Science Record

29

tw A yl A ws A == 3X Cae 6X Cae 3X (445) = 24NGs, 7 B vw A ~ at A 3X (Pn) + ox (43) + 3x (45) = 24NOe. (8)

In the above, N@,, NO; denote the numbers of A, B atoms; Xx’, X” are numbers determined by (6), (7), -(8), and their substitution into the right hand side of (5) gives the numbers X44, Xa, Xen of AA, AB, BB pairs of

nearest neighbours.

In this connection it may be pointed out that if we call three atoms forming mutually nearest neighbours as a triplet and denote by Cis Xap??? the various numbers of the different types of triplets, then for a solid solution on a face-centred lattice, we may guess (by analogy to (4) )

x La)l = x(ss)I eee ee ee (9) COG EG uke

These X’s will satisfy

A A A\_ ax(_4,)+2x( 1/5) +*(p’p) = 24NO0 B A A\_ 3x(pPy) + 2X(a45) +X(u/g) = 24ND: (10)

and the numbers X44, X4s, Xoe of pairs of nearest neighbours will be con-

nected to them by x(i4) 5 x(n) ;

1 4 eee) ese) ae (11)

It may be worthwhile to add that the difference between (5)—(8) and (9)(11) is actually small in spite of their appearances.

Combinatory formulas corresponding to (4) and (9) are easily derived. In fact, from (4) (which holds for multi-component solutions), we get

log g = N(z — 1)26; log 0; + = Na log Ae = 2 2

= D1 Xi log Xi — x, log =X G,j=1,2, sss) (12)

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