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Isomer shift of 57Fe at substitution sites of divalent fluorides
Volume 16, twin&r 2
1 October 1972
CHEMICAL PHYSICS LETTERS
.
ISOMER
SHIFT
OF 57Fe AT SUBSTI’I’U-I-ION
SITES
OF DIVALENT
FLUOIZIDES
A. CRUSET Laboratoire de Cilimfe _kkcf~airc, Certtre de Resherches NttcleTaircs, associb Zrf ‘Ut~iversit~ Louis Pasteur, 6 703 7 Srmsborug, Frame
Received 30 June 1972
57Fe2* substituting Ca2+.m R~C;IF~ shows a large isomer shift due to the decrease of the ~?erlap-~~d~s~d electron density at the nucleus accompanying the incrmse of the Fe-F distance (2.06 W in Fe??2 and 2.36 A in RSCnF3).
fn the course of the investigation of the chemical after-effects of 57Co electron capture (EC) decay in
IS {mm
8) 1.70
various host lattices, a large isomer shift (IS) displayed by rlucleogenet~c s7Fe7,+ substituting Cazi in CaFz has been noticed f I ] . The iS increases fram 1.41 mm S@Y1 in FeF, to 1.55 mm see-l in CaF2 versus Na4Fe(CN)6-10H20 at room temperature (see fig. 1). Iron in CaFz has an elghtfoid cubic coord~a~io~. To decide whether the IS increase is due to this un-
conlI~lo~ coord~at~on number, the ~~~ssbauer emission spectrum of 57Co : RbCaF, has been analysed. Co’+ substituting Ca’+ 111 _ the perovski k-type RbCaF3 Iattice forms CoFz- octahedral cltisters with Oh symmetry. The room temperature emission spectrum of $?Co : RbcaFg consists of a singe line (IS = I.55 t 0.01 mm set-1) and a quadrupole split doublet (IS = 0.44 mm see-l TQS = 0.42 mm secWf). The single line is characteristic of Fez+ in a strictly cubic environment: after s7C02+ EC decay, 57Fe2q is stabilized in substitution of Ca”*. The qu~drupoIe split doublet (38% of the total area of the spectrum) originates from 57Fe3” stabilized in the lattice as a consequence of the nuclear decay. Thus it appears that 57Fe2+ substituting CaZt in CaF, and’& RbCaF:, have identical IS values, irrespective of the coordination number. Other ~~~bauer saurce’s had been previously studied: the IS values of !?Fe2+ formed at the ~~erturbed substitution site, .’ .3$5.. ‘: : . :. ., ._
2.30 l.9
2.0 t
#&+
t+
*.lt
C2’Fe””
22
Mn
2*
2’3
I
2*4
d F.+F(A)
CS12’
Fig. I. Variation of the 57 Fe’* isomer shift (at 295°K and 80°K) as a function of the Fe-F distance for ferrous substitution impurities in hfgF2, CoF2(= RCoF& MnFt, RbCnF3(= CaF2).
after 57Cozt EC decay. in MgFz f I] , CoF2 f2f and KCoF3 f3f , MnF2 [4] and RbCaF, increase regularly with the metal--fluorine bond length. When Fe2+ substitutes a cation of larger ionic radius (i.e., Ca2+) the Fe-F distance is larger than in FeF, (2.36 a and Z.06 A respectively if bond Iength relaxation is neglected). The increase of the distance lowers the overlap-indu~d electron density at the nucleus: ; ,’ . .
Volume
16, number
2
CHEMICAL
PHYSICS LEl-I’ERS
1 October 1972
The author is grateful to Professor J.P. Adloff Dr. J.M. Friedt for helpful discussions. 6 I$ (0) I2 can be evaluated as a function of Fe-F distance, as Simanek and Wang [S] did for the interpretation of the pressure dependence of the chemical isomer shift in KFeF3. From the computed 6 l@(O) I* value and the esperimental isomer shift difference. the relative change of the nuclear charge radius AR/R 1 (Rexc-Rgd)/Rgd could be estimated. This calculation is now in progress. A higher accuracy is expected in the present case since the Fe-F distance can be more precisely estimated than in pressure experiments (relaxation can be taken into account); moreover the i$(O)l* and IS changes are about five times larger than the pressure induced variation of these parameters in KFeF3.
and
References [l] A. Crxct and J.bI. Friedt, Phys. Stat. Sol. 47b (1971) 655 [2] J..LI. Fricdt and J.P. Adloff, Compt. Rend. Acad. Sci. (Paris) 264 C (1967) 1356. [3] J.&i. Friedt, J. Inorg. Nucl. Chcm. 32 (1970) 2123. [4] G.K. Werrheim, H.J. Gukqenhcim and D.N.E. Buchanan, 3. Chem. Phys. 51 (1969) 1931. [.5] E. Simanekand A.Y.C. Wang, Phys. Rev. 166 (1968) 348.
327
1 October 1972
CHEMICAL PHYSICS LETTERS
.
ISOMER
SHIFT
OF 57Fe AT SUBSTI’I’U-I-ION
SITES
OF DIVALENT
FLUOIZIDES
A. CRUSET Laboratoire de Cilimfe _kkcf~airc, Certtre de Resherches NttcleTaircs, associb Zrf ‘Ut~iversit~ Louis Pasteur, 6 703 7 Srmsborug, Frame
Received 30 June 1972
57Fe2* substituting Ca2+.m R~C;IF~ shows a large isomer shift due to the decrease of the ~?erlap-~~d~s~d electron density at the nucleus accompanying the incrmse of the Fe-F distance (2.06 W in Fe??2 and 2.36 A in RSCnF3).
fn the course of the investigation of the chemical after-effects of 57Co electron capture (EC) decay in
IS {mm
8) 1.70
various host lattices, a large isomer shift (IS) displayed by rlucleogenet~c s7Fe7,+ substituting Cazi in CaFz has been noticed f I ] . The iS increases fram 1.41 mm S@Y1 in FeF, to 1.55 mm see-l in CaF2 versus Na4Fe(CN)6-10H20 at room temperature (see fig. 1). Iron in CaFz has an elghtfoid cubic coord~a~io~. To decide whether the IS increase is due to this un-
conlI~lo~ coord~at~on number, the ~~~ssbauer emission spectrum of 57Co : RbCaF, has been analysed. Co’+ substituting Ca’+ 111 _ the perovski k-type RbCaF3 Iattice forms CoFz- octahedral cltisters with Oh symmetry. The room temperature emission spectrum of $?Co : RbcaFg consists of a singe line (IS = I.55 t 0.01 mm set-1) and a quadrupole split doublet (IS = 0.44 mm see-l TQS = 0.42 mm secWf). The single line is characteristic of Fez+ in a strictly cubic environment: after s7C02+ EC decay, 57Fe2q is stabilized in substitution of Ca”*. The qu~drupoIe split doublet (38% of the total area of the spectrum) originates from 57Fe3” stabilized in the lattice as a consequence of the nuclear decay. Thus it appears that 57Fe2+ substituting CaZt in CaF, and’& RbCaF:, have identical IS values, irrespective of the coordination number. Other ~~~bauer saurce’s had been previously studied: the IS values of !?Fe2+ formed at the ~~erturbed substitution site, .’ .3$5.. ‘: : . :. ., ._
2.30 l.9
2.0 t
#&+
t+
*.lt
C2’Fe””
22
Mn
2*
2’3
I
2*4
d F.+F(A)
CS12’
Fig. I. Variation of the 57 Fe’* isomer shift (at 295°K and 80°K) as a function of the Fe-F distance for ferrous substitution impurities in hfgF2, CoF2(= RCoF& MnFt, RbCnF3(= CaF2).
after 57Cozt EC decay. in MgFz f I] , CoF2 f2f and KCoF3 f3f , MnF2 [4] and RbCaF, increase regularly with the metal--fluorine bond length. When Fe2+ substitutes a cation of larger ionic radius (i.e., Ca2+) the Fe-F distance is larger than in FeF, (2.36 a and Z.06 A respectively if bond Iength relaxation is neglected). The increase of the distance lowers the overlap-indu~d electron density at the nucleus: ; ,’ . .
Volume
16, number
2
CHEMICAL
PHYSICS LEl-I’ERS
1 October 1972
The author is grateful to Professor J.P. Adloff Dr. J.M. Friedt for helpful discussions. 6 I$ (0) I2 can be evaluated as a function of Fe-F distance, as Simanek and Wang [S] did for the interpretation of the pressure dependence of the chemical isomer shift in KFeF3. From the computed 6 l@(O) I* value and the esperimental isomer shift difference. the relative change of the nuclear charge radius AR/R 1 (Rexc-Rgd)/Rgd could be estimated. This calculation is now in progress. A higher accuracy is expected in the present case since the Fe-F distance can be more precisely estimated than in pressure experiments (relaxation can be taken into account); moreover the i$(O)l* and IS changes are about five times larger than the pressure induced variation of these parameters in KFeF3.
and
References [l] A. Crxct and J.bI. Friedt, Phys. Stat. Sol. 47b (1971) 655 [2] J..LI. Fricdt and J.P. Adloff, Compt. Rend. Acad. Sci. (Paris) 264 C (1967) 1356. [3] J.&i. Friedt, J. Inorg. Nucl. Chcm. 32 (1970) 2123. [4] G.K. Werrheim, H.J. Gukqenhcim and D.N.E. Buchanan, 3. Chem. Phys. 51 (1969) 1931. [.5] E. Simanekand A.Y.C. Wang, Phys. Rev. 166 (1968) 348.
327