Raman spectroscopy in AB2X4 pseudoternary layered compounds

We have synthesized several pseudoternary layered compounds by cation or anion cross substitution in ternary AB₂X₄ compounds. Here we report on the low frequency Raman spectra obtained from Zn_xCd_1-xIn₂S₄, Zn(In_xGa_1-x)₂S₄ and ZnIn₂(S_xSe_1-x)₄ single crystals. Within these systems we have identified five compositionally or dynamically different phases. Each of these phases may be characterized by its peculiar low frequency Raman spectrum which is connected to the dynamics of the layers in the unit cell. Abrupt structural/dynamical changes are observed as a function of composition between different phases. Within each phase compositional changes cause only smooth and small spectral variations.     

Vaporization chemistry and thermodynamics in the CdGa2S4-Ga2S3 system

The chemistry and thermodynamics of vaporization of CdGa₂S₄(s), CdGa₈S₁₃(s), and Ga₂S₃(s) were studied by computer-automated, simultaneous Knudsen-effusion and torsion-effusion, vapor pressure measurements in the temperature range 967–1280 K. The vaporization was incongruent with loss of Cd(g) + 1/2 S₂(g) and production of CdGa₈S₁₃(s), a previously unknown compound, in equilibrium with CdGa₂S₄(s), until the solid became CdGa₈S₁₃ only. Then, incongruent vaporization continued with production of Ga₂S₃(s) until the solid was Ga₂S₃ only. The latter vaporized congruently. The ΔH°(298 K) of combination of one mole of CdS(s) with one mole of Ga₂S₃(s) to give CdGa₂S₄(s) was ?22.6 ± 0.9 kJ mole^?1. The 2H2(298 K) of combination of one mole of CdS(s) with four moles of Ga₂S₃(s) to give CdGa₈S₁₃(s) was ?25.5 ± 1.1 kJ mole^?1. The 2H2(298K) of CdGa₈S₁₃(s) with respect to disproportionation into CdGa₂S₄(s) and 3 Ga₂S₃(s) was ?2.8 ± 0.6 kJ mole^?1. CdGa₈S₁₃(s) was not observed at room temperature. The 2H2(298 K) of vaporization of the residual Ga₂S₃(s) was 663.4 ± 0.8 kJ mole^?1, which compared well with a value of 661.4 ± 0.3 kJ mole^?1 already available from the literature. Implications of small variations in stoichiometry of compounds in this study were observed and are discussed.     

Röntgenographische und schwingungsspektroskopische Untersuchungen an Spinell-Mischkristallen des Systems (Zn,Ga) Cr2Se4

X-ray and I. R. Spectroscopic Studies on Spinel Solid Solutions of the Zn_1–xGa_0.67xCr₂Se₄ System With the aim to get new compounds with spinel defect structure of the ß-In₂S₃ type, we studied the phase diagram of the Zn_1–xGa_0.67xCr₂Se₄ system. The spinel type solid solutions formed within x = 0—0.6 show a relatively large phase width with respect to the metal selenium ratio, i. e. the parameter z in the formula Zn_1–xGa_0.67(x+0.5z)Cr_2–z^IIICr_z^IISe₄. Ternary Ga_0.67Cr₂Se₄ does not exist, it decomposes to Cr₂Se₃ and Ga₂Se₃. Instead of the ß-In₂S₃ type, superstructure reflections of LiFeCr₄O₈ type are observed.     

Probing the Metal Composition of Ternary 12–12′‐16 Nanoclusters via Electrospray Ionization Mass Spectrometry

The reaction of [(3,5‐Me₂–C₅H₃N)₂Zn(SeSiMe₃)₂] with a solution of Cd(OAc)₂, Se(Ph)SiMe₃ and PPr₃ at low temperature was used to prepare single crystals of ternary group 12–12′‐16 nanoclusters with the composition [Zn_1.8Cd_8.2Se₄(SePh)₁₂(PPr₃)₄]. A ligand exchange reaction using Na[SePh] was performed to displace the neutral PPr₃ ligands. The resulting clusters were probed using electrospray ionization mass spectrometry to determine the number of zinc and cadmium atoms in the cluster and compared to the all cadmium cluster [Cd₁₀Se₄(SePh)₁₂(PPr₃)₄]. The dianionic clusters [Zn_xCd_10–xSe₄(SePh)₁₄]^2– where x = 0, 1, 2 were assigned in the mass spectra, revealing that the clusters exhibit elemental distributions that are quite narrow in these experiments.     

Spinelle mit substituierten Nichtmetallteilgittern. IV. Rötgenographische Untersuchung der Systeme CuCr2(S1−xSex)4 und CuCr2(Se1−xTex)4

Spinels with substituted Nonmetal Sublattices. IV. CuCr₂(S_1?xSe_x)₄ and CuCr₂(Se_1?xTe_x)₄ Polycrystalline samples of the spinel system CuCr₂(S_1?xSe_x)₄ have been prepared with 0 ≤ x ≤ 1. We found that in the spinel system CuCr₂(Se_1?xTe_x)₄ no solid solution is existent in the range 0.01 ≤ x ≤ 0.70. When S is substituted by Se and Se by Te the lattice constants increase linearely by 0.52 Å and 0.81 Å respectively. The anion-sublattice shows random distribution of the chalcogen atoms, the chalcogen parameters u are constant in the system CuCr₂(S_1?xSe_x)₄ with a mean value of u = 0.382₉. The calculated anion-cation-distances lead to a covalent tetrahedral radius r_Cu = 1.23 Å. This radius is in agreement with the radius r_Cu = 1.22 Å of Cu spinels with Cu in the valence +1.     

Spinelle mit substituierten Nichtmetallteilgittern. VI. Röntgenographische und elektronische Eigenschaften,Mößbauer- und IR-Spektren des Spinellsystems CuCrSn(S1−xSex)4

Spinels with Substituted Nonmetal Sublattices. VI. X-Ray Investigation, Electronic Properties, Mössbauer and I.R. Spectra of the Spinel System CuCrSn(S_1?xSe_x)₄ Polycrystalline samples of the spinel system CuCrSn(S_1?xSe_x)₄ have been prepared in the range 0 ≤ x ≤ 1. The lattice constants linearly increase with x while chalcogen parameters remain constant. The calculated distances copper-chalcogen are in agreement with Cu(I). From the Mössbauer spectra we conclude that the bonding is mostly covalent and that Sn is in the oxidation state +4. The substances are p type semiconductors. Resistivities, Seebeck coefficients, and activation energies decrease with increasing x. The electrical properties are compared to those of the system ZnCr₂(S_1?xSe_x)₄. I.R. spectra have been measured from 50 cm^?1 to 600 cm^?1.     

Spinelle mit substituierten Nichtmetallteilgittern. VIII. Röntgenographische und elektrische Eigenschaften,Mößbauer- und IR-Spektren des Systems FeCr2(S1−xSex)4

Spinels with Substituted Nonmetal Sublattices. VIII. X-Ray Investigation, Electric Properties, Mössbauer and I.R. Spectra of the System FeCr₂(S_1?xSe_x)₄ In the system FeCr₂(S_1?xSe_x)₄ the spinel structure exists in the range 0 ≤ x ≤ 0.3₃, the monoclinic Cr₃S₄-structure in the range 0.6 ≤ x ≤ 1. Lattice parameters have been determined and I.R. spectra have been measured between 200 cm^?1 and 600 cm^?1. Room temperature Mössbauer spectra consist of several overlapping doublets of almost identical isomer shifts but different quadrupole splittings. The Fe doublets are attributed to the coordination polyhedrons S₄, S₃Se and S₂Se₂. The spinels are p type semiconductors.     

Röntgenographische und schwingungsspektroskopische Untersuchung der Sulvanitmischkristalle Cu3Nb(SxSe1−x)4, Cu3Nb(SexTe1−x)4, und Cu3Ta(SxSe1−x)4 und Cu3Ta(SexTe1−x)4

X-Ray and Vibrational Studies of Sulvanite Mixed Cystals Cu₃Nb(S_xSe_1?x)₄, Cu₃Nb(Se_xTe_1?x)₄, Cu₃Ta(S_xSe_1?x)₄ and Cu₃Ta(Se_xTe_1?x)₄ Solid solutions Cu₃Nb(S_xSe_1?x)₄, Cu₃Nb(Se_xTe_1?x)₄, Cu₃Ta(S_xSe_1?x)₄ and Cu₃Ta(Se_xTe_1?x)₄ with sulvanite structure have been prepared in the range 0 ≤ x ≤ 1. The lattice constants in all systems obey the Vegard rule. Infrared and Raman spectra have been measured. The spectra of the compounds with mixed anion sublattices show additional peaks, compared to those of the end members, because besides the polyhedra MX₄ and MY₄ also groups MX₃Y, MX₂Y₂, and MXY₃ are present, and all groups are able to oscillate independently. By comparison of the peak intensities and the statistical frequency of the groups according to the composition, the additional valence vibrations could be attributed to the groups.     

Absorption Spectra of CrIII in some lattices of spinel and pseudo-brookite Type

Spinel mixed crystals ZnCr_xAl_2?xO₄, Cd_yZn_1?yCrAlO₄, Cd_0.5Zn_0.5Cr_0.4Ga_1.6O₄ and pseudo-brookite compounds Al_2?xGe_yCr_xTi_1?yO₅ were synthesized and x-rayed. The reflectance spectra were measured. The Δ-dependent absorption band was shifted towards IR-region in case of the spinels, whereas it remains nearly unshifted in pseudo-brookite. Generally, the results are discussed with the help of the ligand field parameters Δ and B.     

Spinelle mit substituierten Nichtmetallteilgittern. V. Röntgenographische Untersuchung des Spinellsystems CuRh2(S1−xSex)4

Spinels with Substituted Nonmetal Sublattices. V. X-Ray Investigation of the Spinel System CuRh₂(S_1?xSe_x)₄ Polycrystalline samples of the spinel system CuRh₂(S_1?xSe_x)₄ were prepared with 0 ≤ x ≤ 1. When S is substituted by Se the lattice constants increase linearly by 0.48 Å. The anion sublattice shows random distribution of the chalcogen atoms with a mean value for the chalcogen parameter of u = 0.381. The cation-anion distances were calculated.     

Spinelle mit substituierten Nichtmetallteilgittern. VII. Röntgenographische und elektronische Eigenschaften,Mößbauer- und IR-Spektren des Spinellsystems AgCrSn(S1−xSex)4

Spinels with Substituted Nonmetal Sublattices. VII. X-Ray Investigations, Electronic Properties, Mössbauer, and I.R. Spectra of the Spinel System AgCrSn(S_1?xSe_x)₄ Polycrystalline samples of the spinel system AgCrSn(S_1?xSe_x)₄ have been prepared in the range 0 ? x ? 1. The lattice constants linearly increase with x by 50 pm, the chalcogen parameter has the mean value 0.384. The Mössbauer spectra consist of a weakly split doublet, they are in agreement with Sn(IV) and covalent bonding. The substances are n type semiconductors. I.R. spectra have been measured from 50 cm^?1 to 600 cm^?1.     

Zinc cadmium ammine aqua monophosphate and its thermal transformations

Synthesis of amorphous zinc cadmium ammine aqua monophosphates Zn_3?x Cd _x (PO₄). 2n(NH₃) · m(H₂O) (x = 0.6–2.4, n = 1.3–3.1, m = 2.3–3.4) with variable molar ratio of the cations described. The sequence of thermal transformations of compound [Zn_1.5Cd_1.5(NH₃)_1.4(H₂O)_3.2(PO₄)₂] with equimolar ratio of cations is studied, and schemes of its transformation into the crystalline zinc cadmium monophosphate Zn_1.5Cd_1.5(PO₄)₂ are suggested.     

Crafting Core/Graded Shell–Shell Quantum Dots with Suppressed Re‐absorption and Tunable Stokes Shift as High Optical Gain Materials

The key to utilizing quantum dots (QDs) as lasing media is to effectively reduce non‐radiative processes, such as Auger recombination and surface trapping. A robust strategy to craft a set of CdSe/Cd_1?xZn_xSe_1?yS_y/ZnS core/graded shell–shell QDs with suppressed re‐absorption, reduced Auger recombination rate, and tunable Stokes shift is presented. In sharp contrast to conventional CdSe/ZnS QDs, which have a large energy level mismatch between CdSe and ZnS and thus show strong re‐absorption and a constrained Stokes shift, the as‐synthesized CdSe/Cd_1?xZn_xSe_1?yS_y/ZnS QDs exhibited the suppressed re‐absorption of CdSe core and tunable Stokes shift as a direct consequence of the delocalization of the electron wavefunction over the entire QD. Such Stokes shift‐engineered QDs with suppressed re‐absorption may represent an important class of building blocks for use in lasers, light emitting diodes, solar concentrators, and parity‐time symmetry materials and devices.     

CdGa2S4-MGa2S4 (M = Zn and Mg) systems

A phase microdiagram of the system CdS-Ga₂S₃ in the CdGa₂S₃ homogeneous region was constructed, and the composition corresponding to congruent melting was determined (Cd_0.498Ga_1.004S_2.004). A fragment of the CdGa₂S₄-ZnGa₂S₄ phase diagram was studied, and the solid solution composition suitable for growing homogeneous single crystals with respect to the isotropic wavelength λ₀ within 492.7–532 nm was determined. A CdGa₂S₄-MgGa₂S₄ phase diagram was constructed, and the isotropic wavelength was studied as a function of magnesium prevalence in cadmium thiogallate. Magnesium and zinc codoping produces gyrotropic single crystals suitable for manufacturing optical elements of filtering devices with λ₀ within 492.7–880 nm.     

Spinelle mit substituierten Nichtmetallfeilgittern. II. Herstellung von Einkristallen im System CdCr2(S1−xSex)4

Single crystals of the system CdCr₂(S_1?xSe_x)₄ have been prepared by chemical transport with I₂/AlCl₃ mixtures and by flux growth from solutions in molten CdCl₂.     

Enhanced Photocatalytic Hydrogen‐Production Performance of Graphene–ZnxCd1−xS Composites by Using an Organic S Source

In response to the increasing concerns over energy and environmental sustainability, photocatalytic water‐splitting technology has attracted broad attention for its application in directly converting solar energy to valuable hydrogen (H₂) energy. In this study, high‐efficiency visible‐light‐driven photocatalytic H₂ production without the assistance of precious‐metal cocatalysts was achieved on graphene–Zn_xCd_1?xS composites with controlled compositions. The graphene‐Zn_xCd_1?xS composites were for the first time fabricated by a one‐step hydrothermal method with thiourea as an organic S source. It was found that thiourea facilitates heterogeneous nucleation of Zn_xCd_1?xS and in situ growth of Zn_xCd_1?xS nanoparticles on graphene nanosheets. Such a scenario results in abundant and intimate interfacial contact between graphene and Zn_xCd_1?xS nanoparticles, efficient transfer of the photogenerated charge carriers, and enhanced photocatalytic activity for H₂ production. The highest H₂‐production rate of 1.06 mmol h^?1 g^?1 was achieved on a graphene–Zn_0.5Cd_0.5S composite photocatalyst with a graphene content of 0.5 wt %, and the apparent quantum efficiency was 19.8 % at 420 nm. In comparison, the graphene–Zn_xCd_1?xS composite photocatalyst prepared by using an inorganic S source such as Na₂S exhibited much lower activity for photocatalytic H₂ production. In this case, homogeneous nucleation of Zn_xCd_1?xS becomes predominant and results in insufficient and loose contact with the graphene backbone through weak van der Waals forces and a large particle size. This study highlights the significance of the choice of S source in the design and fabrication of advanced graphene‐based sulfide photocatalytic materials with enhanced activity for photocatalytic H₂ production.     

Festkörperreaktionen in Chalkogenidsysfemen,IV [1]: Röntgenographische und elektrische Untersuchungen am System HgCr2(SexS1–x)4

Inhaltsübersicht. Im Spinellsystem HgCr₂Se_xS_1–x)₄ besteht im Gegensatz zu den entsprechenden Zink- und Cadmiumverbindungen, die lückenlose Mischkristallreihen bilden, zwischen 0,20 < x < 0.75 einp Mischungslücke. Im Bereich der Mischungslücke werden HgSe und Cr₂S_3–ySe_y-Mischkristalle gebildet. Die Gitterkonstanten der Spinellmischkristalle erfüllen nur auf der selenreichen Seite des Phasendiagramms die Végardsche Regel. Der Reaktionsverlauf wurde mit Hilfe von Leitfähigkeitsmessungen sowie thermoanalytischer Untersuchungen verfolgt. Über die Möglichkeit der Spinellbildung des Systems wird diskutiert. X-ray and Electric Measurements on the HgCr₂(Se_xS_1–x)₄ System Abstract. In the HgCr₂(Se_xS_1–x)₄ system there is no spinel structure in the 0.20 < x < 0.75 concentration range. In the miscibility gap the formation of HgSe and Cr₂8_3–ySe_y mixed crystals has been noticed. The lattice constants of the spinel solid solutions obey Végard's law only on the selenium-rich side of the phase diagram. Both the temperature dependence of electric conductivity and the thermal analysis of the starting mixtures were studied. The possibility of formation of spinels in the system is discussed.     

IR-Spektroskopische und Röntgenographische Untersuchungen an Thiospinellmischkristallen

The effect of the tetrahedral and octahedral coordinated metal and nonmetal atoms on the vibrational spectra of spinels is studied by investigation of mixed crystals and defect spinels like In₂S₃. The following solid solutions of chromium thiospinels and indium sulfides have been prepared and investigated by X-rays and FIR-spectroscopy: Hg_xZn_{1 ? x}Cr₂S₄ (I), ZnIn_xCr_{2 ? x}S₄ (II), CdIn_xCr_{2 ? x}S₄ (III), ZnCr₂Se_xS_{4 ? x} (IV), α-In₂S₃ (V), β-In₂S₃ (VI) and Cr_xIn_{2 ? x}S₃ (VII). The lattice constants of (I), (III), (IV) and (VII) obey Vegard's rule. (III) has a miscibility gap between x = 0.3 and x = 1.8. The spectroscopic behavior of the solid solutions (all the four peaks of the spinel spectra split or shift) can not be interpreted on the basis of internal vibrations of different coordination polyhedra. An explanation of the additional peaks in the spectra of the mixed crystals is given according to order of the atoms or distortion of the spinel structure.     

Third- and second-order optical nonlinearity of Ge-Ga-S-PbI2 chalcohalide glasses

Two series of metal iodide doped chalcohalide glasses (100−2x)GeS₂·xGa₂S₃·xPbI₂ (0?x?20) and (100−x)(0.8GeS₂·0.2Ga₂S₃)·xPbI₂ (0?x?15) were prepared and characterized. The microstructure of these glasses has been studied by Raman scattering spectra. Utilizing femtosecond time-resolved optical Kerr effect (OKE) technique at the wavelength of 820 nm, a largest third-order nonlinearity χ⁽³⁾ of 2.07×10⁻¹³ esu was obtained for the 90GeS₂·5Ga₂S₃·5PbI₂ glass, and it decreases with the addition of PbI₂ in both two series. After thermally poled, second-harmonic generation (SHG) has been observed in these glasses according to Maker fringe method and a large second-order nonlinearity χ⁽²⁾ as well as 4 pm/V was obtained for the 70GeS₂·15Ga₂S₃·15PbI₂ glass. The variations of χ⁽²⁾ and χ⁽³⁾ on glass composition are ascribed to the evolution of micro-structural units in glass. These novel chalcohalide glasses would be expected to be the promising candidate materials for nonlinear optical devices.     

Preparation of the HgCr2(SexS1−x)4 type compounds and the X ray control of the process of formation of their spinel structures

Compounds of the HgCr₂(Se_xS_1?x)₄ type were prepared for 0.750 ? x ? 0.250 by thermal synthesis from parent elements. Individual reaction stages were controlled röntgenographically. The values of electrical conductivity activation energy of the compounds have been calculated and chemical analyses of the substances prepared have been developed.