Chemical alloying induced collapse of reversibility windows in ternary AsSI glasses

1
Chemical alloying induced collapse of
reversibility windows in ternary As-S-I glasses

• Fei Wang
• - California Polytechnic State University
• P. Boolchand
• --University of Cincinnati

2
Concept of Intermediate Phase

• Our controlled experiments on glasses performed
  as a function of their connectivity ( or chemical
  composition) show, in general, three distinct
  elastic phases to occur.

3
Thermally Reversing Window in Studied Systems

• Reversibility Windows in indicated glass
  systems.

4
Results on Ge-Se-I Ternary
Ge1/4Se7/12I1/6
ltrgt2.4-0.4(n1/N)
F. Wang, MS Thesis, University of Cincinnati
(2002) Y. Wang et al. Phys.Rev.Lett.  87, 18,
5503 (2001) P. Boolchand and M.F. Thorpe,
Phys. Rev. B50,10366 (1994)
5
As-S-I ternary glasses

• As-S-I glasses show wide glass forming region as
  shown in figure.
• Constraint Counting Prediction of optimal
  constrained compositions are showed as TU line
  (assume As form quasi-tetrahedra) and RS line
  (assume As form pyramids)
• Intermediate phase of binary glasses AsxS1-x was
  defined in previous work.
• (As40S60)1-x(AsI3)x and (As30S70)1-x(AsI3)x
  glasses were synthesized and studied.

M.Mitkova, P.Boolchand , J.Non-Cryst.Solids,
240, 1(1998) Daniel Geogiev, PhD Dissertation,
University of Cincinnati, 2003
6
Molecular Structures in As-S-I glasses
Pyramids (m-units)
Quasi-tetrahedra (n-units)
As
m0
n0
I
S
m1
n1
m2
n2
m3
n3
7
T-Modulated DSC
Ge25Se75
8
Glass Transition Temperature
9
Non-reversing Heat
10
Intermediate Phase in As-S-I glasses
D.G.Geogiev, PhD Dissertation, U. of Cincinnati
(2003)
11
Raman Results for (As.40S.60)1-x(AsI3)x
As2S3
12
Raman Results for (As.3S.7)1-x(AsI3)x
13
Conclusions

• In both (As.40S.60)1-x(AsI3)x and
  (As.30S.70)1-x(AsI3)x series, we observed Tg to
  decrease systematically upon alloying AsI3.
• Non-reversing heat show thermally reversing
  windows in (As.40S.60)1-x(AsI3)x and
  (As.30S.70)1-x(AsI3)x series. These results
  combined with results on binary AsxS1-x glasses
  define the intermediate phase in As-S-I ternary.
• Raman line-shape in both series show evolution of
  bands from 180-225cm-1, which are signatures of
  mixed pyramids and mixed-tetrahedra units.

14
Tg for (AsI3)x(As.30S.70)1-x
15
Constraint Counting

• Bond Stretching Constrain (a)
• r/2
• Bond Bending Constrain (b)
• (2r-3)