Plasma‐Sprayed Semiconductor Electrodes: Characterization and Photoelectrochemical Properties of Coatings Obtained by the Projection of Doped and Undoped

powders, 99.9% pure, and [1 atom percent (a/o)] Si, (1 a/o) In, and (1, 10, 30 a/o) Mg doped have been plasma sprayed on titanium substrates. In the plasma, is transformed into , which can be partially reoxidized by acting on the substrate cooling rate during the projection. The coating surfaces are highly textured. Optical microscopy and x‐ray diffraction confirm that the reoxidation of happens on the coating surface and also in the bulk of the film along a tridimensional pattern. The uniform dopant distribution in the coatings is demonstrated by SIMS. The actual dopant concentration and impurity content of have been determined by neutron activation analysis. The photoelectrochemical properties of the coatings have been measured. Si doped is characterized by a photoanodic behavior only, but 99.9% and In or Mg doped all show photoanodic and/or photocathodic currents, depending upon the voltage applied to the electrode. This electrochemical behavior has been interpreted in terms of differently doped microregions coexisting in the photoactive layer of the electrode as a result of an inhomogeneous distribution of Fe2+ in nonstoichiometric. The best anodic photocurrents have been obtained for (1 a/o) Si. The action spectrum of this electrode, from 280 to 600 nm, is characterized by the contribution of three charge transfer transitions, whereas the near‐UV charge transfer seems unactive in the photocurrent generation of all the other plasma sprayed electrodes.