Shock-induced transformation of β-Si3N4 to a high-pressure cubic-spinel phase

Article abstract of DOI:10.1063/1.126756

β-Si₃N₄ powders were shock compressed and quenched from 12 to 115 GPa. β-Si₃N₄ transforms to the spinel-type Si₃N₄ (c-Si₃N₄) by a fast reconstructive process at pressures above about 20 GPa. The yield of c-Si₃N₄ recovered from 50 GPa and about 2400 K reaches about 80% and the grain sizes are about 10-50 nm. It is proposed that the fast transformation to c-Si₃N₄ occurs by rearrangement of nitrogen stacking layers, which initiates partial breakup of the SiN₄ tetrahedra and formation of SiN₆ octahedra at high density. Because of the advantages of massive production and the nanometer characteristics of shock-synthesized c-Si₃N₄, it is possible to investigate the mechanical properties experimentally and to develop new industrial applications.

Full text of DOI:10.1063/1.126756

Shock-induced transformation of β- Si 3 N 4 to a high-pressure cubic-spinel phase
T. Sekine, Hongliang He, T. Kobayashi, Ming Zhang, and Fangfang Xu
Citation: Applied Physics Letters 76, 3706 (2000); doi: 10.1063/1.126756
View online: http://dx.doi.org/10.1063/1.126756
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APPLIED PHYSICS LETTERS
VOLUME 76, NUMBER 25
19 JUNE 2000
Shock-induced transformation of ␤-Si N to a high-pressure
3
4
cubic-spinel phase
T. Sekine,a) Hongliang He, T. Kobayashi, Ming Zhang, and Fangfang Xu
National Institute for Research in Inorganic Materials, Namiki 1-1, Tsukuba 305-0044, Japan
͑
Received 24 January 2000; accepted for publication 24 April 2000͒
-Si N powders were shock compressed and quenched from 12 to 115 GPa. ␤-Si N transforms
␤
3
4
3
4
to the spinel-type Si N (c-Si N ) by a fast reconstructive process at pressures above about 20 GPa.
3
4
3
4
The yield of c-Si N recovered from 50 GPa and about 2400 K reaches about 80% and the grain
3
4
sizes are about 10–50 nm. It is proposed that the fast transformation to c-Si N occurs by
3
4
rearrangement of nitrogen stacking layers, which initiates partial breakup of the SiN tetrahedra and
4
formation of SiN octahedra at high density. Because of the advantages of massive production and
6
the nanometer characteristics of shock-synthesized c-Si N , it is possible to investigate the
3
4
mechanical properties experimentally and to develop new industrial applications. © 2000
American Institute of Physics. ͓S0003-6951͑00͒02025-8͔
Silicon nitride is an advanced ceramic and has the po-
tential to be used in various applications due to good perfor-
mance in mechanical, chemical, electronic, and thermal
of the crystal density or pressed mixtures of ␤-Si N and
3 4
copper powders with 50%–80% of the theoretical density
were encapsulated in containers of platinum or copper. De-
tailed descriptions of the shock recovery experiments have
been published elsewhere.8
properties. This is due to highly covalent chemical bonding
1
͑
70% covalence͒. In addition to the two known polymorphs
of ␣-Si N and ␤-Si N , a third cubic form (c-Si N ) with a
Metal flyer plates such as steel and platinum impacted
samples in containers. The pressure generated in the sample
3
4
3
4
3
4
2
spinel structure has been found recently at pressures above
5 GPa and at temperatures over 2000 K, in several tens of
9
1
was calculated by the impedance match method using the
8
measured flyer velocity. The flyer velocities ranged between
nanograms, in a laser-heated diamond anvil cell for reaction
1
.5 and 2.1 km/s. The shock pressure varied from 12 to 115
times of about 1–10 min. This phase, c-Si N , is expected to
3
4
1
0
GPa, depending on the Hugoniot of the flyer material and
impact velocity, and the compression lasted about a micro-
second. The bulk temperature for each sample was computed
be a hard material because of its greater bulk modulus and
shear modulus than those of ␣-Si N and ␤-Si N ͑Ref. 2͒
3
4
3
4
and should also be a semiconductor due to its possible
smaller band gap induced by the characteristic structure of
1
1
by the thermodynamic method. We used the Birch–
Murnaghan equation12 and thermodynamic parameters for
13
3
octahedral silicon. Because of the highly covalent nature of
1
0
␤
-Si N and Hugoniot for copper powders to estimate the
3 4
Si–N bonding, the high-pressure behavior of ␣- and ␤-Si N
3
4
Hugoniot for mixtures. In our calculation the fusion energy
of copper is taken into account but the transformation energy
of ␤-Si N to c-Si N is not included due to lack of data.
is of great interest over a wide range of pressure and tem-
perature. Although the high-pressure behaviors of Si N have
3
4
4
,5
3
4
3
4
been studied at static high pressures and dynamic high
pressures, only the spinel-type high-pressure phase has
been observed experimentally as the high-pressure and high-
6
,7
After successful recovery, the container was cut open to
take out the sample. To remove the copper matrix nitric acid
was used at room temperature. The residue was collected
after washing repeatedly with water. The color of the re-
2
temperature phase. In this structure 2/3 of the silicon atoms
are octahedrally coordinated and 1/3 of the silicon atoms
remain tetrahedrally coordinated. It would be expected that
all silicons have octahedral coordinations with increasing
pressure, analogous to stishovite SiO2.
For synthesis of the high-pressure and high-temperature
form of Si N , we investigated the shock-induced transfor-
3
4
mation of ␤-Si N powders using a propellant gun, because
3
4
shock compression generates high-pressure and high-
temperature simultaneously. We used two starting ␤-Si N4
3
powders. The first one contained about 5 wt % ␣-Si N and
3
4
less than 1.9 wt % oxygen impurity and the second was pure
-Si N with 0.5 wt % oxygen and did not show the pres-
␤
3
4
ence of ␣-Si N in x-ray analysis ͓Fig. 1͑c͔͒. The grain sizes
3
4
of both ␤-Si N powders were in the submicron range. In the
3
4
experiments, either pressed ␤-Si N powder with 50%–60%
FIG. 1. XRD patterns of two recovered samples ͑a͒ from 49 GPa and 2400
K and ͑b͒ from 33 GPa and 1770 K and the starting material, pure ␤-Si N
3
4
3
4
͑
c͒. The peaks marked by c correspond to the cubic spinel-type Si N . The
3 4
a͒Electronic mail: sekine@nirim.go.jp
peak broadening is due to the fine grains.
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003-6951/2000/76(25)/3706/3/$17.00 3706 © 2000 American Institute of Physics
29.21.35.191 On: Fri, 19 Dec 2014 08:01:10
0
1

Appl. Phys. Lett., Vol. 76, No. 25, 19 June 2000
Sekine et al.
3707
TABLE I. XRD data of cubic spinel-type c-Si N . aϭ0.774 40
3
4
3
Ϯ0.001 06 nm, dϭ4.012 g/cm .
2
␪obs
dobs
dcal
hkl
͑deg͒
͑nm͒
I/I0
͑nm͒
Ical
1
2
3
4
4
5
4
6
5
4
6
7
8
7
8
11
20
11
00
22
11, 333
40
20
33
44
42
31, 553
00
19.80
32.74
38.49
46.82
58.26
62.33
68.39
77.88
81.56
87.01
97.42
99.71
105.38
119.20
125.74
0.448 02
0.273 63
0.233 70
0.193 88
0.158 24
0.148 85
0.137 06
0.122 56
0.117 93
0.111 89
0.102 52
0.100 77
0.096 85
0.089 31
0.086 55
11
27
100
35
10
33
56
4
11
5
5
21
11
16
12
0.447 17
0.273 84
0.233 53
0.193 63
0.158 10
0.149 06
0.136 92
0.122 46
0.118 12
0.111 79
0.103 50
0.100 84
0.096 816
0.089 435
0.086 595
10
27
100
35
10
34
57
4
11
5
5
19
10
15
12
FIG. 3. Microphotographs of TEM and electron nanodiffraction of shock-
51, 555
40
synthesized, nanometer grains of spinel-type Si N . The observed d values
3
4
are 0.273, 0.193, and 0.138 nm for diffractions ͑220͒, ͑400͒, and ͑440͒,
respectively.
sidual powder was gray, compared with the milky white of
-Si N . We used x-ray diffraction ͑XRD͒ ͑Rigaku RINT
Si and N, with the same ratio as the starting ␤-Si N , and
3
4
␤
detected a small amount of oxygen as a very weak shoulder
on the N peak.14 Therefore, the slight difference in the lattice
parameter is due to the low precision of the measurement by
3
4
2
3
200 V/pc͒ and analytical electron microscopy ͑TEM͒ ͑JEM
000F͒ equipped with energy dispersive x-ray spectroscopy
2
͑EDX͒ to investigate the structure and chemistry of the
electron diffraction. The grain sizes of c-Si N are 10–50
3
4
shock-recovered sample.
nm, which is about one tenth of the initial ␤-Si N , as shown
3
4
Figure 1 illustrates a comparison of typical XRD pat-
in Fig. 3 together with an electron nanodiffraction pattern
indicating the presence of a cubic, nanometer-size single
crystal.
terns of the starting ␤-Si N and two recovered samples
3
4
from mixtures with copper powders shock compressed at 33
GPa and 1770 K ͓Fig. 1͑b͔͒ and 49 GPa and 2400 K ͓Fig.
The minimum shock pressure required for the formation
of c-Si N from ␤-Si N is less than 20 GPa, but the yield
1͑a͔͒, respectively. In the recovered samples the peaks of
3
4
3
4
␤
-Si N become weaker with increasing shock pressure and
3
4
from the run at 19 GPa and about 3000 K was the smallest
that we could detect in the course of electron microscopy
observation. The change to c-Si N was not detected in
the newly appearing peaks correspond to the cubic spinel
structure. The yield of c-Si N reaches about 80%. Table I
3
4
3
4
lists XRD data of c-Si N produced from pure ␤-Si N , to-
3
4
3
4
samples subjected to shock temperatures of 1270 K at a pres-
sure of 21 GPa, indicating the presence of a threshold mini-
mum temperature. Too high a temperature causes decompo-
sition and/or melting of Si N . In the case of samples of
gether with the calculation results of the Rietveld method.
The lattice parameter of c-Si N is 0.774 40Ϯ0.001 06 nm
3
4
3
and the calculated density is 4.012 g/cm , which is 26%
3
4
denser than that of ␤-Si N . The XRD measured lattice pa-
3
4
␤-Si N powders, the platinum container was broken and all
3 4
rameter of c-Si N is slightly ͑0.7%͒ smaller than the value
3
4
the samples were exploded out above 80 GPa. This indicates
that Si N decomposed to Si and N during shock compres-
2
(
0.780Ϯ0.003 nm) measured by electron diffraction and the
3
4
2
3
result ͑0.783 67 nm͒ calculated by first principles. As shown
in Fig. 2, EDX analyses of c-Si N showed the presence of
sion, or during the adiabatic release process after shock com-
pression, because of the higher temperatures. Even in the
presence of copper in the mixture, the containers of highly
porous samples were blown out when the calculated shock
3
4
temperature was higher than 3000 K at 50 GPa. The ␣-Si N4
3
phase, coexisting in one of our starting ␤-Si N powders,
3
4
survived under shock conditions where most of the ␤-Si N4
3
transformed to c-Si N , suggesting that ␣-Si N has a higher
3
4
3
4
activation barrier for phase transformation. The higher acti-
vation energy for the transformation of ␣-Si N to c-Si N
3
4
3
4
has also been demonstrated by the survival of ␣-Si N after
3
4
being subjected to pressures of 37 GPa and temperatures of
3
700 K in the diamond anvil cell.5
Compared with the duration of static high pressure
2
work, the present shock wave study has verified that the
transformation to c-Si N phase occurs within a microsec-
3
4
ond. This suggests that a fast and probably diffusionless
mechanism has played an important role. A fast phase trans-
FIG. 2. EDX spectrum of shock-synthesized cubic spinel-type Si N . Only
N and Si are observed and a very weak shoulder can be seen due to oxygen
3
4
formation of ␤-Si N to c-Si N , through a solid–solid re-
͑0.5 keV͒ near the N peak. High backgrounds near 1 and 4.5 keV corre-
3
4
3
4
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spond to Cu and Ti impurities, respectively.
action, can be explained in terms of the anisotropic compres-
1
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3708
Appl. Phys. Lett., Vol. 76, No. 25, 19 June 2000
Sekine et al.
1
sion of SiN4 tetrahedra in ␤-Si N . In ␤-Si N , the
yet, although the phases as a possible hard material have
been predicted theoretically.1 In this sense the transforma-
tion to the high-pressure cubic spinel form of Si N can be
3
4
3
4
7,18
structure units consist of slightly distorted tetrahedral SiN
sp hybridization of Si͒ and planar NSi (sp hybridization
4
3
3
(
3
3
4
of N͒. Tetrahedra SiN are linked by sharing nitrogen corners
used as a guide for making C N .
4
3 4
so that each nitrogen is common to three tetrahedrons. The
puckered rings of alternating Si and N atoms have a stacking
sequence of ABAB...and form channels ͑diameter about 0.15
nm͒ along the c direction. The lattice parameters are a
ϭ0.2911 nm and cϭ0.7595 nm and the density is 3.19
This research was carried out in the COE project in
NIRIM while H. L. He, M. Zhang, and F. F. Xu were sup-
ported as STA fellows. The Rietveld analysis was carried out
by Dr. F. Izumi and Dr. T. Ikeda. The ␤-Si N starting ma-
terials were kindly provided by Dr. M. Mitomo and Dr. G.
D. Zhan. The authors wish to thank Dr. James Hester for
improving the manuscript.
3
4
3
g/cm . On the other hand, in the spinel structure tetrahedral
SiN and octahedral SiN are the basic units. The N atoms
4
6
are cubic close packed in a stacking sequence ABCABC... .
The SiN tetrahedron is linked to the SiN octahedra by shar-
4
6
1
W. Dressler and R. Riedel, Int. J. Refract. Met. Hard Mater. 15, 13 ͑1997͒.
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2
6
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4
3
4
4
distorted, and only the longest bond in the SiN tetrahedron
4
1803 ͑1966͒; Y. M. Li, M. B. Kruger, J. H. Nguyen, W. A. Caldwell, and
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1
6
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2
2
3
4
2
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6
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3
4
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tion number of 2/3 of the Si atoms increases from 4 to 6. As
a result, this transformation involves a change of stacking
sequence of N layers from ABAB...to ABCABC... .
7
8
9
The shock compression technique has verified a fast
transformation of ␤-Si N to c-Si N , a spinel-type high-
3
4
3
4
10
pressure phase. This implies that the shock compression
technique could be useful for synthesizing a high-pressure
c-C N phase and other related materials such as a spinel
11
3
4
12
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3
4
3
4
shock synthesis of diamond in industry, it has been thought
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compression for material synthesis. For example, higher
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13
14
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2
3
4
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2
3
spinel solid solution.15 Our sample contains only a little oxygen, which
does not affect the lattice parameter significantly. The lattice parameter of
c-Si N produced from ␤-Si N with 1.9 wt % oxygen is measured to be
3
in each synthesis. Therefore, shock-synthesized c-Si N4
3
4
3
4
could become an important industrial material. The shock
0
.775 05Ϯ0.000 69 nm.
1
1
5
6
synthesis of high-pressure Si N has important implications
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3
4
for making hypothetical, hard materials of ␤-C N with the
3
4
1
7
␤
-Si N structure and cubic C N with the structure of
high-pressure Zn SiO4 ͑willemite II͒. The presence of
3 4 3 4
17
1
8
2
1
8
stable C N forms has not been confirmed experimentally
D. M. Teter and R. J. Hemley, Science 271, 53 ͑1996͒.
3
4
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