The electrochemical properties of semiconducting anodes of TiO2, SrTiO3, BaTiO3, Fe2O3, CdO, CdFe2O4, WO3, PbFe12O19, Pb2Ti1.5W0.5O6.5, Hg2Ta2O7, and Hg2Nb2O7 in photoassisted electrolysis of water were determined. All of these oxides formed a rectifying junction with the electrolyte and anodic photocurrents were generated only with larger-than-band-gap illumination. For Fe2O3, the optical absorption spectrum was different from the photoelectrochemical spectrum due to crystal field transitions. These oxides were found to be stable over certain range of pH. In a given electrolyte, the flatband potential Vfb varied linearly with the band gap. A good correlation was obtained between Vfb and the heat of formation of the oxide per metal atom per metal-oxygen bond, but not between Vfb and the calculated Fermi energy of the oxide. This suggests that a semiconductor-electrolyte interface may be approximated by a semiconductor-metal junction where the barrier height is determined by the heat of formation of the metal-semiconductor compound. The practical aspect of using a photoassisted electrolysis cell for solar energy conversion is discussed.

We describe here a metallic ferromagnetic system Fe1 Co S2 and Co1 &Ni S2 that appears to have a single doubly degenerate band. The electrons in the band are itinerant as manifested by metallic electrical conductivity, but the magnetic moment is that of the isolated ion.For several decades localized as opposed to itinerant-electron ferromagnetism in metals has been investigated theoretically. ' However, experimental systems on which to base theoretical models of band ferromagnetism are often complicated by the presence of composite bands as, for example, in the elemental transition metals which are comprised of overlapping broad s and narrow d bands. Such quantities as density and itinerancy of d electrons, magnetization of the & electrons, and the magnitude of +-d exchange are difficult to measure directly. The compounds to be discussed appear to avoid the complicating features introduced by the presence of such & electrons.All transition metal disulfides, FeS, through ZnS2, crystallize in a cubic pyrite structure in which the cations are in face-centered positions.The physical properties of the series' are summarized in Table I. Each successive member of the series represents the progressive addition of one d electron. In much of this series, a continuous range of solid solutions of adjacent members, e.g. , Fe1 xCoxS2 and Co1 &Ni~S2 for 0 &x~1 , can be formed. 3 The unit cell dimension increases monotonically with increasing atomic number of the cation. These solid solutions are metallic conductors' (Fig. 1) except for dilute concentrations (&0.1%) of CoS2 in either FeS, or NiS2. Since the beginning and end members of the series are both semiconducting while all other members (except near NiS, ) show metallic conductivity, it is not inconsistent to conclude that Table I. Magnetic and transport properties of pyrite compounds. FeSs Temp. independent paramagnetic -6 X = 0.31 + .04 x 10 emu/gm Semiconductor M = 0.92 + .05 ev M 0.96 + .02 ev 6 2g CoS~Ferromagnetic =0. 9~~T = 120K Metallic Plasma Edge

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