Annealing effects on electrical resistivity, crystallization and thermoelectric power of iron-rich metallic glasses containing molybdenum

Journal of Non-CrystallineSolids65 (1984) 423-428 North-Holland,Amsterdam

423

A N N E A L I N G EFFECTS ON E L E C T R I C A L RESISTIVITY, C R Y S T A L L I Z A T I O N AND THERMOE L E C T R I C P O W E R OF IRON-RICH M E T A L L I C GLASSES C O N T A I N I N G M O L Y B D E N U M

S. V E N K A T A R A M A N + , K.V. R E D D Y * , U.N. V I R A T A S W A R O O P * , G. V E N U G O P A L A RAO # and A.K. B H A T N A G A R School of Physics,

U n i v e r s i t y of Hyderabad,

Hyderabad

500 134,

India

The effect of long annealing (20 hrs) at v a r i o u s t e m p e r a t u r e s on electrical resistivity, c r y s t a l l i z a t i o n and t h e r m o e l e c t r i c power of F e 7 8 M o 2 B 2 0 , Fe40Ni38Mo4BI8

and F e 3 9 N i 3 9 M o 4 S i 6 B I 2

has been investigated.

Room tempera-

ture r e s i s t i v i t y of these m e t a l l i c glass'es d e c r e a s e s on annealing regardless of the a n n e a l i n g temperature. C r y s t a l l i z a t i o n b e h a v i o u r does not get much affected on the annealing used in this investigation. T e m p e r a t u r e d e p e n d e n c e of p(T)/p(RT) remains u n a f f e c t at low t e m p e r a t u r e s but shows increase in its slope at higher t e m p e r a t u r e s before onset of the crystallization. A prelim i n a r y study on the low t e m p e r a t u r e b e h a v i o u r of t h e r m o e l e c t r i c power of F e 4 0 N i 3 8 M o 4 B I 8 shows that there is only a slight affect due to annealing of the sample at 373 K for 20 hrs.

1. I N T R O D U C T I O N M e t a l l i c glasses p r o d u c e d by the rapid q u e n c h i n g of a melt are in a thermodynamic m e t a s t a b l e state. glass t r a n s i t i o n

Therefore,

annealing of these glasses below the

temperature leads to the structural r e l a x a t i o n as a result

of t h e r m a l l y induced changes in the c o m p o s i t i o n a l order.

d e p e n d e n c e of electrical r e s i s t i v i t y (METGLAS

and t o p o l o g i c a l

short-range

We report in this paper the results of a n n e a l i n g on the temperature (p) and c r y s t a l l i z a t i o n of F e 7 8 M o 2 B 2 0

2605A) @, Fe40Ni38Mo4B1B (METGLAS 2826MB)@ and Fe39Ni39Mo4Si6B12

(VITROVAC 4040),

and p r e l i m i n a r y results on the t h e r m o e l e c t r i c power

(S) of

Fe40Ni38Mo4B18-

2. E X P E R I M E N T A L E l e c t r i c a l r e s i s t i v i t y was m e a s u r e d using the four probe m e t h o d between 80 K - 900 K, and t h e r m o e l e c t r i c power was d e t e r m i n e d by the integral m e t h o d b e t w e e n 80 K - 400 K using Pt wire as the r e f e r e n c e material. Experimental 1 details can be found elsewhere . M e a s u r e m e n t s were p e r f o r m e d on 'as received' samples, + * # @

and fresh samples annealed at 5 0 ° C , i 0 0 ° C , 2 0 0 ° C , 3 0 0 ° C

in vacuunl for

Junior R e s e a r c h Fellow, Council of S c i e n t i f i c & Industrial Research, India. S u p p o r t e d by CSIR (India) Grant N o . 3 ( 4 8 1 ) / 8 1 - E M R . I I S u p p o r t e d by D e p a r t m e n t of A t o m i c E n e r g y (India) Grant NO.34/10/79-G. M E T G L A S is a r e g i s t e r e d trade mark of A l l i e d Chemical, USA, for amorphous alloys of metals.

0022-3093/84/$03.00 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division

S. Venkataraman et al.

424

/ Annealing effects on electrical resistivity

I

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A N N E A L I N & T I M E Z O HRS.

METGLAS 2826ME

-.OB l--

-.0S

" ~ -.0/-., t-.---

~ ~ T R V O IV A C

6o5t

4040

, -.02 cY

I

373

I

I

<,73 573

I

673

ANNEALING TEMR(K) Fig.l

Change in room temperature electrical resistivity as a function annealing temperature

20 hrs respectively, and then quenched in ice water.

Data were taken with a

heating rate of 5 f 0.5 K/min.

3. RESULTS AND DISCUSSION The fractional change in the electrical resistivity at room temperature p(RT) for each of Fe78Mo2B20, Fe40Ni38Mo4BI8 and Fe39Ni39Mo4Si6BI2 metallic glass samples, i.e., {Qa(RT)-p(RT)}/p(RT) where Qa(RT) is the resistivity of the annealed sample, is shown in Fig.l as a function of annealing temperature for a fixed annealing time of 20 hrs.

It is observed that the annealing

produces lower Q(RT) for all the samples.

METGLAS 2826MB (Fe40Ni38Mo4BI8)

shows a steeper decrease in p(RT) in comparision with the same of METGLAS 2605A (Fe78Mo2B20) and VITROVAC 4040 (Fe39Ni39Mo4Si6BI2).

In case of METGLAS

2605A, where higher annealing temperatures (TA) have also been used, a kind of saturation behaviour with TA is observed. Our observations are in disagreement 2 who have found that annealing of Fe-Ni-MO-B alloys

with those of P. Allia et al

at lower temperatures (TA<500K) produces higher p(RT) while higher temperatures

S. Venkataraman et al. /Annealing effects on electrical resistivity

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METGLAS

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TEMR (K)

Q(T)/p(RT) vs T (a) Fresh sample, (b) , (c) , (d) and (e) samples annealed at 323 K, 473 K, 573 K, 6"73 K r e s p e c t i v e l y for 20 hrs. Data points are not shown for clarity.

Fig.2

p r o d u c e lower Q(RT). We have also i n v e s t i g a t e d dence of Q(T)/Q(RT), p(T)/p(RT) vely.

the effect of a n n e a l i n g on the t e m p e r a t u r e depen-

and on the crystallization.

vs T for M E T G L A S

It is observed that p(T)/Q(RT)

essentially unaffected

F i g u r e s 2,3 and 4 show curves

2605A, M E T G L A S 2826MB and V I T R O V A C 4040, r e s p e c t i at t e m p e r a t u r e s

for M E T G L A S samples.

lower than 500 K remains

Q(T)/Q(RT)

for V I T R O V A C sample does

show a n n e a l i n g effects on its t e m p e r a t u r e d e p e n d e n c e even at low temperatures. At higher temperatures,

the effect is more pronounced.

For example,

the inset

in Fig.2 shows that a n n e a l i n g of F e 7 8 M o 2 B 2 0 p r o d u c e s higher Q(T)/Q(RT) temperatures,

just before onset of the crystallization.

at 673 K p r o d u c e s a strong n o n l i n e a r b e h a v i o u r in Q(T)/p(RT) zation.

On the contrary,

similar results for M E T G L A S

at high

P a r t i c u l a r l y annealing before c r y s t a l l i -

2826MB show that the

S. Venkataraman et al. / Annealing effects on electrical resistivity

426

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._.1.04 ~-~.1.03

~.,

(d) "

i--

1.02

1.01 I

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598 648 698 748 798 848 TEMP.(K) Fig.3

p(T)/p(RT) vs T (a) Fresh sample, (b) , (c) , (d) samples annealed at 323 K, 373 K and 473 K, respectively

annealing at higher temperatures produce Fig.3.

lower Q(T)/p(RT)

curves as shown in

The VITROVAC sample shows a different and unsystematic behaviour as

shown in Fig.4, but p(T)/p(RT) curve for 'as received' interpretation

curves for annealed samples remain above the

sample in the higher temperature region.

of these observations

is as follows.

A possible

Annealing of amorphous

alloys results in structural relaxations which lead to either compositional reordering through short-range atomic diffusion, topological

or irreversible

changes in the

short-range order with reduction of frozen-in free volume.

observation of decrease studied indicates

An

in Q(T) on annealing in each of the metallic glass

that defects are being annealed out and some compositional

reordering taking place which is homogeneous throughout the sample, and which results in the reduction of free volume.

Thus, samples go into another thermo-

dynamic metastable amorphous state which has lower resistivity. that Q(T)/p(RT) proposition.

Our observation

vs T curves are not much affected by annealing confirms above

However,

higher Q(T)/p(RT)vs T curves at high temperatures

annealed samples when compared with the same of 'as received' that the annealing of Fe78Mo2B20 and Fe39Ni39Mo4Si6BI2 clusters due to a compositional

for

sample, indicates

has produced some

'seed'

reordering which grow at higher temperatures

just before onset of the crystallization

and affecting the resistivity as

S. Venkatararnan et al. / Annealing effects on electrical resistivity

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588

888

TEMR(K)

Fig.4

observed.

This also indicates

most p r o b a b l y phase.

takes place by

However,

p(T)/p(RT)

p(T)/Q(RT) vs T. (a) F r e s h sample, (b),(c) and (d) samples annealed at 323 K, 373 K and 473 K. Data p o i n t s are not shown for clarity that the c r y s t a l l i z a t i o n

'clustering'

in a n n e a l e d samples

of c r y s t a l l i t e s

results on M E T G L A S 2826MB are opposite,

in the amorphous i.e.,

it shows lower

vs T curves for a n n e a l e d samples and indicates that the c l u s t e r i n g

p h e n o m e n a is not taking place in this sample as o b s e r v e d for other two samples. Which one of the above two r e l a x a t i o n m e c h a n i s m s may be i m p o r t a n t in a given m e t a l l i c glass, we believe,

may depend upon c o m p o s i t i o n and the actual q u e n -

ching c o n d i t i o n s of the glass,

therefore,

it is p o s s i b l e that a m e t a l l i c glass

of similar c o m p o s i t i o n but of a d i f f e r e n t batch may show d i f f e r e n t r e s i s t i v i t y behaviour. We have further looked into the d e p e n d e n c e of other p a r a m e t e r s on annealing. These are t e m p e r a t u r e s T2, respectively, the p a r a b o l i c

the t e m p e r a t u r e

fit p(T)/p(RT)

for V I T R O V A C 4040 and approximately

for onset and c o m p l e t i o n of the crystallization, interval AT 2 = T2-TI,

= a + bT = cT 2.

T 1 and

and the c o e f f i c i e n t s

in

It is o b s e r v e d that T 1 and T 2

M E T G L A S 2826MB do not change with a n n e a l i n g w h i c h are

693 K and 808 K and 688 K and 773 K, respectively.

M E T G L A S 2605A some changes were observed.

Samples

fresh,

and 423 K had T 1 = 725 K and T 2 = 750 K approximately,

However,

for

and annealed at 323 K

samples annealed at

473 K, and 573 K had T 1 = 738 K and T 2 = 763 K, while the one annealed at 673 K had T 1 = 733 K and T 2 = 763 K, respectively.

The t e m p e r a t u r e over which the

428

S. Venkataraman et al. / Annealing effects on electrical resistivity

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:1 -2

:r,, e-

~

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ANNEALED IO0°C-zohrs. 2826MB

-1 -2

.....

/',,.. """ ....... 4,.,.,,.

-3 I

100

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300

400

TEMR(K) Fig.5

T h e r m o e l e c t r i c power vs t e m p e r a t u r e

for

Fe40Ni38Mo4B18 (METGLAS 2826MB) crystallization

took place,

by the annealing.

i.e., T2-T 1 seemed to remain e s s e n t i a l l y u n a f f e c t e d

The c o e f f i c i e n t s b and c were t y p i c a l l y 10 -4- 10 -5 K -I and

10 -7 - 10 -8 K -2, respectively,

and did not seem to show any systematic varia-

tion although a n n e a l i n g seem to reduce these c o e f f i c i e n t s by 1% or so. Figure 5 shows p r e l i m i n a r y results of t h e r m o e l e c t r i c power m e a s u r e m e n t s on M E T G L A S 2826MB.

It is seen that 373 K a n n e a l i n g does not have a p p r e c i a b l e

effect at low t e m p e r a t u r e s

except for some minor changes.

sample shows some structure at ~350 K. c o n f i r m e d by m e a s u r e m e n t s

However,

annealed

Whether it is real or not has to be

to be repeated.

F u r t h e r work on the a n n e a l i n g effect

on t h e r m o e l e c t r i c p o w e r will be r e p o r t e d at a later date. ACKNOWLEDGEMENT One of us

(AKB) would like to thank SERC

(DST, New Delhi,

India)

for the

financial support on m e t a l l i c glass researches.

REFERENCES i. B. Bhanu Prasad, A.K. B h a t n a g a r and R. Jagannathan, J. Appl. Phys. 54 (1983) 2019; B.B. Prasad, A.K. Bhatnagar, J. Magn. Magn. Mat. 31-34 (1983) 1479. 2. P. Allia, D. Andreone, R. Sato Turtelli, F. Vinai and G. Riontino, App. Phys. 5_~3, (1982) 8798.

J. of