Distribution of Electrons in Cadmium Sulfide Crystals

Very accurate x-ray diffraction intensities from a "pure" CdS crystal and one doped with chlorine were used to calculate electron density maps of their crystal structures projected along the $c$ axis. To eliminate series termination errors, a difference map obtained by subtracting the electron density of the "pure" crystal from that of the doped crystal was also prepared. According to this map, the electron distribution in the doped crystal is smeared out in the vicinity of the atom centers and an excess of electrons occurs in interstitial sites. This is contrary to the recently reported findings of Shuvalov who observed the formation of "electron bridges" along lines joining adjacent atoms. It is concluded that our observations are consistent with a partial disorder introduced in the doped crystal by the substitution of chlorine into sites normally occupied by sulfur atoms. Observed variations between corresponding x-ray intensities of the doped and undoped crystal can be similarly explained by changes in the extinction effect due to this disorder.