Symmetry determination on Pb-free piezoceramic 0.5Ba(Zr_(0.2)Ti_(0.8))O_3-0.5(Ba_(0.7)Ca_(0.3))TiO_3 using convergent beam electron diffraction method

摘要

(1-x)Ba(Zr_(0.2)Ti_(0.8))O_3-x(Ba_(0.7)Ca_(0.3))TiO_3 (BZT-xBCT) Pb-free piezoceramic has been reported showing ultrahigh piezoelectric performance in its morphotropic phase boundary (MPB) region. However, the crystal structure characteristic for the MPB composition of BZT-jcBCT is still under debate-between single orthorhombic phase and tetragonal + rhombohedral two phase mixture. In the present study, we perform the local symmetry determination on the MPB composition x = 0.5 using convergent beam electron diffraction analysis (CBED). Our CBED results from multiple zone axes suggest that there are two coexisting phases with the point group symmetries of 4 mm (tetragonal) and 3 m (rhombohedral) respectively, which agree with two phase mixture model. The strong piezoelectricity can thus be understood by considering the polarization rotation between tetragonal and rhombohedral phases by external field.