Lunar and Planetary Science XXX 1359.pdf

CRYSTAL STRUCTURE OF SCHREIBERSITE FROM . R Skála1 and I. Císarová2, 1Czech Geological Survey, Klárov 3/131, CZ-11821 Praha 1, Czech Republic, e-mail: [email protected], 2Faculty of Science, Charles University, Hlavova 2030, CZ-12843 Praha 2, Czech Republic,e-mail: cisa- [email protected].

Introduction: Basic structure motif found in Vicenice [4]. schreibersite was originally described on chemically Sample and Results: For this study a chip of close isostructural compound – Ni3P – in [1]. Later, skeletal schreibersite crystal from Toluca meteorite the crystal structure of meteoritic schreibersite Fe2NiP from collections of the Natural History Museum in was solved and refined Table 2: Final atomic coordinates, site occupancies, and displacement parame- [2,3] from data collected on ters (in Å2). rhabdite crystals. Both these refinements differ in Site Atom SOF x y z Uiso site occupancies for nickel Me1 Fe 1.00 0.0791(1) 0.1074(1) 0.2297(3) 0.0007(4) and iron. In the first one, Me2 Fe 0.80(7) 0.3610(1) 0.0323(1) 0.9823(3) 0.0014(4) one nickel atom per for- Ni 0.20(7) mula unit was equally par- Me3 Fe 0.30(7) 0.1704(1) 0.2193(1) 0.7510(3) 0.0022(4) titioned between two sites – Ni 0.70(7) here described as Me2 and X P 1.00 0.2930(2) 0.0474(2) 0.4864(6) 0.0016(5) Me3, the site Me1 being Vienna was used. Single crystal data were collected on fully occupied by iron. On the contrary, the second four-circle diffractometer CAD4 – details on data col- refinement led to revision of nickel partitioning, lection and refinement are given in Table 1. Crystal placing 1/3 of nickel atom into site Me2 and 2/3 to structure was refined using the program JANA94 [5]. site Me3 and indicating thus certain preference in Crystal displayed broadened reflections, probably due Fe/Ni partitioning within the schreibersite crystal to strain associated with shear and brecciation, which structure. Similar trend for occupation of site Me3 were noticed from Toluca e.g. by [6]. This fact preferentially by nickel was observed by Rietveld strongly influenced the data quality and thus final R- crystal structure refinement for schreibersite from factors, whose increased values indicate slightly Table 1: Crystal data and structure refinement of poorer fit. Refined atomic coordinates, site occupan- schreibersite from Toluca cies and isotropic displacement parameters are listed in Table 2. The present refinement has also confirmed Enraf-Nonius CAD4- Diffractometer the trend observed in [3] and [4] in which nickel MACHIII dominates in site Me3 in the schreibersite crystal Empirical formula Fe Ni P 2.1 0.9 structure while site Me1 is fully occupied by iron. Temperature [K] 293(2) Acknowledgements: Authors thank to the Grant Wavelength [Å] 0.71073 Agency of the Czech Republic for supporting the re- Crystal system tetragonal search under project number 205/98/0655. Thanks are Space group I 4 also to Professor Gero Kurat of the Natural History Unit-cell dimensions Museum in Vienna for providing a material for pre- a [Å] 9.0555 sented crystal structure refinement. c [Å] 4.4545 References: [1] Larsson E. (1965) Arkiv foer V [Å3] 365.278 Kemi, 23, 335–365, [2] Doenitz F. D. (1968) Natur- Z 8 wissen., 55, 387. [3] Doenitz F. D. (1971) Zeit. Theta range for data col- 3.18-24.83 Kristall., 144, 534–535, [4] Skála R and Frýda J. lection [°2Q] (1995) LPS XXVII, 1211–1212, [5] Dušek M. and Reflections collected 308 Petrírek V. (1998) Material. Struct. Chem. Biol. Phys. Independent reflections 297 Technol., 5, 277, [6] Buchwald V.F. (1975) Handbook Refinement method Full matrix LSQ on F of Iron , Univ. California Press, Berkeley. Data/restraints/parameters 296/2/19 Final R indices R1=0.0851; wR1=0.0851 R indices (all data) R1=0.0880; wR1=0.0893 D(r) [e.Å-3] 2.05; -1.26