Low temperature sintering and properties of piezoelectric PZT-PFW-PMN ceramics with YMnO3 addition

Low temperature sintering of Pb(Zr,Ti)O₃-Pb(Fe_2/3W_1/3)O₃-Pb(Mn_1/3Nb_2/3)O₃ (PZT-PFW-PMN) quaternary piezoelectric ceramics were studied with the use of YMnO₃ as sintering aid. The sintering aid improved the sinterability of PZT-PFW-PMN ceramics due to the effect of YMnO₃ liquid phase. The effects of YMnO₃ contents and sintering temperature on the phase structure, density, dielectric and piezoelectric properties were investigated. The results show that the sintering temperature can be decreased and the electrical properties can be maintained by the YMnO₃ addition. The optimized properties were obtained by doping 0.30 wt.% YMnO₃ and sintering at 1020 °C, which are listed as follows: d₃₃ = 341 pC/N, K_p = 0.57, Q_m = 1393, tan δ = 0.0053, T_c = 304 °C, P_r = 17.13 μC/cm² and E_c = 11.15 kV/cm, which make this system be a promising material for multilayer piezoelectric actuator and transformer applications.     

Effect of CuO on the sintering temperature and piezoelectric properties of lead-free 0.95(Na0.5K0.5)NbO3-0.05CaTiO3 ceramics

The addition of a small amount of CuO to the 0.95(Na_0.5K_0.5)NbO₃-0.05CaTiO₃ (0.95NKN-0.05CT) ceramics sintered at 960 °C for 10 h produced a dense microstructure with large grains due to the liquid phase sintering. Due to the negligible Na₂O evaporation, poling was easy for all specimens sintered at 960 °C. The piezoelectric properties of the specimens were considerably influenced by the relative density, grain size and liquid phase amount. The high piezoelectric properties of d₃₃ = 200 pC/N, k_p = 0.37, and Q_m = 350 were obtained for the 0.95NKN-0.05CT ceramics containing 2.0 mol% CuO sintered at 960 °C for 10 h. Therefore, the 0.95NKN-0.05CT ceramics containing a small amount of CuO are a good candidate material for lead-free piezoelectric ceramics.     

Effects of Cr2O3 doping on the electrical properties and the temperature stabilities of PNW-PMN-PZT ceramics

The ceramics with 0.90Pb(Zr_0.50Ti_0.50)O₃-0.07Pb(Mn_1/3Nb_2/3)O₃-0.03Pb(Ni_1/2W_1/2)O₃ were prepared by adding Cr₂O₃. The effects of Cr₂O₃ doping on the phase structure, the microstructure and the electrical properties of ceramics were investigated. Meanwhile, the temperature stabilities of the resonant frequency (f_r) and the electromechanical coupling factor (K_p) were studied. The results showed that the better temperature stability could be obtained at x = 0.2 wt.% when the calcining temperature was 800 °C and the sintering temperature was 1150 °C. The parameters were Δf_r/f_r25 °C = −0.17% and ΔK_p/K_p25 °C = −1.39%. Moreover, the optimized electrical properties were also achieved, which were K_P = 0.54, Q_m = 1730, d₃₃ = 330 pC/N, ?_r = 2078 and tan δ = 0.0052. The optimized properties make the ceramics with this composition to be a good candidate for high power piezoelectric transformers applications.     

Influence of Bi2O3 and CuO addition on low-temperature sintering and dielectric properties of Ba0.6Sr0.4TiO3 ceramics

In this study, we tried to lower the sintering temperature of Ba_0.6Sr_0.4TiO₃ (BST) ceramics by several kinds of adding methods of Bi₂O₃, CuO and CuBi₂O₄ additives. The effects of different adding methods on the microstructures and the dielectric properties of BST ceramics have been studied. In the all additive systems, the single addition of CuBi₂O₄ was the most effective way for lowering the sintering temperature of BST. When CuBi₂O₄ of 0.6 mol% was mixed with starting BST powders and sintered at 1100 °C, the derived ceramics demonstrated dense microstructure with a low dielectric constant (? = 4240), low dielectric loss (tan δ = 0.0058), high tunability (Tun = 38.3%) and high Q value (Q = 251). It was noteworthy that the sintering temperature was significantly lowered by 350 °C compared with no-additive system, and the derived ceramics maintained the excellent microwave dielectric properties corresponding to pure BST.     

Structure and electrical properties of (1 − x)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3 ceramics near morphotropic phase boundary

The binary lead-free piezoelectric ceramics with the composition of (1 − x)Bi_0.5Na_0.5TiO₃-xBi_0.5K_0.5TiO₃ were synthesized by conventional mixed-oxide method. The phase structure transformed from rhombohedral to tetragonal phase in the range of 0.16 ≤ x ≤ 0.20. The grain sizes varied with increasing the Bi_0.5K_0.5TiO₃ content. Electrical properties of ceramics are significantly influenced by the Bi_0.5K_0.5TiO₃ content. Two phase transitions at T_t (the temperature at which the phase transition from rhombohedral to tetragonal occurs) and T_c (the Curie temperature) were observed in all the ceramics. Adding Bi_0.5K_0.5TiO₃ content caused the variations of T_t and T_c. A diffuse character was proved by the linear fitting of the modified Curie-Weiss law. Besides, the ceramics with homogeneous microstructure and excellent electrical properties were obtained at x = 0.18 and sintered at 1170 °C. The piezoelectric constant d₃₃, the electromechanical coupling factor K_p and the dielectric constant ?_r reached 144 pC/N, 0.29 and 893, respectively. The dissipation factor tan δ was 0.037.     

Effect of oxide additives on the low-temperature sintering of dielectrics (Zn,Mg)TiO3

The effect of oxide additives on the low-temperature sintering and dielectric properties of microwave dielectrics (Zn,Mg)TiO₃ have been investigated. The study showed that a small amount of V₂O₅ accelerated the densification rate of (Zn,Mg)TiO₃ dielectrics as compared with the other oxide additives. In addition to lower sintering temperature of zinc titanate dielectrics, the addition of V₂O₅ decreased the decomposition temperature of (Zn,Mg)TiO₃. Additionally, the increased amount of magnesium raised both the sintering temperature and the decomposition temperature of (Zn,Mg)TiO₃. Relative permittivity of (Zn,Mg)TiO₃ dielectrics decreased accompanied with increase of Q × f as the amount of magnesium content increased. The temperature coefficient of resonant frequency of (Zn,Mg)TiO₃ shifted to more negative values as the amount of magnesium increased.     

Piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 ceramics synthesized by spray drying method

Potassium-sodium niobate was synthesized at 800 °C for 1 h using dried precursors in a powder form obtained by the spray drying method. Different samples were sintered from 1060 to 1120 °C for 2 h reaching a relative density as high as 96% of the theoretical value. Piezoelectric and ferroelectric properties were studied for these samples and some of the most prominent results are: k_p, d₃₁, 2P_r, and 2E_C of 0.36, 39 pC/N, 29 μC/cm² and 16.5 kV/cm, respectively, for the sample sintered at 1080 °C. The methodology presented in this study can be used to synthesize submicrometer powders.     

Effects of complex substitution of La and Nd for Bi on the microwave dielectric properties of BiNbO4 ceramics

La₂O₃ and Nd₂O₃ were used to substitute Bi₂O₃ and the effects of complex substitution on the sintering behavior and the microwave dielectric properties of BiNbO₄ ceramics were studied. With 0.5 wt.% CuO-V₂O₅ mixtures addition, all of the Bi_1−x(La_0.38Nd_0.62)_xNbO₄ ceramics could be densified below 920 °C. The triclinic phases are identified in Bi_1−x(La_0.38Nd_0.62)_xNbO₄ ceramics with x=0.01 sintered at 820 °C and the triclinic intensities increase with increasing the x value and sintering temperature. The saturated bulk density slightly decreases from 7.17 to 7.13 g/cm³ and the ε_r value from 44.24 to 42.76 with increasing x from 0 to 0.07 for Bi_1−x(La_0.38Nd_0.62)_xNbO₄ ceramics. The saturated Q×f value is between 10,300 and 12,400 GHz depending on the x value. The τ_f values of dense Bi_1−x(La_0.38Nd_0.62)_xNbO₄ ceramics decrease from 28.32 to 12.79 ppm/°C with x varying from 0 to 0.01 and remain almost unchanged with further increasing x.     

Effect of temperature on nonlinear electrical behavior and dielectric properties of (Ca, Ta)-doped TiO2 ceramics

TiO₂ ceramics doped with 0.75 mol% Ca and 2.5 mol% Ta were sintered at different temperatures ranging from 1300 to 1450°C. The effects of sintering temperature on the microstructure, nonlinear electrical behavior, and dielectric properties of the ceramics were studied. The sample sintered at 1300°C exhibits the highest nonlinear coefficient (5.5) and a comparatively lower relative dielectric constant.     

Low temperature sintering and microwave dielectric properties of SmAlO3 ceramics

The effects of sintering aids on the microstructures and microwave dielectric properties of SmAlO₃ ceramics were investigated. CuO and ZnO were selected as sintering aids to lower the sintering temperature of SmAlO₃ ceramics. With the additions, the sintering temperature of SmAlO₃ can be effectively reduced from 1650 to 1430°C. The crystalline phase exhibited no phase differences at low addition level while Sm₄Al₂O₉ appeared as a second phase as the doping level was over 0.5 wt.%. In spite of the additions, the dielectric constants showed no significant change and ranged 19-21. However, the quality factor Q×f was strongly dependent upon the type and amount of additions. The Q×f values of 51,000 and 41,000 GHz could be obtained at 1430°C with 0.25 wt.% CuO and ZnO additions, respectively. The temperature coefficients depended on the additions and varied from −40 to −65 ppm/°C. Results of X-ray diffractions, EDS analysis and scanning electron microscopy were also presented.     

Formation and electrophysical properties of Y-containing positive temperature coefficient of resistance ceramics doped by calcium, strontium, and manganese

Formation, microstructure, and electrophysical properties of positive temperature coefficient of resistance ceramics of the systems (Ba_0.996Y_0.004)TiO₃ and (Ba_0.746Ca_0.1Sr_0.15Y_0.004)TiO₃ with manganese as acceptor dopant have been investigated. Is has been shown that manganese ions increase the potential barrier at grain boundaries and form a high-resistance outer layer in PTCR ceramics. The resistance of grains, outer layers and grain boundaries, and the value of the temperature coefficient of resistance as a function of the manganese content of positive temperature coefficient of resistance materials have been investigated.     

Effects of Mn doping on the structure and electrical properties of high-temperature BiScO3-PbTiO3-Pb(Zn1/3Nb2/3)O3 piezoelectric ceramics

The effects of Mn addition on the structure, ferroelectric, and piezoelectric properties of the 0.35BiScO₃-0.60PbTiO₃-0.05Pb(Zn_1/3Nb_2/3)O₃ ceramics were studied. The results demonstrate that the addition of small amounts of Mn did not cause a remarkable change in crystal structure, but resulted in an evident evolution in microstructure and ferro-piezoelctric properties. The addition of Mn can induce combinatory “hard” and “soft” piezoelectric characteristics due to aliovalent substitutions. The optimal electrical properties are obtained in the 0.25 mol% Mn-doped composition with a high Curie temperature, indicating that Mn doping contributes to the electrical properties of the ceramics. It can be expected that the improved piezoelectric material can be a promising candidate for high-temperature piezoelectric applications.     

Effects of Ag particles on sintering and electrical properties of ZnO-based varistor

ZnO-based varistors containing Ag particles (abbreviated as Z-Ag) were prepared using the conventional solid-state reaction method. The sintering and electrical properties of Z-Ag composites show that the composites can be achieved at a lower sintering temperature (920 °C) relative to that of a commercial ZnO-based varistor. The composites possess non-ohmic behavior analogous to that of the ZnO-based varistor, and the nonlinear voltage can be easily controlled by the content of Ag particles in the ceramic matrix. Meanwhile, the dielectric constant and dissipation factor indicate that the composites have enhanced dielectric properties at room temperature with increasing content of Ag particles, especially at frequencies of 0.5-30 kHz. The mechanisms involved are discussed.     

Ferroelectric,dielectric and piezoelectric properties of Sr0.6(BiNa)0.2Bi2Nb2O9 ceramics

Aurivillius-type ceramic, Sr_0.6(BiNa)_0.2Bi₂Nb₂O₉ (SBNBN), was synthesized by using conventional solid-state processing. Phase structure and microstructural morphology were confirmed by X-ray diffraction analyses (XRD) and the scanning electron microscopy (SEM). Dielectric, piezoelectric and electromechanical properties of the SBNBN ceramic were investigated in detail. Curie temperature (T_c), piezoelectric coefficient (d₃₃), electromechanical coupling coefficient k_p, k_t and quality factor Q_m of the SBNBN ceramic were found to be 586.5 °C, 22 pC/N, 5.0%, 8.7% and 651, respectively. In addition, the reasons for varieties of the resistivity and dielectric properties at high temperature were also discussed.     

Microwave dielectric properties and microstructures of the 11Li2O-3Nb2O5-12TiO2 ceramics with B2O3 addition

The effects of B₂O₃ addition, as a sintering agent, on the sintering behavior, microstructure and microwave dielectric properties of the 11Li₂O-3Nb₂O₅-12TiO₂ (LNT) ceramics have been investigated. With the low-level doping of B₂O₃ (≤2 wt.%), the sintering temperature of the LNT ceramic could be effectively reduced to 900 °C. The B₂O₃-doped LNT ceramics are also composed of Li₂TiO₃ss and “M-phase” phases. No other phase could be observed in the 0.5-2 wt.% B₂O₃-doped ceramics sintered at 840-920 °C. The addition of B₂O₃ induced no obvious degradation in the microwave dielectric properties but increased the τ_f values. Typically, the 0.5 wt.% B₂O₃-doped ceramics sintered at 900 °C have better microwave dielectric properties of ?_r = 49.2, Q × f = 8839 GHz, τ_f = 57.6 ppm/°C, which suggest that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures.     

Effects of K4CuNb8O23 on the structure and electrical properties of lead-free 0.94(Na0.5K0.5)NbO3–0.06LiNbO3 ceramics

Dense K₄CuNb₈O₂₃-modified (K_0.5Na_0.5)_0.94Li_0.06NbO₃ ceramics were prepared by normal sintering. The effects of K₄CuNb₈O₂₃ on the phase structure, microstructure and electrical properties of the ceramics were studied. Results showed that K₄CuNb₈O₂₃ induced a perovskite structure transition from coexistence of orthorhombic and tetragonal phases to orthorhombic symmetry. The addition of K₄CuNb₈O₂₃ promoted the sintering of (K_0.5Na_0.5)_0.94Li_0.06NbO₃ ceramics and simultaneously caused the grain growth. Moreover, K₄CuNb₈O₂₃-doping changed the (K_0.5Na_0.5)_0.94Li_0.06NbO₃ to “hard” ceramics and significantly enhanced the mechanical quality factor Q_m. It was found that the (K_0.5Na_0.5)_0.94Li_0.06NbO₃ ceramics doped with 0.60 mol% K₄CuNb₈O₂₃ exhibited a high mechanical quality factor (Q_m  983) as well as relatively large d₃₃ (136 pC/N) and k_p (35.9%), suggesting that this material is a promising candidate for lead-free piezoelectric ceramics for high-frequency applications.     

Structural and electrical characteristics of dysprosium-doped barium stannate titanate ceramics

Effects of dysprosium (Dy) amphoteric doping on the structural, dielectric and electric properties of barium stannate titanate (BTS) ceramics have been studied. X-ray diffraction analyses reveal that all Dy-doped BTS ceramics exhibit cubic perovskite structure until to 1 mol%. Dy doping at the A site shows lower solubility than that at the B site. SEM surface morphologies display that the Dy B site doping is beneficial for the compact and homogeneous grain distribution. The dielectric constant and loss tangent are reduced with increase of the doping levels. Impedance spectroscopy investigation demonstrates that all samples are insulating at room temperature. Doping alters the full resistive regions of pure BTS ceramics to Doped BTS with insulating grain boundaries and semiconducting bulk regions, but the doping contents has little effect on changing the electric structures.     

Effect of Pr substitution on structural and electrical properties of BiFeO3 ceramics

Investigation on structural, vibrational, dielectric and ferroelectric properties of Bi_1−xPr_xFeO₃ (x = 0.0, 0.15, 0.25) ceramic samples has been carried out. Room temperature Rietveld-refined X-ray diffraction pattern shows the crystal structure of Bi_1−xPr_xFeO₃ is rhombohedral for x = 0 and triclinic for x = 0.15, 0.25. The changes in Raman normal modes with increasing doping concentration infer the structural transformation is due to Pr substitution at A-site in BiFeO₃. Raman spectra also reveal suppression of ferroelectric behavior due to Pr doping. The dielectric parameters, namely, dielectric permittivity (ε′) and loss tangent (tan (δ)) were evaluated as a function of frequency at room temperature. The ferroelectric polarization reduces in Pr doped bulk BFO samples due to structural change.     

Influences of poling condition and sintering temperature on piezoelectric properties of (Na0.5Bi0.5)1 − xBaxTiO3 ceramics

The structure, ferroelectric characteristics and piezoelectric properties of (Na_0.5Bi_0.5)_1 − xBa_xTiO₃ (x = 0.04, 0.06, 0.10) ceramics prepared by conventional solid state method were investigated. The influences of poling condition and sintering temperature on the piezoelectric properties of the ceramics were examined. The piezoelectric properties of the ceramics highly depend on poling field and temperature, while no remarkable effect of poling time on the piezoelectric properties was found in the range of 5-25 min. Compared with (Na_0.5Bi_0.5)_0.96Ba_0.04TiO₃ and (Na_0.5Bi_0.5)_0.90Ba_0.10TiO₃, the piezoelectric properties of (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ are more sensitive to poling temperature due to the relatively low depolarization temperature. Moderate increase of sintering temperature improved the poling process and piezoelectric properties due to the development of microstructural densification and crystal structure. With respect to sintering behavior and piezoelectric properties, a sintering temperature range of 1130-1160 °C was ascertained for (Na_0.5Bi_0.5)_0.90Ba_0.10TiO₃.     

Effect of BiFeO3 additions on the dielectric and piezoelectric properties of (K0.44Na0.52Li0.04)(Nb0.84Ta0.1Sb0.06)O3 ceramics

(1 − x) (K_0.44Na_0.52Li_0.04)(Nb_0.84Ta_0.1Sb_0.06)O₃ − x BiFeO₃ (x = 0, 0.002, 0.004, 0.006, 0.008, 0.01) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing. The compositional dependence of the phase structure and the electrical properties of the ceramics were studied. A morphotropic phase boundary between the orthorhombic and tetragonal phases was identified in the composition range of 0.004 < x < 0.006. The ceramics near the morphotropic phase boundary exhibit a strong compositional dependence and enhanced piezoelectric properties. The ceramics with 0.6 mol.% BiFeO₃ exhibit good electrical properties (d₃₃ ∼ 246 pC/N, k_p ∼ 43%, T_c ∼ 285 °C, ?_r ∼ 1871, and tan δ ∼ 1.96%). These results show that the (1 − x) (K_0.44Na_0.52Li_0.04)(Nb_0.84Ta_0.1Sb_0.06)O₃ − x BiFeO₃ ceramic is a promising lead-free piezoelectric material for applications in different devices.