Metal oxide bulk doping concentration

In technological applications, mixed, doped, or multi-metal oxides play an important role, for example, Mo-V-Te-Nb oxide [15] is used for selective oxidation of propane to acrylic acid. For some complex oxides, the bulk oxide structures and distribution of phases are often unknown and there is little knowledge of the atomic surface structure and composition, extent of hydroxylation, type and density of defects, and the location of dopants (homogeneously distributed, concentrated at the surface, grain boundaries, or interfaces). 

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