F. Reidinger

Single‐crystalline, epitaxial cubic SiC films grown on (100) Si at 750 °C by chemical vapor deposition

Single‐crystalline, epitaxial cubic (100) SiC films have been grown on (100) Si substrates at 750 °C by low‐pressure chemical vapor deposition, using methylsilane, SiCH3H3, a single precursor with a Si:C ratio of 1:1, and H2. This epitaxial growth temperature is the lowest reported to date. The films were characterized by means of transmission electron microscopy, x‐ray diffraction, infrared transmission, four‐point probe and other methods. Based on double‐crystal x‐ray diffractometry, the crystalline quality of our films is equivalent to that of commercial films of similar thickness. The letter describes the novel growth apparatus used and the properties of the films.

Yttria migration in Y−TZP during high-temperature annealing

The microstructural and phase changes occurring during the high temperature (1300 to 1550° CO annealing of Y-TZP were studied using X-ray fluorescence, X-ray diffraction, and TEM. Two processes occurred simultaneously involving the diffusion of yttrium. The Y-TZP partitioned into yttria-rich and yttria-poor phases throughout the material, because the material lies in a two-phase two-phase field of the yttria-zirconia phase diagram. The other process involved the segregation of yttrium to the surface, the extent of which was shown to vary with the state of the surface (ground or polished), annealing temperature, and silica content. Migration of yttrium to the surface caused a significant surface composition change (i.e. from 4.7wt% Y2O3 at room temperature to 8.9 wt % Y2O3 at 1550°C for 3 h), resulting in a microstructure and phase composition different from the bulk.

Preparation and characterization of lanthanum silicon nitride

Lanthanum silicon nitride (LaSi3N5) powder has been prepared under the relatively mild conditions of 1400 ° C and 1 atm nitrogen. Chemical, X-ray diffraction, solid state nuclear magnetic resonance spectra and morphological information on this powder is presented. The X-ray diffraction data and previously published information have been used to develop a more complete specification of the unit cell dimensions.29Si magic-angle spinning nuclear magnetic resonance spectra of LaSi3N5 show two chemical shifts at −64.5 and −56.5 p.p.m. These shifts reflect two electronically different “types” of silicon which have been attributed to the effects of quadrupolar139La nuclei and their spatial arrangements around silicon atoms.

Epitaxial Monocrystalline SiC Films Grown on Si by Low-Pressure Chemical Vapor Deposition at 750°C

Monocrystalline, epitaxial cubic (100) SiC films have been grown on monocrystalline (100) Si substrates at 750°C, the lowest epitaxial growth temperature reported to date. The films were grown by low-pressure chemical vapor deposition, using methylsilane, SiCH 3 H 3 , a single precursor with a Si:C ratio of 1:1, and H 2 . The films were characterized by means of transmission electron microscopy, single- and double-crystal X-ray diffraction, infra-red absorption, ellipsometry, thickness measurements, four-point probe measurements, and other methods. Based on X-ray diffractometry, the crystalline quality of our films is equivalent to that of commercial films of similar thickness. We describe the novel growth apparatus used in this study and the properties of the films.

Texture on Ground, Fractured, and Aged Y-TZP Surfaces

The phase composition of Y-TZP surfaces has been shown to vary greatly depending on the thermo-mechanical history of the surface. The orientation of these different phases in the surface region is not always random. There is speculation that the alignment of the tetragonal phase before fracturing may play a part in increasing the toughness of these materials. This article deals with an X-ray diffraction analysis of various Y-TZP surfaces with special emphasis on the texture of the different phases. Surfaces which have been ground (and polished), fractured, and aged (200°C) have been examined. In all cases, the monoclinic component that was formed was strongly oriented. The tetragonal phase may or may not be oriented depending on surface treatment. Annealing above the monoclinic-tetragonal transition temperature had little effect on the tetragonal orientation in most cases. Samples fractured at 1000°C have no unusual orientation on the fracture faces.

Microstructure and superconductivity of shock processed high TC superconductors

Abstract Explosive shock compaction of furnace synthesized 1 micron size powders of YBa 2 Cu 3 O 7 and Bi 2 Sr 2 CaCu 2 O 8 have been carried out both in the planar and cylindrical geometries. In both cases interesting microstructures and near theoretical packing densities are obtained. However bulk superconductivity is degraded but restored with some interesting changes on reannealing. The tetragonal and orthorhombic Tl 2 Ba 2 CuO 6 phases were successfully shock-synthesized in the time domain of microseconds at 100kbar. The products obtained ranged in phase purity from 85 to nearly 100%. The shock-synthesized tetragonal phase is a bulk superconductor with T c (zero) of 55K. High resolution electron microscopy shows double copper layer defects in the shock synthesized tetragonal Tl 2 Ba 2 CuO 6 . The importance of shock induced defects and microstructures in the magnetic flux pinning mechanisms are briefly discussed.

New phases in the YBa(SR)Cu and BiSR, CACU oxides

Abstract The superconducting properties and structure of Y(Ba 2-x Y x )Cu 3 O 7+δ and Bi 2 Sr 2-x Ca x Cu 2 O 7+δ are described. In the former material the Ba sites in the YBa 2 Cu 3 O 7 structure is doped by the smaller sized Y 3+ ion to give a non-superconducting phase. Similar doping by Sr 2+ ions can also be achieved to give a structure which shows a broadened bulk superconducting transition with T c = 85K. When the Ba:Sr ratio is 1:1 a resistive anomaly is observed near ∼200K. The Bi -superconductor becomes superconducting near 90K with a resistive and diamagnetic transition at 112K. The structure of the ordered phase of the Bi superconductor has been obtained by high resolution electron microscope imaging and electron diffraction.