分凝对Pb(Mg1/3Nb2/3)O3-38%PbTiO3单晶的成分及介电、压电性能的影响

研究了用改进的Bridgman法生长的PMNT62／38单晶在其生长过程中的分凝现象，研究了分凝导致的成分不均匀及其对介电和压电性能的影响。XRFA分析表明，PMNT62／38单晶底部的PbTiO3(PT)含量为x=35.2mol%，而顶部的PT含量为43mol%。底部晶体（001），（110）和（111）三种切型的晶片加电场极化后，其介电和压电性能出现了异常的现象。（110）切型的压电模量最大，为1200pC/N；（111）次之，为789pC/N；（001）最低，为371pC/N。极化后的（110）和（111）晶片在室温、1kHz频率下的相对介电常数（两种切型的εr都在10000左右），约为（001）晶片（εr-5000)的1倍，并且介电常数在低温端有上升的趋势。

Effects of Segregation on Composition and Dielectric and Piezoelectric Properties of Pb(Mg1/3Nb2/3)O3-38%PbTiO3 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.