Inconsistencies of the complete sets of electromechanical constants of relaxor-ferroelectric single crystals

Complete sets of elastic, dielectric, and piezoelectric constants of relaxor-ferroelectric single crystals of (1 - x)Pb(A(1/3)Nb(2/3))center dot O-3 - xPbTiO(3) (A = Mg or Zn) and Pb(In1/2Nb1/2)O-3 - Pb(Mg1/3Nb2/3)center dot O-3 - PbTiO3 are analyzed to demonstrate violations of the interrelations between particular groups of electromechanical constants and the resulting influence of the inconsistent properties on the thermodynamic stability and electromechanical coupling in single crystals. The possibilities of refinement and correction of inconsistent constants are discussed and presented for specific examples of relaxor-ferroelectric single crystals.