Single-crystal snowflake of Cu7S4: Low temperature, large scale synthesis and growth mechanism

Non-stoichiometric copper sulfides (Cu₇S₄), with uniform hexapetalous snowflake-like morphology in high yield have been synthesized successfully by a simple and facile one-step solvothermal route with a low temperature (150 °C). Copper chloride and thiourea were chosen as the reactants in an ethylenediamine solution. The role of ethylenediamine as a structure-directing coordination molecular template responsible for the morphologies of the copper sulfides and its role as a reducing agent for the non-stoichiometric have been discussed. In addition, temporal growth of the dendrites can be readily followed in this preparation via time-resolved microscopic analysis. The formation mechanism based on the experiments has been proposed.     

Photoinduced changes in optical properties of obliquely deposited As2S3, As2Se3 and As-Se-Ge films

Photoinduced changes in the absorption edge and refractive index of 0° and 80° angle-of-incidence deposited As₂S₃, As₂Se₃ and As-Se-Ge films have been investigated in the vicinity of the absorption edge. No appreciable effect of oblique deposition has been observed in As₂X₃ (X = S, Se). There are large irreversible changes, however, on exposure of As-Se-Ge films deposited at 80° incidence. The enhancement of photo-effects on addition of Ge in obliquely deposited films is primarily due to the large photoinduced volume changes.     

Effect of silver dissolution on electrical properties of As2S3

The paper reports the effect of dissolution of silver into the chalcogenide As₂S₃. The conductivity of As₂S₃ decreases with doping at lower temperatures. The a.c. conductivity is proportional to ^s for undoped as well as doped samples. The value of the frequency exponent s increases with doping. On the other hand, the dielectric constant of As₂S₃ also increases with doping and the effect is quite prominent at higher temperatures. A new structural model together with the correlated barrier hopping model has been used to explain these results. © 2001 Kluwer Academic Publishers     

Crystal structure of cubic MnSc2S4 and Mn2.29Sc1.14S4

The crystal structure of MnSc₂S₄ ($\text{a}\text{= 10.613}\text{A}\text{?}$, space group Fd3m) and Mn_2.29Sc_1.14S₄ ($\text{a}\text{= 10.523}\text{A}\text{?}$, space groupe Fd3m) were determined by three dimensional X-Ray diffraction. MnSc₂S₄ is a normal spinel structure and the atomic distribution shows that Mn_2.29Sc_1.14S₄ structure is intermediate between the rocksalt (MnS) and the spinel (MnSc₂S₄) types. Similar behaviour of Mn and Fe atoms in MnSSc₂S₃ and FeSSc₂S₃ systems was observed.     

PbSbBiS4-Sb2S3 and PbSbBiS4-Bi2S3 joins in the PbS-Sb2S3-Bi2S3 system

Phase equilibria along the PbSbBiS₄-Sb₂S₃ and PbSbBiS₄-Bi₂S₃ joins of the PbS-Sb₂S₃-Bi₂S₃ system have been studied for the first time using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and the phase diagrams of the joins have been mapped out. The joins are shown to be pseudobinary with limited series of terminal solid solutions. The solid solutions are p-type semiconductors.     

On the ultraviolet light induced oxidation of amorphous As2S3 film

Illumination of amorphous As₂S₃ film by ultraviolet light with an overall light intensity on the sample surface of around 10 W cm^− 2 leads to extensive film oxidation. After 2 min of illumination most of As₂S₃ film of an original thickness at around 0.425 μm was converted into a cubic form of As₂O₃-arsenolite. A considerable amount of arsenolite microcrystals were found at a height of around 2 μm and more which indicated a growth of As₂O₃ microcrystalline particles from the vapor phase.     

Mechanochemically induced amorphous/crystalline phase transition in the Bi4Ti3O12 compound

Concurrent milling of Bi₄Ti₃O₁₂ was carried out in a planetary ball mill with hardened-steel 13 or 6 mm diameter balls with a goal to investigate how the system responds to the constrains imposed by milling. Milling intensity for various milling parameters was derived from the electrical power measurement. The reverse amorphous ↔ crystalline phase transition induced by milling is governed by impact energy and frequency. Below a certain threshold value of impact energy crystallization does not occur, whereas a higher impact frequency accelerates amorphization. Mechanochemical reactions are predominantly discrete processes, which occur at the moment of impact.     

Anisotropy of some physical parameters in As-prepared As2S3 bulk glass

When cooling a melt the cooling rate in different layers varies due to differences in heat transfer. These changes in cooling rate were determined experimentally for the As₂S₃ melt in a quartz ampoule with diameter of 17 mm. The cooling rate at air quenching varies from 1.36 K/s in the bulk middle to 2.11 K/s in the border layers, and from 3.54 to 38.80 K/s for water quenching, respectively. Further, the corresponding changes in the density, microhardness, glass-transition temperature and electrical conductivity in dependence on the choice of the measured sample from various parts of the bulk were found. The anomalous behaviour of these parameters in dependence on the cooling rate corresponds to the polymeric structure of the glass.     

Mechanochemical preparation of magnetite nanoparticles by coprecipitation

A novel simple process for preparing magnetite (Fe₃O₄) nanoparticles by a coprecipitation route without using any additives (e.g., surfactant and oxidizing and reducing agents) has been developed. In this method, a cooled ball mill was used as a synthesis reaction field in order to inhibit progress of both the synthesis reaction and the particle growth by heat energy. The Fe₃O₄ nanoparticles were formed by ball-milling of the starting suspension consisting of ferrous hydroxide and goethite colloids, and the crystallization was simultaneously progressed without heating. The obtained nanoparticles were then characterized through the SEM observation, XRD analysis, EDS analysis and oxidation-reduction titration, and the magnetic properties were measured with a SQUID magnetometer. This preparation process can provide successfully the superparamagnetic Fe₃O₄ nanoparticles of about 10 nm with high crystallinity and saturation magnetization by mechanochemical effect.     

MgFe2O4纳米颗粒制备及其电磁性能研究

将Mg(OH)2/Fe(OH)3混合体超声活化4h,固相合成制备了尖晶石型MgFe2O4粉末。通过TG-DTA、XRD和TEM测试,分析固相反应的机理、材料的化学成分和微观结构。用振动样品磁强计(VSM)、矢量网络分析仪研究材料的电磁性能。结果表明,700℃下制备的MgFe2O4颗粒为纳米级单晶结构,纯度高,结晶性好,粒径分布为20～45nm;Mg-Fe2O4的比饱和磁化强度Ms=21.015A.m2/kg,剩磁Mr=2.5798A.m2/kg,矫顽力Hc=9.017×10-3T,MgFe2O4对7～18GHz范围内的电磁波表现为介电损耗。     

Photoluminescence spectra of MnIn2S4

MnIn₂S₄ single crystals grown by the directional crystallization method were investigated by using the temperature and excitation power dependencies of photoluminescence (PL) spectra. PL spectra consist of one broad band resulting from donor-acceptor pair recombination. The analysis of the temperature quenching of the PL intensity yields one defect donor level with a thermal ionization energy of about 0.17 eV. The broad band of PL spectra indicates that radiative recombination is related to multiphonon optical processes. The energy of the involved phonon was found to be around 0.025 eV and the energy of the acceptor level is about 0.86 eV.     

Preparation of ferrimagnetic SnCr2S4

SnCr₂S₄ has been prepared for the first time. It is hexagonal ($\text{a}\text{= 21.325}\text{A}\text{?}$ and $\text{c}\text{= 3.4690}\text{A}\text{?}$) and ferrimagnetic (T_C = 100 K).     

Refractive index variations induced by femtosecond laser direct writing in the bulk of As2S3 glass at high repetition rate

This paper deals with the refractive index variation (Δn) induced by femtosecond laser irradiation in the bulk of As₂S₃ glass in a high repetition rate regime. Extensive measurements of spatially resolved Δn profiles of photowritten channels are reported for various values of the pulse energy. Nearly Gaussian profiles are obtained for energy slightly above the threshold whereas at higher energies the structure of Δn is more complex with a negative core surrounded by a positive ring. A thermal model is applied to reproduce the behaviour of the overall structure diameter.     

Modeling of low-temperature specific heat data for Ge27As13S60 and As40S60 glasses by means of the phenomenologically modified soft potential model

Experimental results for the low-temperature specific heat C_p of Ge₂₇As₁₃S₆₀ and As₄₀S₆₀ glasses, measured from 70 K down to 0.54 K, are presented. A maximum in the temperature dependence of the scaled specific heat C_p/T³, appearing in the Boson peak range 2-10 K, and a minimum of this quantity in the tunneling-state range below 1 K, typical for all the glassy materials, were obtained. The presented C_p data are modeled in the frames of a phenomenologically modified soft potential model, applicable in wide low-temperature range. The character of the low-energy excitations in the investigated Ge-As chalkogenides is clarified.     

Phase investigations in the system PbSIn2S3 and the crystal structures of PbIn2S4 and Pb6In10S21

The system PbS-In₂S₃ was examined by differential thermal analysis (DTA), chemical vapour transport (CVT), and X-ray diffraction. Five new phases of compositions closely related to the 1:1 ratio were found and prepared as needle-shaped single-crystals; their crystal data are reported. The structures of PbIn₂S₄ (orthorhombic, Pnma, a=11.688(1), b=3.8528(1), $\text{c}\text{=13.763(1)}\text{A}\text{?}$, Z=4) and Pb₆In₁₀S₂₁ (monoclinic, C2/m, a=27.629(3), b=3.8630(5), $\text{c}\text{=15.705(2)}\text{A}\text{?}$, β=95.9°, Z=2 were solved from 808 resp. 3554 independent reflexions and refined to R=0.116 resp. 0.068. In both structures the In-S coordination polyhedra are distorted octahedra, the Pb-S polyhedra are distorted bicapped trigonal prisms.     

The effect of pressure on the superconducting and crystallographic transitions of La3S4, La3Se4 and La3Te4

The superconducting transition temperatures (T_c's) for La₃S₄ and La₃Se₄ vary in a non-linear fashion under hydrostatic compression to 22 kbar. Both T_c and the crystallographic transformation temperature rise with pressure for La₃S₄ and show a maximum near 10 kbar for La₃Se₄. Non-transforming isostructural La₃Te₄ exhibits a linear pressure dependence of T_c. However, the telluride undergoes a pressure induced phase transformation at ～70 kbar. In this case the sign of the pressure dependence is different from the sulfide and selenide. Variation of T_c with the crystallographic transformation temperature shows a new and unexpected behavior.     

Investigation of interdiffusion in Sb/As2S3 nano-layered structures by high-resolution X-ray photoelectron spectroscopy

The photo-stimulated interdiffusion within chalcogenide based nano-layered structures (NLS) produces large changes in properties, which have potential application in optical pattern recording. The mechanism of these changes is investigated for two NLS consisting of 100 alternate layers of antimony and As₂S₃, but of different relative thicknesses, by high-resolution X-ray photoelectron spectroscopy. The results suggest the formation of Sb-S bonds at the expense of As-S bonds, with a consequent increase in the refractive index but minimal change in thickness. The role of oxygen in photoinduced transformations, especially in the top layers, is characterized and discussed.     

Effect of thermal evaporation rate on the basic physical properties of glassy (As2S3)x(As2Se3)1?x films

We have studied the effect of thermal evaporation rate on the basic physical properties of glassy (As₂S₃) _x (As₂Se₃)_1−x thin films on glass substrates and have determined the optimal range of deposition rates corresponding to the highest photosensitivity and long-term stability of the films. The results are interpreted in terms of the interaction between the deposit and the residual gas in the vacuum chamber. Original Russian Text ? T.I. Goglidze, I.V. Dement’ev, V.M. Ishimov, E.A. Senokosov, 2007, published in Neorganicheskie Materialy, 2007, Vol. 43, No. 1, pp. 97–101.     

Irreversible photoinduced changes in As48S52 amorphous thin films prepared by pulsed laser deposition

Thin amorphous As-S films were prepared using pulsed laser deposition. Raman scattering spectroscopy, variable angle spectroscopic ellipsometry, and optical transmittance spectra revealed irreversible photostructural effects, significant photoinduced changes of refractive index, and optical band gap energy in the films. Observed effects are discussed in terms of structural transformations of basic structural units.     

Preparation and properties of ZnIn2S4 thin films

ZnIn₂S₄ thin films prepared by flash evaporation are polycrystalline and exhibit the structure of ZnIn₂S₄ on X-ray analysis. The films are photoconducting with a dark resistivity of about 10³ ω cm. At low temperatures, when illuminated by gap energy light and subsequently measured in the dark, the films exhibit a residual conductivity which can be removed by heating the samples to room temperature.