Thermal expansion of magnesium nitride W. Paszkowicz*, M. Knapp1, J.Z. Domagala, G. Kamler2 and S. Podsiadlo2 Institute of Physics, P.A. S., Al. Lotnikow 32/46, 02-668 Warsaw, Poland (e-mail: [email protected]) 1Materials Science, Darmstadt University of Technology, Petersenstr. 23, D-64287 Darmstadt, Germany 2Faculty of Chemistry, Warsaw University of Technology, ul. Noakowskiego 3, 00-664 Warsaw, Poland Magnesium nitride (as well as some related compounds such as beryllium nitride and calcium nitride) has an anti-bixbyite structure with the body centred cubic cell [1,3] with space group Ia-3. It is known to decompose when exposed to the air [3]. A recent DTA study indicates that apart of the above mentioned phase stable at ambient conditions, there are five other polymorphs stable at high temperatures and/or pressures [4]. Magnesium nitride, Mg3N2, is known for its role as nitriding agent in reactions leading to formation of various nitrides such as rare earth nitrides [5], MgSiN2 [6,7] and AlN [8] ceramics nitrides. It has catalytic properties which are useful in synthesis of silicon nitride and cubic boron nitride (see e.g. [9-11]. Various applications of the above mentioned and other related magnesium-containing nitrides are possible. They are potential high-temperature materials and substrates or other heterostructure components in electronic industry (the bandgaps of Mg3N2 and MgSiN2 are 2.8 and 4.8 eV, respectively [12]). Magnesium is an important dopant for gallium nitride, and in the Ga-Mg-N system a new gallium magnesium nitride semiconductor has been reported [13]. Therefore, there is a need of better understanding of fundamental properties of Mg3N2. The aim of the present paper was to determine the thermal expansion of magnesium nitride in the temperature range from 11 K up to room temperature. The fine magnesium nitride powder studied in the present work was synthesised at Warsaw University of Technology. It was prepared in a two step reaction. 5 g of magnesium powder was heated for 3 hours in a quartz tube reactor in a 5 mm/s stream of ammonia at 873 K. This process was followed by heating for 2 hours in a 3 mm/s stream of nitrogen at 1073 K. Care was taken to minimise the contact with air during storage and sample preparation. Diffraction patterns were collected at a powder diffractometer at the B2 beamline at Hasylab. A helium-closed-cycle cryostat with rotating capillary described in [14] was applied. The instrumental parallel-beam set-up includes a Ge(111) double monochromator, two Soller slits and a NaI scintillation counter. A silicon diode sensor was used for the temperature and a PID controller were used for the temperature control. The accuracy of temperature determination is astimated to be ±1 K. The applied wavelength, λ = 1.20720 Å, was determined using least-squares method from positions of five reflection of silicon (NIST 640b diffraction standard with lattice parameter 5.43094 Å). The powder was mounted within a thin-wall capillary of 25 mm length, 1 mm diameter and 0.01 mm wall thickness. The reflection profiles were fitted assuming the gaussian shape. The lattice parameter, a, was determined from the position of (10 5 1) reflection at each temperature. The room-temperature value, a = 9.9641(2) Å at 300 K, is consistent with the literature data determined by X-ray diffraction, 9.964(1) Å [2] and 9.9657(2) Å [15] and it is somewhat higher than that obtained by neutron diffraction in [1], 9.9528(1) Å. The measured lattice-parameter dependence on temperature is shown in Fig. 1. The solid line is a guide to eye representing a third-order polynomial. The a(T) dependence shows that the thermal expansion coefficient is close to zero at lowest temperatures. It is probable that at the lowest temperatures the expansion is slightly negative. The relative lattice-parameter-increase on rising the temperature in the studied range from 11 K up to room temperature is about 0.14 %. 9.965 9.960 a [A] 9.955 9.950 0 50 100 150 200 250 300 TEMPERATURE [K] Figure 1: Dependence of lattice parameter, a, on temperature for magnesium nitride. The solid line is a guide to eye obtained by fitting the experimental powder- diffraction data using a polynomial of third order. References [1] D.E. Partin, D.J. Williams, and M. O'Keeffe, J. Solid State Chem. 132, 56 (1997) [2] J. David, Y. Laurent, and J. Lang, Bull. Soc. Fr. Miner. Cristallogr. 94, 340 (1971) [3] A.M. Heyns, L.C. Prinsloo, K.J. Range, and M. Stassen, J. Solid State Chem. 137, 33 (1998) [4] I.S. Gladkaya, G.N. Kremkova, and N.A.Bendeliani, J. Mater. Sci. Lett.12, 1547 (1993) [5] I.P. Parkin, and A.M. Nartowski, Polyhedron 17, 2617 (1998) [6] W.A. Groen, M.J. Kraan, and G. de With, J. Eur. Ceram. Soc. 12, 413 (1993) [7] R.J. Bruls. H.T. Hintzen, and R. Metselaar, J. Mater. Sci. 34, 4519 (1999) [8] M. Kobashi, N. Okayama, and T. Choh, Materials Trans. JIM 38, 260 (1997) [9] O. Fukunaga, J. Phys. Coll. 45, 315 (1984) [10] H. Lorenz, T. Peun, and I. Orgzall, Appl. Phys. A 65, 487 (1997) [11] J. von der Gönna, G. Will, G. Nover, and K.-D. Grevel, High Pressure Res. Technol., accepted (2000) [12] C.M. Fang, R.A. de Groot, R.J.. Bruls, H.T. Hintzen, and G. de With, J. Phys.: Condens. Matter 11, 4833 (1999) [13] T. Suski, P. Perlin, A. Pietraszko, M. Leszczynski, M. Bockowski, I. Grzegory, and S. Porowski, J. Cryst. Growth 207, 27 (1999) [14] J. Ihringer, and A. Koester, J. Appl. Cryst. 26, 135 (1993) [15] PDF2 Database, International Centre for Diffraction Data, PDF-350778 (1997).