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Abstract:
The high-pressure behavior of hexagonal Na1.5Y1.5F6 is
investigated with synchrotron angle-dispersive X-ray powder
diffraction in a diamond anvil cell up to 22 GPa at room
temperature. There is no major phase transition in this
material in the entire pressure region studied here. At near
ambient pressures, the structure is of the Na1.5Nd1.5F6 type (P
(6) over bar, Z = 1), found in other low-temperature sodium
lanthanide fluorides. Pressure-induced order-disorder phenomena
lead to the formation of the gagarinite structure (P6(3)/m, Z =
1) above 20 GPa. Alternatively, the pressure-induced order-
disorder phenomena could be related to a polymorphic transition
towards the phase of the beta-Na2ThF6 type with P (6) over bar
2m (Z = 1) symmetry. There is no volume change associated with
all these reversible structural changes. (C) 2002 Elsevier
Science (USA).
