Composition Of Single Crystals Research Articles

Optical properties of single crystals and ceramics based on silver and thallium (I) halides in the range of 0.3–30.0 THz

This paper is devoted to single crystals and two-phase ceramics based on the TlBr0.46I0.54 – AgI, TlCl0.74Br0.26 – AgI, AgBr – AgI systems' properties study in the THz range of 0.3–30.0 THz. Plane-parallel windows were manufactured based on single crystals of composition 6, 13 mol.% AgI in TlBr0.46I0.54 and 3, 13, 25 mol.% AgI in AgBr, as well as based on two-phase ceramic composition 19, 25 mol.% AgI in TlBr0.46I0.54, 7, 14, 20, 27 mol.% AgI in TlCl0.74Br0.26 and 36 mol.% AgI in AgBr. The materials showed high transmission in the THz with an absorption band. Single crystals and ceramics of the TlBr0.46I0.54 – AgI system are transparent in the ranges 0.3–0.67 and 5–30 THz, which corresponds to wavelengths 447–1000 μm and 10–60 μm. The maximum transparency of the materials in the 5–30 THz range is 70 %, in the other ranges it reaches 40 %. Ceramics of the TlCl0.74Br0.26 – AgI system transmit THz radiation in the 0.3–0.85 and 6–30 THz (353–1000 μm and 10–50 μm) regions. The transparency reaches 60 % in the frequency range of 0.3–0.85 THz and 77 % in the range of 6–30 THz. In the case of AgBr – AgI system, the samples were transparent from 0.3 to 1 THz (300–1000 μm) with a maximum transparency of 77 % and from 5.55 to 30 THz (10–54 μm) with transparency up to 60 %. The attenuation coefficients for each system were quite low 0.03–0.8 cm−1 depending on the composition and system. The value of the coefficients decreased with decreasing emission frequency. The paper also compares the developed THz materials with known materials. A multiple characterization of each class of THz optical materials is given. As a result of the studies, it is found that the set of obtained properties makes the developed THz materials based on silver halides and monovalent thallium halides promising potential materials for application in THz devices and devices for a wide range of purposes.

A 2D coordination polymer assembled from a nickel(II) tetraazamacrocyclic cation and 4,4'-(dimethylsilanediyl)diphthalate(3-) linker.

The preformed nickel(II) complex of the 14-membered macrocyclic ligand 1,4,8,11-tetraazacyclotetradecane (cyclam, L), when treated with 4,4'-(dimethylsilanediyl)diphthalic acid (H4A) in a DMF/H2O mixture (4:1 v/v) under heating, leads to [Ni(L)]3(HA)2·3DMF (I·DMF). Redissolution of this compound in a DMF/H2O/MeOH mixture (4:1:30 v/v/v) with mild acidification under gentle heating results in the formation of a similar compound but containing water and methanol molecules of crystallization, [Ni(L)]3(HA)2·5H2O·2MeOH (II·H2O). At lower temperature and concentration of reactants and longer reaction time, single crystals of composition {[{Ni(L)}3(HA)2]·4CH3OH}n (II·MeOH) were isolated. Single-crystal X-ray diffraction analysis of this compound, which, according to PXRD is isostructural with II·H2O but different from I·DMF, revealed its two-dimensional (2D) polymeric structure, i.e. poly[[bis{μ3-4-[(4-carboxy-3-carboxylatophenyl)dimethylsilyl]benzene-1,2-dicarboxylato-κ3O1:O2:O3'}tris(1,4,8,11-tetraazacyclotetradecane-κ4N)trinickel(II)] methanol tetrasolvate], {[Ni3(C18H13O8Si)2(C10H24N4)3]·4CH3OH}n. It is built up of the monoprotonated tricarboxylate HA3- ligand coordinated in a monodentate manner in the axial positions of two crystallographically independent NiII cations, one of which is located on a crystallographic inversion centre. Both metal ions adopt a slightly tetragonally elongated trans-N4O2 octahedral geometry. The compound has a lamellar structure with polymeric layers oriented parallel to the (10-2) plane, which are in turn linked via hydrogen bonds involving protonated carboxylic acid groups of the ligand. Bulk compounds I·DMF and II·H2O were characterized by FT-IR and diffuse reflectance spectroscopy and thermogravimetry, which provide evidence of their structural differences.

The effect of sintering temperature and time on the growth of single crystals of 0.75 (Na0.5Bi0.5)TiO3–0.25 SrTiO3 by solid state crystal growth

Materials in the (Na0.5Bi0.5)TiO3–SrTiO3 system are of interest for use as lead-free piezoelectric actuators due to high electric-field induced strains. Piezoelectric properties may be further improved by growing single crystals but as yet work on single crystal growth in this system is limited. In the present work, single crystals of composition 0.75 (Na0.5Bi0.5)TiO3−0.25 SrTiO3 were grown by solid state crystal growth (SSCG) on [001] SrTiO3 seed crystals and the dependence of crystal growth distance and matrix grain growth on sintering temperature investigated. Electron backscattered diffraction and X-ray diffraction analysis show that the single crystals grow epitaxially on the seed crystals. Energy dispersive spectroscopy indicates that the grown crystals are slightly Na-deficient, while X-ray photoelectron spectroscopy indicates the presence of oxygen vacancies. Single crystal growth distance, mean matrix grain size and grain size distribution as a function of sintering temperature and time are presented. Increasing the sintering temperature increases both single crystal and matrix grain growth rates. The optimum single crystal growth temperature is found to be 1250°C. The effect of sintering temperature on the single crystal and matrix grain growth behavior is explained using the mixed control mechanism of microstructural evolution.

(Ph4P)2[Be3(μ‐OH)3(H2O)6]Cl5: Crystal Structure and DFT Calculations

AbstractBis(tetraphenylphosphonium)‐tris(μ‐hydroxo)hexaaquatriberylliumpentachloride, (Ph4P)2[Be3(μ‐OH)3(H2O)6]Cl5 (1), was surprisingly obtained by reaction of (Ph4P)N3·n H2O with BeCl2 in dichloromethane suspension and subsequent crystallization from acetonitrile to give single crystals of composition 1·5.25CH3CN. According to the crystal structure determination space group P$\bar{1}$, Z = 2, lattice dimensions at 100 K: a = 1354.8(2), b = 1708.7(2), c = 1753.2(2) pm, α = 114.28(1)°, β = 94.80(1)°, γ = 104.51(1)°, R1 = 0.0586] the [Be3(μ‐OH)3(H2O)6]3+ cations form six‐mem‐bered Be3O3 rings with boat conformation and distorted tetrahedrally coordinated beryllium atoms with the terminally coordinated H2O molecules. The structure ist characterized by a complicated three dimensional hydrogen‐bridging network including O–H···O, O–H···Cl, and O–H···NCCH3 contacts. DFT calculations result in nearly planar [Be3(OH)3] six‐membered ring conformations.

Possible Anisotropics−fHybridization in a Cubic Heavy-Fermion Compound:CeIn1Sn2

Polarized neutron scattering measurements on a single crystal of composition CeIn1Sn2 show a broad, single-ion, spectral response centered on a characteristic energy of approximately 9+/-1 meV at the zone boundary point (0 0 1.5). The zone center spectral response is closely similar in form but has a slightly reduced amplitude, smaller by some 20%. Constant-omega scans show that these intensity modulations, of amplitude approximately 10%, resembling intersite antiferromagnetic correlations, are superimposed on a mean variation that follows the Ce3+, 4f;{1}, single-ion form factor, and are tentatively attributed to q-dependent hybridization of the localized 4f state with the conduction electrons.

Flux Growth and Dielectric Studies of (1-x)PbMg1/3Ta2/3O3−xPbTiO3 Single Crystals

(1-x)PbMg 1/3 Ta 2/3 O 3 – xPbTiO 3 (PMT-PT) single crystals of composition 0 ≤ x ≤ 0.6 were grown by the flux method. The PbO – Pb 3 O 4 – B 2 O 3 system was used as a solvent. The light yellow, transparent and rectangular shaped PMT-PT single crystals of dimensions up to approximately 4 × 4 × 3 mm 3 were obtained. The chemical composition of single crystals was determined by energy dispersion spectrometry technique. Strong separation effect was found in the PMT-PT crystallisation process. The Ti contents in the grown crystals are much smaller than in the solutions. X-ray tests showed that only the crystals of the perovskite structure have been grown. With the increase of Ti content the room temperature symmetry changes from cubic to tetragonal. The low frequency dielectric studies showed that with Ti concentration increasing the observed phase transition transforms gradually from the relaxor type to normal ferroelectric one and shifts towards higher temperatures. The PMT-PT crystals from the morphotropic phase boundary region MPB exhibit the highest values of dielectric permittivitty.

Observation of magnetoelectric effect in epitaxial ferroelectric film/manganite crystal heterostructures

A multiferroic heterostructure is constructed by growing an epitaxial piezoelectric $\mathrm{Pb}({\mathrm{Zr}}_{0.3},{\mathrm{Ti}}_{0.7}){\mathrm{O}}_{3}$ film on a magnetostrictive layered manganite single crystal of composition ${\mathrm{La}}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$. The efficient mechanical coupling at the interface results in a remarkable magnetoelectric (ME) effect. The ME voltage is $\ensuremath{\sim}87%$ of the theoretical value predicted by a phenomenological thermodynamic model. The ME effect peaks at the ferromagnetic transition temperature of the manganite, a consequence of its magnetostrictive characteristics.

Magnetic and mechanical properties of Ni-Mn-Ga single crystals

A method is presented to obtain large field-induced strain in NiMnGa-oriented single crystals. The magneto-mechanical results here presented are measured on an oriented single crystal of composition Ni/sub 50/Mn/sub 29.5/Ga/sub 20.5/ with {100} and {110} faces. The method relies on the stress-strain characterization of the sample. Once a repeatable pseudoplastic behavior is obtained by a sequence of mechanical cycles and thermal treatments, a combination of stress and magnetic field is applied, achieving a 1.2% irreversible strain by applying a 450 kA/m magnetic field along the [100] direction and maintaining a [100] stress value to about 12.5 MPa.

Growth and characterization of rare-earth iron garnet single crystals modified by bismuth and ytterbium substituted for yttrium

A new bismuth-substituted mixed rare-earth iron garnet bulk single crystal of composition (YYbBi) 3Fe 5O 12 (YYbBiIG) has been grown by the improved flux method, whose temperature derivative β of Faraday rotation angle at 45° has been modified by substituting Y 3+ and Yb 3+ ions in garnet crystals. The Faraday rotation and the optical absorption coefficient of Y 1.53Yb 0.92Bi 0.55Fe 5O 12 at 1550 nm were found to be −634° cm −1 and 2.56 cm −1, respectively. The Faraday rotation temperature derivative β was 0.01° (°C) −1 at 1550 nm wavelength, the saturation magnetization 4 πM s has been estimated to be about 1200 G. The larger Faraday rotation, low optical loss, low saturation magnetization and nearly zero temperature derivative β of Faraday rotation of YYbBiIG crystal promise its use in high-performance magnet-optical applications.

Mo¨ssbauer spectra and magnetic anisotropy of garnet crystal BiCaInVIG

The position of ln3+ ions in garnet single crystals of composition {Bi0.4Ca2.6} [Fe2-yln y ] (Fe1.7V1.3)O12(y < 0.15) was qualitatively determined by the Mo¨ssbauer spectroscopy method. According to the single-ion model, the Fe3+ ions on octahedral and tetrahedral sites provided about the same contribution for the magnetic anisotropy of single-crystal BiCaVIG (K 1 a V =-0.0125 cm-1, K 1 d V =0.0127 cm-1 for y = 0) and BiCaInVIG (K 1 a In = -0.0024 cm-1, K 1 d In =-0.002 cm-1, for y=0.144) at room temperature.

Reactions of the multiply-bonded dirhenium(II) complexes Re2X4(?-dppm)2(CNR) (X = Cl or Br; R = t-Bu or xylyl) with alkynes. Structural characterization of [Re2Cl3(?-dppm)2(CN-t-Bu)(? 2-HCCH)]O3SCF3 and a comparison with the related carbonyl species(1)

The reactions of the triply-bonded monoisocyanide complexes Re2X4(μ-dppm)2(CNR) (X = Cl or Br; dppm = Ph2PCH2PPh2; R = t-Bu or xylyl) with the alkyne ligands HCCH and n-PrCCH in the presence of TlO3SCF3 afford the complexes [Re2X3(μ-dppm)2-(CNR)(η2-HCCR)]O3SCF3 (R = H or n-C3H3). The structure of this set of complexes has been established by an X-ray structure determination on a single crystal of composition [Re2Cl3(μ-dppm)2(CN-t-Bu)(η2-HCCH)]-O3SCF3·CH3C(O)OC2H5(2a). The structure of the dirhenium(II) cation, [(t-BuNC)Cl2Re(μ-dppm)2ReCl-(μ2-HCCH)]+, involves different coordination numbers for the two Re centres and an anti arrangement of the t-BuNC and μ2-HCCH ligands. The 625-01 bond length of 2.3171(5) A accords with the retention of a 625-02 bond.

Microstructural changes due to ion irradiation in β-CuZnAl alloys

The {beta}-phase CuZnAl alloys undergo martensitic transformations to several close-packed structures, depending on the alloy composition. In order to study the effects of higher doses of irradiation on the phase stability in these alloys, ion irradiation experiments are now being carried out. In this work, results on microstructural changes after light and heavy ion irradiation in the {beta} phase of CuZnAl alloys followed by Transmission Electron Microscopy are reported. Single crystals of composition Cu-22.7at.%Zn-12.7at.%Al were used. At this composition, the B2 ordering temperature is about 810K, the L2{sub 1} ordering temperature is about 530K and the martensitic transformation temperature is below liquid nitrogen temperature. At room temperature, the alloy has then an L2{sub 1} long-range-ordered structure. Disks of 3mm diameter were prepared by spark erosion. In most experiments the orientation of the foil was close to (110). The samples were irradiated on one side and then back-polished from the other side to perforation, for observation in TEM. Irradiations were carried out with 300 keV Cu{sup +} ions with a flux of 5 {times} 10{sup 12} ions/cm{sup 2}s and 300 keV He{sup +} ions with a flux of 5 {times} 10{sup 13} ions/cm{sup 2}s. The dose rates, calculated using cross sectionsmore » obtained from TRIM simulations, with an average threshold energy of 25 eV, were 10{sup {minus} 2} dpa/s. for the Cu{sup +} and He{sup +} irradiations respectively. The irradiation temperature for the former was about 316K. For the later, a cooling holder was used to keep the temperature between 283K and 289K during irradiation. Before irradiation, the samples were annealed at 1,120K for 20 minutes and cooled in air to room temperature.« less

Vibrating reed study of the flux line dissipation of ceramic and single-crystal (Ba, K)BiO3

Vibrating reed (VR) and dc and ac magnetic susceptibility measurements were performed on a nominal single crystal of composition (Ba0.64K0.36)BiO3 in an applied magnetic fieldH. Field-cooling and field-sweep data revealed multiple peaks in the reed dissipation 1/Q located below the superconducting transition temperatureT c (≈29.6 K forH=0). A shoulder or onset (with increasingT) of dissipation appears forT≤18 K, which may be a signature of a flux lattice melting transition. VR data for dense ceramic samples of composition (Ba0.625K0.375)BiO3 (Tc=28.6K) exhibit a relatively narrow and smooth peak in 1/Q that corresponds well to a broad, intermediate-temperature peak in the crystal data. Resistivity experiments demonstrate that the single ceramic peak occurs well below the temperature at which the electrical resistanceR≈0, suggesting that the higher-temperature crystalline peaks are positioned close to the upper critical field line and may be strongly dependent upon grain size or surface properties. Both ac and dc susceptibility data show no clear evidence for multiple phases or gross compositional inhomogeneities in the crystalline sample. Our results demonstrate that the VR technique is an extremely sensitive method to probe sample inhomogeneities and their role in flux pinning phenomena.

Faraday rotation of bismuth substituted terbium iron garnets

The spontaneous magnetization and the Faraday rotation FR, or [110]-oriented single crystal of composition Bi/sub x/Tb/sub 3-x/Fe/sub 5/O/sub 12/ with x=0.60 have been investigated as a function of temperature and compared with bismuth-free terbium iron-garnet. The experimental data, obtained at 1150 nm wavelength in the 10-300 K temperature range, are discussed in terms of electric and magnetic dipole transitions within the three magnetic sublattices. Assuming that the contribution of the Fe/sup 3+/ ions to FR is the same as bismuth-substituted yttrium iron garnet (for identical Bi content), the contribution to FR of the Tb dodecahedral ion exhibits a strong reduction induced by the bismuth incorporation. A strong temperature variation of the 1st order electric dipole coefficient for the rare earth is found; in a first approximation, this coefficient presents a linear temperature dependence in the 100-300 K temperature range as previously observed in the pure TbIG.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Composition dependence of the magnetooptical properties of HoIG:Al single crystals

The Faraday rotation of aluminum substituted holmium iron garnets single crystals of composition Ho/sub 3/Fe/sub 5-z/Al/sub z/O/sub 12/ has been investigated at 1152 nm wavelength in the 6 K<T<T/sub Neel/ temperature range. A magnetic field up to 20 kOe was applied along the [111] easy axis of five platelets of composition z=0.45, 0.57, 1.15, 2.05 and 2.5 obtained from as grown single crystals. The experimental data were extrapolated to H=O to get the spontaneous Faraday rotation /spl Phi//sub s/(z, T) and linear susceptibility /spl chi//sub F/(Z, T) values. In contrast to the absolute values of /spl Phi//sub s/, the temperature variation of /spl chi//sub F/ shows a discontinuity at the compensation temperature. /spl chi//sub F/ is Al-concentration dependent particularly when T<100 K due to the decrease of the Ho/sup 3+/-F/sup 3+/ interactions. The gyroelectric coefficient of the Ho/sup 3+/ ions due to electric dipole transitions C/sub e/(z, T) deduced from the experimental values is independent of z for z<1.15, and is linearly temperature dependent when T>50 K.<<ETX>>

Resolved and unresolved crystallographic disorder between cyano-.eta.3-[hydrotris(3-tert-butylpyrazolyl)borato]zinc and the halo analogs.

Crystallographic disorder between structurally inequivalent groups has been investigated by X-ray diffraction studies. By use of a technique in which a crystal is doped with an impurity, the disorder at a single site was varied in a controlled fashion. Specifically, single crystals of composition {η 3 -HB(3-Bu t pz) 3 }Zn(CN) x X 1-x (3-Bu t pz=3-C 3 N 2 H 2 Bu t ; X=Cl, Br, I; 0≤x≤1) were obtained by cocrystallization of {η 3 -HB(3-Bu t pz) 2 }ZnCN

The niobium phosphate bronze K 5− xNb 8P 5O 34, a new tunnel structure, first member of the series (K 3Nb 6P 4O 26) n · KNb 2PO 8

A new niobium phosphate bronze K 5− x Nb 8P 5O 34 has been isolated. The structure of this phase has been determined from a single crystal of composition K 4Nb 8P 5O 34 by X-ray diffraction. It crystallizes in the space group P2 c with a = 13.904 (6) Å, b = 6.453 (3) Å, c = 20.64 (1) Å, β = 125.05° (1). This structure consists of [Nb 3P 2O 13] ∞ layers parallel to (100) linked through PO 4 tetrahedra and [Nb 2O 11] units. The structural relationships between this bronze and the other members of the series (K 3Nb 6 P 4O 26) n KNb 2PO 8 are discussed. Attention is drawn to the fact that for this particular n = 1 value two structural forms can be expected.

Magnetic order of the Cu planes and chains in RBa2Cu3O6+x.

Polarized and unpolarized neutron-diffraction measurements have been taken to determine the magnetic structure of the Cu spins in the R${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ system as a function of temperature. Most of the results have been obtained on two (semiconducting) oxygen-deficient single crystals of composition ${\mathrm{NdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.1}$ and ${\mathrm{NdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.35}$. On cooling from the paramagnetic state, the Cu-O ``plane'' layers first order at a N\'eel temperature ${\mathit{T}}_{\mathit{N}1}$ in a simple antiferromagnetic arrangement of spins, with ${\mathit{T}}_{\mathit{N}1}$=430 K for x=0.1 and ${\mathit{T}}_{\mathit{N}1}$=230 K for x=0.35, and with a saturated moment of \ensuremath{\sim}0.65${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. At a lower temperature ${\mathit{T}}_{\mathit{N}2}$ the Cu ``chain'' layer also orders, with ${\mathit{T}}_{\mathit{N}2}$=80 and 10 K for x=0.1 and 0.35, respectively. Hence both transition temperatures decrease with increasing oxygen concentration in this range of x, and the qualitative behavior for these two samples is found to be identical.We have not, however, observed this low-T structure in polycrystalline samples of either ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ or ${\mathrm{NdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$, and some possible explanations for this difference in behavior are discussed. For the single crystals in the low-T phase the Cu spins in all three copper-oxygen layers are ordered in a simple antiferromagnetic arrangement, with the magnetic unit cell double the chemical unit cell along all three crystallographic directions. On the basis of the measured integrated intensities of over 40 magnetic reflections in both ordered phases, the results can be accounted for quantitatively with the assumption of a 3d magnetic form factor on the Cu ions, with no need for a significant moment on any of the oxygen ions. At low T, site-averaged moments of \ensuremath{\sim}0.35${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ and \ensuremath{\sim}0.8${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ are obtained in the ``chain'' and the ``plane'' layers, respectively. The fact that the ordered moment on the plane layers increases in the low-T phase is direct evidence that two-dimensional quantum fluctuations play an important role in the plane layers in the high-T ordered phase. The evolution of the low-T spin structure into the high-T structure involves a noncollinear configuration in which the spins rotate as a function of temperature in the ``plane'' layers, while the ``chain'' layer becomes thermally disordered. The temperature dependence of the structure indicates that competing interactions between the layers are important, and this is discussed in detail. Finally, exploratory measurements as a function of applied magnetic field indicate that the magnetic anisotropy in the tetragonal plane is much smaller than the exchange energies.

Synthesis, structure and spectroscopic properties of two models for the active site of the oxygenated state of cytochrome P450 [corrected

Two dioxygen adducts of thiolato-iron(II) porphyrins, [K(222)][Fe(TPpivP)(SC6HF4)(O2)] 1a and [Na(18c.6)][Fe(TPpivP)(SC6HF4)(O2)] 2 were synthesized by reaction of O2 with five-coordinate, high-spin, cryptated alkali metal thiolato-iron(II) 'picket fence' porphyrinate. They were characterized by visible and infrared spectroscopy: lambda max (log epsilon) = 360 nm (4), 427 nm (4.69), 560 nm (3.69), 610 nm (3.40) for both compounds; v(16O-16O) = 1139 cm-1 in chlorobenzene and fluorobenzene for 1a and 2. Single crystals of composition [K(222)][Fe(TPpivP)(SC6HF4)(O2)].[K(222)](SC6HF4)(C 6H5Cl)(H2O) 1b were obtained by diffusion of pentane/xylene mixtures into chlorobenzene solutions of 1a at -5 degrees C. Single crystals of composition [Na(18c.6)][Fe(TPpivP)(SC6HF4)(O2)] were obtained by slow diffusion of pentane into benzene solutions of 2. Structures of 1b and 2 were studied at 20 degrees C (1b) and -100 degrees C (1b and 2). 1b: space group P2(1)/c (monoclinic), a = 16.806(5) A (1.6806 nm), b = 14.331(4) A (1.4331 nm), c = 52.000(15) A (5.2000 nm), beta = 92.95(2) degrees, V = 12.507 A3 (12.507 nm3), Z = 4, Dcal = 1.28 g.cm-3 (t = 20 degrees C). The final R1 factor was 0.085 for 5238 reflections having I greater than 3 sigma(I). 2: space group P2(1)/c (monoclinic), a = 13.107(3) A (1.3107 nm), b = 27.055(4) A (2.7055 nm), c = 25.029(4) A (2.5029 nm), beta = 96.84(2) degrees, V = 8812 A3 (8.812 nm3), Z = 4, Dcal = 1.18 g.cm-3 (t = -100 degrees C). The final R1 factor was 0.088 for 6587 reflections having I greater than 3 sigma(I). The iron atom is, in both compounds, bonded to the four porphyrinato nitrogens (Np), the sulfur atom of the axial thiolate and one oxygen atom of the axially end-on bonded dioxygen molecule. The average Fe-Np distance found in 1b [1.994(4) A, 0.1994 nm] is not significantly different from that found in 2 [1.993(3) A, 0.1993 nm]. The Fe-S bond length is 2.367(3) A (0.2367 nm) in 1b and 2.365(2) A (0.2365 nm) in 2. The Fe-O1 distances with the oxygen atom of O2 bonded to iron are respectively 1.837(9) A (0.1837 nm) and 1.850(4) A (0.1850 nm). The end-on bonded O2 molecule is disordered in both complexes 1b and 2.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid anisotropic diffusion of lithium in electrochromic thin films based on the hexagonal tungsten bronze structure

The chemical diffusion coefficient of lithium in oxidized potassium hexatungstate and reduced hexagonal potassium tungsten bronze films was measured by the galvanostatic transient method. Two-dimensional anisotropic diffusion was found in the hexagonal hexatungstates, while no appreciable anisotropy was observed in samples with the potassium hexagonal tungsten bronze structure. The chemical diffusion coefficients along the c-axis in thin films of the tungstates K 0.33WO 3.165 and K 0.3WO 3.15 (about 6000 Å thick) are about 10 −10 cm 2/s, while those along the a-axis are about 10 −7 cm 2/s. This latter value is about the same to those measured in a potassium hexagonal tungsten bronze single crystal of composition K 0.28WO 3 which was grown electrochemically. It is most likely that the presence of the additional oxygen atoms in the tunnels within the hexatungstate structure is responsible for the large decrease in the rate of motion of lithium along the c-axis that leads to the anisotropy in the macroscopic diffusion coefficient in this crystal structure.