Denjiro Watanabe

New Type of A5B3 Structure in Al–Ti and Ga–Ti Systems; Al5Ti3 and Ga5Ti3

By electron diffraction and X-ray powder diffraction, a new type of A5B3-structure based on the L10-type was found in the Al–Ti and Ga–Ti systems; Al5Ti3 and Ga5Ti3. The structure has a tetragonal symmetry with the space group, P4/mbm, and the lattice constants, 2√2af and cf, where af and cf are those of the fundamental L10-type cell. 20 Al (or Ga) and 12 Ti atoms are contained in the unit cell. The structure can be described as follows: it consists of the domains based on the L12, containing 3×2 columns of Ti atoms, and the domain boundaries have the L10-type atomic arrangement.

Long-Period Antiphase Domain Structures of Al-Ti Alloys near Composition Al3Ti

Superstructures of Al-Ti alloys in the composition range from Al3Ti to Al2Ti were studied by electron diffraction. It was shown that the Al24Ti8 which has been reported to be a low temperature modification of the Al3Ti phase has a long-period one-dimensional antiphase domain structure (1d-APS) with average domain size M=8/6, where M is measured in unit cell length of the fundamental lattice. In addition, the 1d-APSs with M=1.60–1.91 were found in the specimens containing 26.5 to 32.5 at.% Ti and it was suggested that the 1d-APSs with M=1.67–1.91 correspond to the high temperature phase Al5Ti2 (or Al11Ti5).

The study of zeolites by HVHREM

Abstract It is shown that high-resolution electron microscopy is a very important technique in the study of both the fine structure of zeolites and the materials confined in the cages, cavities and channels of zeolites; and the advantages of using high-voltage electron microscopy are also emphasized by showing a few examples.

Transmission Electron Microscopic Study on the “K-State” in Iron-Aluminium Alloys

Transmission electron microscopy and diffraction study and electrical resistivity measurement of iron-aluminium alloys containing 17.87 to 21.54 at.% aluminium have revealed the nature of the “ K -state” in this alloy system. It has been conclusively demonstrated by the observations of dark field images that the so-called “ K -state”, which appears on annealing at a low temperature after quenching from a high temperature, is characterized by the inhomogeneous formation of very small Fe 3 A1 type ordered particles of 20∼30A in diameter in the matrix α-solid solution. The specimens slowly cooled from a high temperature and isothermally annealed have also been examined to compare the structures with those showing the “ K -state”. A discussion on the equilibrium phase diagram of the iron-aluminium solid solution is given.

Observations on the Role of Crown Ether Templates in the Formation of Hexagonal and Cubic Polymorphs of Zeolite Y

Intergrowths of hexagonal and cubic polymorphs of zeolite Y have been synthesized using crown-ether templates and the manner of the intergrowth between the polymorphs was studied by high-resolution electron microscopy. The images reveal that both polymorphs grow via a layer mechanism and it is suggested that double-six ring units are the key unit for crystal growth. The growing mechanism accounts for surface structures, defect structures and overall particle morphology. Oscillatory growth occurs in syntheses from multiple crown ether preparations whereby the crystal makeup changes from hexagonal to cubic as surface concentrations of crown ethers fluctuate during crystallization. Finally, the structure directing role of the crown ethers is discussed.

Two-Dimensional Antiphase Structures of the 2d-Cu3Pd Type Studied by High Voltage, High Resolution Electron Microscopy

Structure images of the Cu-28 at.%Pd, Au-17 at.%Zn and Au-16.1 at.%Mg alloys having the 2d-Cu3Pd type structure were studied by 1 MV electron microscope. It was shown that deviation of alloy composition from stoichiometric A3B is accommodated at the second kind boundaries; a strong tendency of avoiding the formation of nearest neighbour pairs of Zn (or Mg) atom across the boundaries is observed in the Au-Zn and Au-Mg alloys, whereas an opposite tendency is seen in the Cu-Pd alloy. Part of the deficiency of Zn (or Mg) atoms is accommodated also at the first kind boundaries.

Electron Microscopic Study on the Structure of TinO2n-1 (4≤n≤10) Phases

Transmission electron microscopy and diffraction study of the homologous series of oxides TinO2n-1 (4≤n≤10) reveals that the structures of these oxides are derived from rutile by regular crystallographic shear on planes parallel to (121), as previously suggested by Andersson and Jahnberg (Arkiv Kemi. 21 (1963) 413). Electron microscope images clearly show microstructures. Micro-twin structures of fine scale are observed very often for specimens with n≥7 but never detected when n≤6. The interface plane of the twin bands is parallel to the (200)r in most cases, although the twin structure with the interface plane (002)r or (020)r is seen occasionally. A mode of two phase mixture for the specimen in the two phase region is clarified.

Structure of Very Thin Evaporated Films of Cobalt

Radial distribution functions for very fine multiply-winned particles are calculated and compared with Morimoto and Sakatas experimental data obtained from intensities of electron diffraction patterns of very thin cobalt films evaporated at 20°C on amorphous substrates. It is concluded from the result of the present calculations that aggregate of multiply-twinned icosahedron particles and their derivatives, having the sizes of about 5 A to 15 A, can explain fairly well the unusual peaks shown in the radial distribution functions obtained from cobalt films. This conclusion seems more natural than the explanation of Morimoto and Sakata that the thin cobalt films contain both h.c.p. and diamond-type crystallites having anomalously large amplitude of thermal vibration.

Determination of Atomic Scattering Factors of B.C.C. Metals by the Critical-Voltage Method

The critical-voltage effect in electron diffraction has been applied to the 400 reflexion of b.c.c. metals, V, Cr, Fe and Nb, and the X-ray atomic scattering factors f x for the first-order reflexion 200 have been determined from the measured values of critical voltages E c by many-beam calculations. The results are compared with X-ray experimental data and theoretical scattering factors for free and solid atoms, and it is shown that the theoretical values for solid atoms calculated, e.g. by Wakoh and Yamashita agree well wiht the present results for V, Cr and Fe. It is pointed out that the reproducibility of the experimental data given by the present method is superior to that of the X-ray intensity measurements, and that the accurate measurement of scattering factors such as the present study serves as a sensitive and useful test of the band calculation.

Study of the Temperature Dependence of the Magnetization Direction in Cobalt Single Crystals by 1 MV Lorentz Electron Microscopy

The changes in domain structures of h.c.p. cobalt single crystals of (110) and (100) orientations with temperature in the range 20–380°C have been studied dynamically in a 1000 kV electron microscope and recorded on the VTR. The results show unambiguously that the easy direction of magnetization in the domain rotates from the c-axis to a direction in the c-plane and vice versa with increasing and decreasing temperature in the range 200–330°C. The temperature dependence of the angle of rotation from the c-axis measured on the images agrees well with that calculated from the known anisotropy data.