Ralph G. Tissot

Preparation and Properties of Icosahedral Borides

The electronic and thermal transport properties of refractory icosahedral boron-rich solids suggest the utilization of these unique solids as high-temperature semiconductors. Such applications will require high-quality, well-characterized materials. A variety of techniques have been used to prepare powders, ceramics, and single crystals of boron carbides and the icosahedral boron pnictides. X-ray diffraction, Raman spectroscopy, and ultrasound measurements have been used to probe boron carbide sample quality. Each of these measurements supports the structural model of boron carbides developed from analysis of transport data. Initial electrical conductivity measurements on these samples show no thermal hysteresis. The thermally-activated conductivity (Ea ≈ 0.17 eV) is consistent with a bipolaronic hopping mechanism.

UNIT CELL EXPANSION IN ErT2 FILMS

XRD analysis of plasma-vapor-deposited ErT2 films during aging (T decay to 3 He) reveals an hkl-dependent unit-cell expansion in which (200) grains expand out-of-plane as much as 0.01 A more than (111) out-of-plane grains. Texture analysis of an aged ErT2 film reveals a bimodal (111)/(200) out-of-plane preferred orientation. Sin 2 ψ analysis reveals significant in-plane macrostrain due to 3 He formation/growth. The mechanistic origins regarding these observations are also discussed.

Microdiffraction applications utilizing a two-dimensional proportional detector

Two-dimensional proportional detectors with their faster data collection, large dynamic range, and more available information than point or linear proportional detectors make them ideal for microdiffraction analysis. The unique capabilities of these detectors coupled with a rotating anode source, capillary optics, and a variety of accessories allow for a wide range of applications.

X-ray powder diffraction study of synthetic Palmierite, K 2 Pb(SO 4 ) 2

Palmierite (K 2 Pb(SO 4 ) 2 ) has been prepared via a chemical synthesis method. Intensity differences were observed when X-ray powder data from the newly synthesized compound were compared to the published powder diffraction card (PDF) 29-1015 for Palmierite. Investigation of these differences indicated the possibility of preferred orientation and/or chemical inhomogeneity affecting intensities, particularly those of the basal (00 l ) reflections. Annealing of the Palmierite was found to reduce the effects of preferred orientation. Electron microprobe analysis confirmed K:Pb:S as 2:1:2 for the for the annealed Palmierite powder. Subsequent least-squares refinement and Rietveld analysis of the annealed powder showed peak intensities very close to that of a calculated Palmierite pattern (based on single crystal data), yet substantially higher than many of the PDF 29-1015 published intensities. Further investigation of peak intensity variation via calculated patterns suggested that the intensity discrepancies between the annealed sample and those found in PDF 29-1015 were potentially due to chemical variation in the K 2 Pb(SO 4 ) 2 composition. X-ray powder diffraction and crystal data for Palmierite are reported for the annealed sample. Palmierite is trigonal/hexagonal with unit cell parameters a =5.497(1) A, c =20.864(2) A, space group R -3 m (166), and Z =3.

Microtubule Templated Synthesis of Inorganic Nanomaterials

Protein microtubules (MTs) have been used as templates for the biomimetic synthesis of metal oxide, metal sulfide, and metallic nanomaterials. These materials were coated onto MTs via three distinct synthetic pathways: metal ion hydrolysis which yielded iron oxide or zinc oxide-coated microtubules, metal ion/sulfide co-precipitation which yielded zinc sulfide coated MTs, and metal ion reduction which yielded gold-coated MTs. The growth process of metal oxide coating involves heterogeneous nucleation on the MT surface and produces even, microcrystalline films. Metal sulfide and metal coating initially involves the formation of nanoparticle arrays that decorate the MT surface and can eventually lead to either semi- or fully continuous coatings.

Three-dimensional interactive Data Language pole figure visualization

The Interactive Data Language has been used to produce a software program capable of advanced three-dimensional visualizations of pole figure and θ -2 θ data. The data can also be used to calculate quantitative properties such as strain level and to minimize the peak-height texture effects in individual θ -2 θ scans. The collection of the large data sets necessary for the analyses is facilitated by use of a position sensitive detector or area detector.

Determination of Activation energy of Intermixing in Textured Metal-Metal Multilayer Films Via Two-Dimensional X-ray Diffraction.

Activation energies for the intermixing reaction of textured metal-metal multilayer thin films have been determined using x-ray diffraction analysis. Kinetic data were collected utilizing an area detector so as to reduce intensity bias from changes in out-of-plane texture during the intermixing reaction. Activation energies for Al/Pt, Ni/Ti, and Co/Al metal-metal multilayer thin films have been determined as 95.4(2) kJ/mol, 201(13) kJ/mol, and 247(19) kJ/mol, respectively.

D-9 DETERMINATION OF ACTIVATION ENERGY IN TEXTURED METAL-METAL MULTILAYER FILMS VIA 2D XRD

Metal-metal multilayer thin films have found use in many electronic, optical and magnetic applications. In order to estimate the thermal stability of multilayer films, we investigated the behavior of films subjected to slow heat treatment at moderate temperatures (~100–300 o C). XRD analysis observed intensity decay for diffraction peaks associated with the constituent metal phases due to inter-diffusion of the differing metal bilayer species (e.g., Al/Pt and Ni/Ti). This slow diffusion process is important with regard to long term functionality of the film. Monitoring the peak intensities of the decaying chemical species as a function of temperature allows the derivation of the activation energy for the diffusion reaction in the metal-metal multilayer films. However, there is one caveat — the metal layers often demonstrate significant out-of-plane texture. The peak intensity decay due to reaction may also be coupled with significant increase of mosaic spread of the decaying peak intensities. Hence, there are two possible sources of intensity loss which makes quantification difficult with standard q-2q analysis. We therefore have employed an area detector methodology to monitor both peak intensity loss and mosaic spread in order to better derive the activation energy of textured films. The results of this method for the determination of activation energies in various multilayer film systems will be presented.

Chemical preparation of powders and films for high temperature superconductors

A precipitation process has been developed to prepare precursor powders which can be calcined and sintered to form high critical temperature superconductors such as YBa/sub 2/Cu/sub 3/O/sub 7-x/. Precursor powders are prepared using a continuous precipitation system in which a solution containing highly soluble salts of the desired metal cations is rapidly and completely mixed with a solution containing precipitating anions such as hydroxide and carbonate ions. The resulting amorphous powder can be calcined to form submicron particles of desired superconducting phases which are useful in preparing inks for the ink-jet printing of superconducting interconnects. The powders can be redissolved in organic solvents to form solutions which can be used in spin or dip coating substrates with thin superconducting films. Finally, the powders have been used to prepare bulk ceramics which exhibit the highest reported critical currents of any chem-prep ceramics. Bulk samples prepared from chloride doped precursors exhibit large, oriented grains and extensive flux pinning. 11 refs., 8 figs.