Gd2O3 (0–0.8 wt.%)-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state process. The effects of Gd2O3 on the microstructure, the dielectric, ferroelectric and piezoelectric properties were investigated. X-ray diffraction (XRD) data shows that Gd2O3 in an amount of 0.2–0.8 wt.% can diffuse into the lattice of BNKT18 ceramics and form a pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain size of BNKT18 ceramics decreases with the increase of Gd2O3 content; in addition, all the modified ceramics have a clear grain boundary and a uniformly distributed grain size. At room temperature, the ferroelectric and piezoelectric properties of the BNKT18 ceramics have been improved with the addition of Gd2O3, and the BNKT18 ceramics doped with 0.4 wt.% Gd2O3 have the highest piezoelectric constant (d33 = 137 pC/N), highest relative dielectric constant (εr = 1023) and lower dissipation factor (tan δ = 0.044) at a frequency of 10 kHz. The BNKT18 ceramics doped with 0.2 wt.% Gd2O3 have the highest planar coupling factor (kp = 0.2463). 相似文献
Ceramics of the series (0.97-x)Bi1/2Na1/2TiO3-xBi1/2K1/2TiO3-0.03NaNbO3 (x = 0, 0.02, 0.06, 0.10, 0.16, 0.20, 0.30) were prepared by the conventional mixed oxide method. Influence of Bi1/2K1/2TiO3 content on the crystal structure, microstructure, dielectric and piezoelectric properties were studied. All compositions
showed single perovskite phase and the morphotropic phase boundary (MPB) between rhombohedral and tetragonal phase existed
at the point of x = 0.16. Temperature dependences of permittivity and dissipation factor of unpoled samples revealed that permittivity increased
with Bi1/2K1/2TiO3 content and it reached maximum value near the MPB. At the same time, the peak value of dissipation factor increased with
the addition of Bi1/2K1/2TiO3. All the samples experienced two phase transitions: from ferroelectric to antiferroelectric at the first transition temperature
(Td) and from antiferroelectric to paraelectric at the temperature (Tm) corresponding to maximum value of permittivity. The phase transition from ferroelectric to antiferroelectric had relaxor
characteristic and Td shifted to lower temperature while increasing Bi1/2K1/2TiO3 content. The best piezoelectric properties were obtained in 0.81Bi1/2Na1/2TiO3-0.16Bi1/2K1/2TiO3-0.03NaNbO3 ceramic with a piezoelectric constant (d33) of 146pC/N, planar electromechanical coupling factor (kp) of 30.3% and thickness electromechanical coupling factor (kt) of 53.2%. Abnormal piezoelectric properties were observed in the sample (x = 0.20), which was attributed to the co-existence of ferroelectric and antiferroelectric phases in it. 相似文献
Er2O3 (0–0.8 wt.%)-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The effects of Er2O3 on the microstructure and electrical properties were investigated. X-ray diffraction (XRD) data shows that Er2O3 in an amount of 0.2–0.8 wt.% can diffuse into the lattice of the BNKT18 ceramics and form the pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain sizes of BNKT18 ceramics decrease with the increase of Er2O3 content; in addition, the modified ceramics have the clear grain boundary and a uniformly distributed grain size. At room temperature, the electrical properties of the BNKT18 ceramics have been improved with the addition of Er2O3, and the BNKT18 ceramics doped with 0.6 wt.% Er2O3 have the highest piezoelectric constant (d33 = 138 pC/N), the highest planar coupling factor (kp = 0.2382), the highest remnant polarization (Pr = 25.2 μC/cm2), the higher relative dielectric constant (εr = 936) and lower dissipation factor (tanδ = 0.047) at a frequency of 10 kHz. Moreover, the Tm and Td of the samples increase with the addition of Er2O3. 相似文献
The phase-transition temperatures and piezoelectric properties of x(Bi(1/2)Na(1/2))TiO3-y(Bi(1/2)Li(1/2))TiO3-z(Bi(1/2)K(1/2))TiO3 [x + y + z = 1] (abbreviated as BNLKT100(y)-100(z)) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T(d), rhombohedraltetragonal phase transition temperature T(R-T), and dielectric-maximum temperature T(m) were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100(y)-100(z)) show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor k(33), piezoelectric constant d(33) and T(d) of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171 degrees C, and 0.590, 190 pC/N, and 115 degrees C, respectively. In addition, the relationship between d33 and Td of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high Td and high d(33), the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d(33) and T(d) of BNLKT4-28 were 135 pC/N and 218 degrees C, respectively. Moreover, this study revealed that the variation of T(d) is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a. 相似文献
Bismuth sodium titanate, (Bi1/2Na1/2)TiO3(BNT) additive effect for the improvement of piezoelectric and mechanical properties in PZT ceramics were discussed from the viewpoint of high-power applications. The addition of 5 wt% BNT in Pb(Zr0.52Ti0.48)O3 ceramics showed suppressive effect for electro-mechanical coupling factor (kp) value. On the other hand, the addition of 0.5 and 1.0 wt% BNT contributed to improve the four point mechanical bending strength when it was sintered at 1150°C. 相似文献
Compositions in (Na1/2Bi1/2)TiO3 based ternary system, (0.97 – x) (Na1/2Bi1/2)TiO3-0.03NaNbO3-xBaTiO3 (x = 0, 0.01, 0.02, 0.04, 0.05, 0.06, 0.08) are synthesized using conventional solid state reaction method. Influence of BaTiO3 on crystal structure, dielectric and piezoelectric properties are investigated. All compositions can form single perovskite phase. Powder x-ray diffraction patterns can be indexed assuming a pseudo-cubic structure. Lattice constant increases with the increase of BaTiO3 concentration. Rhombohedral distortion is observed in poled samples with BaTiO3 concentration up to 6 mol%. Temperature dependence of dielectric constant and dissipation factor measurement reveals that all compositions experience two phase transitions: from ferroelectric to antiferroelectric and from antiferroelectric to paraelectric. Both transition temperatures, Tc and Tf, are lowered due to introduction of BaTiO3. Ferroelectric to antiferroelectric phase transition has relaxor characteristics. Piezoelectric properties have relatively higher value around 1 mol% to 4 mol% BaTiO3. In ceramics with x = 0.02, thickness electromechanical coupling factor (kt) of 0.51 and piezoelectric charge constant (d33) of 110 × 10–12 C/N are obtained. Addition of small amount of BaTiO3 (x = 0.01, 0.02) improves piezoelectric properties compared to NBT-NN binary system, while Tf remains above 140°C, higher than that of NBT-BT binary system composition with similar piezoelectric properties. This is in favor of the possible application of them as lead-free piezoelectric ceramics. 相似文献
Quenching from sintering temperature enhances the depolarization temperature (Td) in Na1/2Bi1/2TiO3-based ceramics without significant deterioration of piezoelectric properties (d33). In this work, quenching effects in an ergodic relaxor 0.97(0.94Na0.5Bi0.5TiO3–0.06BaTiO3)–0.03AgNbO3 (NBT–6BT–3AN) were investigated based on structure, ferroelectric, and dielectric properties. The ergodicity to nonergodicity transition was obtained by quenching NBT–6BT–3AN above 1000 °C. The temperature stability of the quenching-induced nonergodicity was examined by annealing the quenched sample at 300 °C and 600 °C. The effect of oxygen vacancy on ergodicity to nonergodicity transition was investigated by comparing ferroelectric and electrostrain responses of the quenched and nitrogen-atmosphere-annealed samples. The influence of quenching on the structure including the average crystal structure, phase fraction and lattice distortion and the local structure including bond lengths and ordering of ions was analyzed. The ergodicity to nonergodicity transition upon quenching is ascribed to the contribution of the off-centered Bi3+ ions and ordered local structure.
Lead-free positive temperature coefficient of resistivity (PTCR) ceramics of 99 mol%BaTiO3–1 mol%(Bi1/2Na1/2)TiO3 (BBNT1) and 90 mol%BaTiO3–10 mol%(Bi1/2Na1/2)TiO3 (BBNT10) were prepared by the conventional solid state reaction method. The effect of donor concentration on the microstructure and PTCR behavior of the BBNT ceramics were investigated. The results show that all BBNT1 and BBNT10 ceramics have formed a single perovskite structure with tetragonal phase when sintered in air or N2. 0.2 mol% Y-doped BBNT1, sintered at 1,330 °C for 30 min in air, has room-temperature resistivity (ρ25) of ~60 Ω cm and resistivity jump [maximum resistivity (ρmax)/minimum resistivity (ρmin)] of ~4.2 orders of magnitude with Tc about 150 °C. 0.4 mol% Y-doped BBNT10, sintered at 1,250 °C for 3 h in N2, has ρ25 of ~100 Ω cm and resistivity jump of ~4.7 orders of magnitude with Tc about 180 °C. The BBNT10 has higher breakdown voltage of 200 V/mm (a.c.) than that of BBNT1, making these BBNT10 ceramics promising candidates for high temperature lead-free PTCR materials. 相似文献