High-pressure behaviour of Li2CaHfF8 scheelite

High-pressure behaviour of Li2CaHfF8 scheelite (, Z = 2) has been studied with synchrotron angle-dispersive powder and laboratory single-crystal x-ray diffraction using diamond anvil cells to 9.2 GPa at room temperature. The zero-pressure bulk modulus, its first pressure derivative, and the unit-cell volume at ambient pressure are B0 = 78(3) GPa, B' = 4.42(64), and V0 = 273.67(19) A3, respectively. The structural parameters obtained from the refinement of the single-crystal data show that all the polyhedra around the cations become more regular upon compression. The softest polyhedra are the CaF8 units. Compared with previous investigations on LiMF4 scheelites (I41/a, Z = 4; M: Y3+, Gd3+, or Lu3+), in which the structural units most sensitive to increasing pressure are the LiF4 tetrahedra, our observations indicate that the compressibility mechanism in fluoride scheelites depends on the cationic substitution and distribution.