THE QUATERNARY CHALCOGENIDE COMPOUND Ag2FeGeSe4: A REVISION OF THEIR CRYSTAL STRUCTURE AND MAGNETIC PROPERTIES

Background: Quaternary compounds bellowing to the I2-II-IV-VI4 system are of considerable technological interest due to their possible use in the preparation of solar cell and thermoelectric materials devices. In recent years, considerable attention has been focused on the detailed study of quaternary chalcogenide compounds related to the chalcopyrite compounds, particularly AgInSe2, which has emerged as a leading material for the preparation of photovoltaic devices due to their potential applications in solar cell technology. Aims: This work focuses on synthesis, chemical analysis, thermal study, magnetism measurement, and crystal structural characterization of the quaternary semiconductor Ag2FeGeSe4, an essential member of the family I2-II-IV-VI4. Methods: This material was synthesized by the melt and anneal technique. The chemical analysis was carried out by scanning electron microscopy (SEM) and differential thermal analysis (DTA). Magnetic susceptibility () as a function of temperature and magnetization as a function of the magnetic field were also performed, and crystal structure analysis was made employing the Rietveld method with powder X-ray diffraction data. Results and Discussion: The preparation confirms the formation of the quaternary compound with stoichiometric 2:1:1:4 according to the chemical analysis. This quaternary compound melt at 1015 K, and show an antiferromagnetic behavior with Neel temperature TN of 240 K. The Debye temperature (D) estimated for this compound was 194 K. The quaternary chalcogenide compound Ag2FeGeSe4 crystallizes in the orthorhombic space group Pmn21, Z = 4, with unit cell parameters: a = 7.6478(1) Å, b = 6.5071(1) Å, c = 6.4260(1) Å, and V = 319.79(1) Å3, in a wurtzite-stannite arrangement with a Cu2CdGeS4-type structure, which is characterized by a three-dimensional arrangement of slightly distorted AgSe4, FeSe4, and GeSe4 tetrahedra connected by corners. In this structure, each Se atom is coordinated by four cations located at the corners of a slightly distorted tetrahedron, and each cation is tetrahedrally bonded to four anions. Conclusions: The melt and anneal method remains effective for preparing compounds chalcogenides as the quaternary Ag2FeGeSe4, a new member of I2-II-IV-VI4 family of semiconductors, which crystallizes in the non-centrosymmetric space group Pmn21 with diamond-like structure. The crystal structure information of this compound allows explaining their magnetic properties, which in combination with its semiconductor properties make this material a potential aspirant for different applications, mainly in solar cells.

Ab Initio High-Pressure Study of Semiconductor-Metal Phase Transition of the Chalcogenide Compound KPSe6

We report the results of pressure-induced semiconductor-metal phase transition of the semiconducting chalcogenide compound KPSe6 under high pressure using the ab initio methods. The ground-state energy calculations were performed within density functional theory and the generalized gradient approximation using the pseudopotential method with plane-wave basis sets. The projector augmented-wave (PAW) pseudopotentials were used in our calculation. The optimized lattice parameters were found from total energy calculations as 13 Bohr, 1.6 Bohr, and 1.8 Bohr for cell dimensions one, two, and three, respectively, which are in good agreement with experimental calculations. At zero pressure, the material portrayed a semiconducting property with a direct bandgap of ≈1.7 eV. As we subjected the material to pressure, the band gap was observed to reduce until it disappeared. The phase transition from the semiconductor to metal was found to occur at ∼45 GPa, implying that the material underwent metallization as pressure was increased further.

Preparation, Structure, Optical and Morphological Properties of Co, Ga2O3 Co-Doped ZnS/Se

The material of doping transition metal (TM) in chalcogenide compound such as ZnS and ZnSe can be used in sensors, nonlinear optics, optical thin-films and mid-infrared area because of their faster optical response time, wider transparency range of mid-infrared and higher mid-infrared transmittance, low optical loss and phonon energy. In this paper, the ceramic targets of (ZnS/Se)0.4(Co)x(Ga2O3)0.6-x(x=0.1, 0.3 and 0.5) were prepared by high temperature solid state reaction. The mass loss rate, shrinkage rate and molar ration were calculated. XRD, absorption spectrum and AFM&OM were investigated. All of the results are shown that the optimum doping concentration is (ZnS/Se)0.4(Co)0.5(Ga2O3)0.1(namely x=0.5), and the optimum intering temperature are in the range 1000~1200°C. Besides, the zinc-blende structure on ceramics targets was confirmed by XRD. A broad application range from VIS to Mid-infrared was suggested by absorption spectra. The optimal base material ZnSe was proved by AFM and OM. All these results indicate that bulks of (ZnS/Se)0.4(Co)x(Ga2O3)0.6-xare most promising materials in future

Synthesis, structural characterization and differential thermal analysis of the quaternary compound Ag2MnSnS4

The quaternary chalcogenide compound Ag2MnSnS4 belonging to the system I2-II-IV-VI4 and synthesized by the melt and anneal technique, was characterized by Rietveld refinement of the powder X-ray diffraction data and differential thermal analysis (DTA). It was found that nS4 crystallizes in the orthorhombic space group Pmn21, with unit cell parameters a = 8:1705(5) Å, b = 6:9413(5) Å, c = 6:6532(5) Å, and V = 377:33(5) Å3, in a wurtzite-stannite structure. The DTA indicates that this compound melts at 790°C and that the phase relations which occurs in the material would be: α ➝ α + α1 ➝ α1 ➝ α1 + β ➝ β ➝ 1 + L ➝ L, were α is the orthorhombic wurtzite-stannite Pmn21 structure; α1 is a high temperature modification; and β and β1 are the zinc-blende structure and its high-temperature modification, respectively.

STRUCTURAL CHARACTERIZATION OF THE NEW DIAMOND-LIKE SEMICONDUCTOR CuNbGaSe3

The chalcogenide compound CuNbGaSe3, belonging to the system I-II-III-VI3, has been investigated by means of X-ray powder diffraction and its crystal structure has been refined by the Rietveld method.This is a material of the semiconductor type, which improves the properties of a simple semiconductor like CuGaSe2 because it ads spintronic applications due to its magnetic behavior. The powder pattern was composed by 94.2% of the principal phase CuNbGaSe3 and 5.8% of the secondary phase Cu0.667NbSe2. This material crystallizes with a CuFeInSe3-type structure in the tetragonal space group P4 2c (Nº 112), unit cell parameters a = 5.6199(4) Å, c = 11.0275(2) Å, V = 348.28(4) Å3, with a normal adamantane-structure where occurs a degradation of symmetry from the chalcopyrite structure I4 2d to a related structure P4 2c.