Diffraction-derived spontaneous polarization in lithium sulfate monohydrate at 80 and 298K.

The charge and electric dipole moment distributions in the sulfate ion and in the water molecule are derived for Li sub 2 SO sub 4 . H sub 2 0 on the basis of previously determined net atomic charges [J. Chem. Phys. 85, 5221 (1986)]. The sulfate ion has a nonzero dipole moment of about 2.3 x 10 sup (-30) C. m at 80K that rotates 9degrees in the crystallographic a, c plane between 298 and 80K. The dipole moment of the water molecule increases from about 6.7 x 10 sup (-30) C . m at 298K to 7 . 8 x 10 sup (-30) C . m at 80K, as it rotates 3 . 6degrees in the b, c plane. The total spontaneous polarization at 298K is calculated to be 3 . 19(62) x 10 sup (-2) C . m, and at 80K it is 4.37(51) x 10 sup (-2) C . m sup (-2), along the positive direction of the polar axis. The sense and magnitude of the resulting calculated 1 . 18 x 10 sup (-2) C . m sup (-2) polarization change compares well with the experimental value of 1 . 04 x 10 sup (-2) C. m sup (-2) measured on heating through the same temperature interval.