INELASTIC PROPERTIES OF Se BASED GLASSES IN THE VERY LOW FREQUENCY RANGE

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INELASTIC PROPERTIES OF Se BASED GLASSES

IN THE VERY LOW FREQUENCY RANGE

S. Etienne, J. Cavaille, F. Fouquet, J. Perez

To cite this version:

JOURNAL DE PHYSIQUE

Co ZZoque C5, suppZ&ment au n O 1 0 , M e 42, octobre 1982 page C5-575

INELASTIC PROPERTIES OF

Se BASED GLASSES IN

THE VERY LOW FREQUENCY

RANGE

S. Etienne, J.Y. Cavaille, F. Fouquet and J. Perez

Groupe dtEtudes de Me'taZZurgie Physique e t Physique des Mat&riaux, E.R.A. 463

I n s t i t u t NationaZ des Sciences AppZique'es de Lyon, 69621 ViZZeurbanne C e d ~ x , France

Abstract.- Experimental r e s u l t s avout i n e l a s t i c p r o p e r t i e s o f non c r y s t a l l i n e

--

S? and As-% A l l o y a r e reported. D i f f e r e n t behaviors above and under t h e glass t r a n s i t i o n temperature a r e discussed.

1. I n t r o d u c t i o n . - S t r u c t u r a l r e l a x a t i o n e f f e c t s near the t r a n s i t i o n temperature Tg have a l r e a d y been observed i n the v i t r e o u s selenium by m a n o f micro mechanical mea- surements. These experiments have been made a t constant frequency i n t h e

PIHz,

Hz

and low frequency ranges (1) (2) ( 3 ) . I n o r d e r t o extend the i n v e s t i g a t i o n range o f b o t h temperature and frequency, we have designed an apparatus working i n forced o s c i l l a - t i o n s ( 4 ) ; so, i t has been p o s s i b l e t o study t h e p r o p e r t i e s o f t h e sample a l s o f o r temperatures h i g h e r than Tg. IJe s h a l l present r e s u l t s obtained on one hand i n the low temperature range (T 28OC) where t h e aged glass remains i n an i s o c o n f i g u r a t i o n n a l s t a t e and, on t h e o t h e r hand, i n t h e h i g h temperature range ( T . > Tg) where t h e sample j s i n the metastable e q u i l i b r i u m . The temperature e f f e c t i n each range w i l l be compa- red. The i n f l u e n c e o f cross l i n k i n g between ( S e ) n m ~ l e c u l e s w i l l be c a l l e d t o mind p r e s e n t i n g some r e s u l t s obtained w i t h an As2 Se18 a l l o y .

2. Ex e r i m e n t a l r e s u l t s . - Shear modulus G and i n t e r n a l f r i c t i o n t a n

4

s p e c t r a have been :btained i n isothermal c o n d i t i o n by frequency scanning (10-4 + 1 Hz)

2.1. Non c r y s t a l l i n e selenium

2.1.1. Low temperature range (T < 2 8 9

The m a t e r i a l aged several weeks a t room temperature presents t h e s p e c t r a shown i n t h e f i g u r e 1.

The weak dependence o f Tan versus frequency F suggests a very wide r e l a x a t i o n times d i s t r i b u t i o n . I f the temperature T does n o t exceed 2g°C, t h e m a t e r i a l s t r u c t u r e r e

-

mains constant d u r i n g experiment. Above 2B°C, t h e spectra s h i f t d u r i n g experiment and measurements can be c a r r i e d o u t p r o p e r l y o n l y above Tg.

2.1.2. High temperature range (T>Tg)

S t r u c t u r a l r e l a x a t i o n i s then f a s t enough t o o b t a i n metastable 3 e q u i l i - brium i n a time s h o r t i n comparison w i t h experiment delay. Thus t h e sample s t a t e i s o n l y temperature dependent o f course i f T i s n o t t o o h i g h t o prevent c r y s t a l l i s a t i o n ( 5 ) ) . The s p e c t r a are shown i n f i g u r e 2. A d r a s t i c decrease of G, t o g e t h e r w i t h a maximum o f t a n

Q,

f o l l o w e d by a 'kubbewp1ateau"can be observed. This r e s u l t agrees w i t h t h a t o f Tobolsky e t a1 ( 6 ) where t h i s "rubbery" behavior c o u l d be detected du- r i n g s t r e s s r e l a x a t i o n t e s t .

2.1.3. Vitreous t r a n s i t i o n range

As r e c a l l e d above, t h e p r o p e r t i e s of t h e m a t e r i a l a r e time dependent i n t h i s temperature range. So, t h e isothermal s t r u c t u r a l re1 a x a t i o n can be observed by measurement o f mechanical p r o p e r t y P versus time. This r e l a x a t i o n can t a k e p l a c e under ( B -+ C),above Tg ( D -+ E) ( f i g u r e 3 ) .

JOURNAL DE PHYSIQUE

Fig.2:High temperature internal friction

F (H.) of pure Se

The k i n e t i c i s self-braked in the former case while s e l f c a t a l y t i c in the l a t t e r . The figure 4 shows the r e s u l t s obtained, P being the shear modulus a t

10-~HZ.

2 . 2 . As2Se18 Alloy

The glass temperature of such an alloy l i e s around 65°C. The r e s u l t s pre- sented in the f i g . 5 are related t o the low temperature rance where the sample, aged during several weeksat room temperature, l i e s in an isoconfigurationnal s t a t e . A broad maximum of tan

4

i s observed near 10°C a t 1 Hz. This r e s u l t i s i n agreement

w i t h

t h a t of Imaoka and Sakamura ( 7 ) , but these authors have performed measurements

only on one decade frequency range. Experiments a r e now in progress t o i n v e s t i s a t e the properties of t h i s material in glass t r a n s i t i o n zone and above.

F i g . 3 : Schematic thermal h i s t o r y fcr isothermal s t r u c t u r a l r e l a x a t i o n study

I

tempera-

1

time t , T, -ture T

Fig.4:Isothermal variation of shear modulus ~(10-'HZ) versus time t

curve. I n our case, and above Tg, i t i s v e r i f i e d t h a t t h e s h i f t f a c t o r UT i s the same f o r the two p r o p e r t i e s G ' and G''. on t h e f i g u r e 6, Log C%T i s represented versus t h e r e c i p r o c a l temperature (we have added t h e r e s u l t s given by t h e same k i n d o f t r e a t - ment on t h e curves o f t h e f i g u r e 1 ) . I t can be seen t h a t simple A r r h e n i u s ' l a w i s n o t able t o y i e l d the r e s u l t s f o r both h i g h and low temperature ranges. This f a c t i s now w e l l known i n the case o f glass forming m a t e r i a l ( 8 ) . So, we have t r i e d t o d e s c r i b e our r e s u l t s assuming on one hand wLF law f o r t h e metastable e q u i l i b r i u m s t a t e (Log CXT = C i ( T

-

To)

/

(C +.T

-

To) w i t h C 1 = 6,5 = 6,5 ; C2 = 20,l K ; To = 309 K) and on t h e o t h e r hand ~ r r i e n ~ u s

'

law f o r the i s o c o n f i g u r a t i o n n a l s t a t e . The apparent a c t i v a t i o n energy i s 93 Kcal/mole and 42 Kcal/mole f o r t h e h i g h and low temperature range r e s p e c t i v e l y .

I n the temperature and frequency range where pure Se sample presents an i n t e r n a l f r i c t i o n anomaly (1) ( 7 ) , As2Se18 sample presents a peak. A r r h e n i u s ' p l o t corresponding t o t h i s peak ( f i g . 7 ) i n d i c a t e s an a c t i v a t i o n energy : 15 Kcal/mole and ro = 6.10-11s. Our value o f t h e a c t i v a t i o n energy agrees w e l l w i t h t h a t o f r e f . 7 b u t t h e use o f a wide frequency range leads us t o more r e l i a b l e values, e s p e c i a l l y f o r T,.

C5-578 JOURNAL DE PHYSIQUE

t

-4

t

Fig.5 : Low temperature internal f r i c t i o n Fig.6 : Log of s h i f t f a c t o r CfT f o r dynamic of aged As2Se18

as

a function modulus of pure

Se

f o r metastable

of temperature T equilibrium s t a t e (*) and isocon-

figurationnal s t a t e

(a)

Arrhenius'pl o t f o r low temperature internal f r i c t i o n peak of A s ~ S e l ~

a s p e c i f i c chemical p r o p e r t y o f glassy selenium i n s t e a d o f a common behavior o f a l l glass forming systems. On t h e o t h e r hand, our a n a l y s i s i s t o be compared, a t l e a s t q u a l i t a t i v e l y , t o t h a t o f SPAEPETJ (10) a p p l i e d t o m e t a l l i c glasses.

The problem now t o compare t h e damping phenomenon r e l a t e d t o anomaly a t low temperature o f pure Se (1,7) ( o r peak i n t h e case o f As-Se a l l o y ) t o recove- r a b l e s t r a i n observed d u r i n g creep experiments performed a t room temperature ( 2 ) I n o t h e r words, i f we assume ( i ) t h a t deformation mechanisms occur by c r e a t i o n and a n n i h i l a t i o n of shear microdomains under s t r e s s

(6

and a mechanisms l e a d i n g respec- t i v e l y t o recoverable and permanent deformation ( 1 1 ) ) and ( i i ) t h a t anomaly ( o r peak) corresponds t o B r e l a x a t i o n , a wide times d i s t r i b u t i o n must be evocated. Another assumption may be t h a t t h e anomaly ( o r peak) i s a consequence o f w e l l d e f i n e d and l o c a l i s e d atomic displacements ( l i k e s i d e group r o t a t i o n i n organic polymers o r c a t i o n i c l o c a l movement i n oxide glasses). Another question i s connected t o the va- l u e s o f a c t i v a t i o n energies : on one hand, t h i s value i s much lower f o r t h e peak ( 1 6 Kcallmole) than f o r low temperature i n t e r n a l f r i c t i o n b a c k ~ r o u n g (42 Kcal/mole)

,

which seems t o favour t h e second assumption ; on t h e o t h e r hand these values are n o t y e t c l e a r 1 y understood.

Numerical computations are i n prosress i n order t o t e s t t h e f i r s t assump- t i o n . Furthermore, t h e i n v e s t i g a t i o n performed on As-Se a l l o y where secondary r e l a - x a t i o n i s c l e a r l y resolved w i l l be u s e f u l t o c l a r i f y these p o i n t s .

REFERENCES

1. S. ETIENNE, J . PEREZ, Revue Physique AppliquGe, 12 (1977) 837 2. S. ETIENNE, J. PEREZ, Revue Physique AppliquGe, 14, (1979) 607

3. S. ETIENNE, G. GUENIN, J. PEREZ, J . Phys. D : P.ppl. Phys., 12 (1979) 2189

4. S. ETIENNE, J.Y. CAVAILLE, J. PEREZ, bl. SALVIA, Paper t o be presented a t t h i s conference

5. J. CORNET, D. ROSSIER, Proceed 5 t h I n t e r . Conf. Amorphous and l i q u i d semiconduc- t o r s , Ed. Stuke J. and Brening b!., 1 (1973) 267

6. A, EISENBERG, TOBOLSKY A.V., 3. Polym. S c i . 61 (1962) 433 7.

F!.

IIIAOKA, H. SAKAMURA, Glass Tech. 15 (1974) 105

8. J.D. FERRY, V i s c o e l a s t i c p r o p e r t i e s o f polymers, John !!iley and Sons, I n c . New-York, (1970) 298

9. R.B. STEPHENS, The v i s c o s i t y and s t r u c t u r a l r e l a x a t i o n r a t e o f evaporated s e l e - nium o f f i c e o f Naval Research (1977) Technical r e p o r t n o 1

10. F. SPAEPEN, J. non c r y s t . Solids, 31 (1978) 207