PbFCl-type Structure Research Articles

Rietveld refinement of the structure of Sr 0.3Ba 0.7FCl

The structure of Sr 0.3Ba 0.7FCl, formula weight 176.87, was determined by the Rietveld refinement procedure from X-ray powder diffraction data. This structure was solved in space group P2 n , Z = 2 with a = 4.335(1), b = 4.304(1), c = 7.146(3), Å, and γ = 90.379(2)°; R f = 0.055, R wp = 0.141. The compound exhibits a distorted tetragonal PbFCl-type structure. Interatomic distances are presented and compared with those of SrFCl and BaFCl.

Cryogenic luminescence studies of YOCl:Eu with the YOF and PbFCl type structures

YOCl:Eu was obtained in two different crystal structures (with 1% Eu substitution). The low temperature reaction (330 °C) yielded material having the YOF structure, where the lanthanide ion exhibits a coordination number of seven. The high temperature reaction (500 °C) yielded material having the PbFCl structure (coordination number of nine). While the luminescence associated with the PbFCl polymorph is well known, the luminescence associated with the YOF polymorph has not been reported before. The luminescence of the two YOCl: Eu materials was found to be significantly different, indicating the presence of non-equivalent crystal fields.

Heat capacity, neutron diffraction and crystal field models for AnNY (An ev Th, U; Y ev Se, Te)

New thorium and uranium ternary compounds AnNY (An ev Th, U; Y ev Se, Te) with tetragonal PbFCl-type crystal structure and metallic conductivity have been synthesived. Neutron diffraction investigations show the absence of magnetic order in UNSe down to 5 K and the presence of a simple collinear ferromagnetic order below 52 K for UNTe with magnetic moment μ ord = (0.85 ± 0.16) μ B aligned along the c avis. Heat capacity measurements are consistent with these conclusions. The electronic low temperature contributions are unusually large: 22 mJ mol −1 K −2 and 60 mJ mol −1 K −2 for UNTe and UNSe respectively. Tentative interpretations based on crystal field models and molecular field approvimation are given for the magnetic properties of UNTe as well as for the Schottky contribution to the heat capacity of both uranium compounds.

Zur Hochdruckpolymorphie der Seltenerdsulfidfluoride LnSF (Ln: Er, Yb, Lu) / High Pressure Polymorphism of Rare Earth Sulfidefluorides LnSF (Ln: E r, Yb, Lu)

Abstract The sulfidefluorides LnSF with Ln = Er, Yb, Lu undergo a high pressure transformation from the β-YSF- to a PbFCl-type structure. The structures involved and a proposed reaction mechanism are explained in terms of a topological description

Neue ternäre Alkaliphosphide mit Kupfer, Zink und Cadmium: K2CuP, NaZnP und K4CdP2 / On New Ternary Alkali Metal Phosphides: K2CuP, NaZnP and K4CdP2

The new compounds K2CuP, NaZnP and K4CdP2 have been prepared and structurally charac­terized. The crystallographic data are: K2CuP: orthorhombic, space group Cmcm (No. 63). Na2CuAs structure type with a = 983.9(5) pm. b = 739.7(4) pm, c = 579.5(3) pm. There are CuP2- zigzag chains, which are isosteric to the chains in HgO. NaZnP: tetragonal, space group P4/nmm (No. 129). PbFCl structure type with a = 406.6(2) pm. c = 689.3(3) pm, c/a = 1.695. K4CdP2: monoclinic, space group C2/m (No. 12). New structure type with a = 984.0(5) pm, b = 568.1(3) pm. c = 957.5(5) pm. β = 110.0(1)°. There are discrete [P−Cu−P]4- anions, which are isosteric to the HgCl2 molecules.

Crystal chemistry and 237Np mossbauer investigations on neptunium oxide chalcogenides NpOS and NpOSe

The preparation, the X-ray identification and 237Np Mössbauer spectrometry measurements of isostructural Np oxide chalcogenides NpOS and NpOSe are reported. They crystallize with the tetragonal PbFCl type structure. The isomer shifts of nuclear γ-ray resonance spectra indicate a tetravalent Np ion in these two compounds in agreement with the crystallographic considerations. Only NpOSe exhibits a magnetic order at 4.2 K.

Crystal structure and magnetic and electrical properties of GdMSi (M = first-row transition metal)

Abstract The crystal structure of the GdMSi compounds (M  first-row transition metal) was divided into two types: the tetragonal PbFCl-type structure for M  Mn , Fe , Co and the hexagonal AlB 2 -type structure for M  Ti , Cu , Zn . Examination of crystallographic data and the results of the electrical and magnetic measurements suggested that the change in the crystal structure of GdMSi depends on the atomic radii of the first-row transition metals and the concentration of the conduction electrons in the conduction bands of the compounds.

X-ray diffraction and absorption spectrophotometric studies of AmI 3 and AmOI

The anhydrous tri-iodides and the oxyiodide of americium were investigated by X-ray diffraction and absorption spectrophotometry. From the X-ray analysis of the tri-iodide, an orthorhombic form (PuBr 3-type structure) was identified, which is isostructural with the lighter actinide (uranium through plutonium) tri-iodides. A hexagonal form (BiI 3-type structure) of the tri-iodide was also found. The transition temperature for converting the orthorhombic form to the hexagonal form was established to be 400 ± 30° C. Room temperature lattice parameters for the tri-iodide are (1) a 0 = 0.428(4) nm, b 0 = 1.394(1) nm and c 0 = 0.9974(7) nm for the orthorhombic form, and (2) a 0 = 0.7637(4) nm and c 0 = 2.091(2) nm for the hexagonal form. The room temperature parameters for the tetragonal oxyiodide (PbFCl-type structure) are a 0 = 0.4010(4) nm and c 0 = 0.9200(6) nm. From differences in the absorption spectra of the solids at 25°C, it is possible to differentiate between these three materials by absorption spectrophotometry.

Synthesis, crystallographic and magnetic properties of the trivalent uranium oxyhalides UOCl, UOBr and UOI

The trivalent uranium oxyhalides UOCl, UOBr and UOI have been prepared. They crystallize with the PbFCl-type structure. Their magnetic properties have been investigated in the temperature range 4.2–300K. All are weak ferromagnets with nearly the same transition temperature (190–193K) and exhibit Curie-Weiss behaviour in the higher temperature region.

The crystal structure of americium(III) oxybromide

Americium (III) oxybromide has been prepared by vapor phase hydrolysis of americium (III) bromide, which in turn was obtained by hydrobromination of Am (OH) 3 in a stream of HBr at 590°C. The structure was evaluated from powder patterns. AmOBr crystallizes in a tetragonal PbFCl-type structure, space group P4/ nmm- D 4 h 7, with a = 3.982 A ̊ , c = 7.644 A ̊ , c a = 1.920 and V = 121.2 A ̊ 3 . With Z = 2 formula units per unit cell, the density was calculated as 9.23 g cm −3. There are 2 Am atoms in (0,0, u 1) and ( 1 2 , 1 2 , u ̄ 1 ), 2 O atoms in ( 1 2 , 0, 0) and (0, 1 2 , 0), and 2 Br atoms in (0, 0, u 2 ) and ( 1 2 , 1 2 , u ̄ 2 ) The parameters were found to be u 1 = 0.1789 ±0.0080 and u 2 = 0.6183 ± 0.0206. The interatomic distances are Am-O = 2.415 A ̊ and Am-Br = 3.36 and 3.210 Å.

Zur Hochdruckpolymorphie der Oxidchloride (MOCI) von Er, Tm, Yb und Lu und neue Verbindungen des Formeltyps Ln3O4Cl / High Pressure Polymorphism of Rare Earth Oxychlorides of Er, Tm, Yb and Lu and New Compounds with the General Formula Ln3O4Cl

Abstract Rare earth oxychlorides crystallizing in the SmSI arrangement undergo a high pressure transformation to a PbFCl-type structure. An intermediate phase appearing during the transition supports a proposed mechanism of displacive and martensitic movements in several steps. The decomposition of PbFCl-type oxychlorides to new Ln3O4Cl compounds is discussed as a topotactic reaction.

High-pressure phases with ordered defect PbFCl-type structures in the systems V–P and Nb–P

High-pressure phases with ordered defect PbFCl-type structures in the systems V–P and Nb–P

Some ternary uranium chalcogenides

The synthesis and crystal structures of the ternary uranium compounds UYX, where Y = Si, Ge, Sn, Sb, and X = S, Se, Te, are reported. USiS, UGeS, USnTe, USbS, USbTe and also UTe 2 − x are isotypic with ZrSiS which has a distorted PbFCl-type structure. USiSe, UGeSe and UGeTe have structures of a new type, closely related to that of ZrSiS. The compounds USiTe, USnS and USnSe could not be prepared. The instability of these compounds and the occurence of ZrSiS and UGeTe-type compounds are discussed.

Crystallography of the compounds of californium—II crystal structure and lattice parameters of californium oxychloride and californium sesquioxide

Californium oxychloride has been found to exhibit the tetragonal PbFCl-type structure. X-ray diffraction data from three polycrystalline samples give the average lattice parameters a = 3·956±0·002 A and c = 6·662±0·009 A, where the error limits represent the 95 per cent confidence interval. Three samples of a low-temperature californium sesquioxide have been prepared. Two of these samples, prepared by the hydrolysis of other californium compounds, were found to exhibit the cubic, Mn 2O 3-type structure with the average lattice parameter a = 10·838±0·020 A. The third sample, reacted in oxygen, had the lattice parameter a = 10·809±0·003 A, where the error limits represent the 95 per cent confidence level and reflect the internal consistency of the data for that particular sample. In an earlier study [1], the lattice parameter of an air-ignited oxide sample was 10·811±0·005 A; upon treatment with H 2(g) the lattice parameter increased by 0·49 per cent. These changes in the lattice parameter may reflect small departures from the sesquioxide stoichiometry and thus may constitute evidence for higher and/or lower oxidation states of californium.

Zirconium silicide and germanide chalcogenides preparation and crystal structures

AbstractThe tetragonal sublimates obtained by prolonged tempering of preparations of compositions about ZrX0.75 (X = S, Se, Te) in evacuated quartz tubes1, 2, are found to be ternary compounds ZrSiX. These novel compounds can be prepared conveniently by reaction of “SiX” with zirconium metal at elevated temperatures. The analogous germanium compounds are prepared in a similar way. The crystal structures of the ZrSiX and ZrGeX phases are related to the PbFCl structure type. Unit‐cell dimensions, atomic parameters (see Table I) and interatomic distances (see Table II) have been determined; they are discussed in some detail.

The crystal structure of the lanthanide oxyiodides, SmOI, TmOI and YbOI

patterns of the lanthanide oxyiodides SmOI, TmOl, and YbOI is given. These oxyiodides crystallize in the tetragonal PbFCl structure type; the unit cell dimensions are presented. For TmOI the atomic position parameters and the interatomic distances are also tabulated. (N.W.R.)