Search

Structures and properties of ternary and quaternary sulfides and selenides containing gallium and/or indium and transition elements like Se, V, Ti, Cr, Mn, Fe, Co, Ni, Zn, Cd, and Hg crystallising in layered structures of the ZnIn 2 S 4 -type are reviewed. A survey of the different polytypic structures observed in these systems is given along with a compilation of the known compounds, their structures, their range of homogeneity and their lattice parameters. As far as available data on high pressure phase transformations, thermal stability, and band gap energies of these compounds are tabulated, too.

The present paper deals with the microstructural parameters calculated from X-ray diffraction data, electrical and optical investigations, and scanning tunneling microscopy (STM) studies on ZnIn2S4 IIIa layer type CdIn2S4-xSex (1.75 ≤ x ≤ 2.75) quaternary chalcogenides. Microstructural parameters such as dislocation density, root-mean-square strain, stacking fault probability, crystallite size anisotropy, and layer disorder parameters of these compounds have been calculated. The temperature variation of electrical conductivity (25−400 °C) confirmed semiconducting behavior. The band gaps of all these compounds obtained from STM and optical measurements are in the range 1.57−1.77 eV and are comparable to each other irrespective of the technique used.

The crystal structures of MnSc2S4 and CdSc2S4 have been determined from single crystal X-ray diffraction data. MnSc2S4 crystallises in a normal spinel structure (space group Fd 3 m) while for CdSc2S4 prepared at 900°C space group F 4 3m is observed. In the structure of CdSc2S4 the tetrahedral 8a site of the spinel structure is split into two different sites one of which exhibits a site occupation factor (sof) of only 0.9. A corresponding amount of Cd is found in an additional octahedral site (sof=0.1). The structure can be looked at as a transition state between the spinel and the sodium chloride structure. CdSc2S4 prepared at 600°C adopts a normal spinel structure (space group Fd 3 m) as has been elucidated from X-ray powder diffraction data by Rietveld analysis. The structure of FeSc2S4 has been determined from X-ray powder data by Rietveld analysis. FeSc2S4 crystallises in a normal spinel structure.

The system (1 - x)NiIn 2 S 4 - xNiIn 2 Se 4 has been investigated by X-ray powder methods. The subsolidus phase diagram is constructed in the temperature interval 600 -1000 °C. The spinel type NiIn 2 S 4 exhibits a phase width up to the composition NiIn 2 S 2 Se 2 at 900 °C and NiIn 2 S 2 . 8 Se 1 . 2 at 600 °C. A new layered compound is formed for 0.7 > x > 0.5 at 600 °C and for x = 0.6 at 900 °C which crystallizes in the MgAl 2 S 4 -type with a = 392.4 and c = 3739.6 pm (x = 0.6) for the hexagonal cell.

The systems MnGa2S4MnV2S4, MnGa2S4MnTi2S4 and the corresponding magnesium systems MgGa2S4MgV2S4 and MgGa2S4MgTi2S4 were studied by x-ray diffraction methods on quenched powder samples. In all four systems new quaternary compounds crystallizing in a layered structure have been obtained. MgGa1.6Ti0.4S4 (a = 370.9, c = 1219.1 pm) adopts a structure of α-FeGa2S4-type while MnGa1.6Ti0.4S4 (a = 370.9, c = 1219.0 pm) and MnGa1.8V0.2S4 (a = 370.2, c = 3652 pm) are of ZnIn2S4(IIIa)-type at 700 °C and undergo a phase transition to the α-FeGa2S4 type at 960 °C. Samples of MgGa1.6V0.4S4 consist of a mixture of both layered structures.

The influence of substitution of Mn 2+ by Co 2+ , Ni 2+ , and Zn 2+ in the olivine Mn 2 GeS 4 has been investigated by x-ray powder methods on polycrystalline samples. Contrary to similar systems starting from spinel type compounds we could not obtain new layered materials in these systems. A series of olivine type mixed crystals are formed in the system Mn 2−x Co x GeS 4 for 1 ≥ x ≥ 0. In the corresponding Ni system the olivine type region reaches from x = 0 to at least x = 1.7. Zn 2+ cannot replace Mn 2+ in the olivine structure. Substitution of Zn 2+ in Zn 2 GeS 4 by Mn 2+ changes the structure from a defect sphalerite to defect wurtzite type. Co 2 GeS 4 and Ni 2 GeS 4 could not be obtained.

The systems CoGa 2- x Sc x S 4 , ZnGa 2- x Sc x S 4 and CdGa 2- x Sc x S 4 were investigated by X-ray powder methods on polycrystalline samples quenched at 800 and 1000°C. Three new compounds were obtained: CoGa 1.8 Sc 0.2 S 4 ( a =366.1 pm, c =1208.4 pm) and ZnGaScS 4 ( a =373.3 pm, c =1222.8 pm), both crystallizing in an FeGa 2 S 4 -type structure, and a spinel-type CoGa 0.2 Sc 1.8 S 4 ( a =1043.3 pm). Formation of a quaternary compound could not be obtained in the cadmium system.

Quaternary tellurides Cu2MM′Te4 (M = Zn, Cd, Hg and M′ = Si, Ge, Sn) have been prepared by solid state reactions and characterized by X-ray powder methods. All 9 compounds crystallize in a stannite type structure.

Far-infrared and Raman spectroscopic studies were performed on compounds of composition A2BCX4 (A = Cu, Ag; B = Zn, Cd, Hg, Mn, Fe, Co; C = Si

The systems CoGa2S4CoV2S4 and CoGa2S4CoTi2S4 were studied by x-ray diffraction methods on quenched powder samples. In both systems new quaternary compounds CoGa1.8V0.2S4 and CoGa1.8Ti0.2S4 crystallizing in the trigonal layered structure of FeGa2S4 type (a=364.5, c=1203.8 pm and a=364.3, c=1205.8 pm, respectively.) have been obtained. They are formed only at temperatures above 800 and 900 °C, respectively, but can be quenched without decomposition. The phase width of both compounds increases with increasing temperature. For the end member compounds no phase width could be detected.

The system MnGa2S4-MnSc2S4 was studied by X-ray diffraction methods on quenched samples. Two intermediate phases are described: (1) a compound MnGa2−2xSc2xS4 for 0.2 ⩽ x ⩽ 0.3 crystallizing in the FeGa2S4-type structure and (2) a new olivine-type compound MnGaScS4 (x = 0.5), which exhibits no phase width. The structure of MnGaScS4 was determined from single-crystal X-ray diffraction data and refined to R = 0.018 (space group Pnma, No. 62, a = 1279.6(1), b = 742.6(1), c = 608.6(1) pm, Z = 4). The IR spectra of the new phases and the two border compounds are given.

The crystal structure of CoGaInS4 has been determined from single crystal X-ray diffraction data and refined to R = 0.03. It crystallizes in the trigonal FeGa2S4 type (space group P 3 m1 , No. 164, a = 3.759(1), c = 12.184(2) A, Z = 1) with the following cation distribution: (Co0.61In0.39Ga)t(Co0.39In0.61)oS4. The system xCoGa2S4-(1 − x)CoIn2S4 is quasibinary. The compound CoGaInS4 has a large region of homogeneity with a marked dependence on temperature, ranging from x = 0.2 to x = 0.8 at 800°C. Compounds with high indium content show a phase transition to the ZnIn2S4(IIIa) type at 1000°C. Electronic spectra have been recorded on samples with different composition and on samples quenched from different temperatures.

Lattice dynamical calculations of the spinel type MCr2S4 (M = Mn, Fe, Cd) have been done using various potential models (short-range, rigid-ion, polarizable-ion). The main results are that (i) the vibrational modes (eigenvectors) and potential energy distributions of the Raman and IR allowed phonon modes of the three chromium sulfides are very similar, (ii) the A-X and B-X short-range force constants (referring to AB2X4) strongly depend on the structural parameter u, i.e., the tetrahedral A-X force constants are smaller than the respective octahedral B-X ones opposite to previous calculations on the basis of an ideal spinel structure with u = 0.25, (iii) bending force constants (X-A-X and X-B-X), but not X-X and B-B repulsive forces, are negligible, (iv) in the case of the breathing mode of the tetrahedral AX4 unit (species A1g) the demand on B-X and X-X (stretching and repulsion) forces is larger than that on the A-X force, and (v) the effective dynamic charges of the bivalent metal ions are nearly zero.

Structure field maps for ternary sulfides crystallizing in common AB 2 X 4 structures are given. They have been obtained from a plot of mean values of pseudopotential radii. There is a good separation of the fields for the different structures. The maps are used to predict possible compositions for new quaternary compounds of ZnIn 2 S 4 type.

The system MgGa2S4MgSc2S4 was studied by X-ray diffraction methods on samples quenched from 800 to 1000°C. Two new compounds MgGaxSc2−xS4 are obtained: for x = 1.6 a new material with FeGa2S4 type structure (trigonal, P 3 m1 (No. 164), a = 373.7(1), c = 1222.0(2) pm) and for x = 1.0 a new olivine type compound (orthorhombic, Pnma (No. 62), a = 1278.5(3), b = 741.9(1), c = 607.2(1) pm). The crystal structure of the olivine type compound MgGaScS4 was determined from single-crystal X-ray diffraction data and refined to R = 0.025. The octahedral 4a site is occupied by 0.7 Sc and 0.3 Mg, the 4c site, which is octahedrally coordinated also by 0.3 Sc and 0.7 Mg, and the tetrahedrally coordinated 4c site by Ga. An analogous cation distribution is found for the olivine MnGaScS4.

The present paper deals with the preparation of ZnIn2S4−IIIa layer-type CdIn2S4-xSex (1.75≤ x ≤ 2.75) quaternary chalcogenides and their characterization. X-ray diffraction studies of CdIn2S4-xSex (1.75 ≤ x ≤ 2.75) confirmed that all of these compounds possess the ZnIn2S4−IIIa type of structure. The variation of the composition x shows that both lattice parameters a- and c increase with a growing amount of selenium in the crystals. The calculation of microstructural parameters by an X-ray line profile analysis has shown that the intercalation of lithium in the host CdIn2S2Se2 is accompanied by a decrease in crystallite size while the dislocation density and the rms strain are increasing. The process of intercalation results in no expansion along the c-axis, probably due to no increase in the c-parameter at all in a given intercalation process; which does not have purely geometric origin but also comes from electronic effects. A radial distribution function (RDF) analysis of these quaternary chalcogenides ...

The system MnGa2S4-MnSc2S4 was studied by X-ray diffraction methods on quenched samples. Two intermediate phases are described: (1) a compound MnGa2−2xSc2xS4 for 0.2 ⩽ x ⩽ 0.3 crystallizing in the FeGa2S4-type structure and (2) a new olivine-type compound MnGaScS4 (x = 0.5), which exhibits no phase width. The structure of MnGaScS4 was determined from single-crystal X-ray diffraction data and refined to R = 0.018 (space group Pnma, No. 62, a = 1279.6(1), b = 742.6(1), c = 608.6(1) pm, Z = 4). The IR spectra of the new phases and the two border compounds are given.

The results of a factor group analysis, the symmetry coordinates and vibrational modes of the lattice vibrations of compounds crystallizing in NiAs structure respectively NiAs defect structure (Fe3Se4 type) are presented. A normal coordinate treatment of the NiAs structure is performed using the GF-matrix-method assuming a valence force field with 3 force constants.

Force constants and normal coordinates of MnS2 , FeS2 , RuS2, RuSe2, RuTe2, OsS2 and PtP2 are calculated based on the five ir active vibrations of the pyrite lattice. By setting up a valence force field consisting of short and long range M -X, X2 -X2 and M -M stretching constants it has proved possible to obtain good agreement between experimental and calculated frequencies with expection of FeS2 and RuS2 . The force constants corresponding to the shortest metal chalcogen distances (MnS2: 0.30, RuSe2: 0.88, RuTe2: 0.62, OsS2: 1.32, PtP2: 1.22 mdyn/Å) are mainly responsible for the ir frequencies. For RuSe2 and RuTe2, the forces between adjacent X2 groups are not negligible. Whereas the force constants of OsS2 and PtP2 are of comparable strength, the forces in MnS2 are significantly weaker than those in the other compounds. The normal coordinates of MnS2, OsS2 and PtP2 , and RuSe2 and RuTe2 show significant differences according to both the contribution of the 6 symmetry coordinates to the 5 ir active vibrations and the assignment of the spectra.

GaCr2S4 has been prepared from the binary sulfides by solid state reaction at 1150°C. It crystallizes in the spinel structure with a = 993.6 pm. Thecompoundismetastableatroomtemperatureandcanonlybeobtainedbyquenchingfromthereactiontemperature. Above 1150°CacompleteseriesofmixedcrystalsbetweenGaCr2S4andGa2/3Cr2S4 can be obtained. The IR spectra of the compounds are given and discussed.

The Raman and infrared reflection spectra of the spinel-type halidesLi 2 M II Cl 4 ( M II = Mg, V, Cr, Mn, Fe, Co, Zn, Cd) and Li 2 MnBr 4 including Kramers-Kronig analyses and oscillator-fit calculations are presented. These results are discussed in terms of (i) fast ionic conductivity, (ii) cation distribution, i.e., normal (Li 2 ZnCl 4 ) and inverse spinels, 1:1 ordering of Li and M II in the octahedral sites (Li 2 CoCl 4 ), (iii) phase transitions to an ordered (LiVo 2 type) and disordered NaCl defect structure, and (iv) two-mode behavior of the phonon modes.

On the basis of the rigid ion model and polarizable ion model, lattice dynamical calculations have been carried out for the fluorohalides BaFCl and BaFBr and for the oxyhalides LaOCl, LaOBr, YOCl, SmOCl and GdOCl which crystallize with the tetragonal Matlockite-type structure (PbFCl-type). The results of these calculations: short range force constants, effective dynamical charges and polarizabilities are communicated and discussed. Bonding in the fluorohalides is much more ionic than in the oxyhalides.

The Raman and i.r.-spectra of trirutiles AB2O6 with A = Mg, Zn, Ni, Co and B = Sb, Ta and A′2TeO6 with A′ = Al, Ga, Cr, Mn, Fe have been recorded on powder samples. For the trirutile-type structure Cartesian symmetry coordinates are given. Based on these coordinates a normal coordinate and force constant calculation has been performed. The TeO stretching force constant has a value of 3.1 mydn A−1 which corresponds to the value predicted for a covalent single bond. The normal modes are discussed in relation to the potential energy distribution and to the vibrations of a free octahedron. Correlation splitting for the Raman-active octahedral vibrations of species A1g and B2g is computed to be very small.

Auf der Basis eines modifizierten Valenzkraftmodells werden die Kraftkonstanten, Eigenvektoren und Schwingungsformen der Chromthiospinelle ACr2S4 (A = Zn, Cd, Hg, Mn, Fe, Co) berechnet. Die beste Ubereinstimmung zwischen den beobachteten und berechneten Frequenzen der 4 IR-aktiven Schwingungen des Spinellgitters ergibt ein Potentialmodell mit den 2 Bindungskraftkonstanten fAS und fCrS, der Wechselwirkungskonstante zwischen diesen beiden Bindungen und einer der beiden Winkeldeformationskraftkonstanten ΔφSCrS und ΔφSAS. Die Cr – S-Bindungskraftkonstante ist entsprechend dem groseren Abstand zwischen dem Schwefel und dem oktaedrisch koordinierten Chrom im Vergleich mit dem Bindungsabstand im AS4-Tetraeder deutlich kleiner als die A – S-Bindungskraftkonstante. Die Wechselwirkungs- und die Winkeldeformationskonstanten sind positiv und konnen nicht vernachlassigt werden. Die Normalkoordinatenrechnung ergibt, das an jeder der 4 IR-aktiven Schwingungen alle Atome der Basiszelle beteiligt sind. Es zeigen sich jedoch signifikante Unterschiede bei der Beteiligung der 5 Symmetriekoordinaten an den verschiedenen Schwingungen. Force constants, eigenvectors and vibrational modes of the chromium thiospinels ACr2S4 (A = Zn, Cd, Hg, Mn, Fe, Co) are calculated based on the frequencies of the four ir-active vibrations of the spinel lattice. Best agreement of the observed and calculated frequencies is reached with a modified short range valence force field consisting of an A – S- and a Cr – S-bond stretching constant, the interaction constant between these two bonds and the ΔφSAS or ΔφSCrS bond bending force constant. According to the longer distance between sulfur and the octahedral coordinated chromium atoms compared with the bond length in the AS4-tetrahedron the Cr – S-stretching constant is much smaller than the A – S-stretching constants. The interaction constant and the bond bending force constants are positive and not negligible. The results of the normal coordinate calculations show that all atoms of the unit cell contribute to each one of the four vibrations of species F1u but there are significant differences according to the contribution of the 5 symmetry coordinates to the 4 ir-active vibrations.

Im System ZnInSSe wurde das Teilsystem ZnIn2S4ZnIn2Se4In2Se3In2S3 rontgenographisch an Praparaten, die von 800°C abgeschreckt worden waren, untersucht. Danach weisen ZnIn2S4 bzw. ZnIn2Se4 nur kleine, die Spinelldefektstruktur im In2S3-reichen Teil des Phasendiagramms dagegen einen ausgedehnten Homogenitatsbereich auf. Neu beobachtet wurden drei Verbindungen: 1. trigonales ZnIn2S2Se2 (ahex = 3,937, chex = 31,97 A) mit ebenfalls grosem Homogenitatsbereich 2. Zn0,4In2Se3,4 und 3. In2S3−xSex fur 2,1 ≤ x ≤ 2,7. Fur die beiden ternaren Verbindungen bleiben die Strukturen noch unbekannt. The Quaternary System ZnIn2S4ZnIn2Se4In2Se3In2S3 The title system has been investigated on the indium rich side (ratio In/Zn ≥ 2) on samples quenched from 800°C to room temperature using x-ray methods. In this section 7 different phases could be identified the phase borders of which are given. ZnIn2S4-type and thiogallate type mixed crystals only show a small region of homogeneity while the monophase region of spinel type mixed crystals in the indiumsulfide rich part of the phase diagram has a larger extension. There is a new trigonal compound ZnIn2S2Se2 (ahex = 3.937, chex = 31.97 A) with a large region of homogeneity. In the indiumselenide rich part there are two new phases: (i) Zn0.4In2Se3.4 with unknown structure and (ii) a ternary phase of unknown structure in the system In2S3−xSex for 2.1 ≤ x ≤ 2.7.

The phase diagrams of the quaternary systems M SCr 2 S 3 In 2 S 3 , with M = Co, Cd, and Hg, were studied with the help of X-ray powder photographs of quenched samples, high-temperature X-ray diffraction patterns, DTA and TG measurements, and far-infrared spectra. Because indium sulfides do react with silica tubes, alumina crucibles must be used for annealing the samples. Complete series of mixed crystals are formed among the spinel-type compounds M Cr 2 S 4 , M In 2 S 4 ( M = Cd, Hg), and In 2 S 3 . HgIn 2 S 4 is decomposed at temperatures above 300°C. In the sections CoCr 2 S 4 CoIn 2 S 4 and CoCr 2 S 4 In 2 S 3 relatively large miscibility gaps exist due to the change from normal to inverse spinel structure. But the interchangeability of both systems increases with increasing temperature, and at temperatures above 1000°C, complete series of solid solutions are formed, which can be quenched to ambient temperature. Superstructure ordering like that of ordered α-In 2 S 3 has been found in the In-rich region of the M In 2 S 4 In 2 S 3 solid solutions. The unit cell dimensions of all stoichiometric and phase boundary compounds, e.g., Cd 1.15 In 1.9 S 4 , including the chromium spinels M Cr 2 S 4 ( M = Mn, Zn) and ZnCr 2 Se 4 , are given and discussed in terms of possible deviations from stoichiometry.

CoGaInS has been prepared by solid state reaction from the binary sulfides at 800°C. It crystallizes trigonally (space group P3m1) with a = 375.9 and c = 1218.4 pm and is isotypic with α-FeGa 2 S 4 . Co 2+ and In 3+ occupy partly octahedral and partly tetrahedral voids. The FIR spectrum of CoGaInS 4 is communicated and discussed in comparison with those of CoGa 2 S 4 and CoIn 2 S 4 .

The quasibinary systems MGa2S4MCr2S4 are studied for M = Zn, Cd, and Hg by X-ray investigations on powdered samples. The end members of these series show no detectable phase width. The formation of quaternary compounds is not observed. A new sulfide CoGa1.5Cr0.5S4 is obtained in the system CoGa2S4CoCr2S4 and characterized by X-ray and IR studies. CoGa1.5Cr0.5S4 is isomorphous with α-FeGa2S4 and crystallizes trigonally (space group P 3 m1 ) with a = 363.7(1) and c = 1200.7(1) pm. A study of the extension of the phase fields for this compound and the spinel CoCr2S4 in the system CoGa2S4CoCr2S4Cr2S3Ga2S3 is also undertaken.

The infrared spectra of spinel-type compounds A+A3+ Cr4X8 (A+ = Li, Cu, Ag; A3+ = Al, Ga, In; X = S, Se) have been measured. The spectra show that the spinels LiGaCr4S8, LiInCr4S8, CuGaCr4S8, CuInCr4S8, AgInCr4S8, CuGaCr4Se8, CuInCr4Se8, and AgInCr4Se8, whose structures cannot be determined by X-ray methods in all cases, have a structure with 1:1 ordering on the tetrahedral site (space group F 4 3m ). No ordering takes place in AgGaCr4S8. The spectra of the ordered spinels are discussed in relation to two-mode type spectra of spinel mixed crystals.

The quasi-binary systems Zn1-xCdxAl2S4, ZnAl2(1-x)Ga2xS4 and ZnAl2S4(1-x)Se4x have been investigated by X-ray diffraction and vibrational spectroscopy. In the spinel ZnAI2S4 up to 20% of Zn can be replaced by Cd. In the two other systems, ZnAl2S4 has no detectable homogeneity range. The thiogallate phases have much broader ranges of homogeneity. The compositions of the compounds at the phase boundary of the thiogallate phase are Zn0.4Cd0.6Al2S4, ZnGa0.4Al1.6S4, and ZnAl2S2.8Se1.2. At approximately 950 °C ZnAl2Se4 undergoes a reversible phase transition to a wurtzite-type structure. This phase transition is also observed for the solid solutions ZnAl2S4(1-x)Se4x; with 1.0 > x > 0.3. The FIR spectra are discussed.

Single crystals of LaOBr and SmOBr were grown from a flux of the corresponding anhydrous rare earth bromide by slow cooling. The crystals were obtained as thin platelets with dimensions up to 5×5×0.1 mm. In the case of LaOBr the formation of needle-like crystals (1×0.1×0.1 mm) was also observed. The crystal structures of LaOBr and SmOBr were determined from single crystal X-ray diffraction data. They both crystallize in the PbFCl structure with z(La) = 0.16206(6)z(Br) = 0.6352(2) (LaOBr) and z(Sm) = 0.1464(4) z(Br) = 0.6550(7) (SmOBr).

With the intention to prepare new compounds with layered structures we have studied the quasibinary system MnGa 2 S 4 MnCr 2 S 4 by X-ray investigations on powdered samples. The parent compounds MnGa 2 S 4 and MnCr 2 S 4 have no detectable phase widths. A new compound MnGa 2 x Cr 2−2x S 4 (0.75 2 S 4 (IIIa) type structure is observed in the gallium rich part of the system. Magnetic measurements on MnGa 1.5 Cr 0.5 S 4 in the temperature range 77–300 K show paramagnetic behaviour with θ = − 88 K and C = 4.418.

The far-infrared reflection spectra of hot-pressed samples of the spinels M Cr 2 S 4 with M =Mn, Fe, Co, Zn, Cd, and Hg, MCr 2 Se 4 with M =Zn, Cd, and Hg, and M In 2 S 4 with M =Mn, Fe, Co, Ni, Cd, Hg have been recorded in the range from 40 to 700 cm −1 . The spectra show four reststrahlen bands in the case of normal spinels and up to five in the case of inverse spinels. The transverse and longitudinal optical phonon frequencies at wave vector ∣ q ∣ ⋍ 0 are determined by Kramers-Kronig analysis and the classical oscillator-fit method. Effective ionic charges (normalized splitting, transverse effective charge, Szigeti charge) were calculated from the experimentally determined TO–LO splittings and from the high frequency dielectric constants. The obtained data reveal an increasing covalency of the chalcide spinels in the order selenides > sulfides, chromium compounds > indium compounds, inverse spinels > normal spinels,Ni M′ 2 X 4 > Co M′ 2 X 4 > Fe M′ 2 X 4 ,Mn M′ 2 X 4 > Hg M′ 2 X 4 > Zn M′ 2 X 4 >CD M′ 2 X 4 .

The sections Li 2 M Cl 4−4x Br 4x of the quaternary systems LiCl-LiBr- M Cl 2 - M Br 2 with M = Mn, Cd, and Fe were studied by high-temperature X-ray diffraction patterns and DTA and DSC measurements. In the quasibinary lithium manganese halide system complete series of solid solutions exist between the inverse spinels Li 2 MnCl 4 and Li 2 MnBr 4 . Li 2 MnBr 4 and solid solutions with x > 0.54 undergo phase transitions to tetragonal spinels at lower temperatures. In the nonquasibinary system with M = Cd, only at temperatures near 400°C a complete series of mixed crystals is formed. At lower temperatures the system is mainly two-phase with rock salt-type Li 1− y Cd 0.5 y Cl 1− x Br x and cadmium chloride-type Cd 1− y Li 2 y Cl 2−2 x Br 2 x solid solutions in equilibrium. The lithium iron halide system is similar to that of cadmium, but spinel-type Li 2 FeBr 4 does not exist at any temperature. The manganese and cadmium halide spinels and spinel solid solutions undergo phase transitions to NaCl defect structures at elevated temperatures.

Die Ergebnisse FIR- und Raman-spektroskopischer sowie rontgenographischer Untersuchungen an den im Spinelltyp kristallisierenden Chloriden Li2TCl4 (T = Mg, Mn, Fe, Cd) werden mitgeteilt. Die Schwingungsspektren zeigen, das keine 1:1-Ordnung der Kationen auf den Oktaederplatzen vorliegt. Thermoanalytische Messungen sowie Rontgenheizaufnahmen zeigen, das sich die Chlorid-Spinelle beim Erhitzen auf 535°C (Li2MgCl4), 460°C (Li2MnCl4) sowie 385°C (Li2CdCl4) reversibel in eine kubisch indizierbare Hochtemperatur-Defektstruktur mit gegenuber dem Spinellgitter um den Faktor 2 kleineren Gitterkonstanten umwandeln. Die Fehlordnung des Lithiumteilgitters setzt jedoch, wie Messungen der elektrischen Leitfahigkeit zeigen, schon bei erheblich niedrigeren Temperaturen ein.

The polarized far-infrared reflection spectra of single crystals of the defect chalcopyrites CdGa2S4 CdGa2Se4, HgGa2S4, and HgGa2Se4 grown by vapour phase transport technique are presented in the range from 40 to 600 cm−1. The spectra reveal ten reststrahlen bands as predicted by group theoretical treatment. The oscillator parameters eα∞, ωαf, ωαf, and γαf, the transverse and longitudinal optical phonon frequencies ωTO and ωLO, and the dynamic effective ionic charges are calculated using classical oscillator fit method. The high-frequency dielectric constants eα∞ show an anisotropic behaviour, the effective charges (Szigeti charges), however, are approximately scalar quantities. From the obtained oscillator parameters the directional dispersion of the extraordinary polar phonons is determined. The reflection spectra calculated for oblique phonons are discussed and compared to those of pellets hot-pressed from polycrystalline samples. Die polarisierten FIR-Reflexionsspektren von Einkristallen der Thiogallate CdGa2S4, CdGa2Se4, HgGa2S4 und HgGa2Se4 werden im Bereich von 40 bis 600 cm−1 untersucht. Die Darstellung der Kristalle erfolgt durch Gasphasentransport. Nach der Methode des Oszillatorfits werden die Oszillatorprameter eα∞, ωαf, ωαf und γαf, die transversalen und longitudinalen optischen Gitterschwingungsfrequenzen ωTO und ωLO sowie die dynamischen effektiven Ionenladungen (Szigeti-Ladung) ermittelt. Wahrend sich die effektiven Ionenladungen annahernd wie Skalare verhalten, zeigen die hochfrequenten Dielektrizitatskonstanten eαω ein anisotropes Verhalten. Mit Hilfe der Oszillatorparameter wird die Richtungsdispersion der auserordentlichen polaren Phononen bestimmt. Die Spektren polykristalliner Proben werden mit Spektren, die fur nicht-orthogonale Phononen erhalten wurden, verglichen und diskutiert.

The vibrational frequency of free OH− ions, which cannot be directly measured, has been claimed to be 3700 cm−1. In solid hydroxides the OH stretching frequency has been found in the range from 3690 to 3100 cm−1. The decrease of the vibrational frequency has been interpreted to be caused by hydrogen bridges or the increase of the metal oxygen bond strength. We suggest an alternative explanation. The vibrational frequency of unperturbed OH− ions is 3570 ± 10 cm−1. In ionic hydroxides this frequency is increased due to repulsion effects of the lattice or decreased if hydrogen bonds are present, to a large extent (up to 400 cm−1) in the case of common OH−….X bridges and only up to 70 cm−1 in the case of XH….OH− bonds.

The crystal structure of Zn 1.25 In 2.5 S 3 Se 2 was determined from single crystal data. The compound crystallizes in the trigonal space group P3m1-D 3 3d (No 164) with Z = 2 . The lattice constants (hexagonal setting) are a = 3.927(1) and c = 31.83(1) A˚. The structure is of a layer type and may be described as a slightly distorted hexagonal closed packing of the anions with two In 3+ in octahedral voids and all other cations in tetrahedral coordination. The isotypic compounds Cd 0.5 Ga 2 InS 5 and Hg 0.8 Ga 1.6 In 1.2 S 5 have lattice parameters a = 3.809(1), c = 30.64(1) A˚, and a = 3.820(1), c = 30.929(3) A˚, respectively.

A normal coordinate and force constant calculation was carried out for lanthanoid oxyhalogenides LnOX with Ln = La, Pr, Nd, Sm, Eu and X = Cl, Br on the basis of a modified valence force field by fitting in the frequencies of the i.r. active vibrations. From the obtained force constants frequencies of the Raman-active lattice vibrations are calculated and compared with experimental determined frequencies.

A normal coordinate and force constant calculation for BaFBr was carried out on the basis of the rigid ion model. There is a strong anisotropy of the effective dynamical charges of the barium, fluoride, and bromide ions, which are 1.57e, −0.78e, and −0.79e for the degenerate vibrations and 1.04e, −0.71e, and −0.33e for the vibrations in the z-direction. In accordance with the ionic nature of BaFBr the short range force constants have only small values.

The chloride spinels Li2MCl4 with M = Mg, Mn, Fe and Cd show very high lithium ionic conductivity in the solid state. The ionic conductivity in the compounds under investigation was established with the help of emf measurements. The specific conductivities measured by both frequency response analysis and the four probe ac method are 1.3 Ω−1 · cm−1 for Li2CdCl4, and about 0.9Ω−1 · cm−1 for Li2MnCl4, Li2MgCl4, and Li2FeCl4 at 773 K. There are several indications that the ternary chlorides become highly disordered at elevated temperatures. Thus the Arrhenius plots, i.e. In σ · T vs 1/T-curves, exhibit significant bends, the slopes below the transition temperature being considerably higher than those above.