Donald C. DeGroot

Phase‐selective route to high Tc superconducting Tl2Ba2Can−1CunO2n+4 films: Combined metalorganic chemical vapor deposition using an improved barium precursor and stoichiometry‐controlled thallium vapor diffusion

Films of the Tl2Ba2Can−1CunO2n+4 high Tc superconductors (n=2 or 3) can be prepared with a high degree of phase selectivity using a combination of metalorganic chemical vapor deposition (MOCVD) and vapor diffusion. Ba‐Ca‐Cu‐O films are first prepared by MOCVD using the volatile metalorganic precursors Ba(hexafluoroacetyl‐ acetonate)2(tetraglyme), Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2. The ‘‘second‐generation’’ barium precursor exhibits significantly improved thermal stability and volatility over previously used compounds. Thallium is then incorporated into these films by vapor diffusion using a Tl‐Ba‐Ca‐Cu oxide mixture of controlled composition as the source of volatile thallium oxides. Phase control is achieved by a combination of improved stoichiometry of the deposited film, a result of the new Ba source, and annealing with the appropriate oxide mixture. The resultant films consist predominantly of the Tl2Ba2Ca2Cu3Ox or Tl2Ba2CaCu2Ox phase, each having preferential orientation of the cryst...

Preparation of high‐Tc superconducting Bi‐Sr‐Ca‐Cu‐O films by organometallic chemical vapor deposition using second‐generation fluorocarbon‐based precursors

High‐Tc superconducting Bi‐Sr‐Ca‐Cu‐O thin films with good electrical properties and smooth surface morphologies have been prepared by low‐pressure organometallic chemical vapor deposition using the new fluorocarbon‐based precursors Sr(hexafluoroacetylacetonate)2⋅tetraglyme and Ca(hexafluoroacetylacetonate)2⋅triglyme together with Cu(acetylacetonate)2 and triphenylbismuth [Bi(C6H5)3]. The fluorinated precursors are air‐stable and exhibit high, stable volatility even after prolonged heating. X‐ray diffraction measurements reveal that the films deposited at 650 °C contain some fluoride phases but no high‐Tc phases. However, post‐annealing in oxygen produces films composed predominantly of the Bi2Sr2CaCu2Ox phase with high preferential orientation of the crystallite c axes perpendicular to the substrate surface. Four‐probe resistivity measurements indicate the onset of film superconductivity at ∼100 K and zero resistivity achieved at 73 K.

Inclusion of poly(aniline) into MoO3

Protonated emeraldine [poly(aniline)] has been encapsulated in MoO3 by first inserting aniline into its lattice followed by successful polymerization with (NH4)2S2O8; the new material is characterized by X-ray diffraction, IR spectroscopy, scanning electron microscopy and charge transport measurements.

Heteroepitaxy of high-Tc superconducting TlBaCaCuO films on metal-coated substrates

Abstract Superconducting TlBaCaCuO thin films have been successfully grown on gold-coated oxide substrates (yttria-stabilized zirconia (YSZ)) using a combination of metal-to-organic chemical vapor deposition (MOCVD) and Tl vapor diffusion. BaCaCuO films are first prepared by MOCVD using “second-generation” precursors with improved thermal stability and volatility. Thallium is then incorporated into these films by annealing in the presence of a mixture of oxides (Tl 2 O 3 , BaO, CaO and CuO) of a specific composition. The resultant films consists predominantly of single-phase Tl 2 Ba 2 CaCu 2 O x superconductor with preferential orientation of the crystallite c -axes perpendicular to the substrate surface. A magnetically determined T c value of about 95 K for Tl 2 Ba 2 CaCu 2 O x on Au/YSZ compares well with a transport T c value of 94 K. Attempts to form superconductors on platinum-coated oxide substrates (MgO) led to the formation of a PtTlO phase.

Intercalation of polyfuran in FeOCl.

Abstract The intercalation of polyfuran, by in-situ intercalative oxidative polymerization of terfuran in FeOCl is reported. The intercalation reaction proceeds to completion in methanol in a sealed tube at 100 °C. The resulting compound, polyfuran/FeOCl (I), is crystalline. An interlayer expansion of ≈7.7 A is observed upon intercalation. The formation of polyfuran in the interlayer space of the host material was confirmed by FTIR spectroscopy and by isolation of the polymers from the host. Tetrafuran could not be intercalated completely under the conditions employed. Electrical conductivity and thermoelectric power data from pressed pellets of (I) are reported and the results are compared with other FeOCl intercalated polymers. X-ray diffraction, magnetic, infrared spectroscopic and scanning and transmission electron microscopic characterization of (I) are reported.

A theoretical and experimental study of the electronic transport properties of the compounds Cu2MTe3 (M =Ti, Zr, Hf)

Abstract A theoretical model that involves metal nonstoichiometry is proposed to explain the unexpected electronic conductivities in the close-packed ternary tellurides Cu2MTe3 (M =Ti, Zr, Hf). Conductivity, thermoelectric power, and Hall effect measurements indicate that these compounds are hole carriers with a concentration of the order of 5 × 1019 cm−3 for M =Zr at 300 K. Such a concentration corresponds to roughly 0.4% Cu vacancies or 0.2% Zr vacancies, levels below the detection limit by X-ray diffraction methods of the corresponding elements in theM =Hf compound.

Electrochemical synthesis and electronic properties of poly(3,4-dibutyl-α-terthiophene)

Abstract Electrochemically prepared poly(3,4-dibutyl-α-terthiophene) has been investigated and the relationship between the electronic properties, the chemical structure of the monomer and the electrolyte used during the electropolymerization was studied. Doping studies were carried out with various electrolytes. We have electrochemically oxidized (p-doping) and reduced (n-doping) thin films of this polymer on platinum electrode under the same electrochemical conditions. We find that the films show a reversible oxidation wave yielding an electrically conducting polymer and a reversible reduction wave which is sensitive to the nature of the electrolyte. A value for the band gap derived electrochemically compares well with that obtained by optical absorption measurements and X-ray photoelectron spectroscopy. The electrical conductivity varies by 10 12 S cm −1 between the doped and undoped states of the polymer. The temperature-independent magnetic susceptibility above 100 K is consistent with the conducting properties of this polymer. The electrochemically prepared material is compared with the chemically prepared one using the same monomer.

Metal-organic chemical vapor deposition-derived lead- and bismuth-doped high-Tc superconducting TlBaCaCuO films

Abstract Superconducting Pb- and Bi-doped TlBaCaCuO films can be prepared on a variety of substrates by a two-step process, based on metal-organic chemical vapor deposition (MOCVD). MBaCaCuO films (M  Pb or Bi) are first prepared by MOCVD using precursors exhibiting improved thermal stability and volatility over previously used complexes. These characteristics allow better control over the stoichiometry of the deposited films. In the second step, thallium is incorporated into these films by a vapor diffusion process using mixtures of Tl2O3, BaO, CaO and CuO of specific composition as the source of volatile thallium oxides. The resultant films consist predominantly of single-phase TlMBaCaCuO exhibiting preferential orientation of the CuO planes parallel to the substrate surface. The superconducting properties of these films have been examined by resistivity and magnetization measurements.

Stabilization of anilinium in vanadium(V) oxide xerogel and its post-intercalative polymerization to poly(aniline) in air

We report the oxygen-induced polymerization of anilinium to poly(aniline) in the layered compound (C6H5NH3)0.4V2O5·0.40H2O forming {1/n(–C6H4NH–)nV2O5·0.40H2O.

Oxidative polymerization of pyrrole and aniline in Hofmann-type inclusion compounds

Abstract The reaction of the Hofmann-type inclusion compounds (CP 4 H 5 N)Ni(CN) 2 NH 3 (I) and (C 6 H 5 NH 2 )Ni(CN) 2 NH 3 (II) with various oxidants is reported to yield electrically conductive polypyrrole/Ni(CN) 2 NH 3 (III) and polyaniline/Ni(CN) 2 NH 3 (IV) type composites. (III) is a conductive material while (IV) is an insulator. The synthetic details as well as spectroscopic electron microscopic and X-ray diffraction data on the state of the polymers inside the Ni(CN) 2 NH 3 host material are presented. Data obtained from single crystals of these materials are presented, as well as variable temperature charge transport measurements such as electrical conductivity and thermopower.