Origin of Improvement in Mechanical Quality Factor in Acceptor-Doped Relaxor-Based Ferroelectric Single Crystals

The mechanical quality factor Qm in ferroelectric materials can be improved via acceptor doping to extend their application in high-power devices. It is generally believed that the improvement of Qm originates from the pinning effect of internal bias. However, the contributions from restricted spontaneous polarization (PS) rotation and clamped domain-wall motion are difficult to separate, leading to some ambiguities about the effect of doping. We report on a strong anisotropic pinning effect in Mn-doped 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystals and investigate the related mechanism. We observe that the domain-wall motion is not clamped by the internal bias but are strongly pinned by charged defects at the charged domain walls, whereas the PS rotation is suppressed by the internal bias. We also confirm that the enhancement of longitudinal factor Q33 is attributed mainly to the restricted polarization rotation, whereas the enhancement of shear factor Q15 is ascribed to both the restricted polarization rotation and the clamped domain-wall motion. Our results reveal the fundamental mechanism of the acceptor doping effects in relaxor-based ferroelectric materials, and they also provide important design principles to achieve high-Qm piezoelectric materials to satisfy the demands of high-power electromechanical devices.