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In lead-free (Bi0.5Na0.5)TiO3–BaTiO3 (BNT–BT) ceramics, the BNT-rich side has R3c ferroelectric domains at room temperature, and modulated P4bm tetragonal nanodomains develop within the R3c rhombohedral phase at approximately the depolarization temperature Td. Such structural phase transitions have conventionally been modulated by doping with additives or by controlling the composition. However, it is considered that the coexistence region between the R3c and P4bm phases is important for enhancing the energy storage behavior because the phase reversal between them, caused by the electric field, can cause the BNT-based ceramics to exhibit an antiferroelectric-like pinched hysteresis loop. In this study, the structural phase transition of BNT–BT ceramics is promoted through process control, that is, by adjusting the cooling rate, and then the stabilization of the P4bm phase and the expansion of the coexistence region of the R3c and P4bm phases were examined, which results in enhanced energy storage behavior. Consequently, BNT–BT ceramics prepared at a slower cooling rate (0.01 °C s−1) than that of normal firing (0.05 °C s−1) demonstrate the stabilization of the P4bm phase and expansion of the coexistence region of the R3c and P4bm phases. Therefore, process control modulates the structural phase transition, which can cause enhanced energy storage behavior. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics based on 0.90(Bi0.5Na0.5)TiO3 – 0.04(Bi0.5Li0.5)TiO3 – 0.06BaTiO3 with additives MnCO3 (0.1 wt%) [BNLBT4-6 + Mn0.1], which have a morphotropic phase boundary composition, were prepared by controlling the quenching rate (QR) and, their high-power piezoelectric and electrical properties were examined. The depolarization temperature Td could be increased by controlling the QR. The Td with QR = 15.0 and 0.05 °C/s was 166 and 119 °C, respectively. Thus, Td was increased by about ∼40 °C due to the quenching effect. Moreover, vibration velocities (v0−p) were observed at 1.3 m/s even after quenching. Additionally, the values of d31, ɛ33T/ɛ0, and s11E decreased, whereas Qm increased after quenching. The quenching effect promoted the dielectric and elastic hardening of BNLBT4-6 + Mn0.1 ceramics. After quenching, Td increased, and the value of d31 × Qm maintained the same value as for ordinary firing (OF) with QR = 0.05. Consequently, quenching was found to be effective for increasing the Td and Qm, hence, a promising effect for high-power piezoelectric applications. [ABSTRACT FROM AUTHOR]

The relationship between phases and the electrical properties of bismuth perovskite ([Bi.sub.1/2][Na.sub.1/2])Ti[O.sub.3] (BNT)- and ([Bi.sub.1/2][K.sub.1/2])Ti[O.sub.3] (BKT)-based lead-free ferroelectric ceramics is studied. BKT ceramics are prepared by the hot-pressing (HP) method and BKT ceramics doped with a small amount of Bi have shown a relatively high remanent polarization and high piezoelectric properties.

The phase-transition temperatures and piezoelectric properties of ([Bi.sub.1/2][Na.sub.1/2])Ti[O.sub.3]-([Bi.sub.1/2][Li.sub.1/2])Ti[O.sub.3]-([Bi.sub.1/2][K.sub.1/2])Ti[O.sub.3] 9BNLKT100y-100z) ceramics are examined. Findings reveal the effectiveness of a small amount of Li-substitution for increasing the depolarization temperature of BNLKT4-100z from 185 degree Celsius to 221 degree Celsius at the rhombohedral composition.

The electric and the electromechanical properties measured are studied as a function of temperature for lead-free piezoelectric ceramics with compositions around the morphotropic phase boundary (MPB). The properties are found to be optimum for the MPB composition but their temperature dependence reveals evidence of a curved rhombohedral to tetragonal phase boundary and a phase transformation to ferroelectric occurs.

Lead-free piezoelectric (Bi0.5Na0.5)TiO3 (BNT) ceramics, which exhibit a Bi-based A-site complex perovskite structure with rhombohedral symmetry, were prepared by controlling: the quenching temperature and the quenching rate (QR). We examined the relationship between structural order and quenching effect of the structural phase transition behavior, which was obtained from the dielectric properties. Additionally, the electrical properties were evaluated. These measurements showed that the depolarization temperature (Td) increased by approximately 50 °C during these two control processes. Furthermore, the full width at half maximum (FWHM) for temperature dependence of tan δ decreased with increasing quenching temperature and QR. In conclusion, the increase in Td is strongly correlated with the decrease in FWHM, which suggests a more ordered arrangement of cations, Bi3+ and Na+, in the Bi-based A-site complex perovskite structure. Moreover, the quenching effect does not deteriorate the piezoelectric properties. [ABSTRACT FROM AUTHOR]

Lead-free ferroelectric and piezoelectric ceramics, (Bi0.5Na0.5)TiO3 (BNT), with Mn dopants were prepared by a quenching procedure after sintering to examine the depolarization temperature Td, and then their electrical properties were investigated. The Td of quenched BNT + xMn (Mn x) decreased with Mn doping. Also, the Td of quenched Mn x was ∼60 °C higher than that of ordinary firing (OF) samples. Furthermore, the difference of Td (ΔTd) between the OF and the quenched process increased with increasing of the Mn-substituted amount. The electromechanical coupling factors k33 of Mn x exhibited the same value after quenching. The coercive electric field Ec was increased from 62 to 95 kV cm−1 with increasing of Mn-substituted amount. Thus, the quenching procedure is an effective way of elevating the Td of Mn-doped BNT-based solid solution systems. [ABSTRACT FROM AUTHOR]

(Bi1/2Na1/2)TiO3 (BNT) is one of the candidates for lead-free piezoelectric ceramics. Recently, we found that the depolarization temperature Td of BNT could be increased by approximately 40 °C–80 °C with a quenching treatment after the sintering. To elucidate the mechanism, high-energy synchrotron X-ray powder diffraction data were collected in SPring-8 to analyze their crystal structures in detail. In the case of a quenched BNT-based sample, Bi ions displaced more to the off-center position of the A-site in a perovskite structure with a more ordered structure. The increase in rhombohedral distortion then affects the Td elevation in the quenched sample. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT) ceramics were prepared by quenching and the correlation among a depolarization temperature Td, the mechanical strength, and their piezoelectric properties were investigated. We controlled the quenching rate in the temperature range from 1100°C to 800°C. We examined the 5 patterns of the quenching rate (QR): 0.05 (ordinary firing, OF), 3.85, 5.77, 6.67, and 15.0 (quenching) oC/s. Td of the rapid quenched sample reached 229°C (QR = 15.0), but its mechanical strength decreased to a quarter of that of the OF ceramics. On the other hand, Td was 211°C at QR = 3.85 which was higher than that of OF-ceramic (QR = 0.05) at about 180°C. Moreover, three-point bending strength (227 MPa) of the quenched BNLT4 (QR = 3.85) was equivalent to that of the OF ceramics (235 MPa). Therefore, both Td and the mechanical strength were improved by controlling the quenching rate. [ABSTRACT FROM AUTHOR]

Stoichiometric and nonstoichiometric (Bi0.5Na0.5)TiO3 (BNT) ceramics were prepared by a conventional ceramic fabrication process. This study revealed that the high conductivity of BNT ceramics is associated with Bi vaporization during sintering. An x-ray study revealed that a tetragonal phase exists in the temperature range between 330 and 480 °C in BNT ceramic as well as BNT single crystals. In addition, the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature Tm of the maximum dielectric constant were determined to be 187, approximately 300, and 325 °C, respectively, from the temperature dependences of dielectric properties using unpoled and poled specimens. The piezoelectric properties of all vibration modes and the temperature dependences of the piezoelectric properties were measured using fully poled BNT ceramics. It was also revealed that BNT ceramics exhibit three thermal depoling processes at Td, between Td and TR-T, and between TR-T and Tm from the effects of annealing on the field-induced strain, x-ray diffraction patterns, and dielectric constant of poled specimens. [ABSTRACT FROM AUTHOR]

In this study, we demonstrated the relationship between the phase diagrams and the electrical properties of (Bi1/2Na1/2)TiO3 (BNT)-based solid solutions. In this study, (1-x)(Bi1/2Na1/2)TiO3–xNaNbO3 and (1-x)(Bi1/2Na1/2)TiO3–xKNbO3 (abbreviated to BNT-NN100x and BNT-KN100x) ceramics were prepared by a conventional ceramic fabrication process, and (1-x)(Bi1/2Na1/2)TiO3–x(Bi1/2K1/2)TiO3 (abbreviated to BNKT100x) ceramic was prepared for comparison. We revealed the phase transition temperatures, such as the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature Tm of the maximum dielectric constant, from the temperature dependence of dielectric properties using poled and unpoled specimens. As a result, it was shown that the BNT-based solid solutions form three types of phase diagrams. In addition, we clarified the relationship between the phase diagrams and the electrical properties of BNT-NN100x, BNT-KN100x, and BNKT100x. The piezoelectric properties were markedly enhanced when TR-T shifted to a lower temperature, and a large piezoelectric constant d33 of 168 pC/N was obtained at the morphotropic phase boundary (MPB) between the ferroelectric rhombohedral and ferroelectric tetragonal phases for BNKT100x. Although the piezoelectric properties almost disappeared when Td shifted to room temperature, the field-induced strain S and the normalized strain d33* (=Smax/Emax) abruptly increased to 0.22% and 259 pm/V, respectively, for BNT-NN100x. In particular, a very large reversible strain of S=0.40 with d33*=498 pm/V was obtained at the MPB between the ferroelectric rhombohedral and ferroelectric relaxor with pseudocubic (tetragonal) phases for BNT-KN100x. This very large reversible strain was clarified to be due to non-180° (71° and 109°) domain switching of the field-induced ferroelectric rhombohedral phase. [ABSTRACT FROM AUTHOR]

(1-x)(Bi1/2Na1/2)TiO3–x(Bi1/2Li1/2)TiO3 and (1-x)(Bi1/2Na1/2)TiO3–x(Bi1/2K1/2)TiO3 (abbreviated as BNLT100x and BNKT100x, respectively) ceramics were prepared by the conventional ceramic fabrication process. In this study, the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature of the maximum dielectric constant Tm were determined from the temperature dependences of the dielectric and piezoelectric properties. The results showed that Td of BNLT100x and BNKT100x increased to 199 and 209 °C, respectively, at the rhombohedral composition. In addition, we revealed that Td is related to the magnitude of the rhombohedrality 90-α and the tetragonality c/a. We studied the piezoelectric properties in detail, and the relationship between Td and piezoelectric properties was clarified. Moreover, we discussed the ferroelectricity of the middle phases of Td-TR-T and TR-T-Tm. [ABSTRACT FROM AUTHOR]