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New Phases in the Lithiumnitridovanadate System — The Solid Solution Li 7‐2x Mg x [VN 4 ] with 0 ≤ x ≤ 1
Author(s) -
Niewa Rainer,
Zherebtsov Dmitry A.
Publication year - 2004
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200300317
Subject(s) - orthorhombic crystal system , crystallography , crystal structure , neutron diffraction , superstructure , solid solution , powder diffraction , materials science , analytical chemistry (journal) , chemistry , physics , chromatography , metallurgy , thermodynamics
Solid solution phases Li 7‐2 x Mg x [VN 4 ] (0 < x ≤ 1) with varying Mg‐content are obtained as yellow microcrystalline powders from heat treatment of mixtures of VN, Li 3 N and Mg 3 N 2 or from mixtures of Li 7 [VN 4 ] and Mg 3 N 2 at 1370 K in N 2 atmosphere at ambient pressure. At substitution parameter values of x > 0.5 a subsequent distortion from the ideal cubic unit cell to an orthorhombic unit cell is observed. The crystal structure of Li 7‐2 x Mg x [VN 4 ] with x ≈ 1 was refined from neutron and X‐ray powder diffraction data (space group Pbca , No. 61, a = 963.03(3) pm, b = 958.44(3) pm, c = 951.93(2) pm, neutron pattern 14° — 156° 2θ, step non‐linear ≈ 0.0782° 2θ, No. of measured points 1816, R p = 0.089, R wp = 0.115, R Bragg = 0.155, R F = 0.114; X‐ray pattern 10° — 98° 2θ, step 0.005° 2θ, No. of measured points 17600, R p = 0.028, R wp = 0.045, R Bragg = 0.113, R F = 0.133, structure variables: 45). The crystal structure resembles a Li 2 O type superstructure with the atomic arrangement of β‐Li 7 [VN 4 ] and with two crystallographic Li‐sites each substituted by Mg with statistical occupation factors of 0.5. Chemical analyses prove the composition and XAS spectroscopy at the V K ‐edge support the +5 oxidation state assignment for vanadium. XAS data also support the tetrahedral coordination of vanadium by N as indicated by the structure refinements.