PHASE COEXISTENCE IN PROTON GLASS. V.H. Schmidt, Physics Dept., Montana St. U., Bozeman, MT 59717, Z. Trybula, Inst. Molec. Physics, Polish Acad. Sci., Poznan, Poland, N.J. Pinto, Dept. Physics & Elec., U. Puerto Rico, Humacao, PR 00661, S.M. Shapiro, Physics Dept., Brookhaven Nat. Lab., Upton, NY 11973

Proton glasses are crystals of composition M_l-X(NW₄)_XW₂AO₄, where M=K,Rb, W=H,D, A=P,As. For x=0 there is a ferroelectric (FE) transition, while for x=1 there is an antiferroelectric (AFE) transition. In both cases, the transition is from a paraelectric (PE) state of tetragonal structure with dynamically disordered hydrogen bonds to an ordered state of orthorhombic structure. For an intermediate x range there is no transition, but the hydrogen rearrangements slow down, develop a spread in time constants, and eventually display nonergodic behavior characteristic of glasses. For x near 0, we have shown that the FE and PE phases coexist over a wide temperature range, and that similar AFE/PE coexistence occurs for x near 1. One evidence for coexistence is dielectric permittivity [[epsilon]] that decreases gradually rather than abruptly below the FE or AFE transition. Another is spontaneous polarization P_s that increases gradually rather than abruptly below the FE transition. The FE order parameters deduced from the [[epsilon]] and P_s measurements agree very well. Evidence for coexistence appears also in deuteron NMR spectra. A fourth evidence is coexistence of neutron diffraction spots for the FE and PE phases, and for the AFE and PE phases, over wide temperature ranges. Remaining to be determined are the correlation lengths for the coexisting phases, the temporal vs. spatial nature of the coexistence, and the rate and detailed nature of the hydrogen rearrangements responsible for the dynamic behavior. In general, these dynamics are associated with correlated hydrogen intrabond transfers responsible for creation, effective diffusion, and annihilation of WAO₄ and W₃AO₄ groups. Such groups are much more numerous in the PE than in the FE or AFE phases, so one can expect much faster dynamics in the PE phase than in the ordered phases in the coexistence regime.