Full text of DOI:10.1557/JMR.2002.0341

Effects of heat treatment and sintering additives
on thermal conductivity and electrical resistivity
in fine-grained SiC ceramics
Guo-Dong Zhana)
Department of Chemical Engineering and Materials Science, University of California,
Davis, California 95616
Mamoru Mitomo
National Institute for Materials Science, Namiki 1-1, Tsukuba-shi, Ibaraki 305, Japan
Amiya K. Mukherjee
Department of Chemical Engineering and Materials Science, University of California,
Davis, California 95616
(Received 4 December 2001; accepted 12 June 2002)
The effects of heat treatment and sintering additives on the thermal conductivity and
electrical resistivity of fine-grained SiC materials were investigated. The thermal
conductivity and the electrical resistivity of dense SiC materials were measured at
room temperature by a laser flash technique and a current-voltage method,
respectively. The results indicated that the thermal conductivity and electrical
resistivity of the SiC materials were dependent on the sintering additives and the
resultant microstructure. Annealed materials with oxide additives developed
microstructures consisting of elongated grains of various ␣/␤–SiC polytypes. In
contrast, annealed materials with oxynitride additives had microstructures consisting of
fine equiaxed grains entirely of ␤–SiC phase. For the annealed materials with oxide
additives the observed thermal conductivity was over 110 W/mK. For the annealed
materials with oxynitride additives the observed value was 47 W/mK. The electrical
resistivity of a hot-pressed material with oxide sintering additives decreased after
annealing. For annealed materials with oxynitride additives, the electrical resistivity
was even lower. High-resolution electron microscopy revealed a thin amorphous phase
along the grain boundaries. Energy dispersive x-ray spectroscopy results showed that
there was segregation of both Al and O atoms and a very small amount of Y atoms at
grain boundaries. The results indicated that the chemistry and structure of the grain
boundary has significant influence on thermal and electrical properties in SiC.
close to that of silicon (3 × 10−6/°C), SiC is an almost
I. INTRODUCTION
ideal candidate for the substrate material in Si semicon-
ductors. However, SiC is usually a semiconductor and
lacks sufficiently high electrical resistivity for some ap-
plications. A thermal conductivity of 490 W/mK5 has
been reported for a high-purity single crystal. Also, a
thermal conductivity of 270 W/mK and electrical resis-
tivity of over 103 ⍀ cm at room temperature9,10 have
been reported for a polycrystalline SiC doped with BeO.
However, environmental concerns regarding the use
of toxic beryllium have prompted the investigation of
alternative doping agents to achieve high thermal con-
ductivity. For example, the thermal conductivity of a
vapor-deposited SiC material was enhanced by boron
doping and improved even further by subsequent anneal-
ing treatment.13 Thermal conductivities of up to 235 and
90 W/mK were observed for a material with 0.15 wt%
Silicon carbide (SiC) is an important structural mate-
rial due to its excellent chemical stability, wear resis-
tance, and high-temperature mechanical properties.1–4 It
also is a potential electronic material.5–8 The develop-
ment of low-cost, high-quality, single-crystal SiC sub-
strates has been pursued since the first Lely (nonseeded
growth process) platelets were used to make devices.7
Recently, the development of polycrystalline SiC for
electronic device applications has been a subject of in-
tense research.9–16 As it has high thermal conductivity10
and a thermal expansion coefficient (4 × 10−6/°C) that is
a)Address all correspondence to this author.
e-mail: gzhan@uedavis.edu
J. Mater. Res., Vol. 17, No. 9, Sep 2002
© 2002 Materials Research Society
2327
http://journals.cambridge.org
Downloaded: 14 Mar 2015
IP address: 130.102.42.98

G-D. Zhan et al.: Effects of heat treatment and sintering additives on therm. cond. and elec. resist. in fine-grained SiC ceramics
Al2O3 and a material with Al2O3 and Y2O3 additives,
respectively.14,15 The electrical resistivity of these mate-
rials was not reported.
oxide glass modifies the physical properties by increas-
ing softening temperatures, elastic modulus, and the
hardness of the glasses.21,22 Accordingly, Y–Mg–Si–Al–
O–N (G1) and Y–Al–Si–O–N (G2) oxynitride glasses,
which have appreciable SiC solubility, were selected as
the grain-boundary phases. To directly compare the ef-
fects of the oxide or oxynitride additives on the thermal
and electrical properties, the total additive amounts were
kept the same (10 wt%).
More recently, we have reported that liquid-phase-
sintered SiC with rare-earth additives exhibits desirable
thermal and electrical properties for an electronic sub-
strate application.17 In the present study, oxide and oxy-
nitride additives were used to enhance densification of
fine-grained SiC. A seeding technique and annealing
treatment were used to control grain growth.18–20 The
thermal and electrical properties of these materials meas-
ured at room temperature are reported here. High-
resolution electron microscopy (HREM) and energy
dispersive x-ray spectroscopy (EDS) were used to exam-
ine the state and compositions at the grain boundaries
and within the grains. The electrical and thermal proper-
ties were analyzed in terms of the geometry and chem-
istry of the microstructure and grain boundaries.
For the oxide additives, either 2.7 wt% coarse ␣–SiC
powder (A-1 grade, 0.45 ␮m, Showa Denko, Tokyo, Ja-
pan) or ␤–SiC powder (B-1, grade, 0.43 ␮m, Showa
Denko, Tokyo, Japan) was added as a nuclei for grain
growth, which corresponds to 3.0 wt% SiC powder. The
ultrafine SiC powder was eventually blended with
10 wt% of these sintering additives. The powder mixture
was dried and hot pressed at 1750 °C for 40 min under a
pressure of 25 MPa in Ar atmosphere for the mixture
with oxide additives and in N2 atmosphere for the mix-
ture with oxynitride additives. The hot-pressed materials
were further annealed at different temperatures and for
different times. The processing conditions and the result-
ing densities of the hot-pressed and annealed materials
are given in Table I. The chemical vapor deposition sili-
con carbide (CVD-SiC) with ␤-phase polycrystalline and
thermal expansion coefficient of 4.5 × 10−6/°C was pre-
pared in reactant gases of SiC14 and CH4. The total im-
purities were less than 1 ppm, including Cu < 100 ppb,
K < 60 ppb, Cr ס 26 ppb, Mo < 40 ppb, and
Fe ס 35 ppb. The bending strength, Vickers hardness,
and Young’s modulus were 784 MPa, 34.3 GPa, and
490 GPa, respectively.
The density of the hot-pressed and annealed materials
was determined by the Archimedes method using dis-
tilled water as an immersion medium. The materials were
cut, polished, and then etched by a plasma of CF4 con-
taining 7.8% O2. The microstructures were observed by
scanning electron microscopy (SEM). Note that the ob-
served surfaces for all materials were perpendicular to
the hot-pressing direction. SEM micrographs were ana-
lyzed using image analysis (Model Luzex III, Nireco
Co., Tokyo, Japan) to determine grain size and aspect
ratio (R95).23 X-ray diffraction (XRD) patterns were
II. EXPERIMENTAL
The starting material was an ultrafine ␤–SiC powder
with an average particle size of 90 nm (Sumitomo-Osaka
Cement Co., Tokyo, Japan). Oxide and oxynitride addi-
tives were used. The oxide additive was a mixture of
7 wt% Al2O3 (99.9% pure, Sumitomo Chemical Co.,
Tokyo, Japan), 2 wt% Y2O3 (99.9% pure, Shin-Etsu
Chemical Co., Tokyo, Japan), and 1.785 wt% CaCO3
(high-purity grade, Wako Chemical Co., Osaka, Japan)
that decomposes to 1 wt% CaO at high temperature. The
oxynitride additive was a mixture of 42 wt% SiO2 (re-
agent grade, Kanto Chemical Co., Tokyo, Japan),
10.9 wt% MgO (high-purity grade, Wako pure Chemical
Industries, Ltd., Osaka, Japan), 23.7 wt% Y2O3 (99.9%
pure, Shin-Etsu Chemical Co., Tokyo, Japan), 13.0 wt%
Al2O3, and 10.4 wt% AlN (Grade F, Tokuyama Soda
Co., Tokyo, Japan) powders. The oxynitride composition
of Y0.124 Mg0.160 Si0.414 Al0.302 O1.4 N0.151, designated
as G1, was prepared by ball milling in hexane for 3 h
using SiC media and a SiC container. A second mixture
of 36.9 wt% Y2O3, 55.8 wt% Al2O3 and 7.3 wt% AlN
powders was designated as G2. For the case of oxynitride
additives, the incorporation of nitrogen atoms into the
TABLE I. Sintering additives, processing conditions, and densities of fine-grained SiC ceramics.
Materials
Additives
Processing conditions
HP: 1750 °C/40min
HP: 1750 °C/40min + HT: 1850 °C/4h
HP: 1750 °C/40min + HT: 1850 °C/4h
HP: 1750 °C/40min + HT: 2000 °C/3h
HP: 1750 °C/40min + HT: 2000 °C/3h
Chemical vapor deposition
Density (g/cm3)
SC0
SC1
SC2
SC3
SC4
CVD-SiC
Oxide additives + ␣–SiC seeds
Oxide additives + ␣–SiC seeds
Oxide additives + ␤–SiC seeds
Oxynitride additives, G1
Oxynitride additives, G2
Reactant gases: SiC14 and CH4
3.21
3.19
3.18
3.17
3.21
3.21
HP: hot-pressing; HT: heat treatment.
2328
J. Mater. Res., Vol. 17, No. 9, Sep 2002
http://journals.cambridge.org
Downloaded: 14 Mar 2015
IP address: 130.102.42.98

G-D. Zhan et al.: Effects of heat treatment and sintering additives on therm. cond. and elec. resist. in fine-grained SiC ceramics
made from finely ground samples. Volume fractions for
each SiC polytype were calculated from the relative in-
tensities of certain peaks.24,25
painting on a silver paste. To eliminate any surface cur-
rent effect, a guard ring was also formed around the
upper side electrode.
Disks used for diffusivity measurements were ma-
chined such that their diameters were 10 mm and their
thickness approximately 2 mm. The disks were polished
to uniform thickness across the sample. In each case, the
disks were fabricated so the direction of heat flow would
be parallel to the hot-pressing axis. Thermal diffusivity
was measured at room temperature using the laser flash
technique (Model TC-3000, ULVAC, Yokohama, Japan)
after specimens were coated with a layer of carbon black
to enhance the absorption of the laser beam on the front
side. Thereby the sample front side was heated by a short
laser pulse. The heat absorbed was transported by ther-
mal diffusion processes described by Fourier’s equation
to the sample’s rearside. There the temperature rise was
recorded for the determination of thermal diffusivity. The
specific heat was also measured with same apparatus by
pulsed-laser flash. The relative value was determined
by using a comparative method (JIS R1611, Japanese
standard for measuring thermal conductivity). Thus, the
thermal conductivity ␬ was determined according to
the following equation:
Microstructural analysis of the SC1 material was per-
formed using transmission electron microscopy (TEM;
Topcon 002BF, Tokyo, Japan) and EDS. A thin foil was
prepared for TEM by the standard procedures of grind-
ing, dimpling, and argon-ion-beam thinning. The nano-
structure of grain boundaries was examined by HREM
using a microscope with a point-point resolution of
0.18 nm at 200 kV. The elemental composition of grain
boundaries was analyzed by EDS (Noran Voyager in
the Topcon microscope with a probe size <0.5 nm). All
EDS analysis were performed using the same effective
counting time.
III. RESULTS
The SiC compositions doped with 7 wt% Al2O3,
2 wt% Y2O3, and 1 wt% CaO were hot pressed to den-
sities >98% of theoretical density without difficulty at
1750 °C. The microstructure of the hot-pressed material
[SC0, Fig. 1(a)] consisted of relatively fine equiaxed
grains with an average diameter of 110 nm and an aspect
ratio of 1.8. In the annealed material with ␣–SiC seeds
doped with 7 wt% Al2O3, 2 wt% Y2O3, and 1 wt% CaO
[SC1, Fig. 1(b)], the microstructure consisted entirely of
elongated SiC grains with a diameter of 920 nm and an
aspect ratio of 5.2. In contrast, the microstructure of the
annealed SiC material with ␤–SiC seeds [SC2, Fig. 1(c)]
consisted of 60 vol% of fine matrix grains with a diam-
eter of 750 nm and an aspect ratio of 3.5 and 40 vol% of
␬ ס ␳Cp␣
,
(1)
where ␳ is density, Cp is heat capacity, and ␣ is thermal
diffusivity of the solid.
The specimens used for the electrical resistivity meas-
urements were the same specimens used for the
measurements of thermal diffusivity. Electrodes were
formed on the upper and lower sides of the disks by
FIG. 1. SEM micrographs of polished and plasma etched specimens of (a) as-hot-pressed material, SC0; (b) annealed material with ␣-seeds, SC1;
(c) annealed material with ␤-seeds, SC2; and (d) annealed material with G1, SC3.
J. Mater. Res., Vol. 17, No. 9, Sep 2002
2329
http://journals.cambridge.org
Downloaded: 14 Mar 2015
IP address: 130.102.42.98

G-D. Zhan et al.: Effects of heat treatment and sintering additives on therm. cond. and elec. resist. in fine-grained SiC ceramics
large elongated grains with a diameter of 2.1 ␮m and an
aspect ratio of 6.4. The SiC ceramics with the 10 wt%
oxynitride additives of either G1 [SC3, Fig. 1(d)] or G2
(SC4) exhibited microstructures similar to each other
consisting of fine SiC grains with d ∼ 500 nm. Phase
analysis showed that the annealed materials with ␣-seeds
doped with oxide additives consisted of 57 vol% ␤–SiC
and 43 vol% ␣–SiC, whereas the annealed materials
with ␤–SiC doped oxide additives consisted of 75 vol%
␤–SiC and 25 vol% ␣–SiC. Moreover, the majority of
the annealed material with ␣–SiC seeds was 6H, while
4H was the majority in the annealed material with ␤–SiC
seeds. In contrast, no phase transformation occurred in
the annealed materials with oxynitride additives (SC3
and SC4) due to the fact that oxynitride glass increases
the stability region of ␤–SiC and suppresses ␤ to ␣ trans-
formation in a nitrogen atmosphere.26 Detailed data
concerning the microstructural parameters and phase
compositions are given in Table II.
The measured room-temperature thermal diffusivity
and heat capacity and the calculated thermal conduc-
tivity of the SiC ceramics are shown in Table III. In
comparison to the hot-pressed material, the thermal dif-
fusivity greatly increased in the annealed materials with
␣ and ␤ seeds doped with oxide additives. The thermal
diffusivity of the annealed materials with oxynitride ad-
ditives is less than that of the materials with oxide addi-
tives. The heat capacity was slightly higher for the
materials with oxide additives than those with oxynitride
additives. The thermal conductivity of the materials with
oxide additives (>110 W/mK) was far higher than that of
the materials with oxynitride additives (47 W/mK). A
maximum value of 115 W/mK for thermal conductivity
was obtained for the material with ␤ seeds doped with
oxide additives. This value is similar to that reported for
sintered SiC in Ref. 27. As shown in Table III, the CVD-
SiC exhibited higher thermal conductivity (132 W/mK)
than that of the present polycrystalline SiC systems. This
value is higher than the report on CVD-SiC in Ref. 28 but
lower than the report on CVD-SiC in Ref. 29.
As shown in Table III, these materials exhibited rela-
tively higher electrical resistivity (>105 ⍀ cm). This is
consistent with the report on hot-pressing SiC.28 More-
over, electrical resistivity of the material doped with ox-
ide additives was at least one order of magnitude higher
than that of the material doped with oxynitride additives.
However, the electrical resistivity of the hot-pressed ma-
terial was far higher than that of the materials with oxide
and oxynitride additives, even though thermal conduc-
tivity was the lowest. On the other hand, it is very inter-
esting to note that the present CVD-SiC exhibited an
extremely high electrical resistivity (up to 109 ⍀ cm) that
is different from other CVD-SiC.29,30
Figure 2 is a TEM showing a representative micro-
structure for the annealed material with ␣ seeds in which
the elongation of the SiC grains is clearly visible. Amor-
phous grain boundary films were observed for the an-
nealed material with ␣ seeds by HREM, as shown in
Fig. 3. All observed films appeared to be 1 nm thick.
EDS was conducted to examine the chemical composi-
tion along and near the grain boundaries for the material
SC1, with measurements taken from at least five inter-
faces. EDS spectra were obtained across the grain bound-
ary at every 2 nm along the array of asterisks indicated
TABLE II. Polytypes and microstructural parameters of fine-grained
SiC ceramics.
Polytypes (vol%)
Microstructural parameters
Materials
3C
6H
4H
d (␮m)
R95
SC0
SC1
SC2
SC3
SC4
93
57
75
100
100
0
40
5
0
0
7
3
20
0
0.11
1.8
5.2
6.4
1.8
2.0
0.92
2.10a
0.408
0.510
0
d is the average grain size; R95 is the aspect ratio.
abimodal distribution, large grain only.
TABLE III. Measured thermal properties and electrical properties for
SiC ceramics.
Thermal properties
Thermal Thermal
capacity diffusivity conductivity
Electrical properties
Heat
Materials Cp (J/gK) ␣ (cm2/s)
Electrical
resistivity
␳ (⍀ cm)
v
␬ (W/mK)
SC0
SC1
SC2
SC3
SC4
CVD-SiC
0.76
0.74
0.75
0.71
0.73
0.89
0.13
0.45
0.48
0.21
0.20
0.49
32
106
115
47
47
132
1.8 × 108
иии
2.2 × 106
иии
1.1 × 105
1.2 × 109
FIG. 2. A representative microstructure by TEM of the annealed ma-
terial with ␣-seeds (SC1), showing elongation of the SiC grains.
2330
J. Mater. Res., Vol. 17, No. 9, Sep 2002
http://journals.cambridge.org
Downloaded: 14 Mar 2015
IP address: 130.102.42.98

G-D. Zhan et al.: Effects of heat treatment and sintering additives on therm. cond. and elec. resist. in fine-grained SiC ceramics
in Fig. 3. The probe size for this analysis was 0.5 nm.
Figure 4(a) is a profile for the atom fraction of Al within
and near the grain boundary. It shows that Al atom was
preferentially segregated along the amorphous grain
boundary with a small amount into the SiC grains. How-
ever, very small amounts of Y atoms were observed at
the grain boundary, as shown in Fig. 4(b). On the other
hand, although O atoms were preferentially segregated
along the grain boundary, a significant amount was found
to be incorporated into the SiC grains. It should be
pointed out that Ca was not detected along the grain
boundaries or within the SiC grains for the present ma-
terial. These differences in the compositions of the grains
and grain boundaries have an important influence on
thermal conductivity and electrical resistivity.
The SC1 and SC2 materials exhibited thermal conduc-
tivity values of 106 and 115 W/mK, respectively. On the
other hand, the use of oxynitride additives completely
suppressed ␤– to ␣–SiC phase transformation during an-
nealing, as has been observed by others31–33 and in our
previous work.34 A nitrogen atmosphere retards the
phase transformation from ␤– → ␣–SiC and results in a
fine microstructure, while an Ar atmosphere enhances
the ␤ → ␣ phase transformation and the formation of a
coarse microstructure. This is consistent with our present
results. The microstructure of the materials with oxyni-
tride additives consisted of fine, equiaxed grains with a
continuous glassy interphase, leading to relatively low
thermal conductivity value of 47 W/mK. Regardless of ox-
ide or oxynitride additives, the heat capacity in these ma-
terials is almost the same, ranging from 0.71 to 0.76 J/gK,
IV. DISCUSSION
The thermal conductivity of a material is a typical
transport property; thus it is closely related to the micro-
structure of the material. The microstructure of SiC is
dependent on sintering additives. The introduction of
larger seed grains into the fine-grained SiC promoted
grain growth. The annealed material with ␣ seeds (SC1)
exhibited a relatively uniform microstructure consisting
mostly of elongated grains. In contrast, the annealed ma-
terial with ␤ seeds (SC2) had a duplex microstructure
with fine matrix grains and much larger elongated grains.
FIG. 4. EDS profiles at every 2 nm across the grain boundary for (a)
the atom fraction of Al along and near the grain boundary and (b) the
atom fraction of Y along and near the grain boundary for the annealed
material with ␣-seeds (SC1).
FIG. 3. High-resolution electron microscopy of the annealed material
with ␣-seeds (SC1), showing an amorphous grain boundary film.
J. Mater. Res., Vol. 17, No. 9, Sep 2002
2331
http://journals.cambridge.org
Downloaded: 14 Mar 2015
IP address: 130.102.42.98

G-D. Zhan et al.: Effects of heat treatment and sintering additives on therm. cond. and elec. resist. in fine-grained SiC ceramics
consistent with sintered SiC materials.27 These results
suggest that the differences in the thermal conductivity of
the materials with either oxide or oxynitride additives are
due mainly to grain-boundary effect. Generally speaking,
small grains lead to more extensive grain-boundary
scattering.
by the grain-boundary scattering but also by point-defect
scattering due to the solid solution of Al, O, and N in the
SiC grains in the present study.
Depending on impurities, SiC can be a p- or n-type
semiconductor or an insulator with extrinsic ranges of
10 < ␳ < 1012 ⍀ cm. The lower the carrier concen-
trations, the higher the electrical resistivity. The high
electrical resistivity is likely due to the continuous grain-
boundary insulating barriers.9 The smaller the grain size,
the more the grain boundaries, and the higher the elec-
trical resistivity. This is consistent with the results for the
materials with oxide additives but not for the materials
with oxynitride additives. For example, the electrical re-
sistivity in the material with oxynitride, which has a fine
grain size, is lower than that in the material with oxide
additives that has a coarse microstructure. Nitrogen ei-
ther from the decomposition of additives or from the
sintering atmosphere can dissolve into the SiC grains and
act as the main electrically actived impurity35 and thus
lower both the thermal conductivity and electrical resis-
tivity of SiC materials with oxynitride additives. These
results suggest that electrical resistivity is related to both
the grain boundary and the chemistry of the grain bound-
ary. It is expected that increasing the thermal con-
ductivity and electrical resistivity can be achieved by
controlling the composition and heat treatment of the
grain boundary and the solid-solution effect.
SiC polytypes also exert an important influence on
thermal conductivity.12,15,16 The Al atoms in both 4H
and 6H could substitute for Si because of the similar
tetrahedral covalent radius of Al (0.126 nm) and Si
(0.117 nm). The incorporation of Al into the SiC is in
favor of ␤–SiC-to-4H phase transformation, as the solid
solubility limit for 4H is higher than that for 6H. Thermal
conductivity decreased with increasing contents of 4H
polytype because the incorporation of the Al2O3 into the
3C–SiC grains leads to a solid–solution effect that re-
duces thermal conductivity. However, it is not reason-
able, on this evidence alone, to interpret that the thermal
conductivity in the present study for the material with ␤
seeds, in which 4H was the major ␣–SiC, was higher than
that of the material with ␣ seeds in which 6H was the
major of ␣–SiC. On the other hand, theoretically, a poly-
crystalline SiC material with a cubic structure is expected
to exhibit the highest thermal conductivity due to the
high symmetry and order in the crystal lattice. However,
the materials with oxynitride additives consisted entirely
of 3C polytype (cubic structure), but the thermal conduc-
tivity was quite low. Therefore, the dependence of ther-
mal conductivity on the distribution of SiC poly-
types was less pronounced for the present fine-grained
materials.
V. CONCLUSIONS
In contrast to metals, in which electrons carry heat,
SiC ceramics transport heat primarily by phonons. Point
defects (i.e., substitute atoms, vacancies, and interstitial
spaces) in the crystal greatly influence thermal conduc-
tivity. Such impurities are introduced either from the
starting powder or from the sintering additives. The pres-
ence of impurities (dominated by Al and O) and vacan-
cies significantly decreases thermal conductivity due to
scattering of high-frequency phonons by point defects.14
Therefore, the incorporation of some amount of Al and O
into the SiC grains in the annealed material with ␣ seeds
(SC1) doped with oxide additives limited thermal con-
ductivity. When materials were annealed in a nitrogen
atmosphere and oxynitride additives were applied, the
materials consisted entirely of ␤ phase. The mechanism
for the retarded phase transformation from ␤– → ␣–SiC
is related to a reduced mass transport rate caused by
lattice strains resulting from the introduction of nitrogen
into the ␤–SiC.31 Therefore, the lower thermal conduc-
tivity in the materials with oxynitride additives might be
directly related to the incorporation of nitrogen into the
SiC grains. The segregation along the grain boundary
would also reduce thermal conductivity. These results
indicate that thermal conductivity is influenced not only
The annealed material with ␤ seeds exhibited a higher
thermal conductivity of 115 W/mK compared to the ma-
terial with ␣ seeds. On the other hand, the use of oxyni-
tride additives completely suppressed ␤ to ␣–SiC phase
transformation during annealing. The microstructure in
these materials consisted of fine, equiaxed grains, exhib-
iting low thermal conductivity (47 W/mK).
High electrical resistivity in the range of 105–108
⍀ cm can be obtained in these annealed materials. The
CVD-SiC material exhibits high thermal conductivity of
132 W/mK and extremely high electrical resistivity of
1.2 × 109 ⍀ cm.
The chemical compositions and microstructure (amor-
phous or crystallites) of the grain boundaries has the most
influence on thermal and electrical properties of hot-
pressed and annealed SiC.
ACKNOWLEDGMENT
One of the authors, Guodong Zhan, is presently sup-
ported by the United States Army Research Laboratory
and the United States Army Research Office under Grant
No. G-DAAD 19-00-1-0185.
2332
J. Mater. Res., Vol. 17, No. 9, Sep 2002
http://journals.cambridge.org
Downloaded: 14 Mar 2015
IP address: 130.102.42.98

G-D. Zhan et al.: Effects of heat treatment and sintering additives on therm. cond. and elec. resist. in fine-grained SiC ceramics
19. G-D. Zhan, Y. Ikuhara, M. Mitomo, R-J. Xie, T. Sakuma, and
REFERENCES
A.K. Mukherjee, J. Am. Ceram. Soc. 85, 430 (2002).
20. Y-W. Kim, M. Mitomo, and G-D. Zhan, J. Mater. Res. 14, 4291
(1999).
21. R.E. Loehman, J. Am. Ceram. Soc. 62, 491 (1979).
22. S. Sakka, J. Non-Cryst. Solids 181, 215 (1995).
23. M. Mitomo, H. Hirotsuru, H. Suematsu, and T. Nishimura, J. Am.
Ceram. Soc. 78, 211 (1995).
24. H. Tanaka and N. Iyi, J. Ceram. Soc. Jpn. 101, 1313 (1993).
25. J. Ruska, L.J. Gauckler, J.L. Lorenz, and H.U. Rexer, J. Mater.
Sci. 14, 2013 (1979).
26. Y-W. Kim and M. Mitomo, J. Am. Ceram. Soc. 82, 2731 (1999).
27. http://www.ceramics.nist.gov/srd/summary/scdscs.htm (2001).
28. http://www.ceradyne.com/dtsic.htm (2001).
29. http://www.cvdmaterials.com/sicprop1.htm (2001).
30. A.K. Collins, M.A. Pickering, and R.L. Taylor, J. App. Phys. 68,
(1990).
1. N.P. Padture and B.R. Lawn, J. Am. Ceram. Soc. 77, 2518 (1994).
2. N.P. Padture, J. Am. Ceram. Soc. 77, 519 (1994).
3. G-D. Zhan, M. Mitomo, and Y-W. Kim, J. Am. Ceram. Soc. 82,
2924 (1999).
4. G-D. Zhan, R-J. Xie, M. Mitomo, and Y-W. Kim, J. Am. Ceram.
Soc. 84, (2001).
5. K. Moore and R.J. Trew, MRS Bull. 22(3), 50 (1997).
6. R.C. Glass, D. Henshall, V.F. Tsvetkov, and C.H. Carter, Jr.,
MRS Bull. 22(3), 30 (1997).
7. D.J. Larkin, MRS Bull. 22(3), 36 (1997).
8. M.A. Capano and R.J. Trew, MRS Bull. 22(3), 19 (1997).
9. Y. Takeda, K. Nakamura, K. Maeda, and Y. Matsushita, J. Am.
Ceram. Soc. 70, C-266 (1987).
10. Y. Takeda, Ceram. Bull. 67, 1961 (1988).
11. S. Ogihara, K. Maeda, Y. Takeda, and K. Nakamura, J. Am.
Ceram. Soc. 68, C-16 (1985).
31. W.S. Seo, C.H. Pai, K. Koumoto, and H. Yanagida, Solid State
12. T. Sakai and T. Aikawa, J. Am. Ceram. Soc. 71, C-7 (1988).
13. W. Kowbel, F. Gao, J.C. Withers, and G.E. Youngblood, J. Mater.
Syn. And Proc. 4, 195 (1996).
14. T. Kinoshita and S. Munekawa, Acta. Mater. 45, 2001 (1997).
15. D-M. Liu and B.W. Lin, Ceram. Inter. 22, 407 (1996).
16. M. Landon and F. Thevenot, J. Europ. Ceram. Soc. 8, 271 (1991).
17. G-D. Zhan, M. Mitomo, R-J. Xie, and A.K. Mukherjee, J. Am.
Ceram. Soc. 84, 2448 (2001).
Phenomena 25&26, 133 (1992).
32. H-W. Jun, H-W. Lee, G-H. Kim, H-S. Song, and B-H. Kim,
Ceram. Eng. Sci. Proc. 18, 487 (1997).
33. M. Nader, F. Aldinger, and M.J. Hoffmann, J. Mater. Sci. 34,
1197 (1999).
34. G-D. Zhan, M. Mitomo, Y-W. Kim, R-J. Xie, and A.K. Mukherjee,
J. Mater. Res. 16, 2189 (2001).
35. Y.A. Vodakov, G.A. Lomakina, E.N. Mokhov, V.G. Oding, and
18. G-D. Zhan, M. Mitomo, H. Tanaka, and Y.W. Kim, J. Am.
E.I. Padovanova, Sov. Phys. Solid State 20, 258 (1978).
Ceram. Soc. 83, 1369 (2000).
J. Mater. Res., Vol. 17, No. 9, Sep 2002
2333
http://journals.cambridge.org
Downloaded: 14 Mar 2015
IP address: 130.102.42.98