129 I and 119 Sn Mössbauer spectroscopy , reversibility window and nanoscale phase separation in binary Ge x Se 1 x glasses
The molecular structure of the prototypical chalcogenide glass system—GexSe1 x in the 0oxo3 range, has received much scrutiny over the years. These glasses have been probed by modulated DSC, Raman scattering, Sn absorption and I emission Mössbauer spectroscopy, and neutron scattering. The I measurements utilize Te parent as a dopant in glasses, and reveal a bimodal (A, B) distribution of sites, with the site intensity ratio, IB/IA (x), tracking changes in glass structure as a function of x. At low x (o0.15) Senchains are stochastically cross-linked by Ge additive, and IB/IA (x) sharply declines with x. But at x40:15, rigid regions nucleate at the expense of floppy ones, and the ratio IB/IA (x) reverses slope to display a global maximum in the 0:20oxo0:25 range. The latter coincides with the reversibility window usually taken as signature of self-organization of these networks. At x40:26, these glasses enter a stressed-rigid elastic phase and in the 0:31oxo1 3 range nanoscale phase separate into Se-rich and Ge-rich regions. The signature of the latter is saturation of IB/IA (x) at a high value of 1.5 at x 1⁄4 13. Sn Mossbauer spectroscopy measurements independently support the picture of broken chemical order of the stoichiometric glass inferred from the I Mössbauer experiments. These observations using local probes are well correlated to Raman scattering, modulated differential scanning calorimetric and diffraction measurements. r 2006 Elsevier B.V. All rights reserved. PACS: 61.40.Fs; 63.50.+x; 78.30.Ly; 76.80.+y
Intermediate phases, boson and floppy modes, and demixing of network structures of binary As-S and As-Se glasses
Binary AsxS1-x glasses are studied in modulated-DSC, Raman scattering, IR reflectance and molar volume experiments over a wide range (8% < x < 41%) of compositions. Calorimetric experiments reveal a reversibility window, which permits fixing the three elastic phases; flexible at x < 22.5%, intermediate in the 22.5% < x < 29.5% range, and stressed-rigid at x > 29.5%. Raman vibrational density of states supported by first principles cluster calculations show features of both pyramidal (PYR) [As(S1/2)3] and quasi-tetrahedral (QT) [S=As(S1/2)3] local structures. The QT unit concentrations maximize in the intermediate phase (IP) and both PYR and QT local structures contribute to the width of the IP. The IP centroid in the sulfides is shifted to lower As content x than in corresponding selenides, a feature identified with excess chalcogen partially segregating from the backbone in the sulfides, but forming part of the backbone in selenides. These ideas are corroborated by the proportionately larger free volumes of sulfides than selenides, and the absence of chemical bond strength scaling of Tg’s between As-sulfides and As-selenides. Low-frequency Raman modes (Boson modes) increase in scattering strength linearly as As content decreases from x = 20% to 8%, with a slope that is close to the floppy mode fraction in flexible glasses predicted by rigidity theory, showing that floppy modes contribute to the excess vibrations observed at low frequency, the Boson modes. Long term aging, extending from months to several years, is studied on several families of chalcogenide glasses including the Ge-Se, As-Se, Ge-P-Se and Ge-As-Se systems. Our results show all samples display sub-Tg endotherms typically 10°C to 70°C below Tg in glassy networks possessing a mean coordination number r in the 2.25 < r < 2.45 range. Special attention is given to the As-Se binary and XRD, m-DSC and Raman scattering experiments are undertaken. Two
Influence of naloxone on the antinociceptive effects of some antidepressant drugs.
The antinociceptive effects of tricyclic and atypical antidepressants were studied using the rat tail mechanical method. Clomipramine produced analgesia at the doses of 30 and 40 mg/kg, desimipramine at 10, 20 and 40 mg/kg, maprotiline at 20 and 30 mg/kg, mianserin at 30 mg/kg, nomifensine at 1, 2.5 and 5 mg/kg, indalpine at 10, 20 and 40 mg/kg, viloxazine at 60 and 80 mg/kg. Naloxone (0.8 mg/kg) abolished the antinociceptive action of these antidepressant drugs. These results suggest that the antinociceptive activity of these six antidepressant drugs in acute experimental pain could involve opiate mechanisms.