| High performance piezoelectric materials are widely used in medical ultrasound imaging,industrial nondestructive testing,underwater sonar,ultrasonic motor and other fields.Perovskite type relaxor ferroelectrics,Pb(Mg1/3Nb2/3)O3-x Pb Ti O3(PMN-x PT)single crystal exhibits the highest performance,such as piezoelectric coefficient d33 > 4100 p C/N,electromechanical coupling coefficient k33 > 94%,and is the core material of high-end piezoelectric devices.Researchers have done extensive and in-depth research on the origin of its giant piezoelectric properties,and hope to design and develop new giant piezoelectric materials with higher performance.Among them,the study of PMN-x PT ferroelectric domain structure and its polarization reversal characteristics is one of the important ways to understand its high performance.In the early stage,scientists have carried out in-depth and systematic research on the domain structure of PMN-x PT near the Morphotropic Phase Boundary(MPB),and many important achievements have been made.In this paper,the static domain structure in different crystal directions and the in-situ polarization reversal characteristics along the applied electric field in different crystal directions of PMN-38%PT single crystal(4mm point group),which has with high Curie point,high piezoelectric performance and high light transmittance,were studied by polarizing microscope(PLM)and PFM.The specific work is as follows:1)by the newly improved sample preparation method,the(100)-,(110)-and(001)-cut high quality PMN-38%PT single crystal sheet with a thickness of 5-50 ?m,and flat smooth surface was prepared.A platform module which can apply high strength electric field(0-200 kv/cm)onto sample is designed,and which can solve the problem of image jitter and real-time of image acquisition when applying electric field.High quality ferroelectric domain structure pictures and dynamic experimental results under in situ applied electric field were obtained.2)the static domain structure of(100)-,(110)-and(001)-cut tangential PMN-38%PT single crystal was observed with PLM,and large-scale and high-resolution domain structure photos were obtained,and the three-dimensional domain structure distribution form was constructed.The spatial distribution and projection of 90° domain wall are analyzed in detail.The orientation and angle values of the primary domain walls in the three cut directions are verified,and the formation of the widened primary domain walls is confirmed.Combined with the PFM experimental results,the quasi-parallel or vertical relationship between the needle-like micro domain and the main macrodomain walls is explained.These results provide a strong support for the study of domain structure of tetragonal ferroelectric single crystal.3)In-situ polarization reversal process of ferroelectric domains under the electric fields along [100],[011],[001] and [110] of PMN-38%PT single crystals was studied.Results show that,when the electric field is along [001],the direction of spontaneous polarization of the single crystal,the single domain can be formed under a lower electric field(10k V/cm),and the single domain can still be maintained after the electric field is removed.An electric field is applied along the [101]/[011] single crystal.When the electric field strength reaches 20 kV/cm,the locally unstable mono-domain can be achieved.At the same time,a field-induced phase change will occur under this electric field,resulting in extinction.The applied electric field along [011] two-steps 90° domain reversal was observed.In the first step,it flips intensively under a low electric field(3-5 k V/cm),and slowly under a high electric field(5-15 k V/cm)in the second step.In this paper,the domain structures and their polarization reversal characteristics under different cut type and electric field directions are important for understanding the piezoelectric anisotropy of tetragonal phase ferroelectric single crystal. |
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