High resolution electron microscopy of bismuth oxides with perovskite layers

Layered bismuth oxides of the general formula $(Bi_2O_2)^{2+}$ $(A_{n-1}B_nO_{3n+1})^{2-}$ where A = Bi or Ba, B = Ti, Fe, W and n = number of perovskite layers have been investigated by high resolution electron microscopy. Lattice images obtained for n = 1 to 6 members show stacking of (n-1) perovskite layers sandwiched between dark bands due to the $(Bi_2O_2)^{2+}$ layers. It was possible to resolve the perovskite layer structures in some of the oxides. A highly ordered structure was observed upto the n = 3 member, whereas higher members show superstructures, dislocations and stacking faults arising from the side-stepping of $(Bi_2O_2)^{2+}$ layers as well as ferroelectric domain walls

Influence of Structural Defects on Gas Adsorption Properties of Anthophyllite Asbestos

The surface area of anthophyllite asbestos variants with different stages of fiber development is found to be not proportional to the fineness of the fibrils. Coarser variants have transitional pores whereas the asbestiform is microporous. HRTEM images show structural intergrowths of $Mg(OH)_2$ in an anthophyllite lattice, whereas the intergrowths are absent in the asbestiform anthophyllite. Conversion of brucite intergrowth into a noncrystalline phase results in the generation of transitional pores

Metal-Ceramic Composites: A Study Of Small Metal Particles (Divided Metals)

Metal particles in $Pt-Al_2O_3$ and $Ni-Al_2O_3$ composites prepared by the reduction of the xerogels have been investigated by high resolution electron microscopy and x-ray diffraction. The alumina phase is essentially amorphous while the metal particles are crystalline. The average size of the metal particles increases with the metal content in the composites. Pt atoms exhibit a greater tendency to form metal clusters than the Ni atoms. At low metal concentrations ($\leq$0.25 wt%), the number of atoms in the metal particles is in the range 100–400. Lattice resolution of the metal particles has been observed in HREM images. The cubic phase of $ZrO_2$ is stabilized in $Ni-ZrO_2$ composites, the stability increasing with the Ni content

High Resoulution Electron Microscopy of Chloritoid Minerals From Different Geological Melieu

Structural defects of three chloritoid minerals from distinet geologic melieu have been investigated by high resolution electron microscopy. X-ray powder and electron diffraction patterns indicate that the chloritoid from one geological source (A) is2M 1+2M2 monoclinic variant while those from another geological source (B) are 2M 2 monoclinic variants. In a typical one-dimensional lattice image of a crystal from sourceA, the 2M 2 matrix is broken by insertion of triclinic inter-growths. Another crystal with the 2M 2 matrix showed single, triple, quadruple and quintuple layers displaying an unusually high degree of disorder. Lattice images of 2M 2 monoclinic variants from sourceB yielded more homogeneous micrographs. The important finding from the present studies is that the chloritoid from sourceA is a severely disordered low-temperature intermediate phase in the conversion of the triclinic chloritoid to the high-temperature ordered monoclinic variants of sourceB. Severely disordered chloritoids, marking the beginning of low grade metamorphism, are generated as intermediates between the state of complete disordered arrangement towards the end of low grade metamorphism within the narrow stability range of 400°–500°C

Precipitation of acicular hydrogoethite (α−FeOOH⋅xH2O;0.1<x<0.22)(\alpha-FeOOH·xH_2O; 0.1 < x < 0.22) using morphology controlling cationic additives

Acicular hydrogoethite $(\alpha-FeOOH·xH_2O; 0.1<x<0.22)$ particles of high aspect ratio of $\geq10$ and narrow size distribution with length ~0.5 μm are prepared by air oxidation of $Fe(OH)_2{\cdot}xH_2O$ (80<x<120) in presence of morphology controlling cationic additives (0.01 at.% of $Pd^{2+}$ or $Rh^{3+}$). Growth of hydrogoethite particle proceeds by the oxidation of $Fe(OH)_2{\cdot}xH_2O$ to an intermediate phase through the nucleation within the amorphous ferric oxy-hydroxide [FeO_x(OH)_3_-_2x{\cdot}yH_2O] and growth of $\alpha-FeOOH·(H_2O)_x$ acicular particles with the aid of morphology controlling agents, as evidenced from X-ray diffraction (XRD) and transmission electron microscope (TEM) studies. Preferential adsorption of additives on certain crystallographic planes and thereby retarding the growth in the perpendicular direction, allows the particles to acquire acicular shape with high aspect ratio ~10. Thermal analyses of hydrogoethite samples show excess weight loss (3–4%) compared to goethite samples. Presence of $H\cdot\cdot\cdot O\cdot\cdot\cdot H$ vibrational absorptions arising from strongly coordinated water molecules in hydrogoethite and its absence in goethite is evidenced from IR spectra. $H_2O$ molecules in hydrogoethite are located in the strands of channel formed in between the double ribbons of $4FeO_6$ octahedra running parallel to c-axis of goethite, wherein the water molecules are bridging between the nearest neighbour cations

An investigation of bimetallic clusters by a combined use of electron microscopy and photoelectron spectroscopy: additive effects of alloying and cluster size on core-level binding energies

Bimetallic clusters of Ni-Pd, Cu-Ni, Cu-Au and Au-Ni deposited on amorphized graphite have been in- vestigated by a combined use of photoelectron spectroscopy and electron microscopy. Metal core-level binding energies (Pd 3d, Au 4f and Ni/Cu 2p) of the bimetallic clusters deposited on amorphized graphite have been measured for different coverages or mean cluster sizes. When the cluster is large, the core-level binding energy the major metallic component in the bimetallic clusters $(e.g. \hspace{2mm} Cu\hspace{2mm} in\hspace{2mm} Cu_3Au \hspace{2mm} or \hspace{2mm} Cu_7Ni_3)$ is close to that of the bulk metal while that of the minor component $(e.g. \hspace{2mm} Au \hspace{2mm} in \hspace{2mm} Cu_3Au \hspace{2mm} or \hspace{2mm} Ni \hspace{2mm} in \hspace{2mm} Cu_7Ni_3)$ shows the effect of alloying. The effect of alloying is found in the core-level energies of both Ni and Pd in the large clusters of $Ni_3Pd_2$. With the decrease in cluster size or coverage, the core-level binding energies of both the metals increase, just as in the case of monometallic clusters. The present results show the occurrence of parallel shifts in the core-level binding energy of metals due to alloying and cluster size effects, both the effects manifesting themselves in the small clusters. It is noteworthy that the core-level binding energy shifts in bimetallic clusters are distinctly different from those in bimetallic overlayers. Although alloy formation does not occur in the Au-Ni system in the bulk, the $Au_3Ni$ and $Ni_3Au$ clusters show variations in binding energies similar to the alloy clusters. It appears that alloying in the Au-Ni system may indeed occur in the nanometric regime of clusters

Structural and Dielectric Charactersics of Strontium Tetraborate-Bismuth Vanadate Glass-Ceramics

Glasses of strontium tetraborate, containing up to 50 mole-percent bismuth vanadate [(1-x)SBO-xBiV (x = 0 to 0.50)], were prepared by splat quenching method. The glassy nature of these samples was confirmed by differential thermal analysis (DTA). The glass transition temperature $(T_g)$ and the crystallization temperature $(T_{cr})$ of the glasses decrease with increase in bismuth vanadate, $Bi_2VO_{5.5}$ (BiV) content. High resolution transmission electron microscopic studies reveal the presence of spherical particles of amorphous BiV (less than 10 nm in size) dispersed in the glassy matrix of strontium tetraborate, $SrB_40_7$ (SBO). The glasses of the compositions x = 0.25 to 0.50, on annealing at 500 $^oC (T_g)$ gave rise to crystalline BiV phase. Physical properties such as density, dielectric and optical transmission of these SBO:BiV glass-ceramics have been studied. The dielectric constant $(\in_r)$ of these glass-ceramics increases with increasing BiV content. The measured $\in_r$ values are found to be in good agreement with those predicted by the logarithmic mixture rule

Light-Induced Microstructural Ordering: Study Of Lithium-Incorporated Cobalt Oxide Films On Aluminium And Glass Substrate

Photocrystallization is a phenomenon whereby an amorphous matrix undergoes structural changes to micro- or nano-crystals upon irradiation with photons. Topologically, a crystalline phase embedded in an amorphous matrix is expected to be advantageous over a fully crystalline phase, in applications such the as cathode material in thin film lithium-ion rechargeable batteries. As this particular microstructural feature provides a high surface area and enables smooth contacts, it may be expected to result in fast ion conduction between cathode and electrolyte, while retaining the electrochemical property associated with the specific crystal structure of the material. Amorphous films of lithium- incorporated cobalt oxide were obtained on glass and aluminium substrate using a sol gel spin-coating technique. The photocrystallization and microstructural changes in these films upon irradiation with unpolarised light were investigated using XRD, SEM, and TEM analysis

Phase transformation and semiconductor-metal transition in thin films of VO2 deposited by low-pressure metalorganic chemical vapor deposition

Thin films of the semiconducting, monoclinic vanadium dioxide, VO2(M) have been prepared on ordinary glass by two methods: directly by low-pressure metalorganic chemical vapor deposition (MOCVD), and by argon-annealing films of the VO2(B) phase deposited by MOCVD. The composition and microstructure of the films have been examined by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Films made predominantly of either the B or the M phase, as deposited, can only be obtained over a narrow range of deposition temperatures. At the lower end of this temperature range, the as-deposited films are strongly oriented, although the substrate is glass. This can be understood from the drive to minimize surface energy. Films of the B phase have a platelet morphology, which leads to an unusual microstructure at the lower-deposition temperatures. Those grown at similar to370 degreesC convert to the metallic, rutile (R) phase when annealed at 550 degreesC, whereas those deposited at 420 degreesC transform to the R phase only at 580 degreesC. (When cooled to room temperature, the annealed films convert reversibly from the R phase to the M phase.) Electron microscopy shows that annealing leads to disintegration of the single crystalline VO2(B) platelets into small crystallites of VO2(R), although the platelet morphology is retained. When the annealing temperature is relatively low, these crystallites are nanometer sized. At a higher-annealing temperature, the transformation leads to well-connected and similarly oriented large grains of VO2(R), enveloped in the original platelet. The semiconductor-metal transition near 68 degreesC leads to a large jump in resistivity in all the VO2(M) films, nearly as large as in epitaxial films on single-crystal substrates. When the annealed films contain well-connected large grains, the transition is very sharp. Even when preferred orientation is present, the transition is not as sharp in as-deposited VO2(M), because the crystallites are not densely packed as in annealed VO2(B). However, the high degree of orientation in these films leads to a narrow temperature hysteresis. (C) 2002 American Institute of Physics