Electron diffraction study of CdInGaS4 thin films

The electron diffraction patterns of mono- and polycrystalline films of CdInGaS₄ were studied. The lattice parameters were found to be as follows: $\text{a = b = 6.62}\text{A}\text{?}\text{; c = 24.7}\text{A}\text{?}\text{.}$ The values of a and b differ fromthose reported in the literature. The discrepancy between these values is explained as due to specific errors in the X-ray investigation of laminated crystals.     

Some properties of GaSe thin films formed by the three-temperature method

Thin films of the semiconducting compound GaSe have been prepared by the three-temperature method (two-source vacuum evaporation) and deposited onto Pyrex substrates at temperatures between 230° and 290°C. Micrographs and X-ray diffraction analysis of the thin films have shown that they are poly-crystalline. The diffraction maxima have been indexed in terms of a hexagonal lattice of GaSe with unit cell dimensions $\text{a = 3.76}\text{A}\text{?}\text{and}\text{c = 15.95}\text{A}\text{?}$. Very strong and sharp 00l peaks indicate a highly preferred orientation of the crystallites with their c-axis normal to the plane of the film. The electrical resistivity versus temperature behaviour has revealed intrinsic conduction above 130°C with an activation energy equal to 1.88 eV. The optical energy gap value determined from transmission data has been found to be approximately 2.0 eV, which is close to the value obtained for a single-crystal specimen. The exciton peak found in the absorption spectrum of the GaSe single crystal at 2.002 eV is not present in the case of thin films.     

Syntheses and magnetic properties of Eu3B2O6 and Sr3B2O6

Europium orthoborate and strontium orthoborate crystallize in the rhombohedral system with two formula units in a cell of dimensions $\text{a}{}_{\mathrm{R}}\text{=6.697}\text{A}\text{?}$, α_R=85.17° for Eu₃B₂O₆, and $\text{a}{}_{\mathrm{R}}\text{=6.695}\text{A}\text{?}$, α_R=85.00° for Sr₃B₂O₆. The equivalent hexagonal lattice parameters are $\text{a}{}_{\mathrm{H}}\text{=9.069}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.542}\text{A}\text{?}$, and $\text{a}{}_{\mathrm{H}}\text{=9.046}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.566}\text{A}\text{?}$ respectively. Eu₃B₂O₆ appears to be ferromagnetic below 7.5K.     

Epitaxial intergrowth of the layered crystals SnTaS2 and SnS2

Layered crystals were obtained, with an overall composition of about Sn₃Ta₂S₆, which gave unusual electron diffraction patterns. The patterns are explained in terms of an intergrowth of thin, alternating layers of SnTaS₂ and epitaxially deformed SnS₂. The SnS₂ has a monoclinic structure with $\text{a}\text{= 15.78}\text{A}\text{?}$, $\text{b}\text{= 5.67}\text{A}\text{?}$ and β = 95°. Similar crystals based on Nb rather than Ta have also been obtained.     

The preparation,crystal structures and properties of the potassium vanadium sulfides KXV5S8 (0.5≦x≦0.7)

The crystal structures of the potassium vanadium sulphides K_0.7V₅S₈ and K_0.5V₅S₈ (=KV₁₀S₁₆) have been determined. K_0.7V₅S₈ has a C-centered monoclinic unit cell of dimensions $\text{a}\text{=17.499(3)}\text{A}\text{?}$, $\text{b}\text{=3.2986(6)}\text{A}\text{?}$, $\text{c}\text{=8.489(1)}\text{A}\text{?}$, ß=103.98(1)°, spacegroup C2/m; isomorphous with TIV₅S₈; K_0.5V₅S₈ has essentially the same structure, but due to ordering of the K atoms, the monoclinic b-axis is doubled, thus forming a superstructure. The cell parameters are: $\text{a}\text{=17.462(4)}\text{A}\text{?}$, $\text{b}\text{=6.556(2)}\text{A}\text{?}$, $\text{c}\text{=8.4595(9)}\text{A}\text{?}$, ß=103.86(1)°, spacegroup P2. The structures are characterized by a three-dimensional framework of VS₆ octahedra with channels in which the K atoms are situated. Both compounds exhibit metallic behaviour.     

Crystallography of human tooth enamel: Initial structure refinement

A first crystal structure refinement of human tooth enamel, per se, has been achieved. For this, both x-ray and neutron powder diffraction data were analyzed with the Rietveld method of whole-pattern fitting. The dense fraction (sp.g. >2.95) of pooled human tooth enamel was used. Refinement in space group P6₃/m led to $\text{a}\text{= 9.441(2)}\text{A}\text{?}$, $\text{c}\text{= 6.878(1)}\text{A}\text{?}$ and locations of the principal atoms similar to those in hydroxyapatite. The observed scattering density distributions along the hexad axis, including the differences between x-ray and neutron measures, would accommodate H₂O in some orientational disorder centered at z= 0.11 to 0.14 and the known small quantity of Cl^? ions partially substituting for OH^? (e.g. 1 in 20). This structure refinement constitutes the first direct evidence of both similarity and differences in the atomic-scale structural details of hydroxyapatite and human tooth enamel.     

Crystal growth and magnetic properties of NdFeTiO5

Single crystals of NdFeTiO₅ have been grown for the first time by using the flux technique. The observed X-ray reflections were compatible with the space group Pbam and the lattice parameters deduced from both single crystal rotation photographs and powder diffraction patterns are $\text{a}\text{= 7.500}\text{A}\text{?}$, $\text{b}\text{= 8.746}\text{A}\text{?}$ and $\text{c}\text{= 5.847}\text{A}\text{?}$. The crystals were found to undergo a magnetic transition to an antiferromagnetic state at T_N = 18.5 ± 0.5 K. The calculated temperature dependence of the Fe³⁺ and Nd³⁺ sublattice magnetizations based on the results of magnetic susceptibility measurements is presented.     

Preparation and structure of EuIINb4O11

The occurrence of compound in the system has been studied by means of X-ray powder diffraction. A compound, Eu^IINb₄O₁₁, was found. The X-ray powder diffraction data for Eu^IINb₄O₁₁ could be indexed on a tetragonal cell with $\text{a}\text{=52.52}\text{A}\text{?}$, $\text{C}\text{=7.69}\text{A}\text{?}$. The temperature dependence of the magnetic susceptibility for this compound is expressed by the equation, $\text{X}{}_{\mathrm{M}}\text{=}\text{7.10}\text{(}\text{T}\text{+0.20)}$. This compound is oxidized at about 290°C or above in air.     

BiPbVO5 — A new bismuth lead vanadate

BiPbVO₅ was prepared for the first time and single crystals were grown by the Czochralski technique. Precession x-ray photographs indicated triclinic symmetry with space group 1 or 1?. The lattice parameters are $\text{a}\text{= 7.082}\text{A}\text{?}$, $\text{b}\text{= 7.802}\text{A}\text{?}$, $\text{c}\text{= 5.203}\text{A}\text{?}$, a = 111.788 deg., β = 95.207 deg., γ = 108.717 deg.     

High temperature form of Pb2WO5 and transformation phenomena to its low form

The phase transformation of Pb₂WO₅ was studied by means of high temperature x-ray diffractometry, differential scanning calorimetry ( DSC ) and visual observation of the crystal growth in the range between room temperature and to its melting point. Two forms were found to be stable in the range studied. The Pb₂WO₅, which had been reported by DeVries and Fleischer was confirmed to be low temperature form. The newly synthesized high temperature form is isomorphous with Pb₂MoO₅ and its cell parameters are; $\text{a}\text{=14.206 (2)}\text{A}\text{?}$, $\text{b}\text{=5.799 (1)}\text{A}\text{?}$, $\text{c}\text{=7.346 (1)}\text{A}\text{?}$ and β=113°54 (0.9)′. The transition temperature was determined by DSC measurements as 330±10°C. The transition from high to low form is remarkably affected by the crystal size of its high form. Large crystals easily transform to its low temperature form. However, small crystalline sample (?100 μm), the rate of transformation is quite low and the high form is easily retained to the room temperature. One of the previously reported x-ray diffraction pattern of Pb₂WO₅ was revealed to be the mixture of high and low form of this compound.     

Polymorphisme sous pression de Sm2Ge2O7 et identification de la nouvelle phase H de la serie des digermanates de terres rares

The pressure-temperature phase diagram of Sm₂Ge₂O₇ was determined up to 80 kbar and 1400°C. In this pressure-temperature range only two phases were found. The B″ triclinic phase synthetised at atmospheric pressure is stable up to 40 kbar and at higher pressures appears the H phase which is a new type of structure in the rare earth digermanate series. The lattice parameters of the H phase were determined on small single crystals which were grown with water as mineralizer. The symmetry of the H phase is hexagonal with a space group P 6/m m m. The cell parameters of H-Sm₂Ge₂O₇ are $\text{a}\text{= 11,26}\text{A}\text{?}$ and $\text{c}\text{= 31,80}\text{A}\text{?}$. The measured density is 7,01 g/cm³ and therefore the cell contains twenty seven Sm₂Ge₂O₇ units. The calculated density is 7,16 g/cm³. The X-ray diffraction pattern of H-Gd₂Ge₂O₇ previously obtained can be indexed with similar parameters $\text{a}\text{= 11,19}\text{A}\text{?}$ and $\text{c}\text{= 31,65}\text{A}\text{?}$.     

The crystal structures of Ba2LaRuO6 and Ca2LaRuO6

Neutron diffraction experiments have been performed to determine the structures of Ba₂LaRuO₆ and Ca₂LaRuO₆. Both are ordered, distorted perovskites. Ba₂LaRuO₆ is monoclinic, space group $\text{P}\text{2}{}_{\mathrm{<mtext>1</mtext>}}\text{n}$ with $\text{a}{}_0\text{=6.0285(7)}\text{A}\text{?}$, $\text{b}{}_0\text{=6.0430(7)}\text{A}\text{?}$, $\text{c}{}_0\text{=8.5409(6)}\text{A}\text{?}$, β=90.44(1)^o. The A sites are occupied by barium and the B sites by an ordered arrangement of lanthanum and ruthenium. Ca₂LaRuO₆ is triclinic, space group P1 with a₀=5.6179(5), b₀=5.8350(5), c⁰=8.0667(4), α=90.0^o, β=89.76(1)^o, γ=90.0^o. The A sites are occupied by calcium and lanthanum in a disordered manner, and the B sites are occupied by an ordered arrangement of calcium and ruthenium. The results reported in this paper thus contradict those of previous workers. The low-temperature magnetic structures are discussed briefly.     

Synchrotron X-ray diffraction study of the incommensurate graphite-bromine compound: Change in the c-axis repeat distance during the incommensurate-commensurate transition

Synchrotron X-ray diffraction showed that the incommensurate-commensurate transition of stage-2 graphite-bromine at 319 K involved a change of the c-axis repeat distance from $\text{10.40 ± 0.01}\text{A}\text{?}$ to $\text{10.22 ± 0.01}\text{A}\text{?}$. This suggests that the transition is three-dimensional in nature and that the bromine atoms between two carbon layers in the incommensurate phase are not confined to a plane.     

The preparation and characterization of Ba3Te2O9; a new oxide structure

The structure of Ba₃Te₂O₉ has been determined from x-ray powder diffraction data and by profile refinement of neutron diffraction data. We find tellurium octahedrally coordinated as expected and the same face-shared [B₂O₉]^6? unit as observed in Ba₃W₂O₉. The phase Ba₃Te₂O₉ has, however, a Cs₃Fe₂F₉ type structure ($\text{P}\text{6}{}_3\text{mmc}$, $\text{a}\text{=}\text{5}\text{.8603(1)}\text{A}\text{?}$, $\text{c}\text{=14.3037(6)}\text{A}\text{?}$) rather than the Cs₃Tl₂Cl₉ structure (R3c) found for the tungsten analogue. The two oxide structures have the same BaO₃ layer sequence but differ only in the spatial arrangement of the [B₂O₉] groups in the lattice. Infrared and Raman spectra confirm the different site symmetries associated with the different packing of the tungstate and tellurate anions in their respective structures.     

The crystal structure of the intercalates SnTaS2 and SnNbS2

The crystal structure of SnTaS₂ was determined by X-ray and neutron powder diffraction. SnTaS₂ is hexagonal, $\text{a}\text{=3.307}\text{A}\text{?}$, $\text{c}\text{=17.442}\text{A}\text{?}$, space group P6₃/mmc with Ta and Sn at special positions. Ta is in trigonal-prismatic coordination by sulfur forming TaS₂ slabs; Sn is linearly coordinated by sulfur atoms of adjacent TaS₂ slabs. X-ray powder diffraction showed that SnNbS₂ is isostructural with SnTaS₂.     

On a new structural type of fluorine compounds : Crystal and magnetic structures of a high pressure form of PdF2

A new structural type of MF₂ fluorine compounds has been studied using neutron diffraction. The structure of the high pressure form of Pd difluoride has been shown to derive from the fluorite type by a rhombohedral distortion of the cubic environment of the cations. The coordination number of the cations is VI + II : the six nearest neighbor fluorine atoms form a distorted octahedron with $\text{M}\text{?}\text{F}{}_1\text{? 2.18}\text{A}\text{?}$, while two further anions correspond to $\text{M}\text{?}\text{F}{}_2\text{? 3.17}\text{A}\text{?}$. Distances and angles have been compared with those of other Pd compounds. The structure of the high pressure form of PdF₂ has been refined via neutron diffraction ($\text{a}\text{= 5.329}\text{A}\text{?}$, space group Pa3 or P2₁3). This phase orders antiferromagnetically below 190 ± 5 K and the magnetic structure has been determined on the basis of both collinear and noncollinear models. The magnetic data have been compared with results obtained for other d⁸ or d⁹ difluorides.     

Preparation and properties of EuFBr

EuFBr has been prepared for the first time and its lattice parameters and luminescence were measured. It crystallizes in P4/nmm symmetry with $\text{a}\text{= 4.217}\text{A}\text{?}$, $\text{c}\text{= 7.306}\text{A}\text{?}$. At room temperature it fluoresces in a narrow band centered around 393 nm. Contrary to EuFC1, no f → f transition could be observed for this compound.     

Bi5PO10 — A new bismuth phosphate

The title compound has been prepared for the first time and single crystals were grown by the Czochralski technique. Precession x-ray photographs indicated space groups C2, Cm, or C2/m with $\text{a}\text{= 19.642}\text{A}\text{?}$, $\text{b}\text{= 11.441}\text{A}\text{?}$, $\text{c}\text{= 21.131}\text{A}\text{?}$, and β = 112.37 deg.     

Polymorphism and phase transitions of K2TeBr6 (293–473 K)

The powder diffraction pattern from 293 to 473 K was recorded by a modified Guinier camera. The cubic high temperature phase with the K₂PtCl₆-type structure (spacegroup Fm3m, Z=4, $\text{a}\text{=10.78 (1)}\text{A}\text{?}$ at 473 (5) K) transforms below 445 (5) K into a tetragonally distorted structure (spacegroup P4/mc, z=2, $\text{a}\text{=7.572 (7)}\text{A}\text{?}$ and $\text{c}\text{=10.80 (1)}\text{A}\text{?}$ at 418 (5) K). This second order phase transition is result of a softening of the A_2g (X) rotary phonon corresponding with an antiferrorotative tilt of the TeBr₆-octahedra in adjacent (001) planes. From 410 – 334 K another second order phase transition yields the monoclinic P2₁/n-structure which is stable at room temperature. From the group-subgroup relations of the spacegroups an orthorhombic phase (spacegroup Pnnm) could be possible within this large transition range.     

Crystal structure of Li2 CaUF8

Compound Li₂CaUF₈ is tetragonal. The unit cell, with $\text{a}\text{=5.2290(12)}\text{A}\text{?}$,$\text{c}\text{=11.0130(18)}\text{A}\text{?}$, contains two formula units and the space group is I$\text{bar}\text{?}$m2. The crystal structure has been solved from single crystal diffractometer data by Patterson and Fourier synthesis and refined by a least-squares method. The final value of R is 0.062 for 602 reflections. The cationic distribution is the same as in the scheelite structure, with an additional cationic ordering. Moreover, we observe that the fluorine atoms are randomly distributed at two half occupied sites.