Theory of related to shear strain u₆ physical properties of ferroelectrics and antiferroelectrics of the KH₂PO₄ family

Abstract

We propose an extension of the proton tunneling model in order to study related to the shear strain u 6 dielectric, piezoelectric, and elastic properties of ferro-and antiferroelectrics of the KH 2 PO 4 family. This strain is introduced into the proton Hamiltonian via the linear contributions into the configurational energies of protons surrounding an oxygen tetrahedron. In the four-particle cluster approximation for the short-range interactions and the mean field approximation for the long-range interaction we explore the phase transition and piezoelectric effect in the KH 2 PO 4 ferroelectrics. In the paraelectric phase the dielectric, piezoelectric, and elastic characteristics of the NH 4 H 2 PO 4 antiferroelectrics are calculated. At the proper choice of the theory parameters a good agreement between theoretical and experimental results is obtained. Taking into account of the piezoelectric coupling with the shear strain u 6 allows one to calculate the static dielectric permittivities of free and clamped crystals as well as to obtain a good description of ferroelectric spontaneous shear strain u 6 .

Longitudinal relaxation of ND_{4}D_{2}PO_{4} type antiferroelectrics. Piezoelectric resonance and sound attenuation

“…The obtained results for the ADP crystals are compared with the calculations performed in [6,7]. It is established that tunneling practically does not affect the static dielectric, piezoelectric, and elastic characteristics of ADP.…”

“…Important results for strained ferroelectric compounds of the KH 2 PO 4 type were obtained in [3][4][5][6][7][8][9][10][11]. In [3,4] the proton ordering model was modified by taking into account the ε 6 contributions to the proton subsystem energy linear in strain.…”

“…The obtained Hamiltonian contains a deformational molecular field and takes splitting of lateral proton configurations into account. Later [5][6][7] all possible splittings of proton configuration energies by the strain ε 6 were taken into account. In [5] a phase transition in the strained K(H 0,12 D 0,88 ) 2 PO 4 crystal was explored; its thermodynamic, longitudinal dielectric, piezoelectric, and elastic characteristics were calculated; the effect of the stress σ 6 on the calculated quantities was studied.…”

“…In [5] a phase transition in the strained K(H 0,12 D 0,88 ) 2 PO 4 crystal was explored; its thermodynamic, longitudinal dielectric, piezoelectric, and elastic characteristics were calculated; the effect of the stress σ 6 on the calculated quantities was studied. Similar calculations of thermodynamic, longitudinal and transverse dielectric, piezoelectric, and elastic characteristics of KH 2 PO 4 type ferroelectrics were performed in [6][7][8] with tunneling taken into account. A good description of experimental data for the KH 2 PO 4 ferroelectrics and NH 4 H 2 PO 4 antiferroelectrics in the paraelectric phase was obtained.…”

“…In [5][6][7][8][9][10][11], the dynamic properties of KH 2 PO 4 type ferroelectrics were not studied with taking into account the piezoelectric coupling. Such a problem, however, is very important.…”