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Vol. 79 capillary tubes were mounted in a 114.6 mm. camera and exposed 24 hours to the K-alpha (X 1.5418 Á.) radiation of copper with an open port and two nickel screens over the film. Samples of different preparations gave identical powder patterns regardless of the capillary size. Lindemann capillaries of 0.5 mm. permitted sample absorption which resulted in line splitting. The observed ¿-spacings (Á.) and visually observed intensities are: 6.09(Broad)(VF); 5.57(Broad)(VF); 3.47(M); 3.24(S); 3.07(H); 3.04(H); 2.40(H); 2.36(H); 2.02(H); 1.

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The electronic structure of sodium tungsten bronzes, Na x WO 3 , for full range of x is investigated by highresolution angle-resolved photoemission spectroscopy ͑HR-ARPES͒. The experimentally determined valenceband structure has been compared with the results of ab initio band-structure calculation. The HR-ARPES spectra taken in both the insulating and metallic phase of Na x WO 3 reveal the origin of metal-insulator transition ͑MIT͒ in the sodium tungsten bronze system. In the insulating Na x WO 3 , the near-E F states are localized due to the strong disorder caused by the random distribution of Na + ions in WO 3 lattice. While the presence of an impurity band ͑level͒ induced by Na doping is often invoked to explain the insulating state found at low concentrations, there is no signature of impurity band ͑level͒ found from our results. Due to disorder and Anderson localization effect, there is a long-range Coulomb interaction of conduction electrons; as a result, the system is insulating. In the metallic regime, the states near E F are populated and the Fermi level shifts upward rigidly with increasing electron doping ͑x͒. The volume of electronlike Fermi surface ͑FS͒ at the ⌫͑X͒ point gradually increases with increasing Na concentration due to W 5dt 2g band filling. A rigid shift of E F is found to give a qualitatively good description of the FS evolution.