Pseudospin Hamiltonian parameters evaluated with regard to alkali metal ions in K₃(H/D)(SO₄)₂ materials

Abstract

An analysis of ferroelectric behavior of K 3 (H/D)(SO 4 ) 2 as members of the M 3 (H/D)(AO 4 ) 2 family is examined quantum chemically in the cluster approach using the structural models extended through the incorporation of K ions in an explicit form. We apply several structural models that describe the different types of (H/ D)(SO 4 ) 2 -dimer surrounded by K ions, the geometry of the dimer being borrowed from the corrected diffraction data of the K 3 D(SO 4 ) 2 crystal in its ordered phase at the temperature below critical point T c ϭ 85 K. The calculations of the pseudospin Hamiltonian parameters-the Ising coupling parameters J ij and tunneling integrals ⍀-were performed on the Hartree-Fock and second-order Møller-Plesset perturbation theory levels with the 6-31G-type basis sets. It is demonstrated that an effect of the K ions incorporation on the J ij values is minor (about several Kelvins). At the same time an influence of these ions on the double-well potential characteristics (particularly, on the barrier heights) and thus on the tunneling integral value is more pronounced for both D-and H-containing species. Despite the changes of the Hamiltonian parameters found, the major conclusion obtained earlier, referring to the suppression of the structural phase transition in H-containing specimens due to proton quantum fluctuations, remains valid. The numerical estimations of the critical temperature T c for completely deuterated materials that are obtained with and without regard to alkali metal ions are discussed.

Compressed H-bonds in solids. Pressure-dependent ferroelectric behavior of KDP/DKDP

“…Thus the presence of K ions does not substantially affect the gap (E À À E + ) although may affect E À and E + itself. The calculations verifying this conclusion were made for K 3 (H/D)(SO 4 ) 2 [12]. These calculations confirmed also the minor influence of K ions presence on J ij values.…”

“…These calculations confirmed also the minor influence of K ions presence on J ij values. The calculations made in [12] demonstrated also the absence of the noticeable influence of the K ions presence on the J ij values in the Hamiltonian (2).…”