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ELECTRIC QUADRUPOLE INTERACTION OF 178Hf IN NONCUBIC METALS
B. Perscheid, G. Kaindl
To cite this version:
B. Perscheid, G. Kaindl. ELECTRIC QUADRUPOLE INTERACTION OF 178Hf IN NONCUBIC METALS. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-139-C1-140.
�10.1051/jphyscol:1980135�. �jpa-00219704�
JOURNAL DE PHYSIQUE Colloque C1, suppl6ment au no 1 , Tome 41, janvier 1980, page C1-139
ELECTRIC QUADRUWLE INTERACTION OF 1 7 8 ~ f IN NONCUBIC VETALS
B. Perscheid and G. Kaindl
I n s t i t u t filr Atom- und Festkarperphysik, Freie Universitift, Berlin, Germany.
The extensive experimental work of t h e l a s t few y e a r s on e l e c t r i c - f i e l d g r a d i e n t s
(EFG) a t nuclear s i t e s i n noncubic metals has r e s u l t e d i n an empirical c o r r e l a t i o n proposed by Raghavan e t a l . /I/, accord- i n g t o which the t o t a l EFG i s proportion- a l t o t h e i o n i c contribution. The v a l i d i - t y of t h i s c o r r e l a t i o n , however, i s doubt- f u l s i n c e a considerable number of excep- t i o n s has been found and s i n c e t h e sign of t h e EFGs i s known only i n r e l a t i v e l y few cases. This s i t u a t i o n motivates f u r - t h e r s t u d i e s of EFGs i n metals especial- l y by such methods where t h e sign of t h e EFG can a l s o be determined. For an up-to- d a t e review on experimental and theoret- i c a l r e s u l t s of EFGs i n metals s e e /2/.
We r e p o r t here on a study of EFGs a t 1 7 8 ~ f probe atoms i n t h e t r a n s i t i o n metals T i , Z r , Ru, and Os, a s well a s i n Be met- a l , using t h e 93-keV Massbauer t r a n s i t i o n of 17%f. This gamma resonance with t h e s p i n sequence 0
-
2 allows t o evaluate s i g n and magnitude of t h e EZ'G even from p o l y c r y s t a l l i n e samples.The d i l u t e a l l o y s were prepared by 100 argon-arc melting of 17% a c t i v i t y i n me-
t a l l i c form with t h e corresponding h o s t 3
-
metals keeping t h e r e s u l t i n g impurity .- o c concentration below 1 a t . % i n a l l cases.
f
98The source a c t i v i t y was produced by a * c e 181~a(d,5n)17% reaction. HfN was ueed a s a s i n g l e - l i n e absorber, and both source
-
'G-
and absorber were kept a t l i q u i d helium 96 temperature i n a l l experiments.
temperature gradient w i l l be r e f e r r e d t o as t h e sample axis. A l l s p e c t r a of t h e t r a n s i t i o n metal hosts were taken with t h e sample a x i s p a r a l l e l t o t h e d i r e c t i o n of t h e observed Massbauer quanta. I n case of t h e Be metal h o s t t h r e e s p e c t r a with d i f f e r e n t o r i e n t a t i o n s of t h e sample a x i s were recorded with t h e same sample.
Fig. 1 shows, a s an example, t h e t r a n s - mission spectrum obtained f o r T i a s host metal. From t h e asymmetry of t h e spectrum a p o s i t i v e s i g n of t h e EFG i s r e a d i l y de- rived. The r e s u l t s of t h e least-squares- f i t a n a l y s i s of t h e s p e c t r a a r e summa- r i z e d i n tab. 1. I n case of t h e Be a l l o y t h e a n a l y s i s revealed a strong o r i e n t a t i o n of t h e sample. The s p e c t r a of T i and Z r , on t h e o t h e r hand, could be f i t t e d well only by assuming n e a r l y random o r i e n t a t i o n . I n case of t h e Ru and 0 s a l l o y s t h e o r i - e n t a t i o n of t h e samples could not be de- termined from least-squares f i t s of t h e spectra.
his
causes some ambiguity onI I I 1 I I
Argon-arc melting of noncubic metals -10 -5 0 5 10
always produces more o r l e s s o r i e n t e d Relative velocity [rnm/sl samples caused by a temperature gradient
i n t h e sample during t h e cooling process. F i ure 1: Mtssbauer spectrum of d i l u t e I n t h e following t h e d i r e c t i o n of t h i s *be atoms i n T i metal
11
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980135
C1-140 JOURNAL DE PHYSIQUE
Table 1: EFGs a t t h e nuclear s i t e of HI probe atoms i n several noncubic metals
metal B e Ti Z r
L U ~
~f~
Ru 0s
a Ref. /3/, Ref 14/
t h e s i g n of t h e EFGs i n these two cases.
The magnitude of t h e EFGs, however, was found t o be not affected within t h e quo- ted e r r o r l i m i t s by assuming d i f f e r e n t types of o r i e n t a t i o n of the two samples.
The EFG a t nuclear s i t e s i n noncubic metals i s usually assumed t o be composed of an f onic conSribution
v:ln=~lat
(1-r, )"81
and an electronic contribution VZZ:
vexp= Z; lt
v;Et (1-8- + v::
vlat
z z represents t h e point charge l a t t i c e sum over the p o s i t i v e ions and )r-, i s the Sternheimer antis hi el din,^ factor. Raghavan e t a l . /1/ have proposed a proportionality betweenv::
andv : : * :
VZ; =
-
K v;Et(l-, . & ,
with-a "universal" constant Ir; taking val- ues between +2 and +4. The e q e r i m e n t a l r e s u l f s f o r t h e EFGs of Hf probe atoms i n t r a n s i t i o n metals do not follow t h i s cor- r e l a t i o n . Recently Ernst e t a l . /j/ showed t h a t t h e EFGs of pure systems can be di- vided i n t o two groups with proportionality constants X
=
-3 f o r metals with t h e out- ermost 6-shell l e s s than half f u l l an&K +2 f o r a l l other hsxagonal metals.
The EFGs of Hf probe a t o m i n host metals with l e s s than half f u l l d-shell arrzage themselves i n t h e K -3 regian. Thas t h e overall systematics found f o r pure systems by Ernst e t a l . seems t o apply a l s o f o r t h e impurity systems studied here. It should a l s o be noted t h a t t h e EFGs found f o r l a probe atoms i n t h e sane host metals /2,
5/
f i t i n a s i m i l a r way i n t h e COP-r e l a t i o n proposed by Ernst e t a l .
This work was supported by t h e Sonder- forschungsbereich 161 of t h e Deutsche Forschungsgemeinschaft and by t h e Gesell- schaft fiir Kernforsohung GmbH, Karlsruhe.
Valuable discussions with G. Wortmann a r e grate? u l l y acknowledged.
/I/ R. S. Raghavaq, E. 37. Kaufmnnn, 3.
Raghavan, Phys. Rev. Lett.
34,
(1975), 1280/ 2 / E. N. Kaufmam, R. Vianden, Rev. Mod.
Phys.
2,
(19791, 161/3/ H. Ernst, E. Hagn, E. Zeck, G. Eska, Phys, Rev.
9,
(19791, 4460;H, Ernst, t h e s i s T U Munich (1979) /4/ P. Boolchand, B. L. Robinson, S. Jha,
Phys. Rev.
187,
(19691, 475/5/ G. Haindl, D. Salomon, G. Wortmann, Phys. Rev. Lett. 28, (1972), 952;
G. Kaindl, D. Salomon, Phys. Lett.
