QUANTUM PHASE-TRANSITION IN K3D1-XHX(SO4)2

Dielectric and thermodynamic properties have been investigated in isotopically mixed crystals K3D1-xHx(SO4)2 with isolated hydrogen bonds interconnecting the dimeric SO42- units. The critical temperature T(c) for the antiferroelectric phase transition decreases with increasing proton concentration (x) and eventually the phase transition vanishes for x greater-than-or-equal-to x(c) approximately 0.66. The x-dependent behavior of T(c), the dielectric constant epsilon(T), and the specific heat jump DELTAC at T(c) are described by simple transverse Ising Hamiltonian. This indicates a determinative role of the proton tunneling in the phase transition and related properties.