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Author Fouad, M. ♦ Sadel, A. ♦ Chaminade, J. P.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword MATERIALS SCIENCE ♦ POTASSIUM COMPOUNDS ♦ PHASE TRANSFORMATIONS ♦ SODIUM COMPOUNDS ♦ RUBIDIUM COMPOUNDS ♦ MOLYBDENUM COMPOUNDS ♦ TUNGSTEN COMPOUNDS ♦ OXIDES ♦ FLUORIDES ♦ DIFFERENTIAL THERMAL ANALYSIS
Abstract X-ray diffraction, differential thermal analysis, polarized light microscopy, and dielectric measurements have been used to study phase transitions and solid solutions in the K{sub 3}MO{sub 3}F{sub 3}-A{sub 3}MO{sub 3}F{sub 3} (A = Rb, Na; M = Mo, W) systems. K{sub 3}MO{sub 3}F{sub 3}-Na{sub 3}MO{sub 3}F{sub 3} (M = Mo, W) systems show two solid solutions; the first (SSI) near x - 0 (K{sub 3-x}Na{sub x}MO{sub 3}F{sub 3}) involves only one transition at T{sub c} which is practically independent of composition. The sharp transition at T{sub 1}(<T{sub c}) for x = 0 disappears or vanishes for x = 0.03. The second solid solution (SS2) near K{sub 2}NaMO{sub 3}F{sub 3} retains cubic symmetry down to 80 K. Rb{sub 3}MO{sub 3}F{sub 3}-K{sub 3}MO{sub 3}F{sub 3} systems show three solid solutions. The SS1 and SS3 exist close to the rubidium and potassium extremes of the binary lines. The pure phases display transitions at T{sub 1} and T{sub c}. For compositions far from {gamma} = 0 or {gamma} = 3 (Rb{sub 3-{gamma}}K{sub {gamma}}MO{sub 3}F{sub 3}), Tc decreases and T{sub 1} decreases abruptly and for SS1 becomes indetectable. The solid solution SS2 (near {gamma} = 1) has cubic symmetry down to 80 K for M = W, and a cubic-noncubic transition at low temperature for M = Mo. In any case, the phase transitions are of first order, reversible, and improper character. The transition at T{sub c} is ferroelectric, ferroelastic-paraelectric, prototype. The extent of each solid solution depends on the ratio of alcaline cations present in the 6- and 12-fold coordination sites of the perovskite structure.
ISSN 00224596
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-06-01
Publisher Place United States
Journal Journal of Solid State Chemistry
Volume Number 124
Issue Number 1


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