Koichiro Sakata

Ferroelectric and antiferroelectric properties of (Na 0.5Bi 0.5)TiO3-SrTiO3 solid solution ceramics

Abstract Phase transitions in the solid solution Sr χ(Na 0.5Bi 0.5)l-χTiO3 have been studied by dielectric, pyroelectric and D-E characteristic measurements. An intermediate antiferroelectric phase has been observed in the composition range of 0 ⩽ χ ⩽ 0.5 of this system. These compositions undergo a ferroelectric-antiferroelectric-paraelectric sequence of transitions at elevated temperatures. The antiferroelectric phase transition temperature and Curie point decrease monotonically with increasing SrTiO3 concentration.

Grain orientation effects on electrical properties of bismuth layer‐structured ferroelectric Pb(1−x)(NaCe)x/2 Bi4Ti4O15 solid solution

Electrical properties, such as dielectric, resistive, ferroelectric, and piezoelectric properties, of bismuth layer‐structured ferroelectrics (BLSF) are studied on grain orientation prepared by the hot‐forging (H.F.) method. The BLSF compound which can stand the high temperature poling process is Pb(1−x) (NaCe)x/2 Bi4Ti4O15 (PNC‐100x) consisting of PbBi4Ti4O15 modified by partial substitution of (NaCe)1/2 for Pb. The effects of the solid solution introduced on piezoelectric properties are mentioned. The piezoelectrically activated PNC solid solution has a larger value of electromechanical coupling factors kt and k33 than those of nonmodified samples. The grain orientation makes the piezoelectric properties of BLSF ceramics much more pronounced than those of the nonoriented ceramics. Coupling factor k33 along with piezoelectric constants d33 and g33 of H.F. PNC ceramics are enhanced and their anisotropies in k33/k31, d33/d31, and g33/g31 are emphasized.

Dielectric, piezoelectric and pyroelectric properties of (BiNa)1/2TiO3- based ceramics

Abstract A bismuth sodium titanate, (BiNa)1/2 TiO3 (BNT)-based solid solutions, (1−x) (BiNa)1/2TiO3 + x(a·SrTi03 +b·PbTiO3 +c·CaTiO3) (a + b + c = l), (BNTX [100x-100a/100b/100c]), were studied for their dielectric, piezoelectric and pyroelectric properties. X-ray diffraction data show that a rhombohedra1 (Fα-tetragonal (Fβ) phase boundary (MPB) exists at x = 0.13 for a = b = 0.5 and c = 0, for a = 0 and b = c = 0.5, or for a = 0, b = 0.75 and c = 0.25, respectively. (Sr/Pb/Ca)-modified BNTs (BNTX [13-50/50/0], [13-0/50/50] and [13-0/75/25]) ceramics are superior for piezoceramics, with a lower free permittivity, eT33/e0 (≌240–430) and a high electromechanical coupling factor, kt or k33 (≌50%). along with a higher frequency constant, N, (≌ 3200 Hz.m). Figures of merit for pyrosensor materials of the BNTX [10-50/50/0] are comparable to those of PZT or PbTi03-based ceramics.

Phase relations, dielectric and piezoelectric properties of ceramics in the system (Bi0.5Na0.5)TiO3-PbTiO3

Abstract A part of the phase diagram of the (Bi0.5Na0.5)1-x Pb x TiO3 system at the (Bi0.5Na0.5)TiO3 side was constructed on the basis of X-ray diffraction data, dielectric measurements and D-E hysteresis observations. A rhombohedral (Fα)-tetragonal (Fβ) morphotropic phase boundary (MPB) at room temperature is shown to exist at x = 0.13. An intermediate antiferroelectric phase has been observed in the composition range of 0 ⩽ x ⩽ 0.16 of this system. Near the MPB rhombohedral compositions (x ≒ 0.12) undergo a ferroelectric rhombohedral (Fα)-ferroelectric tetragonal (Fβ)-antiferroelectric(A)-paraelectric (P) sequence of transitions at elevated temperatures. It was found that the Mn-doped MPB material (x = 0.12) has a lower free permittivity ϵ T 33 (= 338), a higher longitudinal coupling factor k33 (= 53%), a higher mechanical quality factor QM (= 944) and favorable mechanical characteristics for piezoelectric ceramics in high power ultrasonic uses, or actuator applications. These low-lead-content ceramics ...

Sr1-xCaxBi2Ta2O9 Piezoelectric Ceramics with High Mechanical Quality Factor

The dielectric, ferroelectric and piezoelectric characteristics of Sr1-xCaxBi2Ta2O9 (x=0–1) ceramics were examined. The samples were prepared by a conventional ceramic technique at 1260°C to 1340°C for 2 h. The Curie temperature of samples gradually rose from 324°C to 896°C when x was increased. The coercive field Ec of the sample with x=0.75 was approximately 16 MV/m, and the value of Ec was about 3 times that of x=0. In the x=0.75, the maximum value of the mechanical quality factor Qm was obtained, approximately 11000.

Hot-forged ferroelectric ceramics of some bismuth compounds with layer structure

The presintered layer structure bismuth compounds of PbBi2Nb2O9, Na0.5Bi4.5Ti4O15, PbBi4Ti4O15 and Pb2Bi4Ti5O18 are hot-worked by press forging under the maximum load of 200 kg/cm2 at a temperature of 1000°C to 1200°C. The reduction ratio of height is more than 70%. The well-oriented polycrystalline samples with an orientation degree of more than 0.8 can be obtained. The measured results of dielectric and ferroelectric properties are correlated with SEM observations and x-ray diffractions.

Piezoelectric and pyroelectric properties of calcium-modified and grain-oriented (NaBi)1/2Bi4Ti4O15 ceramics

Abstract Grain orientation effects of (NaBi)(l-x)/2Ca x Bi4Ti4O15 (NCBT-100x) ceramics, which belong to a bismuth layer-structured ferroelectric (BLSF) family, are studied using the hot-forging (H.F.) method on the piezoelectric and pyroelectric properties. The dielectric constant e s is small and almost constant at the wide range of composition (x = 0tox = 1). The Curie temperature, Tc , increases as the Ca concentration increases. The grain orientation (H.F.) effects enhance the piezo- and pyroelectric properties by a factor of two or more if compared with non-oriented ones. The H.F. and Mn-doped NCBT-5 ceramics, with a lower free permittivity e33 T/e0 (= ∼ 130) and higher electromechanical coupling factor k 33 (= 33 ∼ 40%), along with a higher anisotropy k 33/k 31 (= 13 ∼ 17), are very attractive candidate materials for hydrophone applications at high temperatures or for high-frequency ultrasonic transducers. Pyroelectric properties are also very interesting for sensor materials, and the figure of meri...

Fabrication and Characterization of LnBi2TiNbO9-Based Ceramics

LnBi2TiNbO9 (LnBTN) ceramics which have a rare metal Ln (=La, Nd, Sm, and Gd) in the A-site were examined. To study the characteristics of these compounds, SmxBi3-xTiNbO9 (SmB) ceramics, which are SmBi2TiNbO9 (SmBTN), [any of the LnBTN ceramics], and the Bi3TiNbO9 (BTN) system were also examined. The samples were prepared by a conventional sintering technique at 1150°C to 1250°C for 2 h. In X-ray powder diffraction (XRD), the phases of the LnBTN and SmB ceramics were identified to be single phase. The lattice constants of the a and c axes decreased with increasing atomic number of Ln in LnBTN ceramics. Based on the increasing amount of substitution of SmBTN, the orthorhombic structure of SmB ceramics gradually became the pseudotetragonal-structured. In SmB ceramics, the Curie temperature of samples gradually decreased when x increased. In the sample, the phase curve showed no spurious in the thickness extensional vibration mode (TE mode).

Pyroelectric properties of bismuth layer-structured ferroelectric ceramics

Abstract Pyroelectric properties of a bismuth layer-structured ferroelectric (BLSF) family are studied on ordinarily fired (OF) (nonoriented) and grain-oriented ceramics for pyrosensor materials. The pyroelectric figure of merit, Fv and FD , are evaluated from the measured values of the pyroelectric coefficient, p, the dielectric constant, e = e33 T/e0, and the loss tangent, tan δ. Infrared frequency response measurements give the voltage responsivity, R v, and the detectivity, D* , for infrared sensing figure of merits, which are related with the Fv and FD , respectively. The grain orientation effects using the hot-forging (HF) method enhance the pyroelectric properties by two or more times those of nonoriented (OF) ones. The Mn-doped and grain-oriented (HF) (Na1/2 Bi1/2)1-xCaxBi4Ti4O15[NCBT] ceramics with a lower free permittivity, e33 T/e0(= ∼130), a higher electromechanical coupling factor, k 33(= 33 ∼ 40%) and a higher anisotropy, k 33/k 31(= 13 ∼ 17) have a comparable value of Fv and D* to that of P...

Electrical and mechanical characteristics of PbnBi4Tin+3O3n+12 ceramics

The electrical and mechanical characteristics of Pb n Bi 1 Ti n+3 O 3n+12 ceramics were examined. With increasing n, the dielectric constant e y increased, and the temperature dependence of e s broadened. e s , at room temperature, reached a value of approximately 750 at n = 3 and n = 4 at 100 kHz. The dielectric breakdown strength E b and the three-point bending strength σ decreased with increasing n. For example, σ of the sample at n = 4 was approximately a 70% value of the sample at n = 0. On the other hand, the examination of the characteristics of grain-oriented samples clarified that E b and σ can be improved in the direction perpendicular to the polarization axis.