THE STATE OF THE IMPURITY IRON CATIONS IN LiNbO3

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THE STATE OF THE IMPURITY IRON CATIONS IN LiNbO3

V. Belogurov, P. Senkov

To cite this version:

V. Belogurov, P. Senkov. THE STATE OF THE IMPURITY IRON CATIONS IN LiNbO3. Journal

de Physique Colloques, 1980, 41 (C1), pp.C1-455-C1-456. �10.1051/jphyscol:19801178�. �jpa-00219666�

JOURNAL DE PHYSIQUE Colloque C l

,

supplhnent au n ^O 1, Tome 41, janvier 1980, Page C1-455

ME STATE OF

ME

IMPURITY IRON CATIONS IN W3

V.N. Belogurov and P.E. Senkov

P h y s i c s Insti-tzte, Latvian SSR Academy of S c i e n c e s , 229021 Riga, SaZaspiZs -1, USSR.

Polycrystalline samples of LiNbO doped by 3

the enriched 5 7 ~ e isotope have been investigated a t temperatures 80 and 300K by the method of nuclear gamma-resonance (NGR)

.

The samples had been re-

-4 0

duced by annealing in 10 Torr vacuum at 1000 C.

From e a r l i e r works [I-71 it follows that Fe impurity ions can exist in LMbO matrix in the Fe 2+

3+ 3

and Fe states; and oxidizing and reducing anneal-

2+ 3+

i n g can transfer iron from the Fe into the Fe state, and vice versa. This paper deals with the discussion of results of an investigation of such

samples, in which impurity atoms were transform- ed by reducing annealing into the ~ estate. The ~ + Fe3* ions have been traced in NGR-spectra of one sample only (with 1.02 at.% 57Fe).

The experimental NGR-spectra of all the samp- les under study a t the temperatures 80 and 30012 a r e similar; they are doublet's of asymmetric intensities with a noticeably widened left line (near zero velo- city) and with lesser intensity and the right line of a lesser width and greater intensity, their a r e a s being equal. Spectra computing performed by a spe- cial programme 181 using two single fit curves of Lorentzian form gives the mean values 0.3 15 and 0.290 mm/s for half-widths the intensities differing by

-

^5%.

The possible reasons of asymmetry of quadru- pole doublets might be the following:

a ) the Goldanskii-Karyagin effect 191;

b) the effect of sample texture [10,14

,

c ) electron and nuclear spin-lattice and spin- spin relaxation 12

_{[ 1} .

In the presence of the Goldanskii-Karyagin ef- f ect both intensities of lines and their a r e a s should be different in size, and their asymmetry should in- c r e a s e with temperature (e.g. from 80 t o 3 0 0 ~ ) . Therefore the observed asymmetry cannot a r i s e due

t o the Goldanskii-Karyagin effect.

The texture effects

-

preferred orientation of non-spherical sample grains

-

also might s e r v e a s a reason for the asymmetry of NGR doublet. Chang- ing the

8

angle between the sample plane normal and the direction of Mijssbauer gamma-ray should change the ration of line intensities and, moreover, give an inverse (comparing to

8

^r 0 ) intensity ra- t io.

The samples with 0.07 at.%, 0.30 at.%, 1.02 at.%, 2.06 at.% 57 Fe concentrations have been

t e s t e d fdr the texture effect for the angles

0

^{= 0;}

0

⁼ 30° and the "magicN angle

8

^{= 54.7} 0

.

^Spectra

computing gives the results, similar to those listed i n Table 1 for 1.02 at.$ 57Fe concentration and on t h i s basis we draw a conclusion about the absence of texture effects.

Table 1. NGR spectra parameters for polycrys- talline LiNbO3: Fe ( 57 Fe concentration 1.02 at.$) a t

different angles between the normal to the sample surface and the -ray). T r 300K.

0 1.700 1.224 1.700 1.275 0.280 30 1.732 1.225 1.720 1.274 0.281 57.4 1.720 1.230 1.693 1.274 0.288

Supposing doublet asymmetry due t o electron and nuclear spin-spin and spin-lattice relaxation, one is to observe the form dependence of quadrupole doublet lines on impurity concentrations and tempe- r a t u r e changes. However, in our experiment impu- rity concentrations had been changed in the range f r o m 0.07 at.% to 2.06 at.%, and temperatures from 80 to 300K no form changes have been observ- ed. The relaxation reasons of asymmetry, therefore, may be excluded.

A complex structure of NGR asymmetric

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801178

c1-456 JOURNAL DE PHYSIQUE

spectra observed s e e m s to s e r v e a s the most pro- bable explanation of experimental data. Using the minimal number of additional parameters we get the best fit t o experimental curves by t h e sums of two doublets with equal intensities and half-widths and with close parameters

8

^{and A} ( s e e Table 2 ) .

Table 2. NGR spactra parameters for coupled states of t h e Fe 2+ ions in differently doped LiNb03:

Fe.

L i m b oping A,

a;

^{AZ 82}

r

at.% mm/s mm/s mm/s mm/s mm/s

2 Keune, W., Date, S.K., Dezsi, I. and Gon- ser, U., J.Appl.Phys. 46(1975)3914.

3 Keune, W., Date, S.K., Gonser, U. and Bun- zel, H., Ferroelectrics, 13 ( 1976)443.

4 Belogurov, V., Bilinkin, V., Gotlib, I., Ru- binina, N. and Sencov, P.

,

Fiz.Tv.Tela 18 (1976) 143

5 Date, S.K., Keune, W., Engelmann, H. ,Gon- ser, U. and Dezsi, I., J.Physique colloq. 37 (1976)C6-117.

6 Gonser, U., Sakai, H. and Keune, W., J.

Physique colloq. 37 (1976)C6-709. . -

T-8 OK

7 Kurz, H . , Kratzig, E., Keune, W., Engel- 1.000 0.30 2.487 1.356 2.227 1.362 0.302

mann, H., Gonser, U., Dischler, B. and 0.935 1.02 2.454 1.361 2.263 1.374 0.298

Bauber, A., Appl.Phys. 12(1977)355.

0.990 2.06 2.518 1.376 ,2.332 1.4060.315

8 Belogurov, V. and Bilinkin, V.

,

Prepr.Inst.

The presence of doublet p a i r s with equal doub- 1 et intensities within the whole concentration range 1 eads t o the natural assumption that Fe 2+ impurity

cations exist with equal probability in two states described by Lorentzians with close parameters. We could assign such doublet p a i r s corresponding t o the coupled Fez+ cations p a i r s located in neighbour lat- t i c e sites o r t o t h e p a i r s Fe 2+ +lattice defect provid-

i n g thus partly o r thoroughly the local electroneut- rality of crystal.

The formation of coupled p a i r s providing local electroneutrality of t h e crystal is most probably a widespread phenomenon in the c a s e of impurity ions t h e valence of which differ from those of matrix o n e s Exchange-coupled p a i r s of impurity ions have been a l s o found by EPR in some compounds [13-171.

Fiz. Akad.Nauk LSSR, Zinatne, Riga, 1977.

Goldansky, V.I., Makarov, E.F. and Khra- pov, V., Phys-Let. 3(1963)344.

Gonser

,

U. and Pfannes, J., J.Physique col- 10q. 35( 1974)C6-395.

Ericsson, T. and Wappling, R., J.Physique

~0110q. 37(1976)C6-719.

Blume, M., Phys.Rev.Let. 14( 1965) 96.

Garifullina, R.

,

^Zaripov, M. and Stepanov, V., Fiz.Tv.Tela 12(1970)55.

Birgeneau, R. J., ~ u t c h i n ~ s , M .T. and Wolf, W.P., Phys.Rev. 168(1968)1026.

Birgeneau, R.J., Hutchings, M.T. and Wolf, W.P., Phys.Rev. 169(1969)257.

McPherson, G .L. and Wai-ming Heung, Solid St.Comm. 19(1976)53.

McPherson, G.L. and Henling, L.M., Phys.

Rev.B 16(1977)1889.

References

1 Rubinina, N., Shagdarov, V., Jankovsky, V.

and Kuzmin, R.

,

Quant.Electronics 2( 1975)

.