Hajime Nagata

Additive effects on electrical properties of (Bi1/2Na1/2)TiO3 ferroelectric ceramics

Microstructure, dielectric, ferroelectric and piezoelectric properties of bismuth sodium titanate (Bi1/2Na1/2)TiO3 (BNT) were studied for a candidate as lead-free piezoelectric ceramics. In the case of Mn addition, the Curie temperature, Tc, decreases rapidly with increasing amount of doped MnCO3. The resistivity, ρ, is enhanced to 3×1014 (Ωcm) (at 40°C) for BNT+MnCO3 0.2 (wt.%) and electromechanical coupling factor, k33, was obtained the relatively high value under the condition of the low poling field, Ep for the Mn-doped BNT ceramics. It seems that Mn ions exist in the grain, and substitute for the A- or B-site of the perovskite structure, and eject Bi ions to the air.

Lead-free piezoelectric ceramics of (Bi1/2Na1/2)TiO3-BaTiO3-BiFeO3 system

Abstract Bismuth sodium titanate, (Bi1/2Na1/2)TiO3 (BNT)-based solid solution, a(Bi1/2Nal/2)TiO3-bBaTiO3-cBiFeO3, [BNBTF(100a/100b/100c)], was studied for its dielectric, ferroelectric and piezoelectric properties, as a new group of lead-free piezoelectric ceramics. Curie temperatures, Tc . of the BNBTF ceramics shift to the higher temperature with an increasing amount of modified Bi ion, and temperature dependence of the resonance frequencies, fr is smaller with increasing amount of modified BiFeO3.

Piezoelectric Properties of Bismuth Layer-Structured Ferroelectric Ceramics with Sr-Bi-Ti-Ta System

Grain orientation effects of Sr-Bi-Ti-Ta system, especially Sr x Bi 4-x Ti 3-x Ta x O 12 (m=3, x=0-2) [SBTT3(x)] ceramics which belong to a bismuth layer-structured ferroelectric (BLSF) family, are studied using the hot-forging (HF) method on their piezoelectric properties. The grain orientation (HF) effects enhance the piezoelectric properties by a factor of two or more if compared with non-oriented ones. The electromechanical coupling factor, k 33 and the piezoelectric constant, d 33 of the grain oriented SBTT3(0.3) ceramics were relatively high values of 0.40 and 49.5 pC/N.

Electrical properties of bismuth layer-structured ferroelectrics

Abstract Bismuth layer-structured ferroelectrics (BLSF), Srm-3+xBi4-xTim-xTaxO3m+3 (m=2, x = 1∼2 m=3, x=0∼2) [SBTTm(x)] ceramics are studied on their ferroelectric and piezoelectric properties. From the measurement of D-E hysteresis, the remanent polarization, P r of SBTT3(0.3) was the largest (P r=12.3 μC/cm2) in the SBTT3(x) system and coercive field, E c of SBTT2 becomes larger with decreasing the amount of Ta concentration. The electromechanical coupling factor, k 33 and the piezoelectric constant, d 33 of the hot-forged SBTT3(0.3) were relatively high values of 0.37 and 45.3 pC/N. The mechanical quality factor, Q m, of the SBTT2(1.5) ceramic was a high value of more than 8000.

Ferroelectric properties of bismuth layer-structured oxides

Abstract Basic ferroelectric properties of SrBi2Ta2O9 (SBT) ceramics are mainly studied on the effects of the ratio of Sr/Bi/Ta and grain orientation on dielectric constant ϵs, loss tangent tan δ, Curie temperature, Tc , and D—E hysteresis loops, that is, the remanent polarization, Prand the coercive field, Ec . The maximum value of the ϵ s MAX (=849), Pr (=∼7 μC/cm2) and the minimum value of the Tc (=435°C) was obtained for the stoichiometry (Sr/Bi/Ta = 1/2/2) composition. The value of ϵ s MAX (=890) of the grain orientation direction perpendicular to the forging axis has been enhanced than that of non-oriented ceramics.

Fatigue properties of bismuth titanate annealed in the reduced atmosphere

Abstract Bi4Ti3O12 (BIT) ceramic is one of a typical bismuth layer-structured ferroelectrics (BLSF) and shows strong anisotropic properties with relatively large remanent polarization. However, it is unknown the mechanism of the fatigue behavior for BIT ceramic. The most obvious candidate for the fatigue behavior is oxygen vacancies. In this study, the fatigue characteristics of BIT ceramic were investigated for various annealing conditions in the reduction atmosphere. The BIT ceramic shows the fatigue or fatigue-free behavior by means of changing the reduced condition regardless the layer number m of the bismuth layer-structure.

Effects of substitution on electrical properties of (Bi/sub 1/2/Na/sub 1/2/)TiO/sub 3/-based lead-free ferroelectrics

Dielectric, ferroelectric and piezoelectric properties of bismuth sodium titanate, (Bi/sub 1/2/Na/sub 1/2/)TiO/sub 3/ (BNT) were studied on some additive dopants for a candidate as lead-free piezoelectric ceramics. Electromechanical coupling factors, k/sub 33/ in the longitudinal mode of BNT ceramics depend on the purity of starting raw materials and additive dopants. The k/sub 33/ for high and normal purities are 0.38 and 0.43, respectively. It is considered that impurities in starting materials are influence on piezoelectric properties. In the case of Mn addition, the Curie temperature, T/sub c/, decreases rapidly with increasing amount of doped MnCO/sub 3/, and the resistivity, /spl rho/, is enhanced to 3/spl times/10/sup 14/ (/spl Omega/cm) (at 40/spl deg/C) for BNT+MnCO/sub 3/ 0.2 (wt.%). In the case of Nb addition, Nb/sup 5+/ ions substitute for Ti/sup 4+/ ions as a donor. The k/sub 33/ (=0.42) of Nb-doped BNT ceramics are larger than that of undoped BNT ceramic (=0.28) under the condition of the low poling field (E/sub p/=5 kV/mm). In the case of Fe addition, Fe /sup 3+/ ions substitute for Ti/sup 4+/ ions as a acceptor. The k/sub 33/ (=0.18) of Fe-doped BNT ceramics are smaller than that of undoped BNT ceramic (E/sub p/=5 kV/mm).