Abstract
The proton ordering model of the phase transition and physical properties of antiferroelectric crystals of squaric acid is modified by taking into account the influence of diagonal lattice strains and of the local geometry of hydrogen bonds, namely of the distance $\delta$ between the H-sites on a bond. Thermal expansion, the spontaneous strain $\varepsilon_1-\varepsilon_3$, and specific heat of squaric acid are well described by the proposed model. However, a consistent description of hydrostatic pressure influence on the transition temperature is possible only with further modifications of the model.
Highlights
The crystals of squaric acid, H2C4O4 (3,4-dihydroxy-3-cyclobutene-1,2-dione) are an epitome of two-dimensional antiferroelectrics
In [12] the proton-phonon coupling was added, and hydrostatic pressure effects on the phase transition temperature and dielectric permittivity of pure and deuterated squaric acid crystals were described by assuming the model parameters to be pressure dependent and by performing a new fitting procedure for each considered value of pressure
Since the antiferroelectric phase transition in squaric acid is usually attributed to proton ordering, which triggers displacements of heavy ions and rearrangement of electronic density, it is expected that just like in the KH2PO4 family crystals, in the squaric acid the pressure-induced changes in the geometry of the hydrogen bonds should play an important role in the pressure influence on the phase transition
Summary
The crystals of squaric acid, H2C4O4 (3,4-dihydroxy-3-cyclobutene-1,2-dione) are an epitome of two-dimensional antiferroelectrics. In [12] the proton-phonon coupling was added, and hydrostatic pressure effects on the phase transition temperature and dielectric permittivity of pure and deuterated squaric acid crystals were described by assuming the model parameters to be pressure dependent and by performing a new fitting procedure for each considered value of pressure. Since the antiferroelectric phase transition in squaric acid is usually attributed to proton ordering, which triggers displacements of heavy ions and rearrangement of electronic density, it is expected that just like in the KH2PO4 family crystals, in the squaric acid the pressure-induced changes in the geometry of the hydrogen bonds should play an important role in the pressure influence on the phase transition. We think it safe to assume that in our calculations tunneling can be neglected
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
