Medium range order and optical properties of As2S3 glass

Journal of Non-Crystalline Solids 59 & 60 (1983) 863-866 North-Holland Publishing Company

863

MEDIUM RANGE ORDER AND OPTICAL PROPERTIES OF As2S3 GLASS H. KAWAMURA*, T. TAKASUKA, T. MINATO, T. HYODOand T. OKUMURA School of Science, Kwansei Gakuin U n i v e r s i t y , I - I - 1 5 5 Uegahara, Nishinomiya 662, Japan

Low frequency Raman s c a t t e r i n g and o p t i c a l absorption edge were measured f o r As2S3 glasses quenched at temperature in the supercooling region of the glasses. I t was found t h a t both the Raman spectrum and the o p t i c a l absorpt i o n edge s h i f t to the lower energy side with the r i s e of the quenching temperature. The e f f e c t s were i n t e r p r e t e d in terms of the order of the arrangements of the l a y e r - l i k e c l u s t e r s , which become more random as the quenching temperature goes higher. I . INTRODUCTION In the previous paper~ we have reported t h a t the low frequency Raman scatt e r i n g from As2S3 glass s h i f t s to the lower frequency side with rapid quenching or with the r i s e of the temperature.

We have suggested t h a t t h i s s h i f t of the

spectrum is associated with the decrease of the i n t e r - c l u s t e r coupling due to the increase of the randomness of the arrangement of the c l u s t e r s . In the present work, we have i n v e s t i g a t e d the dependence of the low frequency Raman spectrum and the o p t i c a l absorption edge of As2S3 glass on the quenching temperature and discuss the e f f e c t of quenching on the medium range structure of the glass. 2. EXPERIMENTS The low frequency Raman spectra from 5 to 60 cm-I were measured with 90 ° s c a t t e r i n g c o n f i g u r a t i o n with the use of Jobin Yvon HRD-2 double monochrometer -I furnished with 1800 grooves mm , O.5um brazed holographic gratings. As the l i g h t source, He-Ne laser(6328A) of 50mW was used.

The p o l a r i z a t i o n of the

i n c i d e n t and scattered l i g h t s were in the s c a t t e r i n g plane. The o p t i c a l absorption in the range from 540nm to 620nm were measured with Jobin Yvon H-25 monochrometer combined with a tungsten lamp and a photomultiplier.

The output of the p h o t o m u l t i p l i e r was detected with a l o c k - i n a m p l i f i e r

and a d i g i t a l

voltmeter.

The abserption c o e f f i c i e n t was a u t o m a t i c a l l y calcu-

lated with a microcomputer. The 6N pure s u l f u r and arsenic were weighted and mixed in a mortar. *Present address, Department of Natural Science, Okayama U n i v e r s i t y of Science. I - I , Ridai-machi, Okayama, 700 Japan. 0022-3093/83/0000-0000/$03.00 © 1983 North-Holland/Physical Society of Japan

The

864

H. Kawamura et al.

/As2S3 glass

mixture was vacuum sealed in a quartz tube of inner diameter of 8mm. The tube was kept at 40O°C for 8 hours and then at 7OO°C f o r 8 hours.

The obtained

glass ingot was cut and sealed in a evacuated quartz tube again.

The tube was

kept at a fixed temperature T ranging from 170°C to 400°C f o r 8 hours, and q then quenched in ice water. The specimens were polished with diamond past in a rectangular shape f o r Raman scattering experiments and in a thin plate with the thickness of 0.7~O.9mm f o r the absorption measurements. 3. RESULTS AND DISCUSSIONS In Figure l , the low frequency Raman spectra measured at room temperature of As2S3 glasses, quenched at various temperature from 170°C to 400°C are shown.

I t is observed that the peak position of the spectrum s h i f t s to the lower frequency as the quench-

'

I

'

I_

ing temperature is increased.

'

In Figure 2, the peak position is plotted as a function of quenching temperature Tq.

It

is seen that the peak position moves in the range from Tg

~--~~\350oc

(glass t r a n s i t i o n temperature

f~--.~~

=lTO°C) to Tm(melting tempera-

3,5"C

ture=315°C).

2 ooc /

C

~, ~ ' , , , ~ .'~

260oc 250"C

In the tempera-

ture range higher than the melting temperature, the spectrum does not change.

rr

These results can be reasonably understood, i f the low frequency spectrum is associated with the shear v i b r a t i o n of l a y e r - l i k e c l u s t e r s , which has been called "outrigger r a f t " by P h i l l i p s 2,

[

0

20 40 Rarnan shift ( c r r c l )

60

FIGURE l Low frequency Raman spectra of g-As2S3, quenched at various temperatures. The peak position of the spectrum s h i f t s to the lower frequency with the rise of the quenching temperature.

coupled

each other through the van der Waals force due to the lonep a i r electrons of chalcogen atoms 1'2. The arrangement of the clusters may be i r r e g u l a r in the glass quenched at the higher temperature, r e s u l t i n g

865

H. Kawamura et al. / As2S 3 glass in the smaller coupling force between clusters.

I t is i n t e r e s t i n g that the low

frequency Raman spectrum indicates the medium range order of the glassy state, which is assiciated with the order of the stacking of the l a y e r - l i k e c l u s t e r of "outrigger raft".

Rarnal~-~

30

2.150

g - ~ Sa E u

>

v

>20

2~25~

(3..

t-

U-

o 2.100

00

100

200 300 Temperature(°C)

400

FIGURE 2 Peak position of low frequency Raman spectra(open c i r c l e ) and optical gap (closed c i r c l e ) as functions of quenching temperature. Both decrease with the r i s i n g of quenching temperature in the range between Tg and Tm. I t is expected that the medium range order of the structure connected with the randomness of the arrangement of the clusters w i l l affect the electronic structure of the glass.

We have measured the optical band gap for the glasses

quenched at various temperature, in order to find any change in the band structure with the change of the medium range order, resulting from the various quenching conditions.

absorption edge.

Figure 3 is an example of the spectrum near the

The spectrum s h o w s ( ~ ) I / 2

the absorption c o e f f i c i e n t and ~

as a function of ~ ,

is the photon energy.

where ~ is

The optical gap was

determined from the i n t e r s e c t i o n of the l i n e a r l y extrapolated l i n e with the abscissa.

The e x t r a p o l a t i o n l i n e was determined with the method of least

square from the absorption curve in the nearly l i n e a r range.

In Figure 2. the

optical gap obtained in this way is also p l o t t e d vs quenching temperature. Small but d e f i n i t e change in the optical gap can be observed in the range from 170°C to 300°C.

The change of the optical gap is quite p a r a l l e l with the

peak s h i f t of the low frequency Raman spectrum.

The s i m i l a r change was

11. Kawamura et al.

866

/As2S3 glass

observed by Kimura et al 3 in the range from 170°C to 210°C.

When the quenching

temperature is increased, the arrangement of the clusters becomes i r r e g u l a r , r e s u l t i n g in the narrowing of the o p t i c a l gap, because of the enhancement of the random p o t e n t i a l and/or the increase of the t a i l

I

i

I

states.

I

i

t

I

g -A~S3 I

quenched

--.-.

I 1.75

fro

I 2~0

/ ,11

2.25

2.50

photon energy ~ u (eV) FIGURE 3 Fundamental absorption edge of g-As2S3: Square r o o t of the absorption c o e f f i c i e n t m u l t i p l i e d by the photon energy is p l o t t e d vs photon energy. The o p t i c a l energy gap is determined from the e x t r a p o l a t i o n of the l i n e a r part of the curve as shown by the broken l i n e . In conclusion, we have found t h a t the s h i f t of the low frequency Raman spectrum as well as the change of the o p t i c a l band gap with the change of the quenching temperature of As2S3 glass,

when the quenching temperature is in-

creased in the supercooling region (from Tg=I70°C up to Tm=315°C), the arrangement of the l a y e r - l i k e clusters becomes more random, r e s u l t i n g in the red s h i f t of the low frequency Raman spectrum and o p t i c a l absorption edge. range order w i l l

The medium

be defined in terms of these physical e n t i t i e s .

REFERENCES I) H. Kawamura, F. Fukumasu and Y. Hamada, Solid State Commun. 43 (1982) 229 2) J.C. P h i l l i p s , J. Non-Crystalline Solids 43 (1981) 34 3) K. Kimura, H. Nakata, K. Murayama and T. Ninomiya, Solid State Commun. 40

(1981)

551.