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Anisotropic growth of aluminium nitride under neutron irradiation
JOURNAL
OF NUCLEAR
LETTERS ANISOTROPIC
29 (1969)
MATERIALS
TO THE
GROWTH
121-122.
EDITORS
-
OF ALUMINIUM
Division,
A.A.E.C.
Research
Received
LETTRES
NITRIDE
B. S. HICKMAN* Materials
0 NORTH-HOLLAND
PUBLISHINU
AUX
UNDER
CO., AMSTERDAM
REDACTEURS NEUTRON
IRRADIATION
and A. JOSTSONS Establishment,
15 August
Sutherland,
N.S. W.,
Australia
1968
The anisotropic lattice growth in beryllium oxide under neutron irradiation has been the subject of considerable study and speculation because of the potential technological impor-
a number of structurally related oxides has been studied in this laboratory. Zinc oxide has
tance of the material and because of the detrimental effect this growth has on the properties of polycrystalline material 1). However, no satisfactory explanation of the phenomenon exists. Explanations in terms of anisotropic elastic distortions arising from the planar defect clusters, which are known to exist parallel to the basal plane I), run into difficulty because of the different annealing behaviour of the anisotropic growth and the planar defect clusters 3). It has been suggested 3) that the effect is associated with the formation of domains of a second phase, but no direct evidence has been found for the presence of a sufficient quantity
manner 4) ; basal plane clusters are formed and the lattice growth is anisotropic. On the other hand, aluminium oxide which has the same hexagonal oxygen sub-lattice as the wurtzite structure, expands in an essentially isotropic manner 5). Chrysoberyl (Al3O3. BeO), which also has essentially the same oxygen lattice expands anisotropically 3) but to a much lesser degree than in Be0 and ZnO. In this note we report
the same wurtzite structure as beryllium oxide and has been shown to behave in a similar
results on a third wurtzite type material, aluminium nitride. Single crystal whiskers of aluminium nitride, approximately 0.5 mm in diameter by 20-30 mm long, obtained from Semi Elements Inc., were neutron irradiated to a range of fast neutron doses at 75-100 “C in the reactor HIFAR.
of these domains to give the observed effect. In view of the uncertainty regarding the mechanism of anisotropic growth in beryllium oxide the growth
under neutron
irradiation
Lattice parameters were measured using a Bond spectrometer 7). The results in table 1 show that the lattice growth is again highly anisotropic,
of
TABLE 1 Lattice
growth of almmm ’ ‘um nitride under neutron
Neutron nvt
*
Present
irradiation
dose
(> 1 MeV)
Aala
(%)
at 75 to 100 “C
Av/v (%) (from X-ray data)
AC/C (%)
3.8 x 10’9
0.126 & 0.003
0.202 & 0.004
0.454 f
0.010
6.8 x 10’S
0.177 If: 0.004
0.277 & 0.003
0.631 f
0.011
1.3 x 1020
0.176 -& 0.004
0.423 & 0.004
0.775 *
0.012
2.1 x 1020
0.203 + 0.004
0.614 + 0.005
1.020 *
0.013
2.8 x 1020
0.193 & 0.003
0.747 & 0.005
1.133 f
0.011
3.7 x 1020
0.185 f
0.864 & 0.005
1.234 f
0.017
address:
Science Center/North
0.006
/
American 121
Rockwell
Corporation,
Thousand
Oaks,
California.
122 although
B.
S.
the degree of anisotropy
HICKMAN
AND
is less than
that in BeO. As with both Be0 and ZnO, the a-parameter change saturates at a low dose. Examination
of the data suggests
is a tendency
towards saturation
meter change at the higher doses. The material did exhibit a major to both beryllium
that there
of the c-para-
A.
JOSTSONS
similarity of the reciprocal lattice streaking to that in Be0 suggests that these clusters are of similar form, i.e., interstitial
those previously difference
oxide and zinc oxide in that
up to a dose of 2.8 x lo20 nvt (> 1 MeV), the X-ray reflections remained sharp. Reciprocal lattice photography using a precession camera showed no evidence for reciprocal lattice streaking at this dose although very weak diffuse streaks in the C * direction through (100) reflections in (HOL) projections were detected after long exposures (170 h with filtered MoK, radiation) of specimens irradiated to 3.7 x 1020 nvt. Transmission electron microscopy on flakes obtained by crushing the irradiated crystals showed evidence of cluster formation in specimens irradiated to 2.8 x lo20 nvt and 3.7 x lo20 nvt. The number of defect clusters, observed as “black dots” in images of (0002) reflections, increased with dose. The observation of “black images in irradiated flakes and the dot”
plates parallel
to the basal plane. The similarity of the present observations materials vations
to
reported for the other wurtzite
and the limited
extent of the obser-
do not permit any further speculation
regarding
the nature
of the mechanisms
ponsible for the anisotropic growth materials on neutron irradiation.
re-
in these
Useful discussions with T. M. Sabine D. G. Walker are acknowledged.
and
References 1)
B. S. Hickman, Studies in radiation effects, series A, 1 (1967) 77 2) D. G. Walker, J. Nuol. Mat. 15 (1965) 111
3)
J. M. Cowley,
4)
B.
5)
18 (1966) 6) A.
Cryst.
21 (1966)
192
W.
197
Jo&sons and B. S. Hickman, J. Nucl. Mat.
25 (1968) 7)
Acta
Hickman, J. Nucl. Mat. 17 (1965) 270 B. S. Hickman and D. G. Walker, J. Nucl. Mat’. S.
278
L. Bond,
Acta
Cryst.
13 (1960)
814
OF NUCLEAR
LETTERS ANISOTROPIC
29 (1969)
MATERIALS
TO THE
GROWTH
121-122.
EDITORS
-
OF ALUMINIUM
Division,
A.A.E.C.
Research
Received
LETTRES
NITRIDE
B. S. HICKMAN* Materials
0 NORTH-HOLLAND
PUBLISHINU
AUX
UNDER
CO., AMSTERDAM
REDACTEURS NEUTRON
IRRADIATION
and A. JOSTSONS Establishment,
15 August
Sutherland,
N.S. W.,
Australia
1968
The anisotropic lattice growth in beryllium oxide under neutron irradiation has been the subject of considerable study and speculation because of the potential technological impor-
a number of structurally related oxides has been studied in this laboratory. Zinc oxide has
tance of the material and because of the detrimental effect this growth has on the properties of polycrystalline material 1). However, no satisfactory explanation of the phenomenon exists. Explanations in terms of anisotropic elastic distortions arising from the planar defect clusters, which are known to exist parallel to the basal plane I), run into difficulty because of the different annealing behaviour of the anisotropic growth and the planar defect clusters 3). It has been suggested 3) that the effect is associated with the formation of domains of a second phase, but no direct evidence has been found for the presence of a sufficient quantity
manner 4) ; basal plane clusters are formed and the lattice growth is anisotropic. On the other hand, aluminium oxide which has the same hexagonal oxygen sub-lattice as the wurtzite structure, expands in an essentially isotropic manner 5). Chrysoberyl (Al3O3. BeO), which also has essentially the same oxygen lattice expands anisotropically 3) but to a much lesser degree than in Be0 and ZnO. In this note we report
the same wurtzite structure as beryllium oxide and has been shown to behave in a similar
results on a third wurtzite type material, aluminium nitride. Single crystal whiskers of aluminium nitride, approximately 0.5 mm in diameter by 20-30 mm long, obtained from Semi Elements Inc., were neutron irradiated to a range of fast neutron doses at 75-100 “C in the reactor HIFAR.
of these domains to give the observed effect. In view of the uncertainty regarding the mechanism of anisotropic growth in beryllium oxide the growth
under neutron
irradiation
Lattice parameters were measured using a Bond spectrometer 7). The results in table 1 show that the lattice growth is again highly anisotropic,
of
TABLE 1 Lattice
growth of almmm ’ ‘um nitride under neutron
Neutron nvt
*
Present
irradiation
dose
(> 1 MeV)
Aala
(%)
at 75 to 100 “C
Av/v (%) (from X-ray data)
AC/C (%)
3.8 x 10’9
0.126 & 0.003
0.202 & 0.004
0.454 f
0.010
6.8 x 10’S
0.177 If: 0.004
0.277 & 0.003
0.631 f
0.011
1.3 x 1020
0.176 -& 0.004
0.423 & 0.004
0.775 *
0.012
2.1 x 1020
0.203 + 0.004
0.614 + 0.005
1.020 *
0.013
2.8 x 1020
0.193 & 0.003
0.747 & 0.005
1.133 f
0.011
3.7 x 1020
0.185 f
0.864 & 0.005
1.234 f
0.017
address:
Science Center/North
0.006
/
American 121
Rockwell
Corporation,
Thousand
Oaks,
California.
122 although
B.
S.
the degree of anisotropy
HICKMAN
AND
is less than
that in BeO. As with both Be0 and ZnO, the a-parameter change saturates at a low dose. Examination
of the data suggests
is a tendency
towards saturation
meter change at the higher doses. The material did exhibit a major to both beryllium
that there
of the c-para-
A.
JOSTSONS
similarity of the reciprocal lattice streaking to that in Be0 suggests that these clusters are of similar form, i.e., interstitial
those previously difference
oxide and zinc oxide in that
up to a dose of 2.8 x lo20 nvt (> 1 MeV), the X-ray reflections remained sharp. Reciprocal lattice photography using a precession camera showed no evidence for reciprocal lattice streaking at this dose although very weak diffuse streaks in the C * direction through (100) reflections in (HOL) projections were detected after long exposures (170 h with filtered MoK, radiation) of specimens irradiated to 3.7 x 1020 nvt. Transmission electron microscopy on flakes obtained by crushing the irradiated crystals showed evidence of cluster formation in specimens irradiated to 2.8 x lo20 nvt and 3.7 x lo20 nvt. The number of defect clusters, observed as “black dots” in images of (0002) reflections, increased with dose. The observation of “black images in irradiated flakes and the dot”
plates parallel
to the basal plane. The similarity of the present observations materials vations
to
reported for the other wurtzite
and the limited
extent of the obser-
do not permit any further speculation
regarding
the nature
of the mechanisms
ponsible for the anisotropic growth materials on neutron irradiation.
re-
in these
Useful discussions with T. M. Sabine D. G. Walker are acknowledged.
and
References 1)
B. S. Hickman, Studies in radiation effects, series A, 1 (1967) 77 2) D. G. Walker, J. Nuol. Mat. 15 (1965) 111
3)
J. M. Cowley,
4)
B.
5)
18 (1966) 6) A.
Cryst.
21 (1966)
192
W.
197
Jo&sons and B. S. Hickman, J. Nucl. Mat.
25 (1968) 7)
Acta
Hickman, J. Nucl. Mat. 17 (1965) 270 B. S. Hickman and D. G. Walker, J. Nucl. Mat’. S.
278
L. Bond,
Acta
Cryst.
13 (1960)
814