Charge density in Pyroelectric Lithium Sulfate Monohydrate at 80 and 298K.

Temperature dependent changes in electronic distribution can best be detected by diffraction methods in crystals having all atoms of low atomic number. Pyroelectric Li(2)S0(4).H (2)0 has hence been studied at 80 and 298K by x-ray and neutron diffraction. The monoclinic crystal with space group P2, has lattice dimensions at 298K of a = 5.4553(1), b = 4.8690(1), c = 8.1761(2)Angstroms and beta = 107.337(2)omicron; lattice dimensions at 80K were reported in our neutron study [J. Chem. Phys. 80, 423 (1984)]. Least-squares refinement based on 3486 (80K) and 3390 (298K) independent reflections, assuming a spherical atom model, results in final R(F(2)) values of 0.024(80K) and 0.026(298K). Static deformation and charge density model refinement, based on Hirshfeld-type multipole functions, greatly reduces the residual electron density and gives R(F(2)) values of 0. 017(80K) and 0.016(298K). Refinement of the resulting multipole parameters within the Gaussian radial dependence model allows a qualitative estimation of the differences in electron densities between 80 and 298K.