TITLE:
Descent in Symmetry during Solid State Transitions and Other Anomalies in Mixed Valence Compounds AxMxⅡM1-xⅢF3 (A = K, Rb, Cs; M = V, Cr; x = 0.0 - 1.0)
AUTHORS:
William O. J. Boo, Daniell L. Mattern, Robert M. Metzger
KEYWORDS:
Descent in Symmetry, Ionic Ordering, Magnetic Ordering, Magnetic Susceptibility, Reconstructive Transitions
JOURNAL NAME:
Natural Science,
Vol.11 No.6,
June
30,
2019
ABSTRACT: The
scope of solid-state transitions, from melting temperatures down to 4.2 K, is described for
six systems: KxVF3, RbxVF3, CsxVF3,
KxCrF3, RbxCrF3, and CsxCrF3 (for x = 0.0 to 1.0). Connections are drawn between the compounds’ compositions
and structures with the various transitions
and ordering events. Upon solidification from the melt and gradual cooling to
room temperature, a sequential descent of symmetry appears to occur, from high-symmetry
perovskite phases, through possible reconstructive transitions, to phases
designated α, β, and δ, within which ionic ordering finally
sets in, forming many new lower-symmetry structures. Many stable new structures
are seen at room temperature. Finally, at cryogenic temperatures, magnetic
ordering sets in. Other anomalies for these systems are also described. The
analysis underscores the overall correspondence of structure, composition, and
magnetic properties in these compounds. This lowering of symmetry mirrors what
has been chronicled for oxygen-bearing perovskites that have yielded so many
high-temperature ceramic superconductors.