Solubility and microstructure in the pseudo-binary PbTe-Ag2Te system

The solvus lines of the PbTe and Ag₂Te phases in the pseudo-binary PbTe-Ag₂Te system have been determined using diffusion couples and unidirectional solidification by the Bridgman method. The solubilities of both Ag₂Te in PbTe and PbTe in Ag₂Te decrease with decrease in temperature. For the former, this change is from 14.9 at% Ag (694 °C) to 0.5 at% Ag (375 °C), while for the latter it is from 12.4 at% Pb (650 °C) to 3.1 at% Pb (375 °C). The decrease in solubilities leads to the formation of precipitates of Ag₂Te in PbTe and PbTe in Ag₂Te. In particular, fast atomic diffusion in Ag₂Te results in the precipitation of PbTe even in quenched samples. From the temperature dependence of these solubilities, heats of solution have been determined. In the diffusion couple, the phase boundary moves toward PbTe. In the region between the phase boundary and the initial interface, PbTe transforms to β-Ag₂Te (cubic) retaining the cube-on-cube orientation relationship.     

The phase diagrams of Ag2XAgY (X = S,Se, Te; Y = Cl,Br, I): Mixtures and the structure of Ag5Te2Cl

The phase diagrams of Ag₂SAgI, Ag₂SeAgI, Ag₂TeAgI, Ag₂TeAgBr, and Ag₂TeAgCl were investigated. The system Ag₂S-AgI shows two broad regions of solid solution which are based on the structure of the high-temperature phases of the constituent compounds. The high-temperature modification of Ag₃SI is part of one of these regions. The system Ag₂SeAgI resembles the system Ag₂TeAgI; both contain limited regions of terminal solid solutions. The AgI-based solid solutions decompose peritectically. In the system Ag₂TeAgBr a compound Ag₃TeBr was found. Ag₃TeBr undergoes a phase transition at 590 ± 20 K. The low-temperature form has hexagonal symmetry with the lattice parameters a = 748.8(1) pm and c = 4357.6(6) pm. The compound Ag₅Te₂Cl was found in the Ag₂TeAgCl system. In both systems a restricted terminal solid solution, based on the high-temperature form of Ag₂Te, was observed. Ag₅Te₂Cl has a reversible phase transformation at 329 ± 3 K with ΔH_tr = 9.82 ± 0.4 kJ mole^?1. β-Ag₅TeCl, the low-temperature form probably has the space group $\text{P2}{}_{\mathrm{<mtext>1</mtext><mtext>n</mtext>}}\text{, a = 1365.5(1), b = 1386.1(1), c = 764.23(2)}$, β = 90.201(1)°, and Z = 4, α-Ag₅Te₂Cl has the space group $\text{I4}{}_{\mathrm{mcm}}$ with a = 975.5(3), c = 783.0(1) pm, and Z = 4. The anion sublattice is built of octahedra, which share all their vertices with neighboring octahedra. The Ag⁺ ions are distributed over octahedral holes of this network. The phase is similar in behavior to Ag₈GeTe₆ and may be a silver-ion conductor.     

Synthesis and complexation of a new facultative tridentate S2Te donor ligand MeS(CH2)3Te(CH2)3SMe: crystal structures of [Rh(Cp*)(S2Te)][PF6]2 and [PtCl(S2Te)]PF6

The syntheses and spectroscopic characterisation of the new facultative tridentate tellurium containing ligands MeS(CH₂)₃Te(CH₂)₃SMe (S₂Te) and H₂N(CH₂)₃Te(CH₂)₃NH₂ are described. The complexes of the former, fac-[Mn(CO)₃(S₂Te)]CF₃SO₃, [Rh(Cp*)(S₂Te)][PF₆]₂, [MCl(S₂Te)]PF₆ (M=Pd or Pt), [Cu(S₂Te)]BF₄ and [Ag(S₂Te)]CF₃SO₃ have been prepared and characterised by analysis, IR, ¹H-, ¹³C{¹H}-, ¹²⁵Te- and ¹⁹⁵Pt-NMR spectroscopy and mass spectrometry. The X-ray crystal structures of [Rh(Cp*)(S₂Te)][PF₆]₂ and [PtCl(S₂Te)]PF₆ are described. The results are compared with those obtained from complexes of the related tridentates Te{(CH₂)₃TeR}₂, Se{(CH₂)₃SeMe}₂ and S{(CH₂)₃SR}₂.     

The enthalpies of formation of XeF6(c), XeF4(c), XeF2(c), and PF3(g)

The energies of reaction of XeF₆(c), XeF₄(c), and XeF₂(c) with PF₃(g) were measured in a bomb calorimeter. These results were combined with the enthalpy of fluorination of PF₃(g), which was redetermined to be −(151.98 ± 0.07) kcal_th mol⁻¹, to derive (at 298.15 K) ΔH_f^o(XeF₆, c, I) = −(80.82 ± 0.53) kcal_th mol⁻¹, ΔH_f^o(XeF₄, c) = −(63.84 ± 0.21) kcal_th mol⁻¹, and ΔH_f^o(XeF₂, c) = −(38.90 ± 0.21) kcal_th mol⁻¹. The enthalpies of formation of the solid xenon fluorides were combined with reported enthalpies of sublimation to derive (at 298.15 K) ΔH_f^o(XeF₆, g) = −(66.69 ± 0.61) kcal_th mol⁻¹, ΔH_f^o(XeF₄, g) = −(49.28 ± 0.22) kcal_th mol⁻¹, and ΔH_f^o(XeF₂, g) = −(25.58 ± 0.21) kcal_th mol⁻¹. The average bond dissociation enthalpies,〈D^o〉(XeF, 298.15 K), are (29.94 ± 0.16), (31.15 ± 0.13), and (31.62 ± 0.16) kcal_th mol⁻¹ in XeF₆(g), XeF₄(g), and XeF₂(g), respectively. The enthalpy of formation of PF₃(g) was determined to be −(228.8 ± 0.3) kcal_th mol⁻¹.     

Phase equilibria in the Ag2Te-PbTe-Bi2Te3 system

Phase equilibria in the Ag₂Te-PbTe-Bi₂Te₃ quasi-ternary system were studied by differential thermal analysis, X-ray powder diffraction, and measurements of microhardness and emf of concentration circuits with an Ag₄RbI₅ solid electrolyte. Some polythermal sections and isothermal (600 and 800 K) sections of the phase diagram, and also a projection of the liquidus surface were constructed. The primary crystallization fields of phases were determined, and the types and coordinates of invariant and monovariant equilibria were found. The system is characterized by the formation of a wide continuous band of high-temperature solid solutions (γ phase) with a cubic structure along the PbTe-AgBiTe₂ section. With decreasing temperature (T ≤ 715 K), AgBiTe₂ and γ solid solutions, close in composition to this compound, experience solid-phase decomposition to form Bi₂Te₃, ternary tetradymite-like phases of the PbTe-Bi₂Te₃ boundary system, and the low-temperature phase of Ag₂Te.     

Simple synthesis of ultra-long Ag2Te nanowires through solvothermal co-reduction method

Ultra-long single crystal β-Ag₂Te nanowires with the diameter of about 300 nm were fabricated through a solvothermal route in ethylene glycol (EG) system without any template. The long single crystal wires were curves, with high purity, well-crystallized, and dislocation-free and characterized by using X-ray powder diffraction (XRD), Differential scanning calorimetry (DSC) analysis, X-ray photoelectron spectroscope (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission microscopy (HRTEM). The detailed topotactic transformation process from particles into single crystal wires was studied. Furthermore, the electrical conductivity and Seebeck coefficient have been systematically studied between 300 and 600 K.     

Silver Halide and Silver Chalcogenide Systems. IV. Excess enthalpies of the liquid mixtures of AgCl + Ag2Se,Agl + Ag2Se,AgCl + Ag2Te,AgBr + Ag2Te,and Agl + Ag2Te

The integral enthalpies of mixing of the liquid mixtures AgCl + Ag₂Se, AgI + Ag₂Se, AgCl + Ag₂Te, AgBr + Ag₂Te and AgI + Ag₂Te were determined in an isoperibolic calorimeter. The systems have endothermic effects which can be explained by a misfit energy, due to the substitution of ions of different size in the polymeric network of these melts.     

Thermoelectric properties of p-type pseudo-binary (Ag0.365Sb0.558Te)x-(Bi0.5Sb1.5Te3)1−x (x=0-1.0) alloys prepared by spark plasma sintering

In this paper, pseudo-binary (Ag_0.365Sb_0.558Te)_x-(Bi_0.5Sb_1.5Te₃)_1−x (x=0-1.0) alloys were prepared using spark plasma sintering technique, and the composition-dependent thermoelectric properties were evaluated. Electrical conductivities range from 7.9×10⁴ to 15.6×10⁴ Ω⁻¹ m⁻¹ at temperatures of 507 and 318 K, respectively, being about 3.0 and 8.5 times those of Bi_0.5Sb_1.5Te₃ alloy at the corresponding temperatures. The optimal dimensionless figure of merit (ZT) of the sample with molar fraction x=0.025 reaches 1.1 at 478 K, whereas that of the ternary Bi_0.5Sb_1.5Te₃ alloy is 0.58 near room temperature. The results also reveal that a direct introduction of Ag_0.365Sb_0.558Te in the Bi-Sb-Te system is much more effective to the property improvement than naturally precipitated Ag_0.365Sb_0.558Te in the Ag-doped Ag-Bi-Sb-Te system.     

Etude radiocristallographique et calorimetrique des transitions de phase de Ag8GeTe6

Powder and single crystals of the Ag₈GeTe₆ phase have been prepared by direct synthesis and chemical vapor transport reaction (iodine), respectively. The low-temperature phase of this material has been investigated by differential scanning calorimetry analysis and X-ray diffraction. The phase transitions are interpreted as a result of low-temperature ordering of the Ag⁺ ions.     

Syntheses, structures, and properties of Ag4(Mo2O5)(SeO4)2(SeO3) and Ag2(MoO3)3SeO3

Ag₄(Mo₂O₅)(SeO₄)₂(SeO₃) has been synthesized by reacting AgNO₃, MoO₃, and selenic acid under mild hydrothermal conditions. The structure of this compound consists of cis-MoO₂²⁺ molybdenyl units that are bridged to neighboring molybdenyl moieties by selenate anions and by a bridging oxo anion. These dimeric units are joined by selenite anions to yield zigzag one-dimensional chains that extended down the c-axis. Individual chains are polar with the C₂ distortion of the Mo(VI) octahedra aligning on one side of each chain. However, the overall structure is centrosymmetric because neighboring chains have opposite alignment of the C₂ distortion. Upon heating Ag₄(Mo₂O₅)(SeO₄)₂(SeO₃) looses SeO₂ in two distinct steps to yield Ag₂MoO₄. Crystallographic data: (193 K; MoKα, λ=0.71073 Å): orthorhombic, space group Pbcm, a=5.6557(3), b=15.8904(7), c=15.7938(7) Å, V=1419.41(12), Z=4, R(F)=2.72% for 121 parameters with 1829 reflections with I>2σ(I). Ag₂(MoO₃)₃SeO₃ was synthesized by reacting AgNO₃ with MoO₃, SeO₂, and HF under hydrothermal conditions. The structure of Ag₂(MoO₃)₃SeO₃ consists of three crystallographically unique Mo(VI) centers that are in 2+2+2 coordination environments with two long, two intermediate, and two short bonds. These MoO₆ units are connected to form a molybdenyl ribbon that extends along the c-axis. These ribbons are further connected together through tridentate selenite anions to form two-dimensional layers in the [bc] plane. Crystallographic data: (193 K; MoKα, λ=0.71073 Å): monoclinic, space group P2₁/n, a=7.7034(5), b=11.1485(8), c=12.7500(9) Å, β=105.018(1) V=1002.7(2), Z=4, R(F)=3.45% for 164 parameters with 2454 reflections with I>2σ(I). Ag₂(MoO₃)₃SeO₃ decomposes to Ag₂Mo₃O₁₀ on heating above 550 °C.     

Anti-fungal activity of SiO2/Ag2S nanocomposites against Aspergillus niger

Submicron particles of amorphous SiO₂ have been used to grow Ag₂S nanophases at their surfaces. SEM and TEM analysis showed morphological well-defined nanocomposite particles consisting of Ag₂S nanocrystals dispersed over the silica surfaces. These SiO₂/Ag₂S nanocomposites were investigated as anti-fungal agents against Aspergillus niger in different experimental conditions, including as nanofillers in cellulosic fibres. The anti-fungal activity in these composite systems is suggested to result from a synergistic effect due to Ag₂S anti-fungal centres and the SiO₂ surfaces in promoting the adsorption of the fungus.     

A Novel Ag3PO4/Ag/Ag2Mo2O7 Nanowire Photocatalyst: Ternary Nanocomposite for Enhanced Photocatalytic Activity

Ag₃PO₄/Ag/Ag₂Mo₂O₇ composite photocatalyst was successfully prepared via an in situ precipitation method. The as-prepared Ag₃PO₄/Ag/Ag₂Mo₂O₇ nanocomposite included Ag₃PO₄ nanoparticles (NPs) as well as Ag NPs assembling on the surface of Ag₂Mo₂O₇ nanowires. Under visible light irradiation (λ > 420 nm), the Ag₃PO₄/Ag/Ag₂Mo₂O₇ composite degraded rhodamine B (Rh B) efficiently and showed much higher photocatalytic efficiency than pure Ag₃PO₄, Ag₂Mo₂O₇, or Ag₃PO₄/Ag₂Mo₂O₇. It was elucidated that the excellent photocatalytic performance of Ag₃PO₄/Ag/Ag₂Mo₂O₇ for the degradation of Rh B under visible light could be ascribed to the high specific surface area, the extended absorption in the visible light region resulting from the Ag₃PO₄/Ag loading, and the efficient separation of photogenerated electrons and holes through the ternary heterostrucure composed of Ag₃PO₄, Ag and Ag₂Mo₂O₇.     

Ag2S/Ag3PO4/Ni复合薄膜的制备及其光催化性能

采用电化学方法制备Ag₂S/Ag₃PO₄/Ni复合薄膜,以扫描电子显微镜（SEM）、X射线衍射（XRD）、紫外-可见漫反射光谱（UV-Vis DRS）对薄膜的表面形貌、晶相结构、光谱特性及能带结构进行了表征,以罗丹明B为模拟污染物对薄膜的光催化活性和稳定性进行了测定,采用向溶液中加入活性物种捕获剂的方法对薄膜的光催化机理进行了探索。结果表明：最佳工艺制备的Ag₂S/Ag₃PO₄/Ni是由均匀的球形纳米颗粒构成的薄膜,其光催化活性明显优于纯Ag₃PO₄/Ni薄膜和纯Ag₂S/Ni薄膜,且在保持薄膜光催化活性基本不变的前提下可循环使用6次。提出了可见光下Ag₂S/Ag₃PO₄/Ni复合薄膜光催化降解罗丹明B的反应机理。     

Ag2S/Ag3PO4/Ni复合薄膜的制备及其光催化性能

采用电化学方法制备Ag_2S/Ag_3PO_4/Ni复合薄膜,以扫描电子显微镜(SEM)、X射线衍射(XRD)、紫外-可见漫反射光谱(UVVis DRS)对薄膜的表面形貌、晶相结构、光谱特性及能带结构进行了表征,以罗丹明B为模拟污染物对薄膜的光催化活性和稳定性进行了测定,采用向溶液中加入活性物种捕获剂的方法对薄膜的光催化机理进行了探索。结果表明:最佳工艺制备的Ag_2S/Ag_3PO_4/Ni是由均匀的球形纳米颗粒构成的薄膜,其光催化活性明显优于纯Ag_3PO_4/Ni薄膜和纯Ag_2S/Ni薄膜,且在保持薄膜光催化活性基本不变的前提下可循环使用6次。提出了可见光下Ag_2S/Ag_3PO_4/Ni复合薄膜光催化降解罗丹明B的反应机理。     

Ag3PO4/Ag2S/g-C3N4复合光催化剂的制备与性能

通过沉积法和离子交换法成功地制备了Ag_3PO_4/Ag_2S/g-C_3N_4复合型光催化剂。利用X射线多晶粉末衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、N_2吸附-脱附等温线、紫外-可见漫反射光谱、荧光光谱等手段对样品进行了表征。通过降解罗丹明B考察其可见光催化活性及稳定性,研究了硫化钠与磷酸银物质的量的比值(n_(Na_2S)/n_(Ag_3PO_4))、g-C_3N_4添加量对所制备复合光催化材料性能的影响,同时对光催化机理进行了探讨。结果表明,随着n_(Na2S)/n_(Ag3PO4)的增加,所得复合催化材料活性先增加后降低;当n_(Na2S)/n_(Ag_3PO_4)为1.5%、g-C_3N_4与Ag_3PO_4的质量比为3∶7时制备的催化剂ASC1.5的光催化活性最好,在可见光照射下,40 min内可将罗丹明B完全降解,且5次循环使用后仍保持较高的催化活性。和Ag_3PO_4相比,Ag_3PO_4/Ag_2S/g-C_3N_4复合型光催化材料的活性与稳定性都得到明显提高,这主要归因于复合催化剂比表面积和孔结构的增加,载流子分离效率的提高。光催化机理研究表明,空穴(h~+)、超氧阴离子自由基(·O~(2-))和羟基自由基(·OH)都是光催化过程中的主要活性物种。三者作用大小依次为:h~+·O~(2-)·OH。     

Neue Silber‐Tellurid Cluster stabilisiert mit zweizähnigen Phosphanen: Synthese und Struktur von {[Ag5(TePh)6(Ph2P(CH2)2PPh3)](Ph2P(CH2)2PPh2)}∞, [Ag18Te(TePh)15(Ph2P(CH2)3PPh2)3Cl] und [Ag38Te13(TetBu)12(Ph2P(CH2)2PPh2)3]

Novel Silver‐Telluride Clusters Stabilised with Bidentate Phosphine Ligands: Synthesis and Structure of {[Ag₅(TePh)₆(Ph₂P(CH₂)₂PPh₃)](Ph₂P(CH₂)₂PPh₂)}_∞, [Ag₁₈Te(TePh)₁₅(Ph₂P(CH₂)₃PPh₂)₃Cl], and [Ag₃₈Te₁₃(Te t Bu)₁₂(Ph₂P(CH₂)₂PPh₂)₃] Bidentate phosphine ligands have been found effective to stabilise polynuclear cores containing silver and chalcogenide ligands. They can act as intra and intermolecular bridges between the silver centres. The clusters {[Ag₅(TePh)₆(Ph₂P(CH₂)₂PPh₃)](Ph₂P(CH₂)₂PPh₂)}_∞ ( 1 ), [Ag₁₈Te(TePh)₁₅(Ph₂P(CH₂)₃PPh₂)₃Cl] ( 2 ), and [Ag₃₈Te₁₃(TetBu)₁₂(Ph₂P(CH₂)₂PPh₂)₃] ( 3 ) have been prepared and their molecular structure determined. Compound 2 and 3 are molecular structures with separated cluster cores while 1 forms a polymeric chain bridged by phosphine ligands. ( 1 : space group P2₁/c (No. 14), Z = 4, a = 3518,1(7) pm, b = 2260,6(5) pm, c = 3522,1(7) pm, β = 119,19(3)°; 2 : space group R3 (No. 148), Z = 6, a = b = 3059,4(4) pm, c = 5278,8(9) pm; 3: space group Pccn (No. 56), Z = 4, a = 3613,0(9) pm, b = 3608,6(7) pm, c = 2153,5(8) pm)     

Infrared spectra of Ag2BrNO3 and Ag2ClNO3

The infrared spectra of Ag₂BrNO₃ and Ag₂ClNO₃ are reported. Vibration assignments are proposed on the basis of the group theoretical analysis and D_2h symmetry. Factor group, site and TO-LO splittings are observed. The internal and external mode frequencies are correlated with those of AgNO₃ and KNO₃(II).     

High-pressure dissociation of silver mercury iodide, Ag2HgI4

High-pressure X-ray diffraction has been used to probe the behavior of the superionic conductor silver mercury iodide (Ag₂HgI₄) at pressures up to 5 GPa and at temperatures from 295 to 370 K. Significant changes in the diffraction spectra, indicative of structural transitions, are observed around 0.7 and 1.3 GPa across the range of temperatures studied. The change at 0.7 GPa is shown to correspond to the dissociation of silver mercury iodide into silver iodide and mercury iodide, i.e., Ag₂HgI₄→2AgI+HgI₂. The second transition, at 1.3 GPa, is due to a structural phase transition within HgI₂. Rietveld analysis of the diffraction data is used to confirm and refine all the known crystal structures.     

Synthesis and structure of tetrakis(phenylenethiourea)tellurium(II) chloride dihydrochloride,C28H26N8S4Cl4Te

Reaction of tellurium(IV) with excess phenylenethiourea(2-mercaptobenzimidazole) in aqueous methanolic hydrochloric acid leads to the formation of Te(II) complex, tetrakis(phenylenethiourea)tellurium(II) chloride dihydrochloride. The characterisation and crystal structure of the complex are reported. The crystals are monoclinic, space group P2₁/c, a = 13.939(5), b = 26.523(9), c = 4.873(2) Å, β = 100.29(4)°, V = 1772.6 ų, M = 872.4, D_c = 1.651 g cm^?3, Z = 2, F(000) = 868, μ(MoK_α) = 1.298 mm^?1. Final R = 0.055 and R_W = 0.056 for 918 independent reflections. The tellurium atom in the molecule lies at the crystallographic centre of symmetry and is bonded to four phenylenethiourea sulphur atoms in a square planar arrangement with TeS(1) = 2.678(6), TeS(2) = 2.674(5) Å and S(1)TeS(2) is 90.5(3)°. The ligand behaves as a thione. Chlorine atoms remain outside the coordination sphere of the Te and stabilise the packing arrangement in the unit cell through hydrogen bondings to nitrogen atoms.     

Preparation and chemistry of cis- and trans- F4Te(OH)2

Trans-tetrafluoro-orthotelluric acid (mp. 118°) is formed from orthotelluric acid and aqueous HF. Cis-tetrafluoro-orthotelluric acid (mp. 160°) is the only product of the hydrolysis of pentafluoro-orthotelluric acid. With the above compounds as starting materials the stereochemistry of the hydrolysis of TeF₆ can be followed up closely. Interaction of cis- and trans-F₄Te(OH)₂ with CH₂N₂ leads to cis- and trans-F₄Te(OCH₃)₂ and cis- and trans-CH₃OTeF₂OH. Differences in chemical reactivity of these compounds are presented.