Orbital correlations in doped manganites

We review our recent X-ray scattering studies of charge and orbital order in doped manganites, with specific emphasis on the role of orbital correlations in Pr_1-xCa_xMnO₃. For x=0.25, we find an orbital structure indistinguishable from the undoped structure and long-range orbital order at low temperatures. For dopings 0.3≤x≤0.5, we find scattering consistent with a charge and orbitally ordered CE-type structure. While in each case the charge order peaks are resolution limited, the orbital order exhibits only short-range correlations. We report the doping dependence of the correlation length and discuss the connection between the orbital correlations and the finite magnetic correlation length observed on the Mn³⁺ sublattice with neutron-scattering techniques. The physical origin of these domains, which appear to be isotropic, remains unclear. We find that weak orbital correlations persist well above the phase transition, with a correlation length of 1–2 lattice constants at high temperatures. Significantly, we observe similar correlations at high temperatures in La_0.7Ca_0.3MnO₃, which does not have an orbitally ordered ground state, and we conclude that such correlations are robust to variations in the relative strength of the electron–phonon coupling. Received: 22 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

Calcium-Mediated Adsorption of Neutral Amino Acids to Carboxymethylated Chitin

Among various divalent metal ions, calcium has been found to be adsorbed tightly onto carboxymethylated chitin. The adsorption was completed not only by induced carboxyl groups but also by the support of acetamide, as well as primary and secondary hydroxyl groups. Although the adsorption capacity for transition metal ions was enhanced appreciably by regeneration into fibrous form, only that of calcium ion, among alkali-earth metals, was at the same level as that of transition metals. Since little effect was shown on the adsorption of phenylalanine by the blocking of α-amino and α-carboxyl groups of L-Phe, and since D-Phe was so a little adsorbed, the chiral specific adsorption of phenylalanine might be supported by mediation of calcium ion and by the contribution of hydrophobicity of the β-phenyl group.     

Silver Loading on DBD Plasma-Modified Woven PET Surface for Antimicrobial Property Improvement

In this work, the hydrophilic improvement of a woven PET surface was accomplished by a plasma technique. The woven PET surface was plasma-treated by dielectric barrier discharge (DBD) under various operating conditions (electrode gap distance, plasma treatment time, input voltage, and input frequency) and various gaseous environments (air, O₂, N₂, and Ar) in order to improve its hydrophilicity. It was experimentally found that a decrease in electrode gap distance and an increase in input voltage increased the electric field strength, leading to higher hydrophilicity of the PET surface characterized by wickability and contact angle measurements. In comparisons among the studied environmental gases, air gave the highest hydrophilicity, being comparable to O₂, while Ar and N₂ gave lower hydrophilicity of the woven PET surface. The optimum conditions for a maximum hydrophilicity of the PET surface were an electrode gap distance of 4 mm, a plasma treatment time of 10 s, an output voltage of 15 kV, and a frequency of 350 Hz under air environment. After the plasma treatment under the obtained optimum conditions, the woven PET was loaded with Ag particles using a AgNO₃ aqueous solution in order to obtain the antimicrobial property. The plasma-treated woven PET loaded with Ag particles exhibited good antimicrobial activity against both E. coli (gram-negative bacteria) and S. aureus (gram-positive bacteria).