The change of crystal symmetry and cation ordering in Li–Mg ferrites

• Published in: Journal of alloys and compounds Vol. 336; no. 1-2; pp. 286 - 291
• Main Authors: Antic, B, Rodic, D, Nikolic, A.S, Kacarevic-Popovic, Z, Karanović, Lj
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 18-04-2002; Elsevier
• Subjects: Condensed matter: structure, mechanical and thermal properties; Crystal structure; Disordered solids; Exact sciences and technology; Inorganic compounds; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Synthesis; X-ray diffraction and symmetry; Synthesis; X-ray diffraction and symmetry; Crystal structure; Cubic lattices; Lithium oxides; FCC lattices; Inorganic compounds; Space groups; Thermal decomposition; Ternary compounds; Transition element compounds; Ion distribution; Ultrafine powder; Crystal symmetry; Ferrites; Ordered systems; Solid solutions; Spinels; Primitive cell; Magnesium oxides; Ordering; Crystallographic site; Iron oxides; Quaternary compounds; Software tools
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/S0925-8388(01)01885-0

In this work we present results of synthesis and structural investigation of the spinels with general formula LixMg1−2xFe2+xO4, where 0.00≤x≤0.50. Ultrafine powder of MgFe2O4 (x=0.00) was prepared by thermal decomposition of a mixture of complex compounds [Mg(AA)2] and [Fe(AA)3] at 500°C (AA=acetylacetone). The solid solutions of LixMg1−2xFe2+xO4 (0.10≤x≤0.45) were synthesized by conventional ceramic method. The samples with x≥0.40 belong to ordered spinels with primitive cubic cell, space group P4332 and the samples with x≥0.35 are spinels with face-centered cubic cell, space group Fd-3m. Crystal structures of samples with x=0.00, 0.40 and 0.45 were refined by the Rietveld method using DBWS-9411 software package. In ordered spinels (x=0.40, 0.45) Li+ ions occupy both 4b (preferentially) and 12d octahedral sites. At tetrahedral 8c positions Li+ ions were not found (within the experimental error). Mg2+ ions occupy octahedral 12d and tetrahedral 8c sites and Fe3+ ions occupy all three different cationic sites. Cation ordering in 1:3 type ordered spinel (the occupancy ratio of the Wyckoff’s positions 4b and 12d) of Li+ and Fe3+ at octahedral sites is not complete as in Li0.5Fe2.5O4. In MgFe2O4 spinel, cation distribution in the tetrahedral sites was determined and given by occupation numbers N: N(Mg2+8a)=0.183(7) and N(Fe3+8a)=0.817(7).