We have used a YBCO de SQUID at 77 K to image room-temperature magnetic thin film samples. Samples imaged include Fe/sub 3/O/sub 4/, rare earth magnets such as samarium cobalt, and CMR materials. We typically saturate the magnetization of the sample in fields up to 8.5 Tesla, and then image the remanent (zero applied field) state. To help quickly interpret and quantify the SQUID microscope data, we have developed several analytical techniques. These techniques yield quantifiable results of magnetic properties, including magnetization, total dipole moment, and the demagnetizing field. We will present our results and discuss applications and limits of SQUID microscopy to the characterization of bulk and thin-film magnetic materials.

The synthesis and crystal structure determinations of Zr(0.30)ZrTe(2) and M(x)Zr(2)Te(2)As (M = Zr, Na) compounds are reported. The structure of Zr(0.30)ZrTe(2) was refined in the hexagonal space group P6(3)mc (No. 186, Z = 2) with lattice parameters a = 3.9840(3) Å and c = 13.366(3) Å; Zr(0.29)Zr(2)Te(2)As was refined in the rhombohedral space group R&thremacr;m (No. 166, Z = 3) with lattice parameters a = 3.9329(4) Å and c = 29.564(5) Å. Zr(0.30)ZrTe(2) and Zr(0.29)Zr(2)Te(2)As have close structural similarities to Zr(2)Se(3) and Ta(2)S(2)C, respectively, and are built up by stacking hexagonal layers with [Zr(0.30)-Te-Zr-Te] and [Zr(0.29)-Te-Zr-As-Zr-Te] sequences. Four-probe resistivity measurements (77-300 K) show both Zr(0.30)ZrTe(2) and Zr(0.29)Zr(2)Te(2)As to be metallic (Zr(0.29)Zr(2)Te(2)As: 8.9 x 10(-)(5) Omega cm at 273 K). Both compounds exhibit structures wherein Zr atoms are included between layers (ZrTe(2) and Zr(2)Te(2)As) by partially filling trigonal antiprismatic holes. The replacement of the included Zr ions in Zr(0.29)Zr(2)Te(2)As by Na ions has been demonstrated. Powder diffraction data showed that NaZr(2)Te(2)As is isostructural with Zr(0.29)Zr(2)Te(2)As. By use of Rietveld refinements, sodium ions were found to reside in the trigonal antiprismatic sites between the layers. Extended Hückel band calculations on the [Zr(2)Te(2)As](1.16)(-) layer indicate that it should be a metallic conductor and that the [Zr(2)Te(2)As] layer can bear a greater negative charge than has so far been observed. We suggest that the [Zr(2)Te(2)As] layered compounds may offer new opportunities as electron-donating hosts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

An X-ray diffraction procedure for quantitative chrysotile asbestos analysis in a gypsum-based matrix is discussed, The procedure includes calibration standards preparation, an EDTA treatment to remove gypsum, sample milling, and X-ray diffraction analysis, The effect of each step is discussed. Morphological and crystal structural changes due to the sample preparation procedure were also characterized using techniques such as SEM, IR, NMR and ICP. Through a statistically designed experiment, it is demonstrated that-X-ray diffraction can be used as a reliable technique in gypsum-based matrices to determine chrysotile concentration from 0.25% to 2.5% with a standard deviation of 0.07%.

The development of the electronic structure in Nd1-xSrxTiO3 as a function of x was investigated using resonant photoelectron spectroscopy. Attention is focussed indication of changes in the Ti 3d-O2p hybridization and on electron-electron correlation effects evident in the Ti 3d intensity within similar to 3 eV of the Fermi level (E-F). The energetic position of the Ti 3d intensity signals the importance of electron correlation effects. The total intensity in this region is found to correlate linearly with composition and changes in the spectral structure are discussed in terms of the one-electron spectral function. For x < 0.25 (insulating or semiconducting compositions), only incoherent intensity associated with the lower Hubbard band is present Additional intensity, attributed to a coherent quasiparticle contribution, appears at the composition of the metal-insulator transition, x similar to 0.25. Ti 3d intensity also occurs in the higher binding energy region of the predominantly O 2p band due to Ti 3d O-2p hybridization. Composition-dependent changes in this region are analyzed to determine changes in the Ti 3d-O2p hybridization with composition and structure.

Photoelectron spectroscopy was employed to follow the development of the Ti 3D spectral intensity within {approximately} 3 eV of the Fermi level (E{sub F}) in Nd{sub 1{minus}x}Sr{sub x}TiO{sub 3} as a function of x. The total intensity in this region is found to correlate linearly with composition as the nominal Ti valence is varied from +3 to +4. Changes in the spectral structure in this binding energy region are discussed in terms of the one-electron spectral function. For x < 0.25, (semiconducting compositions) only incoherent intensity associated with the lower Hubbard band is present. Additional intensity, attributed to a coherent quasiparticle contribution, appears at the composition of the metal-insulator transition, x {approximately} 0.25. The relative intensities of these two components are determined as a function of x, and connections with theoretical models and experimental results on related systems are discussed.

Photoelectron spectroscopy was employed to follow the development of the Ti 3d spectral intensity within approximately 3 eV of the Fermi level (EF) in Nd1-xSrxTiO3 as a function of x. The total intensity in this region is found to correlate linearly with composition as the nominal Ti valence is varied from plus 3 to plus 4. Changes in the spectral structure in this binding energy region are discussed in terms of the one-electron spectral function. For x less than 0.25, (semiconducting compositions) only incoherent intensity associated with the lower Hubbard band is present. Additional intensity, attributed to a coherent quasiparticle contribution, appears at the composition of the metal-insulator transition, x approximately 0.25. The relative intensities of these two components are determined as a function of x, and connections with theoretical models and experimental results on related systems are discussed.

Synchrotron radiation-based ultraviolet photoelectron spectroscopy (UPS was used to investigate the electronic structure of BaTiO3 and related mixed oxides. In particular, resonant photoelectron effects at the Ti 3p threshold provide a picture of the contribution of the Ti 3d states to the predominantly O 2p valence band, and thus produce information on Ti 3dO 2p hybridization. This is used to determine the TiO hybridization in BaTiO3 and comparisons are made to the Ti partial density of states obtained from first principles calculations of the band structure of BaTiO3. We have also investigated the effects of substitution of Nd for Sr in SrTiO3 to form the mixed oxide Nd1 − xSrxTiO3. These studies illuminate the effects of changing crystal structure and bandfilling on Ti 3dO 2p hybridization.

The structure of a zeolite ZSM-5 complex with ca. 4 molecules/unit cell of bithiophene was determined by high-resolution synchrotron X-ray powder diffraction. It adopts monoclinic symmetry in space group P2(1)/n (a unique) between room temperature and 25 K, with refined lattice parameters at 25 K of a = 20.0614(4), b = 19.8251(4), c = 13.3623(4) Angstrom, and alpha = 90.848(2)degrees. Structural modeling and Rietveld refinements showed that there are two crystallographically unique bithiophene molecules, each with an occupancy factor of ca. 0.5. One bithiophene is localized at the center of the straight channels with one of the rings residing at the intersection with the sinusoidal channels. The other molecule lies in the sinusoidal channels and projects partially into the straight channels. The relationship between polythiophene chain length and the formation of conducting polythiophene molecular wires in the ZSM-5 framework is discussed.

A series of LaTi1-xVxO3 compounds (0 less than or equal to x less than or equal to 1) have been prepared by the de are-melting method and characterized by conventional powder X-ray diffraction, thermogravimetric analysis, four-probe resistivity, and magnetic susceptibility studies. Selected members of this series have been characterized by synchrotron X-ray diffraction, neutron diffraction, selected area electron diffraction. Samples in the 0.2 less than or equal to x less than or equal to 0.3 region are similar to 3-4% La deficient (e.g., La0.97Ti0.8V0.2O3) Like the LaMO(3) end members where M = Ti, V, the LaTi1-xVxO3 phases are barely orthorhombic (almost tetragonal) and adopt the perovskite-type GdFeO3 structure (space group Pnma). Most of the LaTi1-xVxO3 phases are antiferromagnetic (AF) insulators including LaTiO3 (T-N = 148 K) and LaVO3 (T-N = 140 K). For the LaTi1-xVxO3 phases in the O < x < 0.10 region, the AF ordering temperatures and resistivities are reduced with increasing vanadium concentration. The 0.10 less than or equal to x less than or equal to 0.25 region comprises poorly metallic (rho(298) approximate to 10(-2) Omega cm), paramagnetic phases that represent rare examples of B-site-substituted metallic perovskites. Magnetic susceptibility studies in this region show Curie-Weiss behavior below 200 K with large temperature independent susceptibilities of ca. 10(-3) emu/mol. Variable-temperature synchrotron X-ray diffraction experiments on the La0.97Ti0.8V0.2O3 phase showed a marked orthorhombic distortion below 150 K but a nearly tetragonal cell at 298 K. Rietveld refinements of neutron diffraction data for this phase at 50 K showed a prototypical GdFeO3 structure with disordered Ti and V (refined occupancies of 82(1)% and 18(1)%, respectively) distributed over the octahedral site and a slight La deficiency (refined occupancy = 97(1)%). The structural parameters (bond distances, angles, cell constants) are intermediate to those of the LaMO(3) end members as expected. Electron diffraction experiments on the La0.97Ti0.8V0.2O3 phase revealed diffraction patterns that were also consistent with the prototypical Pnma cell with no evidence of microdomain ordering or supercell formation. In the 0.25 < x less than or equal to 1.0 region, the samples again show AF ordering and insulating behavior. The magnetic susceptibilities of the samples in this region show unusual peaking that is compositionally dependent. The field-cooled magnetic susceptibility of the x = 0.90 and 1.0 samples show large diamagnetic signals of unexplained origin. The zero-field cooled susceptibilities of these samples showed paramagnetic behavior. The formation of metallic phases from B-site substitution is discussed in terms of the Hubbard model.

The sorption behavior of strontium and barium on kaolinite, bentonite and chlorite-illite mixed clay was studied by radioanalytical techniques using the batch method.90Sr (29.1 y) and133Ba (10.5 y) were used as radiotracers. Characterization of the solid matrices was done by FTIR and XRD spectrometries and specific surface area measurements. Synthetic groundwater was used as the aqueous phase. The variation of the distribution ratioR d, as a function of metal ion loading was examined. The sorption isotherms were fitted to various isotherm models. The sorption energies were calculated to be in the range of 8–10 kJ/mol suggesting an ion exchange type of sorption mechanism. In detailed experiments, chlorite-illite mixed clay was first presaturated with K+, Sr2+, Ca2+ and Al3+ ions, respectively, prior to sorption studies with Ba2+ ions. The results of Ca2+ pretreated chlorite-illite were very similar to those of natural chlorite-illite, suggesting that the Ba2+ ion exchanges primarily with the Ca2+ ion on the clay minerals.

We have employed photoelectron spectroscopy to follow the development of the one-electron spectral function for Ti 3d electrons in Nd1−xSrxTiO3 as a function of x. For x<0.25, only incoherent intensity associated with the lower Hubbard band is present. Additional intensity, attributed to a coherent quasiparticle contribution, appears at the composition of the metal-insulator transition, x ∼ 0.25. The relative intensities of these two components are determined as a function of x.

A new series of compounds of composition (Ba1-xSrx)2(Sr0.67Bi0.33)(Pb1-yBiy)O6-δ has been prepared and characterized by powder X-ray and neutron diffraction studies. The phases adopt the cubic (NH4)3FeF6 type structure (space group Fm3m) with Sr2+ ions occupying the B sites. TGA and neutron refinements show oxygen vacancies and a large anisotropy associated with the O atoms. The anisotropy is discussed in terms of a vacancy model.

Photoelectron spectroscopy has been employed to follow the development of the electronic structure in Nd1-xSrxTiO3 as a function of x. Resonant effects at the Ti 3p threshold were used to highlight Ti 3d contributions in the valence bands. Particular attention is focused on Ti 3d intensity within similar to 3 eV of the Fermi level(E(F)) The total intensity in this region is found to correlate linearly with composition, as expected. Changes in the shape of this spectral structure are discussed in terms of the one-electron spectral function. For x<0.25 (insulating or semiconducting compositions), only incoherent intensity associated with the lower Hubbard band is present, Additional intensity, attributed to a coherent quasiparticle contribution, appears at the composition of the metal-insulator transition x similar to 0.25. The relative intensities of these two components are determined as a function of x. Ti 3d intensity also occurs in the higher binding-energy region of the predominantly O 2p band due to Ti 3d-O 2p hybridization. Composition-dependent changes in this region are analyzed in order to determine changes in the Ti 3d-O 2p hybridization with composition and structure.

A series of perovskite Nd1-xAxTiO3 (A = Ca, Sr, Ba) compounds has been prepared by the dc-arc melting technique in the composition range 0 ≤ x ≤ ∼1.0. The substitution of Sr and Ba in NdTiO3 results in structural phase transitions from orthorhombic (Pbnm) to cubic (Pm3m). The Nd1-xCaxTiO3 series remains orthorhombic throughout the range studied. Low field magnetic susceptibility measurements and remanent magnetic moment studies suggest that the Ti sublattice in the insulating Nd1-xAxTiO3 compounds (0 ≤ x ≤ ∼0.2) orders as canted antiferromagnets. The Nd1-xAxTiO3 compounds show compositionally dependent metal-insulator transitions that coincide with the disappearance of the magnetic ordering. The correlations between the structure and transport properties are discussed in terms of the Ti-O-Ti angle and Ti-O bond distance. The perovskite tolerance factor, t, is also shown to be a useful parameter to sort insulating and metallic phases in these compounds.

Changes induced in the electronic structure of BaTiO3 by substitutions of R = Y, La or Nd for Ba to form the mixed oxides R x Ba1−xTiO3−δ have been investigated using ultraviolet photoelectron spectroscopy. Substitution of formally R+3 ions for Ba+2 leads to the introduction of filled states in the band gap that are shown by resonant photoemission measurements to have significant Ti 3d character, consistent with a Mott-Hubbard insulator description for these oxides. It is suggested that the dominant factor is electron-electron correlation and this leads to the estimatesU∼Δ∼3 eV for this system, whereU is the correlation energy for the 3d and Δ is the charge transfer energy. Changes are observed in the photoelectron spectral shape for these states as a function of increasing substitution in the Nd system and discussed in the context of the opening of the Hubbard gap.

Changes induced in the electronic structure of BaTiO by substitutions of R = Y, La or Nd for Ba to form the mixed oxides RBaTiO have been investigated using ultraviolet photoelectron spectroscopy. Substitution of formally R ions for Ba leads to the introduction of filled states in the band gap that are shown by resonant photoemission measurements to have significant Ti 3 character, consistent with a Mott-Hubbard insulator description for these oxides. It is suggested that the dominant factor is electron-electron correlation and this leads to the estimates∼Δ∼3 eV for this system, where is the correlation energy for the 3 and Δ is the charge transfer energy. Changes are observed in the photoelectron spectral shape for these states as a function of increasing substitution in the Nd system and discussed in the context of the opening of the Hubbard gap.

The transport and magnetic properties of a series of Nd1-xCaxTiO3 perovskites where 0 less-than-or-equal-to x less-than-or-equal-to 0.8 were investigated. The transition from a Mott-Hubbard insulator (NdTiO3) with a 3d1 configuration to a metallic state was observed to take place near x = 0.15. Low-field susceptibility and remanent-moment measurements suggest that Nd1-xCaxTiO3 orders antiferromagnetically in the composition region 0 less-than-or-equal-to x less than or similar to 0.15. The metallic Nd1-xCaxTiO3 compounds behave as Fermi-liquid systems where the. effective mass increases as the metal-insulator boundary (x almost-equal-to 0.15) is approached.