Rokuro Miida

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).

A Modulated Structure in a Fluorite-Type Fast-Ion-Conductor δ-(Bi2O3)1-x(Nb2O5)x

The modulated structure of the fluorite-related δ-(Bi2O3)1-x(Nb2O5)x compounds was investigated by electron diffraction, high-resolution electron microscopy and X-ray powder diffraction. It was described by the substitutional and displacing waves with a common wave number vector qk111. The value of q increased from 0.360 to 0.383 with increasing x from 0.13 to 0.24. The substitutional waves were expressed by 0.2–0.042cos 2πqx/d111 for cations and 0.15+0.039cos 2πqx/d111 for anions. The displacing waves were expressed by 0.0029d111sin 2πqx/d111 and 0.171d111sin 2πqx/d111 for cations and anions, respectively. The Debye-Waller factor for O2- ions was determined as about 10 A and 4.2 A2 with O2- ions to occupy the 8(c) and 32(f) sites, respectively.

Crystal Structure and Ionic Conductivity in Bi2O3-Rich Bi2O3–Ta2O5 Sintered Oxides

Aside from the already known fluorite phase in (Bi2O3)1-x(Ta2O5)x with 0.18x0.25, a second fluorite phase was found in heated samples (800°C) with x0.07 and quenched samples with 0.05x0.07; we called these two phases F I and F II, respectively. The decrease in conductivity with increasing x at temperatures between 650°C and 800°C was classified into three degrees, (i) low, (ii) medium and (iii) high corresponding to F II, F I + F II and F I zones, respectively. The appearance of these degrees was explained in terms of the growth of low-conductivity F I domains within the high-conductivity F II matrix. The sample held at 630°C, 600°C or 550°C after slow cooling from 800°C showed a gradual decrease in conductivity depending on the holding temperature, and this phenomenon was interpreted by relating the growths of γ-Bi2O3-type structure (630°C and 600°C) and α-and β-Bi2O3-type structures (550°C).

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.