The crystal structure of Kotoite (Mg₃B₂O₆), a new mineral found from Suan Mine, Korea by T. Watanabe, has been determined by X-ray methods using oscillation and Weissenberg photographs (Co-Ka) and the ionization spectrometer (Mo-Ka) . The space group is D¹²_2h-Pnmn, (hk0) and (0kl) reflexions beiog absent respectively when h+k and k+l are odd. The unit cell has the dimensions a=5.33₅A, b=8.40₀ A and c=4.48₇ A. There are two molecules of Mg₃B₂O₆ (sp. gr. 3.11.) .
Closelyy resembling the olivine group, the structure is based fundamentally on the hexagonal closest packing of oxygen atoms. Each B atom is at the center of a triangle formed by three oxygen atoms and each Mg atom is surrounded by eight oxygen atoms arranged nearly octakedrally. Each oxygen atom is shared by three Mg and one B atoms.

View full abstract

The structure of lievritie (ilvaite) has been analysed using X-ray methods (Wcissenberg and oscillation photographs, CoKα λ=3.79A, MoKαλ=0.71A) . The unit cell has the dimensions a=8.84A., b=13.06A. and c=5.88A. The space group is D¹⁶_2h—Pbnm. The structure, built on a hexagonal close packing of oxygen atoms bearing a striking resemblance to olivines, is composed of separate SiO₄ groups held together by Ca, Fe⁺² atoms and Fe⁺³OH groups. Ca has a seven-coordination, Fe⁺³ a six-Coordination and Fe⁺³ a five-coordination surrounded respetively by seven O atoms, six O atoms and four O atoms and one OH group.

View full abstract

Hajime Koto and Kunio Suzuki, Mitsubishi Mining and Metallurgical Institute.
Tungsten and carbon powders were mixed in 1 to _??_ atomic ratio and then pressed with 50 kg/mm².
The pressed powder compacts were heated in vacuum furnace or in the hydrogen atmosphere.
The heating temperature was varied from 650°C to 1850°C, and the heating duration from 10 minutes to 5 hours.
Carbonization of tungsten was studied by X-ray diffraction method in connection with the specimens thus obtained.
These results are as follows: -
1. Below 650°C, W₂C is formed.
2. Below 850°C, WC iss formed, large quantity of WC is prcduced by the carbonization of W₂C.
3. The duration of heating has also a considerable effect.
4. Above 1350°C WC is stable.

View full abstract

In spite of the fact that the crystal structure of ammonium dihydrogen phosphate is said to be analogous to that of the potassium salt, electrical properties of the two salts are not similar. To develop the theories on the transition of dihydrogen
phosphates, the author revealed the detailed structure of the ammonium salt by the Bragg-Fourier series' method. Lattice' constants are a=7.479±0.000A., c=7.516±0, 005A., space group D¹²_2d-I42d. Atomic parameters and interatomic distances compared to those of the potassium salt are given in tables I and II.
Characteristic differences between the two structures are found to be:
i) The axial ratios are reversed.
ii) Hydrogen bonds O-H…O lie almost parallel to the (001) plane in the ammonium salt whereas those of the potassium salt are inclined to the same plane about 4°.
iii) Interatomic distances between nitrogen and oxygen atoms in the ammonium salt are 2.87A which may be comparable to the hydrogen bond distances N—H…O in crystals of urea, glycine and diketopiperazine and the existence of such hydrogen bonds in the ammonium salt is highly, suggested.

View full abstract

Timmermans has shown that a number of molecular crystals which have low entropy of fusion possess high crystallographic symmetries, plasticity, specific heats, dielectric ptoperties, etc. comparable with their liquid state. He considers such a state of aggregation as an intermediate phase between liquid and crystalline states and calls them “plastic crystals”.
X-ray examination on these plastc crystals including cubic pentaerythritol C (CH₂OH) ₄, tetranitromethane C (NO₂) ₄ and cyclohexanol C₆H₁₁OH has now been extended to cubic cyclohexane C₆H₁₂ (m.pt. 6.3°C) which may be taken as a good example of such crystals.
The methods for preparing single crystals and X-ray photographs were almost the same as in the cases of tetranitromethane and cyciohexanol, except a slight change of cooling device. The unit was found to be cubic face-centerd, a=8.73A., containing four molecules in it. The possible space group was given as T²_d-F43m, O³-F43 or O⁵_h-Fm8m. From the same symmetry consideration as was done in the cases of the above mentioned crystals, it was concluded that the four molecules in the unit should be placed at 000, 1/2 1/2 0, 1/2 0 1/2, and 0 1/2 1/2, their orientations, however, being not fixed but rather statistical, statically or dynamically. In other words, only the average centers of molecules lie at the lattice points, as in Ehe case of cyclohexunol. Such a structure explains well its low entropy of fusion and other liquid-like characters, as well as the rapid decrease of intensities with increasing reflection angles.
Besides the Bragg reflections, we rbserved remarkable diffuse scattering of considerable intensity, similar to that shown by cyclohexanol (plate 1), Namely, there appear on the Laue and oscillation photographs a number of so-called diffuse spots and apparently circular diffuse haloes which resemble to the liquid diffraction haloes. The intensity distribution of the diffuse scattering of both types might be related closely with each other. As a first approximation, we made a calculation based on a simple model of free spherical rotation of molecules, and the results account roughly for the circular haloes (Fig.2) . It must be pointed out further that, whereas in the case of cyclohexanol we have observed some intense diffuse spots at small scattering angles, such ones could not be observed in the case of cyclohexane. This difference would perhaps be due to that in the manner of mutual orientations of neighbouring molecules in the crystals.

View full abstract

The crystal structure of aniline hydrobromide C₆H₅NH₂IIBr has been examined by the X-ray method. It was found on Laue and oscillation photographs several anomalous spectra of some new kinds. Disregarding these anomalous spectra, all the data could be accounted for as having the following unit cell and space group: a=6.10A., b=8.44A., c=6.91A., Z=2, space group P2₁22₁. Making use of the intensities of (h0l) and (CkO) reflections, atomic parameters were deduced by the trial and error method. The bromine and the nitrogen atoiris occupy different special positions with two fold symmetry, their y parameters being yyBr=0.05 and yN=0.15. The axis of the anilinium group N-C₁……C₄ lies also on that of two fold symmetry, inclination of its plane to (001) -plane being 25°. The structure obtained is given in Fig. 6. This structure is a new type and may be taken as a radical-ionic one. The relation to the structures of alkyl ammonium halogenides and some physical properties of this crystal are discussed.
Anomalous spectra can be divided into two groups. The one is of the type shown in Fig. and suggests the existence of structural irregularities of a certain kind along the b-axis. The other which is shown in Fig. 9 indicates the existence of the A twinned lattice. The detailed structure and the irregularities of lattice will be given in the following papers.

View full abstract

The strucutre of orthorhombic calcium formate was analysed by the method of Fourier series. Oscillation-rotation photographs were taken with Cu-Kα radiation around the three principal axes and the following unit cell dimensions and space group were obtained, which confirmed the results of the previous work (Nitta, 1927) ; a=10.163A., b=13.381A., c=6.27.1A. (at 18°C) ; space group, D¹⁵_2h—Pcab; Z=8. All the atoms are on the general positions 8 (c) :
± (xyz; 1/2+x, 1/2-y, z; x, 1/2+y, 1/2-z; 1/2-x, y, 1/2+z) .
with the parameters shown in Table I.
The analysis was effectuated by the method of two-dimensional and three-dimensional Patterson syntheses, the latter being evaluated along lines through several points corresponding to peaks in P (xy) .
The structure obtained may be explained as consisting of chains of the type shown in the figure parallel to the c-axis, which are laterally bound through formate ions to form a compact spatial network (Fig.2) . Three types of interionic linkage are found (Fig.3), two of which were already found in sodium formate, analysed by Zachariasen. A remarkable feature is the asymmetrical type of coordination (type II), which might be characteristic to ions of lower symmetry such as this. The calcium ions are surrounded by eight oxygen atoms as shown in Fig.4, one of them being somewhat more apart (Table III) . Pauling's rule concerning the stability of ionic crystals are shown to be strictly hold in its extended form. The shape of the formate, groups were found to be :
C-C=1.25, 1.25, 1.25, 1.24 (±0.03A.) ; OCO=125°, 124° (±4°) .
These results suggest an almost complete resonance between the two forms proposed by Pauling.

View full abstract

Contradictory experiments on the lowering of melting point and the increase of solubility with decrease of the size of crystal-particles are discussed from authors' affirmative view-point. Sintering of crystal powders are also explained from the same consideration.

View full abstract

[in Japanese]

View full abstract