Phase transitions in K{sub 3}AlF{sub 6}

Journal Article · Wed Feb 15 00:00:00 EST 2006 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2005.10.044· OSTI ID:20784878

Abakumov, Artem M ^[1]; Rossell, Marta D ^[2]; Alekseeva, Anastasiya M ^[1]; Vassiliev, Sergey Yu ^[1]; Mudrezova, Svetlana N ^[1]; Tendeloo, Gustaaf van ^[2]; Antipov, Evgeny V ^[1]

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1. Department of Chemistry, Moscow State University, Moscow 119992 (Russian Federation)
2. EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp (Belgium)

Phase transitions in the elpasolite-type K{sub 3}AlF{sub 6} complex fluoride were investigated using differential scanning calorimetry, electron diffraction and X-ray powder diffraction. Three phase transitions were identified with critical temperatures T{sub 1}=132 deg. C, T{sub 2}=153 deg. C and T{sub 3}=306 deg. C. The {alpha}-K{sub 3}AlF{sub 6} phase is stable below T{sub 1} and crystallizes in a monoclinic unit cell with a=18.8588(2)A, b=34.0278(2)A, c=18.9231(1)A, {beta}=90.453(1){sup o} (a=2a{sub c}-c{sub c}, b=4b{sub c}, c=a{sub c}+2c{sub c}; a{sub c}, b{sub c}, c{sub c}-the basic lattice vectors of the face-centered cubic elpasolite structure) and space group I2/a or Ia. The intermediate {beta} phase exists only in very narrow temperature interval between T{sub 1} and T{sub 2}. The {gamma} polymorph is stable in the T{sub 2}<T<T{sub 3} temperature range and has an orthorhombic unit cell with a=36.1229(6)A, b=17.1114(3)A, c=12.0502(3)A (a=3a{sub c}-3c{sub c}, b=2b{sub c}, c=a{sub c}+c{sub c}) at 250 deg. C and space group Fddd. Above T{sub 3} the cubic {delta} polymorph forms with a{sub c}=8.5786(4)A at 400 deg. C and space group Fm3-bar m. The similarity between the K{sub 3}AlF{sub 6} and K{sub 3}MoO{sub 3}F{sub 3} compounds is discussed.

• OSTI ID: 20784878
• Journal Information: Journal of Solid State Chemistry, Vol. 179, Issue 2; Other Information: DOI: 10.1016/j.jssc.2005.10.044; PII: S0022-4596(05)00510-4; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALUMINIUM FLUORIDES
CALORIMETRY
CRITICAL TEMPERATURE
ELECTRON DIFFRACTION
FCC LATTICES
MONOCLINIC LATTICES
ORTHORHOMBIC LATTICES
PHASE TRANSFORMATIONS
POTASSIUM FLUORIDES
SPACE GROUPS
X-RAY DIFFRACTION