ON THE ORIGIN OF THE SHORT INTERSLAB TE-CENTER-DOT-CENTER-DOT-CENTER-DOT-TE CONTACTS IN THE NEW MA(X) TE-2 PHASES (M=NB, TA, A=SI, GE, 1 ESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1/2)/

The powder pattern characteristics of the new MA(x)Te(2) phases (M = N b, Ta; A = Si, Ge; 1/3 less than or equal to x less than or equal to 1 /2) are analyzed. It is shown that two MA(x)Te(2) with very close Jc v alues can be easily distinguished solely on the basis of their 0k0 ref lections, which can be singled out in a pattern by intensifying the pr eferred orientation. The origin of the short interslab Te ... Te conta cts in the MA(x)Te(2) compounds is then investigated. The study demons trates that the short interlayer Te ... Te contacts (approximate to 3. 75 Angstrom) observed in all MA(x)Te(2) phases are due to steric effec ts, regardless of a possible charge transfer. The striking variation o f the shortest contacts as a function of x is shown to be directly rel ated to the relative position of the Te atoms within the slabs. (C) 19 95 Academic Press, Inc.