Microscopic Theory of the Phase Transitions in Rochelle Salt

Local field at general positions in Rochelle salt crystals is considered on the basis of the symmetry. The variation in dipole moments on each sublattice caused by applied electric field is obtained. The conditions for the instability of dipole arrangement are given for P2 1 2 1 2, P2 1 11, P12 1 1, P112 crystals in terms of susceptibility of dipolar radicals and Lorentz factors. The nature of electrostatic interaction energy of Rochelle salt is clarified, by taking into account the dipole-dipole interaction as well as the dipole-charge interaction between sublattices and also the electronic polarizability of ions situated on the two-fold axes along the c direction. Some coefficients which appear in Mitsui theory are reexamined under the light of the present results.