A high-pressure NMR study of sodium tungsten bronze: NaxWO3

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Abstract
Cubic NaxWO3 has been studied at helium temperatures in samples ranging from x=0.22 up to x=0.84. The Knight shifts, the spin-lattice relaxation times T1, their dependences on pressure up to 45 kbar, the T2 of the free-induction decays and the T2 of the spin-echo signals have all been measured by nuclear resonance techniques. In the low-x region, evidence is produced suggesting that the conduction electrons acquire 3d character and an impurity band is formed. The data on the lowest-x sample is consistent with Mott's suggestion (1977) that at this value of x the impurity band is narrow, with the metal-non-metal transition occurring in the impurity band where the electrons are localised through an Anderson-type mechanism.