Potassium triyttrium decafluoride, KY3F10, synthesized at high pressures and high temperatures

Potassium triyttrium decafluoride, KY3F10, has been studied at high pressures and high temperatures using in situ synchrotron angle-dispersive X-ray powder diffraction in a Paris-Edinburgh cell and syntheses in a multi-anvil apparatus. At ambient conditions this compound exhibits a 2 x 2 x 2-fluorite superstructure (Fm (3) over barm, Z = 8, a = 11.54315(1) Angstrom) with yttrium atoms displaced from the ideal fcc positions. Upon compression to above 7.5 GPa at room temperature, a new polymorph is formed (Pm (3) over barn, Z = 1, a = 5.70485(8) Angstrom for the sample synthesized at 10.5 GPa and 298 K) with potassium and yttrium atoms in the ideal fluorite positions. Fluorine atoms are disordered and split on partially occupied sites. The same phase of KY3F10 is obtained at lower pressures and high temperatures. This new structure is discussed in relation to other fluorite superstructures. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.