The metastable Ni7 +/- xS6, and mixed Ni-6 +/- x(S1-ySey)(5), phases

摘要

The closely related, narrowly non-stoichiometric, metastable as well as thermodynamically stable "phases" in the metal-rich part of the Ni-S phase diagram near the nominal composition Ni7+/-xS6 have been carefully re-investigated via electron diffraction and transmission electron microscope imaging. Two quite distinct polymorphs have been identified, a minority incommensurate interface-modulated polymorph and a (heavily twinned) majority Ila1, a = 2a(p), b = 2b(p), c = -a(p) + c(p) superstructure (of an underlying Bmmb, a(p) similar to 3.3, b(p) similar to 16.4, c(p) similar to 11.3 Angstrom parent structure) polymorph. The incommensurate polymorph is shown to be very closely related to the only known polymorph of Ni6+/-xSe5 and is rapidly stabilized to room temperature upon doping of the sulfide compounds with selenium. (C) 2002 Elsevier Science (USA). All rights reserved. [References: 17]