Equation of state and thermal stability of Al3BC

Article abstract of DOI:10.1016/j.ssc.2006.01.015

The lattice parameters of Al₃BC have been measured up to 5 GPa at ambient temperature using energy-dispersive X-ray powder diffraction with synchrotron radiation. A fit to the experimental p-V data using Birch-Murnaghan equation of state gives values of the Al₃BC bulk modulus 116(4) GPa and its first pressure derivative 9(2). In the 1.6-4.8 GPa range at temperatures above 1700 K Al₃BC undergoes incongruent melting that results in the formation of Al₃BC₃, AlB₂ and liquid aluminum.

Full text of DOI:10.1016/j.ssc.2006.01.015

Solid State Communications 137 (2006) 533–535
www.elsevier.com/locate/ssc
Equation of state and thermal stability of Al3BC
b
c
Vladimir L. Solozhenko a, , Elena G. Solozhenko , Christian Lathe
*
a
´
´
´
LPMTM-CNRS, Institut Galilee, Universite Paris Nord, 99, av. J.B. Clement, F-93430 Villetaneuse, France
b Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Kiev 04074, Ukraine
c Hamburger Synchrotronstrahlungslabor (HASYLAB-DESY), D-22607 Hamburg, Germany
Received 19 September 2005; received in revised form 12 January 2006; accepted 12 January 2006 by B. Jusserand
Available online 31 January 2006
Abstract
The lattice parameters of Al3BC have been measured up to 5 GPa at ambient temperature using energy-dispersive X-ray powder diffraction
with synchrotron radiation. A fit to the experimental p–V data using Birch–Murnaghan equation of state gives values of the Al3BC bulk modulus
116(4) GPa and its first pressure derivative 9(2). In the 1.6–4.8 GPa range at temperatures above 1700 K Al3BC undergoes incongruent melting
that results in the formation of Al3BC3, AlB2 and liquid aluminum.
q 2006 Elsevier Ltd. All rights reserved.
PACS: 61.10.Eq; 64; 64.30.Ct
Keywords: A. Aluminum boroncarbide; C. XRD; E. High pressure
1. Introduction
a Al:B:C ratio of about 3:1:1. Secondary ion mass spectroscopy
showed that the oxygen impurity content is less than 1 at%.
The high-pressure experiments up to 5 GPa were carried out
using a multianvil X-ray system MAX80 at beamline F2.1,
HASYLAB-DESY. The experimental set-up has been
described elsewhere [4]. Energy-dispersive data were collected
on a Canberra solid state Ge-detector with fixed Bragg angle
2qZ9.238(5)8 using a white beam collimated down to 100!
100 mm2 and the detector optics with 2q acceptance angle of
0.0058, which ensures a high resolution of the observed
diffraction patterns. The detector was calibrated using the Ka
and Kb fluorescence lines of Cu, Rb, Mo, Ag, Ba, and Tb.
To decrease the deviatoric stress that was generated during
‘cold’ compression and, thus, attain quasi-hydrostatic pressure
conditions during equation-of-state measurements, the samples
were preannealed at 900 K and a given pressure for 10 min.
The sample pressure was determined from the lattice constant
of NaCl (pressure marker) using Decker’s equation of state [5].
The temperature of the high-pressure cell was controlled by
a Eurotherm PID-regulator within G4 K in the 400–1900 K
range. The sample temperature was measured by a Pt/Pt10%Rh
thermocouple. The correction for the pressure effect on the
thermocouple emf was made using the data of Getting and
Kennedy [6]. Pressures at different temperatures were
evaluated from the lattice parameters of highly ordered
graphite-like hexagonal boron nitride using the p–V–T equation
of state of hBN [4]. The pressure variations with increasing
temperature were found not to exceed G200 MPa in the 2-mm
Aluminum-rich phases of the Al–B–C system have been the
topic of several recent investigations because cermets based on
aluminum boroncarbide are promising ceramic materials of
high hardness and low density. In fabrication of advanced
Al/B/C cermets, the basic product of a reaction between
aluminum and boron carbide at relatively low temperatures is
Al3BC [1]. This phase was first described as phase X [2]. Later
Meyer and Hillebrecht [3] synthesized the pure compound and
defined its composition and crystal structure (Fig. 1). As no
data are found in the literature on the Al3BC high-pressure
behavior, our interest has been in studying the equation of state
and thermal stability of this phase up to 5 GPa using X-ray
powder diffraction with synchrotron radiation.
2. Experimental
Pure Al3BC was synthesized at 1150 K from the elements
with an excess of aluminum as described in [3]. Combustion
elemental analysis and electron probe microanalysis gave
*
Corresponding author. Tel.: C33 1 49 40 34 89; fax: C33 1 49 40 39 38.
E-mail address: vls@lpmtm.univ-paris13.fr (V.L. Solozhenko).
0038-1098/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2006.01.015

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V.L. Solozhenko et al. / Solid State Communications 137 (2006) 533–535
1.000
0.995
0.990
0.985
0.980
0.975
0.970
0.965
0
1
2
3
4
5
Pressure (GPa)
Fig. 3. The p–V data for Al3BC at ambient temperature. The solid line is the
best fit of the experimental data to the Birch–Murnaghan equation of state, with
B0Z116 GPa and B00 Z9. The dashed line is equation of state of Al3BC3 [7].
(006), (105), (110), (106), and occasionally (004), (108), (202),
(204), (116). Lattice parameters of the subcell at ambient
Fig. 1. Crystal structure of Al3BC is a closest packing of Al atoms with a layer
sequence ABACBC. Isolated boron atoms are placed in all octahedral voids
between the layers A and C while isolated carbon atoms occupy half of the
trigonal voids in the layers B [3].
˚
pressure were calculated to be aZ3.491G0.002 A and
˚
cZ11.54G0.01 A, in good agreement with those reported in
[3]. With increasing pressure, the diffraction lines of Al3BC
broaden and weaken considerably and above 5 GPa only the
lines associated with the (102), (103), (104) and (006)
reflections could be resolved.
central part of the cell over the experimental temperature
range.
In studying Al3BC thermal stability, the samples were
compressed to a given pressure at ambient temperature, and
then the diffraction patterns were collected in the ‘autose-
quence’ mode at a linear heating at a rate of 25 K/min.
Collection time was 60 s for each pattern.
Fig. 2 shows the lattice parameters of Al3BC versus
pressure. The one-dimensional analog of the first-order
Murnaghan equation of state of the form
0
ꢂ
ꢀ
ꢁ ꢃ
K1=b
r
b0
Z 1 C
p
(1)
3. Results and discussion
r0
b0
3.1. Equation of state of Al3BC
was used for approximation of the non-linear relation between
normalized lattice parameters and pressure. Here r is the lattice
parameter (index 0 refers to ambient pressure); b0 is the axial
compression modulus1, and b0 is the pressure derivative of b0.
The dashed lines in Fig. 2 correspond to Eq. (1) with
parameters obtained from a least-squares fit to the experimental
data. The ratio between axial compression moduli towards the
a and c axes is 1.19G0.03, which points to the higher
compressibility of Al3BC in the c-direction. This fact can be
attributed to a pronounced two dimensional character of the
Al3BC crystal structure in which layers of edge sharing Al6B
octahedra alternate with layers of trigonal bipyramidal Al5C
polyhedra linked by common corners [3].
Synchrotron radiation diffraction patterns of the Al3BC
subcell exhibit broadened reflections (101), (102), (103), (104),
11.50
11.45
11.40
c
11.35
3.48
Experimental values of the Al3BC relative volume versus
pressure are plotted in Fig. 3. A non-linear three-parameter
least-squares fit to the experimental p–V data using Birch–
Murnaghan equation of state gave zero-pressure value of
bulk modulus B0Z116G4 GPa and its pressure derivative
dB0/dpZ9G2. These values point to a higher compressibility
of Al3BC as compared to Al3BC3 (B0Z153 GPa [7]).
3.46
3.44
a
0
1
2
3
4
5
Pressure (GPa)
Fig. 2. Lattice parameters of Al3BC versus pressure at ambient temperature.
The dashed lines represent least-squares fits to the experimental data using
Eq. (1).
1 (b0)K1ZkrZK(d1n r/dp)pZ0 is the linear compressibility.

V.L. Solozhenko et al. / Solid State Communications 137 (2006) 533–535
535
of Al3BC takes place:
3Al3BC Z Al3BC3 CAlB2 C5Al
(2)
Complete disappearance of the Al3BC lines is observed at
about 1700 K. With further temperature increase up to 1850 K,
the phase composition of the system does not change because
of the high thermal stability of Al3BC3 [7]. Diffraction patterns
of the samples quenched down to ambient conditions exhibits
lines of Al3BC3, AlB2 and metallic aluminum.
At 4.8 GPa, Al3BC decomposition starts at higher tempera-
tures (1720G20 K) and also results in the formation of
Al3BC3, AlB2 and liquid aluminum.
1831
1764
1698
1631
Acknowledgements
25
30
35
40
45
50
Energy, keV
The authors thank Dr F.D. Meyer for supplying us with the
Al3BC specimen and Prof. H. Hillebrecht for fruitful
discussions. High-pressure experiments at HASYLAB-DESY
were supported by the GFZ-Potsdam under the MAX80
program.
Fig. 4. Diffraction patterns of Al3BC taken at a linear-heating rate of 25 K/min
at 1.6 GPa.
The latter is probably due to a clearly ionic character of Al3BC3
[8] while Al3BC seems to be more metallic [3].
References
3.2. Phase stability of Al3BC
[1] J.C. Viala, J. Bouix, V. Gonzalez, C. Esnouf, J. Mater. Sci. 32 (1997) 4559–
4573.
At 1.6 GPa heating of Al3BC up to 1680 K results in a
decrease of the lines’ width, which is indicative of the
structural ordering of the phase at a temperature increase
under pressure. Starting with 1680 K, the lines of Al3BC3 and
AlB2 appear in the diffraction patterns (Fig. 4). At the same
time a drastic decrease in the intensity of the lines of initial
Al3BC is observed. A considerable increase of the background
points to the formation of a liquid in the system, which gives
grounds to conclude that a process of incongruent melting
[2] D.C. Halverson, A.J. Pyzik, I.A. Aksay, Ceram. Eng. Sci. Proc. 16 (1985)
736–744.
[3] F.D. Meyer, H. Hillebrecht, J. Alloys Compd. 252 (1997) 98–102.
[4] V.L. Solozhenko, T. Peun, J. Phys. Chem. Solids 58 (1997) 1321–1323.
[5] D.L. Decker, J. Appl. Phys. 42 (1971) 3239–3244.
[6] I.C. Getting, C. Kennedy, J. Appl. Phys. 41 (1970) 4552–4562.
[7] V.L. Solozhenko, F.D. Meyer, H. Hillebrecht, J. Solid State Chem. 154
(2000) 254–256.
[8] H. Hillebrecht, F.D. Meyer, Angew. Chem. Int. Ed. Engl. 35 (1996) 2499–
2500.