Refinement of Crystal Structure of Ferroelectric Ca2Sr(C2H5CO2)6 in the Paraelectric Phase

The absolute structure of Ca 2 Sr(C 2 H 5 CO 2 ) 6 at room temperature was determined by using X-ray reflection data collected by a four-circle automatic diffractometer with the R -factor of 0.027. The space group of levorotatory crystals is D 4 4 -P4 1 2 1 2 and that of dextrorotatory ones D 4 8 -P4 3 2 1 2. A difference Fourier synthesis revealed that electron densities of the methyl groups exhibited doubly peaked or largely elongated contours. The split-atom calculation has established that four of the methyl groups together with one of the α-carbons in a formula unit are in disordered state occupying respectively two equilibrium atomic positions with the same probability.