Guinier Powder Data Research Articles

ScFe5P3, ScRu6P4, U2Mo30P19, and Other Ternary Phosphides with a Metal to Phosphorus Ratio close to 2:1

AbstractThe title compounds and several other new ternary phosphides – all with closely related crystal structures – were prepared mostly by using elemental tin as a flux. ScFe5P3, Sc(Ta0.18Fe0.82)Fe4P3, and ZrFe5P3 are isotypic with YCo5P3. The crystal structure of the tantalum containing compound was determined from single‐crystal X‐ray counter data: space group Pnma, a = 1212.5(2) pm, b = 363.0(2) pm, c = 1052.2(2) pm with a residual R = 0.036 for 505 unique structure factors and 30 variable parameters. The Ta atoms occupy only that Fe site with the highest coordination number. The crystal structure of ScRu6P4 (α‐UCr6P4 type) was refined from single‐crystal data: P$\bar{6}$m2, a = 690.0(2) pm, c = 362.5(3) pm; R = 0.023 for 226 Fo and 15 variables. The same structure was also found from Guinier powder data for ErRu6P4 and ZrCr6P4. However, single‐crystal film data for the latter compound suggest a superstructure with a doubling of the hexagonal axis. The new compound Nd2Ru12P7 is shown from Guinier powder data to crystallize with a hexagonal Zr2Fe12P7 type structure. X‐ray powder data also confirm Zr2Ru12P7 and SmCo3P2 to crystallize with Zr2Fe12P7and HoCo3P2 type structures, respectively. The crystal structure of the phosphide U2Cr30P19 is confirmed to be isotypic with Zr2Cr30P19. The same structure was found for the new compound U2Mo30P19. The crystal structures of these and other compounds with a metal to phosphorus ratio close to 2:1 are briefly discussed including that of LiCo6P4.

Transition metal–tin ordering in SrPtSn, SrAuSn and BaAuSn and 119Sn Mössbauer spectroscopy of CaPdSn, CaPtSn and SrAuSn

Abstract Pure samples of CaPdSn, CaPtSn, SrPtSn, SrAuSn and BaAuSn can be prepared by reacting the elements in glassy carbon crucibles or in sealed tantalum tubes in a water-cooled sample chamber of a high-frequency furnace. The stannides have been investigated by X-ray diffraction on powders. Single crystal data yielded: TiNiSi type, Pnma , a =764.16(7), b =470.74(4), c =799.64(7) pm, wR 2 =0.0622, 469 F 2 values, 20 variables for SrPtSn, and CaCuGe type, Pnma , a =2341.4(3), b =481.80(5), c =826.7(1) pm, wR 2 =0.1368, 1136 F 2 values, 56 variables for SrAuSn. The platinum (gold) and tin atoms form two-dimensional layers of puckered Pt 3 Sn 3 and Au 3 Sn 3 hexagons with short PtSn (276 and 278 pm) and AuSn (279–286 pm) intralayer distances. These condensed two-dimensionally infinite nets are interconnected to each other via PtSn contacts (279 pm) in SrPtSn. In SrAuSn very weak interlayer AuSn (312 pm) and AuAu (340 pm) contacts occur, but stronger SnSn (304 pm) interactions. The SrAuSn structure is a superstructure of SrPtSn resulting from an isomorphic transition of index 3 from Pnma to Pnma . The KHg 2 type subcell of BaAuSn was determined from Guinier powder data: Imma , a =493.5(1), b =817.2(1), c =844.5(1) pm. 119 Sn Mossbauer spectra of TiNiSi type CaPdSn and CaPtSn show a single signal at 77 K at isomer shifts of δ =1.964(5) and 1.857(4) mm s −1 , respectively, subject to quadrupole splitting of ΔE Q =0.94(3) and 0.89(1) mm s −1 . SrAuSn shows two superimposed signals in a ratio of 2:1 at 77 K: δ 1 =2.03(5), δ 2 =2.12(5) mm s −1 , ΔE Q1 =0.9(1) and ΔE Q2 =0.6(2) mm s −1 .

Intermetallic Cerium Compounds with Ordered U3Si2 Type Structure

Abstract New intermetallic cerium compounds Ce2T2Mg (T = Ni, Cu, Pd), C2T2Cd (T=Pd, Pt, Au), and C2T2Pb (T = Pt, Au) were prepared by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. Most C2T2X (X = Mg, Cd, Pb) compounds are stable after annealing at about 1000 K, while Ce2Pd2Mg is obtained as single phase only after melting and quenching. A thermal treatment at about 1000 K leads to decomposition in CePdMg and CePd. The eight compounds were investigated by X-ray diffraction both as powders and single crystals, and most structures were refined from single crystal data. They adopt an ordered U3Si2 type structure with space group P4/mbm: a = 759.6(1), c = 376.71 (9) pm, wR2 = 0.0562, 294 F2 values, 12 parameters for Ce2Ni2Mg, a = 787.41(9), c = 387.23(7) pm, wR2 = 0.0438, 222 F2 values, 12 parameters for Ce2Cu2Mg, a = 777.14(8), c = 400.03(7) pm, wR2 = 0.0276, 221 F2 values, 13 parameters for Ce2Pd2.03Mg0.97, a = 777.90(6), c = 393.28(6) pm, wR2 = 0.0360,317 F2 values, 12 parameters for Ce2Pd2Cd, and a = 779.90(7), c = 389.97(7) pm, wR2 = 0.0453, 315 F2 values, 12 parameters for Ce2Pt2Cd. Refinement of the occupancy parameters revealed full occupancy for most sites. A mixed palladium/magnesium (97 % Mg / 3 % Pd) occupancy was observed only for the 2a site of Ce2Pd2.03Mg0.97, indicating a small homogeneity range for this compound. Ce2Au2Cd (a = 804.93(7), c =393.36(6) pm) and the plumbides Ce2Pt2Pb (a = 794.63(7), c = 381.50(6) pm) and Ce2Au2Pb (a = 810.70(7), c = 394.85(7) pm) were characterized through their Guinier powder data. The structures of the Ce2T2X compounds can be interpreted as an intergrowth of distorted AIB2 and CsCl related slabs of compositions CeT2 and CeX. The course of the lattice parameters and chemical bonding within the series of Ce2T2X compounds are briefly discussed.

Preparation and crystal structure of the ternary carbides Ln 12Mn 5C 15 with Ln = Y, Pr, Nd, Sm, Gd-Tm, Lu

The title compounds have been prepared from the elemental components and their lattice constants were determined from Guinier powder data. Well-developed crystals of Dy 12Mn 5C 15 were obtained by annealing the powder of a prereacted sample in a lithium flux. Their structure was determined from four-circle diffractometer X-ray data:, a = 1046.8(1) pm, c = 503.8(1) pm, Z = 1, R = 0.035 for 853 structures factors and 28 variable parameters. It is isotypic with the structure of La 12Re 5C 15. The C-C distance of the carbon pairs is 132(3) pm, corresponding to a double bond.

Experiences with a structure determination on the basis of powder data

The result of a crystal structure determination on the basis of Guinier powder data is compared with the structure based on single-crystal data. Both determinations agree roughly regarding the arrangement of the atoms; however, the powder-data result shows strong deviations with respect to the correct atomic positions

Synthesis and properties of two novel line phases that contain linear scandium chains, lithium scandium iodide (LiScI3) and sodium scandium iodide (Na0.5ScI3)

The title compounds are produced through reactions of Sc, ScI[sub 3], and LiI or NaI at 750-850C in sealed niobium tubing. The slightly paramagnetic lithium phase has a fixed composition near LiScI[sub 3] judging from Guinier powder data and direct analyses. The structure refined from single-crystal X-ray data (P[bar 6]c2, Z = 2, a = 7.2861 (9) [angstrom], c = 6.768 (2) [angstrom], R/R[sub w] = 0.96/3.2%) contains equally spaced scandium atoms (d(Sc-Sc) = 3.384 (1) [angstrom]) in chains of confacial ScI[sub 6/3] octahedra that lie normal to hcp iodine layers. Lithium in iodine octahedra is ordered so as to define confacial trigonal prisms about each chain. The sodium phase has a fixed composition close to Na[sub 0.5]ScI[sub 3] according to the same criteria as well as the structural refinement (Na[sub 0.53(2)]ScI[sub 3]: P31c, Z = 4, a = 7.492 (2), c = 13.699 (3) [angstrom], R/R[sub W] = 2.2/3.2% for data to 2[theta] = 60[degree]). The scandium atoms are paired within slightly distorted chains of confacial octahedra normal to hcp iodine layers (d(Sc-Sc) = 3.278 (5), 3.572 (5) [angstrom]). Sodium at [approximately]50% occupancy within iodine octahedra presents a novel arrangement, trigonal prisms centered around each dimer that are alternatelymore » rotated by [approximately]60[degree] along the chain. The phase exhibits a small, temperature-independent paramagnetism. The results are compared with those for other nominal d[sup 1] trihalides.« less

Pr 2ReC 2 and other ternary rare earth metal rhenium carbides with filled PbCl 2 (Co 2Si) structure

The carbides R 2ReC 2 ( R = Y, CeNd, Sm, GdTm, Lu) were prepared by arc-melting of cold-pressed pellets of the elemental components. They crystallize with the orthorhombic space group Pnma and Z = 4 formula units per cell. The lattice constants for Pr 2ReC 2 are; a = 655.69(6) pm, b = 509.46(5) pm, c = 984.42(8) pm. The crystal structure was determined from quantitative evaluations of Guinier powder data for Y 2ReC 2 and Pr 2ReC 2, which refined to conventional residuals of R = 0.088 and R = 0.072, respectively. The structure of the isotypic carbide Er 2ReC 2 was determined from single-crystal diffractometer data: R = 0.032 for 842 structure factors and 26 variable parameters. The positions of the metal atoms correspond to those of the Co 2Si-branch of the “anti”-PbCl 2 structure. The carbon atoms are isolated from each other and occupy two different octahedral voids (4 R + 2Re, 5 R + 1Re). There are no bonding ReRe interactions in the one-dimensionally infinite [ReC −6 2] n polyanions. The ReC bond lengths of between 192 pm and 203 pm suggest bond orders of about two and the rhenium atoms seem to obey the 18-electron rule. The metal atom positions of the Pr 2ReC 2 type carbides correspond to those of a distorted cubic body-centered structure, as is also found for several other complex carbides. The average valence electron number of the metal atoms is usually greater in unfilled (host) structures than in the corresponding filled (interstitial) structures.

Magnetic and electrical properties of the equiatomic cerium germanides CeMGe (M = Rh, Ir, Pd, Pt)

From X-ray Guinier powder data the crystal structures of the ternary germanides Ce(Rh or Ir)Ge and Ce(Pd or Pt)Ge were confirmed to be of the TiNiSi-type and the CeCu 2-type, respectively. Magnetic, electrical and thermodynamic properties of these materials have been studied in the temperature range 1.5 K ⩽ T ⩽ 300 K. CeRhGe orders antiferromagnetically below 9.3 K, whereas in CeIrGe cerium is in an intermediate valence state and no magnetic transition is observed down to 1.5 K. Resistivity and specific heat measurements reveal a magnetic transition near 3.4 K for both CePdGe and CePtGe. According to the present investigations the compounds CeMGe, with M = Rh, Pd, Pt are classified as magnetically ordered Kondo systems.

Crystallographic study of AgTl(VO 3) 2, a metavanadate(V) with diopside type structure

Using 293 K diffractometer intensity data the structure of AgTl(VO 3) 2 has been determined by single crystal X-ray technique and refined to a final R w of 0.062. The crystals are monoclinic (space group C2/c) with a=10.736(2), b=10.227(2), c = 5.8299(9) A ̊ , β=102.32(1)° and Z=4 (lattice parameters from Guinier powder data). The structure is essentially identical with that of diopside MgCa(SiO 3) 2 showing an octahedral coordination of the Ag +-ions and an eightfold coordination of the Tl +-ions with the (VO 3) ∞ chains formed by vertex sharing VO 4 tetrahedra.

Refinement of the crystal structure of tetraphosphorus decaoxide

The crystal structure and lattice constants of P4O10 were redetermined applying diffractometer data and Guinier powder data, respectively [R3c; a = 10.3035(9), c = 13.5102(19) Å; Rw = 0.023]. In contrast to earlier investigations the geometry of P4O10 in the crystalline state proved to be in accordance with Td-symmetry.

Thorium-containing pnictides with the LaFe 4P 12 structure

The new compounds ThFe 4P 12, ThRu 4P 12 and ThOs 4P 12 were prepared by reaction of the elements in evacuated silica ampoules. Guinier powder data show them to crystallize with the filled skutterudite (LaFe 4P 12) structure. Single crystals of ThFe 4P 12 were obtained from a tin flux. The crystal structure was refined from four-circle diffractometer data to a conventional R value of 0.016 for 204 structure factors and 12 variable parameters. Chemical bonding in these compounds is briefly discussed. It is suggested that thorium in ThRu 4P 12 is not fully tetravalent.

Quenchable High Pressure Phases of GdYbS3

Three new modifications of GdYbS3 can be retained metastably, after quenching from high pressure and temperature. The Guinier powder data is presented and indexed. The three modifications include a cubic defect Th3P4-type phase with a = 8.310(2) Å, an orthorhombic A-type phase with a = 7.279(4) Å, b = 15.119(6) Å and c = 3.875(3) Å, and an orthorhombic U2S3-type phase with a = 10.603(5) Å, b = 3.869(3) Å and c = 10.385(5) Å. Structural relationships between the present group of structures and the structures of the rare earth sulfides with formula Ln2S3 are discussed.