No abstract

A, and 0.003 rad (0.2 °) in the final cycle, the r.m.s, average of the translations of the rigid bodies totaled over all the rings is 0.082 A. The same average over the rotations is 0.029 rad (1.7°). A second measurement of the similarily between the observed and calculated structures is the r.m.s, displacement of the atoms. Since the phenyl rings were refined as rigid bodies, the comparison must be made between the final atomic coordinates of the calculated structure and the idealized coordinates based on Daly's work. The r.m.s, displacements between the atoms of the two structures are then 0.174, 0.117 and 0.195 A,, respectively, for the three phenyl rings. The phosphorus atom is translated by 0.147 A,, and the total r.m.s, displacement over all the atoms is 0.165 A,. These shifts are small; the experimental structure appears to be well reproduced.

A T‐x‐section of the phase diagram is proposed for the system CuMnO in air between 750 and 1,400°C. From X‐ray and chemical analyses on quenched samples and from high‐temperature X‐ray diffraction studies the occurrence of the following phases is deduced: a cubic phase α‐Mn2O3, a phase CuxMn3−xO4+γ (0 ⩽ x < 0.2 and 0 < γ < 0.02) with a tetragonally deformed spinel structure, a cubic spinel phase CuxMn3−xO4+γ (0 ⩽ x ⩽ 1.03 and −0.08 < γ < 0.02), a crednerite‐like phase CuyMn1−yO (0.50 < y < 0.53) with monoclinic structure, a delafossite‐like phase CuyMn1−yO (0.54 < y < 0.60) with hexagonal structure, a liquid phase, the phase Cu2O and the phase CuO. CuMn2O4 was found to be cubic or tetragonal at room temperature, depending on the temperature of quenching. The po2‐x‐section of the system CuMnO at 1,000°C, as determined by SCHMAHL and MÜLLER (1964), was confirmed and could be farther extended to lower oxygen pressures. The valencies of the cations, especially of those in the spinel structure, are discussed.

The crystal structure of koechlinite has been redetermined by single-crystal X-ray analysis. The space group is Pea21, with cell dimensions: a = 5.487 (2); b = 16.226 (6); e = 5.506 (2) A,. There are four molecular units per unit cell. The structure was refined with block-matrix least-squares methods. The final R on F value was 8.7 % for 788 independent reflexions, including the unobserved reflexions. Molybdenum is octahedrally surrounded by six oxygen ions. These octahedra share four corners with neighbouring octahedra in one plane. The other two apex ions points towards a BiO layer of the type that occurs, for example, in BiOC1.

The phase diagram of the quasi‐binary Mn3O4Al2O3 system in air has been redetermined at temperatures from 850 to 1550°C with the help of the X‐ray powder diffraction technique including high‐temperature diffractometry. Lattice constants of manganese aluminates and the powder diffraction patterns of Mn3O4, MnAl2O4 and Mn2AlO4 are presented. The influence of specimen cooling on the cubic‐to‐tetragonal transition of MnAl spinels is demonstrated. The inversion degree of the spinal compounds is discussed.