The Composition Segregation And Electric Properties Of PMN-PT Based Single Crystal

As a typical representative of the second generation of relaxor-Pb Ti O₃(PT)ferroelectric single crystals,Pb(Mg_1/3Nb_2/3)-Pb Ti O₃(PMN-PT),Pb(Zn_1/3Nb_2/3)-Pb Ti O₃(PZN-PT)and Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)-Pb Ti O₃(PIN-PMN-PT)have excellent piezoelectric,dielectric and electromechanical properties.In recent years,high quality and large size PMN-PT and PIN-PMN-Pt single crystals have been successfully grown by the Bridgman method,which has promoted their application.However,there is always compositional segregation in the process of growing PMN-PT and PIN-PMN-PT single crystals by the Bridgman method,which results in the compositional difference and electrical properties change along the growth direction from bottom to top of single crystals.It is very important to use seed crystal in the growth process to grow single crystal with high quality and high uniformity.Commonly used seed directions are<110>and<001>orientation.In the process of crystal growth,there are always some differences in composition segregation between different directions and different systems.It is of great significance to study the composition segregation and properties of PMN-PT and PIN-PMN-PT single crystals during their growth by Bridgman method for guiding their growth and promoting their application.The previous studies show that the properties of ferroelectric single crystals can be controlled by different polarization modes and different conditions.For the single crystal of different components after composition segregation,the uniformity of properties can be achieved through different polarization modes and conditions.Therefore,this paper systematically studied the composition segregation and property changes of PMN-PT and PIN-PMN-PT single crystals grown along<110>oriented which is the direction of seed crystal,PIN-PMN-PT single crystal grown along<001>oriented which is the direction of seed crystal and the effect of different DC poling electric field intensities on different components PIN-PMN-PT single crystal.In this article,we have successfully grown high-quality PMN-PT and PIN-PMN-PT with the length more than 100mm and the diameter about 70mm along the direction of the seed crystal using the<110>orientation seed crystal and the<001>orientation seed crystal by the vertical Bridgman method.The composition segregation and property changes of PMN-PT and PIN-PMN-PT single crystals grown in<110>orientation along the growth direction from bottom to top were studied respectively;the results showed the variation of component and properties of PMN-PT and PIN-PMN-PT single crystal are similar.The contents of PMN decreased from 73.81 mol%and 43.12 mol%to 69.75mol%and 40.94 mol%,respectively.The contents of PT increased from 26.19 mol%and23.13 mol%to 30.25 mol%and 26.86 mol%,respectively.In terms of electrical properties,along the single crystal growth direction from bottom to top,the electrical properties of PMN-PT single crystals showed an overall increased trend.The piezoelectric constant and dielectric constant increased from 1435p C/N and 4600 to1885p C/N and 5700 respectively.The dielectric and piezoelectric properties of PIN-PMN-PT single crystal show a trend of first increasing,then oscillating and then decreasing,the piezoelectric constant and dielectric constant vary from 1140-1720p C/N and 3800-4570 respectively.The composition segregation and properties changes of the PIN-PMN-PT single crystal grown in the<001>orientation along the growth direction were studied;the results showed that the segregation law is the same as that of the PIN-PMN-PT single crystal grown in the<110>orientation,and the PIN content is basically stable at 24mol%,PMN content decreased from 45 mol%to 42 mol%,and PT content increased from 31 mol%to 35 mol%.In terms of performance changes,the phase transition temperature and the Curie temperature gradually increase,the piezoelectric and dielectric constants show a similar trend of first increasing and then decreasing slowly.The relationship between the intensity of the DC poling electric field and the dielectric and piezoelectric properties of crystals of different components was studied.By modifying the traditional consistent poling method,the uniformity of dielectric and piezoelectric properties of PIN-PMN-PT single crystal from the bottom to the top is improved.After modified poling,the dielectric constants and piezoelectric constants of about 80%of the single crystal boule can be maintained at 4500-5000 and 1700-1900p C/N,respectively.The excellent uniformity of piezoelectric and dielectric properties is more conducive to the commercial application of PIN-PMN-PT single crystal.