Refinement of the structure of K2Cr2O7

The parameters for the structure of K₂Cr₂O₇ have been refined from 7511 observed reflections; $\text{a}{}_{\mathrm{o}}\text{= 7.4200(6)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{o}}\text{= 13.399(3)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 7.3845(9)}\text{A}\text{?}$, cosα = ?0.1396(2) (α = 98°2'), cosβ = ?0.0154(2) (β = 90°53'), cosγ = ?0.1078(2) (γ = 96°11'). The discrepancy factor R(F_o²) = 0.0702 with a type 2 extinction correction. The average CrO distances are 1.609Å (unshared) and 1.783Å (shared).     

The absolute configuration of RbClO3

The positional parameters of the structure of RbClO₃ have been determined from 171 x-ray reflections; $\text{a}{}_{\mathrm{<mtext>no</mtext>}}\text{= 6.092(1)}\text{A}\text{?}$$\text{c}{}_{\mathrm{<mtext>o</mtext>}}\text{= 8.173(2)}\text{A}\text{?}\text{, ?}\text{cal}\text{= 3.203}\text{g/cc}{}^3\text{and S.G.}\text{=}\text{R}\text{3}\text{m}$. The absolute configuration of the structure was determined by a least-squares adjustment of the complex anomalous dispersion of Rb and Cl. The ClO distances are 1.478(5)Å and the RbO distances are 3.530(8)Å.     

New phase with K2NiF4 structure in the LaLiFeO system

The existence has been proved, for the first time, in the LaLiFeO system of the phase (La_1.75Li_.25) (Fe_.5Li_.5)O_4?x with tetragonal symmetry ($\text{a}{}_{\mathrm{o}}\text{=3.765±0.001}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{=12.918±0.01}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}\text{=3.43}$) and K₂NiF₄-type structure.This phase gives probably the first example of lithium distribution in both A and B sites of A₂BO₄-type mixed oxides. The high $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}$ ratio suggests a strong elongation of FeO₆ octahedra induced by a high spin Fe(IV) d⁴ configuration. The results of structural studies and of Mössbauer analysis, confirming the above conclusions, are reported.     

A series of rare earth silicates RE3+2M3+[SiO4]2 (OH)

A series of isotypic silicates of composition RE₂M[SiO₄]₂ (OH) with RE = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and M = Al³⁺, Fe³⁺ has been synthesized under hydrothermal conditions. Lattice constants of two members as determined from single crystal X-ray diffraction data are: La₂Al[SiO₄]₂ (OH) (La₂Fe[SiO₄]₂ (OH)) $\text{a}{}_{\mathrm{o}}\text{= 7.401 (7.346)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{o}}\text{= 5.702 (5.862)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 17.072 (97.196)}\text{A}\text{?}$, gb = 112.4 (112.5°), $\text{P}\text{2}{}_1\text{c}$, Z=4.     

Structure determination of (3D) P2NbS8

Tridimensional P₂NbS₈ crystallizes in P4?n2 tetragonal space group, with $\text{a}\text{= 12.0483(4)}\text{A}\text{?}$, $\text{c}\text{= 7.2070(5)}\text{A}\text{?}$, $\text{V}\text{= 1046.2(1)}\text{A}\text{?}{}^3$ and Z = 4. The structure was anisotropically refined down to R = 2.3% from 468 reflexions and 53 variables. It is built from [Nb₂S₁₂] biprismatic bicapped units (average $\text{d}{}_{\mathrm{Nb?S}}\text{= 2.571}\text{A}\text{?}$) made of S^?II and S^?II₂ anions (dianionic distance of 2.014(3) Å). The niobium atoms are found as isolated Nb^IV ? Nb^IV pairs ($\text{d}{}_{\mathrm{Nb?Nb}}\text{= 2.859(1)}\text{A}\text{?}$) in these niobium group otherwise linked to each other through (PS₄) tetrahedral units (average $\text{d}{}_{\mathrm{P?S}}\text{= 2.051}\text{A}\text{?}$) themselves constituting interbonded [P₄S₁₂] rings. The P₂NbS₈ three-dimensional network thus obtained is compared to the (2D) P₂NbS₈, layered phase already described.     

A correlation of critical points

Critical points were correlated for fluids which obey the three-parameter equation of state according to which the compressibility factor, $\text{Z=}\text{P}\text{dRT}$, is given by Z=1 + k_Bδκ (θ, δ), in which κ (θ, δ) is a universal function of reduced temperature, $\text{θ =}\text{T}\text{T}{}_{\mathrm{B}}$, and reduced density, $\text{δ =}\text{d}\text{d}{}_{\mathrm{<mtext>O</mtext>}}$. The three parameters which distinguish one fluid from another are k_B, T_B, and d_O. It is shown that experimental inflection points of the pressure versus density isotherms of gases obeying this equation of state all fall on the same reduced curve of θ versus δ. Critical points also must lie on this curve, at a location dependent on k_B. Critical densities are too uncertain experimentally to permit a definite correlation, but the critical temperatures of sixteen fluids are shown to fall on a common θ_c versus k_B curve with an average deviation of 0.4 degrees. The critical pressures of these same fluids lie within a few tenths of an atmosphere on a common π_c ($\text{π =}\text{P}\text{d}{}_{\mathrm{<mtext>O</mtext>}}\text{RT}{}_{\mathrm{<mtext>B</mtext>}}$) versus k_B line. This correlation of critical points is accomplished using values of the three parameters that had previously been determined by fitting supercritical PVT data to the equation of state.     

Dependence of the crystallization rate of vacuum-deposited amorphous antimony films on the film thickness

The crystallization rate of vacuum-deposited amorphous antimony (a-Sb) films was investigated as a function of the film thickness d. Experimental plots of the observed growth rate v against d^-1 for systems such as Sb/glass and Sb/Ge show that the relationship between v and d^-1 are convex towards the origin. Such a feature is well interpreted by a model in which

$\text{v=}\text{1}\text{d}\text{∫}\text{d}\text{0}\text{u}\text{d}\text{z}$

where u is the actual growth rate of the crystallite in the a-Sb film and z the distance from the film surface adjacent to the substrate. The quantity u is assumed to vary as follows: u = αzⁿ + u_s when 0 ? z ? d_s0, u = u_i when d_s0 ? z ? d ? d_v0 and u = β(d ? z)ⁿ + u_v, when d ? d_v0 ? z ? d where $\text{α =}\text{(u}{}_{\mathrm{i}}\text{? u}{}_{\mathrm{<mtext>s</mtext>}}\text{)}\text{d}{}_{\mathrm{<mtext>s</mtext><mtext>0</mtext>}}{}^{\mathrm{n}}$, $\text{β =}\text{(u}{}_{\mathrm{i}}\text{? u}{}_{\mathrm{<mtext>v</mtext>}}\text{)}\text{d}{}_{\mathrm{<mtext>v</mtext><mtext>0</mtext>}}{}^{\mathrm{n}}$, d_s0 and d_v0 are thickness of surface regions near the substrate and the vacuum respectively, u_i is the growth rate inside the film, u_s and u_v are the rates at surfaces adjacent to the substrate and the vacuum respectively and n an adjustable numerical parameter. As a typical example, for the Sb/Ge system at 30°C, u_i, u_s and u_v are estimated to be 139 μm s^-1, 25.4 μm s^-1 and 0.2 μm s^-1 respectively and d_s0 and d_v0 to be 133 Å and 143 Å respectively with n = 3.     

Temperature dependence of the surface diffusion distance of bismuth atoms adsorbed on mica,carbon and silicon monoxide surfaces

The mean distance of surface diffusion of bismuth adatoms on mica, carbon and silicon monoxide surfaces has been determined at different temperatures by measurement of the instantaneous sticking coefficient and the nucleus density.The surface diffusion distance has been found to increase with decreasing temperature in accordance with the formula

$\text{X=}\text{1}\text{2}\text{a}{}_0\text{v}{}_{\mathrm{0d}}\text{v}{}_{\mathrm{0a}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{exp}\text{E}{}_{\mathrm{a}}\text{? E}{}_{\mathrm{d}}\text{2RT}$

at temperatures above 413, 373 and 383 K for mica, carbon and silicon monoxide respectively. Here X is one-half of the diffusion distance, E_a is the adsorption energy, E_d the activation energy for surface diffusion, a₀ the diffusion jump distance and v_0a and v_0d the vibrational frequencies associated with re-evaporation and with surface diffusion respectively. Below these temperatures it has been found that the temperature dependence of the diffusion distance deviates from the above formula; this can be explained by the presence of residual gas molecules adsorbed on the surfaces.From the temperature dependence of the diffusion distance, the respective values of the pre-exponential term $\text{a}{}_0\text{(}\text{v}{}_{\mathrm{0d}}\text{v}{}_{\mathrm{0a}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and the difference of energies E_a?E_d have been estimated as 7.6 Å and 5.8 kcal mol^?1 for mica, 17 Å and 3.2 kcal mol^?1 for carbon and 58 Å and 1.3 kcal mol^?1 for silicon monoxide.     

Structure de PbU2Se5

PbU₂Se₅ crystallizes in a monoclinic unit cell $\text{a}\text{= 8,605}\text{A}\text{?}$; $\text{b}\text{= 7,788}\text{A}\text{?}$; $\text{c}\text{= 12,27}\text{A}\text{?}$; β = 90° of space group $\text{P}\text{2}{}_1\text{c}$, Z = 4. The crystal structure has been determined for 1251 independant reflections and refined to a final R value of 0,068. Two kinds of uranium sites are found; the average U-Se distances are 2,97 Å for eight-coordination and 2,88 Å in seven-coordination. The average Pb-Se distance for eight-coordination is 3,20 Å. This structure explains the solid solution between PbU₂Se₅ and U₃Se₅.     

Crystal structure of KHSO4 · KH2PO4

KHSO₄ · KH₂PO₄ is monoclinic $\text{P}\text{2}{}_1\text{n}$ with Z = 2 and the following unit cell dimensions: a = 7.434(3); b = 7.341(3); $\text{c}\text{= 7.148(3)}\text{A}\text{?}$; β = 99.56(5)°.Crystal structure of this salt has been solved, using 1699 independent reflexions with a final R value: 0.034. PO₄ and SO₄ tetrahedra are randomly distributed in the arrangement with a resulting (P.S)-O mean distance of 1.508(3) Å.     

Crystal data and thermal expansion of tricalciumborate

Single crystals of tricalciumborate were grown by the flux method. Ca₃B₂O₆ crystallizes in the rhombohedral system with the unit cell parameters $\text{a}{}_{\mathrm{R}}\text{= 6.3577(7)}\text{A}\text{?}$, α_R = 85.68(8)°, Z = 2. The equivalent hexagonal lattice parameters are a_H = 8.640(1), $\text{C}{}_{\mathrm{H}}\text{= 11.854(1)}\text{A}\text{?}$. The anisotropic thermal expansion parameters α_a = (1.00 ± 0.14) × 10^?5, α_c = (3.60 ± 0.47) × 10^?5 were determined by X-ray methods in the temperature interval 25 – 1000°C.     

Ordering of interstitial nitrogen and oxygen in vanadium near to V8N and V8O

The ordered structure of the V₈N subnitride was studied by X-rays, electron diffraction and electron microscopy. V₈N exists in two different modifications (α′ and α″). The vanadium sublattice of both phases is pseudo-tetragonal, in reality triclinic, with lattice parameters: $\text{α}{}_{\mathrm{<mtext>o</mtext>}}\text{=}\text{b}{}_{\mathrm{o}}\text{= 3.114}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 2.994}\text{A}\text{?}$, α_o = β_o = 90.5^o ± 0.1^o, γ_o = 90^o. The proposed unit cell of α′-V₈N has dimensions: a = 2√2 a_o, c = 2c_o and corresponds to V₃₂N₄. Doublets of nitrogen atoms occupy two sets of octahedral cavities whose shortest axes are aligned along the x and y directions of the sublattice in an ordered fashion. The α″-V₈N phase is a periodically twinned modification of the α′-V₈N, the twin plane being of the (001) type. The V₈O suboxide has the same structure as the α″-V₈N, the sublattice parameters being: $\text{a}{}_{\mathrm{o}}\text{=}\text{b}{}_{\mathrm{o}}\text{= 3.11}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 2.994}\text{A}\text{?}$, α_o = β_o = 90.3^o ± 0.1^o, γ_o = 90^o.     

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.     

Fracture toughness characterization of several aluminum alloys in semi-brittle fracture

A method has recently been developed for determining a nonlinear fracture toughness parameter defined by the relation $\text{G}\text{?}{}_{\mathrm{c}}\text{=}\text{C}\text{?}\text{G}{}_{\mathrm{c}}$ where G_c is the critical elastic strain energy rate as defined by Irwin. The $\text{C}\text{?}$ term is a function of the nonlinearity of the load-displacement test record and has been evaluated using the three parameter Ramberg-Osgood approach, although other curve fitting techniques could be applied as well. The method is quite straightforward and is applicable to plane stress, plane strain and mixed mode testing although only plane stress conditions are considered in this paper. For the case of a linear load-displacement record $\text{C}\text{?}\text{→ 1}$ and $\text{G}\text{?}{}_{\mathrm{c}}$ reduces to the linear elastic result.The toughness parameter $\text{G}\text{?}{}_{\mathrm{c}}$ has been evaluated for a number of high strength aluminum alloys and compared with published G_c values for these materials. The tests were conducted on center-cracked sheets of 2014-T6, 2024-T81, 7075-T6 and 7475-T61 aluminum alloys under conditions of varying specimen geometry and displacement gage length. It was found that the values of $\text{G}\text{?}{}_{\mathrm{c}}$ obtained from displacement readings with a gage length of 2 in. generally agreed with published values of $\text{G}{}_{\mathrm{c}}\text{=}\text{K}{}_{\mathrm{c}}{}^2\text{E}$. The $\text{G}\text{?}{}_{\mathrm{c}}$ values were found to vary inversely with gage length and a/w ratios. The variation in values for $\text{G}\text{?}{}_{\mathrm{c}}$ is of the same order of magnitude as the scatter in published values for G_c. However, $\text{G}\text{?}{}_{\mathrm{c}}$ appears to be less sensitive than G_c to changes in a/w.     

Un compose a structure feuilietee (LaO)4Ag1,5Ga1,5S5

The compound (LaO)₄Ag_{1 · 5}Ga_{1 · 5}S₅ belongs to the quasi-binary La₂O₂SAgGaS₂ system. It undergoes a peritectic decomposition at 1040°C and a order-disorder transition at 750°C. The high temperature variety is tetragonal, with $\text{a}{}_0\text{= 4.18}\text{A}\text{?}$; $\text{c}{}_0\text{= 18.74}\text{A}\text{?}$; Z = 1; space group 1422; it has the same structural type as (CeO)₄Ga₂S₅. The low temperature variety is an orthorhombic superstructure of the preceding one. with a = 17.58 (3 a₀√2); b = 5.90 (a₀√2) and $\text{c}\text{= 18.66}\text{A}\text{?}$ (c₀). The electrical conductivity is mainly of ionic nature. The e.m.f. measurements of a cell Ag/(LaO)₄Ag_{1 · 5}Ga_{1 · 5}S₅/S.C./Pt support this conclusion.     

Crystal structures and crystal chemistry in the system Na1+xZr2SixP3−xO12

As part of a search for skeleton structures for fast alkali-ion transport, the system Na_1+xZr₂Si_xP_3?xO₁₂ has been prepared, analyzed structurally and ion exchanged reversibly with Li⁺, Ag⁺, and K⁺ ions. Single-crystal x-ray analysis was used to identify the composition NaZr₂P₃O₁₂ and to refine its structure, which has rhombohedral space group R3?c with cell parameters $\text{a}{}_{\mathrm{<mtext>r</mtext>}}\text{= 8.815(1)}\text{A}\text{?}$ and $\text{c}{}_{\mathrm{<mtext>r</mtext>}}\text{= 22.746(7)}\text{A}\text{?}$. A small distortion to monoclinic symmetry occurs in the interval 1.8 ≤x≤ 2.2. The structure for Na₃Zr₂Si₂PO₁₂, proposed from powder data, has space group $\text{C}\text{2}\text{c}$ with $\text{a}{}_{\mathrm{<mtext>m</mtext>}}\text{= 15.586(9)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{<mtext>m</mtext>}}\text{= 9.029(4)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{<mtext>m</mtext>}}\text{= 9.205(5)}\text{A}\text{?}$, and β = 123.70(5)° Both structures contain a rigid, three-dimensional network of PO₄ or (SiO₄) tetrahedra sharing corners with ZrO₆ octahedra and a three-dimensionally linked interstitial space. Of the two distinguishable alkali-ion sites in the rhombohedral structure, one is completely occupied in both end members, the occupancy of the other varies across the system from 0 to 100 percent. Several properties are compared with the fast Na⁺-ion conductor β-alumina.     

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.     

Estimation of density changes associated with growth in vacuum-deposited amorphous films of antimony

Amorphous antimony films consisting of separate islands were deposited onto SiO_x and GeO_x film substrates at room temperature in a vacuum of 10^-5 Torr. By comparison of the interferometrically determined thickness and the total mass of incident vapour determined with a quartz oscillator, it was found that a sudden change in film density occurs at a certain film thickness d₀. Another change in film density, which is gradual, occurs in the vicinity of a certain thickness $\text{d}{}_{\mathrm{<mtext>c</mtext>}}\text{(d}{}_{\mathrm{<mtext>c</mtext>}}\text{\&\#62; d}{}_{\mathrm{<mtext>0</mtext>}}\text{)}$. The change at d₀ is caused by the coalescence of neighbouring islands. The change at d_c, at which the coalescence of amorphous islands is almost completed, is associated with crystallization.     

Growth and some properties of barium-cadmium formate single crystals: (II) X-ray and infrared studies

An analysis of the powder pattern of BaCd(HCO₂)₄ ·2H₂O shows that the structure belongs to space group p $\text{2}{}_1\text{c}$$\text{a}\text{= 11.907 (4)}\text{A}\text{?}$, $\text{b}\text{= 13.204(4)}\text{A}\text{?}$, $\text{c}\text{= 13.823(3)}\text{A}\text{?}$, β = 31.188(9)° with four molecules per unit cell. The infrared spectra of polycrystalline barium-cadmium formate has been measured in the region 650–4600 cm^?1. The influence of metal ion on carboxylate stretching frequencies of formate ion is investigated and the possible correlations between spectra and structure considered.     

Epitaxial films of the low temperature modification of the compound Cu2Se

Epitaxial films of the low temperature modification of Cu₂Se deposited onto NaCl single-crystal substrates at 200°C and 400°C have been investigated. The diffraction pattern of this phase was indexed on the basis of a hexagonal lattice with unit cell parameters a = 7.07 and $\text{c = 6.68}\text{A}\text{?}$. These parameters are related to the parameters of the f.c.c. phase by the relations $\text{a}{}_{\mathrm{<mtext>h</mtext>}}\text{= (}\text{√3}\text{√2}\text{) a}{}_{\mathrm{<mtext>c</mtext>}}$ and $\text{c}{}_{\mathrm{<mtext>h</mtext>}}\text{= (}\text{2}\text{√3}\text{) a}{}_{\mathrm{<mtext>c</mtext>}}$.