A TEM study of Ni ordering in the Ni₆Se_5-xTe _x, 0<x<∼1.7, system

The Ni₆Se_5-xTe_x, 0<x<∼1.7, system has been carefully investigated via electron diffraction and TEM imaging. They reveal a somewhat disordered modulated superstructure phase arising from Ni ion ordering within an essentially well-defined chalcogen sub-structure. As x, and the underlying parent substructure cell dimensions increase, the incommensurate primary modulation wave-vector q characteristic of this Ni ion ordering quickly swings from close to 12a* for x=0 towards 12[101]* for x≥0.5. A lock-in to 12[101]* would formally transform the underlying parent Bmmb (a_p, b_p, c_p) structure into a P1a1 (a_s=2a_p, b_s=b_p, c _s=-12a_p+12c_p) superstructure phase.