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Defect cascades and point defects in low-temperature neutron irradiated α-tin monitored by Mössbauer spectroscopy
Solid State Communications, Vol. 17, pp. 1029—1033, 1975.
Pergamon Press.
Printed in Great Britain
DEFECT CASCADES AND POINT DEFECTS IN LOW-TEMPERATURE NEUTRON IRRADIATED a-TIN MONITORED BY MOSSBAUER SPECTROSCOPY W.VoglandG.Vogl Physik-Department, Technische Universität Munchen, 8046 Garching, Germany (Received 13 June 1975 byP.H. Dederichs)
Neutron irradiation of cubic a-tin at 4.6 Kleads to a new component in the Mossbauer spectra similar to tetragonal (3-tin, disappearing again during annealing between 90 and 160 K. From the striking difference between the fractions of the new component in absorber spectra and in source spectra we conclude that it is due (a) to defect cascades from fast neutron collisions and (b) to point defects from the (n, y) recoil. WITH MöSSBAUER spectroscopy as a tool for investigating structural lattice defects (e.g. reference 1) it is on the one hand possible to perform microscopic studies of low energy recoil defects from (n, 7)-reactions or other nuclear reactions which excite the Mössbauer level as well. Such studies are performed with the sample as Mossbauer source (e.g. references 2 and 3). On the other hand one can study macroscopic (overall) damage as e.g. produced by fast neutron collisions in experiments with the sample as Mössbauer absorber (e.g. reference4). This is a report on a study of structural lattice defects in the elementaiy semiconductor a-tin (grey tin).5 In a-tin the atoms are completely covalently bonded, forming a cubic diamond lattice as in silicon and germanium. Former Mossbauer studies of defects in the diamond lattice are to be found in references 6 and 7. The tin nucide Sn”~appears to be particularly suitable for Mossbauer investigations of lattice defects produced by the (n, y) recoil because the Sn118 (n, ~) Sn’1~reaction does not produce a transmutation to another chemical element and also because of the long halflife (245 days) of Snl~~1. Therefore, after the end of a neutron irradiation of a tin sample the defects in the pure sample can be studied by Mossbauer spectroscopy for a long time by performing extensive defect annealing studies. 1029
Mi important advantage of MOssbauer studies in tin is the possibility of getting both Mossbauer source spectra (from Sn~9mnuclei) and absorber spectra (absorption at stable Sn’19 nuclei) from the same sample. For this purpose we used a specially equipped cryostat8 which permits the simultaneous registration of the two type of spectra with additional MOssbauer absorber and MOssbauer source. This allows one to distinguish between defects from the (n, ~y)recoil which are locally correlated with the Sn”~atoms being created by the same event (significant influence merely on source spectra) and overall damage (equal influence on source spectra and on absorber spectra). Finally, a special feature of a-tin is the phase transition from cubic a-tin (grey tin, semiconductor) to tetragonal (3-tin (white tin, tin metal) at 13.2°C. a-tin is stable only below 13.2°C,whereas at higher temperatures fl-tin is the stable modification, though (3-tin can be kept in metastable state (undercooled) at lower temperature. We thought that defects might give rise to a phase transition in local regions, and that it might be possible to monitor by Mossbauer studies of this phase transition the defect cascades from fast neutrons. Several years ago Goland9 attempted to use this phase transition in a similar manner, but he irradiated at 0°Cand found no radiation damage effect. The necessity of low irradiation temperature to prevent defect annealing in a-tin can also be deduced from electrical resistivity ~ which showed radiation damage annealing far below room temperature.
1030
DEFECT CASCADES AND POINT DEFECTS IN a-TIN
Vol. 17, No.8
Table 1. Isomer shift ~ relative to BaSnO, of the originala-tin line and the irradiation induced new line, quadrupole splitting AEQ andfraction F ofthe area of the new line to the total area of the MOssbauer spectrum. Irradiation: duration 68.9 hr, fast neutron dose (E> 0.1 Me V): 3.5 x 1018 n/cm2, sample temperature: 4.6 K. Mössbauer effect measurement: sample temperature 4.2 K, BaSnO, source temperature ~ 240K, PdSn absorber temperature ~ 140 K
Before irradiation, sample is absorber After irradiation at 4.6 K, sample is absorber After irradiation at 4.6 K, sample is source After 10 miii annealing at 274 K, sample is source or absorber
I
I
Original line
Irradiation induced new line ~IEQ
F
mm/sec
mm/sec
mm/sec
%
2.04 ±0.01
—
—
—
2.04 ±0.02
2.7
±0.1
0.4
±0.2
31
±5
2.05
2.67
±0.03
0.4 ±0.2
60
±10
±0.03
2.04 ±0.01
—
0
—
I
±5
I
F 10
~
0.95 b.ti~ton
40 20
V
/f” ~
-
...4”absorber
0.90 1.00
/
•
after irradiation
0
‘\
0
I
I
2 4 frradiatton time [days]
2. Dependence of the transmutation on irradiation induced component in the MOssbauer spectrum ation time. F is the fraction of the area of the irradito the total area of the snectrum Fast neutron flux (E>0.l MeV): 1.2 x l0~~ n/cm2sec. FIG.
0.97
0.94 -~
_
-~
0
.~
+ [~nmisecJ
FIG. 1. Spectra with the a-tin sample as source before and after a 68.9 hr irradiation at 4.6 K (fast neutron dose (E > 0.1 MeV): 3.5 x 10~n/cm2). Mössbauer effect measurement: sample temperature 4.2 K, PdSn absorber temperature ~ 140 K. The dashed curves show the a-tin component. In component order to refer andthethespectra irradiation to BaSnO induced 3 instead of PdSn as absorber 1.51 mm/sec have to be added to the velocity.
a-tin powder samples were produced by transformation of foils of 13-tin (chemical purity 99.98%, enriched 98% Sn”8 but containing enough Sn”9 nuclei to permit the use of the sample as Mossbauer absorber, too)1’ and checked by X-ray powder diffraction and Mossbauer absorber spectra. The isomer shift relative to BaSnO 3 was 2.04 ±0.01 mm/sec12inNo good residual agreement conwith the values from the literature. tamination with (3-tin could be detected. The samples were irradiated in aluminium holders at 4.6 K in helium atmosphere in the liquid helium neutron
Vol. 17, No.8
DEFECT CASCADES AND POINT DEFECTS IN a-TIN
irradiation facility of the Munich research reactor. The flux of thermal neutrons was 1.3 x 1013 neutrons/cm2 sec, of fast neutrons (E >0.1 MeV) 1.2 x 1013 neutrons/cm2 sec and the 7-ray flux 7 x io~rad/hr. After the end of the irradiation the MOssbauer spectra were measured without further warming up8 with the sample as Mossbauer absorber and as Mossbauer source as well. We used a BaSnO 3 source and a PdSn absorber with an additional palladium filter in order to reduce the tin X-ray background. The linewidth was 1.0 mm/sec and reached the theoretical value expected from effective source and absorber thicknesses. After the irradiation at 4.6°Ka line broadening and shifting appears in the source and in the absorber spectra which is interpreted as due to the appearance of an additional quadrupole split line at about 2.7 mm/sec relative to BaSnO, or 1.2 mm/sec relative to PdSn. In Table 1 the Mossbauer 2parameters for anare (E>0.1 MeV) irradiation n/cm summarizedwith and 3.5 Fig.x 11018 shows two of the spectra. An isochronal annealing program with 10 mm holding times was performed. The irradiation induced line disappeared completely in an annealing stage at 90— 160 K in the source spectra as well as in the absorber spectra. By comparing the irradiation time dependence of the fraction F of the area of the new line to the total area of the MOssbauer spectrum in the source and in the absorber spectra (Fig. 2) a striking difference was found. In the source spectra there is only a slight dependence ofF on irradiation time. Therefore we conclude that the new MOssbauer componentin the spectra is mainly due to defects locally correlated with the Mossbauer atoms. They must be caused by the 7-recoil from the Sn”8 (n, 9m reaction. 7)Snhihand there is a In the absorber spectra on the other nearly linear dependence of F on irradiation time. Here the new Mössbauer component must be due to statistically distributed irradiation defects (macroscopic or overall damage) increasing in number with increasing irradiation dose. This latter effect naturally contributes to F in the source spectra as well but gives a much smaller contribution than the correlated defects do up to the maximum irradiation doses of this work. Thus in one sample we can clearly distinguish between defects which are locally correlated with the probe atoms and statistically distributed defects.
1031
The isomer shift of the new line (2.7 ±0.1 mm/sec) is a little larger than that of (3-tin (2.56 mm/sec).” The quadrupole splitting of the new line (0.4 ±0.2 mrnfsec) contains a large uncertainty because of the unresolved spectrum, thus a comparison with the quadrupole splitting of tetragonal (3-tin (0.18 ±0.03 mm/sec at 80 K’8) can only show the principal agreement in the range of the error bars. First we shall discuss the. changes detected in the absorber spectra. It is well-known that fast neutrons generate highly energetic primary knock-on atoms, which in turn created great number of lattice defects in a disordered region, the so-called defect cascade, associated with a “thermal spike”. The most probable interpretation of the present results is a transmutation of a-tin in the defect cascades into a configuration similar to tetragonal tin (ft-tin). From the fraction of the sampleintransmuted (F corrected for theassuming slight difference the Debye—Waller factors”) a mean elastic cross section of 5 ±I barn for the elastic collisions of fast neutrons with tin atoms14 one can estimate a mean diameter of the transmuted regions of 110 ±15 A which each contain 2.2 ±0.6 x 1 o~atoms. We think it is interesting and surprising that a complete lattice transmutation might take place in regions of this size. Some more information about this transmutation may be obtained by comparing the isomer shift of the irradiation induced component with that found by Bolz and Pobell’5 for amorphous (3-tin with 10—20%
copper produced by quenched condensation. They measured an isomer shift of 2.75 ±0.02 mm/sec relative to BaSnO, similar to the value for our irradiation induced component (Table 1), corresponding to an increased s-electron density compared to crystalline (3-tin. The authors interprete this increase as due to p-to-s transfer of electrons in the formation of the amorphous state, since the tin atoms do not have the possibility to adjust themselves in the regular (3-tin lattice. The similarity of the isomer shifts of the amorphous state of tin and of the irradiation induced cornponent in our work both slightly larger than the isomer shift of (3-tin, favours the view that in the region of the defect cascades a highly disturbed quasi-amorphous (3-tin phase is formed.
It is tempting to attribute such a transmutation to the “temperature” increase (more exactly: the strong
1032
DEFECT CASCADES AND POINT DEFECTS IN a-TIN
increase of the atomic mobility and of the vibrational motion) in the defect cascades (the “thermal spikes”), (3-tin being the phase which is stable at higher temperatures (above 13.2°C).The “disturbed (3-tin phase” would then be stabilized by the sudden quench during the “cooling” of the “thermal spike” within about I0_12_10_ht sec.16 The thermal treatment between 90 and 160 Kenables defect migration leading to the retransformation to the a-tin phase which is the stable phase at these temperatures. It might be interesting to compare our results with those of Gonser and Okkerse’7 who found mdication for a transition to a “liquid-like” phase in irradiation damage cascades in GaSb. Secondly, the (it, ~)-effectshall be discussed. Myrha and Gardiner have reported a minimum displacement ener~’of 12 eV for a-tin.’0 With the mean value 50 eV of the (n, 7)-recoil energies after the Sn”8 (n, y) Snll9m reaction’8 the consequence of the (n, 7)-reaction can be understood, namely a possible displacement of the Sn 119ifl Mossbauer atom. Smce some recoils will have lower energies than 12 eV the fraction F is not 100%. •.
.
.
Vol. 17, No.8
From simple blilard ball arguments1’ one may conclude that focusing collisions are impossible in
the diamond lattice and that the recoiling atom should therefore probably stop at an interstitial site with possibly very few furtherpoint defects in its environmeut. The value of isomer shift and unresolved quadrupole splitting of the new line as produced by the (n, 7)-recoil in the source spectra resemble the values of the new line in the absorber spectra (compare Table 1). The agreement in the annealing behaviour of the irradiation induced componentIn source and absorber spectra indicates that for the retransformation of transmuted regions of irradiation damage cascades into a-tin and for the annealing of local (n, y) damage the migration of the same type of defect, probably an interstitial defect, might be responsible.
Acknowledgements WeMansel thank for Ursel Wagner forhelp much helpful advice, W. experimental —
and discussions and H. Vonach for his continuous supporting interest in this work.
REFERENCES 1. VOGLG.,/. Phys. Coil. C6 (supplement au Tome 35), 165 (1974). 2. CZJZEK G. & BERGER W.G.,Fhys. Rev. Bi, 957 (1970). 3. SIMOPOULOS A. & VOGL G., Phys. Status Solidi (b) 59, 505 (1973). 4. 5.
FRIEDT J.M. & VOGL W., Phys. Status Solidi (a) 24,265 (1974). An extended abstract of part of this work was contributed to the Int. Conf on the Applications of the Mössbauer Effect, Bendor, Sept. (1974); J. Phys. Coil. C6 (supplement au Tome 35), 297 (1974). 6. HAFEMEISTER D.W. & DE WAARD H.,Phys. Rev. B7, 3014 (1974). 7. 8. 9. 10. 11.
12. 13. 14. 15.
WEYER G., DEUTCH B.I., NYLANDSTED-LARSEN A., ANDERSEN J.U. & NIELSEN H.L.,J. Phys. Coil. C6 (supplement au Tome 35), 297 (1974); WEYER G., ANDERSEN J.U., DEUTCH B.!., GOLOVCHENKO J.A. & NYLANDSTED-LARSEN A.,Rad. Effects 24,117(1975). ROSNER P., VOGL W. & VOGL G., NucL Instrum. Methods 105,473(1972). GOLAND A.N.,J. Phys. Chem. Solids 16,46 (1960). MYRHA A. & GARDINER R.B., Phys. Lett. 39A, 405 (1972). VOGL W., Dissertation, Technische UniversitatMUnchen (1974). STEVENS 1G. & STEVENS V.E., Mossbauer Effect Data index, 1970, 1972, 1973. Adam Huger, London. GOLOVNIN V.A., IRKAEV S.M. & KUZMIN R.N.,Sov. Phys. JETP 32,372(1971). HUGHES D.J. & SCHWARTZ R.B.,Neutron Cross Sections, 2nd edn. BNL (1958). BOLZ J. & POBELL F., Z. Phys. B20, 95(1975).
Vol. 17, No.8 16. 17. 18.
DEFECT CASCADES AND POINT DEFECTS IN a-TIN
ThOMPSON M.W., Defects and Radiation Damage in MetaLs. Cambridge University Press (1969). GONSER V. & OKKERSE B., Phys. Rev. 109,663(1958). HANNAFORD P. & WIGNALL J.W.G.,Phys. Status Solidi 35, 809 (1969).
1033
Pergamon Press.
Printed in Great Britain
DEFECT CASCADES AND POINT DEFECTS IN LOW-TEMPERATURE NEUTRON IRRADIATED a-TIN MONITORED BY MOSSBAUER SPECTROSCOPY W.VoglandG.Vogl Physik-Department, Technische Universität Munchen, 8046 Garching, Germany (Received 13 June 1975 byP.H. Dederichs)
Neutron irradiation of cubic a-tin at 4.6 Kleads to a new component in the Mossbauer spectra similar to tetragonal (3-tin, disappearing again during annealing between 90 and 160 K. From the striking difference between the fractions of the new component in absorber spectra and in source spectra we conclude that it is due (a) to defect cascades from fast neutron collisions and (b) to point defects from the (n, y) recoil. WITH MöSSBAUER spectroscopy as a tool for investigating structural lattice defects (e.g. reference 1) it is on the one hand possible to perform microscopic studies of low energy recoil defects from (n, 7)-reactions or other nuclear reactions which excite the Mössbauer level as well. Such studies are performed with the sample as Mossbauer source (e.g. references 2 and 3). On the other hand one can study macroscopic (overall) damage as e.g. produced by fast neutron collisions in experiments with the sample as Mössbauer absorber (e.g. reference4). This is a report on a study of structural lattice defects in the elementaiy semiconductor a-tin (grey tin).5 In a-tin the atoms are completely covalently bonded, forming a cubic diamond lattice as in silicon and germanium. Former Mossbauer studies of defects in the diamond lattice are to be found in references 6 and 7. The tin nucide Sn”~appears to be particularly suitable for Mossbauer investigations of lattice defects produced by the (n, y) recoil because the Sn118 (n, ~) Sn’1~reaction does not produce a transmutation to another chemical element and also because of the long halflife (245 days) of Snl~~1. Therefore, after the end of a neutron irradiation of a tin sample the defects in the pure sample can be studied by Mossbauer spectroscopy for a long time by performing extensive defect annealing studies. 1029
Mi important advantage of MOssbauer studies in tin is the possibility of getting both Mossbauer source spectra (from Sn~9mnuclei) and absorber spectra (absorption at stable Sn’19 nuclei) from the same sample. For this purpose we used a specially equipped cryostat8 which permits the simultaneous registration of the two type of spectra with additional MOssbauer absorber and MOssbauer source. This allows one to distinguish between defects from the (n, ~y)recoil which are locally correlated with the Sn”~atoms being created by the same event (significant influence merely on source spectra) and overall damage (equal influence on source spectra and on absorber spectra). Finally, a special feature of a-tin is the phase transition from cubic a-tin (grey tin, semiconductor) to tetragonal (3-tin (white tin, tin metal) at 13.2°C. a-tin is stable only below 13.2°C,whereas at higher temperatures fl-tin is the stable modification, though (3-tin can be kept in metastable state (undercooled) at lower temperature. We thought that defects might give rise to a phase transition in local regions, and that it might be possible to monitor by Mossbauer studies of this phase transition the defect cascades from fast neutrons. Several years ago Goland9 attempted to use this phase transition in a similar manner, but he irradiated at 0°Cand found no radiation damage effect. The necessity of low irradiation temperature to prevent defect annealing in a-tin can also be deduced from electrical resistivity ~ which showed radiation damage annealing far below room temperature.
1030
DEFECT CASCADES AND POINT DEFECTS IN a-TIN
Vol. 17, No.8
Table 1. Isomer shift ~ relative to BaSnO, of the originala-tin line and the irradiation induced new line, quadrupole splitting AEQ andfraction F ofthe area of the new line to the total area of the MOssbauer spectrum. Irradiation: duration 68.9 hr, fast neutron dose (E> 0.1 Me V): 3.5 x 1018 n/cm2, sample temperature: 4.6 K. Mössbauer effect measurement: sample temperature 4.2 K, BaSnO, source temperature ~ 240K, PdSn absorber temperature ~ 140 K
Before irradiation, sample is absorber After irradiation at 4.6 K, sample is absorber After irradiation at 4.6 K, sample is source After 10 miii annealing at 274 K, sample is source or absorber
I
I
Original line
Irradiation induced new line ~IEQ
F
mm/sec
mm/sec
mm/sec
%
2.04 ±0.01
—
—
—
2.04 ±0.02
2.7
±0.1
0.4
±0.2
31
±5
2.05
2.67
±0.03
0.4 ±0.2
60
±10
±0.03
2.04 ±0.01
—
0
—
I
±5
I
F 10
~
0.95 b.ti~ton
40 20
V
/f” ~
-
...4”absorber
0.90 1.00
/
•
after irradiation
0
‘\
0
I
I
2 4 frradiatton time [days]
2. Dependence of the transmutation on irradiation induced component in the MOssbauer spectrum ation time. F is the fraction of the area of the irradito the total area of the snectrum Fast neutron flux (E>0.l MeV): 1.2 x l0~~ n/cm2sec. FIG.
0.97
0.94 -~
_
-~
0
.~
+ [~nmisecJ
FIG. 1. Spectra with the a-tin sample as source before and after a 68.9 hr irradiation at 4.6 K (fast neutron dose (E > 0.1 MeV): 3.5 x 10~n/cm2). Mössbauer effect measurement: sample temperature 4.2 K, PdSn absorber temperature ~ 140 K. The dashed curves show the a-tin component. In component order to refer andthethespectra irradiation to BaSnO induced 3 instead of PdSn as absorber 1.51 mm/sec have to be added to the velocity.
a-tin powder samples were produced by transformation of foils of 13-tin (chemical purity 99.98%, enriched 98% Sn”8 but containing enough Sn”9 nuclei to permit the use of the sample as Mossbauer absorber, too)1’ and checked by X-ray powder diffraction and Mossbauer absorber spectra. The isomer shift relative to BaSnO 3 was 2.04 ±0.01 mm/sec12inNo good residual agreement conwith the values from the literature. tamination with (3-tin could be detected. The samples were irradiated in aluminium holders at 4.6 K in helium atmosphere in the liquid helium neutron
Vol. 17, No.8
DEFECT CASCADES AND POINT DEFECTS IN a-TIN
irradiation facility of the Munich research reactor. The flux of thermal neutrons was 1.3 x 1013 neutrons/cm2 sec, of fast neutrons (E >0.1 MeV) 1.2 x 1013 neutrons/cm2 sec and the 7-ray flux 7 x io~rad/hr. After the end of the irradiation the MOssbauer spectra were measured without further warming up8 with the sample as Mossbauer absorber and as Mossbauer source as well. We used a BaSnO 3 source and a PdSn absorber with an additional palladium filter in order to reduce the tin X-ray background. The linewidth was 1.0 mm/sec and reached the theoretical value expected from effective source and absorber thicknesses. After the irradiation at 4.6°Ka line broadening and shifting appears in the source and in the absorber spectra which is interpreted as due to the appearance of an additional quadrupole split line at about 2.7 mm/sec relative to BaSnO, or 1.2 mm/sec relative to PdSn. In Table 1 the Mossbauer 2parameters for anare (E>0.1 MeV) irradiation n/cm summarizedwith and 3.5 Fig.x 11018 shows two of the spectra. An isochronal annealing program with 10 mm holding times was performed. The irradiation induced line disappeared completely in an annealing stage at 90— 160 K in the source spectra as well as in the absorber spectra. By comparing the irradiation time dependence of the fraction F of the area of the new line to the total area of the MOssbauer spectrum in the source and in the absorber spectra (Fig. 2) a striking difference was found. In the source spectra there is only a slight dependence ofF on irradiation time. Therefore we conclude that the new MOssbauer componentin the spectra is mainly due to defects locally correlated with the Mossbauer atoms. They must be caused by the 7-recoil from the Sn”8 (n, 9m reaction. 7)Snhihand there is a In the absorber spectra on the other nearly linear dependence of F on irradiation time. Here the new Mössbauer component must be due to statistically distributed irradiation defects (macroscopic or overall damage) increasing in number with increasing irradiation dose. This latter effect naturally contributes to F in the source spectra as well but gives a much smaller contribution than the correlated defects do up to the maximum irradiation doses of this work. Thus in one sample we can clearly distinguish between defects which are locally correlated with the probe atoms and statistically distributed defects.
1031
The isomer shift of the new line (2.7 ±0.1 mm/sec) is a little larger than that of (3-tin (2.56 mm/sec).” The quadrupole splitting of the new line (0.4 ±0.2 mrnfsec) contains a large uncertainty because of the unresolved spectrum, thus a comparison with the quadrupole splitting of tetragonal (3-tin (0.18 ±0.03 mm/sec at 80 K’8) can only show the principal agreement in the range of the error bars. First we shall discuss the. changes detected in the absorber spectra. It is well-known that fast neutrons generate highly energetic primary knock-on atoms, which in turn created great number of lattice defects in a disordered region, the so-called defect cascade, associated with a “thermal spike”. The most probable interpretation of the present results is a transmutation of a-tin in the defect cascades into a configuration similar to tetragonal tin (ft-tin). From the fraction of the sampleintransmuted (F corrected for theassuming slight difference the Debye—Waller factors”) a mean elastic cross section of 5 ±I barn for the elastic collisions of fast neutrons with tin atoms14 one can estimate a mean diameter of the transmuted regions of 110 ±15 A which each contain 2.2 ±0.6 x 1 o~atoms. We think it is interesting and surprising that a complete lattice transmutation might take place in regions of this size. Some more information about this transmutation may be obtained by comparing the isomer shift of the irradiation induced component with that found by Bolz and Pobell’5 for amorphous (3-tin with 10—20%
copper produced by quenched condensation. They measured an isomer shift of 2.75 ±0.02 mm/sec relative to BaSnO, similar to the value for our irradiation induced component (Table 1), corresponding to an increased s-electron density compared to crystalline (3-tin. The authors interprete this increase as due to p-to-s transfer of electrons in the formation of the amorphous state, since the tin atoms do not have the possibility to adjust themselves in the regular (3-tin lattice. The similarity of the isomer shifts of the amorphous state of tin and of the irradiation induced cornponent in our work both slightly larger than the isomer shift of (3-tin, favours the view that in the region of the defect cascades a highly disturbed quasi-amorphous (3-tin phase is formed.
It is tempting to attribute such a transmutation to the “temperature” increase (more exactly: the strong
1032
DEFECT CASCADES AND POINT DEFECTS IN a-TIN
increase of the atomic mobility and of the vibrational motion) in the defect cascades (the “thermal spikes”), (3-tin being the phase which is stable at higher temperatures (above 13.2°C).The “disturbed (3-tin phase” would then be stabilized by the sudden quench during the “cooling” of the “thermal spike” within about I0_12_10_ht sec.16 The thermal treatment between 90 and 160 Kenables defect migration leading to the retransformation to the a-tin phase which is the stable phase at these temperatures. It might be interesting to compare our results with those of Gonser and Okkerse’7 who found mdication for a transition to a “liquid-like” phase in irradiation damage cascades in GaSb. Secondly, the (it, ~)-effectshall be discussed. Myrha and Gardiner have reported a minimum displacement ener~’of 12 eV for a-tin.’0 With the mean value 50 eV of the (n, 7)-recoil energies after the Sn”8 (n, y) Snll9m reaction’8 the consequence of the (n, 7)-reaction can be understood, namely a possible displacement of the Sn 119ifl Mossbauer atom. Smce some recoils will have lower energies than 12 eV the fraction F is not 100%. •.
.
.
Vol. 17, No.8
From simple blilard ball arguments1’ one may conclude that focusing collisions are impossible in
the diamond lattice and that the recoiling atom should therefore probably stop at an interstitial site with possibly very few furtherpoint defects in its environmeut. The value of isomer shift and unresolved quadrupole splitting of the new line as produced by the (n, 7)-recoil in the source spectra resemble the values of the new line in the absorber spectra (compare Table 1). The agreement in the annealing behaviour of the irradiation induced componentIn source and absorber spectra indicates that for the retransformation of transmuted regions of irradiation damage cascades into a-tin and for the annealing of local (n, y) damage the migration of the same type of defect, probably an interstitial defect, might be responsible.
Acknowledgements WeMansel thank for Ursel Wagner forhelp much helpful advice, W. experimental —
and discussions and H. Vonach for his continuous supporting interest in this work.
REFERENCES 1. VOGLG.,/. Phys. Coil. C6 (supplement au Tome 35), 165 (1974). 2. CZJZEK G. & BERGER W.G.,Fhys. Rev. Bi, 957 (1970). 3. SIMOPOULOS A. & VOGL G., Phys. Status Solidi (b) 59, 505 (1973). 4. 5.
FRIEDT J.M. & VOGL W., Phys. Status Solidi (a) 24,265 (1974). An extended abstract of part of this work was contributed to the Int. Conf on the Applications of the Mössbauer Effect, Bendor, Sept. (1974); J. Phys. Coil. C6 (supplement au Tome 35), 297 (1974). 6. HAFEMEISTER D.W. & DE WAARD H.,Phys. Rev. B7, 3014 (1974). 7. 8. 9. 10. 11.
12. 13. 14. 15.
WEYER G., DEUTCH B.I., NYLANDSTED-LARSEN A., ANDERSEN J.U. & NIELSEN H.L.,J. Phys. Coil. C6 (supplement au Tome 35), 297 (1974); WEYER G., ANDERSEN J.U., DEUTCH B.!., GOLOVCHENKO J.A. & NYLANDSTED-LARSEN A.,Rad. Effects 24,117(1975). ROSNER P., VOGL W. & VOGL G., NucL Instrum. Methods 105,473(1972). GOLAND A.N.,J. Phys. Chem. Solids 16,46 (1960). MYRHA A. & GARDINER R.B., Phys. Lett. 39A, 405 (1972). VOGL W., Dissertation, Technische UniversitatMUnchen (1974). STEVENS 1G. & STEVENS V.E., Mossbauer Effect Data index, 1970, 1972, 1973. Adam Huger, London. GOLOVNIN V.A., IRKAEV S.M. & KUZMIN R.N.,Sov. Phys. JETP 32,372(1971). HUGHES D.J. & SCHWARTZ R.B.,Neutron Cross Sections, 2nd edn. BNL (1958). BOLZ J. & POBELL F., Z. Phys. B20, 95(1975).
Vol. 17, No.8 16. 17. 18.
DEFECT CASCADES AND POINT DEFECTS IN a-TIN
ThOMPSON M.W., Defects and Radiation Damage in MetaLs. Cambridge University Press (1969). GONSER V. & OKKERSE B., Phys. Rev. 109,663(1958). HANNAFORD P. & WIGNALL J.W.G.,Phys. Status Solidi 35, 809 (1969).
1033