Standard electrochemical data for high-quality, boron-doped diamond thin-film electrodes are presented. Films from two different sources were compared (NRL and USU) and both were highly conductive, hydrogen-terminated, and polycrystalline. The films are acid washed and hydrogen plasma treated prior to use to remove nondiamond carbon impurity phases and to hydrogen terminate the surface. The boron-doping level of the NRL film was estimated to be in the mid 1019 B/cm3 range, and the boron-doping level of the USU films was approximately 5 x 10(20) B/cm(-3) based on boron nuclear reaction analysis. The electrochemical response was evaluated using Fe-(CN)6(3-/4-), Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, dopamine, ascorbic acid, Fe(3+/2+), and chlorpromazine. Comparisons are made between the apparent heterogeneous electron-transfer rate constants, k0(app), observed at these high-quality diamond films and the rate constants reported in the literature for freshly activated glassy carbon. Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, and chlorpromazine all involve electron transfer that is insensitive to the diamond surface microstructure and chemistry with k0(app) in the 10(-2)-10(-1) cm/s range. The rate constants are mainly influenced by the electronic properites of the films. Fe(CN)6(3-/4-) undergoes electron transfer that is extremely sensitive to the surface chemistry with k0(app) in the range of 10(-2)-10(-1) cm/s at the hydrogen-terminated surface. An oxygen surface termination severely inhibits the rate of electron transfer. Fe(3+/2+) undergoes slow electron transfer at the hydrogen-terminated surface with k0(app) near 10(-5) cm/s. The rate of electron transfer at sp2 carbon electrodes is known to be mediated by surface carbonyl functionalities; however, this inner-sphere, catalytic pathway is absent on diamond due to the hydrogen termination. Dopamine, like other catechol and catecholamines, undergoes sluggish electron transfer with k0(app) between 10(-4) and 10(-5) cm/s. Converting the surface to an oxygen termination has little effect on k0(app). The slow kinetics may be related to weak adsorption of these analytes on the diamond surface. Ascorbic acid oxidation is very sensitive to the surface termination with the most negative Ep(ox) observed at the hydrogen-terminated surface. An oxygen surface termination shifts Ep(ox) positive by some 250 mV or more. An interfacial energy diagram is proposed to explain the electron transfer whereby the midgap density of states results primarily from the boron doping level and the lattice hydrogen. The films were additionally characterized by scanning electron microscopy and micro-Raman imaging spectroscopy. The cyclic voltammetric and kinetic data presented can serve as a benchmark for research groups evaluating the electrochemical properties of semimetallic (i.e., conductive), hydrogen-terminated, polycrystalline diamond.

The (Na1 - x Kx )0.5 Bi0.5 TiO3 perovskite solid solution is investigated using x-ray diffraction (XRD) and Raman spectroscopy in order to follow the structural evolution between the end members Na0.5 Bi0.5 TiO3 (rhombohedral at 300 K) and K0.5 Bi0.5 TiO3 (tetragonal at 300 K). The Raman spectra are analysed with special regard to the hard modes and suggest the existence of nano-sized Bi3+ TiO3 and (Na1 - 2x K2x )+ TiO3 clusters. The complementary use of XRD and Raman spectroscopy suggests, in contrast to previous reported results, that the rhombohedral tetragonal phase transition goes through an intermediate phase, located at 0.5 x 0.80. The structural character of the intermediate phase is discussed in the light of sub- and super-group relations.

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This paper gives a brief review of the effect of temperature and pressure on Raman spectra. Anharmonicity, defined by the cubic, quartic and higher terms in the potential expansion, is shown to be responsible for various properties such as dilatation or for variations of wavenumber and half-width of Raman bands with temperature and pressure, or may be strongly involved in phase transitions. This contribution does not pretend to be an exhaustive review on the subject but aims to introduce some basic concepts in a tutorial way before showing how intricated are these manifestations of anharmonicity. Copyright INTRODUCTIONProperties of materials are dependent on temperature and pressure. All applied research consists in studying the temperature and pressure dependence of their physical properties with a view to preparing the material to exhibit the expected properties in specific conditions of thermal and mechanical stress environment. Basic research consists in relating micro/meso-structural properties with the other physical properties. These relations exist via coupling coefficients which are often defined by a linear relationship. The present review presents the relations which govern the temperature and pressure dependence of the usual spectral parameters such as wavenumber, half-width and intensity of Raman bands. We shall point out the nonlinearity, also defined as anharmonicity, of the corresponding relationships. A tutorial and brief presentation of anharmonic effects in solids can be found in Chapter 8 of Ref. 1. As written by Sherman and Wilkinson, 2,3 in a completely harmonic approximation, where the force constant operating between any two masses is truly a constant and independent of the distance between the masses, the application of pressure would cause no observable frequency shift effects at all. The same statement can be done about the effect of temperature. However, as it becomes evident in the present special issue, this is not verified experimentally.Ł Correspondence to: Guy Lucazeau, LEPMI, (CNRS UMR 5631), Institut National Polytechnique de Grenoble, BP 75, F-38402 St. Martin d'Hères, Cedex, France. E-mail: guy.lucazeau@lepmi.inpg.fr † In memory of Evangelos Anastassakis, who should have been solicited for writing a review paper on such a subject.One of the aims of this paper is to point out that the measurements of temperature-or pressure-induced frequency shifts are measurements of the anharmonicity of the interactions that supply the restoring force constants. Let us point out that because pressure or temperature induces isotropic or anisotropic deformations of molecules and crystals, the pressure or stress-induced and the temperatureinduced frequency shifts  / are mainly determined by the associated deformation V/V. It is thus important to analyze the effects of temperature and pressure together. The origin of the deformation induced by these two external parameters is different. Pressure affects the equilibrium spacings between nuclei, distorts the electron clouds and through them...