Geometric and quantum aspects of phase transition and isotope effect in hydrogen-bonded ferroelectrics and related materials

摘要: Structural phase transitions in hydrogen-bonded (H-bonded) ferroelectrics and related materials are reviewed from the geometrical viewpoint of H-bond system. It is pointed out that isotope effect transition temperature Tc has a correlation with symmetry its geometric effect. shown among isomorphous members, liner relation between O c distance R valid three dimensionally (3-D) H-bonded tetragonal KH2PO4-, 2-D squaric acid (H2C4O4)-, 1-D CsH2PO4-, PbHPO4-, 0-D M3H(SeO4)2-type crystals. Implication linear as negative evidence for proton-tunnelling model discussed. emphasised characteristic responsible even low-temperature M3H(XO4)2-type crystals which members have no quantum ferroelectrics. The disappearance discussed manifestation at low isotopic downward shift temperatu...