ORDER PARAMETER IN THE GLASS TRANSITION OF VITREOUS S-Ge

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ORDER PARAMETER IN THE GLASS TRANSITION OF VITREOUS S-Ge

H. Kawamura, K. Hattori, K. Matsunaga, Y. Akagi, A. Kawamori

To cite this version:

H. Kawamura, K. Hattori, K. Matsunaga, Y. Akagi, A. Kawamori. ORDER PARAMETER IN THE

GLASS TRANSITION OF VITREOUS S-Ge. Journal de Physique Colloques, 1981, 42 (C4), pp.C4-

357-C4-360. �10.1051/jphyscol:1981476�. �jpa-00220933�

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JOURNAL DE PHYSIQUE

CoZZoque C4, suppZ6ment au nO1O, Tome 42, octobre 1981 page C4-357

ORDER PARAMETER I N T H E G L A S S T R A N S I T I O N OF V I T R E O U S S-Ge

H. K a w a m u r a , K. H a t t o r i , K. Matsunaga, Y. A k a g i and A. K a w a m o r i

School of Science, Kwansei Gakuin University, 1-1-155 Uegahara, Nishinorniya, 662 Japan

Abstract.- Raman spectra of sulfur-rich S-Ge glasses prepared under different c o n d i t i ~ s were measured. It Was found that a side peak at 440 cm is skronger for the slowly quenched glass than for the rapidly quenched one.

This peak also becones smaller with the rise of temperature. The intensity of this peak is discussed in relation to the medium-range order of the glassy state.

Introduction.- It is believed that the medium-range order in chalco- genide glass depends on the condition of preperation [I], e.g. the cooling rate of the molten specimen or annealing. In Raman spectra of S-rich S-Ge bulk glass, we found that a side peak at 440 cm-I of air-quenched specimen is larger than that of water-quenched specimen.

We also observed that the intensity of this peak decreases with the rise of temperature below the glass transition point. These facts suggest us that this side peak is correlated with the medium-range order of the glassy state. In the following we shall describe the experimental results and their possible interpretations.

Experiments.- Specimens were prepared by melt-quench method from powdered germanium and sulfur of 6-N grade. The mixture of the powder was sealed into a silica tube under vacuum. The silica tube was heated at 1000°C for 10 hours. After maintaining the temperature about 100°C above the melting point for an hour, the tube was either ice water quenched or air quenched. Specimens were polished on both the

surfaces with diamond paste and then chemically etched.

The Raman spectra were obtained in the backscattering configu- ration with the use of He-Ne laser. The experimental data were multi- plied by a factor

-

4

w (wi-w) [1-exp (-hw/k~) 1

,

for Stokes side. Here, w and w. are the phonon and laser frequency, respectively, and T is the temp&rature. The resultant "reduced Raman spectra" will give the approximate density of vibrational states [ 2 1 . For the measurements at elevated temperatures, the specimen was set on a heated stainless steel block, which is inserted in a heat insulated double walled glass tube. Argon gas was passed through the glass tube in order to prevent the specimen from the oxidation.

Ffg. 1 shows the reduced Raman spectra for S-Ge glasses with 10% Ge, In which the ice water quenched is compared with the air quenched. It can be observed that both spectra are similar except for a small side peak at 440 cm-l. This peak is larger for the air

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981476

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JOURNAL DE P H Y S I Q U E

I

S-Ge glass(lO% Ge)

1

quenched glass. We have also observed the growth of 440-peak by the annealing at the glass transition temperature in the water quenched specimen. The glass transition temperature of S-Ge with 10% Ge was measured to be 150°C by the differential thermal analysis.

In Fig. 2, the reduced Raman spectra of 10%

Ge at elevated temperatures are shown. It can be

observed that the intensity of 440-peak decreases with the increases of temperature. When the temperature was decreased to the room temperature again, the intensity almost recovered as shown in spectrum D.

Discussions.- It is believed that the sharp peak at 150 cm I, 220 cm-1 and Fig. 1. Reduced Raman spectra

of S-Ge glass with 10% Ge.

(a) : water quenched.

(b) : air quenched.

480

6 '

are associated with bond bending Eg-mode, bond bending A1-mode and bond stretching A1-mode of the vibration of eiqht-membered ring of sulfur molecule (s8) , respectively [3]

,

as shown in Fig. 1. The peak at 340 cm-' followed by a plateau ranging to 440 cm-I is ascribed to the stretching

Fig. 2. Reduced Raman spectra of S-Ge glass of 10% Ge at elevated temperature.

(A) : 25OC, (B) : 100°C, (C) : 140°C and (D) : 2S°C 2nd time.

The peak at 440 cm-' decreases with the rise of temperature.

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vibration of GeS4 tetrahedral molecules and their clusters 141 or "outrigger- SULFUR ( liquid ) ed rafts" of G ~ S Z + ~ [I].

From the observation of Raman and infrared spectra, Lucovsky et a1. [4] suggest- ed that the S-rich S-Ge glass is a solid solution consisting of networks of very short S-chains cross linked by tetrahedrally coordinated Ge atom, and

c

U) S8-ring molecules. This

W

C model should be compared

t- with chain-crossing model

z for Se-rich Se-Ge glass,

I in which every atoms is

4 a incorporated into a single

a w network [51, [6].

U 3 n

w Our experimental

a results may allow us to

propose two alternative models as will be discussed in the followings.

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.

There is an evidence that 440-peak is associated with the S8-ring.

Raman spectra of pure loo 200 300 COO 500 liquid sulfur at elevated

RAMAN SHIFT ( ~ ~ - 1 ) temperatures were measured

by Ward [ 3 1 . Fig. 3 shows Fig. 3. Reduced Raman spectra of liquid the result of our measure- sulfur at 120°C, 130°C, 150°C, 160°C and ment. Pure sulfur melts

170°C. at about 120°C and trans-

form from A-sulfur to IT-sulfuk at about 160°C.

The former is mainly composed of S8-ring molecule, while the latter is composed of chain molecule. In Fig. 3, it is observed that the intensity of 440-peak decreases with the rise of temperature around 160°C, suggesting that this peak is associated with the S8-ring molecule.

Therefore, wemay conjecture that a rapid quenched glass is a solid solution consisting of short chains of sulfur atoms and small S-Ge networks, while a slowly cooled glass is composed of S8-ring molecules and of S-Ge networks. The S8-ring will break into chain with the rise of temperature, resulting in the decay of 440-peak.

(2). We have observed that the ESR singnal of S-Ge glass with 10% Ge increases with the rising temperature from 20°C to 130°C by 2 times as shown in Fig. 4 which suggests that the S-S bonds break as the temperature is increased. Moreover, the g-value of tile unpaired electron was found to be 2.003, which is much smaller than that observed for pure sulfur which is 2.024 [7], indicating that the observed unpaired electrons are not associated with the S-chain or the broken bonds of S8-ring. The large g-value of the dangling bond electrons in pure sulfur is supposed to be due to the small value of crystalline field for the unpaired electron at an end atom of S-chain. On the other hand, the crystalline field for the electron at a dangling bond of sulfur neighboring with Ge-atom will be larger [ 8 ] , because the ionicity

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JOURNAL DE PHYSIQUE

o o n h e a t i n g

+ o n c o o l i n g

l l l t l l l l , , l

0 50 100 150

temperature in "C

Fig. 4 Spin density of S-Ge glass of 10% Ge vs. temperature.

Spin density is normalized against ESR signal of ~ r 3 + . in the c.onfiguration of S-Ge is larger than in that of S-S.

From these facts, we come to the second model. The 440-peak is ascribed to the stretching vibration of S-S bonds which combine small networks composed of GeS4 tetrahedral molecules or outriggered rafts. By slow cooling or by annealing, the small networks or outriggered rafts will be developed to larger ones. With the rise of temperature, these S-S bonds connecting the small clusters will break, resulting in the decrease of the medium-range order. According to this model, the intensity of 440-peak may be taken as a parameter for medium-range order.

Since both models are lacking in decisive evidence unfortunate- ly, we have to reserve any definite conclusion at this moment.

Acknowledgements.- We would like to thank Dr. M. Kodama for the

differential annalysis of our specimens, and to Professor K. Yoshimitsu for his helpful discussions. The work is partly supported by the Grant-in-Aid for Scientific Research from the Ministry of Education.

References

.-

EL] PHILLIPS J. C., J. Non-crystalline Solids

43

^{(1981) 37}

[2] KOBLISKA R. J. and SOLIN S. A., Phys. Rev.

3

(1973) 756 131 WARD A. T., J. Phys. Chem.

3

(1968) 4133

141 LUCOVSKY G., GALEENER F. L., KEEZER R. H., GEILS R. H. and SIX H. A., Phys. Rev.

a

(1973) 5134

[5] TRONC P., BENSOUSSAN, M., BRENAC A. and SEBENNE C., Phys. Rev.

B8 (1973) 5974

[6]

KMANICH

R. J., SOLIN S. A. and LUCOVSKY G. Solid State Commun.

21 (1977) 273

[7] ~ R D N E R D. M. and FRANKEL G. K., J. Am. Chem. Soc. 78 (1956) 3279 [8] CERNY V. and FRUMAR M., J. Non-Crystalline Solids c ( 1 9 7 9 ) 23