Multiple-data-set Rietveld analysis using isotopes in powder neutron diffraction. I. Accurate determination of the doping level in the ternary system Ni_xMg_1-xO, 0.005 < x < 0.1

The use of isotopes to extract precise and very accurate structural information in complex Rietveld analysis has been demonstrated by comparison of results obtained for single-data-set analysis with those from multiple-data-set single-crystallographic-model analysis of Ni_xMg_1-xO doped with various nickel isotopes. Fractional occupancies of dopants can be accurately determined down to at least the 0.5% doping level, which cannot be obtained through single-sample-data-set refinements because of correlation effects, even when a large contrast exists between the nickel isotope used and magnesium.