Effect of oxygen stoichiometry on T(sub c) of Bi-based superconductors

The role of oxygen stoichiometry on T(sub c) is relatively well established on La2CuO(4+x) and the YBa2Cu3O(7-x) (123) superconductors, as compared to the Bi-based superconductors. Results are presented of investigations on the effects of oxygen stoichiometry on the transition temperature T(sub c) of Bi2Sr2CaCu2O(8+x) (2212 phase), and Pb-doped Bi2Sr2Ca2Cu3O(10+X) (2223 phase). It is shown that the effects of oxygen stoichiometry on T(sub c) of these two phases are very different. These results may be helpful in understanding the mechanism of superconductivity in the Bi-based superconductors

Dependence of transition temperature on hole concentration per CuO2 sheet in the Bi-based superconductors

The recently observed variations of the transition temperature (T sub c) with oxygen content in the Bi based (2212) and (2223) superconductors are analyzed in terms of p+, the hole concentration per CuO2 sheet. This analysis shows that in this system, T sub c increases with p+ initially, reaching maxima at p+ = 0.2 approx. 0.3, followed by monotonic decrease of T sub c with p+. The forms of these variations are similar to those observed in the La(2-x)Sr(x)CuO4 and YBa2Cu3Oy systems, suggesting that p+ may be an important variable governing superconductivity in the cuprate superconductors

Transition from N-Type to P-Type Destroys Ferromagnetism in Semiconducting Sn\u3csub\u3e1-X\u3c/sub\u3eCo\u3csub\u3ex\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e and Sn\u3csub\u3e1-X\u3c/sub\u3eCr\u3csub\u3ex\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e Nanoparticles

This work reports strong correlations between the structural, magnetic and electronic properties of room temperature ferromagnets (RTFM) Sn1-xCoxO2 and Sn1-xCrxO2 for x = 0 to 0.1. The samples prepared by the sol-gel chemical method show RTFM for x \u3c xL with the limiting concentration xL = 0.01 for Co doping and xL = 0.025 for Cr doping. As doping level x is increased from x = 0, the magnetic moment per ion, μ, increases and the lattice volume VL decreases up to x = xL. For x \u3e xL, μ dramatically decreases toward zero and VL increases, the latter suggesting interstitial doping. Thermoelectric measurements showed that the samples are n-type for x \u3c xL and p-type for x \u3e xL, suggesting that the RTFM is intrinsic and it is electron mediated

Surface and bulk infrared modes of crystalline and amorphous silica particles: a study of the relation of surface structure to cytotoxicity of respirable silica.

Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity

Neutron Scattering Measurements in RbMnF\u3csub\u3e3\u3c/sub\u3e: A Test of Spin-Wave-Region Theories at Low Temperatures and Critical Behavior Near T\u3csub\u3eN\u3c/sub\u3e

With the discovery of magnetic ordering in RbMnF3, this unique antiferromagnetic system was recognized as a prime case for a test of conventional spin-wave theory (CSWT) because of its negligibly small anisotropy and its simple, cubic structure. CSWT predicts a simple T2 power-law fall-off of the sublattice magnetization. Yet to this day, no stringent tests have been made of this prediction. Seiden [(Phys. Lett. 28 A, 239 (1968)] deduced a T3 low-temperature behavior on the basis of antiferromagnetic resonance measurements, concluding that CSWT was not supported. We have recently carried out neutron scattering measurements of both single-crystal and powdered samples of RbMnF3 in order to test for CSWT, Seiden’s result, and two other more recent semiempirical spin-wave schemes, and we present an analysis of the results. Measurements in the critical regime gave values of the critical exponent β and of TN that are in agreement with previous measurements

Photoluminescence spectroscopy of YVO4_{4}:Eu3+^{3+} nanoparticles with aromatic linker molecules: a precursor to biomedical functionalization

Photoluminescence spectra of YVO$_{4}$:Eu$^{3+}$ nanoparticles are presented,with and without the attachment of of organic linker molecules that are proposed for linking to biomolecules. YVO$_{4}$:Eu$^{3+}$ nanoparticles with 5% dopant concentration were synthesized by wet chemical synthesis. X-ray diffraction and transmission electron microscopy show the expected wakefieldite structure of tetragonal particles with an average size of 17 nm. Fourier-transform infrared spectroscopy determines that metal-carboxylate coordination is successful in replacing the native metal-hydroxyl bonds with three organic linkers, namely benzoic acid, 3-nitro 4-chloro-benzoic acid and 3,4-dihydroxybenzoic acid, in separate treatments. UV-excitation photoluminescence spectra show that the position and intensity of dominant $^{5}D_{0}-^{7}F_{2}$ electric-dipole transition at 619 nm is unaffected by the benzoic acid and 3-nitro 4-chloro-benzoic acid treatments. Attachment of the 3,4-dihydroxybenzoic acid produces an order-of-magnitude quenching of the photoluminescence, due to the presence of high-frequency modes in the linker. Ratios of the dominant electric- and magnetic-dipole transitions confirm infrared measurements, which indicate that the bulk crystal of the nanoparticle is unchanged by all three treatments.Comment: 9 pages, 5 figures, journal articl