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In this article, low dielectric loss pure or Mndoped BiFeO 3 -Bi(Zn 1/2 Ti 1/2 )O 3 -BaTiO 3 (BF-BZT-BT) lead-free piezoceramics with various compositions were prepared using a refined solid state reaction electroceramic processing. The rhombohedral-pseudocubic structural phase boundary was determined with powder X-ray diffraction method and found dependent on ceramic grain size, which shifts far away from the BF-rich corner with increasing microstructure grain size. In contrast to BF-BT binary system, low dielectric loss was understood by mechanism of reduction of oxygen vacancies with doping MnO 2 combined with stabilization of Bi-perovskite phase by adding BZT third member. Full piezoresponse of d 33 C 145 pC/N was obtained in the Mn-doped BF-xBZTyBT (0.01 \ x \ 0.05 and 0.27 B y B 0.31) coarsegrained ceramics near the structural phase boundary, in agreement with prediction by relationship of d 33 = ae 33 -be 33 2 . Ferroelectric polarization subswitching and related low piezoresponse observed in the BZT-riched ceramics were observed and argued extrinsically resulting from residual internal stresses. Primary experiments showed annealing and subsequent quenching treatment eliminate residual internal stresses and increase piezoresponse for the BZT-riched ceramics.

Perovskite-structured 0.696BiFeO 3 -0.014Bi(Zn 1/2 Ti 1/2 )O 3 -0.29BaTiO 3 (BF69.6-BZT1.4-BT29) lead-free piezoceramics with various MnO 2 addition were prepared using a refined solid state reaction electroceramic processing. Powder X-ray diffraction measurements showed their crystallographic structure being of rhombohedral structure and scanning electron microscopy observations revealed that MnO 2 -doping enhances ceramic microstructure grain size growth. In contrast to BF-BT ceramics, low dielectric loss ceramics were obtained with combined strategies of refined electroceramic processing, Mn-doping and adding BZT third member. A good combination of ferroelectric and piezoelectric property was obtained in the 0.22 and 0.26 % in weight MnO 2 -doped BF69.6-BZT1.4-BT29 coarse-grained ceramics and discussed in relation to microstructure grain size effect and point defect effect. Excellent time and thermal aging stabilities of piezoelectric constant d 33 were also experimentally demonstrated and argued resulting from the feature of higher ferroelectric Curie temperature (T C ) and no ferroelectric-ferroelectric structural phase transition below T C of BF-BZT-BT system.

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The details of the ZnO doping effects on the polarization switching are further illustrated in Fig. 2 and vertically a͒