650 Tlie Crystalline Structure of Zinc Oxide. 



The analysis of the structure of wurtzite is of especial 

 interest, as zinc sulphide crystallizes in another form, zinc- 

 blende, which is cubic. 



If CdSand ZnS possess the same structure as ZnO, calcu- 

 lation shows that the reflexion from the basal plane should 

 occur at the following anodes : — 



Plane (0001) ZnS 5° 17' 



,, OdS 5° 0' 



Wurtzite occurs naturally only as a fibrous crystalline mass, 

 and a crystal sufficiently large to measure was not available. 

 Green ockite is a rare mineral occurring as very small crystals. 

 Dr. Gordon, of King's College, London, very kindly lent an 

 unusually large crystal of greenockite lor this investigation, 

 and a well-defined reflexion from the basal plane was found 

 at an angle of 5° 2', thus affording confirmation of the 

 assumption that the structure is the same as that of zinc 

 oxide. It is hoped to make further measurements on this 

 crystal. 



Wurtzite shows a platy structure parallel to the fibres of 

 the crystalline mass, and when this material was mounted in 

 the spectrometer a faint reflexion at a glancing angle of 

 5° 20' was obtained, indicating that the basal planes of the 

 crystals were parallel to the fibres. The effect was so small 

 that very little reliance can be placed on this measurement; 

 further observations are necessary to confirm it. 



It is of interest to compare these structures with that of 

 zinc-blende. In zinc-blende the zinc atoms are arranged 

 on a face-centred cubic lattice, of side 5*42 A.U. The oxygen 

 atoms are on a similar lattice, derived from the former by a 

 movement of translation which brings each oxygen atom 

 into the centre of four zinc atoms arranged on the corners of 

 a regular tetrahedron. The trigonal axes in zinc-blende are 

 polar. If the structure of wurtzite is the same as that of zinc 

 oxide^ as would appear to be the case, then in the crystals 

 both of zinc-blende and wurtzite, every atom of sulphur is 

 surrounded by four atoms of zinc at the corners of a regular 

 tetrahedron, and every atom of zinc by four sulphur atoms 

 similarly arranged. The dimensions of the structures are 

 also almost identical. In wurtzite, for example, the distance 

 between neighbouring zinc atoms is .'^85 A.U., in zinc-blende 

 it is 3*83 A.U. The arrangement of the planes parallel 

 to the plane (0001) of wurtzite is the same as that of the 

 planes (111) in zinc-blende, the axis perpendicular to the 

 planes being in each case polar. 



