ELECTROMECHANICAL DETERMINATION OF THE HIGH-FIELD PHASE-TRANSITION OF PB(MG1/3NB2/3)O-3-PBTIO3-(BA,SR)TIO3 RELAXOR FERROELECTRICS

Ceramics in the (1 - x)[(1 - y)Pb(Mg1/3Nb2/3)O3.yPb-TiO3].xMeTiO3 system, where Me is Sr or Ba, exhibit very large electrostrictive strains at reasonable drive fields. However, the optimum use temperature and frequency vary with the particular composition used. As relaxor ceramics, each composition has a broad transition from electrostrictive to partially piezoelectric behavior. The transition temperature (T(t)) can be roughly determined from strain or polarization properties; however, it can be more quantitatively determined from the effective electro-mechanical Q. A plot of induced transverse strain/induced polarization squared (effective Q12) as a function of temperature shows a sharp and unmistakable change in slope-this defines T(t). The slope of induced transverse strain/polarization (effective g31) also shows a change in slope at T(t), although this is more gradual than that of effective Q. The indicated T(t) correlates with those found from measurement of strain and polarization.