Tunnelling Model for Quasi‐One‐Dimensional Hydrogen‐Bonded Crystals

Abstract
Tunnelling term is included in the Hamiltonian of an anisotropic Ising model which is used to explain the thermodynamic properties of quasi‐one‐dimensional hydrogen‐bonded ferroelectric crystals. A variational approach is used to treat the strong intrachain interactions accurately, while the weak interchain interactions are accounted for in a mean‐field approximation. Also, fittings are presented of some experimental data pertaining to crystals of PbHPO4.