On elastic dipoles in Li metanibate ceramics

It was established that in contrast to triaxial BaTiO₃-type ferroelectrics (FE) the abnormally large values of elastic compliance S₁₁^E (abnormally small values of elastic modulus C₃₃^D) are characteristic for ceramic uniaxial lithium metanibate (LMN) while retaining usual (corresponding to the averaged values of single-domain crystal constants) values of dielectric permittivity. It was suggested that the additional contribution to the strain and elastic compliances of the LMN ceramics is due to the existence of two-minimum asymmetrical potential of Li ions in sonic mechanically strained unit cells inside crystallites that because of the interaction of Li ions with the surrounding lattice leads to the appearance of elastic dipole moments (elastic dipoles) distributed in random way and capable of reorientation in the field of mechanical stress of the acoustic wave that FE crystals with single-particle potential have the specific mechanism of redistribution of incompletely ordered Li ions, induced by mechanical stresses. These stresses lead to essential increase of elastic compliances in comparison with mean ones for corresponding monocrystals. This circumstance causes decrease of the speed of propagation of acoustic waves in ceramics in comparison with theoretically obtainable speeds