The Crystal Structure of Formula-Manganese

A. J. Bradley, J. Thewlis
1927 Proceedings of the Royal Society A  
I. I n t r o d u c t o r. It has been shown independently by Westgren and Phragmen,* and bv one of the present authors, f 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 Phragmen's nomen clature. This latter is preferable because the so-called electrolytic manganese, which we called
more » ... anganese (their y-manganese) is probably a hydride of the metal. It therefore seems better to give the names a-manganese and 6-manganese to the two forms which are known to be metallic, as W. and P. have done. The present paper describes the structure of a-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 th at 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 experi mental 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 th at of a-manganese where the unit cell contains a large number of atoms, and the atomic positions depend upon a large number of parameters. It is possible to avoid ambiguity either by increasing the amount of experi mental data or by increasing the accuracy of the measurements. In the present case we were limited to results obtained by means of the powder method of analysis, because it has not yet been possible to get single crystals of a-manganese which could be used for rotation photographs or for an investigation with the spectrometer. It was therefore necessary to work with powder-photographs *
doi:10.1098/rspa.1927.0103 fatcat:vwiphyttdrdrnlw4b76unv7bva