Positron annihilation study of quasicrystalline phases

Journal of Non-Crystalline Solids 117/118 (1990) 793-796 North-Holland

POSITRON ANNIHILATION

I.KANAZAWA,

T.KIZUKA*,

793

STUDY OF Q U A S I C R Y S T A L L I N E PHASES

M.OHATA,

Y.SAKURAI*,

S.NANAO*,

and T . I W A S H I T A

D e p a r t m e n t of Physics, Tokyo Gakugei University, 4-1-1, N u k u i k i t a m a c h i , Koganeishi, Tokyo 184, Japan * Institute of Industrial Science, U n i v e r s i t y of Tokyo, 7-22-1, Roppongi, Minatoku, Tokyo 106, Japan

We have p e r f o r m e d the p o s i t r o n a n n i h i l a t i o n lifetime and the Doppler b r o a d e n i n g m e a s u r e m e n t s of q u a s i c r y s t a l l i n e phases AlT~Mn20Sis, AI~Mn, A 1 6 8 M n 2 0 S i ~ R u s , and AI6Mg~Cul. It is o b s e r v e d that the mean lifetime and h p a r a m e t e r from the room t e m p e r a t u r e to ~ 250°C in the q u a s i c r y s t a l s A174Mn20Si6 and AI6Mn decrease. Those d e c r e a s e s c o r r e s p o n d to the m i g r a t i o n and a n n i h i l a t i o n of v a c a n c y - l i k e defects. It is shown that v a c a n c y - l i k e defects in the q u a s i c r y s t a l A l 6 ~ M n 2 0 S i 4 R u s are stable until the c r y s t a l i z a t i o n temperature.

1.INTRODUCTION

and AI6Mg4Cul

Since S h e c h t m a n et al. I d i s c o v e r e d

ling.

during isochronal a n n e a l -

V a c a n c y - t y p e defects and the

the q u a s i c r y s t a l l i n e phase, w h i c h pos-

thermal stabilities

sesses long range o r i e n t a t i o n a l order

will be discussed.

in those phases

b e l o n g i n g to the i c o s a h e d r a l point group,

a lot of studies of the s t r u c t u r e s

of those phases have been performed. E s p e c i a l l y two d i f f e r e n t models, three d i m e n s i o n a l

the

Penrose tiling

2.EXPERIMENTAL The AI6Mn, and AI6Mg~Cul

AlT~Mn20Si6,

alloys were p r e p a r e d by

m e l t i n g in the arc

(3DPT) 2, 3 and the dense p a c k i n g of ico-

Al~sMn20Si4Ru8

furnace.

The quasi-

c r y s t a l l i n e specimens were fabricated

sahedra model 4,s, have been proposed.

in ribbon form, about 1 mm in w i d t h and

However,

about 30 ~m in thickness,

little has been known of the

actual atomic p o s i t i o n s

in that phase.

roller technique

by the single

in a He atmosphere.

Now, we shall propose two q u e s t i o n s as

The formations of the q u a s i c r y s t a l l i n e

follows.

phases were c o n f i r m e d by X - r a y

The first q u e s t i o n is w h e t h e r

analysis

the structures of the q u a s i c r y s t a l l i n e

and t r a n s m i s s i o n e l e c t r o n microscopy.

phases are c o m p o s e d of M a c k a y i c o s a h @ d r a

The p o s i t r o n source of 22NaCI of about

w i t h the Mn vacant center or not.

4 x l0 s Bq sealed in an a l u m i n i u m thin

The second q u e s t i o n is what kind of

foil was set up at the center of the

structure does the b o u n d a r y among ico-

specimen.

sahedra construct.

Pyrex glass tube in a v a c u u m of 10 -5

For example,

large are o p e n - v o l u m e

how

spaces c o n t a i n e d

Torr.

The specimen was sealed in a

The m e a s u r e m e n t s of Doppler

in the b o u n d a r y among i c o s a h e d r a ?

b r o a d e n i n g were carried out at room

In this study, we have m e a s u r e d the

t e m p e r a t u r e by use of a solid state

p o s i t r o n a n n i h i l a t i o n lifetime and

detector

Doppler b r o a d e n i n g of q u a s i c r y s t a l l i n e

sion was 1.19 keV

phases AI~Mn,

The p o s i t r o n lifetime spectra were

A174Mn20Si6,

A168Mn20Si4Rus,

0022-3093/90/$03.50 (~) Elsevier Science Publishers B.V. (North-Holland)

(pure Ge) , whose energy resolu(FWHM)

at 512 keV.

I. Kanazawa et al. / Quasicrystalline phases

794

220

o b t a i n e d w i t h a fast-fast c o i n c i d e n c e

I

i

i

~

i

i

i

i

i

i

i

i

i

[

system by using H A M A M A T S U R2076 photom u l t i p l i e r s and 3/4 in. BaF2 s c i n t i l l a tors.

210

The time r e s o l u t i o n of the system

was 260 psec

(FWHM) w i t h the use of

After background

6°Co.

200

L

[

i-Al6Mn

,

d

\,

"

KI._/

s u b t r a c t i o n the line-

shape p a r a m e t e r h was d e t e r m i n e d by the

I

k--~!

/[

,

--~

,,

i

% o_

190

ratio of the central area over 20 c h a n n e l s to the total area of the s p e c t r u m and was n o r m a l i z e d by setting the value of

EL --J

background.

--~~

i-Al?~Mnz0si6 %Xl

the h p a r a m e t e r of well a n n e a l e d A1 to i.

i L

170

P o s i t r o n lifetime spectra were a n a l y z e d by P O S I T R O N F I T 6

180

after s u b t r a c t i n g the

Each x2/q

160

was b e l o w 1.2

0

I

ii00 1

I

200

r

4I

I

I

I

I

I

300 00 500 G00 700 TEMPERATURE (°C)

3. RESULTS AND D I S C U S S I O N S Figure 1 shows the change in h para-

Figure 2: the m e a n lifetimes of i c o s a h e d r a l AIeMn and Alv4Mn20Si6.

m e t e r of the q u a s i c r y s t a l l i n e phases A I e M n and AlT~Y~q20Si6 during the isochronal aging for 20 min intervals.

h p a r a m e t e r and the mean lifetime

Figure 2 shows the change in the m e a n

decrease

from the room t e m p e r a t u r e to

250°C.

The lifetime spectra in the

lifetimes of the q u a s i c r y s t a l l i n e phases A I 6 M n and AlT~Mn20Si6

during the iso-

In the q u a s i c r y s t a l A l ? ~ M n 2 0 S i 6 ,

1.080

q u a s i c r y s t a l AlT~Mn20Si6

both

f

The lifetime,zl, i-Al 6Mn

,~

fitted

Figure

3

shows the changes in the intensity,I2, and the lifetime,T2,

1.070 t

are well

w i t h two lifetime components.

chronal aging for 20 min intervals.

of the c o m p o n e n t 2.

of c o m p o n e n t 1 is

170 ~ 5 psec from the room temperature to ~ 350°C.

The lifetime,Tz,

of compo-

nent 2 is w i t h i n 250 ± i0 psec as shown in Fig.3

1.040

It is thought that the

c o m p o n e n t 2 c o r r e s p o n d s to v a c a n c y - l i k e defects in the q u a s i c r y s t a l l i n e phase.

I.030

\,

< ~- 1.020

Thus,

i-Al 7 ~Mn20 Si6

it is i n t e r p r e t e d that the

d e c r e a s e s of the mean lifetime and h

~.~.~

p a r a m e t e r from the room t e m p e r a t u r e to

~.oio I ooo

~

\~,,

250°C in the q u a s i c r y s t a l AlT~Mn20Si6 reflect the m i g r a t i o n and a n n i h i l a t i o n

I

I

I00

200

300

400

500

GO0

700

TEMPERATURE ('C)

of v a c a n c y - l i k e defects.

crystal AI6Mn, both h p a r a m e t e r and the mean lifetime d e c r e a s e

Figure 1 : h p a r a m e t e r s of i c o s a h e d r a l AI6Mn and AlT~Mn20Si~.

In the quasi-

from % 150 to

300°C and s u b s e q u e n t l y increase

from

I. Kanazawa et al. / Quasicrystalline phases

795

intervals.

The values of h p a r a m e t e r

almost are c o n s t a n t from the room t e m p e rature to ~ 450°C.

We could not observe

the m i g r a t i o n stage of v a c a n c y - l i k e 1

i

defects from the room t e m p e r a t u r e to

,

250°C, w h i c h was o b s e r v e d in the q u a s i .-~ ¢L

crystals A174Mn20Si6

260

and AI6Mn,

q u a s i c r y s t a l Al6eMn20Si~Rus. 240

in the

The life-

time spectra of the q u a s i c r y s t a l as spun A168Mn20Si~Ru8

220

i"

'

~

4~o

'

ANNEALING TEMPERATURE

'

o~o

(~C)

are well fitted w i t h two

lifetime components.

The lifetime,T2,

and the intensity,I2,

of c o m p o n e n t 2

are 250 ± 5 psec and 15 %, respectively. Figure 3:the lifetime and i n t e n s i t y of c o m p o n e n t 2 in i-A174Mn20Si6.

The lifetime,T1,

and the intensity,It,

of c o m p o n e n t 1 are 185 ± 5 psec and 85 from ~ 350 to ~ 500 °C. This increase is

%, respectively.

Taking account of the

not o b s e r v e d in the q u a s i c r y t a l l i n e phase

lifetime,

A174Mn20Si6.

is thought that the c o m p o n e n t 2 corre -

The d e c r e a s e s of h para-

250 psec,

of c o m p o n e n t 2, it

m e t e r and the m e a n lifetime from ~ 150

sponds to v a c a n c y - l i k e defects.

to ~ 300°C in the q u a s i c r y s t a l AI6Mn

intensity,I2,

of c o m p o n e n t 2

The

suggests

c o r r e s p o n d to those from the room t e m p e -

that the q u a n t i t y of v a c a n c y - l i k e

ature to ~ 250°C in the q u a s i c r y s t a l

defects

Al7~Mn20Si6.

RuB is lower than that in the q u a s i c r y t a l

Therefore,

these d e c r e s e s

in the q u a s i c r y s t a l A168Mn20Si4

are a t t r i b u t e d to m i g r a t i o n and a n n i h i -

as

lation of v a c a n c y - l i k e defects in the

point is that

q u a s i c r y s t a l AlsMn.

the q u a s i c r y s t a l A l s s M n 2 0 S i ~ R u e

It is known that

spun A174Mn20Si6.

More important

v a c a n c y - l i k e defects are

the q u a s i c r y s t a l AI6Mn c o n t a i n s

stable until the crystalization.

r e l a t i v e l y m a n y d e f e c t s in c o m p a r i s o n

Because both values of lifetimes,T2,

w i t h the q u a s i c r y s t a l A l T ~ M n 2 0 S i 6 7

of c o m p o n e n t 2 in the q u a s i c r y s t a l s

Because the q u a n t i t y of defects c o n t a i n e d

A174Mn20Si6

in the q u a s i c r y s t a l A I 6 M n is large,

250 psec,

it

and A I 6 B M n 2 0 S i 4 R u 8

in

are

it seems that the open volume

seems that the increases of h p a r a m e t e r and the m e a n lifetime

from ~ 350 to

500°C are d e r i v e d from formation and

~.00£

growth of v a c a n c y clusters.

In the

~ 099C

quasicrystal A168Mn20Si~Rue,

we can

J C ,-0.98

®

\

obtain good d i f f r a c t i o n p a t t e r n s of

\ %

X -ray

in c o m p a r i s o n w i t h those of the

q u a s i c r y s t a l A I - M n - S i ternary alloys 7.

R'T

'

260

'

z,~o

'

600

TEMPERATURE (° C)

Figure 4 shows the change in h p a r a m e t e r of the q u a s i c r y s t a l A l 6 e M n 2 0 S i ~ R u 8 during the isochronal aging for 20 min

Figure 4: h p a r a m e t e r of icosahedal AI6 sMn20Si4Rus.

I. Kanazawa et al. / Quasicrystalline phases

796

the q u a s i c r y s t a l AlT~Mn20Si6

pw

:~

than those in the q u a s i c r y s t a l A168Mn20

i.o8o

Si~Rus.

n

i

is lower

1.070

This deduces

that the lifetime,

TI, of c o m p o n e n t 1 in the q u a s i c r y s t a l

(a)

A 1 6 8 M n 2 0 S i ~ R u s may be shorter than that

1.060

of the q u a s i c r y s t a l A1745~20Si6, Q-

if the

lifetime of c o m p o n e n t 1 reflects the

210

e l e c t r o n d e n s i t y in the bulk.

!___ I I i ' ~ .

the lifetime,T1,

(b)

A168Mn20Si4Ru8

_J

in the q u a s i c r y t a l

is 185 ~ 5 psec and ~ 15

psec longer than that in the q u a s i c r y s t a l

190

A174Mn20Si6.

100

However,

This e x p e r i m e n t a l

suggests that the lifetime,T1, i

!

i

i

i

i

|

i

I

i

i

l

result of

I

100 2oo 300 400 5o0 G00 700

c o m p o n e n t 1 may include

TEMPERATURE ('C)

of structural defects

the i n f o r m a t i o n s

such as Mn v a c a n t

Figure 5 : (a) h p a r a m e t e r of i-Al6Mg~Cul.

centers in M a c k a y icosahedra.

(b) the m e a n l i f e t i m e of iAIGMg~Cu i.

m e t e r and the m e a n lifetime of the quasi-

(a) and

crystal Al6Mg4Cul.

The h p a r a m e t e r and

the m e a n lifetime d e c r e a s e

is a p p r o x i m a t e l y c o m p a r a b l e to a single

line phases.

These results suggest that the

v a c a n c y - t y p e defects

i c o s a h e d r a have been d e t e c t e d in the

the intensity,I2,

to the

q u a s i c r y s t a l AlsMg~Cul may contain

w h e t h e r Mn v a c a n t centers in M a c k a y

As shown in Fig.3,

of c o m p o n e n t 2

changes r e m a r k a b l y

t r a n s i t i o n from the q u a s i c r y s t a l crystal.

Now, we shall c o n s i d e r

p r e s e n t experiments.

from % 300°C.

These d e c r e a s e s c o r r e s p o n d to the phase

space in the b o u n d a r y among i c o s a h e d r a

v a c a n c y 11

Figure 5

(b) show the changes in h para-

in those q u a s i c r y s t a l -

This result suggests that

structurally.

REFERENCES i. D. Shechtman, I. Blech, D. Gratias and J.W. Cahn, Phys. Rev. L e t t . 5 3 ( 1 9 8 4 ) 1 9 5 1 .

v a c a n c y - l i k e defects of c o m p o n e n t 2

2. D. Levine and P.J. Steinhart, Lett.53(1984)2477.

do not c o r r e s p o n d to Mn v a c a n t centers

3. V. Elser, Phys. R e v . B 3 2 ( 1 9 8 5 ) 4 8 9 2 .

in M a c k a y icosahedra.

Phys. Rev

Are not there 4. P.W. S t e p h e n and A.I. Goldman, Rev. L e t t . 5 6 ( 1 9 8 6 ) l 1 6 8 .

Mn v a c a n t centers in M a c k a y i c o s a h e d r a in real q u a s i c r y s t a l l i n e phases

Phys.

?

Here, we shall compare the lifetime,T1,

5. D. S h e c h t m a n and I.A. Blech, Metall. Trans.A16(1985)1005.

of c o m p o n e n t 1 in the q u a s i c r y s t a l A168Mn20Si4Ru8

w i t h that of c o m p o n e n t

1

6. P. K i r k e g a a r d and M. Eldrup, Comput. Phys.Commun.7(1974)401.

in the q u a s i c r y s t a l Al?~Mn20Si6. The c o n c e n t r a t i o n of Mn in the quasicrystal A 1 7 4 M n 2 0 S i 6

is c o m p a r a b l e to

that in the q u a s i c r y s t a l A l 6 a M n 2 0 S i 4 R u s ~ while the c o n c e n t r a t i o n s

of Si and A1 in

7. M. Ymane, K. Kimura, T. Shibuya and S. Takeuchi, Mater. Science F o r u m 22-24 (1987)539.