There are two different types of small spaces.Each octahedral hole is surrounded bysixspheres, three in one layer and three in theother. The centres of the spheres lie at thecorner of an octahedron, hence the nameFigure 3 two layers ofayerclosepackedsphereswiththeenclosedoctahedralholespickedoutincolour
There are two different types of small spaces. • Each octahedral hole is surrounded by six spheres, three in one layer and three in the other. The centres of the spheres lie at the corner of an octahedron, hence the name. Figure 3 two layers of close packed spheres with the enclosed octahedral holes picked out in colour
The second type of space, tetrahedral holes,is shaded in figure 4. Each of these holes issurrounded byfour spheres with centresat thecorners of a tetrahedron.Figure 4 two layers ofclose packed spheres withaverthe enclosed octahedralholes picked out in colourtb
The second type of space, tetrahedral holes, is shaded in figure 4. Each of these holes is surrounded by four spheres with centres at the corners of a tetrahedron. Figure 4 two layers of close packed spheres with the enclosed octahedral holes picked out in colour
2 layers1 layerHolesr=0.225r=0.414TetrahedralOctahedral
(a) A sphere of radius0.414r fitting into anoctahedral hole;a(b) a sphere of radius0.225r fitting into atetrahedral hole(b)
(a) A sphere of radius 0.414r fitting into an octahedral hole; (b) a sphere of radius 0.225r fitting into a tetrahedral hole
Bodycentred and primitivestructureIn a body centred cubic structure, thepacking efficiency is 68%, slightly less thenthat in a close packed structure (74%), andthe coordination number has dropped to 8.Figure 6a bodycentred cubic array
Body centred and primitive structure In a body centred cubic structure, the packing efficiency is 68%, slightly less then that in a close packed structure (74%), and the coordination number has dropped to 8. Figure 6 a body centred cubic array