Low-Temperature Phase Transition and Structure of Ordered Phase in K3H(SO4)2 (TKHS)-Family Materials

摘要: Abstract Suitability of quantum chemistry to describe the structural phase transitions on semi-quantitative level in H-bonded ferroelectrics and related materials has been demonstrated. The low-temperature H/D-ordering have treated for TKHS-like scope static dynamic Ising models. Parameters Ising-type Hamiltonians are evaluated Hartree–Fock/second-order perturbation theory using available diffraction data. type D-ordering M 3 D(AO 4 ) 2 specimens, which is debated so far, proposed limits model. As shown this ordering points out antiferroelectric-type structure with b -doubling paraelectric A 2/ a cell admits c cell. Estimations T fully deuterated specimens obtained by Bethe cluster approximation An absence such transition H(AO explained both proton fluctuations (tunneling effect) differences geometries H- D-bonds (geometric isotope effect).