Effects of Segregation on Composition and Dielectric and Piezoelectric Properties of Pb(Mg_(1/3)Nb_(2/3))O_3-38%PbTiO_3 Single Crystal

Relaxor ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-38%PbTiO3 were grown directly from melt by a modified Bridgman technique. The segregation during the process of crystal growth was studied in details by measuring the Curie temperature and XRFA. The results show that the PbTiO3 content increases with the distance from the seed crystal. Through measuring the Curie temperature of the samples taken from the bottom and top of PMNT62/38 single crystal it is found that there exists variation of PT content along the parallel and perpendicular to the growth direction respectively. Due to the segregation, the PT content in the bottom is 35.2mol% and in the top, 43mol% and the dielectric and piezoelectric properties are different from each other. For the bottom samples the piezoelectric module for (110) is 1200pC/N, for (111) 789pC/N and for (001) 371pC/N. The dielectric constants (poled) in (110) and (111) orientations are larger than that of (001) and tend to increase with the temperature decreasing.