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Neutron Powder Diffraction Studies of Ce 3 B 2 N 4 and Isotypic RE 3 B 2 N 4 Compounds (RE = La, Pr, Nd, MM)
Author(s) -
Rogl Peter,
Klesnar Helmuth,
Fischer Peter
Publication year - 1990
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1990.tb06739.x
Subject(s) - crystallography , octahedron , neutron diffraction , atom (system on chip) , boron , crystal structure , metal , powder diffraction , chemistry , coordination number , rietveld refinement , single crystal , materials science , ion , metallurgy , organic chemistry , computer science , embedded system
The crystal structure of Ce 3 B 2 N 4 (space group Immm , α = 0.35653(5) nm, b = 0.63160(21) nm, c = 1.07131(50) nm) was derived from X‐ray powder photographs; precise atom parameters, atom occupancies, atom order, and interatomic distances were obtained from room‐temperature neutron powder diffraction data employing the Rietveld profile analysis method. The final reliability values of the refinement were R F = 0.059 and R I = 0.068. Boron atoms in triangular prismatic metal coordination [Ce 6 B] are at a distance of 0.1785(7) nm and form pairs. In a tetrakaidecahedral surrounding [Ce 6 B]BN 2 , each boron atom forms single bonds with two nitrogen atoms at a distance of 0.1464(4) nm. Nitrogen atoms thus are in rectangular pyramidal metal coordination [Ce 5 N] with additional boron atom completing a distorted octahedron [Ce 5 BN]. There are no direct N─N bonds. With respect to atom‐site occupancy, the crystal structure of Ce 3 B 2 N 4 is isopointal with the structure type of CeCr 2 B 6 (═(CeCr 2 )B 2 B 4 ) and can furthermore be considered as a filled‐up version of the W 2 CoB 2 ‐type ((W 2 Co)B 2 □ 4 ). Isotypic compounds, RE 3 B 2 N 4 , were synthesized with all the early and large rare‐earth metals (RE = La, Ce, Pr, Nd) and mischmetal (MM). Nd 3 B 2 N 4 was found to be unstable at temperatures higher than 1400°C. No RE 3 B 2 N 4 ‐phase was observed with the smaller rare‐earth elements Gd Lu, Sc, and yttrium.