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A comparative study of the properties of topological insulator Bi2Te2Se (BTS) crystals grown by the vertical Bridgeman method is described. Two defect mechanisms that create acceptor impurities to compensate for the native n-type carriers are compared: Bi excess, and light Sn doping. Both methods yield low carrier concentrations and an n-p crossover over the length of the grown crystal boules, but lower carrier concentrations and higher resistivities are obtained for the Sn-doped crystals, which reach carrier concentrations as low as 8×1014 cm-3. Further, the temperature dependent resistivities for the Sn-doped crystals display strongly activated behavior at high temperatures, with a characteristic energy of half the bulk band gap. The (001) cleaved Sn-doped BTS crystals display high quality Shubnikov de Haas (SdH) quantum oscillations due to the topological surface state electrons. Angle resolved photoelectron spectroscopy (ARPES) characterization shows that the Fermi energy (EF) for the Sn-doped crystals falls cleanly in the surface states with no interference from the bulk bands, which the Dirac point for the surface states lies approximately 60meV below the top of the bulk valence band maximum, and allows for a determination of the bulk and surface state carrier concentrations as a function of Energy near EF. Electronic structure calculations that compare Bi excess and Sn dopants in BTS demonstrate that Sn acts as a special impurity, with a localized impurity band that acts as a charge buffer occurring inside the bulk band gap. We propose that the special resonant level character of Sn in BTS gives rise to the exceptionally low carrier concentrations and activated resistivities observed. [ABSTRACT FROM AUTHOR]

We report the synthesis of MgB[sub 2] with bulk superconducting properties by conventional solid state methods at temperatures as low as 550 °C. Mg deficiencies of the type Mg[sub 1-x]B[sub 2] were tested. T[sub c] was found to decrease by about 1 K at large x, though the amount of nonstoichiometry, if any, is likely to be very small. For specific processing conditions, indications of the 25–30 K transition often seen in thin films were seen in the bulk materials. The lower temperature transition may be associated with the grain boundaries. These results indicate that it should be possible to fabricate MgB[sub 2] with bulk properties in in situ thin films at temperatures of 600 °C or less. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines thermoelectric properties of semiconductor materials. Room-temperature Seebeck coefficient; Thermal conductivity; Sensitivity of transport properties to chemical doping and nonstoichiometry.

Presents a study which measured the real and imaginary parts of the dielectric function of racemic and chiral CE8. Alignment of the molecules in the samarium carbide phase; Determination of the change in the density of states at low frequencies; Values of the direct current electrical conductivities.

Presents a study which examined copper oxide superconductors using nuclear magnetic resonance and nuclear quadrupole resonance. Experimental procedures; Results of spin-lattice relaxation; Conclusion.

Neutron time-of-flight spectroscopy has been employed to study the crystal-field interaction in the pyrochlore titanate Ho[sub 2]Ti[sub 2]O[sub 7]. The crystal-field parameters and corresponding energy-level scheme have been determined from a profile fit to the observed neutron spectra. The ground state is a well separated E[sub g] doublet with a strong Ising-like anisotropy, which can give rise to frustration in the pyrochlore lattice. Using the crystal-field parameters determined for the Ho compound as an estimate of the crystal-field potential in other pyrochlore magnets, we also find the Ising type behavior for Dy. In contrast, the almost planar anisotropy found for Er and Yb prevents frustration, because of the continuous range of possible spin orientations in this case. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses a study which investigated the dielectric properties of polycrystalline ceramics of (Ta[sub2]O[sub5])[sub1-x](SiO[sub2])[subx]. Background on the materials; Methods used; Results.

Reports on the measurement of the temperature dependent dielectric constants in the vicinity of room temperature for bulk ceramics. List of starting materials for ceramic synthesis; Information on the investigations of the Pb-Nb-Mg-Ti-O phase diagram; Summary of dielectric data for pyrochlore based oxides Pb-Nb-Mg-Ti-O.

Presents a study that examined epitaxial thin films of copper-oxide-based isotropic metallic oxide and superconducting heterostructures. Analysis of the crystalline properties and interfaces of the samples; Factors to consider when using copper-oxide-based isotropic metallic oxide materials as a normal-metal barrier; Investigation of the texture of the thin films.

Studies the structure and magnetic properties of epitaxial ferrite multilayer films. Determination of crystal orientation and rocking curve widths; Structural characterization of buffer films; Grain sizes of ferrite films grown on top of buffered substrates.