Fractal Model for Dielectric Relaxation in Deuteron Pseudospin Glass DRADP

Proton and deuteron glasses such as Rb1−x(ND4)xD2PO4 (DRADP) are ideal systems for investigating dynamics of spin‐glass‐type systems because the basic mechanism for their dynamics is well understood. This mechanism consists of three processes; creation, effective diffusion, and annihilation of DPO4 and D3PO4 “Takagi groups.” Each process involves a deuteron transfer from one side of an O–D⋯O bond to the other. The effective diffusion changes the configurational energies of the D2PO4 “Slater groups” traversed by the Takagi groups. Each diffusion step changes this energy by a random amount with magnitude of order ed. This ed is comparable to the basic energy e0 of the Slater model for RbD2PO4, and considerably smaller than the Takagi DPO4‐D3PO4 pair creation energy 2ec. The Takagi group diffusion path between creation and annihilation on average does not change the configurational energy. Thus the energy landscape along the path has an unbiased fractal nature, with small energy barriers superimposed on larg...