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  • La1−x A x MnO3  (1)
  • Oxybutylene/oxyethylene triblockcopolymer  (1)
  • 1
    ISSN: 1572-9605
    Keywords: X-ray-absorption fine-structure (XAFS) ; “colossal” magnetoresistance (CMR) ; Jahn–Teller polarons ; La1−x A x MnO3 ; La1−y MnO3+δ
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We review the distortions of the MnO6 octahedra reduced by magnetization in hole-doped lanthanum manganese perovskites. The systems we consider include the “colossal” magnetoresistance (CMR) samples La1−x Ca x MnO3 (x=0.21, 0.25, 0.30), La0.67Ba0.33MnO3, and a poorer quality La0.67Pb0.33MnO3 sample. We also report preliminary work on three samples of oxygen-doped LaMnO3+δ and a lanthanum-deficient La0.9MnO3 sample. We find the same exponential relationship between the removal of the distortion and the sample magnetization in the Ba- and Pb-doped CMR samples as was found previously for the Ca-doped samples. The MnO6 distortion in the oxygen-doped materials is found to slightly reduce below the magnetic transition, although much less so than in the CMR samples. Above T c, the antiferromagnetic LaMnO3.006 sample shows a softer temperature dependence of the Mn–O bond length distribution broadening. Surprisingly, even this sample shows deviations from thermal (Debye) behavior near T N, possibly due to FM coupling within MnO planes.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1435-1536
    Keywords: Oxybutylene/oxyethylene triblockcopolymer ; micellisation ; gelation properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A triblock-copoly(oxybutylene/oxyethylene), denoted E58 B17 E58 (80 wt-% E), was prepared by sequential anionic copolymerisation and its micellar and gelation properties in aqueous solution were determined. The oxybutylene/oxyethylene copolymer had the advantage over comparable oxypropylene/oxyethylene copolymers of greater uniformity of composition and chain length. The methods generally used were surface tension, light scattering intensity, photon correlation spectroscopy, together with observation of gelation. Measurements were made at 30°, 40° and 55° C over a full concentration range from dilute solution into the gel (〉200 g dm−3) and at specified concentrations, including the gel, over the temperature range from 10° to 70° C. The lower and upper temperature boundaries of the gel region were identified, and the occurrence of syneresis was noted. The properties investigated and discussed include critical micelle and gel concentrations, micellar weights and sizes, and structures and mobilities in the gel.
    Type of Medium: Electronic Resource
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