Single crystals of TiO2 anatase containing 0.22% of Al and traces of V, Zr, Nb, and La were grown by chemical transport reactions employing TeCl4 as the transporting agent. Electrodes having the (101) face exposed doped by reduction with hydrogen were employed. The electrochemical and photoelectrochemical behavior of a single crystal of anatase were scrutinized for the first time. Properties were compared to those of single-crystal rutile having the (001) face exposed. Impedance analysis established that the flatband potential of anatase (101) is shifted negatively by 0.2 V with regards to that of rutile (001). Interfacial capacitance measurements under forward bias indicate smaller density of surface states on anatase. Photoelectrochemical oxidation of water occurs on both rutile and anatase with incident photon-to-current conversion efficiencies close to unity at λ = 300 nm. From the comparison of U fb and E g, it follows that anatase (101) and rutile (001) electrodes differ mainly in the position of the conduction band edge. The complete photoelectrolysis of water to H2 and O2 is thermodynamically possible on anatase only. Photosensitized electron injection from adsorbed cis-Ru[L2(SCN)2] (L = 2,2‘-bipyridyl-4,4‘-dicarboxylic acid) proceeds with similar efficiency on both types of electrodes. However, light-induced charge separation on the single-crystal electrodes is about three times less efficient compared with nanoscopic anatase films. Anatase (101) is strikingly more active for electrochemical insertion of Li+ than rutile (001). The diffusion coefficients for Li+ insertion and extraction were estimated to be 2 × 10-13 and 6 × 10-13 cm2/s, respectively.

Inelastic neutron scattering and magnetic susceptibility measurements have been performed on the distorted perovskite NdGaO3. The magnetic susceptibility data show a Curie-Weiss behaviour with an effective magnetic moment close to 3.6 mu B per mole of Nd ions. No long-range magnetic ordering was detected in the temperature range 2-300 K. The inelastic neutron spectra observed at T=12 K exhibit four peaks of magnetic origin between 11 and 7D meV which can be unambiguously assigned to the complete crystalline-electric-field splitting pattern in the ground-state J multiplet 4I9/2 of the Nd3+ ions. We analysed the spectra in terms of geometrical considerations based on the actual C2 site symmetry of Nd3+. The best agreement between the experimental spectra and the calculated level structure was obtained for a model that takes into account the three nearest-neighbouring coordination polyhedra associated with the O2-, Ga3+ and Nd3+ ions as well as J-mixing between all multiplets of the 4I term. We conclude that single-particle crystal-field theory adequately explains the majority of magnetic and crystal-field properties of NdGaO3.

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The rare-earth gallium oxide perovskites RGaO3 (R=La,Pr,Nd) are promising substrates for epitaxy of high-Tc superconductors. In this paper the crystal structures of orthorhombic and rhombohedral RGaO3 have been studied by neutron diffraction, which allows precise localization of light atoms such as oxygen, which are of importance in phase transitions. The lattice parameters, atom positions and tilt angles of the oxygen octahedra were determined in the temperature range 12-1773 K. Lanthanum gallate LaGaO3 shows a phase transition from an orthorhombic phase (Pbnm) to a rhombohedral phase (Rc) at 425 K. The results are discussed in the classification schemes developed for distorted perovskites.