## 2 Materials and Methods  
At the first stage, a precursor of PbZr\({}_{0.53}\)Ti\({}_{0.47}\)O\({}_{3}\) (PZT) and Sb\({}_{2}\)O\({}_{3}\)/Sb\({}_{2}\)O\({}_{5}\)-doped BiY\({}_{1-x}\)Sb\({}_{x}\)O\({}_{3}\) [BYS(\(x\)), where \(x=0.0\), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6] was prepared by a conventional solid state method. In the final stage, the precursors of PZT and BYS(\(x\)) was mixed stoichiometrically to fabricate \(0.99\)Pb(Zr\({}_{0.53}\)Ti\({}_{0.47}\))O\({}_{3}\)-\(0.01\)Bi[Y\({}_{(1-x)}\)Sb\({}_{x}\)]O\({}_{3}\) (abbreviated as PZT-SYS(\(x\))) containing various amounts of Sb\({}_{2}\)O\({}_{3}\)/Sb\({}_{2}\)O\({}_{5}\) (\(0\leq x\leq 0.6\)). The pre-synthesis method was considered for the fabrication of PZT-SYS(\(x\)) to eliminate the effects associated with the direct co-doping. The stoichiometric amount of the analytical reagent (AR) grade Bi\({}_{2}\)O\({}_{3}\) (\(99.9\%\), High Purity Chemicals, Japan), Sb\({}_{2}\)O\({}_{3}\) (\(99.9\%\), High Purity Chemicals, Japan) and Y\({}_{2}\)O\({}_{3}\) (\(99.9\%\), High Purity Chemicals, Japan) were weighed to synthesize Bi(Y\({}_{1-x}\)Sb\({}_{x}\))O\({}_{3}\) [BYS(\(x\))] (where, \(x=0.0\), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6). The BYS(\(x\)) was then ball milled in distilled water using a ZrO\({}_{2}\) media for 24 h. The same specimens of BYS(\(x\)) were also prepared by using Sb\({}_{2}\)O\({}_{5}\) (\(99\%\)Samchun Pure Chemical, Mokock-dong Pyeongtaek, Korea). According to the thermogravimetric and differential scanning calorimetry (TG/DSC-Mettler Toledo) analysis, both Sb\({}_{2}\)O\({}_{3}\) and Sb\({}_{2}\)O\({}_{5}\)-doped BYS(\(x\)) powders were calcined at 800 \({}^{\circ}\)C for 2 h in alumina crucibles. A detailed synthesis process of Pb(Zr\({}_{0.53}\)Ti\({}_{0.47}\))O\({}_{3}\) (PZT) and BiYO\({}_{3}\) (BY) were described in previous work [13]. The pre-synthesized PZT and BYS(\(x\)) powders were weighed according to reaction stoichiometry to fabricate PZT-BYS(x), and ball-milled for 72 h. The dried powders were pressed as a disk of 15 mm diameter and then cold isostatically pressed (CIP) under a pressure of 147.2 MPa. The pressed pellets were sintered at various temperatures between 1050 \({}^{\circ}\)C and 1250 \({}^{\circ}\)C in air and an oxygen (O\({}_{2}\)) rich atmosphere. An equimolar mixture of PbO and ZrO\({}_{2}\) inside a covered alumina crucible was used to limit PbO loss from pellets during sintering. The sintered specimens were then polished to obtain parallel surfaces and suitable dimensions (diameter/thickness \(\geq\)15) to estimate the piezoelectric properties. The specimens were characterized using an X-ray diffractometer (XRD, D/Max-2500H, Rigaku, Tokyo, Japan and D8 advance, Bruker, Karlsruhe, Germany) with Cu K\(\alpha\) radiation after sintering. The morphologies and the microstructures for all of the powders and sintered samples were investigated using a scanning electron microscope (Hitachi S-2400, Tokyo, Japan). In order to measure the electrical properties, we used silver paste to form electrodes on both sides of the sample, which was then fired at 560 \({}^{\circ}\)C for 30 min. For investigating the proper poling conditions, we poled each specimen in stirred silicon oil at 120 \({}^{\circ}\)C by applying a DC electric field of 3-6 kV/mm for 45 min; subsequently, the sample was aged at 120 \({}^{\circ}\)C for 3 h. The dielectric and the piezoelectric properties of the aged samples were then measured and evaluated. A preliminary study indicated that the spontaneous polarization was fully saturated under a DC electric field of 4 kV/mm. Therefore, the optimum poling voltage was chosen as 4.0 kV/mm. A standard deviation of the electric properties could exist in the measured samples, so five specimens were prepared for each batch and tested.