Synthesis and characterization of large single crystals of NpPd 3 by flux method R. Eloirdi a,n , J.-C. Griveau a , E. Colineau a , M. Ernstberger a , R. Caciuffo a , H.C. Walker b , D. Le c , K.A. McEwen d a European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, 76125 Karlsruhe, Germany b European Synchrotron, Radiation Facility, BP 220, 38043 Grenoble, France c Helmholtz Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany d University College London, Department of Physics and Astronomy, Gower Street, London WC1E 6BT, United Kingdom article info Article history: Received 24 September 2010 Received in revised form 18 January 2011 Accepted 28 January 2011 Communicated by S. Uda Available online 24 February 2011 Keywords: A2. growth from melt A2. single crystal growth B1. Alloys B1. metals B1. NpPd 3 abstract We report on the growth by flux method of large single crystals of hexagonal NpPd 3 . Samples with linear size up to 3 mm were obtained using lead as flux medium. Only polycrystalline samples of NpPd 3 have been previously studied and in particular no information is available on the anisotropy of its physical properties. Considering the double hexagonal closely packed structure of NpPd 3 , important differences in the physical properties measured along the c-axis and in the basal plane can be anticipated. Preliminary magnetic susceptibility measurements performed on NpPd 3 single crystal are compared to previous measurements made on polycrystalline samples. The availability of NpPd 3 single crystals opens new perspectives in the understanding of the magnetic and electronic properties of this system. & 2011 Elsevier B.V. All rights reserved. 1. Introduction While the phase diagrams of uranium–palladium [1], plutonium–palladium [2] and americium–palladium [3] are reported in the literature, no data are available on the binary phase diagram of neptunium–palladium. Only two intermediate phases are reported [4], the a-NpPd 3 and the b-NpPd 3 , exhibiting two distinct crystal structures. While a-NpPd 3 , stable at room temperature, is a TiNi 3 -type (P6 3 /mmc) with double hexagonal close packed (DHCP) phase, b-NpPd 3 is AuCu 3 -type (Pm3m) with cubic phase obtained by quenching of arc-melted ingot. The physical properties of both phases have been studied: b-NpPd 3 is an antiferromagnet below T N ¼ 55 K [5], whereas the a-NpPd 3 exhibits two transitions [6] suggesting quadrupolar ordering at 30 K and antiferromagnetism below 10 K. Whereas single crystals of the UPd 3 counterpart have been obtained using Czochralski pulling and studied [7], for NpPd 3 only polycrystalline samples, prepared by arc melting, were available, which has been a limit- ing factor for physical studies. Due to the difficulty in handling actinide elements on one hand and the lack of neptunium metal on the other hand, very few preparation of Np-based single crystals [8] are currently performed worldwide. In this study we report the first synthesis and characterization of DHCP NpPd 3 single crystals, produced by lead flux method. While studies on single crystal of UPd 3 using Czochralski method have been reported, we do report here the first study on NpPd 3 single crystals prepared by flux. 2. Experimental Single crystals of NpPd 3 with hexagonal structure were grown by Pb flux method. The starting materials were neptunium with 99.9% purity, palladium with 99.999% purity and lead with 99.9999% purity. These materials contained in an alumina cruci- ble were sealed in an evacuated quartz tube with off-stoichio- metric composition of Np:Pd:Pb ¼ 1:5:20. The quartz tube was heated up to 1050 1C and maintained at this temperature for two days, then subsequently cooled down to 500 1C at a rate of 1 1C/h, taking 25 days in total. The excess of flux was removed from the crystal by heating the crucible upside down on a grid. The microstructure of the sample was examined by scanning electron microscopy (PhilipsXL40) equipped with energy dispersive X-ray analysis system (EDX), which provided information on the com- position of the elements. X-ray diffraction (XRD) was performed using a Bruker D8 advanced diffractometer (Cu-Ka 1 radiation) Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2011.01.080 n Corresponding author. Tel.: + 49 7247951 803; fax: + 49 7247951 599. E-mail address: rachel.eloirdi@ec.europa.eu (R. Eloirdi). Journal of Crystal Growth 320 (2011) 52–54