigate the boron concentration dependence of thermoelectric properties. The electrical resistivity observed for samples made at 2 ≤ x ≤ 4 was almost constant over a wide temperature from 300 K to 1000 K, indicating the strongest scattering limit with disordering. All samples possessed the large Seebeck coefficient, mainly, B-1% and B-3% doped sample shows the significant Seebeck coefficient exceeding 450 μVK−1, which was presumably attributed to a sharp peak in the electronic density of states near the valence band edge. As a result, the largest power factor of 2.1 mWm−1K−2 was observed at x = 3. In addition, the lowest thermal conductivity less than 1.3 Wm−1K−1 was observed for x = 2,3, and 4. The significant power factor, together with low thermal conductivity naturally led to obtain high ZT value of 1.63 at 973 K. This value is much higher than that of previously reported other Si-Ge based nanocomposites.

Au and B co-doped p-type Si-Ge nanocomposites possessing ZT = 1.63 synthesized by ball milling and low-temperature sintering

The enhanced value of the dimensionless figure of merit was achieved in a P-type Si-Ge alloy containing a small amount of Au and B, Si0.62Ge0.31B0.03Au0.04. After the 6 h ball milling, the sample was sintered at 873 K under 400 MPa with a soaking time of 4 h. The precipitation of (Au) occurred in Si-Ge alloy matrix. The large Seebeck coefficient of 464 μVK−1 was achieved at 973 K, which might be due to the sharp peak, that consists mainly of 5d states of Au, near the top of the valence band in the electronic density of states. Assisted by the values of electrical resistivity ∼10 mΩcm and thermal conductivity 1.5 Wm−1 K−1, the large Seebeck coefficient led to a value of ZT exceeding 1.6, which is much higher than that of previously reported Si-Ge-based composites.

Solid-solution alloy nanoparticles of a combination of immiscible Au and Ru with a large gap of reduction potential and their enhanced oxygen evolution reaction performance.

Au and Ru are elements that are immiscible in the bulk state and have the largest gap in reduction potential among noble metals. Here, for the first time, Au x Ru1-x solid-solution alloy nanoparticles (NPs) were successfully synthesized over the whole composition range through a chemical reduction method. Powder X-ray diffraction and scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy showed that Au and Ru atoms are homogeneously mixed at the atomic level. We investigated the catalytic performance of Au x Ru1-x NPs for the oxygen evolution reaction, for which Ru is well known to be one of the best monometallic catalysts, and we found that even alloying with a small amount of Au could significantly enhance the catalytic performance.

Hydrogen Production by Photoreforming of Organic Compounds

H2 is gaining attention as energy vector, particularly if produced from renewable sources.It may be produced through photoreforming of organic compounds that act as hole scavengers to improve hydrogen productivity with respect to direct water photosplitting. Methanol is used here as model molecule to investigate the effect of catalyst composition and of substrate concentration on photocatalytic activity. Simple catalysts formulations were selected, in order to propose an easily scalable technology with a poorly expensive material. TiO2 with different structure (anatase, rutile and a mixture of them) was used as semiconductor, doped with a small amount of Au (0.1 wt%) to improve the lifetime of photogenerated charges.A new photoreactor was set up, with external irradiation that improves the scale up feasibility and possible future application with solar energy. Methanol conversion and hydrogen productivity increased with increasing methanol concentration up to 15 wt%. Rutile led to the highest conversion, but TiO2 P25 showed the highest hydrogen productivity.The best result was achieved by treating a 15 wt% methanol solution with 0.1 wt%Au/TiO2 P25, which led to 0.276 mol H2 h-1 kgcat-1.

Highly ordered Au-Ag alloy arrays with tunable morphologies for surface enhanced Raman spectroscopy

A simple approach combining electrochemical reaction self-assembly and photolithography has been proposed for the controlled and reproducible fabricating the highly ordered Au-Ag alloy arrays for SERS. The nucleation and growth processes of the Au-Ag alloy are adjusted easily via changing the applied voltage and reaction time to obtain the flower-like hierarchy nanostructure, which show the strongest SERS properties due to the wealthy Raman “hot spots” provided by the corners and edges in much-branched flower structure. Moreover, the maximum SERS is observed for the Au-Ag alloy with a small amount of Au (12%), which can lead to a charge separation and favor the probe molecules adsorption to the silver domains. By using these flower-like Au-Ag alloy arrays, the Rhodamine 6G (R6G) with the concentration of as low as 10−12M can be detected easily in this study, which would be very promising for the applications in biosensors and nanodevices with molecule-level detection.

Electrocatalytic Activity Enhancement of Pd Nanoparticles Supported on Reduced Graphene Oxide by Surface Modification with Au

The surface modification of Pd nanoparticles supported on reduced graphene oxide (Pd/RGO) with a small amount of Au and the electrocatalytic oxidation of propane-1,2-diol on the Au-modified Pd/RGO (Au/Pd/RGO) are investigated. The modification of Pd/RGO was performed by electrochemically deposing Au on the Pd surfaces. Characterizations by transmission electron microscopy, scanning electron microscopy and X-ray diffraction analyses and electrochemical analysis revealed that Pd nanoparticles were finely distributed on RGO and a small part of the Pd surface was covered by Au. The Au-modified Pd/RGO catalysts show higher activity than Pd/RGO for propane-1,2-diol oxidation in alkaline solution. For example, the peak intensity for Au/Pd/RGO with a Au:Pd atomic percent of 1.67% is about 2 times higher than that for Pd/RGO. On the other hand, the activity enhancement of bulk Pd electrode by the modification with Au is less effective. The results show that the modification of Pd/RGO catalysts with a small amount of Au is very effective for activity improvement, and the as-prepared catalysts also have a great advantage over AuPd alloy or core-shell catalysts in cost.

Highly efficient catalytic reductive degradation of various organic dyes by Au/CeO 2 -TiO 2 nano-hybrid

Highly improved catalytic reductive degradation of different organic dyes, in the presence of excess NaBH4 over Au/CeO2-TiO2 nano-hybrid as the catalyst is reported in this study. CeO2-TiO2 nanocomposite was prepared by a facile co-precipitation method using ultra-high dilute aqueous solutions. Small amount of Au (only 1 wt%) was loaded onto the nanocomposite material by deposition-precipitation with urea (DPU) method to fabricate the ternary Au/CeO2-TiO2 nano-hybrid. The catalysts were characterized by the representative techniques like XRD, BET surface area, ICP-AES, UV-Vis diffuse reflectance spectroscopy, TEM and XPS. The Au/CeO2-TiO2 nano-hybrid along with NaBH4 exhibited remarkable catalytic activities towards all the probed dyes, namely Methylene Blue, Methyl Orange, Congo Red, Rhodamine B and Malachite Green, with a degradation efficiency of ∼100% in a short reaction time. The degradation reaction followed pseudo-first-order kinetics with respect to the concentration of the dye. Different parameters that affect the rate of the reaction are discussed. A plausible mechanism for methylene blue degradation has also been proposed.

(Invited) Design of Highly Sensitive and Selective Diode-Type H2 Sensors

Diode-type gas sensors employing an anodized TiO2 film and Pt electrodes modified with and without a small amount of Au (Au/Pt/TiO2 and Pt/TiO2, respectively) have been fabricated, and their H2-sensing properties have been investigated in detail. The Pt/TiO2 sensor showed much larger H2 response in N2 than that in air, but the surface modification of the Pt electrode with Au was quite effective in reducing the oxygen concentration dependence of the H2 response and enhancing the H2 selectivity against hydrocarbons such as C3H8 and C3H6 in both wet air and wet N2, at a forward bias of +100 mV at 250°C. In addition, the Au/Pt/TiO2 sensor showed relatively good H2-sensing properties at a low forward bias (+ 1 mV) at 250°C as well as at a forward bias of +100 mV at a low temperature (50°C) in both wet air and wet N2.

Modification of Ag nanoparticles/reduced graphene oxide nanocomposites with a small amount of Au for glycerol oxidation

The surface modification of Ag nanoparticles supported on reduced graphene oxide (RGO) with a small amount of Au and the activity of Au-modified Ag/RGO (Au–Ag/RGO) catalysts for the electrooxidation of glycerol have been investigated. The deposition of Au on Ag/RGO nanocomposites was performed electrochemically, and the Au–Ag/RGO catalysts with Au:Ag atomic ratios in a range from 1:303 to 1:43 were prepared. The characterization of catalysts reveals a partial coverage of the Ag nanoparticle surface by Au adatoms. Cyclic voltammetric measurements indicate that the Au–Ag/RGO catalysts show almost the same activity as Au/RGO in terms of the geometric surface area of glassy carbon substrates for glycerol oxidation in alkaline solution, while Ag/RGO shows no catalytic activity. The Au–Ag/RGO catalysts have great advantages over Au/RGO in terms of the Au mass specific activity. A significant improvement in the catalytic activity of Ag/RGO by the deposition of a small amount of Au and a high utilization of Au are achieved, and the result is of significance for preparing highly active catalysts at low cost by using less expensive metal and active metal.

Improved activity and different performances of reduced graphene oxide-supported Pt nanoparticles modified with a small amount of Au in the electrooxidation of ethylene glycol and glycerol

The partial surface modification of reduced graphene oxide-supported Pt nanoparticles with a small amount of Au and the electrooxidation of ethylene glycol and glycerol on Au-modified Pt nanoparticles/reduced graphene oxide (Au/Pt/RGO) catalysts have been investigated. The deposition of Au on Pt/RGO was performed electrochemically, and Au/Pt/RGO catalysts with the Au:Pt atomic ratio of 1:74, 1:41 and 1:20 were prepared. The characterization of catalysts showed the coverage from 4 to 17% of the Pt surfaces by Au adatoms. The Au/Pt/RGO catalysts have the property reflecting the features of both Pt and Au, but behave more similar to Pt/RGO in ethylene glycol oxidation and to Au/RGO in glycerol oxidation. Furthermore, the Au/Pt/RGO catalysts exhibit higher activity than Pt/RGO and Au/RGO in the two reactions. The significant change in the activity of Pt/RGO by the surface modification with a small amount of Au and the different performances of Au/Pt/RGO in the oxidation of ethylene glycol and glycerol are of significance for practical application and theoretical investigation.

UV-Light-Induced Improvement of Fluorescence Quantum Yield of DNA-Templated Gold Nanoclusters: Application to Ratiometric Fluorescent Sensing of Nucleic Acids.

The use of DNA as a template has been demonstrated as an effective method for synthesizing different-sized silver nanoclusters. Although DNA-templated silver nanoclusters show outstanding performance as fluorescent probes for chemical sensing and cellular imaging, the synthesis of DNA-stabilized gold nanoclusters (AuNCs) with high fluorescence intensity remains a challenge. Here a facile, reproducible, scalable, NaBH4-free, UV-light-assisted method was developed to prepare AuNCs using repeats of 30 adenosine nucleotides (A30). The maximal fluorescence of A30-stabilized AuNCs appeared at 475 nm with moderate quantum yield, two fluorescence lifetimes, and a small amount of Au(+) on the surface of the Au core. Results of size-exclusion chromatography revealed that A30-stabilized AuNCs were more compact than A30. A series of control experiments showed that UV light played a dual role in the reduction of gold-ion precursors and the decomposition of citrate ions. A30 also acted as a stabilizer to prevent the aggregation of AuNCs. In addition, single-stranded DNA (ssDNA) consisting of an AuNC-nucleation sequence and a hybridization sequence was utilized to develop a AuNC-based ratiometric fluorescent probe in the presence of the double-strand-chelating dye SYBR Green I (SG). Under conditions of single-wavelength excitation, the combination of AuNC/SG-bearing ssDNA and perfectly matched DNA emitted fluorescence at 475 and 525 nm, respectively. The formed AuNC/SG-bearing ssDNA enabled the sensitive, selective, and ratiometric detection of specific nucleic acid targets. Finally, the AuNC-based ratiometric probes were successfully applied to determine specific nucleic acid targets in human serum.

S, O and Pb isotopic evidence on the origin of the İnkaya (Simav-Kütahya) Cu–Pb–Zn–(Ag) Prospect, NW Turkey

The İnkaya Cu–Pb–Zn–(Ag) prospect is a typical example of the hydrothermal mineralization occurring in the Menderes Massif, which crop out in Western Anatolia. The prospect located approximately 20km west of Simav (Kütahya-Turkey) in northern part of the Menderes Massif have been characterized through the detailed examinations involving geological, mineralogical, whole-rock geochemistry, fluid inclusion, stable isotope and lead isotope.The İnkaya Cu–Pb–Zn–(Ag) prospect is located along an E–W-trending fault in the Cambrian Simav Metamorphics, which consist of quartz–muscovite schist, quartz–biotite schist, muscovite schist, biotite schist and the Arıkayası Formation, which is composed of marbles. Galena, sphalerite, chalcopyrite, pyrite and fahlore are the main minerals, and they are accompanied by small amounts of cerussite, anglesite, digenite, enargite, chalcocite, covellite, bornite, and Fe-oxides with gangue quartz. In addition to Pb, Zn, Cu, Ag, the ore samples contain substantial quantities of As, Cd and Bi and small amount of Au. Average contents of Cu, Pb, Zn and Ag are 77,400ppm, 102,600ppm, 6843ppm and 203ppm, respectively.The δ34S values for galena, chalcopyrite and pyrite formed in the same stage vary in the range from −1.7 to −2.1‰ (average −2.0), 0.1 to 0.3‰ (average 0.2) and −1.5 to 2.6‰ (average +1.5), respectively.δ34S values for H2S, representing the composition of the fluids responsible for the sulfide mineral formations and calculated from the δ34S value are between −2.77 and 1.33‰; it is consistent with the sulfur in sulfide minerals. δ18Oquartz values range from 11.3 to 16.4‰ and estimated δ18Ofluid values range from 5.4 to 10.6‰.Pyrite–galena and pyrite–chalcopyrite pairs calculated to determine equilibrium isotope temperatures based on δ34S values are between 254.6 and 277.4°C for pyrite–galena and 274.7°C for pyrite–chalcopyrite. Sulfur and oxygen isotope values similar to the values for fluid equilibrated with an felsic magmatic source.Fluid inclusion studies on quartz of the same silicification stage coexisting with galena, sphalerite and chalcopyrite collected from the mineralized vein indicate that the temperature range of the fluids is 235°C to 340°C and that the salinities are 0.7 to 4.49wt.% NaCl equivalent. The wide range of homogenization temperatures and relatively lower salinities of the fluid inclusions indicate that at least two different fluid generations were trapped in the quartz from only one fluid type. Also, lower salinities of fluid inclusion probably indicate mixing of meteoric water and magmatic fluid.The galena has 206Pb/204Pb values of 18.862–18.865, 207Pb/204Pb values of 15.707–15.711, and 208Pb/204Pb values of 39.033–39.042. The lead isotope values show a similarity with upper crustal values.

Preparation of Au/TiO2 nanocomposite particles with high visible-light photocatalytic activity in inverse miniemulsions

Au/amorphous TiO2 nanocomposite particles with high visible-light photocatalytic activity were conveniently prepared in inverse miniemulsions. The materials were synthesized through a combination of a sol–gel process and in situ reduction of HAuCl4 by hydrazine to Au nanoparticles in the nanocomposite particles. The photocatalytic activity of the as-synthesized Au/amorphous TiO2 nanocomposite particles is much higher than that of the Au/anatase TiO2 and Au/rutile TiO2 nanocomposite particles prepared by calcination. Therefore, no further heat treatments are required to achieve visible-light photocatalytic active catalysts. The loading of Au in the nanocomposite particles could be conveniently tuned by varying the HAuCl4 loading in the dispersed phase of the inverse miniemulsions. Only a small amount of Au was required to achieve a high photocatalytic activity. The size, particle morphology, TiO2 phase, optical property, elemental content and distribution, and pore properties of the Au/TiO2 nanocomposite particles were systematically characterized by dynamic light scattering, transmission/scanning electron microscopy, X-ray diffraction, Raman spectroscopy, UV–vis spectroscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and N2 sorption measurements.

Effects of surface modification of noble-metal sensing electrodes with Au on the hydrogen-sensing properties of diode-type gas sensors employing an anodized titania film

Diode-type gas sensors employing an anodized TiO2 film and noble-metal (Pt, Pd and Pd–Pt) sensing electrodes modified with and without a small amount of Au (Au/M/TiO2 and M/TiO2, respectively, M=Pt, Pd, Pd–Pt (Pd:Pt=58:42 in weight)) have been fabricated, and the effects of surface modification of the electrodes with Au on their H2-sensing properties have been investigated at 250°C in both air and N2 under dry and wet atmospheres. H2 response of all the M/TiO2 sensors in N2 was much larger than that in air under both dry and wet atmospheres. The Pt/TiO2 sensor showed the smallest H2 response in air among them, but the surface modification of the Pt electrode with Au was quite effective in enhancing the H2 response of the Pt/TiO2 sensor in air. Therefore, the response of the Au/Pt/TiO2 sensor to 8000ppm H2 in air was comparable to that in N2, especially under wet atmosphere, and thus the response of the Au/Pt/TiO2 sensor to 8000ppm H2 was almost independent of oxygen concentration under wet atmosphere. In addition, the annealing of the sensor at 600°C did not affect the response of the Au/Pt/TiO2 sensor to 8000ppm H2. The homogeneous mixing of Au into the Pt electrode also improved the H2 response of the Pt/TiO2 sensor, but the effectiveness was much lower than that of the surface modification of the Pt electrode with Au. On the other hand, the response of the as-fabricated Au/Pd/TiO2 and Au/Pd-Pt/TiO2 sensors to 8000ppm H2 in air was much larger than that of the Au/Pd/TiO2 and Au/Pd–Pt/TiO2 sensors annealed at 600°C, especially under wet atmosphere. The large H2 response observed with the Au/Pt/TiO2 sensor and the as-fabricated Au/Pd/TiO2 and Au/Pd–Pt/TiO2 sensors can be explained by large suppression of H2 oxidation by Au components remained at the surface of their sensing electrodes and then increased amount of dissociatively adsorbed hydrogen species at the sensing electrode surface.

Photoemission and RHEED study of the supported Pt and Au epitaxial alloy clusters

In this paper, we investigated formation and structure of gold, platinum and Pt–Au bimetallic clusters on tungsten oxide surface. Crystallographic structure and orientation were investigated by reflection high energy electron diffraction, chemical composition and cluster's electronic state by synchrotron radiation photoelectron spectroscopy. Small amount of Au and Pt was deposited on WO3 (111) surface prepared by RF plasma oxidation and thermal annealing of (110) tungsten single crystal surface. Formation of 3D Pt or Au clusters with (111) epitaxial plane was observed. On the contrary to Au, strong metal substrate interaction between Pt and oxide was found, leading to the encapsulation of Pt clusters. Formation of Au–Pt bimetallic clusters was investigated at the temperature range of 160–870K. It was found that cluster structure depends on the substrate temperature and order of materials deposition. At the temperatures around 570K, metals formed bimetallic clusters with core–shell structure. Annealing to the temperatures over 770K led to the decomposition of Pt–Au clusters and formation of Pt–W alloy.

Au-Doped Indium Tin Oxide Ohmic Contacts to p-Type GaN

Indium tin oxide (ITO) thin films doped with Au, Ni, or Pt (3.5 at.% to 10.5 at.%) were deposited on p-GaN epilayers (Mg ~4 × 1019 cm−3) using direct-current (DC) sputter codeposition. It was found that undoped ITO con- tacts to p-GaN exhibited leaky Schottky behavior, whereas the incorporation of a small amount of Au (3.5 at.% to 10.5 at.%) significantly improved their ohmic characteristics. Compared with standard Ni/ITO contacts, the Au-doped ITO contacts had a similar specific contact resistance in the low 10−2 Ω cm−2 range, but were more stable above 600°C and more transparent at blue wavelengths. These results provide support for the use of Au-doped ITO ohmic contact to p-type GaN in high-brightness blue light-emitting diodes.

Cadmium-Auride AIICdxAu2– x (AII = Ca, Sr) Synthese, Kristallstruktur, chemische Bindung/ Cadmium-Aurides AIICdxAu2−x (AII = Ca, Sr) – Synthesis, Crystal Structure, Chemical Bonding

Following the observation that the binary dicadmides and diaurides of calcium and strontium (A) both form the KHg2 structure type, the two sections AIICdxAu2−x have been studied systematically by means of synthetic, X-ray structural and theoretical investigations. The binary border compound CaCd2 is dimorphic forming the KHg2 structure at elevated temperatures (orthorhombic, space group Imma, a = 488.63(9), b = 754.1(2), c = 851.3(2) pm, Z = 4, R1 = 0.0498) and the MgZn2-type Laves phase at ambient conditions (hexagonal, space group P63/mmc, a = 599.71(9), c = 962.7(2) pm, Z = 4, R1 = 0.0309). Starting from the known binary calcium auride CaAu2 only a very small amount of Au can be replaced by Cd. Around the 1 : 1 ratio of Au and Cd the TiNiSi structure type (orthorhombic, space group Pnma), an ordered variant of the KHg2 type, has a small homogeneity range (CaCdxAu2−x with x = 1/0.76(2): a = 735.0(1)/731.7(1), b = 433.66(6)/431.43(7), c = 873.7(2)/869.9(2) pm, Z = 4, R1 = 0.0482/0.0539). The analogous structure type is also observed in the Sr compounds with the difference that in this case a continuous transition from the KHg2 type of SrAu2 (i. e. x = 0) towards the distorted TiNiSi structure type (up to x = 0.86) is observed in the series SrCdxAu2−x (for x = 0.86(1)/0.45(1): a = 764.0(1)/758.4(1), b = 458.07(7)/474.6(1), c = 872.16(12)/829.2(2) pm, Z = 4, R1 = 0.0446/0.0410). Attempts to prepare the Ca compounds of intermediate composition around a Cd content of x ≈ 0.5 resulted in the formation of the Aurich phase Ca5Cd2Au10 crystallizing with the Zr7Ni10 structure type (orthorhombic, space group Cmca, a = 1390.6(4), b = 1015.7(3), c = 1025.6(2) pm, Z = 4, R1 = 0.0657). In this compound, Cd and Ca occupy common crystallographic sites, which are occupied by In in the isotypic ternary compound Ca4In3Au10. Similarly, at the Cd-rich parts of the sections AIICdxAu2−x no simple phase width of the KHg2 structure type exists. In the case of the calcium series the new compound Ca11Cd18Au4, which shows only a very small phase width, is formed instead. This compound crystallizes with a new structure type (Ca11Cd18+xAu4−x with x = 0.6/0: tetragonal, space group I41/amd, a = 1030.83(6)/1029.39(6), c = 3062.5(3)/3051.0(3) pm, Z = 4, R1 = 0.0475/0.0379) exhibiting a complicated Cd/Au polyanion with four-, five- and six-bonded Cd/Au atoms. The results of FPLAPWband structure calculations are used to explain the electronic stability of the compounds. The calculated Bader charges of cadmium and gold atoms (and In and Au atoms for comparison) are used to discuss the transition between Cd-rich cadmides (like CaCd2 and Ca11Cd18Au4), auridocadmates (like CaCdAu) and the Cd-poor cadmium aurides (like Ca5Cd2Au10).

Cross-Interaction of Interfacial Reactions in Ni (Au/Ni/Cu)-SnAg-Cu Solder Joints during Reflow Soldering and Thermal Aging

The coupling effect of interfacial reactions between two pads in Ni-SnAg-Cu and Au/Ni/Cu-SnAg-Cu solder joints was investigated in this paper. After reflow soldering, a large amount of Cu can diffuse across the solder joint to the opposite pad to form (Cu,Ni)6Sn5 IMC on the Ni pad in Ni-SnAg-Cu solder joint. A little Ni can also be detected in Cu6Sn5 layer, which contains some trapped solder, on the opposite Cu pad. Some Cu6Sn5 was found in the solder bulk. For as-reflowed Au/Ni/Cu-SnAg-Cu solder joint, (Cu,Ni)6Sn5 and Cu6Sn5 were formed on the Au/Ni/Cu and Cu pad, respectively. A small amount of Au was involved in the (Cu,Ni)6Sn5 and Cu6Sn5 IMCs during the subsequent thermal aging. It is interesting to note that some (Cu,Au)6Sn5 with lower Au concentration was always surrounded by (Cu,Au)6Sn5 with higher Au concentration at the interface or in the solder bulk. Compared with Ni-SnAg-Cu solder joint, the IMCs formed on both interfaces in Au/Ni/Cu-SnAg-Cu solder joint were much thinner. Au plays an important role in inhibiting the growth of interfacial IMCs. At the same time, Cu from Cu pad at one side inhibits the redeposition behavior of (Au,Ni)Sn4.