The crystal structure of α-manganese

Abstract

It has been shown independently by Westgren and Phragmén, and by one of the present authors, that manganese is allotropic. Both investigations pointed to the existence of three crystalline modifications. The names given to the different forms of the metal were not the same in the two papers, and in order to avoid ambiguity we have adopted Westgren and Phragmén’s nomen­clature. This latter is preferable because the so-called electrolytic manganese, which we called α-manganese (their γ-manganese) is probably a hydride of the metal. It therefore seems better to give the names α-manganese and β-manganese to the two forms which are known to be metallic, as W. and P. have done. The present paper describes the structure of α-manganese, which is stable at room temperature and higher temperatures up to about 700°C. In the two investigations referred to above, the powder method of X-ray analysis alone was employed. In order that the results of any method of analysis may be trustworthy, the method must be capable of discriminating between all solutions which are theoretically possible, and it is not sufficient merely to indicate one solution which explains the observations. If the experimental data are not extensive, and the accuracy with which they can be tested is low, it is easy to get a spurious agreement between observation and calculation, which lies well within the limits of experimental error. This is especially the case with a structure such as that of α-manganese where the unit cell contains a large number of atoms, and the atomic positions depend upon a large number of parameters.