Au Substitution Research Articles

Electron-poor SrAu xIn 4−x (0.5⩽ x⩽1.2) and SrAu xSn 4−x (1.3⩽ x⩽2.2) phases with the BaAl 4-type structure

Solid solutions SrAu x In 4− x (0.5⩽ x⩽1.2) and SrAu x Sn 4− x (1.3⩽ x⩽2.2) have been prepared at 700 °C and their structures characterized by powder and single-crystal X-ray diffraction. They adopt the tetragonal BaAl 4-type structure (space group I4/ mmm, Z=2; SrAu 1.1(1)In 2.9(1), a=4.5841(2) Å, c=12.3725(5) Å; SrAu 1.4(1)Sn 2.6(1), a=4.6447(7) Å, c=11.403(2) Å), with Au atoms preferentially substituting into the apical over basal sites within the anionic network. The phase width inherent in these solid solutions implies that the BaAl 4-type structure can be stabilized over a range of valence electron counts (vec), 13.0–11.6 for SrAu x In 4− x and 14.1–11.4 for SrAu x Sn 4− x . They represent new examples of electron-poor BaAl 4-type compounds, which generally have a vec of 14. Band structure calculations confirm that substitution of Au, with its smaller size and fewer number of valence electrons, for In or Sn atoms enables the BaAl 4-type structure to be stabilized in the parent binaries SrIn 4 and SrSn 4, which adopt different structure types.

Anomalous Behaviors in Transport Properties of CeCu6 and CeCu5.9Au0.1

We have investigated the thermoelectric power (TEP) and Hall coefficient ( R H ), along with the field dependence of Hall resistivity (ρ H ) and magnetoresistance (MR) in single crystals of CeCu 5.9 Au 0.1 and CeCu 6 . In both compounds, R H is highly anisotropic with respect to the field direction below ∼10 K. For H ∥[001], a negative minimum in ρ H and a positive MR peak grow at low temperatures near 1.7 T, where a metamagnetic-like anomaly was reported for CeCu 6 . The Au substitution induces drastic changes in R H depending on the magnetic field direction, which is discussed in correlation with the predicted change in the Fermi surface across the quantum critical point. In CeCu 5.9 Au 0.1 , an unexpectedly large positive MR has been found at low temperatures and in low fields; its origin is discussed in comparison with the Hall resistivity. For all the principal axes, the Au-substitution effect on TEP is minor in both magnitude and anisotropy down to ∼1.5 K, suggesting no essential change in the elect...

Substitution of Au or Hg into BaTl2 and BaIn2. New Ternary Examples of Smaller CeCu2‐Type Intermetallic Phases.

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The effect of Zn, Ag and Au substitution for Cu in Finemet on the crystallization and magnetic properties

Soft magnetic ribbons of Finemet compound with Zn, Ag and Au substituted for Cu: Fe 73.5Si 13.5B 9Nb 3Cu 1− x M x (M=Zn, Ag, Au; x=0.5, 1.0) have been fabricated by rapid quenching technique with wheel speeds of 10, 25 and 30 m/s, respectively. The crystallization evolution of samples examined by DSC measurements showed that the high cooling rates make the ribbons in amorphous state whereas the samples with M=Zn; x=0.5, 1.0 showed to be partly crystallized when they fabricated by the wheel speed of 10 m/s. In the case of Zn ( x=0.5, 1.0) and Ag ( x=1.0) substitution there is a sharp peak in the DSC curve corresponding to crystallization of α-Fe(Si) phase. However, the role of Au is similar to that of Cu. Hysteresis loops of as-cast samples exhibited square form which relates to the pinning centers in domain wall displacement. After appropriate annealing, the ultrasoft magnetic properties of studied ribbons are obtained.

Substitution of Au or Hg into BaTl2 and BaIn2. New Ternary Examples of Smaller CeCu2-Type Intermetallic Phases

The compounds BaAu(0.40(2))Tl(1.60(7)) (1), BaAu(0.36(4))In(1.64(4)) (2), and BaHg(0.92(2))In(1.08(2)) (3) have been prepared by high-temperature techniques. Single-crystal X-ray diffraction shows that these have the orthorhombic CeCu(2)-type structure, Imma, Z = 4 (a = 5.140(1), 5.104(1), 5.145(1) A; b = 8.317(2), 8.461(2), 8.373(2) A; c = 8.809(2), 8.580(2), 8.715(2) A, respectively). The structure consists of a four-linked honeycomblike polyanion (4(2)6(3)8) of infinity3[Tr2]2- (Tr = In or Tl) with encapsulated Ba2+ cations. The Au or Hg randomly replace Tr in a single type of site. The two gold phases exhibit appreciable nonstoichiometry ranges. Band calculations (EHTB) demonstrate that the three compounds are electron-poor and metallic, and the latter has been confirmed for 1 through resistivity and magnetic susceptibility measurements. The orthorhombic structure of 1 contrasts with the hexagonal structure of BaTl2 (CaIn2-type, P6(3)/mmc), a change that appears to be driven by substitution of the smaller Au atoms into the polyanion network. Relativistic effects for the heavier Au and Hg are evidently responsible for decreases in lattice parameters and bond lengths from BaIn2 to those in isostructural 2 and 3.

Effect of Minor Au Addition on Glass-Forming Ability and Mechanical Properties of Pd–Cu–Au–Si–P Alloys

The glass-forming ability (GFA), thermal stability and mechanical properties of bulk glassy Pd 79 Cu 6-x Au x Si 10 P 5 (x = 0-6 at%) alloys were studied. The results revealed that the minor substitution of Au for Cu strongly affects the thermal stability and GFA of Pd-Cu-Au-Si-P alloys. The alloy in which 2 at% Au was added to substitute Cu (Pd 79 Cu 4 Au 2 Si 10 P 5 ) exhibits the broadest supercooled liquid region (ΔT x = 80 K) and possesses the highest GFA among the alloys investigated. The critical diameter for glass formation of this alloy reaches ∼7 mm by copper mold casting. The GFA is dramatically reduced when the Au content is more than 5 at%, beyond which no bulk glasses could be formed. The Young's modulus, yield strength and maximum compressive strength of the best glass former (Pd 79 Cu 4 Au 2 Si 10 P 5 ) are 87 GPa, 1525 MPa and 1660 MPa, respectively, with a compressive plastic strain over 13%.

Structure analysis of Au-containing cuprate of Au 1+ xBa 2Ca 2Cu 3− xO 9 (Au-1223)

Single crystals of Au 1+ x Ba 2Ca 2Cu 3− x O 9 (Au-1223) were grown at 6 GPa and 1325 °C. This phase is the third member of the Au-containing cuprate family of AuBa 2Ca n−1 Cu n O 2 n+3 and shows a weak signal of superconductivity. The crystal structure was refined to R1 ( I>2 σ( I))=0.0188 and wR2=0.0485 with F 2 data. The Au-1223 phase crystallizes in the space group Pmmm (no. 47), a=3.8119(1) Å, b=3.8556(1) Å, c=15.4431(5) Å, Z=1. Partial substitution of Au for Cu in the CuO 2 planes was revealed. The Au incorporation to the conduction layers may be a reason for the suppression of superconductivity in Au-1223.

Stability of Supercooled Liquid and Transformation Behavior in Zr-Based Glassy Alloys

We investigated the stability of the supercooled liquid in Zr-based glassy alloys by examination of their transformation behavior. The primary phase is an fcc Zr2Ni phase in a Zr65Al7.5Ni10Cu17.5 glassy alloy with high glass-forming ability (GFA). By substitution of Ag, Pd, Au or Pt for only 1 at%Cu, an icosahedral quasicrystalline phase (I-phase) precipitates with the fcc Zr 2Ni phase. The primary phase changes to the single I-phase at higher noble metal contents. It is further found that the I-phase precipitates by a small amount of substitution for Cu with other elements as well as the noble metals, which have a weak or positive chemical affinity with one of the constitutional elements in the Zr‐Al‐Ni‐Cu glassy alloy. Thus, the slight deviation from the three component rules for high GFA is effective for the I-phase formation. The I-phase is also formed as a primary phase in the Zr65+y Al7.5Ni10Cu17.5−y (y = 1‐7) glassy alloys. A slight change in the composition has the similar effect as the addition of element such as noble metals and so on. An icosahedron is contained as a structure unit in the fcc Zr 2Ni and I-phases and hence the glassy structure is correlated with the local icosahedral atomic configuration. The high-resolution transmission electron microscopy image of the Zr70Al7.5Ni10Cu12.5 glassy alloy reveals a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists in the supercooled liquid as well as in the glassy phase and it stabilizes the supercooled liquid state in the Zr-based alloys. An I-phase also precipitates as a primary phase by substituting Pd, Au or Pt for only 1 at%Cu in the Zr70Cu30 glassy alloy. From these results, the appearance of the supercooled liquid region is attributed to the existence of the icosahedral atomic configuration consisting of Zr and Cu.

Low-temperature resistivity of YbCu5-xAuxunder magnetic fields

YbCu5 shows a typical heavy-fermion behaviour while YbCu4Auexhibits an antiferromagnetic transition below 1 K. We haveinvestigated the low-temperature electrical resistivity, ρ, ofthe pseudo-binary compound YbCu5-xAux (0⩽x⩽1.0) asfunctions of temperature (T) and magnetic field (H). Theρ(T) data indicate that the magnetic transition occurs for x = 1.0, 0.8, and 0.6 at Torder = 0.6, 0.4, 0.1 K, respectively,whereas magnetic ordering is absent for x⩽0.2 down to thelowest temperature. ρ(H) for x = 0, 0.1, and 0.2 measured at0.05 K shows a characteristic behaviour in the non-magneticKondo-lattice state. It has been found that the increase of the Auconcentration x results in a rapid decrease of the Kondotemperature, TK, as well as the evolution of impurity Kondobehaviour, destroying the Kondo-lattice state for x = 0. This mayimply that the Au substitution causes a significant change of thelocal electronic structures. ρ(T) for x = 0.6 varies nearlyas T3/2 at 0.5 T below 0.15 K, while it shows a T2-power lawat 1 T. This behaviour can be interpreted as the crossover caused bya magnetic field from a magnetic ordered state at zero field througha non-Fermi-liquid state to the Fermi-liquid state at high field.

STUDY OF THE ULTRA-LOW TEMPERATURE RESISTANCES OF HEAVY FERMION SYSTEM CeCu6-xNix

CeCu6 is one of heavy fermion materials. The effect of the partly substitution of Cu by Au, Ag, Pd and Pt on the low temperature properties has been intensively studied. In this paper, we study the temperature dependence of resistance of CeCu6-xNix(x=0.00, 0.05, 0.10, 0.15, 0.20) at temperatures below 1K. Experimental result shows that the temperature dependence of resistance changes with increase of doping content x. Below 500mK, the resistance of sample with x≈0.1 has a linear temperature dependence, showing a typical non-Fermi liquid behavior, while other samples behave as Fermi liquid. This means x≈0.1 is the critical doping for this system. In the case of Au substitution of Cu, the critical doping of which is also x=0.1, the ground state of the system is changed from Fermi-liquid to non-fermi liquid and antiferromagnetic ordering by volume expansion. But in the present case, the ground state of Ni doping systems changes from FL to NFL due to the magnetism of Ni.

Hall effect and thermoelectric power in CeCu 5.9Au 0.1 and CeCu 6

We have investigated the Hall coefficient ( R H) and thermoelectric power (TEP) on single crystals of CeCu 5.9Au 0.1, which shows non-Fermi liquid anomaly, and on CeCu 6 as a reference. TEP exhibits a large positive peak at ∼40 K, below which it becomes highly anisotropic. Au substitution causes no drastic change in TEP. The anisotropy in R H( T) is small above 10 K, and it showed a large dependence on the field direction in both compounds below 10 K. Most interesting aspect of the present results is the large anisotropy in the Au substitution effect on R H( T), which might correlate with the anisotropy in the spin fluctuation.

The Au-substituted Al - Cu - Fe icosahedral phase: evidence for bond hybridization

Au-substituted Al - Cu - Fe icosahedral phases, , were prepared by melt spinning. EDS data showed that Cu as well as Al atoms are effectively substituted for with Au. The hypercubic lattice parameter of as-quenched samples slowly increases with x, while phonon- and phason-type disorders are not affected by Au substitution. Experimental structure factors for `sum' lines were used to derive an average radius of the atomic hypersurfaces. Comparison of experimental versus calculated ratios of structure factors for different models yielded information about the Au distribution over the icosahedral sites. It was inferred that a fraction of the gold shapes its Al surrounding in a -type configuration. Evidence was found for d - sp hybridization of Au - Al bonds, on the basis of the `white-line' area at the Au absorption edge.

An AU at the first base pair of helix 3 elevates the catalytic activity of hepatitis delta virus ribozymes

A mutational analysis of the helix 3 (H3) region of hepatitis delta virus (HDV) ribozymes disclosed that an AU at the first base pair of H3 elevates the catalytic activity of various cis- and trans-acting HDV ribozymes. A GC to AU substitution at this position of H3, which is located at the junction of three of the four helices of the pseudoknot-like structure model, altered the structure of HDV ribozymes. This substitution in the H3 did not change the independence of the cleavage rate to pH nor the sensitivity to formamide treatment of the ribozymes.

Substitution experiments in U3Cu3Sn4 and U3Au3Sn4

The results of specific heat and magnetic measurements on samples of the solid solution series U3(Cu3Au1−x)3Sn4 with 0 ⩽ x ⩽ 1 are presented. For all samples, except U3Au3Sn4, the susceptibility shows a peak similar to that seen in antiferromagnets. U3Au3Sn4 shows no indication of a magnetic transition either in the specific heat or susceptibility data. Below 1 K c/T increases very rapidly, which is typical for heavy fermion systems. However, only the specific heat for U3Cu3Sn4 shows a sharp transition. Samples with Au substitution into the Cu sites in U3Cu3Sn4 exhibit no long range order in the specific heat. Even a small amount of Au (10%) destroys the peak in the specific heat of U3Cu3Sn4, due to antiferromagnetic order.

K18Tl20Au3, A Novel Derivative of K8Tl11 with the Unprecedented Polyanion Tl9Au29-, the Parent Tl117- and an Isolated Au- Ion

Attempts to derivatize the novel Tl{sub 11}{sup 7-} ions in K{sub 8}Tl{sub 11} by Au substitution leads to the formation of the title compound from direct reaction of the elements in Ta tubing at 500 and then 350{degrees}C. The crystal structure was established at room temperature by single crystal X-ray diffraction means (space group P{bar 6}m2, Z = 1, a = 10.880 (1), c = 14.552 (2) {angstrom}, R/R{sub w} = 3.8/4.0% for 52 variables and 703 independent reflections). The compound contains separate close-packed layers of Tl{sub 9}Au{sub 2} and Tl{sub 11} clusters, each with D{sub 3h} point symmetry, together with isolated Au atoms and 18 K atoms that sheath and separate the units. The gold-containing cluster can be derived directly from the pentacapped trigonal prismatic Tl{sub 11} through substitution on the two apical (axial) positions followed by a substantial axial compression to generate an Au-Au bond, d = 2.963 {angstrom}, this action causing the antisymmetric equivalent MO a{sub 2}{close_quotes} to become strongly antibonding and empty. The Tl{sub 9} portion of the cluster is otherwise slightly perturbed. EHMO calculations indicated closed shell configurations for Tl{sub 9}Au{sub 2}{sup 9-} and, as before, Tl{sub 11}{sup 7-}, leading to formulation of the compoundmore » as (K{sup +}){sub 18} (Tl{sub 9}Au{sub 2}{sup 9-})(Tl{sub 11}{sub 7-})(Au{sup -})e{sup -}. The phase is appropriately a metallic conductor (Q{sub 290} {approximately} 43 {mu}{Omega}{center_dot}cm) and Pauli-paramagnetic, although some localization below 100 K is suggested by its Curie-Weiss behavior.« less

Oxidation state and site selection of gold in (YBa2Cu3O7 ??)(1 ? x)Au x

Recent experiments on the effect of Au substitution on the superconductivity of YBa2Cu3O7 −δ (YBCO) have revealed that Au, unlike most other dopants, enhances the superconducting transition temperature, Tc, by ∼ 2 K at 10 mole % Au. In the present study. X-ray photoelectron spectra, nominally of 4, 6, 8 and 10 mole % Au-doped YBCO, have been obtained. The Au spectra display a relatively intense peak which is the oxidized component associated with the Au 4f7/2 core level, and an additional component that is most probably due to unreacted gold. The binding energy of the oxidized component is consistent with Au+. This observation, together with previous studies, leads us to postulate a structural model in which Au+ substitutes into a two-ligand c-axis co-ordinated Cu(1) site at a Ba-O (4) surface layer.

Stabilization of superconducting LnPt 2B 2C by partial substitution of gold for platinum

The quaternary intermetallic compounds LnPt 2B 2C (Ln=La, Pr and Y) were recently shown to be superconducting at temperatures up to 10.5 K. Annealing conditions were not found, however, which yielded single-phase material. Here it is reported that the partial substitution of Au for Pt in LnPt 2B 2C yields essentially single-phase polycrystalline material under annealing conditions readily accessible by conventional techniques. This is accomplished through arcmelting LnPt 1.5Au 0.6B 2C, a composition slightly superstoichiometric in transition metal, and annealing at 1100°C in Ta foil: a small amount of melt phase formed in the anneal is wicked away from the sample leaving good-quality material behind.

Atomic exchange and growth of Au on Ag(110)

Synchroton core-level photoemission and electron diffraction were used to study the room temperature growth of Au on Ag(110). Substitution of Au for Ag in the subsurface layer is found to be an important process for the initial adsorption and the subsequent multilayer growth. Our finding will be compared with two recent models: (1) a bilayer growth model based on an ion scattering study, and (2) a model of pure Au growth on a Ag/Au inverted layer based on a scanning tunneling microscopy study and a reinterpretation of the ion scattering data.

Atomic exchange and growth of Au on Ag(110)

Synchrotron core-level photoemission and electron diffraction were used to study the room temperature growth of Au on Ag(110). Substitution of Au for Ag in the subsurface layer is found to be an important process for the initial adsorption and the subsequent multilayer growth. Our finding will be compared with two recent models: (1) a bilayer growth model based on an ion scattering study, and (2) a model of pure Au growth on a Ag/Au inverted layer based on a scanning tunneling microscopy study and a reinterpretation of the ion scattering data.

Identification of a Protein Complex that Binds to a Dodecamer Sequence Found at the 3' Ends of Yeast Mitochondrial mRNAs

An activity from Saccharomyces cerevisiae mitochondria was identified that specifically bound to a 12-nucleotide sequence, AAUAA(U/C)AUUCUU, that is a site for processing of pre-mRNAs so as to generate the mature 3' ends of mRNAs. Because processing occurs 3' to the end of the dodecamer site, all mRNAs in yeast mitochondria terminate with that sequence. RNase T1 digestion fragments which terminated precisely at their 3' ends with the dodecamer sequence bound the activity, indicating that mRNAs in vivo would be capable of binding. Gel mobility shift analyses using RNA oligonucleotides showed that binding was reduced by a U-to-A substitution at position 3 of the dodecamer sequence; a C-to-A substitution at position 10 eliminated binding. UV cross-linking identified three polypeptides with approximate molecular masses of 19, 60, and 70 kDa as constituents of the binding activity. These estimates included the contribution of the 32P-labeled RNA oligonucleotide used to tag these polypeptides. An oligonucleotide with a UA-->AU substitution at positions 3 and 4 of the dodecamer site formed complexes deficient in the 19-kDa species, suggesting that binding specificity was inherent to the higher-molecular-weight polypeptides. Assembly of the complex at a dodecamer site on an RNA protected sequences located 5' to the dodecamer site from digestion by a nucleoside triphosphate-dependent 3' exoribonuclease found in yeast mitochondria. Since mitochondrial mRNAs terminate with an intact dodecamer sequence, the binding activity may function in the stabilization of mRNAs in addition to 3'-end formation of mRNAs.