On the structure of a metastable phase in the lead-bismuth system

A new metastable phase is detected in liquisol-quenched (splat-cooled) lead-bismuth alloys. Its crystal structure of the new phase is established as tetragonal with a maximum of 48 atoms per unit cell and with the lattice parameters $\text{a = 9.931}\text{A}\text{?}\text{, c = 14.99}\text{A}\text{?}$ and c/a = 1.510.     

The lattice parameters of K2SnCl6 at low temperatures determined by high resolution single crystal X-ray diffraction

The temperature dependence of lattice parameters of K₂SnCl₆ was measured in the temperature range 300 K>T>240 K by means of high resolution single crystal X-ray diffraction experiments. The cubic phase ($\text{a=9.986(2)}\text{A}\text{?}\text{,}\text{Z}\text{=4,}\text{T}\text{=280 K}$) was confirmed, whereas in disagreement to earlier authors the intermediate phase was proved to be orthorhombic ($\text{a}\text{=9.966(2)}\text{A}\text{?}\text{, (}\text{b}\text{=9.948(2)}\text{A}\text{?}\text{,}\text{c}\text{=10.002(2)}\text{A}\text{?}\text{,}\text{Z}\text{=4,}\text{T}\text{=258 K}$), and the monoclinic phase to have another unit cell ($\text{a}\text{=9.951(2)}\text{A}\text{?}\text{,}\text{b}\text{=9.948(2)}\text{A}\text{?}\text{,}\text{c}\text{=10.005(2)}\text{A}\text{?}\text{, β=90.099°,}\text{Z}\text{=4,}\text{T}\text{=250 K}$). In a small temperature range between the cubic and the orthorhombic phase reflexion splittings and the occurence of superstructure reflexions indicate a further intermediate phase.     

Anisotropy of X-ray critical scattering in 4,4-di-n-hexyl-biphenyl liquid crystal

We have carried out a high-resolution X-ray critical scattering experiment in the isotropic phase connected with the isotropic-smectic-B transition in 4,4-di-n-hexyl-biphenyl. The measurements yield the following parameter values: $\text{d = 23.92}\text{A}\text{?}$, $\text{q}{}_0\text{= 0.268}\text{A}\text{?}{}^{\mathrm{?1}}$ and the critical exponents γ = 1.51 ± 0.12, ν_∥ = 0.65 ± 0.06, ν_⊥ = 0.70 ± 0.08. At the temperature t = 10^?3 ($\text{t =}\text{T}\text{T}{}_{\mathrm{<mtext>c</mtext>}}\text{?1}$) the correlation lengths are $\text{ξ}{}_{\mathrm{\parallel }}\text{= 390}\text{A}\text{?}$ and $\text{ξ}{}_{\mathrm{\perp }}\text{= 1080}\text{A}\text{?}$.     

Characterization of LiFeCl4 and AgFeCl4 ionic conductors

LiFeCl₄ and AgFeCl₄ are obtained by direct reaction between LiCl or AgCl and FeCl₃ at 300°C and 400°C respectively. Both compounds are monoclinic with $\text{a = 7.02 (1)}\text{A}\text{?}$, $\text{b = 6.33 (1)}\text{A}\text{?}$, $\text{c = 12.72 (4)}\text{A}\text{?}$, β = 92° (30') for LiFeCl₄ and $\text{a = 10.60 (5)}\text{A}\text{?}$, $\text{b = 6.30 (5)}\text{A}\text{?}$, $\text{c = 12.34 (10)}\text{A}\text{?}$, β = 106° (1) for AgFeCl₄.LiFeCl₄ is clearly isotypic of LiAlCl₄. Magnetic measurements characterize in both cases Fe³⁺ ions in a high spin tetrahedral situation. LiFeCl₄ becomes antiferromagnetic at low temperature (T_N?10 K). AgFeCl₄ reveals a more complex situation. On contrary to the silver derivative, LiFeCl₄ is a good ionic conductor with activation energy of 0.78 eV in the solid state below 105°C, and a sharp increase in the lithium mobility at this temperature.     

Structure,vibrational study and conductivity of the trihydrated uranyl bis(dihydrogenophosphate): UO2(H2PO4)2·3H2O

The X-ray structure (293 K) of UO₂(H₂PO₄)₂·3H₂O has been refined (R = 0.062): M_r = 518g, space group: P2₁/c (Z = 4); $\text{a = 10.816(1)}\text{A}\text{?}$, $\text{b = 13.896(2)}\text{A}\text{?}$, $\text{c = 7.481(1)}\text{A}\text{?}$, β = 105.65(1)^°, $\text{V = 1082.7(2)}\text{A}\text{?}{}^3$; D_c = 3.17 Mg m^?3. The structure consists of infinite chains along the (101) axis with U atoms bridged by two H₂PO₄ groups. The U atom is surrounded by a pentagonal bipyramid of oxygen atoms, one of them being an equatorial water molecule. The cohesion between the chains is ensured by hydrogen bonds involving the two last water molecules. An assignment of IR and Raman bands with isotopic substitution spectra is proposed. A phase transition at 128 K was made evident by DSC and spectroscopy. The room-temperature phase is characterized by a high disorder of the OH bond orientation while in the low-temperature phase H₂O and POH species appear well oriented. The conductivity seems to occur by proton transfer and protonic-species rotation at the POH-water molecular interface between the chains. ac conductivity has been determined by means of the complex-impedance method ($\text{σ}{}_{\mathrm{<mtext>RT</mtext>}}\text{～ (3?12) × 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$; E ～ 0.20 eV).     

The accommodation of trivalent gold in Silver Chloride

Gold-doped silver chloride annealed in a chlorine atmosphere at 300°C is shown to contain precipitates of AgAuCl₄, a compound not previously reported. The substance melts at 265 ± 2°C and has a monoclinic unit cell with $\text{a = 11.124 ± 0.008}\text{A}\text{?}$, $\text{b = 4.105 ± 0.002}\text{A}\text{?}$, $\text{c = 6.539 ± 0.006}\text{A}\text{?}$ and β = 93.11 ± 0.05°. Its optical absorption spectrum is discussed and the method of precipitate formation in silver chloride is described in terms of an internal oxidation type of process.     

Loss of ferromagnetism in YNi3 after H2 absorption

The compound YNi₃ ($\text{PuNi}{}_3\text{-}\text{type}\text{,}\text{a}\text{= 4.973}\text{A}\text{?}\text{,}\text{c}\text{= 24.42}\text{A}\text{?}$) is ferromagnetic below T_c = 35 K. After hydrogen absorption it loses its ferromagnetic character and becomes Pauli paramagnetic. The composition of the ternary hydride is approximately YNi₃H₄. The lattice constants are $\text{a}\text{= 5.267}\text{A}\text{?}$, $\text{c}\text{= 26.57}\text{A}\text{?}$.     

Isotope shifts in dysprosium measured by high resolution laser spectroscopy

Using a pulsed dye laser, acting on a collimated atomic beam, the isotope shifts between the dysprosium isotopes 164, 162, and 160 were measured with high precision in three lines, $\text{λ=5547}\text{A}\text{?}$, $\text{λ=5640}\text{A}\text{?}$ and 5652 Å.     

Etude Cristallographique Et Magnetique De Fe2GeS4 Structures Magnetiques A 85 Et 4,2°K

Fe₂GeS₄ crystallizes in the orthorhombic space group Pnma; the cell parameters are: $\text{a = 12,467}\text{A}\text{?}$, $\text{b = 7,213}\text{A}\text{?}$, $\text{c = 5,902}\text{A}\text{?}$; the crystal structure is isotype with olivine.A magnetic study by the extraction method shows that Fe₂GeS₄ is paramagnetic until 108°K, then antiferromagnetic until 69°K and finally antiferro- and ferrimagnetic at lower temperatures.Neutron diffraction reveals the magnetic structures at 85 and 4,2°K and explains the anisotropy transition at 69°K.     

Hole mobility anisotropy and crystal structure of β-9,10 dichloroanthracene

Hole drift mobilities have been measured in β-9,10 dichloroanthracene by the transient photoconductivity method. Mobilities were found to be isotropic in the ac plane, 0.6 cm²/V sec, and 0.18 cm²/V sec normal to this plane, b¹, at room temperature. At lower temperatures the mobilities were thermally activated, with an activation energy of ～0.25eV. The crystal structure of β-9,10 dichloroanthracene has been determined; it is triclinic. $\text{a = 8.582}\text{A}\text{?}$, $\text{b = 16.825}\text{A}\text{?}$, $\text{c = 3.869}\text{A}\text{?}$, $\text{α = 97.90}\text{,}\text{?}\text{β = 97.90°, γ = 75.99°}$. The influence of the crystal structures of the α- and β- forms on the intermolecular electronic overlap and hence carrier mobilities are discussed.     

Synchrotron X-ray study of physisorbed films of mixtures of Ar and Xe on graphite

Mixtures of Ar and Xe have been studied in most of the sub-monolayer region of the phase diagram (T ,χ, ?), T = temperature, χ = chemical composition, ? = fraction of a monolayer. The basic feature is a large tendency to form $\text{3}\text{×}\text{3}$ commensurate alloys (Kr-like structures), but none of the commensurate nor of the incommensurate structures form a chemically ordered alloy at 11K. Thus the 2D solid can be thought of as a solid consisting of particles of an average size. This allows us to study the commensurate-incommensurate phase transition driven by average particle size. The transition is indeed a sharp first order transition taking place through coexisting phases $\text{(τ}{}_{\mathrm{<mtext>A</mtext>}}\text{= 1.64}\text{A}\text{?}{}^{\mathrm{?1}}$ and $\text{τ}{}_{\mathrm{<mtext>B</mtext>}}\text{= 1.703}\text{A}\text{?}{}^{\mathrm{?1}}\text{)}$, as was the case for the low temperature pure Kr system [1]. Another interesting feature is the existence of well correlated liquid-like structures which preserve their correlation over a temperature range of 5 K or more. This unusual behaviour is for chemical compositions where there is coexistence of a commensurate and an incommensurate solid at high temperature.     

The critical behaviour of spontaneous magnetization in the antiferromagnetic NiO

The spontaneous magnetization of the sublattice vs temperature in the antiferromagnetic NiO was measured by the neutron diffraction method. Temperature changes of the Bragg peaks (111), (222), (333) and (444) with the wavelengths of neutrons $\text{λ}{}_{\mathrm{I}}\text{= 4.16}\text{A}\text{?}$, $\text{λ}{}_{\mathrm{II}}\text{= 2.08}\text{A}\text{?}$, $\text{λ}{}_{\mathrm{III}}\text{= 1.39}\text{A}\text{?}$ and $\text{λ}{}_{\mathrm{IV}}\text{= 1.04}\text{A}\text{?}$, respectively were simultaneously investigated by the neutron time-of-flight spectrometer. On the basis of these measurements, the transition temperature from the antiferromagnetic into the paramagnetic phase was determined, T_N = (523 ± 1)°K. The temperature function of the (111) magnetic peak intensity has been accepted to be I ～ (T_N?T)^2β. According to the present measurements the critical point exponent is 0.33 ± ^0.02_0.04.     

Ab initio studies on all-trans-polyene

Ab initio crystal orbital calculations have been performed on all-trans-polyene using a minimal STO-3G basis set. Several ground state properties such as the equilibrium structure, the most important force constants, the band structure and the density of states are reported. An alternant structure with $\text{r}{}_{\mathrm{<mtext>C=C</mtext>}}\text{= 1.327}\text{A}\text{?}$, $\text{r}{}_{\mathrm{<mtext>C-C</mtext>}}\text{= 1.477}\text{A}\text{?}$, $\text{?}\text{CCC}\text{= 124.2°}$ and $\text{r}{}_{\mathrm{<mtext>C-H</mtext>}}\text{= 1.085}\text{A}\text{?}$ was found to have the lowest energy.     

Structure parameters and polarity of the wurtzite type compounds Sic—2H and ZnO

The structure parameters of the wurtzite type compounds Sic—2H and ZnO were determined using X-ray intensities from single crystals collected with an automatic single crystal diffractometer. The lattice constants and the u-values are $\text{a}\text{= 3.079}\text{A}\text{?}\text{,}\text{c}\text{= 5.053}\text{A}\text{?}\text{,}\text{u}\text{= 0.3760}$ for Sic—2H and $\text{a}\text{= 3.253}\text{A}\text{?}\text{,}\text{c}\text{= 5.213}\text{A}\text{?}\text{,}\text{u}\text{= 0.3820}$ for ZnO. The final reliability values for refinements with anisotropic temperature factors are equal to R = 0.032 for Sic—2H and R = 0.024 for ZnO.     

Plasmon resonance in Al,deviations from quadratic dispersion observed

The dispersion of the plasmon and its resonance-like penetration into the single particle excitation band has been measured by electron spectroscopy of polycrystalline Al up to wave number $\text{k = 2.1}\text{A}\text{?}{}^{\mathrm{?1}}$. For $\text{k < 0.75}\text{A}\text{?}{}^{\mathrm{?1}}$ there are deviations from the RPA dispersion in the free electron gas due to band effects. Within the experimental accuracy, there is zero dispersion at $\text{k = 1.90}\text{A}\text{?}{}^{\mathrm{?1}}$. This levelling off may be qualitatively explained by electron short range correlations.     

The surface geometry of GaAs(110): A response

A brief survey of the various surface structure analyses for GaAs(110) is presented. The interplay between studies based on low-energy-electron diffraction (LEED), ion channeling, ion scattering, photoemission and isochromat spectroscopy leads to a structure in which a relaxation within the top layer (characterized by a perpendicular displacement of the As and Ga species by $\text{Δ}{}_{\mathrm{1,\; \perp }}\text{= 0.69±0.05}\text{A}\text{?}$ with the As species relaxing outward by $\text{0.21±0.05}\text{A}\text{?}$ and the Ga species inward by $\text{0.48±0.05}\text{A}\text{?}$) is accompanied by a uniform relaxation of the top layer by $\text{0.05±0.1}\text{A}\text{?}$ toward the substrate and a perpendicular displacement in the second layer in the opposite sense by $\text{0.06±0.1}\text{A}\text{?}$. The displacements of the top-layer Ga and As species parallel to the surface remain controversial. LEED and medium-energy ion-scattering analysis favor bond-length-conserving rotated top-layer structures (i.e., large $\text{(Δd}{}_{\mathrm{|}}\text{～ 0.3}\text{A}\text{?}\text{)}$ displacements parallel to the surface) whereas high-energy ion-channeling and isochromat spectroscopy experiments favor small displacements $\text{(Δd}{}_{\mathrm{|}}\text{? 0.1}\text{A}\text{?}\text{)}$ parallel to the surface.     

Lcao-Gáspár-Kohn-Sham energy bands of trans-polyacetylene-chain

The band structure of the dimerised trans-polyacetylene-chain ($\text{d}{}_{\mathrm{<mtext>CC</mtext>}}\text{= 1.35}\text{A}\text{?}$, $\text{d}{}_{\mathrm{<mtext>CC</mtext>}}\text{= 1.46}\text{A}\text{?}$, $\text{?}\text{CCC}\text{= 120°}$, $\text{d}{}_{\mathrm{<mtext>CH</mtext>}}\text{= 1.09}\text{A}\text{?}\text{)}$ is calculated with the (parameter-free, non-self-consistent) linear-combination-of-atomic-orbitals method using the Gáspár-Kohn-Sham (GKS) potential for the exchange and correlation. The calculated dimerisation gap of 1.6 eV agrees closely with experiment and also with other GKS calculations when the degree of dimerisation is taken into account. The calculated density of states agrees closely with the X-ray photoemission spectrum of Brundle.     

Structure factor for a Bose fluid

The structure factor is calculated for a Bose fluid using an expression for S(k), which is approximately valid for all values of k. Marked fluctuations appear for $\text{k = 2.15}\text{A}\text{?}{}^{-1}$, near the roton dip in E_k, and at $\text{k = 3.65}\text{A}\text{?}{}^{-1}$ near the dip in the second branch of E_k. Our calculations are indirectly a theoretical justification for the existence of a second branch in E_k. The results presented here agree fairly well with the experimental values for $\text{k >; 3.0}\text{A}\text{?}{}^{-1}$ along with a dip at $\text{k = 3.67}\text{A}\text{?}{}^{-1}$ which has not been reported earlier. It also suggests the existence of two waves, phonons and rotons, for $\text{k >; 3.0}\text{A}\text{?}{}^{-1}$.     

Ellipsometry of tetragonal lead oxide single crystals

The refractive index of PbO tetragonal single crystals ($\text{n}\text{?}{}_0\text{= 2.73±0.05}$) and parameters of thin dielectric film on their real surfaces (n_f = 1.56±0.01, $\text{d = 10?85}\text{A}\text{?}$) have been measured by the method of ellipsometry at $\text{λ = 6328}\text{A}\text{?}$. For the first time the photo-induced changes of optical properties of PbO^(t) surface film have been observed.     

NMR in single crystal metallic ferromagnets: GdAl2

Necessary conditions to observe NMR in wall-free metallic single crystal ferromagnets are formulated. ²⁷Al NMR study in a magnetized single crystal GdAl₂ confirms the validity of the preconditions. Improved resolution and control over orientation, both inherent to single crystal study, enable for the first time an angular dependent NMR measurement of hyperfine interaction in metallic ferromagnetic system. The significance of the measured hyperfine tensor $\text{A}\text{?}\text{(A}{}_{\mathrm{\chi \chi }}\text{/λ}\text{h}\text{?}\text{= A}{}_{\mathrm{yy}}\text{/λ}\text{h}\text{?}\text{= - 14.825}\text{kG}$; $\text{A}{}_{\mathrm{zz}}\text{/gl}\text{h}\text{?}\text{= - 15.313}\text{kG}$) is briefly discussed.