High-temperature DTA studies of AxMF3 compounds (, Rb, Cs; , Cr; and )

Magnetic properties of linear trimers in fluoride analogs of tetragonal tungsten bronze

“…The fact that the crystal structure of KCrScF 6 is tetragonal is surprising since KCr 2 F 6 is orthorhombic at room temperature [18]. KCr 2 F 6 , however, undergoes a Jahn-Teller phase transition to the tetragonal form between 300 and 400 1C [19].…”

Descent in Symmetry during Solid State Transitions and Other Anomalies in Mixed Valence Compounds A<sub>x</sub>M<sub>x</sub><sup style="margin-left:-10px;">Ⅱ</sup>M<sub>1-x</sub><sup style="margin-left:-16px;">Ⅲ</sup>F<sub>3</sub> (A = K, Rb, Cs; M = V, Cr; x = 0.0 - 1.0)

“…The melting temperatures of the A x MF 3 compounds [7] are shown in Figure 3. Remarkably, the A x CrF 3 compounds all melt 200˚ lower than their A x VF 3 analogs.…”

“…The other striking feature of Figure 3 is that the melting temperature vs. x plots of the A x MF 3 systems are all linear. These plots include the binary parent compounds VF 3 and CrF 3 , which have cubic perovskite-like structures at high temperatures [7,17]. This suggests that the A x MF 3 compounds also initially solidify to cubic-perovskite-like structures.…”

“…At first, perovskite-like solid phases apparently form from the melt [7]. Upon cooling, new structures are formed, designated α, β, and δ [8][9][10]; when these are cooled further, ionic ordering sets in [7,[11][12][13][14][15]. Such transitions are characteristic of mixed-valence compounds [1,16].…”

“…Such transitions are characteristic of mixed-valence compounds [1,16]. Three ordered structures are possible in the α-phases, three in the β-phases, and two in the δ-phases [7]. At very low temperatures (below 50 K), magnetic ordering sets in [11][12][13][14].…”