*2.3. Characterization*

X-ray diffractometer (XRD) patterns were obtained to validate the phase purity and crystallinity of the powders on the XRD equipment (Rigaku Smartlab Beijing Co, Beijing, China). Scanning electron microscope (SEM) images of the prepared catalysts, including energy dispersive X-ray spectroscopy (EDS) capabilities, were measured with an SEM Regulus 8230, Hitachi Co, Tokyo, Japan. The transmission electron microscope (TEM) was used by JEOL JEM-F200 (Tokyo, Japan). The absorption spectra of these powders were tested in a UV-vis spectrophotometer (PerkinElmer Lambda 35, Waltham, MA, USA). X-ray photoelectron spectroscopy (XPS) was carried out with a ESCALAB 250, Thermo-VG Scientific, Waltham, MA, USA to analyze the components and the valence states. The specific surface areas of the samples were tested by Micromeritics ASAP 2460 Brunauer-Emmet-Teller (BET, Shanghai, China) equipment with N2 as the carrier gas. The polarization electric field (P-E) loops and electric-field-induced strain (S-E) were tested in silicone oil at room temperature with 1 Hz frequency using a MultiFerroic II, Radiant technologies Inc., Albuquerque, New Mexico. The sample powders were pressed in a pellet (1 cm diameter and 0.20 mm thick) with Polyvinyl Alcohol (PVA) solution as a binder and then annealed at 600 ◦C to burn out the PVA binder. The pellets were coated on both sides with Au electrodes.
