(H_2O)[V_2~(III)F_6]and Pyr-VF_3: Hydrothermal Synthesis, Structure Determination, and Magnetic Characterization of New Fluorides with the Pyrochlore Type

摘要

Small green triangular crystals of a new tridimensional by hydrated vanadium (III) fluoride have been hydrothermally prepared in a simple way by heating a mixture of V:HF:H_2O in the molar ratio:1:1:50 at 200 deg C for 3 days. Its structure was solved by X-ray diffraction in the cubic space group Fd3M (No.227) with a=104636(2)A.(H_2O)[V+2~(III)F_6] presents the structure of the well-known pyrochlore type. The cavities contain water molecules which are lost by heating (T<250 deg C) without any structural change. The thermal stability of this new form of VF_3 (Pyr-VF_3) with the pyrochlore structure is compared to that of the already known Pyr-FeF_3 (1). The magnetic behavior of pyr-VF_3 si described