Structural Characterization of Cæsium Antimonide: Temperature Factors in Cubic Crystals

Abstract

WE have completed an X-ray investigation of cæsium–antimony alloys which shows that the photoelectric surface material cæsium antimonide is a ‘normal valency’ intermetallic compound with a small range of homogeneity probably from Cs₃Sb to Cs_3+xSb_1−x, where x, estimated from the observed variation of unit-cell dimensions, is of the order of 0.05. The atomic arrangement is pseudo body-centred cubic with a structure based upon the B32 sodium thallide type (NaTl). The cubic unit cell (a = 9.14–9.19 A.) contains sixteen atoms at special positions of space group Fd3m—O _h ⁷. Eight equivalent sites at (0,0,0; 0,½,½; ½,0,½; ½,½,0) + 0,0,0; ¼,¼,¼ are occupied solely by cæsium atoms and eight other sites, at (0,0,0; 0,½,½; ½,0,½; ½,½,0) + ½,½,½; ¾,¾,¾, are occupied randomly by four cæsium and four antimony atoms. The structure may be described as consisting of two interpenetrating diamond-type lattices, one of cæsium atoms and the other of equal numbers of cæsium and antimony atoms. The semi-conducting properties of the material are explained by a filled Brillouin zone containing two electrons per atom. A full report of the investigation, together with a discussion of the cæsium antimonide structure and its correlation with other properties of the material, will be made elsewhere¹.