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Title: Crystal structure of Mn{sub 2}Ln{sub 3}Sb{sub 3}O{sub 14} (Ln=La, Pr and Nd): A new ordered rhombohedral pyrochlore

Manganese rare earth antimonates with the formula Mn{sub 2}Ln{sub 3}Sb{sub 3}O{sub 14} (Ln=La–Yb and Y) have been prepared and their structures were determined by the Rietveld method using X-ray diffraction data. The compounds with Ln=La, Pr and Nd crystallize in a rhombohedral supercell of the cubic fluorite with the space group R3{sup ¯}m and with the lattice parameters a{sub h}≈√2a{sub c} and c{sub h}≈2√3a{sub c}, where a{sub c} denotes the lattice constant of the cubic fluorite. The structure is pyrochlore-like but differs from the common cubic pyrochlore A{sub 2}B{sub 2}O{sub 7} in that it consists of fully ordered Mn:Ln in the A sites and Mn:Sb in the B sites with the ratio 1:3. The most interesting feature of Mn{sub 2}Ln{sub 3}Sb{sub 3}O{sub 14} is that the divalent Mn ions have different coordination numbers with oxygen and the Mn(II)O{sub 6} (octahedron) and Mn(II)O{sub 8} (hexagonal bipyramid) alternate along the parent cubic fluorite axes. For medium sized lanthanides, i.e. from Ln=Sm, the rhombohedral phase coexists with the cubic phase and Mn{sub 2}Y{sub 3}Sb{sub 3}O{sub 14} is cubic a pyrochlore. - Graphical abstract: Crystal structure of rhombohedral pyrochlore Mn{sub 2}Ln{sub 3}Sb{sub 3}O{sub 14} (Ln=La, Pr, and Nd) showing the staking of Ln{sub 3}Mnmore » and MnSb{sub 3} layers (a). (b) and (c) show the connections between Mn1O{sub 6} and LnO{sub 8} and between Mn2O{sub 8} and SbO{sub 6} polyhedra, respectively. - Highlights: • Pyrochlores of the formula Mn{sub 2}Ln{sub 3}Sb{sub 3}O{sub 14} (Ln=La–Yb and Y) were synthesized for the first time. • Mn{sub 2}Ln{sub 3}Sb{sub 3}O{sub 14} with Ln=La, Pr, Nd are rhombohedral consisting of fully 1:3 ordering of metal ions. • With medium-sized Ln, rhombohedral phase co-exists with cubic phase. • Two divalent Mn ions have coordination numbers of 6 and 8, respectively.« less
Authors:
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Publication Date:
OSTI Identifier:
22334216
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 213; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; FLUORITE; LATTICE PARAMETERS; MANGANESE; MANGANESE IONS; OXYGEN; PYROCHLORE; RARE EARTHS; SPACE GROUPS; TRIGONAL LATTICES; X-RAY DIFFRACTION