Abstract
The quasi-one-dimensional crystals with phase transition (PT) attract much attention because thermodynamical properties of such cryetals can be described theoretically with high accuracy and it is possible to check them experimentally. Quaei-one-dimensional ferro- and anti ferroelectrics PbHPO4 and CsH2PO4 with their deuterated isomorphs have been the subject of a number of recent studies1-12.