Size effects of the dielectric prop

Size effects of the dielectric properties indicate a strong correlation between particle size and dielectric properties. As particle size decreases in the micrometer range, dielectric constant first increases significantly, reaching to a maximum value (B6000) at some particle size, and finally decreases when further decreasing particle size to below the micrometer range, as shown in Fig. 2a. The particle size, where dielectric constant reaches maximum, depends heavily on the synthesis methods and process histories. For example, maximum dielectric constant (e0) of 6079 was achieved for BaTiO3 ceramics prepared by two-step sintering method with the particle size of approximately 1 mm.Another change accompanying the grain/particle size decrease is a reduction in the Curie temperature (TC), which is the transition temperature between tetragonal and cubic phases (Fig. 2b). As a result, the room-temperature tetragonal distortion and hence ferroelectricity is gradually reduced with decreasing particle size. The critical size below which the room-temperature ferroelectricity of BaTiO3 nanoparticles disappears varies greatly with the synthesis methods and is normally in the range of 10–100 nm.46 Other factors, such as microstructure, composition, stress, defect concentration and interfacial effects, can also affect the critical size of ferroelectricity in BaTiO3 nanocrystals.