Tm-169 MÖSSBAUER STUDY OF THULIUM HYDRIDES (II) : TmH3

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Tm-169 MÖSSBAUER STUDY OF THULIUM HYDRIDES (II) : TmH3

G. Wortmann, G. Kalkowski, A. Heidemann, F. Wagner

To cite this version:

G. Wortmann, G. Kalkowski, A. Heidemann, F. Wagner. Tm-169 MÖSSBAUER STUDY OF

THULIUM HYDRIDES (II) : TmH3. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-233-

C1-234. �10.1051/jphyscol:1980176�. �jpa-00219745�

JOURNAL DE PHYSIQUE Colloque

C1,

suppldment au

n

O 1 , Tome

41,

janvier

1980,

page C1-233

Tm-169 ~ S S B A U E R

STUDY OF

THULIUM

HYDRIDES ( I I ) :

TrrH3

G. Wortmann, G. Kalkowski, A. Heidemann

+

and F.E. wagner+

I n s t i t u t fQr Atom- und Festkarperphysik, Freie Universittit Berlin, 1000 Berlin, W. G e m y .

+

Physik-Department, Technische Universittit MUnchen, 8046 Garching, W. Germany.

I n t r o d u c t i o n

The a p t i t u d e o f t h e 8.4 keV r e s o n a n c e o f I 6 ' ~ m f o r t h e s t u d y o f t h u l i u m h y d r i d e s h a s been d e m o n s t r a t e d i n a p r e c e e d i n g c o n t r i b u - t i o n t o t h i s c o n f e r e n c e [I]. The r e a s o n f o r t h i s l i e s , b e s i d e t h e low gamma e n e r g y , i n t h e r e s o l u t i o n power o f t h e r e s o n a n c e f o r q u a d r u p o l e i n t e r a c t i o n s .

' ~ m ,

a 100%

i s o t o p e ,

i s

i n i t s t r i v a l e n t s t a t e a non- Kramers i o n w i t h a 3 ~ 6 c o n f i g u k a t i o n o f t h e 4f e l e c t r o n s h e l l , which r e s p o n d s v e r y s e n s i t i v e l y t o c r y s t a l l i n e e l e c t r i c f i e l d

(CEF) i n t e r a c t i o n s . When t h e

~ m

s i t e sym-

~ +

metry i s lower t h a n c u b i c , r a t h e r l a r g e q u a d r u p o l e s p l i t t i n g s can b e o b s e r v e d w i t h t h e 8.4 keV 3/2 + 1 / 2 t r a n s i t i o n o f I6'~m.

They may r e a c h v a l u e s up t o 150 m m / s a t li- q u i d h e l i u m t e m p e r a t u r e s , where o n l y t h e l o w e s t CEF l e v e l s o f t h e J=6 I f - c o n f i g u r a - t i o n a r e p o p u l a t e d . A t h i g h e r t e m p e r a t u r e s , e q 4 £ , t h e 4f c o n t r i b u t i o n t o t h e o b s e r v e d e l e c t r i c f i e l d g r a d i e n t e q , i s t e m p e r a t u r e averaged and t h e l a t t i c e c o n t r i b u t i o n , eqlatt, becomes dominant. T h i s b e h a v i o u r has been o b s e r v e d and a n a l y s e d i n t h e e a r l y d a y s of Mbssbauer s p e c t r o s c o p y [21.

The i n f o r m a t i o n o b t a i n e d from t h e p r e s e n t s t u d y o f TmH3 w i l l b e used t o d i s c u s s t h e c o n t r o v e r s i a l r e s u l t s o f two r e c e n t s t u d i e s o f

~ r

i n

~

YH3

'

and ErH3, r e s p e c t i v e l y l3,4].

Sample P r e p a r a t i o n and Experiments

a b o u t 100 mg o f Tm m e t a l a t 870 K t o a H2 p r e s s u r e o f 1400 T o r r f o r one hour. During t h e t h e c o o l i n g o f t h e sample, t h e H2 p r e s - s u r e was r a i s e d t o a b o u t 3000 T o r r . The X- r a y d i f f r a c t i o n a n a l y s i s showed o n l y t h e hexagonal r a r e e a r t h (R.E.) t r i h y d r i d e pha- s e [51. The g r a v i m e t r i c d e t e r m i n a t i o n o f t h e H c o n t e n t of t h e sample y i e l d e d a f o r - mula TmH3.,(2). The Mbssbauer measurements were performed s i m i l a r a s d e s c r i b e d i n [I].

t *

^{h m n m 6 ' n o o * t f i '}

- 90 - ⁶⁰ - 30 0 30 60 90

RELATIVE VELOCITY (mmls

F i g u r e 1 : MSssbauer s p e c t r a o f TmH3 a t v a r i o u s t e m p e r a t u r e s The TmH3 sample was p r e p a r e d by e x p o s i n g

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980176

C1-234 JOURNAL DE PHYSIQUE

R e s u l t s and D i s c u s s i o n

F i g . 1 shows two s p e c t r a of TmH3 a t 300 K and 4.2 K. Both s p e c t r a r e v e a l a t y p i c a l q u a d r u p o l e d o u b l e t , and, a s i n t h e

1 6 9 ~ m

s t u d y o f t h e Tm d i h y d r i d e s [ l l , n o i n d i c a - t i o n o f any m a g n e t i c h y p e r f i n e i n t e r a c t i o n s . The t e m p e r a t u r e dependence o f t h e quadrupo- l e s p l i t t i n g , = e qQ/2, 2 i s g i v e n i n Tab. 1 f o r a s e r i e s of measurements between 4.2 K and 350 K. Measurements a t T > 3 0 0 K

w e r e

f o l l o w e d by s t u d i e s a t lower tempera-

t u r e s t o e n s u r e t h a t no hydrogen l o s s o f t h e sample h a d o c c u r e d . A p l o t of t h e d a t a of Tab. 1 shows t h a t n E Q a p p r o a c h e s a v a l u e of 14 (1) mm/s a t h i g h t e m p e r a t u r e s .

From t h e q u a d r u p o l e s p l i t t i n g s o b s e r v e d i n TmH3, i n f o r m a t i o n on t h e CEF g r o u n d s t a t e o f t h e

~ m

i o n c a n b e e x t r a c t e d by arguments

~ +

s i m i l a r t o t h o s e a p p l i e d r e c e n t l y t o a Mbssbauer s t u d y o f

~ r

i n E r H 3 and YH3 131

~ '

and t o a s u s c e p t i b i l i t y and m a g n e t i z a t i o n s t u d y of ErH3 143, r e s p e c t i v e l y . I t was as- sumed t h a t i n t h e i s o s t r u c t u r a l R.E. t r i h y - d r i d e s t h e CEF i n t e r a c t i o n o f t h e R.E. i o n s can b e d e s c r i b e d by hexagonal CEF parame- t e r s , a l t h o u g h t h e H l a t t i c e a c t u a l l y low- e r s t h e p o i n t symmetry a t t h e R.E. i o n s t o C2. T h i s assumption i s s u p p o r t e d by a lS56d 2lbssbauer s t u d y 161, where a n a x i a l l y sym- m e t r i c eqlatt was o b s e r v e d , i n d i c a t i n g t h a t t h e hexagonal l a t t i c e o f t h e R.E. i o n s

i s

mainly r e s p o n s i b l e f o r eqlatt.

Using t h e CEF-level diagrams o f S e g a l and Wallace [7] f o r hexagonal f i e l d s (which, however, u s e o n l y f o u r t h and s i x t h o r d e r CEF o p e r a t o r s ) , F l o o d 147 d e r i v e d from t h e magnetic d a t a o f ErH3 a n e g a t i v e v a l u e o f x, t h e r a t i o o f f o u r t h o r d e r t o s i x t h o r d e r CEF p a r a m e t e r s . I n c o n t r a s t t o t h i s , S u i t s e t a1.131 found from t h e i r Mbssbauer d a t a of

~r~~

i n YH3 a p o s i t i v e v a l u e of x.

Transforming t h e

~ r

CEF p a r a m e t e r s t o t h e

~ +

~ m

c a s e , t h e n e g a t i v e s i g n .(and t h e mag-

~ +

n i t u d e ) o f x from Ref. 4 would l e a d t o two s i n g l e t s w i t h p r e d o m i n a n t l y

mJ

= 6 cha- r a c t e r f o r t h e l o w e s t CEF s t a t e s i n TmH3, w h i l e t h e p o s i t i v e s i g n o f

x

from Ref. 3

r e s u l t s i n a

~ m

s i n g l e t g r o u n d s t a t e w i t h

~ + mJ

= 5 3 c h a r a c t e r [7]. Using

a

v a l u e of eqlatt = 5

.

l 0 I 7 v/cm2 from Ref. 6 and t h e above CEF s t a t e s ( i n c l u d i n g t h e s h i e l d i n g p a r a m e t e r s o f Ref. 2), a rough e s t i m a t e y i e l d s

eO

150 mm/s a t 4.2 K f o r t h e f o r - mer and % 50 m m / s f o r t h e l a t t e r c a s e .

8

T o g e t h e r w i t h o u r e x p e r i m e n t a l r e s u l t s , t h i s c l e a r l y f a v o u r s t h e CEF p a r a m e t e r s ob-- t a i n e d from t h e 6 6 ~ r Mbssbauer s t u d y [3].

I n p r i n c i p l e , t h e t e m p e r a t u r e dependence o f PF:

Q

can be u s e d t o f u r t h e r e l u c i d a t e t h e

CEF l e v e l s o f

~ m ) +

i n TmH3. However, s i n c e

a. -

d e c r e a s e s q u i t e f a s t i n t h e low temper- a t u r e r e g i o n , a d d i t i o n a l d a t a a r e needed f o r a more d e t a i l e d a n a l y s i s .

F i n a l l y , it s h o u l d b e n o t e d t h a t t h e h i g h t e m p e r a t u r e v a l u e o f e q

(AE

(T+400 K ) =

Q

14

mm/s

c o r r e s p o n d s t o e q = 6

.

^{10' v/cm2,}

which most l i k e l y can be r e g a r d e d a s an approach t o eqlatt) i s a b o u t 20% l a r g e r t h a n t h e v a l u e o b t a i n e d f o r GdH3 [6]. such a s m a l l d i f f e r e n c e c a n e a s i l y be a t t r i b u t e d t o t h e s m a l l e r volume of t h e u n i t c e l l o f TmH3. T h i s work w i l l b e c o n t i n u e d .

T a b l e 1: Temperature dependence o f t h e

1 6 9 ~ m

q u a d r u p o l e s p l i t t i n g i n TmH3 Temperature

( K )

a~

(

m/s

1

4.2 6 5 . 5 ( 2 )

55 56.2 ( 2 )

7 7 48.7(2)

260 18.1 ( 6 )

R e f e r e n c e s

1 ) F. Waibel et a l . , c o n t i b u t e d p a p e r t o t h i s c o n f e r e n c e .

2 ) R.G. B a r n e s , R.L. Mbssbauer, E. Kanke- l e i t , J . M . P o i n d e x t e r , Phys. Rev.

136

(1964) A 175.

3 ) B. S u i t s , G.K. Shenoy, B.D. Dunlap, D.G.

Westlake, J. Mag. Magn. Mat.

5

(1977) -34.

4 ) D . J . F l o o d , J . Appl. P h y s . g ( l 9 7 8 ) 1495.

5 ) A. P e b l e r and W.E. Wallace, J. Phys.

Chem.

66

(1962) 148; M. Mansmann and W.E.

Wallace, J . Physique

25

(1964) 454.

6 ) S.J. L y l e , P.T. Walsh, A.D. W i t t s , J.W.

Ross, J . Chem. Soc. D a l t o n (1975) 1406.

7 ) E. S e g a l , J . S o l . S t a t e Chem.

2

(1 970) 347.