P 48 ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012)
THERMAL EXPANSION OF POLYCRYSTALLINE cBN IN THE LOW-TEMPERATURE RANGE
W. Paszkowicz1∗, P. Piszora2, R. Minikayev1, M. Brunelli3, and A. Fitch4
1Institute of Physics PAS, al. Lotnik´ow 32/46, 02-668 Warszawa, Poland
2Adam Mickiewicz University, Faculty of Chemistry, ul. Grunwaldzka 6, Pozna´n 60-780, Poland
3ILL Institut Laue-Langevin, BP 156, 38042 Grenoble cedex 9, France
4European Synchrotron Radiation Facility (ESRF), 6, rue Jules Horowitz, BP 220, 38043 Grenoble Cedex, France
Keywords: lattice parameter, thermal expansion, X-ray diffraction
∗e-mail : paszk@ifpan.edu.pl
Strong covalent bonding determines the elastic properties of hard materials such as diamond, cu- bic boron nitride (cBN) and a number of other bi- nary or ternary carbides and nitrides. In particu- lar, these crystals are characterized by high hard- ness, high bulk modulus and low thermal expan- sion (down to about 1 MK−1at room temperature), accompanied by high melting point, and many of their applications are connected with these proper- ties. Zincblende type boron nitride, a polymorph of boron nitride formed at high-pressure and con- sidered as metastable one, has been discovered by Wentorf [1]. Its thermal expansion at low tempera- tures is expected, based on theoretical calculations, to be comparable to that of diamond, but exper- imental data are not available. To get a smooth experimental a(T ) curve and to derive a thermal expansion coefficient dependence on temperature, the conditions are challenging: the data must be collected at numerous temperature points and it is highly desirable that the lattice-parameter accuracy reaches the level of 10 – 4 ˚A or better.
The measurements were performed with a com- mercial sample (Sigma-Aldrich), purity 3N grain size ∼ 5 µm, using Debye-Scherrer geometry at beamline ID31 (ESRF). The cryostat (Janis)
ascertained a temperature stability and accuracy better than ±0.1 K over the studied temperature range. The applied detection system was based on a bank of nine point detectors, a Si(111) analyser crystals is located at each detector. Lattice param- eters were calculated using the Rietveld refinement via the Fullprof program [3]. The obtained experi- mental a(T ) dependence shows a qualitative agree- ment with an earlier measured preliminary dataset.
The resulting thermal expansion coefficient values are shown to be consistent with previously reported theoretical data.
References
[1] R.H. Wentorf, Jr., “Cubic form of boron nitride,”
J. Chem. Phys. 26 (1957) 956 – 960.
[2] V.V. Brazhkin, E.A. Ekimov, A.G. Lyapin, S.V.
Popova, A.V. Rakhmanina, S.M. Stishov, V.M.
Lebedev, Y. Katayama, K. Kato, “Lattice param- eters and thermal expansion of superconducting boron-doped diamonds,” Phys. Rev. B 74 (2006) 140502(R).
[3] J. Rodrguez-Carvajal, Physica B 192 (1993) 55 – 69.
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