CS Phase Research Articles

Thermal behaviour of Langmuir-Blodgett films. II. X-ray and polarized reflection microscopy studies on coexisting polymorphism, thermal annealing and epitaxial layer growth of behenic acid multilayers

The structure and thermal behaviour of behenic (docosanoic) acid multilayers deposited onto silanized silicon surfaces with the Langmuir-Blodgett technique were investigated by X-ray diffraction and polarized light microscopy. Various multilayer samples were prepared from the L2, L2' and CS monolayer phase. Irrespective of the different phases of the precursor monolayers on water, all deposited multilayers showed similar Bragg peak triplets from three coexisting phases with 48.3 AA, 52.8 AA and 55.8 AA bilayer thickness, corresponding to tilt angles of approximately=36 degrees , approximately=28 degrees and approximately=21 degrees , respectively. The samples differed only in the relative peak intensities. The observed layer spacings exactly match the large repeat units of the three behenic acid bulk phases. None of the obtained multilayer phases equalled the structures of the precursor monolayers from which the samples were prepared. Once heated to approximately=65 degrees C, all multilayer samples annealed irreversibly into the maximum tilted phase with 48.0 AA. bilayer spacing; the Bragg peaks of the 52.8 AA and 55.8 AA bilayer spacings disappeared. Regardless of the annealing, the multilayers remained a film of uniform thickness, as proved by pronounced Kiessig fringes. Reflection polarized microscopy revealed a grainy morphology (grains approximately=1 mu m diameter) with locally varying brightnesses (birefringence) for the unannealed samples. In the case of the annealed samples, domains with diameters of several tens of micrometres and uniform birefringence were observed. Additional layers deposited on top of annealed (monophasic) multilayer templates were again triphasic and qualitatively not different from those directly deposited on silanized silicon wafers. Based on the experimental results, models of the multilayer architectures are presented. It is suggested that the layers consist of stacks of epitaxially grown domains of uniform bilayer spacings.

Relationships between fatty acid monolayer structure on the subphase and on solid substrates

Docosanoic acid monolayers with known molecular packings on the water surface have been deposited on thin polymer films and then investigated using transmission electron diffraction at normal and tilted incidence. The diffraction patterns from monolayers deposited under all conditions investigated could be indexed as arising from the same conformationally disordered centred rectangular packing with molecules standing perpendicular to the substrate, although with a spread of unit cell parameters within and between each deposition condition significantly greater than the experimental error. This packing has been seen in monolayers on the water surface, but only under conditions completely different from any of those used for deposition. The patterns from CS phase samples gave spot profiles and relationships between grains distinctly different from those of L 2 and L 2 phase samples. The latter were sufficiently well defined to rule out interpretation in terms of any of the known dense crystalline packings of aliphatic chains. However, similar patterns have been reported before and appear to be related to Kitaigorodskii monoclinic subcell packing. The orientational statistics of the grain orientations provide evidence that the film morphology is influenced by that on the water surface.

An electron diffraction study of deposited docosanoic acid monolayers

AbstractDocosanoic acid monolayers deposited on thin polymer films under different water surface conditions have been investigated using transmission electron diffraction at normal and tilted incidence. Diffraction patterns obtained from the L2 and L2' phase are quite similar, but distinctly different to samples coated from the CS phase. The former were consistent with molecules perpendicular to the substrate, arranged in a texture of grains with unusual orthorhombic packing. There is evidence for a phase transition from a liquid crystalline phase on the water surface.

Mesophases and crystalline phases in fatty acid monolayers

The polymorphism in docosanoic (behenic) acid monolayers at the air/water interface is investigated by means of X-ray diffraction. Analysis of the diffraction spot profiles parallel and perpendicular to the surface provides detailed data on the unit cells of five different phases (L2, Li, S, CS, and LS) with uniform aliphatic tail alignment and regular two-dimensional lattice structure. The first four of these display centered rectangular symmetry, while the LS phase is hexagonal. In the LS, S, and CS phases the tails are oriented normal to the surface, whereas in Lz and Li they are tilted toward the nearest and next-nearest neighbors, respectively. The unit cells of the S and CS phases have the same symmetry. However, the latter is the only phase to display the packing density (C0.19 nmz aliphatic chain cross section), the very low compressibility (<3 X 10-4 m/mN), and the resolution-limited peak width (C0.03 nm-l, corresponding to a characteristic length for exponential decay of positional correlations equal to more than 160 lattice spacings) expected from a close-packed crystalline solid. In contrast, the peak width in the Lz, L2/, LS, and S phases is more than 0.09 nm-', corresponding to a correlation length of less than 54 lattice spacings. Their similarities to mesophases of liquid crystals are pointed out.

Nonstoichiometric phases in the TiWO system

The phases occurring in the TiWO system close to WO 3 at 1273 and 1373 K were determined using X-ray diffraction and electron microscopy. In samples heated for up to 2 weeks an extended phase field of {001} crystallographic shear structures was found to exist between MO 2.88 and MO 2.93 along the Ti x WO 3 line. These CS structures intergrew with {103} CS structures in the composition region between Ti x WO 3 and the binary WO line to form an operationally nonstoichiometric CS phase region. A disordered structure related to W 12O 34 with an extended homogeneity range was found for compositions Ti x W 1− x O 2.83 with 0 < x < 0.04. This phase was surrounded by a composition region in which disordered PC units were dispersed in the WO 3-like matrix to form another nonstoichiometric phase region. Intergrowth between these PC structures and both CS phases and W 18O 49 were encountered. Heating for up to 2 months caused the ternary {001} CS and (Ti x W 1− x ) 12O 34 phases to slowly decompose and their apparent phase ranges to narrow.

A phase analytical study of the GeWO system near WO 3

The phases occurring in the WO 3WO 2GeO 2 region of the GeWO phase diagram at 1373 K were determined by electron microscopy and X-ray diffraction. Preparations were heated for 3, 14, or 35 days. The structures found were WO 3, {102} CS structures, {103} CS phases, W 24O 68, W 5O 14, W 18O 49, and WO 2. The presence of GeO 2 was inferred. The tungsten oxides appear to contain very little Ge and are best regarded as pseudobinary phases. Equilibrium was slow to achieve and samples heated for up to 5 weeks were still not perfectly ordered. However, formation and ordering of the phases seemed faster than in equivalent binary samples, and either Ge or GeO 2 appears to act as a promotor in the reaction. The distribution of the {103} CS phase homologs is in good agreement with the predictions of stability based upon minimization of elastic strain energy.

Notes on phases occurring in the binary tungsten-oxygen system

The phases occurring in the binary tungsten-oxygen system in the composition region WO 3WO 2 have been clarified by electron microscopy and powder X-ray diffraction in the temperature range from 723 to 1373 K. There are five structure types in the binary system, besides WO 3, viz., the {102} CS structures, the {103} CS structures, W 24O 68, W 18O 49, and WO 2. The {102} and {103} CS structures, and W 24O 68 structures, were always disordered and true equilibrium was not achieved even after 5 months of heating at 1373 K. The lowest temperature for the formation of the CS phases was of the order of 873 K, and the disordered W 24O 68 structure formed at somewhat higher temperatures. The formation of the latter phase was also slower than the formation of the CS phases. The results suggest that elastic strain energy is of importance in controlling the microstructures found in the nonstoichiometric regions.

Phase relations in the ternary WMoO system

The phases in the ternary WMoO system have been determined using X-ray diffraction and electron microscopy. Series of mixed crystals occur for the fully oxidized compounds W x Mo 1− x O 3. Slightly reduced crystalline samples consist of CS phases containing {102} CS planes which are ordered when the Mo content is high. These latter have overall compositions (W x Mo 1− x ) n O 3 n−1 with n increasing with increasing W content from 9 to 16. More substantially reduced crystals show less tendency to form mixed crystals. In samples of overall composition near MO 2.90 phase separation occurs into {102} containing CS phases which are molybdenum rich and {103} CS phases which are tungsten rich. The tungsten oxides WO 2.82 and W 18O 49 seem to contain little or no Mo. These results are summarized on a phase diagram.

Hydrothermal interactions of basalts with Cs and Sr of spent fuel elements: Implications to basalt as a nuclear waste repository

The immobilization reactions of Cs, Sr, U and Mo from spent fuel elements (SFE) in the presence of basalts and basalt phases were investigated under hydrothermal, closed-system conditions. The exact Cs and Sr phases in SFE are not known with certainty, but Cs 2MoO 4, CsI, Cs 2O, β-Cs 2U 2O 7 and SrZrO 3 are some of the predicted possibilities. These phases were mixed with basalts and basalt phases along with water, sealed in gold capsules and reacted at 100, 200 and 300°C under a confining pressure of 300 bars. The Cs and Sr concentrations of the product solutions were measured to determine the partitioning of these elements between the liquid and solid phases. Results varied substantially, depending on the particular basalt or basalt phase or Cs phase, the temperature and the duration of run. For example, a Deep Drill Hole (DDH-3) basalt-Cs 2MoO 4 reactions resulted in 15, 78 and 99% fixation of added Cs at 100, 200 and 300°C respectively. Fixation of up to 99.7 and 99.8% of the added Cs and Sr respectively were observed in some cases. X-Ray diffraction (XRD) analysis of the solid products revealed that Cs was immobilized by the formation of pollucite, (Cs, Na)AlSi 2O 6 in most cases and the formation of CsAlSiO 4 in some cases. The interactions of basalts and basalt phases with Cs 2MoO 4 also resulted in the immobilization of Mo by the formation of powellite, CaMoO 4 because Ca is available in the reaction mixtures. The U 6+ in β-Cs 2U 2O 7 was reduced to form uraninite, UO 2 by the divalent iron component of basalts. The exact nature of Sr reaction with basalts is not clear because no new Sr phases could be detected by XRD. The reaction products, pollucite, CsAlSiO 4, powellite and uraninite from SFE-basalt interactions serve to immobilize Cs, Mo and U because Cs in pollucite and CsAlSiO 4 is difficult to exchange and Mo and U in powellite and uraninite are quite insoluble.

Deuteron magnetic resonance and relaxation study of the pseudo-one-dimensional ferroelectric transition in CsD2PO4

The deuteron quadrupole coupling tensors and spin-lattice relaxation rates ${T}_{1}^{\ensuremath{-}1}$ have been determined as a function of temperature both in the paraelectric and in the ferroelectric phase of Cs${\mathrm{D}}_{2}$P${\mathrm{O}}_{4}$. The results demonstrate the order-disorder nature of the transition and show the presence of dynamic short-range ordered clusters along the O-H(2) \ifmmode\cdot\else\textperiodcentered\fi{} \ifmmode\cdot\else\textperiodcentered\fi{} \ifmmode\cdot\else\textperiodcentered\fi{} O chains, which are responsible for the H(2) deuteron ${T}_{1}^{\ensuremath{-}1}$. The noninteracting H(2) deuteron intrabond jump time equals 0.9 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}12}$ s, and is of the same order as in K${\mathrm{D}}_{2}$P${\mathrm{O}}_{4}$. The anomalously short values of both the H(1) and the H(2) deuteron ${T}_{1}$ are the result of an "anisotropy slowing down" of the order-parameter fluctuations due to the pseudo-one-dimensional nature of the transition.

An electron microscope study of tin dioxide and antimony-doped tin dioxide

Crystals of tin dioxide, SnO 2, have been grown pure or doped with a few percent of antimony using vapor growth methods in order to investigate the microstructures of reduced and oxidized SnO 2. They were examined by X-ray diffraction and by optical and electron microscopy. SnO 2 crystals were found to contain few faults, but the antimony-doped crystals were extensively twinned in some regions. Reduction of SnO 2 crystals to yield CS phases was unsuccessful. These results are discussed in terms of the known crystal chemistry of the oxides involved.

High-temperature rutile-derived crystallographic shear structures. I. (020) rCS structures

Electron diffraction and single-crystal X-ray diffraction techniques have been applied to a study of the structures of phases in the Fe 2O 3TiO 2 system, for compositions in the range 14–16 wt% Fe 2O 3 and for temperatures above 1450°C. The compounds in this system may be described as (020) r CS phases in which adjacent rutile slabs, infinitely extended along [100] r and [001] r , are displaced by 1 2 [011] r across (020) r CS planes. In the CS planes, about two-thirds of the available metal-atom octahedral sites are occupied in a deficient NiAs arrangement. The composition range studied is spanned by a continuous series of (020) r intergrowths formed by the ordered mixing of structures with two different CS plane spacings, namely, 9 × d (020) r and 11 × d (020) r . Conventional structure solution methods could not be applied to these infinitely adaptive structures because of the small intensity data to parameter ratios for the high-order intergrowths. We describe a method of structure solution based on a series of successive approximations. The method was applied to determine the structure of one of the intergrowths using single-crystal X-ray diffraction data. For the temperature range studied, the CS phases are within a few degrees of their melting points, and this is reflected in a departure from complete structural order. The results show both long-range disorder in the intergrowth sequences and an absence of correlation between the metal-atom ordering in one CS plane and the next. This disorder is manifested by diffuse scattering in the diffraction patterns. The (020) r CS structures transform reversibly to the well-known (121) r –(132) r family of ordered rutile CS structures below 1450°C.

An electron microscope study of tungsten oxides in the composition range WO 2.90WO 2.72

The structures of tungsten oxides occurring in the composition range WO 2.90WO 2.72 have been studied by transmission electron microscopy. In the oxygen-rich part of the phase range W n O 3 n−2 CS phases exist. The lowest value of n found for extensive areas of ordered material was 16. At the oxygen-poor end of the phase range, W 18O 49 exists. No evidence was found to indicate that this phase has an appreciable composition range. Between the W n O 3 n−2 oxides and W 18O 49 a previously unreported oxide was found. Its structure has been partly elucidated by high-resolution electron microscopy and it has been shown to bear more resemblance to a tunnel structure than to a CS phase.

The dioxide-trioxide region of the vanadium-tungsten-oxygen system

The phases existing at 1373°K in the ternary vanadium-tungsten-oxygen system between the compounds WO 3, WO 2, VO 2, and V 2O 5 have been characterized by X-ray diffraction and electron microscopy. In the region close to WO 3, no evidence of substantial substitution of vanadium into the tungsten trioxide structure was found and extensive formation of ternary CS phases was not found. In samples heated for 14 days, the major ternary phase observed was a rutile phase (V, W)O 2, although some other less stable ternary compounds were also recorded in the V 2O 5 rich region of the phase field. Besides these, an orthorhombic modification of tungsten trioxide was found coexisting with the usual monoclinic form, disordered W n O 3 n−1 (102) crystallographic shear phases and the binary oxide W 18O 49. These results are summarized in a phase diagram. Samples heated for short periods of time contained, in addition to the compounds listed above, another unidentified phase and disordered W n O 3 n−2 (103) crystallographic shear phases. A comparison of both sets of results allows a possible mechanism to be put forward for the reaction between the original tungsten and vanadium oxides.

Phase relations in the oxygen rich region of the CrWO ternary system

The phases occurring in the ternary CrWO system at 1370 K have been determined using x-ray diffraction and electron and optical microscopy. It was found that at this temperature no Cr enters WO 3 or the other tungsten oxides and no ternary CS phases appear to form. Instead, the Cr reacts to form one or two ternary rutile phases and equilibrium lies between them and the appropriate binary tungsten oxide. The compositions of these ternary oxides are Cr 2WO 6 and a previously unreported phase CrWO 4. No extended homogeneity ranges have been detected for these oxides. A phase diagram summarises the results which are also considered in the light of the formation of crystallographic shear phases in tungsten oxides.

Effect of pressure on the crystal structure of CsMnCl 3 and RbMnCl 3

The hexagonal 9 R structure of CsMnCl 3 has been found to transform at ∼10 kbar to the 6 H polytype structure ( a = 7.268 Å, c = 17.85 Å) and further transform above ∼25 kbar to the 3 C polytype structure ( a = 5.111 Å). A pressure-temperature phase diagram is presented. At pressures greater than 7 kbar the 6 H polytype structure of RbMnCl 3 transforms to the 3 C polytype structure ( a = 5.058Å). The quenched high pressure phases of Cs and Rb are stable at atmospheric pressure to 300 and 400°C, respectively. These polytype transformations are related to similar ones found for ABX 3 compounds where X is fluorine or oxygen.