Phase coexistence in proton glass

Proton glasses are crystals of composition M1-x(NW4)(x)W(2)AO(4), where M = K, Rb, Cs, W = H, D, A = P, As. For x = 0 there is a ferroelectric (FE) tr ansition, while for x = 1 there is an antiferroelectric (AFE) transition. I n both cases, the transition is from a paraelectric (PE) state of tetragona l structure with dynamically disordered hydrogen bonds to an ordered state of orthorhombic structure. For an intermediate x range there is no transiti on, but the hydrogen rearrangements slow down, and eventually display noner godic behavior characteristic of glasses. We and others have shown from spo ntaneous polarization, dielectric permittivity, nuclear magnetic resonance, and neutron diffraction experiments that for smaller x there is coexistenc e of ferroelectric and paraelectric phases, and for larger x there is coexi stence of antiferroelectric and paraelectric phases. We present a method fo r analytically describing this coexistence, and the degree to which this co existence is spatial and/or temporal. We discuss also the experimental dete rmination of these coexistence parameters.