High-temperature DTA studies of AxMF3 compounds (A=KA=K, Rb, Cs; M=VM=V, Cr; and x=0–1.0x=0–1.0)

AxVF3 (A=KA=K, Rb, Cs; x=0–1.0x=0–1.0) and AxCrF3 compounds were sealed inside high-temperature DTA molybdenum sample cups using electron beam welding techniques. Melting temperatures of the AxVF3 compounds ranged from 1050 to 1400 °C; those of AxCrF3 from 850 to 1200 °C. Reconstructive transitions were observed for AxVF3 compounds between 650 and 950 °C, and for AxCrF3 compounds between 550 and 825 °C. A displacive transition was observed to occur in VF3 at 490 °C. Order–disorder transitions were determined by X-ray diffraction techniques. In the AxVF3 compounds, electronic ordering and ordering of partially filled A+ sites were observed to occur between 100 and 300 °C. Ordering phenomena in the AxCrF3 compounds (in addition to electronic ordering and ordering of partially filled A+ sites) included Jahn–Teller cooperative ordering. These compounded transitions occurred between 300 and 500 °C.

Melting temperature versus x of KxVF3 and KxCrF3.Figure optionsDownload as PowerPoint slide