CEMS OF 57Fe IMPLANTS IN ALKALI HALIDES

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CEMS OF 57Fe IMPLANTS IN ALKALI HALIDES

J. Kowalski, J. Stanek, B. Sawicka, J. Sawicki, M. Drwiega

To cite this version:

J. Kowalski, J. Stanek, B. Sawicka, J. Sawicki, M. Drwiega. CEMS OF 57Fe IMPLANTS IN ALKALI HALIDES. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-451-C1-452.

�10.1051/jphyscol:19801176�. �jpa-00219664�

JOURNAL DE PHYSIQUE Colloque Cl

,

suppl&ment au n O 1, Tome 41, janvier 1980, page C1-451

C W OF 5 7 ~ e IMPLANTS I N ALKALI HALIDES

J. Kowalski, J. dtanek, B.D. sawickax, J.A. Sawicki and M. ~ r w i e g a *

I n s t i t u t e of Physics, Jagiellonian University, Poland.

x I n s t i t u t e of Nuclear Physics, Cracm, Poland.

Conversion e l e c t r o n Miissbauer spectro- scopy of 5 7 ~ e implants was extended f o r t h e f i r s t time t o chemical compounds, Seve- r a l p o l y c r y s t a l l i n e a l k a l i - h a l i d e s having the NaCl s t r u c t u r e were implanted with 70 keV 5 7 ~ e + i o n s a t a dose of 1016 at/cm2.

Implantation and CEMS measurements were c a r r i e d out a t room temperature. The pre- s e n t e q e r i m e n t showed t h a t t h e technique previously applied i n s t u d i e s .of 5 7 ~ e i m - p l a n t a t i o n i n metals and semiconductors /e.g. i n r e f . 2 and 3/ a l s o can be useful t o study i o n i c c r y s t a l s .

The CEMS s p e c t r a measured presented e i t h e r symmetric quadrupole doublets (LiJ

,

NaC1, KBr, KJ, RbC1) o r unresolved broad s t r u c t u r e s (Hal?, Kl?) with t h e isomer s h i f t values t y p i c a l f o r a f e r r i c iron. I n t h e case of LiF and K C 1 an a d d i t i o n a l l i n e ap- p a r e n t l y due t o the f e r r o u s i r o n f r a c t i o n , was a l s o observed; t h e Fe2+/Fe3+ r a t i o was about 0.2

-

^0.3. Three t y p i c a l s p e c t r a a r e presented i n Fig. 1.

For t h e sample of 5 7 ~ e : ~ ~ r t h e e f f e c t of annealing was studied. The sample was heated i n a vacuum a t f o u r consecutive tem- p e r a t u r e s from 200'~ up t o 600°c, f o r 1 hour

a t each s t e p ; a f t e r each heating t h e spec- trum was measured a t room temperature, A notable gradual i n c r e a s e i n t h e qua9rupo-1

l e coupling was observed. The resonant p a t t e r n disappeared a f t e r heating a t 600'~.

The d a t a obtained i n d i c a t e t h a t i r o n implants i n a l k a l i h a l i d e s e x i s t mainly i n t h e form of ~ e ions, ~ + This i s i n d r a s t i c disagreement with t h e d a t a of chemically doped 5 7 ~ o sources; f o r 5 7 ~ o sources s p e c t r a u s u a l l y showed i r o n i o n s i n the Fe2+ s t a t e 4*5/. This marked d i f f e r e n c e i n t h e s p e c t r a

may r e f l e c t t h e d i f f e r e n t chemsitqr of i r o n and cobalt. It can a l s o be thought t o be due, Dartly, t o a f t e r - e f f e c t s of t h e decay of 5 7 ~ o , absent i n absorber spectra.

I ^I

"Fe NaCl IO'lcm' 70 keV

!

1 I

7-

"FeNaF

lo' k m '

-

70 kev

8

YI Z

0, lo5 -

>

C

5

a

I I I

-2 1 0 1 2 3

VELOCITY Irnmlsl

Fig. 1. CEMS s p e c t r a of 5 7 ~ e implanted i n a l k a l i halides.

One of t h e p a r t i c u l a r l y i n t e r e s t i n g problem i n 5 7 ~ e implanted a l k a l i h a l i d e s i s t h e nature of impurity-vacancy c l u s t e r s formed. The existence of impurity-vacancy

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801176

C1-452 JOURNAL DE PHYSIQUE

states was demonstrated in I B R experiments the

vl- -

^E'e3*

- ^vl-

basic configurations 6

'

, but the evidence of these in M6ssbauer the magnitudes and directions of the i m h - emission spectra of 5 7 ~ o doped crystals ced dipolu moments were calculated by the was not clear

4 , 5 ' .

The present work sug- self-consistent field technique, Contribu- gests that the quadrupole splittings obser- tions were appreciable up to 4 coordination ved are caused by iron-vacancy clusters, at spheres. This effLct is indicated in Fig, 2 least for some of +he samples under study. for two of the four possible vacancy confi- This assumption appears to be confirmed by gurations. The magnitudes of the electronic calculations of the electric field gradients polarizabilities of the ions were taken from in NaC1-type lattiees with vacancy pertur- Ref. 8.

bed configurations

7/

which will be discus- ii/ Quite satisfactory agreement was sed briefly below. already found in a few cases between the theoretical and experimental quadrupole splittings:

L i J

0.79

0.56

NaCl

0.75

0.86

KJ 0.81 0.58

RbCl O*

77

0.84

The theoretical splittings were weighted with the probabilities of four basic confi- gurations.

Fig. 2. Two from among the four possible

configurations of the

vl- -

~ e j +

- ^vl-

Referenees

complex in NaC1-type host, the planar 1/ BOD, Sawfcka, J.A, Sawicki, Conf. on and the linear. M8ssb. Spectr., Bucharest

1977,

Vol. 2,

p, 35-70; Nucl. Instr. Neth, 130, 613 For the calculations it was assumed

/1975/

9

that ae3* ions substitute for the alkali B,D, sadcka, J,A.

s ~

^J, Stanek,

~ ~ ~ ~ ~ ,

cations, MI+, and that charge-compensating

1- Phys, Plett,

s, ⁵⁹

^/1976/,

vacancies V occupy two of the neighbourine

3/

B,D,

sadcka,

J,A, sawicki, phys. L ~ ~ ~ . catiion sites, There are four nonequivalent

e,

³¹¹ /I97713

V1-

-

^~ej'

-

V1- configurations to be cons%- 4/ A.N, _Seregin, Pws. Stat.

dered in the NaCl structure: one linear,and Solidi

14 2, 663 /1970/,

three planar- An iron impurity is surroun- _cj/ B,R, Anand,

ws.

Stat, Solid5 /b/

g+,

ded, by 6 anions as n.n. atoms, XI-, and by 227 /1977/,

10 cations, MI+, and two vacancies,

vl',

_{6/ G.D. Watkins, Phys. Rev.}

_{J 3 l . , 79}

_/1959/,

Qietributed randomly in next n.n. positions.

7/ J.

Kowalski, B,D. Sawicka, Sawicki, Calculations of the EFG tensors were made J. Stanek, to be published,

in the point var- _{8/ J.R. f essman,} A.H. gahn, Phys. Rev,

z,

ious arrangements of atoms in the surroun-

890 /1953/*

ding of the iron probe atom,

Two conclusions which were already men- tioned deserve consideration;

i/ In view of a very high electronic

~olarizibility of halogen ions the dipolar coneribution to the KFG was found to be larger by about an order of magnitude than the monopolar contribution. For each of