Grain-size effects on dielectric properties in barium titanate ceramics

Abstract

Measurements of the dielectric constant κ in high-purity BaTiO3 ceramics as a function of temperature show that κ is quite dependent on grain size in the ferroelectric state while it is almost independent of grain size in the paraelectric state. In the ferroelectric orthorhombic and rhombohedral phases, κ decreases rapidly with lowering temperature when grain size is reduced smaller than 3 μm. It is also observed that the Curie temperature Tc is decreased very slightly, but the lower two transition points are shifted to higher temperatures as grain size decreases.

Domain Wall Displacement is the Origin of Superior Permittivity and Piezoelectricity in BaTiO3 at Intermediate Grain Sizes

“…It is further understood that domain wall motion within polycrystalline materials never results in a complete c-axis-oriented domain state due to intergranular mechanical constraints; remanent a-axis oriented domains remain in nearly all materials. These remanent a-axis oriented domains are 16 observed in the present experiments in the (200) intensity of the tetragonal phase. If the energy barrier for transition into an alternate polymorphic phase is low (e.g., due to the residual or induced stress state in polycrystals, proximity to the phase transition in temperature or composition, etc.…”

“…In polycrystalline ferroelectrics, size effects are chiefly evident in materials properties such as the relative dielectric permittivity ( r ) and piezoelectric coefficients (e.g., d 33 and d 31 ). For polycrystalline barium titanate (BaTiO 3 ), the effect of grain size on the relative permittivity has been extensively reported over the past decades [3,4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and is of particular relevance to the continuous size reduction of BaTiO 3 capacitors. Within the grain size range of 1-10 µm, it is now widely accepted that  r of polycrystalline BaTiO 3 increases with decreasing grain size, reaching a value of 5000, or higher, as the grain size approaches 1 µm.…”

Testing the Tube Super-Dielectric Material Hypothesis: Increased Energy Density Using NaCl

“…of magnitude higher than ever claimed for solid dielectric materials, such as barium titanate, [25][26][27] colossal dielectric constant materials [28][29][30][31][32] and even polymer-derived dielectric materials. The values obtained are similar in magnitude, however, to earlier reported values for SDM, but significantly higher (nearly a factor of two) than NaNO 3 -loaded anodized titania.…”

Phase states of nanocrystalline ferroelectric ceramics and their dielectric properties

“…[23][24][25][26][27][28][29][30] In the present paper, we combine the method of effective medium with the nonlinear thermodynamic theory of ferroelectrics [31][32][33] to calculate the actual polarization states and material constants of BaTiO 3 and Pb͑Zr 1−x Ti x ͒O 3 ceramics with single-domain grains. Since this nonlinear approach takes into account the polarization changes caused by the elastic 3D clamping of crystallites, it enables the correct determination of the physical properties of ferroelectric ceramics.…”

“…[2][3][4][5][6] A further reduction of crystallite dimensions down to the nanoscale may lead to the appearance of unusual physical properties as compared to those of conventional polycrystals. Some data on the microstructure and behavior of nanocrystalline powders, ceramics, and thin films of BaTiO 3 , PbTiO 3 , and Pb͑Zr 1−x Ti x ͒O 3 have been already obtained, [7][8][9][10][11][12][13] and the experimental results indicate even the disappearance of ferroelectricity below a critical crystal size.…”