| Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-Pb Ti O3（PIN-PMN-PT）single crystal has a wide application in ultrasonic medical detection,ultrasonic electromechanical conversion devices,energy acquisition and so on because of its improved Curie temperature and higher coercive field,as well as its huge electric properties.However,the mechanical quality factor（Qm）is too small and the loss is too high to applicated in high-power ultrasonic devices.Acceptor doping（e.g.,Mn-doping）in PIN-PMN-PT single crystal is an effective method to improve the mechanical quality factors.The physics mechanism of this enhancement by doping Mn is still unclear,and the physics mechanism needs to be clarified.The mechanical quality factor improvement always accompanies the decrease of the piezoelectric constant.The two performances are difficult to enhance simultaneously,limiting PIN-PMN-PT application in high power devices.It was reported that the alternating current poling（ACP）method is an effective method to enhance the piezoelectric constant with the dielectric loss reduction.It gives a possibility to realize the simultaneous improvement of the mechanical quality factor and piezoelectric constant.However,there are few studies about the ACP method’s influence on the mechanical quality factor.The specific effects and related physical mechanisms of the ACP method need to be further studied.Although numerous researchers have made many efforts and achievements in the physics mechanism of doping Mn in the perovskite ferroelectric materials and the ACP method,several scientific and technical issues need to be clarified.At present,there are several issues in this field as follows:Firstly,the intrinsic relationship between the“pinning effect”of the defect dipoles and the mechanical quality factor enhancement in Mn-doped PIN-PMN-PT single crystal is still not deep enough.Secondly,the ACP method might realize the mechanical quality factor’s and piezoelectric property’s enhancement simultaneously.At present,the physical mechanism of the ACP method’s influence on the mechanical quality factor has not been reported.In addition,the physics mechanism that the piezoelectric and dielectric constants can be significantly improved by the ACP method is still controversial.Because of the above problems,the main contents of this paper are as follows:Firstly,it is revealed that doping Mn makes the anisotropy of the parent ferroelectric material enhanced.The domain structures measured by PFM and the domain wall motion calculated by the Rayleigh analysis method of PIN-PMN-PT single crystal with and without Mn are carried.It demonstrates the physical mechanism of the Mn-doped effect anisotropy principally comes from the following:1)The clamping effect of defect dipoles would be different due to the different spontaneous polarization responses under varied vibration modes.2)Charged domain walls are more stable than neutral domain walls,and the distribution of charged domain walls is space-dependence in Mn-doped single crystal.The interaction of the defect dipoles and the charged domain walls makes the mechanical quality factor enhancement anisotropy.The mechanical quality increase is 156%for Q15,100%for Q24 and 81%for Q33.Secondly,for the unclear physical mechanism of the ACP method,the properties of the ACP and DCP samples are studied in the lead niobium indium magnesium-lead titanate single crystal with“2R”engineering domain structure,wishing to realize the mechanical quality factor’s and the piezoelectric property’s improvement at the same time.The electrical properties,mechanical quality factor,domain wall motion and domain patterns of the ACP samples are measured,compared with those of the DCP samples.It demonstrates that the ACP method increases the domain wall density,which leads to the irreversible domain wall motion improving 17%,and the intrinsic lattice distortion contribution of the ACP sample increases slightly.As a result,the mechanical quality factor Q33 reduced 18%,the piezoelectric constant d33 increased 6%,and dielectric permittivityε33 improved 16%.Finally,in view of the controversial physical mechanism of the ACP method for enhancing piezoelectric and dielectric coefficients and the unclear influence on the mechanical quality factors,the properties（e.g.,the intrinsic lattice distortion contribution,the domain wall motions,the domain patterns,and so on）of different engineering domain structure single crystals poling by the ACP/DCP method were measured.It revealed that the piezoelectric/dielectric property and the mechanical quality factor could be improved simultaneously by the ACP method because of the increasing intrinsic lattice distortion and the larger domain size.The ACP method could regulate the domain structure,reducing the 71o domain walls and remaining the 109odomain walls.And then,the decreasing internal strain enhances the piezoelectric constant and the dielectric permittivity by 20%,respectively,and improves the mechanical quality factor by 148%. |
