X rays and crystal structure . ,. The arrangements of planes parallel tothe faces (100), (no), (m) can be got from theplanes of zincblende by considering Zn and Sequivalent. The planes parallel to the face (100)are closer tooether, and therefore throw the firstspectrum farther out than either of the other setsof planes. The planes (no) are J2 times, the (iii) planes. -^ times, as far apart as the planes (100). Our arrangement satisfactorily explains both the posi-tions of the first spectrum from each face, and thepeculiar fact that the face (iii) has no secondspectrum. The arrangement remains
X rays and crystal structure . ,. The arrangements of planes parallel tothe faces (100), (no), (m) can be got from theplanes of zincblende by considering Zn and Sequivalent. The planes parallel to the face (100)are closer tooether, and therefore throw the firstspectrum farther out than either of the other setsof planes. The planes (no) are J2 times, the (iii) planes. -^ times, as far apart as the planes (100). Our arrangement satisfactorily explains both the posi-tions of the first spectrum from each face, and thepeculiar fact that the face (iii) has no secondspectrum. The arrangement remains to be tested,. ANALYSIS OF CRYSTAL STRUCTURE 105 however, on one important point. Does it assignthe rioht number of carbon atoms to each unit cubeof the structure? If we are right in placing an. Fig. atom of carbon for each of zinc and sulphur in thestructure, the diamond must fall into line with theother crystals as regards the relation we have foundto exist between d, p, and M. To compare diamondwith zincblende, we must compare the mass of two 106 ANALYSIS OF CRYSTAL STRUCTURE carbon atoms with that of the molecule of zincblende,since a carbon atom replaces every atom of zinc-blende, whether of zinc or sulphur. We thereforeput J/= 24. The density of diamond is Forzincblende the distance d was calculated from theposition of the first spectrum, the analogue to whichis absent in the case of diamond. The correspond-ingf distance d for diamond is double that betweensuccessive planes. It is given by 2X = 2rtfsin °,d= ;
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