Journal of Alloys and Compounds 366 (2004) 21–27 The crystal structure and properties of Ga 2 Cr 1.33 Se 5 , a new layered semiconductor I. Oko´ nska-Kozlowska a , K. Szamocka c,∗ , E. Malicka a , A. Wa´ skowska b , J. Heimann c , T. Mydlarz d , A. Gilewski d , T. Gro´ n c a Institute of Chemistry, University of Silesia, 40007 Katowice, Poland b Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50422 Wroclaw, Poland c Institute of Physics, University of Silesia, 40007 Katowice, Poland d International Laboratory of High Magnetic Fields and Low Temperatures, 53529 Wroclaw, Poland Received 10 June 2003; received in revised form 8 July 2003; accepted 8 July 2003 Abstract A new selenide of the ternary system Ga–Cr–Se has been obtained by chemical transport reactions. Single crystals of the pseudobinary compound (Ga 2 Se 3 ) 3x –(Cr 2 Se 3 ) 1-x with x = 0.333, are trigonal and have the unit cell of dimensions a = 3.781(1), c = 46.807(9) Å, V = 579.5(1) Å 3 with Z = 3 in the hexagonal setting of space group R3. The compound has been characterised as to the crystal structure and composition related to the magnetic properties and electric transport behaviour. The structure can be described as a close packed hexagonal arrangement of selenium ions, forming layers perpendicular to the c-axis. The cations occupy tetrahedral and octahedral voids between the layers. Along the c-axis there is a repetition c/3 with five symmetrically different layers. The sequence of the layers results from the metal vacancies having also impact on the properties of the crystal. The temperature dependence of the magnetic susceptibility obeys the Curie–Weiss law with positive θ C-W = 137.7 K, pointing to ferromagnetic interactions. Nevertheless, no evident magnetic transition was found down to 4.2K, and also a thermomagnetic effect was not observed. There was no saturation of magnetisation at 4.2 K in a stationary field of 150 kOe; the moment has scarcely reached the value µ = 2.0µ B /Cr 3+ . The electrical transport measurements showed the compound to be the p-type semiconductor. © 2003 Elsevier B.V. All rights reserved. Keywords: Magnetically ordered materials; Semiconductors; Crystal structure and symmetry; X-ray diffraction; Magnetic measurements 1. Introduction Ternary selenide spinels, exhibiting interesting structural, magnetic and electrical transport properties have been the subject of numerous studies [1–9]. It was shown that replace- ment of the di- or trivalent cation by a third metal resulted in new chemical compounds with essentially changed prop- erties interesting for both basic research and technological aspects [10–15]. Quaternary selenides, crystallising with the spinel-type structure, can usually be obtained in a whole concentration range of the dopant [16–21], while those with non-spinel structure show a limited solubility and often the end-member of the system remains unknown [21–23]. In the course of our studies on the Cd, Zn–Ga–Cr–Se solid solu- tions it was interesting to prepare the end-member of the sys- ∗ Corresponding author. E-mail address: kaysay@wp.pl (K. Szamocka). tem, i.e. Ga 2x/3 Cr 2 Se 4 . To our knowledge, there are reports on the ternary single crystal of GaCrSe 3 with orthorhombic structure [24] and on polycrystalline forms of hexagonal Ga 1.2 Cr 0.8 Se 3 and monoclinic Ga 1.3 Cr 0.7 Se 3 [25]. Using chemical transport reactions we aimed at preparing single crystals of the spinel-type. However, our attempts to grow the compound resulted in the alloy resembling the pseudobinary system (ZnSe) 3x –(In 2 Se 3 ) 1-x [26,27]. The present paper describes a single crystal of Ga 2 Cr 1.33 Se 5 characterised by X-ray diffraction and the results of mag- netic susceptibility and electrical resistivity measurements. 2. Experimental 2.1. Sample preparation Single crystals were grown by chemical vapour trans- port in closed quartz ampoules with anhydrous chromium 0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8388(03)00689-3