Ternary and quaternary layered nitride halides, Ca2N(X,X ') (X,X ' = Cl, Br, I): Evolution of structure with composition

摘要

The quaternary systems Ca-N-Cl-Br and Ca-N-Br-I have been investigated resulting in the synthesis of a number of new layered nitride mixed halides. The evolution of structure with composition has been investigated by powder X-ray and powder neutron diffraction techniques. A continuous solid solution exists between CaNCl and Ca2NBr with intermediate compounds adopting the same anti- alpha-NaFeO2 structure (rhombohedral space group R (3) over barm) as the ternary end members. A phase transition Occurs in the Ca2NBr1-yIy system between y = 0.7 and y = 0.8 corresponding to a switch from cubic close packing to hexagonal close packing of metal-nitrogen layers and corresponding adoption of the anti-beta-RbScO2 (filled anti-CdI2) structure (hexagonal space group P6(3)/mmc). While nitride and halide anions occupy distinct crystallographic sites, there is no ordering of halides in quaternary materials irrespective of stoichiometry or structure type. All the nitride halides show temperature independent paramagnetic behaviour between 2 and 300 K. (c) 2005 Elsevier Inc. All rights reserved.