Time dependence of the mechanical quality factor in "hard" lead zirconate titanate ceramics: Development of an internal dipolar field and high power origin

The time dependences after poling of the mechanical quality factor Q(m), electromechanical coupling coefficient k(31) and dielectric constant K have been investigated for both "soft" and "hard" lead zirconate titanate (PZT) ceramics. A significant increase of Qm with time was observed for "hard" PZTs, however "soft" ones did not exhibit any changes during the same time period. The initial Qm value of rare earth modified Pb(Zr,Ti)O-3-Pb(Sb,Mn)O-3 was only 400 at 10min after poling; however, at t = 2800 min after poling, it had increased to 1600. Correspondingly, a pronounced increase in E-int was observed with In t. The aging rate after poling was found related to the degree of "hard" characteristics. For 10 < t < 2800 min after poling, the value of Qm for Yb modified Pb(Zr,Ti)O-3 increased from 160 to 250, whereas for Yb modified Pb(Zr,Ti)O-3-Pb(Sb,Mn)03 Qm increased from 400 to 1600 during the same time period. Polarization-electric field (P-E) measurements revealed the development of a shift of the response along the E axes with time. It is believed that an internal dipolar field develops with time, due to a reorientation of defect dipoles along the direction of spontaneous polarization. This results in domain stabilization and increased Q(m). It is proposed that internal dipolar field is the high power origin for "hard" type PZTs.