The syntheses, crystal structures, electrical properties, and optical absorbance spectra of six perovskite oxynitrides, AMO 2 N (A ) Ba, Sr, Ca; M ) Ta, Nb) have been investigated. The average crystal structure of BaTaO 2 N is a cubic perovskite, with a Ta-O/N distance of 2.056 Å. SrTaO 2 N and CaTaO 2 N are distorted by octahedral tilting, showing noticeably smaller Ta-O/N distances of approximately 2.02 Å. Electron diffraction studies of BaTaO 2 N are consistent with the simple cubic perovskite crystal structure determined using X-ray powder diffraction methods. Each of the niobium oxynitrides is isostructural with its tantalum analogue, though the Nb-O/N distances are observed to be slightly longer. The optical band gaps are estimated from diffuse reflectance spectra as follows: BaTaO 2 N, 1.8 eV; SrTaO 2 N, 2.1 eV; CaTaO 2 N, 2.4 eV; BaNbO 2 N, 1.8 eV; SrNbO 2 N, 1.9 eV; CaNbO 2 N, 2.1 eV. Impedance spectroscopy was carried out on sintered pellets of the ATaO 2 N and BaNbO 2 N to investigate the dielectric and electrical transport properties. The BaNbO 2 N sample shows metallic-type conductivity apparently from a slight reduction that occurs during sintering. In contrast, the tantalum compounds are semiconductors/insulators with conductivities of ∼10 -5 S/cm (A ) Ba, Sr) and ∼10 -8 S/cm (A ) Ca). Interpretation of the impedance data for BaTaO 2 N and SrTaO 2 N reveals that these two compounds have unexpectedly high bulk dielectric constants, κ ≈ 4900 and 2900, respectively, at room temperature. The dielectric constants of both compounds are frequency dependent and show a relatively weak linear dependence upon temperature with no sign of a phase transition over the temperature range 300-180 K.

The sheet resistance as a function of temperature, magnetic field and its orientation for atomically flat SrTiO 3 / LaAlO 3 interfaces with carrier densities of ϳ3 ϫ 10 13 cm −2 is reported. At low magnetic fields superconductivity is observed below 130 mK. The temperature dependence of the high field magnetoresistance and its strong anisotropy suggest possible magnetic ordering below 35 K. The origin of this ordering and its possible relation to superconductivity are discussed.

A: Ba, Sr, Ca; M: Ta, Nb). -The title compounds are synthesized by ammonolysis of stoichiometric mixtures of ACO3 and M2O5 in acetone (flowing NH3,1223-1273 K, 20 h). As revealed by powder XRD, BaTaO2N and BaNbO2N crystallize in the space group Pm3m with Z = 1, SrTaO2N and SrNbO2N in the tetragonal space group I4/mcm with Z = 4, and CaTaO 2 N and CaNbO 2 N in the orthorhombic space group Pnma with Z = 4. The compounds BaTaO 2 N and SrTaO 2 N exhibit unexpectedly high bulk dielectric constants of about 4900 and 2900, respectively, at room temperature. The dielectric constants of both compounds are frequency dependent and show a relatively weak linear dependence upon temperature with no sign of a phase transition between 300 and 180 K. Once formed, these compounds are very stable in the presence of air, moisture, and acids, providing the possibility for technological applications. -(KIM, Y.-I.; WOODWARD*, P. M.; BABA-KISHI, K

Novel template-free hierarchical-like In(2)S(3) hollow microspheres were synthesized using thiosemicarbazide (NH(2)NHCSNH(2)) as both a sulfur source and a capping ligand in a ethanol/water system. In this study, we demonstrate that several process parameters, such as the reaction time and precursor ratio, strongly influence the morphology of the final product. The In(NO(3))(3)/thiosemicarbazide ratios were found to effectively play crucial roles in the morphologies of the hierarchical-like In(2)S(3) hollow microsphere nanostructure. With the ratios increasing from two to four, the In(2)S(3) crystals exhibited almost spherical morphologies. The synthesized products have been characterized by a variety of methods, including X-ray powder diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffused reflectance spectroscopy (UV-vis DRS). XRD analysis confirmed the tetragonal structure of the In(2)S(3) hollow microspheres. The products show complex hierarchical structures assembled from nanoscale building blocks. The morphology evolution can be realized on both outside (surface) and inside (hollow cavity) the microsphere. The surface area analysis showed that the porous In(2)S(3) possesses a specific surface area of 108 m(2)/g and uniform distribution of pore sizes corresponding to the size of pores resulting from the self-assembled structures with flakes. The optical properties of In(2)S(3) were also investigated by UV-vis DRS, which indicated that our In(2)S(3) microsphere samples possess a band gap of ∼1.96 eV. Furthermore, the photocatalytic activity studies revealed that the synthesized In(2)S(3) hollow microspheres exhibit an excellent photocatalytic performance in rapidly degrading aqueous methylene blue dye solution under visible light irradiation. These results suggest that In(2)S(3) hollow microspheres will be an interesting candidate for photocatalytic detoxification studies under visible light radiation.