Abstract
The crystal structures of phases based on three-layer , with , 0.51, 0.60, 0.75, and 0.92, determined by powder neutron diffraction, are reported. The structures have triangular layers interleaved by sodium ions, and evolve with variation in Na content in a more complex way than has been observed in the two-layer system. The phases with highest and lowest Na content studied ( and 0.32) are trigonal, with three layers per cell and octahedral Na ion coordination. The intermediate compositions have monoclinic structures. The compound has one layer per cell, with Na in octahedral coordination and an incommensurate superlattice. The and 0.51 phases are also single layer, but the Na is found in trigonal prismatic coordination. The magnetic behavior of the phases is similar to that observed in the two-layer system. Both the susceptibility and the electronic contribution to the specific heat are largest for .
7 More- Received 25 January 2006
DOI:https://doi.org/10.1103/PhysRevB.73.174104
©2006 American Physical Society