22 research outputs found
Intermediate phase, network demixing, boson and floppy modes, and compositional trends in glass transition temperatures of binary AsxS1-x system
The structure of binary As_xS_{1-x} glasses is elucidated using
modulated-DSC, Raman scattering, IR reflectance and molar volume experiments
over a wide range (8%<x<41%) of compositions. We observe a reversibility window
in the calorimetric experiments, which permits fixing the three elastic phases;
flexible at x<22.5%, intermediate phase (IP) in the 22.5%<x<29.5% range, and
stressed-rigid at x>29.5%. Raman scattering supported by first principles
cluster calculations reveal existence of both pyramidal (PYR, As(S1/2)3) and
quasi-tetrahedral(QT, S=As(S1/2)3) local structures. The QT unit concentrations
show a global maximum in the IP, while the concentration of PYR units becomes
comparable to those of QT units in the phase, suggesting that both these local
structures contribute to the width of the IP. The IP centroid in the sulfides
is significantly 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 Tgs
between As-sulfides and As-selenides. Low-frequency Raman modes increase in
scattering strength linearly as As content x of glasses decreases from x = 20%
to 8%, with a slope that is close to the floppy mode fraction in flexible
glasses predicted by rigidity theory. These results show that floppy modes
contribute to the excess vibrations observed at low frequency. In the
intermediate and stressed rigid elastic phases low-frequency Raman modes
persist and are identified as boson modes. Some consequences of the present
findings on the optoelectronic properties of these glasses is commented upon.Comment: Accepted for PR
The Proceedings of the Fourth International Conference of the Association of Architecture Schools of Australasia
The Proceedings of the Fourth International Conference of the Association of Architecture
Schools of Australasia.
Each paper in the Proceedings has been double refereed by members of an independent panel
of academic peers appointed by the Conference Committee. Papers were matched, where
possible, to referees in the same field and with similar interests to the authors
Atomic structure of chalcogenide glasses
(As(0.4)S(0.6))(100-x)Ag(x) glasses (x = 0, 4, 8, 12 at.%) have been studied with high-energy x-ray diffraction, neutron diffraction and extended x-ray absorption spectroscopy at As and Ag K-edges. The experimental data were modelled simultaneously with the reverse Monte Carlo simulation method. Analysis of the partial pair correlation functions and coordination numbers extracted from the model atomic configurations revealed that silver preferentially bonds to sulfur in the As(2)S(3)-Ag ternary glasses, which results in the formation of homoatomic As-As bonds. Upon the addition of Ag, a small proportion of Ag-As bonds (N(AgAs)≈0.3) are formed in all three ternary compositions, while the direct Ag-Ag bonds (N(AgAg)≈ 0.4) appear only in the glass with the highest Ag content (12 at.%). Similar to the g- As(2)S(3) binary, the mean coordination number of arsenic is close to three, and that of sulfur is close to two, in the As(2)S(3)-Ag ternary glasses. The first sharp diffraction peak on the total structure factors of As(2)S(3) binary and (As(0.4)S(0.6))(100-x)Ag(x) ternary glasses is related to the As-As and As-S correlations