Electrical conductivity of the systems (Rb4−xMx)Cu16I7Cl13 (M=K,Cs), Rb4Cu16(I7−xBrx)Cl13 and Rb4Cu16I7(Cl13−xBrx)

The solid solution ranges in the systems (Rb_4?xK_x)Cu₁₆I₇Cl₁₃, (Rb_4?xCs_x)Cu₁₆I₇Cl₁₃, Rb₄Cu₁₆(I_7?xBr_x)Cl₁₃, and Rb₄Cu₁₆I₇(Cl_13?xBr_x), have been examined and the electrical conductivity has been measured as a function of temperature and composition. In the system (Rb_4?xK_x)Cu₁₆I₇Cl₁₃, room temperature conductivities increase from 0.32Scm^?1 for x=0 to 0.47Scm^?1 for x=0.40. On the other hand, the conductivities of the systems (Rb_4?xCs_x)Cu₁₆I₇Cl₁₃ and Rb₄Cu₁₆I₇(Cl_13?xBr_x) decrease with increasing x. The system Rb₄Cu₁₆(I_7?xBr_x)Cl₁₃ shows no significant change of the conductivity on x.     

Spectroscopic ellipsometry study of Cu2ZnGeSe4 and Cu2ZnSiSe4 poly-crystals

We report the room temperature spectroscopic ellipsometry study of Cu₂ZnGeSe₄ and Cu₂ZnSiSe₄ crystals, grown by modified Bridgman technique. Optical measurements were performed in the range 1.2–4.6 eV. The spectral dependence of the complex pseudodielectric functions as well as pseudo- complex refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity of Cu₂ZnGeSe₄ and Cu₂ZnSiSe₄ crystals were derived. The observed structures in the optical spectra were analyzed by Adachi's model and attributed to the band edge transitions and higher lying interband transitions. The parameters such as strength, threshold energy, and broadening, corresponding to the E₀, E_1A and E_1B interband transitions, have been determined using the simulated annealing algorithm.     

Effect of heating process on fracture behaviors of Wf/Cu82Al10Fe4Ni4 composites

W_f/Cu₈₂Al₁₀Fe₄Ni₄(30) composites and W_f/Cu₈₂Al₁₀Fe₄Ni₄(60) composites were prepared by penetrating casting method. Three-point bending test and dynamic compression test showed that W_f/Cu₈₂Al₁₀Fe₄Ni₄(30) composites possessed higher mechanical properties than W_f/Cu₈₂Al₁₀Fe₄Ni₄(60) composites. Microstructure observation of W_f/Cu₈₂Al₁₀Fe₄Ni₄(30) composites revealed that a small amount of tungsten diffused into the Fe–Ni solid solution precipitated on the surface of tungsten fibers. The damage occurred mainly within the tungsten fibers after three-point bending test and dynamic compression test in W_f/Cu₈₂Al₁₀Fe₄Ni₄(30) composites, indicating that the composites possessed high interface strength. Dislocation density was high and stacking faults emerged in W_f/Cu₈₂Al₁₀Fe₄Ni₄(30) composites after dynamic compression. Microstructure observation of W_f/Cu₈₂Al₁₀Fe₄Ni₄(60) composites revealed that long strip of tungsten grains occurred at the edge of tungsten fibers, within which damage mainly emerged after three-point bending test, indicating that strength of the edge of tungsten fibers was low in W_f/Cu₈₂Al₁₀Fe₄Ni₄(60) composites. The fibrous structure of tungsten fiber was coarse or even disappeared in some areas, and dislocation density was low in W_f/Cu₈₂Al₁₀Fe₄Ni₄(60) composites after dynamic compression.     

Structures cristallines de Sc3Cu4Ge4, T.R.3Cu4Sn4 (T.R. = Y,Gd, Tb,Dy, Ho,Er), isotypes de Gd3Cu4Ge4, et de la phase apparentee Tm3Cu4Sn4

Tm₃Cu₄Sn₄ has been studied by single - crystal X - ray diffraction analysis. The structure is of a new type with space group C2/m and Z = 2:a = 16.119(2), b = 4.3935(6), $\text{c}\text{= 6.896(1)}\text{A}\text{?}$, β = 115.88(2)°, D_x = 9.32 Mgm^?3, μ(MoKα) = 52 mm^?1, F(000) = 1045, R = 0.056 for 558 independant reflexions (R_w = 0.058). Tm₃Cu₄Sn₄ is a monoclinic distorded variety of the Gd₃Cu₄Ge₄ structure type. Seven other compounds were characterized: Sc₃Cu₄Ge₄ and R. E₃Cu₄Sn₄ where R.E. = Y, Gd, Tb, Dy, Ho, Er, isostructural with Gd₃Cu₄Sn₄.     

High pressure synthesis of Cu2GeO4 with hausmannite structure

Copper(II)metagermanate, CuGeO₃, decomposes at high pressure to rutile-type GeO₂ and Cu₂GeO₄. Very small single crystals of Cu₂GeO₄ can be obtained by direct high pressure synthesis from CuOGeO₂ mixtures. The compound has a distorted spinel structure (Hausmannite structure, space group $\text{I}\text{4}{}_1\text{amd}$) with $\text{a}\text{= 5.593}\text{A}\text{?}$, $\text{c}\text{= 9.396}\text{A}\text{?}$, Z = 4.     

Multi-stage evaporation of Cu2ZnSnS4 thin films

Multi-stage evaporation is a well-established method for the controlled growth of chalcopyrite thin films. To apply this technique to the deposition of Cu₂ZnSnS₄ thin films we investigated two different stage sequences: (A) using Cu₂SnS₃ as precursor to react with Zn-S and (B) using ZnS as precursor to react with Cu-Sn-S. Both Cu₂SnS₃ and ZnS are structurally related to Cu₂ZnSnS₄. In case (A) the formation of copper tin sulphide in the first stage was realized by depositing Mo/SnS_x/CuS (1 < x < 2) and subsequent annealing. In the second stage ZnS was evaporated in excess at different substrate temperatures. We assign a significant drop of ZnS incorporation at elevated temperatures to a decrease of ZnS surface adhesion, which indicates a self-limited process with solely reactive adsorption of ZnS at high temperatures. In case (B) firstly ZnS was deposited at a substrate temperature of 150 °C. In the second stage Cu, Sn and S were evaporated simultaneously at varying substrate temperatures. At temperatures above 400 °C we find a strong decrease of Sn-incorporation and also a Zn-loss in the layers. The re-evaporation of elemental Zn has to be assumed. XRD measurements after KCN-etch on the layers prepared at 380 °C show for both sample types clearly kesterite, though an additional share of ZnS and Cu₂SnS₃ can not be excluded. SEM micrographs reveal that films of sample type B are denser and have larger crystallites than for sample type A, where the porous morphology of the tin sulphide precursor is still observable. Solar cells of these absorbers reached conversion efficiencies of 1.1% and open circuit voltages of up to 500 mV.     

New compounds Cu2MnTi3S8 and Cu2NiTi3S8 with thiospinel structure

Cu₂MnTi₃S₈ and Cu₂NiTi₃S₈ compounds were prepared by high-temperature synthesis. The crystal structure of these quaternary phases was investigated by X-ray powder diffraction. The compounds are described in the thiospinel structure (space group ) with the lattice constants a = 1.00353(1) nm (Cu₂MnTi₃S₈) and a = 0.99716(1) nm (Cu₂NiTi₃S₈). The atomic parameters were calculated in anisotropic approximation (R_I = 0.0456 and R_I = 0.0520 for Cu₂MnTi₃S₈ and Cu₂NiTi₃S₈, respectively).     

Synthesis and characterization of novel nanostructured fishbone-like Cu(OH)2 and CuO from Cu4SO4(OH)6

The Cu₄SO₄(OH)₆ was synthesized by a simple hydrothermal reaction with a yield of ~ 90%. Using Cu₄SO₄(OH)₆ as the starting material, novel fishbone-like Cu(OH)₂ was produced by a direct reaction of Cu₄SO₄(OH)₆ with NaOH solution. The Cu(OH)₂ consists of many needle-like nanorods parallel to each other and perpendicular to the direction of backbone, forming fishbone-like structure. Using the fishbone-like Cu(OH)₂ as the sacrificial precursor, CuO with similar size and morphology was obtained through a simple heat treatment. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, X-ray photoelectron spectroscopy, BET nitrogen adsorption, and UV-Vis absorption spectroscopy were employed to characterize the as-prepared samples. The conversion of the Cu₄SO₄(OH)₆ to the fishbone-like Cu(OH)₂ was visualized by time-dependent SEM images. A mechanism was also proposed based on the observed results.     

Silver alkali halide glasses and a vitreous analog of the RbAg4I5 superionic conductor

We report the existence of silver halide-rich glasses of a type not previously recognized. These contain only monovalent halides and represent perhaps the simplest ionic glasses yet realized. Despite the lack of the usual oxyanion matrix the new glasses show room temperature conductances which equal or exceed those of the best Ag⁺ glasses yet reported. Cu⁺ analogues have also been prepared. At the high conducting extreme apparently lies a vitreous state analog of the well-known crystalline conductor RbAg₄I₅. A crystalline analog of the latter FIC, CsAg₄ (I_0.45Cl_0.55)₅ forms metastably on careful devitrification of the glass. Like its prototype, it has a very high conductivity and exhibits a sharp C_p anomaly at low temperatures, ?77°C, in the vicinity of which the activation energy for conductance changes abruptly.     

Effect of addition of aluminum on the evolution of microstructure in HITPERM class Fe44Co44Zr7B4Cu1 alloy

The paper reports the effect of the addition of small amount of Al on the microstructure and properties of HITPERM class rapidly solidified Fe₄₄Co₄₄Zr₇B₄Cu₁ glassy alloy. Using three dimensional atom probe measurements we present evidence for the formation of Cu clusters on annealing in the metallic glass matrix of the Al containing alloy Fe₄₃Co₄₃Al₂Zr₇B₄Cu₁. Such clusters are otherwise absent in the parent alloy under similar conditions. The Cu clusters provides heterogeneous nucleation sites for the formation of bcc α′-FeCo phase leading to an increase in number density of this nanocrystalline phase and thereby enhancing the magnetic properties.     

Radiative recombination in Cu2ZnSnSe4 monograins studied by photoluminescence spectroscopy

In this study we investigated the optical properties of Cu₂ZnSnSe₄ monograin powders that were synthesized from binary compounds in the liquid phase of flux material (KI) in evacuated quartz ampoules. The monograin powder had p-type conductivity. Radiative recombination processes in Cu₂ZnSnSe₄ monograins were studied using photoluminescence spectroscopy. The detected low-temperature (T = 10 K) photoluminescence band at 0.946 eV results from band-to-impurity recombination in Cu₂ZnSnSe₄. The ionization energy of the corresponding acceptor defect was found to be 69 ± 4 meV. Additional photoluminescence bands detected at 0.765 eV, 0.810 eV and 0.860 eV are proposed to result from Cu₂SnSe₃ phase whose presence in the as-grown monograins was detected by Raman spectroscopy and SEM analysis. Considering photoluminescence results, it is proposed that the optical bandgap energy of Cu₂ZnSnSe₄ is around 1.02 eV at 10 K.     

Synthesis and upconversion luminescence properties of Yb/Er codoped BaGd2(MoO4)4 powder

Synthesis and upconversion luminescence properties of the new BaGd₂(MoO₄)₄:Yb³⁺,Er³⁺ phosphor were reported in this paper. The phosphor powder was obtained by the traditional high temperature solid-state method, and its phase structure was characterized by the XRD pattern. Based on the upconversion luminescence properties studies, it is found that, under 980 nm semiconductor laser excitation, BaGd₂(MoO₄)₄:Yb³⁺,Er³⁺ phosphor exhibits intense green upconversion luminescence, which is ascribed to ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transition of Er³⁺. While the observed much weaker red emission is due to the non-radiative relaxation process of ⁴S_3/2 → ⁴F_9/2 and ⁴F_9/2 → ⁴I_15/2 transition originating from the same Er³⁺. The concentration quenching effects for both Yb³⁺ and Er³⁺ were found, and the optimum doping concentrations of 0.5 mol% Yb³⁺ and 0.08 mol% Er³⁺ in the new BaGd₂(MoO₄)₄ Gd³⁺ host were established.     

Zur kenntnis von Na2Cu4S3 und KCu3Te2

The crystal structures of the new compounds Na₂Cu₄S₃ and KCu₃Te₂ have been solved. Na₂Cu₄S₃ crystallizes in the K₂Ag₄S₃ structure (space group: C2/m, a = 1563(3) pm, b = 386(2) pm, c = 1033(2) pm, β = 107.6^o, N = 4), KCu₃Te₂ in the CsAg₃S₂ structure (space group: C2/m, a = 1645.3(9) pm, b = 429.4(4) pm, c = 866.1(6) pm, β = 111.86^o, N = 4).     

A modified model for calculating lattice thermal expansion of I2-IV-VI3 and I3-V-VI4 tetrahedral compounds

A general empirical formula was found for calculating lattice thermal expansion for compounds having their properties extended for compound groups having different mean ionicity as well as more than one type of cation atoms with that of different numbers of them such as I₂-IV-VI₃ and I₃-V-VI₄. The difference in the valence electrons for cations and anions in the compound was used to correlate the deviations caused by the compound ionicity. The ionicity effects, which are due to their different numbers for their types, were also added to the correlation equation. In general, the lattice thermal expansion for a compound semiconductor can be calculated from a relation containing melting point, mean atomic distance and number of valence electrons for the atoms forming the compound. The mean ionicity for the group compounds forming I₂-IV-VI₃ was found to be 0.323 and 0.785 for the ternary group compounds of I₃-V-VI₄.     

Optical characterization of Cu2ZnSnSe4 grown by thermal co-evaporation

Cu₂ZnSnSe₄ thin films with different substrate temperature and Cu flux were grown by thermal co-evaporation. Raman scattering, photoluminescence, and contactless electroreflectance (ER) measurements were performed. The Raman spectra of Cu₂ZnSnSe₄ show two main peaks at 170 and 192 cm^− 1. The photoluminescence spectrum shows a peak below 1.0 eV. Franz-Keldysh oscillations (FKOs) were observed in the ER spectra. From the analysis of the FKOs, the bandgap energy of Cu₂ZnSnSe₄ thin films is estimated to be 1.07 eV at 90 K and 0.99 eV at room temperature. We conclude that the bandgap energy of Cu₂ZnSnSe₄ thin films is around 1.0 eV.     

Dynamic local lattice distortion in YBa2Cu4O8

Significant changes in the local atomic structure and lattice dynamics were observed by pulsed neutron inelastic scattering measurements on YBa₂Cu₄O₈ both around the superconducting transition temperature and around the spin-gap temperature. These observations and earlier results of numerical calculations on the enhancement of electron-lattice interaction by electron correlation lead to a novel picture of unconventional lattice-induced superconductivity related to antiferroelectric instability.     

Single step synthesis of chalcogenide nanoparticles Cu2ZnSnS4, Cu2FeSnS4 by thermal decomposition of metal precursors

Cu₂ZnSnS₄ (CZTS) and Cu₂FeSnS₄ (CFTS) nanoparticles were synthesized by thermal decomposition of metal precursors. Dispersion of the precursors in the solvent prior to reaction significantly lowered the temperature and time required for the reaction. Extensive characterization of the synthesized nanoparticles was done. Materials characteristics of the synthesized nanoparticles such as elemental composition, band gap and morphology were found to be similar to the nanoparticles prepared by conventional synthesis techniques.     

Effect of the oxygen isoelectronic substitution in Cu2ZnSnS4 and its photovoltaic application

The optoelectronic properties of Cu₂ZnSnS₄ and environmental considerations have attracted significant interest for photovoltaics. Using first-principles, we analyze the possible improvement of this material as a photovoltaic absorber via the isoelectronic substitution of S with O atoms. The evolution of the acceptor level is analyzed with respect to the atomic position of the nearest neighbors of the O atom. We estimate the maximum efficiency of this compound when used as a light absorber. The presence of the sub-band gap level below the conduction band could increases the solar-energy conversion with respect to the host.     

Structure et proprietes physiques des phases Cu2TlX2, Cu3 YTl2X4 (AVEC X = Se,Te et Y = Fe,Ga, Al)

Ternary (Cu₂TlX₂) and quarternary (Cu₃YTl₂X₄) compounds (with X = Se, Te and Y = Fe, Ga, Al) have been prepared and characterized. All of them have the same lamellar structure where tetrahedras (CuYX₄)_n and thallium atoms in coordination eight form successive layers. Some are metallic conductors (Cu₂TlX₂) whereas others are semi-conductors (Cu₃YTlX₄). The metallic behaviour could be due to thallium monovalent-thallium trivalent interactions within the layers.     

Influence of Sm2Ba4CuBiOy phase content on Jc of SmBa2Cu3O7/Sm2Ba4CuBiOy nano-composites

Presence of various nano-scale Y₂Ba₄CuMO_y phase inclusions in YBa₂Cu₃O_7−δ phase matrix are shown to improve magnetic flux pinning over wide range of magnetic fields. We first fabricate single phase of Sm₂Ba₄CuBiO_y (Sm-2411) using a solid-state reaction and then introduced them into SmBCO single grains. Top seeded melt growth (TSMG) has been used to grow SmBCO single grains in air atmosphere. A significant improvement in J_c is observed, over wide magnetic fields, for single grains containing Sm-2411nano-phase inclusions when compared to that of SmBa₂Cu₃O_7−δ/Sm₂BaCuO₅ composites. When compared to YBCO nano-composites, SmBCO composites are shown to exhibit high J_c at medium range of magnetic fields (1–2 T) at 77 K.