Evidence of Wolframite-Type Structure in Ultrasmall Nanocrystals with a Targeted Composition MnWO.

Here, we report a study of white-ochre powders with targeted composition MnWO prepared via a coprecipitation method. Through X-ray total scattering combined with pair distribution function analysis and Rietveld refinement of X-ray diffraction data, we find that their crystal structure is similar to that of bulk-MnWO, despite a mean crystallite size of 1.0-1.6 nm and a significant deviation of the average chemical composition from MnWO. The chemical formula derived from elemental and thermogravimetric analyses is MnWO(OH)·3HO. X-ray absorption and magnetic susceptibility measurements show that Mn and W have the same oxidation states as in MnWO. No magnetic ordering or spin glass or superparamagnetic behavior is observed above 2 K, unlike in the case of MnWO nanocrystals having a mean size higher than 10 nm.