Dielectric and piezoelectric properties of KCT added (Li0.02(Na0.56 K0.46)0.98(Nb0.81Ta0.15Sb0.04)O3 ceramics

In this study, [Li_0.02(Na_0.56 K_0.46)_0.98](Nb_0.81Ta_0.15Sb_0.04)O₃ + x mol% K_5.4Cu_1.3Ta₁₀O₂₉ ceramics were fabricated by conventional solid-state solution processes. Then, their dielectric and piezoelectric properties were investigated. Sinterability of all samples was enhanced because K_5.4Cu_1.3Ta₁₀O₂₉ (abbreviated as KCT) acted as sintering aids. As the result of XRD, phase structure showed orthorhombic symmetry when KCT ≤ 0.2 mol%. Whereas, the phase structure changed from orthorhombic symmetry to tetragonal symmetry when KCT?≥?0.4 mol%. The results suggest that the orthorhombic and tetragonal phases co-exist in the composition ceramics with 0.2 mol% < KCT < 0.4 mol% at room temperature. The effects of the addition of KCT on the dielectric and piezoelectric properties were investigated. As the result, excellent properties of density=4.81[g/cm³], electromechanical coupling factor (k_p)=0.48 and piezoelectric constant(d₃₃)=252[pC/N] were obtained in the composition ceramics with 0.4 mol%KCT.     

Normal sintering and electric properties of (K,Na,Li)(Nb,Sb)O3 lead-free piezoelectric ceramics

0.94(K₀₅Na_0.5)NbO₃?0.03LiNbO₃?0.03LiSbO₃ (KNLNS) lead-free piezoelectric ceramics were prepared by conventional mixed oxide route with normal sintering method. The samples were sintered at different temperatures with KNLNS powder atmosphere to prevent volatilization of alkali metal oxides at high temperature. The effects of sintering temperature on the density, structure and electric properties of KNLNS ceramics were studied. X-ray diffraction (XRD) results showed that the crystal structure of the crushed KNLNS ceramic powders were pure perovskite phase with tetragonal phase structure when sintered at T????1080°C. However a K₃Li₂Nb₅O₁₅ phase with tetragonal tungsten bronze structure began to appear when the sintering temperature was higher than 1080°C. The optimum sintering temperature was 1080°C which was determined by measuring the density of the samples. Scanning electron microscope (SEM) observation indicated that the sintering temperature had a great effect on the microstructure of the samples. The KNLNS ceramics under the optimum sintering temperature showed excellent electric properties: ???=?4.29 g/cm³, ?? _r?=?826, tan???=?0.049, d ₃₃?=?190 pC/N, k _p?=?0.30, and T _c?=?385°C. The results show that the KNLNS ceramics are promising candidate for lead-free piezoelectric ceramics.     

Lead-free Na0.5K0.5NbO3 piezoelectric ceramics fabricated by spark plasma sintering: Annealing effect on electrical properties

Niobate ceramics such as NaNbO₃ and KNbO₃ have been studied as promising Pb-free piezoelectric ceramics, but their sintering densification is fairly difficult. In the present study, highly dense Na_0.5K_0.5NbO₃ ceramics with submicron grains were prepared using SPS, whose density was raised to 4.47 g/cm³ (>99% of the theoretical density) at 920 °C. Reasonably good ferroelectric and piezoelectric properties were obtained in the SPSed Na_0.5K_0.5NbO₃ ceramics after annealing in air. The effect of annealing time on the electrical properties was investigated to determine optimal processing condition. The piezoelectric parameter (d ₃₃) of the Na_0.5K_0.5NbO₃ ceramics annealed properly reached 148 pC/N.     

Structure and dielectric property of Zr-doped (Na0.47Bi0.46Ba0.06K0.01)(Nb0.02Ti0.98)O3 lead-free ceramics

(Na_0.47Bi_0.46Ba_0.06K_0.01)(Nb_0.02Ti_0.98-xZr_x)O₃ lead-free ceramics (BNBKT-xZr, x?=?0, 0.01, 0.02, 0.04) were synthesized via conventional solid state reaction method. Crystallite structure of the ceramics was studied using X-ray diffraction. The rhombohedral phase and tetragonal phase coexist in the BNBKT-xZr ceramics. The doping of Zr⁴⁺ into BNBKT lattice increases the percentage of the tetragonal phase. The size and shape of grains in the ceramics were affected by the doping of Zr⁴⁺ ions. For all the unpoled ceramics, two dielectric anomalies are observed in the dielectric constant-temperature curves. The maximum values of dielectric constant and corresponding temperatures change with the variation of Zr⁴⁺ amount. The doping of Zr⁴⁺ ions causes a decrease in the ferroelectric properties.     

Preparation,characterisation, and electrical properties of (K0.5Na0.5)NbO3 lead-free piezoelectric ceramics

Na_0.5?K_0.5NbO₃ (KNN) ceramics were sintered at different temperatures (970 °C, 1000 °C, 1030 °C, 1060 °C, and 1090 °C) for 3 h by a pressureless sintering method. The powders had been synthesised by sol–gel method, using citric acid as a coordination agent and ethylene glycol as an esterifying agent. The effects of temperature on the phase, microstructure, dielectric, ferroelectric, and piezoelectric properties of the as-prepared ceramics were analysed. The results revealed that all of the ceramics had a pure perovskite phase with orthorhombic symmetry. The piezoelectric constant (d ₃₃), the relative dielectric constant (ε _r), the planar electromechanical coupling coefficient (K _p), and the remnant polarization (P _r) initially increased and then decreased with increasing of temperature in such KNN ceramics. The volatilization of sodium and potassium increased with increasing sintering temperature. Over the range of temperatures studied, those ceramics sintered at 1060 °C had the following optimal properties: (ρ?=?3.97 g/cm³, d ₃₃?=?119 pC/N, ε _r?=?362.46, tan δ?=?0.05, K _p?=?0.23, P _r?=?11.97 μC/cm², E _c?=?10.35 kV/cm, and T _c?=?408 °C).     

Dielectric and piezoelectric properties of (K0.5Na0.5)(Nb0.97Sb0.03)O3 ceramics doped with Bi2O3

In this study, to develop the optimal composition of ceramics for low loss piezoelectric actuator and ultrasonic motor applications, (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃?+?0.009 K_5.4Cu_1.3Ta₁₀O₂₉?+?0.1wt%Li₂CO₃?+?xwt%Bi₂O₃(x?=?0?~?0.9) lead-free piezoelectric ceramics with a fixed quantity of 0.009 K_5.4Cu_1.3Ta₁₀O₂₉ (abbreviated as KCT) were manufactured using the conventional solid-state solution processes. The effects of Bi₂O₃ addition on the dielectric and piezoelectric properties were then investigated. From the X-ray diffraction analysis result the specimens demonstrated orthorhombic symmetry when Bi₂O₃ was less 0.6?wt%, a pseudo-cubic phase appeared when Bi₂O₃ was 0.9?wt%. SEM images indicate that a small amount of Bi₂O₃ addition affect the microstructure. The piezoelectric properties of (K_0.5Na_0.5)(Nb_0.97Sb_0.03)O₃ ceramics were greatly improved by a certain amount of Bi₂O₃ addition. Excellent properties of density?=?4.54?g/cm³, relative densities?=?98.5?%, k _p?=?0.468, Q _m?=?1,715 and d ₃₃?=?183 pC/N were obtained with a composition of 0.3?wt% Bi₂O₃     

Piezoelectric properties of Li, Sb, and Ta co-doped (K,Na)NbO3 ceramics with fine grain size sintered by SPS method

(Na_0.52?K_0.44Li_0.04)(Nb_0.86Ta_0.06Sb_0.08)O₃ (LTS-KNN) nano-powders with the size of 11–34 nm were prepared by a sol–gel method. Using the nano-powders, LTS-KNN ceramics with fine grain size of 200–400 nm and high density were fabricated by spark plasma sintering. The satisfied piezoelectricity is obtained, such as d ^* ₃₃?~?481 pm/V, d ₃₃?~?296 pC/N, K _p?~?49.7 %, ε ₃₃ ^T /ε ₀?~?920, tanδ?~?0.025 at 1 kHz and relative density is 99.4 %, respectively. It is shown that nano-powders are suitable to prepare fine-grained potassium-sodium niobate ceramics with satisfied properties.     

Composition-insensitive enhanced piezoelectric properties in SrZrO 3 modified (K,Na)NbO 3 -based lead-free ceramics

In this work, composition-insensitive enhanced piezoelectric properties are achieved in (1-x)(K0.48Na0.52)0.96Li0.04(Nb0.96Sb0.04)O3-xSrZrO3 (KNN-SZ) lead-     

Piezoelectric and dielectric properties of (Na0.54K0.46)0.96Li0.04(Nb0.80Ta0.20)O3 ceramics substituted with Co

Lead-free [(Na_0.54K_0.46)_0.96Li_0.04](Nb_0.80Ta_0.20)O₃(abbreviated as NKL-NT) ceramics were synthesized by conventional solid state sintering method and the effect of Co substitution on the microstructure and piezoelectric properties were investigated. The crystal structure and microstructure were investigated by X-ray diffraction (XRD) and SEM images. The crystal structure exhibited the tetragonal structure at the composition ceramics less than 1 mol% Co. However, with increasing Co substitution from 1.5 to 2.0 mol%, the ceramics showed morphotropic phase boundary (MPB) and the crystal structure of the ceramic possessed orthorhombic structure at 3 mol% Co. The grain size was increased with increasing of Co contents. The phase transition temperature tetragonal-cubic(T_C) and orthorhombic-tetragonal(T_O-T) were shifted to downward and upward with increasing Co contents, respectively. The high piezoelectric properties of d₃₃?=?259[pC/N], k_p?=?0.43 and Qm?=?109 were obtained from the 1.5 mol% Co substituted ceramics sintered at 1060 °C for 5 h.     

Pyroelectric, dielectric, and piezoelectric properties of MnO2-doped (Na0.82 K0.18)0.5Bi0.5TiO3 lead-free ceramics

MnO₂ doped (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ lead-free piezoelectric ceramics were prepared by conventional solid-state reaction process and the effect of MnO₂ addition on the pyroelectric, piezoelectric and dielectric properties were studied. The experiment results showed that the pyroelectric, piezoelectric, and dielectric properties strongly depended on MnO₂ addition in the (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ ceramics. Excellent electrical properties were obtained in (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ with 0.8?mol% MnO₂. The large dielectric loss of pure BNT ceramics was significantly reduced, the piezoelectric constant was improved, and it also showed excellent pyroelectric properties when compared with other lead free ceramics, with pyroelectric coefficient p?=?17?×?10^?4?C/m²K and figure of merit F _d ?=?6.56?×?10^?5?Pa^?0.5. With these outstanding pyroelectric properties, the 0.8?mol% MnO₂ doped (Na_0.82 K_0.18)_0.5Bi_0.5TiO₃ ceramic can be a promising material for pyroelectric sensor applications in future.     

Effect of La3+ substitution on microwave dielectric properties of (Pb0.5Ca0.5)(Fe0.5Nb0.5)O3 ceramics

Microwave dielectric properties of the [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ and [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics were investigated as a function of La³⁺ content $ {\left( {0.0 \leqslant \times \leqslant 0.2} \right)} $ . A single perovskite phase was detected in [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃, while Pb₃Nb₄O₁₃ were detected as a secondary phase in [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ beyond x?=?0.05 due to the excess of unbalanced charge. The amount of Pb₃Nb₄O₁₃ was proportional to the unbalanced charge. Qf value of [(Pb_0.5Ca_0.5)_1?x La_2x/3](Fe_0.5Nb_0.5)O₃ decreased remarkably with La³⁺ substitution due to the increase of oxygen vacancy. For [(Pb_0.5Ca_0.5)_1?x La _x ](Fe_0.5Nb_0.5)O₃ ceramics, dielectric constant and Qf value increased with La³⁺ content up to x?=?0.03 due to an increase of density and grain size. Temperature coefficient of resonant frequency (TCF) was depended on B-site bond valence in single perovskite phase.     

Effect of microwave sintering on structural, morphological and dielectric properties of Ba(FeNb)0.5O3 ceramics

Polycrystalline Ba(FeNb)_0.5O₃/BFN ceramics were sintered conventionally and in a microwave (MW) furnace, respectively. Conventional and microwave sintering temperatures were same with different soaking times. Microwave sintering of BFN ceramics showed enhanced grain growth with improved dielectric properties. Highest dielectric constant (~29,913 at 1 kHz) at room temperature (RT) was observed in BFN ceramics sintered in MW furnace for 30 min. At RT, a non-Debye type of dielectric relaxation was observed in both conventionally and MW sintered BFN ceramics. The observed giant dielectric constant of conventionally and MW sintered BFN ceramics was attributed to intrinsic (space charge polarization) and extrinsic (Maxwell-Wagner type polarization) effects, respectively.     

Characteristics improvement of Li0.058(K0.480Na0.535)0.966(Nb0.9Ta0.1)O3 lead-free piezoelectric ceramics by LiF additions

In this study, a series of Li_0.058(K_0.480Na_0.535)_0.966(Nb_0.90Ta_0.10)O₃ + (x)LiF (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 wt%) lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method. The incorporation of LiF could significantly improve the sintering ability of LKNNT ceramics by reducing the optimal sintering temperature from 1090°C to 1020°C. The crystal phases and micro-structures were analyzed by means of the X-ray diffraction and scanning electronic microscopy, respectively. The impedance analyzer was used to measure the Curie temperature, phase transition point, and electro-mechanical coupling factor. And the d₃₃ meter was used to measure the piezoelectric constants.

From the results, due to the addition of 0.2 wt% LiF, uniform and condensed grains can be obtained and hence the sintering temperature can be lowered down. As the contents of LiF increased, the orthorhombic to tetragonal phase transition points T_O-T were almost no changed, but the Curie temperature T_C decreased from 425°C (x = 0) to 405°C (x = 0.5). And furthermore, the electro-mechanical coupling factor k_p and piezoelectric constant d₃₃ were all decreased with increases of LiF contents. Hence, even though the reducing of little amount of piezoelectric characteristics, the LiF addition can improve the sintering ability of the LKNNT ceramics effectively.     

Effect of BiAlO3 concentration on the dielectric and piezoelectric properties of lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoelectric ceramics

In this paper, lead-free (1-x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃-xBiAlO₃ (BNBT-BA, x?=?0, 0.010, 0.015, 0.020, 0.025, and 0.030) piezoelectric ceramics were synthesized using a conventional solid-state reaction method. The effect of BiAlO₃ concentration on dielectric, ferroelectric and piezoelectric properties were investigated. The ferroelectric and piezoelectric properties of BNBT ceramics are significantly influenced by the presence of BA. In the composition range studied, X-ray diffraction revealed a perovskite phase with the coexistence of rhombohedral and tetragonal phases. The temperature dependence of dielectric properties showed that the depolarization temperature (T _d) shifted towards lower temperatures and that the degree of diffuseness of the phase transition around T _d and T _m became more obvious with increasing BiAlO₃ content. The remanent polarization increased with increasing BA, and reached a maximum value of 30 μC/cm² at x?=?0.020. As a result, at x?=?0.020, the piezoelectric constant (d ₃₃) and the electromechanical coupling factor (k _p) of the ceramics attained maximum values of 188 pC/N and 34.4 %, respectively. These results indicate that BNBT-BA ceramics is a promising candidate for lead-free piezoelectric materials.     

Nonstoichiometric (K,Na)NbO3 ceramics: Densification and electrical properties

In order to clarify the influence of excess ions in A or B sites on perovskite (K,Na)NbO₃ ceramics, various compositions of (K_0.48Na_0.52)Nb_1+x%O₃ (ABO₃) ceramics where x is in the range of ±1 % were prepared by conventional solid state method and their densification, structure, dielectric and piezoelectric properties were investigated. Results showed that a small amount of excess A-site ions could compensate for the deficiency of K and Na ions in A-sites caused by volatilization resulting in good piezoelectric properties. The ceramics with x?=??0.1 exhibited optimum piezoelectric properties with d ₃₃?=?127pC/N and k _p?=?0.41. However, presence of too much alkali elements (x?<??0.5) led to deterioration of density, dielectric and piezoelectric properties, although the crystal structure was not changed. The electrical properties, on the other hand, were not sensitive to the B-site excess ions. These results are expected to be very useful for further designing of (K,Na)NbO₃-based ceramics as lead-free alternatives to piezoelectric materials.     

Temperature dependent electrical properties of 0.95[(K0.5Na0.5)(1-x)Ag x NbO3]-0.05LiSbO3 ceramics

Lead free 0.95[(K_0.5Na_0.5)_1-x Ag _x NbO₃]-0.05LiSbO₃ (KNAN-LS) ceramics with x?=?0.02, 0.04, 0.06 and 0.08 have been synthesized by conventional solid state reaction route (CSSR). XRD analysis confirmed the presence of a mixed structure for x?=?0.06. The orthorhombic?Ctetragonal polymorphic phase transition (PPT) temperature and the Curie temperature (T_c) decreased with the increase in Ag⁺ ion content in KNAN-LS ceramics. The relationship between the PPT of the ceramics and the temperature dependence of electrical properties of KNAN-LS ceramics were discussed in detail. The KNAN-LS ceramics with x?=?0.06 showed better piezoelectric and electromechanical properties (d₃₃?=?227pC/N and k_p?=?42.5?%).     

Effect of Bi3+ ion on piezoelectric properties of K x Na1−x NbO3

This paper describes the material preparation and characteristics of potassium sodium niobate, K _x Na_{1? x} NbO₃ (KNN), with Bi³⁺ doping. Some physical properties including density, dielectric constant, loss tangent and ferroelectric hysteresis, were examined. The samples were characterized by using X-ray diffraction method and the grain size was measured by using SEM micrographs. Dielectric constant, loss tangent, and electromechanical coupling coefficient of samples were measured at different frequencies. The changes in physical properties are remarkable when KNN is doped with Bi³⁺ ions.     

Dielectric and piezoelectric properties of La2O3 doped (Bi0.5Na0.5)0.92(Ba0.8Sr0.2)0.08 TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (Bi_0.5Na_0.5)_0.92(Ba_0.8Sr_0.2)_0.08 TiO₃+x mol% La₂O₃(x = 0, 0.1, 0.3, 0.5, 0.8) were synthesized by conventional solid state reaction. The crystal structure of all compositions is mono-perovskite ascertained by XRD. The grain size decreased and diffuse phase transition behavior was more evident with the increasing amount of La₂O₃. The piezoelectric constant d₃₃ and the electromechanical coupling factor k_p showed the maximum value of 165 pC/N and 0.322 at 0.3% and 0.1% La₂O₃ addition, respectively, and rapidly decreased when La₂O₃ addition over 0.5%. The loss tangent tanδ linearly increased and the mechanical quality factor Q_m linearly decreased with the increasing amount of La₂O₃.