Metal oxide bulk doping impurity

Enhancement of reactivity of incendiary components has been claimed by the introduction of impurity states, particularly into metallic oxides (Refs 56 86). Impurity states have a twofold effect they disturb the lattice structure of the oxide (and[ so increase the diffusivity of the reactants), and they disturb the electronic distribution on the surface as well as in the bulk. The argument is made that by doping the oxide, or by controlling the formation temp, one may change an oxide from an n-type to a p-type semiconductor and hence cause it to become a better electron acceptor, and vice versa... 

PL measurements for the mechanistic studies (72-75). From detailed studies on n-Ti02 and that doped with transition metal ions such as Cr, we proposed a new mechanism that the reaction in acidic solutions is initiated by the oxidation of bulk OH species, not surface OH species 14). However, we later found a paper (76) reporting that Cr ions contained in Ti02 as an impurity emitted a PL band accidentally at the same wavelength (840 nm) as that observed by us till then. Also, a criticism to our conclusion was reported (77) probably due to confusion of the interpretation of the PL band. Thus it had become necessary to re-investigate our mechanism in detail, and we started systematic studies 18,19). The purpose of the present paper is to give confirmative experimental evidence to our new mechanism. 

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