Property improvement of 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb0.96La0.04(ZrxTi1−x)0.99O3 ceramics by hot-pressing

The piezoelectric ceramics of the compositions expressed by the formula: 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb_0.96La_0.04(Zr_xTi_1−x)_0.99O₃ (x = 0.50–0.53) were prepared by two kind of sintering processes: conventional sintering (CS) and hot-pressing (HP) sintering. By comparing the properties of these two series of ceramics, piezoelectric coefficients (d₃₃), electromechanical coupling factors (k_p), dielectric constants (ɛ_r), etc. were enormously improved by HP sinter procedure, which can be attributed to the highly dense microstructure (bulk density >99%). The most impressive results are the d₃₃ (845pC/N) and k_p (0.703) in the HP specimen with Zr/Ti = 51/49, which have not been observed in the previous relative reports. Additionally, according to the contrast of the experiment data, the origin of the property improvement was analyzed in details.     

Permittivity measurements at millimeter wave frequencies using dielectric rod resonator excited by NRD-guide

A method of measuring the relative complex permittivity (ɛ_r = ɛ′ – jɛ″, tan δ = ɛ″/ɛ′) for low-loss dielectric materials at millimeter wave frequencies has been developed, using a dielectric rod resonator excited by the nonradiative dielectric waveguide (NRD-guide). Relative permittivity (ɛ′) and loss factor (tan δ) of the rod specimen are determined by the resonant frequency (f₀) and unloaded Q-factor (Q_u) of a TE_0m1 mode resonator. The effective conductivity (σ) of conducting plates for short-circuiting the rod resonator is determined using TE₀₂₁ and TE_02δ mode sapphire resonators. Temperature dependence of ɛ′ and tan δ of sapphire and cordierite ceramics were evaluated at 60 GHz. This method has been adopted as the Japanese Industrial Standard (JIS R 1660-3) and is being prepared for the IEC international standard. Several standardized specifications are presented.     

Morphotropic phase boundary in the BNT–BT–BKT system

Lead-free x Bi_0.5Na_0.5TiO₃–y BaTiO₃–z Bi_0.5K_0.5TiO₃ piezoelectric ceramics were synthesized by a conventional solid state reaction method. The microstructure, ferroelectric and piezoelectric properties of the ceramics were investigated. Structure measurements by X-ray diffraction with Rietveld refinement have allowed us to specify more precisely the morphotropic phase boundary (MPB) in this system. For (1 ? x) BNT–x BT solid solution ceramics, the 0.94 BNT–0.06 BT morphotropic composition shows the higher values with d₃₃ = 170 pC/N, k_p = 0.35 and k_t = 0.53. In the case of (1 ? x) BNT–x BKT compositions, the d₃₃, k_p and k_t are, respectively, 137 pC/N, 0.39 and 0.54 for the 0.80 BNT–0.20 BKT ceramic. On the other hand, the ternary 0.865 BNT–0.035 BT–0.100 BKT morphotropic composition shows high piezoelectric constant and electromechanical coupling factors (d₃₃ = 133 pC/N, k_p = 0.26 and k_t = 0.57).     

Notable grain-size dependence of converse piezoelectric effect in BaTiO3 ceramics

Converse piezoelectric effect is of critical importance to device applications like actuators, but no systematical investigation concerning the influence of microstructure on it has been reported for BaTiO₃ ceramics so far. Piezoelectric and ferroelectric properties were inclusively investigated for a group of BaTiO₃ ceramics that are fabricated through solid-state reaction route and show various average grain sizes in this study. It was found that the piezoelectric properties of these BaTiO₃ ceramics display significant grain-size dependences. The direct piezoelectric coefficient d₃₃ increases with decreasing the average grain size (GS) from 170 pC/N at 40 μm, reaches a maximum value of 413 pC/N at 1.2 μm, and then decreases with a further reduction of GS. Converse piezoelectric effect was characterized by measurement of unipolar strain versus electric field (S–E) curve, and the converse piezoelectric coefficient d₃₃*(E) was quantitatively calculated from the slope of S–E curve at relatively large E. Interestingly, d₃₃*(E) is nearly twice as large as d₃₃ and shows a quite similar trend of change with GS to d₃₃. It increases largely from 350 pm/V to 870 pm/V when reducing the GS value from 40 μm to 1.2 μm, and then decreases to 480 pm/V with the further GS reduction to 0.7 μm. Meanwhile, the remanent polarization P_r shows an increase with the decreasing of GS, reaches a maximum at 3.3 μm, and then decreases with the further GS reduction. Domain structure is considered to play an essential role in determining the notable grain-size dependence of converse piezoelectric effect.     

Textured (K0.5Na0.5)NbO3 ceramics prepared by screen-printing multilayer grain growth technique

The screen-printing multilayer grain growth (MLGG) technique is successfully applied to alkaline niobate lead-free piezoelectric ceramics. Highly textured (K_0.5Na_0.5)NbO₃ (KNN) ceramics with 〈0 0 1〉 orientation (f = 93%) were fabricated by MLGG technique with plate-like NaNbO₃ templates. The influence of sintering temperature on grain orientation and microstructure was studied. The textured KNN ceramics showed very high piezoelectric constant d₃₃ = 133 pC/N, and high electromechanical coupling factor k_p = 0.54. These properties were superior to those of conventional randomly oriented ceramics, and reach the level of those of textured KNN ceramic prepared by tape-casting technique. Compared with other grain orientation techniques, screen-printing is a simple, inexpensive and effective method to fabricate grain oriented lead-free piezoelectric ceramics.     

Effects of modified-process on the microstructure,internal bias field,and activation energy in CuO-doped NKN ceramics

In this study, (Na_0.5K_0.5)NbO₃ + xCuO (NKNCx, where x = 0–1 mol%) were separately prepared using the two-step calcination process (BO method) and a conventional mixed oxide method (MO method). The microstructure of NKNCx ceramics prepared using the MO method exhibited obviously inhomogeneous microstructure. In contrast, the BO method improved the compositional homogeneity as well as the electrical properties. A high Q_m value of 2100 was obtained for NKNCx ceramics prepared using the BO method. The ceramics prepared using the BO method exhibited the formation of more oxygen vacancies, resulting in an increase in the internal bias field. The value for the activation energy of the samples supports the presence of oxygen vacancies. The bulk density, dielectric loss, k_p, Q_m, d₃₃ and ?₃₃^T/?₀ of the NKNCx ceramics prepared using the BO method were 4.488 g/cm³, 0.15%, 41.5%, 2100, 95 pC/N and 280, respectively.     

Reaction sintering of lead zinc niobate–lead zirconate titanate ceramics

Lead zinc niobate (PZN)–lead zirconate titanate (PZT) ceramics were produced by the reaction-sintering process. The specimens were prepared directly from a mixture of their constituent oxides without any calcination step. When 50% PZN was added to tetragonal Pb(Zr_0.47Ti_0.53)O₃ ceramics, the densities and electrical properties were found to be optimal (ρ = 7.91 g/cm³, K = 1947 at 1 kHz and room temperature, d₃₃ = 530 pC/N, k_p = 0.61). However, the specimen containing more than 50% PZN showed reduced density and decreased electrical properties, due to the formation of pyrochlore phases. The improved densification behavior of the reaction-sintering process was attributed to the enhanced diffusion of lattice defects, which were created by differences in the ionic valence of the B-sites ions of the perovskite structure.     

Effects of ZnO/Li2O codoping on microstructure and piezoelectric properties of low-temperature sintered PMN–PNN–PZT ceramics

Pb(Mg_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_1/2Ti_1/2)O₃ (designated as PMNT) piezoelectric ceramics codoping with Zn²⁺/Li⁺ were prepared and the effects of ZnO/Li₂O (Z/L) additive on microstructure, piezoelectric and dielectric properties were investigated. The results show that the pure perovskite phase is formed and the phase structure changes from tetragonal to rhombohedral with different Z/L weight ratios. The Curie temperature T_c, dielectric constant ?, electromechanical coupling factor k_p and piezoelectric constant d₃₃ decrease, whereas mechanical quality factor Q_m increases with Z/L weight ratio changing from 1:1 to 1:8. The optimized Z/L weight ratio is 1:1. It is revealed that k_p and d₃₃ first increase then decrease, whereas Q_m changes opposite with increasing content of Z/L additive. The PMNT ceramic with Z/L ratio 1:1 and the amount of 1 wt% has excellent piezoelectric properties: k_p = 0.60, d₃₃ = 397 pC/N, T_c = 251 °C, Q_m = 150, ? = 2628 and tan δ = 0.0296, when sintered at 960 °C. Finally, multilayer piezoelectric actuator is prepared using optimal composition by tape casting. The actuator shows the displacement characteristics of 3.3 μm under electric field 100 V/mm.     

Influence of sintering conditions on piezoelectric properties of KNbO3 ceramics

A homogeneous KNbO₃ (KN) phase was formed in specimens that were sintered at 1020 °C and 1040 °C, without formation of the K₂O-deficient secondary phase, indicating that the amount of evaporation of K₂O during sintering was very small. However, the KN liquid phase was formed during sintering and assisted the densification of the KN ceramics. A dense microstructure was developed in the specimen sintered at 1020 °C for 6 h and abnormal grain growth occurred in this specimen. A similar microstructure was observed in the specimens sintered at 1040 °C for 1.0 h. The dielectric and piezoelectric properties of the KN ceramics were considerably influenced by the relative density. The KN ceramics sintered at 1020 °C for 6 h, which showed a large relative density that was 95% of the theoretical density, exhibited promising electrical properties: ɛ^T₃₃/ɛ_o of 540, d₃₃ of 109 pC/N, k_p of 0.29, and Q_m of 197.     

Effect of composition fluctuation on structural and electrical properties of BZT-xBCT ceramics prepared by Plasma Activated Sintering

Lead-free [Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃, BZT-xBCT] ceramics were prepared by Plasma Activated Sintering (PAS). The effect of composition fluctuation on structural and electrical properties of BZT-xBCT ceramics was investigated. It was found PAS can obtain compact BZT-xBCT ceramics and BZT-0.50BCT ceramic possessed a MPB structure consisting of rhombohedral and tetragonal phases. Impedance spectroscopy confirmed two contributions from grains and grain boundaries, and the ceramics showed typical characteristic of diffuse phase transition. As compared with the BZT-xBCT ceramics with the pseudo-cubic phase, PAS-ed BZT-0.50BCT ceramic exhibited better properties of d₃₃ = 127 pC/N, k_p = 25.1%, ε_r = 2614, ε_m = 6655, and 2P_r = 25.2 μC/cm² due to the existence of the MPB structure.     

Barium modified lead lanthanum strontium zirconium niobium titanate for dielectric and piezoelectric properties

The isovalent Ba²⁺ modified lead lanthanum strontium zirconium niobium titanate (PLSZNT) solid solutions were prepared by solid-state reaction method with the compositional formula [Pb_{1−x−w−y}La_xSr_wBa_y][(Zr_zTi_1−z)_{(1−(x/4)−(5/4)k)}Nb_k]O₃ where Ba content, y, was varied from 0, 0.5, 1 and 1.5 mol%. X-ray diffraction (XRD) studies revealed that all the samples have ferroelectric tetragonal structure (FE_TET). The presence of multiple ions at Pb-site enhanced grain growth and further addition of Ba concentration resulted in restrained grain growth. Dielectric studies suggested that the ɛ_RT increased up to 1 mol% Ba while T_c has shown a continuous decreasing trend throughout the series. The piezoelectric parameters as a function of grain growth were characterized. The optimum piezoelectric charge coefficient (d₃₃ = 538 pC/N) and piezoelectric planar coupling coefficient (k_p = 0.521) was found to be in 1 mol% Ba modified PLSZNT ceramic, respectively, and this composition may be suitable for possible sensor and actuator applications.     

Microstructure and electrical properties of relaxor (1 − x)[(K0.5Na0.5)0.95Li0.05](Nb0.95Sb0.05)O3–xBaTiO3 piezoelectric ceramics

In order to solve the low temperature stability of electrical properties in KNN-based ceramics, (1 ? x)[(K_0.5Na_0.5)_0.95Li_0.05](Nb_0.95Sb_0.05)O₃–xBaTiO₃ [(1 ? x)KNLNS–xBT] lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method. The introduction of BT stabilizes the tetragonal phase of KNLNS ceramics at room temperature, results in a typical ferroelectric relaxor behavior, and shifts the polymorphic phase transition to below room temperature. Moreover, there is a strong BaTiO₃ concentration dependence of relaxor behavior and electrical properties, and the ceramic with x = 0.005 exhibits optimum electrical properties and typical relaxor behavior (d₃₃ = 269 pC/N, k_p = 0.50, ?_r = 1371, tan δ = 0.03, T_C ～ 349 °C and γ = 1.88024). These results indicate that the BT is an effective way to improve the temperature stability as well as the electrical properties of KNN-based ceramics.     

Microstructure and electrical properties of (Ba0.98Ca0.02)(Ti0.94Sn0.06)O3-modified Bi0.51Na0.50TiO3 lead-free ceramics

(Ba_0.98Ca_0.02)(Ti_0.94Sn_0.06)O₃-modified Bi_0.51Na_0.5TiO₃ [(1 ? x)BNT–xBCTS] ceramics were prepared by the normal sintering. A stable solid solution is well formed between BNT and BCTS, and the morphotropic phase boundary of (1 ? x)BNT–xBCTS ceramics is identified in the compositional range of 0.05 ≤ x ≤0.06. The temperature dependence of the dielectric loss and the poling temperature dependence of the d₃₃ value are used to determine the depolarization value (T_d). The T_d value of these ceramics gradually decreases with increasing BCTS content, together with the gradual increase of the dielectric constant. An enhanced electrical behavior of d₃₃ ～ 170 pC/N, k_p ～ 32.8%, P_r ～ 38.5 μC/cm², and E_c ～ 34.3 kV/cm is demonstrated for the ceramic with x = 0.06, which is double than that of pure BNT ceramic.     

Effect of Ba0.85Ca0.15Ti0.90Zr0.10O3 content on the microstructure and electrical properties of Bi0.51(Na0.82K0.18) 0.50TiO3 ceramics

(1?x)Bi_0.51(Na_0.82K_0.18)_0.50TiO₃–xBa_0.85Ca_0.15Ti_0.90Zr_0.10O₃ [(1?x)BNKT–xBCTZ] ceramics were prepared by the conventional solid-state method, and the effect of BCTZ content on their microstructure and electrical properties was investigated. A stable solid solution with a pure perovskite phase is formed between BNKT and BCTZ, and these ceramics have a coexistence of rhombohedral and tetragonal phases in the range of 0 ≤ x < 0.15. Their T_m and T_d values are strongly independent on the BCTZ content. Moreover, the sintering temperature strongly affects the ferroelectric and piezoelectric properties of these ceramics with x = 0.02. These ceramics with x = 0.02 exhibit an optimum electrical behavior of d₃₃ ～ 205, k_p ～ 0.25, P_r ～ 31.8 μC/cm², and E_c ～ 19.1 kV/cm together with a high T_d value of ～91 °C when sintered at 1180 °C and poled at an optimum condition. As a result, the (1?x)BNKT–xBCTZ ceramic is a promising candidate material for lead-free piezoelectric ceramics.     

Phase-formation,microstructure, and piezoelectric/dielectric properties of BiYO3-doped Pb(Zr0.53Ti0.47)O3 for piezoelectric energy harvesting devices

This paper proposes a method for the composition and synthesis of lead zirconate titanate (PZT) piezoelectric ceramic for use in energy harvesting systems. The proposed material consists of (1?x)Pb(Zr_0.53Ti_0.47)O₃–xBiYO₃ [PZT–BY(x)] (x=0, 0.01, 0.02, 0.03, 0.04, and 0.05 mol) ceramics near the morphotropic phase boundary (MPB) region, prepared by a solid-state mixed-oxide method. The optimum sintering temperature was found to be 1160 °C, which produced high relative density for all specimens (96% of the theoretical density). Second phases were found to precipitate in the composition containing x≥0.01 mol of BY. It is shown that the addition of BY inhibits grain growth, and exhibits a denser and finer microstructure than those in the un-doped state. Fracture surface observation revealed predominant intergranular fracture for x=0 and x=0.01, while a mixed mode of transgranular and intergranular fracture appeared for x≥0.02. The optimal doping level was found to be x=0.01, for which a dielectric constant (K₃₃^T) of 750, a Curie temperature (T_C) of 373 °C, a remnant polarization (P_r) of 50 µC/cm², a piezoelectric constant (d₃₃) of 350 pC/N, and an electro-mechanical coupling factor (k_p) of 65% were obtained. In addition, the piezoelectric voltage constant (g₃₃), and transduction coefficient (d₃₃×g₃₃) of PZT–BY(x) ceramics have been calculated. The ceramic PZT–BY(0.01) shows a considerably lower K₃₃^T value, but higher d₃₃ and k_p. Therefore, the maximum transduction coefficient (d₃₃×g₃₃) of 18,549×10^?15 m²/N was obtained for PZT–BY(0.01). The large (d₃₃×g₃₃) indicates that the PZT–BY(0.01) ceramic is a good candidate material for energy harvesting devices.     

High performance Aurivillius-type bismuth titanate niobate (Bi3TiNbO9) piezoelectric ceramics for high temperature applications

This paper reports the significant improved piezoelectric properties of high temperature bismuth titanate niobate (Bi₃TiNbO₉, BTN) polycrystalline ceramics. The piezoelectric performance of BTN ceramics is significantly enhanced by cerium modifications. The dielectric measurements indicate that the Curie temperature T_c gradually decreases over the temperature range of 907–889 °C with cerium contents increasing up to 0.7 wt%. The BTN-5Ce (BTN+0.5 wt% CeO₂) exhibits optimized piezoelectric properties with a piezoelectric constant d₃₃ of 16 pC/N, which is five times the value of unmodified BTN (d₃₃~3 pC/N), while BTN-5Ce maintains a high Curie temperature T_c of 894 °C. The temperature-dependent electrical impedance and electromechanical coupling factors (k_p, and k_t) reveal that the BTN-5Ce exhibits thermally stable electromechanical coupling characteristics up to 500 °C but significantly deteriorates at 600 °C due to high conductivity at a higher temperature. The thermally stable electromechanical properties in combination with the ceramics׳ high electrical resistivity (10⁶ Ω cm at 500 °C) and high Curie temperature (~900 °C) demonstrate that cerium-modified BTN ceramics are good materials for high temperature sensing applications.     

Effects of pore shape and porosity on the properties of porous PZT 95/5 ceramics

Porous lead zirconate titanate (PZT 95/5) ferroelectric ceramics were prepared by sintering compacts consisting of PZT and pore formers. The piezoelectric, dielectric and ferroelectric properties of porous PZT ceramics were investigated as a function of pore shape and porosity. Piezoelectric coefficient (d₃₃), dielectric constant (ɛ₃₃) and remnant polarization (P_r) decreased with an increase in porosity, and the porous PZT ceramics with spherical pores exhibited better properties than that with irregular pores. Furthermore, the electrical conductivities of PZT ceramics were investigated to explain the phenomena that porous PZT ceramics exhibited lower dielectric loss (tan δ) than dense PZT ceramics in the temperature range from 250 to 500 °C.     

Relationships between crystal structure and electrical properties of Li0.055[Agx(K0.5Na0.5)1−x]0.945(Nb1−yTay)O3 ceramics

Electrical properties of perovskite Li_0.055[Ag_x(K_0.5Na_0.5)_1?x]_0.945(Nb_1?yTa_y)O₃ (0.00 ≤ x ≤ 0.04, 0.01 ≤ y ≤ 0.09) ceramics were investigated based on the structural characteristics. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phase was detected through the entire range of compositions. With increasing of Ta⁵⁺ content, the dielectric constant (?_r), piezoelectric coefficient (d₃₃) and electromechanical coupling factor (k_p) of Li_0.055(K_0.5Na_0.5)_0.945(Nb_1?yTa_y)O₃ ceramics were increased up to y = 0.07 and then decreased, while mechanical quality factor (Q_m) was increased. However, the ?_r, d₃₃, k_p and Q_m of Li_0.055[Ag_x(K_0.5Na_0.5)_1?x]_0.945(Nb_0.07Ta_0.03)O₃ ceramics were not changed remarkably with Ag⁺ content. The dependence of temperature coefficient of k_p (TCk_p) on the oxygen octahedral distortion was also discussed by Raman-active vibrations modes.     

Low-temperature sintering and electrical properties of (K,Na)NbO3 based lead-free ceramics with high Curie temperature

Lead-free ceramics (1 ? x)(K_0.48Na_0.52)NbO₃–(x/5.15)K_2.9Li_1.95Nb_5.15O_15.3 (x = 0.3–0.6, KNN–KLN100x) were prepared by conventional sintering technique at a low temperature of 960 °C. The effects of KLN contents on microstructure, dielectric, and piezoelectric properties were investigated. After the addition of KLN, the sintering performance and Curie temperature of the ceramics were markedly improved. The ceramics with x = 0.3 exhibited very good piezoelectric properties: d₃₃ = 138 pC/N, k_p = 45.03%, T_c = 495 °C, the dielectric constant at room temperature ?_r (RT) = 478 and the maximum dielectric constant ?_r (max) = 5067. These results indicated that the KNN–KLN100x lead-free ceramics sintered at low temperatures are promising for high temperature piezoelectric applications.     

Densification behavior and electrical properties of CuO-doped Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary ceramics

CuO modified Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIN–PMN–PT) ternary relaxor based ferroelectrics with the composition near the morphotropic phase boundary were synthesized by two-step columbite precursor method. The introduction of CuO significantly improved the sinterability of PIN–PMN–PT ceramics, resulting in the full densification of samples at lower sintering temperatures. It also profoundly modified the crystal structure and fracture mode of the ceramics. Properly increasing CuO content led to the disappearance of rhombohedral-tetragonal phase transition, remarkably improved the Curie temperature (T_c), and made the ceramics more relaxorlike. The ternary ceramics doped with 0.25 wt% CuO possessed optimum piezoelectric properties (d₃₃=584 pC/N, d₃₃^*=948 pC/N, and k_p=0.68), high ferroelectric properties (E_c=9.9 kV/cm, and P_r=33.1 μC/cm²), low dielectric loss (tan δ=0.9%), and wider temperature usage range (T_c=225 °C). The obtained properties are much higher than those of previously reported PIN–PMN–PT based ceramics, indicating that CuO doped PIN–PMN–PT is a promising candidate for electromechanical applications with high performance and wide temperature/electric field usage ranges.