The HRTEM image [Fig. 2(d)] shows t

The HRTEM image [Fig. 2(d)] shows that the surface of the coated powders of 1-5 have various distinct defects. The defect concentration decreases at the particle surface as the Ba source increases, which indicates that the defects are Ba vacancies. In addition, Ba deficiency occurs because Ba is more soluble than Ti during precipitation [22]. A 2 nm crystalline layer forms at the surface of powder 2-5 and is indexed to BaTiO3, as shown in Fig. 2(f). Upon increasing the Ba source in the precursor solution, an inhomogeneous layer with a crystalline part and an amorphous part appears at the surface of powder 3-5 [Fig. 2(h)]. The composition of the amorphous phase at the surface of powder 3-5 is hard to determine because EDS or mapping cannot analyze such a small area.