Evaluation of the molar volume of silicon crystals for a determination of the Avogadro constant

For a determination of the Avogadro constant by the X-ray crystal density method, the molar volume of three different silicon crystals has been evaluated by absolute measurements of their densities and molar masses. The results have shown that the molar volume is 12.058 8279 (22) cm/sup 3/ mol/sup -1/. When this value is combined with the lattice constant recommended by the CODATA Task Group on Fundamental Constants in 1998, it leads to the Avogadro constant of 6.022 1375 (12)/spl times/10/sup 23/ mol/sup -1/. Details on the sample preparation and the result of the measurement are presented.