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Mechanical properties of several TeXAs glasses
]OURNA L OF
Journal of Non-Crystalline Solids 161 (1993)313-315 North-Holland
~N-CRYSTALI~E SOI~DS
Mechanical properties of several TeXAs glasses A . B e c k e a, R. R e i m a n n a, G . H . F r i s c h a t a, H . L . M a b, C. B l a n c h e t i ~ r e b, X . H . Z h a n g b a n d J. L u c a s b a Institut fiir Nichtmetallische Werkstoffe, Technische Universitiit Clausthal, Clausthal-Zellerfeld, Germany b Laboratoire de Chimie Min&ale D, Universitd de Rennes, 35042 Rennes, France
The Young's modulus, E, and the fracture toughness, K i c , w e r e investigated for the glass series T e 2 S e 7 xAsxI (x = 0-6), Te3_xSe6AsxI (x = 0-2.5), and Tes_xSe3AsxI2 (x = 0-4), respectively. For the glass series Te2SeT_xASxl, E increased from ~ 13 GPa to ~ 19 GPa and Kxc from ~ 0.15 MN m - 3 / 2 t o ~ 0.3 MN m -3/2 for x = 0-6. For the other two glass series E and Kic decreased to some extent with increasing As content. An attempt is made to discuss this dissimilar concentration dependence of the mechanical stability by structural models.
I. Introduction T e X glasses contain Te and a halide X, mostly CI, Br or I. Thus far, there are two T e X glass families, a light one with C1 and S, and a heavy one with Br or I instead of C1 and Se instead o f S, showing different I R cut-offs. T h e light T e X glasses transmit up to 13 txm wavelength, w h e r e a s the heavy glasses have an I R cut-off at a r o u n d 20 ~m. R e c e n t l y it has b e e n r e p o r t e d that fibers can be drawn f r o m these materials and that attenuation losses can be as low as 4 - 1 0 dB m -1 for the different systems [1-3]. However, their glass transition temperatures, Tg, are very low with values b e t w e e n 50 and 85°C. This restricts their possible technical applicability. In o r d e r to increase the Tg by a structural cross-linking of the glasses, Lucas and co-workers [3,4] substituted a part of the divalent Se or Te by the trivalent As, and prep a r e d the following glass systems: T e z S e 7 _ x A s x I with x = 0 - 6 , T e 3 _ x S e 6 A s x I with x = 0 - 2 . 5 and T e s _ , S e 3 A s x I 2 with x = 0 - 4 . T h u s the Tg values could be increased substantially, e.g., for the glass
Correspondence to: Dr A. Becke, Institut fur Nichtmetallische Werkstoffe, Technische Universit~it Clausthal, W-3392 Clausthal-Zellerfeld, Germany. Tel: +49-5323 72 24(~3. Telefax: +49-5323 72 3119.
system Te2Se7_xASxI from 58 to 152°C. Optical m e a s u r e m e n t s showed that there is a small shift of the m u l t i p h o n o n edge only, i.e., to ~ 18 Ixm for the glass of T e 2 S e 3 A s 4 I composition.
2. Experimental T h e following mechanical properties, which are u n k n o w n thus far, were examined in this work: Y o u n g ' s modulus, E, and fracture toughness, K~c. T h e Y o u n g ' s modulus, E, was o b t a i n e d using the ultrasonic technique [5] and KI~ was calculated f r o m the crack lengths of a Vickers indentation [6]. S t a n d a r d deviations were calculated from 25 to 30 individual measurements.
3. Results Figures 1 and 2 contain the results. With increasing x, the glasses of the system Te2Se 7 x A s , I show an increasing mechanical stability. T h u s the Y o u n g ' s modulus, E, increases from ~ 13 G P a to ~ 19 G P a for x = 0 - 6 . T h e fracture toughness, K~c, also increases from ~ 0.15 M N m -3/2 to ~ 0.3 M N m -3/2 for the same series. T h e mechanical behaviour of the two o t h e r glass
0022-3093/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
314
A. Becke et al. / Mechanical properties o f TeXAs glasses
Young's m o d u l u s , E ( O P a ) 22
::
20
[]
TeeSer. A e B r
O
Tes=xSeeA°xl
i ..............................................................................
! ...........................................................
T%..Seahe.I 2 18
_ ~ - -
........................... i.......................................................................... ~i: ~ .... ~!:
6, i ................. i........................... ~~:::U~+
" ....... :::~
..............................
.................i................. i ....
t +~ i-.--.--.-~--:-:-.:.--i~--~-.----::-:-~o--~--.- --:-:~!
.................................... ~.-<--;! .....................................
12 ~
~.......................................................................................................................
..................
10 0
1
2
3
4
A8 c o n t e n t
5
6
x
Fig. 1. Young's modulus of TeXAs glasses. Lines are drawn as a guide for the eye.
series is dissimilar to that of the series discussed before. Thus the Young's modulus decreases with increasing x, and a similar tendency seems to be
0,35
obvious for the fracture toughness. However, the scatter in the Kit values is high, possibly because of some inhomogeneities in the glasses.
K Ic ( MN'm=3/2 for 0,5 N ) Te~er_xAsg
0,3
[]
Te28er_xASxBr
O
Te a xS%Aoxl
i ............................. i................... l- .......................... ~ ..........................
+++ii+"
.............. 4........................ i~--~.......... ~--:-:~ .........
O, 1
I ! ..... ~ ........................... ~ ......... ::
............... -© ................................................................................................ :~.................. i................................
0,05 0
1
2
3
4
5
6
As content x Fig. 2. Fracture toughness of TeXAs glasses. Lines are drawn as a guide for the eye.
315
A. Becke et al. / Mechanical properties of TeXAs glasses 4. Discussion
T h e glass systems i n v e s t i g a t e d d i s p l a y a dissimilar b e h a v i o u r . A n i n c r e a s e in strength, as was s e e n in t h e T e 2 S e 7 xASxI system, m e a n s a m o r e c o m p a c t s t r u c t u r e w h e n p a s s i n g f r o m x = 0 to 6. O n the c o n t r a r y , t h e systems T e 3 _ ~ S e 6 A s x I a n d T % _ ~ S e 3 A G I 2 show an o p p o s i t e b e h a v i o u r with increasing As content. In o r d e r to u n d e r s t a n d this b e h a v i o u r , conside r a t i o n s h o u l d start with t h e s t r u c t u r e s of Se, Te, a n d As, respectively. Se a n d T e consist o f s c r e w e d chains, a n d A s o f a l a y e r e d s t r u c t u r e [7]. F o r Se, the d i s t a n c e S e - S e in t h e chains is 44% less t h a n t h a t b e t w e e n the chains, a n d for T e t h e d i s t a n c e T e - T e in the chains is 20% less t h a n t h a t b e t w e e n d i f f e r e n t chains. F o r As, t h e d i s t a n c e A s A s in the layers is 25% less t h a n t h a t b e t w e e n neighbouring l a y e r s [7]. F o r t h e s y s t e m T e 2 S e 7 ~ A s ~ I the s t r u c t u r e c o u l d be
I I
S e - - S e - - S e - - T e - - S e - - S e - - T e - - S e - - Se . . . .
I,
I 1
w h e r e the e l e m e n t I e i t h e r is b o n d e d to T e o r is t e r m i n a t i n g a chain. W h e n A s is s u b s t i t u t e d for S e a cross-linking b e t w e e n d i s s i m i l a r c h a i n s s e e m s to b e possible, schematically:
x=l~ I I
/... - - S e - - S e - - S e - - T e - - Se--As,~, I I
Se
Se - - T e - - Se
....
B e c a u s e o f its e l e c t r o n e g a t i v i t y a n d t h e value o f t h e b o n d i n g energy, A s s h o u l d p r e f e r to b e l i n k e d to Se i n s t e a d to Te. A f u r t h e r i n c r e a s e of t h e A s c o n t e n t c o u l d also result in t h e f o r m a t i o n o f A s - A s b o n d s , schematically: x = 5, I
....
T e 3 x S e 6 A s x I , x = 2, ....
./Se~ Se - - Se - - Se - - Te - - Se - - As ~ S e / A s - - ! ;
T e 5 x S e 3 A s x I 2 , x = 4, I~ / Se.~ /. Se--Te . . . . As - - • / A s - - A s " S e ' / ~ s - - A S ~ l
Te.
5. Conclusion
X=0, ....
Qualitatively, t h e i n c r e a s e in m e c h a n i c a l stability m a y b e u n d e r s t o o d in this way. In the case of T e 3 _ x S % A s x I a n d T e 5 ~Se 3 AsxI 2 glasses, A s is s u b s t i t u t e d for Te. In this case, A s d o e s not p r o v i d e a cross-linking b e t w e e n d i f f e r e n t chains b u t is b o n d e d in the chains only. G e n e r a l l y I is b o n d e d to Te; however, with dec r e a s i n g Te c o n t e n t , a b o n d i n g to A s b e c o m e s m o r e possible, r e s u l t i n g in a chain t e r m i n a t i o n . S c h e m a t i c a l l y t h e s t r u c t u r e s c o u l d be
As(
4e__Te__Se__As~ " ' ' A s / A s ~ / I S e - - A s \ . . . As As-.. I
''"
As As
This c r e a t e s even m o r e cross-links a n d h e n c e a s t r o n g e r t i g h t e n i n g o f the e n t i r e glass structure.
In this work, the m e c h a n i c a l p r o p e r t i e s of t h r e e T e X A s glass series w e r e d e t e r m i n e d . In p a r t the glass systems d i s p l a y dissimilar behaviours. W h e n A s is s u b s t i t u t e d for Se (glass series Te2Se7_ ~ASxI), the m e c h a n i c a l stability is e n h a n c e d by the i n c r e a s i n g A s c o n t e n t . In t h e case of t h e glass series T e 3 _ x S e 6 A s x I a n d Te 5 x S e 3 A G I 2, w h e r e A s is s u b s t i t u t e d for Te, the s t r e n g t h d a t a show a d e c r e a s e with i n c r e a s i n g A s c o n t e n t , a l t h o u g h s o m e s c a t t e r is still p r e s e n t possibly d u e to inhom o g e n e i t i e s in t h e glasses. This b e h a v i o u r dep e n d s on a c h a n g i n g s t r u c t u r a l s h o r t r a n g e o r d e r o f t h e glasses as a f u n c t i o n o f t h e i r c o m p o s i t i o n s .
References
[1] X.H. Zhang, G. Fonteneau, H.L. Ma and J. Lucas, Mater. Sci. Forum 67&68 (1991) 371. [2] X.H. Zhang, H.L. Ma, G. Fonteneau and J. Lucas, J. Non-Cryst. Solids 140 (1992) 47. [3] H.L, Ma, X.H. Zhang and J. Lucas, J. Non-Cryst. Solids 135 (1991) 49. [4] J. Lucas and X.H. Zhang, J. Non-Cryst. Solids 125 (1990) 1. [5] K.H. Leers and H. D6rr Tonind. Ztg. 100 (1984) 916. [6] K.H. Zum Gahr, Z. Metallkd. 69 (1978) 534. [7] H. Krebs, Festk6rperprobleme 9 (1969) 1.
Journal of Non-Crystalline Solids 161 (1993)313-315 North-Holland
~N-CRYSTALI~E SOI~DS
Mechanical properties of several TeXAs glasses A . B e c k e a, R. R e i m a n n a, G . H . F r i s c h a t a, H . L . M a b, C. B l a n c h e t i ~ r e b, X . H . Z h a n g b a n d J. L u c a s b a Institut fiir Nichtmetallische Werkstoffe, Technische Universitiit Clausthal, Clausthal-Zellerfeld, Germany b Laboratoire de Chimie Min&ale D, Universitd de Rennes, 35042 Rennes, France
The Young's modulus, E, and the fracture toughness, K i c , w e r e investigated for the glass series T e 2 S e 7 xAsxI (x = 0-6), Te3_xSe6AsxI (x = 0-2.5), and Tes_xSe3AsxI2 (x = 0-4), respectively. For the glass series Te2SeT_xASxl, E increased from ~ 13 GPa to ~ 19 GPa and Kxc from ~ 0.15 MN m - 3 / 2 t o ~ 0.3 MN m -3/2 for x = 0-6. For the other two glass series E and Kic decreased to some extent with increasing As content. An attempt is made to discuss this dissimilar concentration dependence of the mechanical stability by structural models.
I. Introduction T e X glasses contain Te and a halide X, mostly CI, Br or I. Thus far, there are two T e X glass families, a light one with C1 and S, and a heavy one with Br or I instead of C1 and Se instead o f S, showing different I R cut-offs. T h e light T e X glasses transmit up to 13 txm wavelength, w h e r e a s the heavy glasses have an I R cut-off at a r o u n d 20 ~m. R e c e n t l y it has b e e n r e p o r t e d that fibers can be drawn f r o m these materials and that attenuation losses can be as low as 4 - 1 0 dB m -1 for the different systems [1-3]. However, their glass transition temperatures, Tg, are very low with values b e t w e e n 50 and 85°C. This restricts their possible technical applicability. In o r d e r to increase the Tg by a structural cross-linking of the glasses, Lucas and co-workers [3,4] substituted a part of the divalent Se or Te by the trivalent As, and prep a r e d the following glass systems: T e z S e 7 _ x A s x I with x = 0 - 6 , T e 3 _ x S e 6 A s x I with x = 0 - 2 . 5 and T e s _ , S e 3 A s x I 2 with x = 0 - 4 . T h u s the Tg values could be increased substantially, e.g., for the glass
Correspondence to: Dr A. Becke, Institut fur Nichtmetallische Werkstoffe, Technische Universit~it Clausthal, W-3392 Clausthal-Zellerfeld, Germany. Tel: +49-5323 72 24(~3. Telefax: +49-5323 72 3119.
system Te2Se7_xASxI from 58 to 152°C. Optical m e a s u r e m e n t s showed that there is a small shift of the m u l t i p h o n o n edge only, i.e., to ~ 18 Ixm for the glass of T e 2 S e 3 A s 4 I composition.
2. Experimental T h e following mechanical properties, which are u n k n o w n thus far, were examined in this work: Y o u n g ' s modulus, E, and fracture toughness, K~c. T h e Y o u n g ' s modulus, E, was o b t a i n e d using the ultrasonic technique [5] and KI~ was calculated f r o m the crack lengths of a Vickers indentation [6]. S t a n d a r d deviations were calculated from 25 to 30 individual measurements.
3. Results Figures 1 and 2 contain the results. With increasing x, the glasses of the system Te2Se 7 x A s , I show an increasing mechanical stability. T h u s the Y o u n g ' s modulus, E, increases from ~ 13 G P a to ~ 19 G P a for x = 0 - 6 . T h e fracture toughness, K~c, also increases from ~ 0.15 M N m -3/2 to ~ 0.3 M N m -3/2 for the same series. T h e mechanical behaviour of the two o t h e r glass
0022-3093/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved
314
A. Becke et al. / Mechanical properties o f TeXAs glasses
Young's m o d u l u s , E ( O P a ) 22
::
20
[]
TeeSer. A e B r
O
Tes=xSeeA°xl
i ..............................................................................
! ...........................................................
T%..Seahe.I 2 18
_ ~ - -
........................... i.......................................................................... ~i: ~ .... ~!:
6, i ................. i........................... ~~:::U~+
" ....... :::~
..............................
.................i................. i ....
t +~ i-.--.--.-~--:-:-.:.--i~--~-.----::-:-~o--~--.- --:-:~!
.................................... ~.-<--;! .....................................
12 ~
~.......................................................................................................................
..................
10 0
1
2
3
4
A8 c o n t e n t
5
6
x
Fig. 1. Young's modulus of TeXAs glasses. Lines are drawn as a guide for the eye.
series is dissimilar to that of the series discussed before. Thus the Young's modulus decreases with increasing x, and a similar tendency seems to be
0,35
obvious for the fracture toughness. However, the scatter in the Kit values is high, possibly because of some inhomogeneities in the glasses.
K Ic ( MN'm=3/2 for 0,5 N ) Te~er_xAsg
0,3
[]
Te28er_xASxBr
O
Te a xS%Aoxl
i ............................. i................... l- .......................... ~ ..........................
+++ii+"
.............. 4........................ i~--~.......... ~--:-:~ .........
O, 1
I ! ..... ~ ........................... ~ ......... ::
............... -© ................................................................................................ :~.................. i................................
0,05 0
1
2
3
4
5
6
As content x Fig. 2. Fracture toughness of TeXAs glasses. Lines are drawn as a guide for the eye.
315
A. Becke et al. / Mechanical properties of TeXAs glasses 4. Discussion
T h e glass systems i n v e s t i g a t e d d i s p l a y a dissimilar b e h a v i o u r . A n i n c r e a s e in strength, as was s e e n in t h e T e 2 S e 7 xASxI system, m e a n s a m o r e c o m p a c t s t r u c t u r e w h e n p a s s i n g f r o m x = 0 to 6. O n the c o n t r a r y , t h e systems T e 3 _ ~ S e 6 A s x I a n d T % _ ~ S e 3 A G I 2 show an o p p o s i t e b e h a v i o u r with increasing As content. In o r d e r to u n d e r s t a n d this b e h a v i o u r , conside r a t i o n s h o u l d start with t h e s t r u c t u r e s of Se, Te, a n d As, respectively. Se a n d T e consist o f s c r e w e d chains, a n d A s o f a l a y e r e d s t r u c t u r e [7]. F o r Se, the d i s t a n c e S e - S e in t h e chains is 44% less t h a n t h a t b e t w e e n the chains, a n d for T e t h e d i s t a n c e T e - T e in the chains is 20% less t h a n t h a t b e t w e e n d i f f e r e n t chains. F o r As, t h e d i s t a n c e A s A s in the layers is 25% less t h a n t h a t b e t w e e n neighbouring l a y e r s [7]. F o r t h e s y s t e m T e 2 S e 7 ~ A s ~ I the s t r u c t u r e c o u l d be
I I
S e - - S e - - S e - - T e - - S e - - S e - - T e - - S e - - Se . . . .
I,
I 1
w h e r e the e l e m e n t I e i t h e r is b o n d e d to T e o r is t e r m i n a t i n g a chain. W h e n A s is s u b s t i t u t e d for S e a cross-linking b e t w e e n d i s s i m i l a r c h a i n s s e e m s to b e possible, schematically:
x=l~ I I
/... - - S e - - S e - - S e - - T e - - Se--As,~, I I
Se
Se - - T e - - Se
....
B e c a u s e o f its e l e c t r o n e g a t i v i t y a n d t h e value o f t h e b o n d i n g energy, A s s h o u l d p r e f e r to b e l i n k e d to Se i n s t e a d to Te. A f u r t h e r i n c r e a s e of t h e A s c o n t e n t c o u l d also result in t h e f o r m a t i o n o f A s - A s b o n d s , schematically: x = 5, I
....
T e 3 x S e 6 A s x I , x = 2, ....
./Se~ Se - - Se - - Se - - Te - - Se - - As ~ S e / A s - - ! ;
T e 5 x S e 3 A s x I 2 , x = 4, I~ / Se.~ /. Se--Te . . . . As - - • / A s - - A s " S e ' / ~ s - - A S ~ l
Te.
5. Conclusion
X=0, ....
Qualitatively, t h e i n c r e a s e in m e c h a n i c a l stability m a y b e u n d e r s t o o d in this way. In the case of T e 3 _ x S % A s x I a n d T e 5 ~Se 3 AsxI 2 glasses, A s is s u b s t i t u t e d for Te. In this case, A s d o e s not p r o v i d e a cross-linking b e t w e e n d i f f e r e n t chains b u t is b o n d e d in the chains only. G e n e r a l l y I is b o n d e d to Te; however, with dec r e a s i n g Te c o n t e n t , a b o n d i n g to A s b e c o m e s m o r e possible, r e s u l t i n g in a chain t e r m i n a t i o n . S c h e m a t i c a l l y t h e s t r u c t u r e s c o u l d be
As(
4e__Te__Se__As~ " ' ' A s / A s ~ / I S e - - A s \ . . . As As-.. I
''"
As As
This c r e a t e s even m o r e cross-links a n d h e n c e a s t r o n g e r t i g h t e n i n g o f the e n t i r e glass structure.
In this work, the m e c h a n i c a l p r o p e r t i e s of t h r e e T e X A s glass series w e r e d e t e r m i n e d . In p a r t the glass systems d i s p l a y dissimilar behaviours. W h e n A s is s u b s t i t u t e d for Se (glass series Te2Se7_ ~ASxI), the m e c h a n i c a l stability is e n h a n c e d by the i n c r e a s i n g A s c o n t e n t . In t h e case of t h e glass series T e 3 _ x S e 6 A s x I a n d Te 5 x S e 3 A G I 2, w h e r e A s is s u b s t i t u t e d for Te, the s t r e n g t h d a t a show a d e c r e a s e with i n c r e a s i n g A s c o n t e n t , a l t h o u g h s o m e s c a t t e r is still p r e s e n t possibly d u e to inhom o g e n e i t i e s in t h e glasses. This b e h a v i o u r dep e n d s on a c h a n g i n g s t r u c t u r a l s h o r t r a n g e o r d e r o f t h e glasses as a f u n c t i o n o f t h e i r c o m p o s i t i o n s .
References
[1] X.H. Zhang, G. Fonteneau, H.L. Ma and J. Lucas, Mater. Sci. Forum 67&68 (1991) 371. [2] X.H. Zhang, H.L. Ma, G. Fonteneau and J. Lucas, J. Non-Cryst. Solids 140 (1992) 47. [3] H.L, Ma, X.H. Zhang and J. Lucas, J. Non-Cryst. Solids 135 (1991) 49. [4] J. Lucas and X.H. Zhang, J. Non-Cryst. Solids 125 (1990) 1. [5] K.H. Leers and H. D6rr Tonind. Ztg. 100 (1984) 916. [6] K.H. Zum Gahr, Z. Metallkd. 69 (1978) 534. [7] H. Krebs, Festk6rperprobleme 9 (1969) 1.