Titanium Doping of the Metallic One-Dimensional Antiferromagnet, Nb12O29

Abstract

Monoclinic Nb12O29 undergoes a charge ordering transition to form antiferromagnetic Nb4+ chains (TN ~ 12 K) spaced 15.7 Å apart, which are coupled through mediation from a subset of metallic electrons which are present over all temperature regimes. We present the effects of disrupting the delicate electronic equilibrium in monoclinic Nb12O29 through doping Nb4+ (d1) with Ti4+ (d0) ions in the series, TixNb12−xO29. Powder neutron diffraction demonstrates that Ti is distributed over all of the 6 crystallographically distinct Nb positions. Magnetic susceptibility measurements reveal a rapid suppression of the magnetic ordered state on Ti doping, with a 3% percolation threshold consistent with the existence of one-dimensional Nb4+ chains. The reduction of the number of unpaired electrons on Ti4+ doping is shown to depopulate both localised and itinerant electron subsets, demonstrating that they are intrinsic to the properties of the system, which is argued to be a direct consequence of the mixture of bonding schemes within the lattice.