Structural and electrical properties of a new ([SnSe]1.16)1(NbSe2)1 polytype

Abstract

A new polytype of the misfit layer compound ([SnSe]1.16)1(NbSe2)1 with extensive rotational disorder was prepared from designed modulated elemental reactants. This polytype, previously referred to as a ferecrystal due to the extensive rotational disorder, formed over a range of compositions and precursor thicknesses and the resulting c-axis lattice parameters ranged from 1.2210(4) to 1.2360(4)nm. These values bracket the value published for the crystalline misfit layer compound prepared at high temperature. The a- and b-axis in-plane lattice parameters of both the SnSe and NbSe2 constituents were incommensurate, which differs from the misfit layer compound formed via high temperature reaction that has a common b-axis lattice parameter for the two constituents. The in-plane area per unit cell of the ferecrystal is 1–2% larger than the compound formed at high temperature. The ferecrystalline ([SnSe]1.16)1(NbSe2)1 compound is 1.6 times more conductive than the misfit layer compound. Hall effect measurements indicate that the ferecrystal is a p-type metal and that the higher conductivity is a consequence of higher mobility of carriers in the ferecrystalline compound.