Ag Te System Research Articles

Vapor–liquid–solid synthesis of Ag2Te using chemical vapor deposition method

Silver telluride, Ag2Te, has been selectively synthesized by conventional chemical vapor deposition (CVD) via the vapor–liquid–solid growth mechanism. The pre-deposited Ag film on the SiO2/Si substrate was chemically reacted with vaporized Te atoms and transformed into liquid-phase Ag–Te during the CVD process. The appropriate supply of Te vapor to the Ag film influenced the stoichiometry of Ag–Te compounds, and the formation of stoichiometric Ag–Te compounds was well-explained by the phase diagram of the Ag–Te system. We found that Ag2Te was grown in the liquid of Ag–Te under the Te-poor condition, while Ag5Te3 and Te were simultaneously solidified under the Te-rich condition. The high-temperature synthesis of Ag2Te showed higher crystallinity and better stoichiometry than the low-temperature synthesis. This study demonstrates that Ag2Te can be selectively synthesized by conventional CVD via delicate control over the phases of the complex Ag–Te system.

Tailoring atomic diffusion for in situ fabrication of different heterostructures

Atomic diffusion has been recognized as a particularly powerful tool in the synthesis of heterostructures. However, controlled atomic diffusion is very difficult to achieve in the fabrication of individual nanostructures. Here, an electrically driven in situ solid-solid diffusion reaction inside a TEM is reported for the controlled fabrication of two different hetero-nanostructures in the Ag-Te system. Remarkably, the morphology and structure of the as-formed heterostructures are strongly dependent on the path of atomic diffusion. Our experiments revealed that the surface diffusion of Te atoms to Ag nanowires leads to a core-shell structure, while the bulk diffusion of Ag atoms give rise to a Ag2Te-Te segmented heterostructure. Heat released by Joule heating caused the surface diffusion process to be replaced by bulk diffusion and thereby determined the structure of the final product. Our experimental results provide an insight into solid-state diffusion reactions under an electric field and also propose a new process for the fabrication of complex nanostructures.

Synthesis, X-ray data, and thermodynamic properties of the AgTe3 high-pressure phase in the Ag–Te system

Silver telluride, AgTe3, was synthesized in a high-pressure gas vessel at a temperature of 473 K and a hydrostatic pressure of pure Ag at 6500 bar. A Rietveld structure refinement of X-ray powder diffraction data has been performed. The structure has been refined in the trigonal space group, R3m(H), and has the following cell parameters: a = 8.653 Å, c = 5.278 Å, and V = 342.24 Å3. It was found that AgTe3 stored in a sealed container for three months partially decomposes into Ag5Te3 (stützite) and tellurium.The thermodynamic properties of AgTe3 have been determined for the first time. The electromotive force (EMF) method for a solid-state galvanic cell with RbAg4I5 solid electrolyte.(−) Pt | Ag | RbAg4I5 | AgTe3, Te | Pt (+).was used to study a virtual chemical reaction of silver telluride formation from the elements;Ag(s) + 3Te(s) = AgTe3(s)The measurements were carried out in the temperature range of 402–474 K and pressures of 3921–6169 bar. The standard Gibbs energy of AgTe3 formation and its standard thermodynamic properties and molar volume at 298 K and 1 bar (105 Pa) pressure were derived from the EMF measurements:ΔrG(T, p)/J mol−1 = (−21470 ± 3880) + (133.0 ± 62.5)∙T – (21.96 ± 8.82)∙Tln(T).– (0.178 ± 0.009)∙(p – 1).ΔfG° (298.15 K, 1 bar) = −19.12 ± 0.24 kJ/mol; ΔfH° (298.15 K, 1 bar) = −14.92 ± 1.25 kJ/mol.S° (298.15 K, 1 bar) = 205.8 ± 3.5 J/(mol K).V° (298.15 K, 1 bar) = 69.93 ± 0.09 cm3/mol.

Silver tellurides: Structural, elastic, and optical properties of AgTe and Ag2Te

In recent years, Ag-Te systems have attracted much attention because of their unique properties of relatively large magnetoresistance and high electrical conductivity. In this article, we consider stoichiometric and silver-excess phases of silver telluride and report the structural, elastic, electronic, and optical properties obtained with density functional theory. Orthorhombic AgTe and monoclinic Ag2Te exhibit nearly isotropic bulk and shear moduli, although the Young's modulus exhibits large anisotropy along crystalline axes. The calculated electronic properties show AgTe to be a direct band-gap semiconductor with high electron mobility and Ag2Te to be nearly metallic. A larger anisotropy in both the real and the imaginary part of the dielectric function is predicted for AgTe relative to Ag2Te, with the plasmon energies being 17.2 eV. The calculated results thus establish a structure-property relationship in defect-free silver tellurides.

An Ex-Post Analysis of Japanese AGT Systems

An Ex-Post Analysis of Japanese AGT Systems

A Chemical, High-Temperature Way to Ag1.9Te via Quasi-Topotactic Reaction of Stuetzite-type Ag1.54Te: Structural and Thermoelectric Properties.

Semiconducting silver tellurides gained reasonable interest in the past years due to its thermoelectric, magneto-caloric, and nonlinear optic properties. Nanostructuring has been frequently used to address quantum-confinement effects of minerals and synthetic compounds in the Ag-Te system. Here, we report on the structural, thermal, and thermoelectric properties of stuetzite-like Ag1.54Te (or Ag4.63Te3) and Ag1.9Te. By a quasi-topotactic reaction upon tellurium evaporation Ag1.54Te can be transferred to Ag1.9Te after heat treatment. Crystal structures, thermal and thermoelectric properties of stuetzite-like Ag1.54Te (or Ag4.63Te3) and Ag1.9Te were determined by ex situ and in situ experiments. This method represents an elegant chemical way to Ag1.9Te, which was so far only accessible electrochemically via electrochemical removal of silver from the mineral hessite (Ag2Te). The mixed conductors show reasonable high total electric conductivities, very low thermal conductivities, and large Seebeck coefficients, which result in a significant high thermoelectric figure of 0.57 at 680 K.

Banded sulfide-magnetite ores of Mauk copper massive sulfide deposit, Central Urals: Composition and genesis

The results of investigation of metamorphosed sulfide-magnetite ores from the Mauk deposit located within the Main Ural Fault at the junction of Tagil and Magnitogorsk massive sulfide zones are discussed. The ore-hosting sequence comprises metamorphic rocks formed from basalt, carbonaceous and carbonaceous-cherty siltstone, and lenticular serpentinized ultramafic bodies. The ores of the deposit are represented by banded varieties and less frequent breccia. The clastic origin of the banded ore is indicated by load casts at the bottom of sulfide beds, alternation of sulfide and barren beds, and the truncation of the growth zones of pyrite crystals. Pyrite, pyrrhotite, chalcopyrite, sphalerite, and magnetite are the major minerals of the banded ores. The internal structure of the listed minerals testifies to the deep metamorphic recrystallization of primary hydrothermal-sedimentary ores accompanied with deformation. Cubanite, pyrrhotite, mackinawite, greigite, and gold are enclosed in metacrysts of pyrite, magnetite, and chalcopyrite. The accessory minerals of the Pb-Bi-Te, Bi-Te, and Ag-Te systems as well as uraninite have been found at the Mauk deposit for the first time. Magnetite predominantly replaces pyrite and less frequently chalcopyrite, pyrrhotite, and gangue minerals. It was established that the major carriers of As and Co are crystals of metamorphic pyrite. Chalcopyrite is the major carrier of Zn, Sn, Te, Pb, Bi, and Ag. Admixture of Fe and Cu is typical of sphalerite, and Se and Ni are characteristic of pyrrhotite. Ti, V, Mn, Sb, As, Ba, and U are concentrated in magnetite. The banded ores of the Mauk deposit are suggested as having been transformed in several stages: diagenesis, anadiagenesis, epidiagenesis (t 500°C).

Effects of livestock exclusion and climate change on aboveground biomass accumulation in alpine pastures across the Northern Tibetan Plateau

To better understand the ecological and economic benefits of short-term grazing exclusion on the aboveground net primary productivity (ANPP) of alpine pastures, we conducted annual multi-site transect surveys in the summers from 2009 to 2011 and calculated the aboveground biomass discrepancy (ABD) between grazed and ungrazed pastures at plant community and economic group levels for three zonal alpine grassland types—meadow, steppe, and desert-steppe—across the northern Tibetan Plateau. Our results indicated that aboveground biomass (AGB) significantly differed among grassland types and declined northwesterly from 64.07 to 11.44 g m−2 with decreasing precipitation and increasing temperature. The mean ABD exhibited considerable community dependency, with meadow (12.47 g m−2) > steppe (6.91 g m−2) > desert steppe (2.54 g m−2), and it declined from 25.42 to 1.29 g m−2 with decreasing precipitation and increasing temperature. ‘Good forage’, i.e. grasses and sedges, benefited most from grazing exclusion, followed by edible forbs. With longer grazing exclusion durations (GEDs), the aboveground biomass of poisonous locoweeds initially decreased and then increased compared with the adjacent grazed sites. In the nested analysis of co-variances with a general linear model, growing season precipitation (GSP; from May to September) accounted for 52.67% of the observed variation in AGB, followed by AGT (9.77 %) and pasture management systems (PMSs; grazing or grazing-excluded, 5.31 %). The variation in ABD was explained primarily by AGT (16.52 %), GED (20.25 %), and the interaction of AGT × GED (19.58 %). Our results confirm that precipitation is the primary factor controlling the ANPP of alpine grasslands on the Northern Tibetan Plateau and that the ecological benefits arising from grazing exclusion are also partly dependent on grassland type and exclusion duration. Therefore, spatial and temporal variations in growing season precipitation and plant functional traits or economic group composition should be jointly considered when developing policies concerning the management and spatial layouts of grazing exclosures in this region.

Experimental thermodynamic study of intermetallic phases in the binary Ag–Te system by an improved EMF method

A thermodynamic study of the solid two-phase regions of the binary Ag–Te system was made by an improved EMF method, using fast ion conductor RbAg4I5 as the solid electrolyte. The EMF measurements were made on three galvanic cells: [Ag | RbAg4I5 | Ag5Te3 + Te], [Ag | RbAg4I5 | Ag5Te3 + Ag1.9Te] and [Ag | RbAg4I5 | Ag1.9Te + Ag2Te].Based on the results obtained, the EMF for each equilibrium phase assembly was expressed as a function of temperature, in the different regions of thermal stability of the substances. By using the observed EMF and temperature relations, the thermodynamic functions of the stoichiometric equilibrium phase assemblages: Ag5Te3–Te, Ag5Te3–Ag1.9Te, Ag5Te3–Ag2Te and Ag2Te–Ag1.9Te, in the low-temperature range 22–204 °C, as well as phase transformation temperatures, have been determined. Agreement between the results obtained and the literature values were established.

Molar Volume and Adiabatic Compressibility in the Molten Ag–Te System

Sound velocity and molar volume have been measured in the liquid Ag–Te system as a function of temperature and composition. Results obtained have been used to deduce the compressibility and thermal expansion coefficient. The molar volume and adiabatic compressibility show a distinct cusp at Ag 2 Te composition where the thermal expansion coefficient takes a minimum, which suggests the existence of stable ionic association in the liquid. Between Ag and Ag 2 Te the adiabatic compressibility for an alloy with a miscibility gap shows a logarithmic temperature dependence being characteristic of the critical behaviour associated with the two-melt phase separation. A very small two-melt region has been confirmed. Discussion has been made in comparison with the results for the isochemical system, Ag–Se.

Ionic Conduction in Liquid Ag–Se and Ag–Te Systems

The ionic conductivity in liquid Ag–Se and Ag–Te systems has been measured using a residual potential technique. The ionic conductivity in the liquid Ag–Se system exhibits a local maximum at the stoichiometric composition of Ag 2 Se. This maximum decreases rapidly with increasing temperature. The liquid Ag–Te system has also a higher value of the ionic conductivity around the composition of Ag 2 Te, but a clear maximum as in the case of Ag–Se system cannot be observed even at lower temperatures. This may be considered to reflect a higher Ag + mobility at Ag 2 Se just after melting. Such the difference of the ionic conduction near the melting point between both liquid systems, and in particular the unusual temperature dependence of ionic conductivity in the liquid Ag–Se system, could be due to the deference of the structural environment of Ag + in the system. The structural analysis of liquid Ag 2 Se and Ag 2 Te focusing on the environmental structure around Ag + has been made employing neutron structure f...

Comparison of Magnetic and Electrical Properties of Liquid Ag–Te and Ag–Se Alloys

Measurements of the magnetic susceptibility, electrical conductivity and thermo-electric power of liquid Ag–Te and Ag–Se alloys have been extended to the whole composition range. The susceptibility data of liquid Ag–Se alloys near the stoichiometry are very similar to those of liquid Ag–Te alloys. However, the composition dependence of conductivity for liquid Ag–Se and Ag–Te systems exhibits a sharp peak and a deep minimum at the stoichiometry, respectively. The thermopower data of liquid Ag–Te and Ag–Se alloys show a p - n transition at c =0.315 and 0.360, respectively. The conductivity and thermopower of liquid Ag–Se and Ag–Te alloys near the stoichiometry were analyzed by using the equations derived from the Kubo-Greenwood formula.

Silver as a dopant and as a constituent in AsAgTe glasses: electrical conductivity

Abstract Electrical conductivity data (from 200 to 360 K) on fifteen glass compositions of the AsAgTe system are reported and discussed. The glasses were prepared using a two-stage melt-quenching method. For the (As2Te3)1−xAgx glasses, features are seen in the electronic properties, corresponding to a change in the role of Ag from a dopant (for Ag ≤ 1 at.%), to a constituent (for Ag > 1 at.%.). At this composition, step-like changes occur, in the activation energy for electrical conductivity and in the pre-exponential factor. Examination of the data indicate that, as a dopant, Ag acts as neutral scattering centres for charge carriers. As a constituent, Ag enhances the hopping channel for conductivity near the valence band edge.

Structure of two liquid semiconductors Ag1-xSex and Ag0.67Te0.33

Neutron diffraction measurements have been carried out on Ag1-xSex and Ag0.67Te0.33 alloys to investigate possible structural causes for the differences in electrical transport properties observed in the two alloys. Ag1-xSex was measured for the compositions, x=0.30, 0.33 and 0.36, at temperatures just above the liquidus (1045, 915 and 855 degrees C, respectively), and for x=0.33 at three temperatures (915, 985 and 1045 degrees C). The Ag1-xTex system was measured at only one composition x=0.33, just above the liquidus (985 degrees C). At the level of the average correlation function, the behaviour of liquid Ag-Se shows no unusual dependence on either concentration or temperature, and the selenium and tellurium alloys show generally similar behaviour. There is no obvious structural connection with the anomalous concentration dependence of the electrical conductivity in Ag1-xSex alloys or with the different behaviour in both electronic and ionic conduction observed in the Ag-Se and Ag-Te systems.

A new phase in the TlAgTe system: crystal structure of Tl 4Ag 24− xTe 15− y

A new stable phase Tl 4Ag 24− x Te 15− y in the ternary TlAgTe system has been identified by X-ray diffraction on single crystals. The space group is P 6 and the lattice parameters are a = 1.1418(4) nm and c = 0.9220(1) nm with one formula per unit cell ( Z = 1). The structure is described as an arrangement of two types of channels parallel to the [001] direction. Two-thirds of these channels are hexagonal and built up with silver and tellurium atoms, hosting thallium atoms. One-third are octahedral chains of silver atoms with centres statistically occupied by tellurium atoms. In addition, the refinement indicates partial occupation of some silver positions.

A new phase in the TiAgTe system: crystal structure of Tl 2Ag 16Te 11

A new phase in the ternary Tl AgTe system has been identified. X-ray diffraction examination of single crystals was used to establish the crystal structure of Tl 2Ag 16Te 11+. The hexagonal space group is R3 c and the lattice parameters are a=1.1442(3) nm, c=4.1971(5) nm and Z=6. The structure is described as a three-dimensional array of large hexagonal channels of silver and tellurium atoms hosting linear chains of atoms. These channels are parallel to the crystallographic c axis. Each channel is built up with hexagonal prisms centred by thallium atoms and with tellurium-centred silver octahedra. The refinement indicates partial occupation of all silver positions.

A new phase in the TlAgTe system: crystal structure of Tl 4Ag 18Te 11

A new stable phase in the ternary TlAgTe system has been identified. X-ray diffraction examination of single crystals was used to establish the crystal structure of Tl 4Ag 18Te 11. The cubic space group is F 43m and the lattice parameter is a = 1.8717(8) nm, Z = 8. The relationship to the cubic BaHg 11-type structure and the In 2Te 3-type structure are established. The structure is described as a three-dimensional array of large channels of silver and tellurium atoms hosting linear chains of thallium atoms. These independent channels are built up with cubes and square antiprisms stacked along the fourfold axis and they are connected by smaller channels built up with smaller square antiprisms and cubes hosting tellurium atoms.

Electronic Properties of Liquid Ag–CuTe and Cu–AgTe Systems

Measurements of the electrical conductivity, magnetic susceptibility and thermoelectric power in both liquid Ag–CuTe and Cu–AgTe systems have been made over a wide composition range. Both systems show a marked minimum in electrical conductivity and a sharp maximum in diamagnetic susceptibility at the stoichiometric composition of AgCuTe, corresponding to the severe occurrence of electron localization. From the comparison of electronic properties between the related systems, it was made clear that the nonmetallic nature of Ag–Te bonds with partial ionicity plays a preferential role for the electron localization. On the other hand, the thermoelectric power in both systems gives a positive maximum near the composition of AgCuTe, which corresponds well to the anomalous composition dependence of the thermoelectric power found in the liquid Cu–Te system. This result seems to suggest that the functional form of the electron density of states near the Fermi level is similar between liquid AgCuTe and liquid Cu2Te. Further, these electronic properties were discussed in the light of the current strong scattering regime for electrons employed in liquid semiconductors.

Phase equilibria and crystal chemistry of silver-nickel-tellurium system

Ternary isotherm in the silver-nickel-tellurium system has been investigated using X-ray diffraction and metallographic techniques. At 873 K, only monoclinic Ag 2Te phase with a = 0.815 nm, b = 0.449 nm, c = 0.811 nm, and β = 112°60' is stable in the Ag-Te system. Existence of two phases viz., Ni 3Te 2 and NiTe 1+x has been established. NiTe 1+x phase has a large homogeneity range in the binary and ternary system. solid solubility of nickel in Ag 2Te as well of silver in Ni 3Te 2 is about 5 at.% at the temperature of investigation. The reasons for the large homogeneity range of NiTe 1+x in binary and ternary system has been discussed in detail.

ChemInform Abstract: Electronic and Thermodynamic Properties of the Liquid Tl ‐ AgTe System.

AbstractElectrical conductivity, magnetic susceptibility, and the thermoelectric power of the liquid Tl ‐ AgTe system have been measured as functions of temp. and composition.