Magnetic Susceptibility of the Cubic Sodium Tungsten Bronzes

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Abstract
The sodium tungsten bronzes (NaxWO3) in the cubic range 0.45<x—6 for x=0.49 to 0.053×10—6 for x=0.85. This feeble paramagnetism was found to be temperature independent from 70° to 300°K for three representative samples with x=0.49, 0.76, and 0.85. The susceptibility of WO3 was determined to be —0.060×10—6 emu/g and is also temperature independent. Satisfactory agreement between calculated and observed susceptibilities was obtained with a model which assumes that the bronzes consist of a dispersion of sodium ions in a WO3 lattice. The molar susceptibility, then, can be calculated from the equation χM=χ(WO3)+xχ(Na+)+χe. The term χe for the Pauli paramagnetism was obtained for two cases: (a) for nearly free electrons (m*=1.6m), and (b) for the density of states taken from the literature data on the low temperature heat capacity of the bronzes. Best quantitative agreement was obtained between the calculated and the observed susceptibilities for case b and indicates a more rapid increase in the density of states than simply E½.

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