**3. Characterization of ceramics**

The crystalline structure of the sintered ceramics was analyzed by X-ray diffraction (XRD) analysis at room temperature. The surface morphology was examined using field emission scanning electron microscopy (SEM), X-ray energy dispersive spectra (EDS) was measured using a Hitachi S-3400N scanning electron microscope with an EDS system Thermo Noran, and the densities of the ceramic samples were measured by the Archimedes method from the ceramic samples weighed in air, in water and the density of water. The grain size is determined from SEM micrographs by a linear intercept method. The dielectric properties of ceramics (relative dielectric constant and dielectric loss) were measured with a HIOKI 3532 impedance analyzer. The electromechanical coupling factors *k*p, *k*t and piezoelectric constant (*d*31) were determined by the resonance method according to the IEEE Standard 61 using an impedance analyzer Agilent 4196B and RLC HIOKI 3532 [32, 33]. The ferroelectric properties were measured by applying the Sawyer-Tower method [34].
