Piezoelectric and dielectric properties of PZT–PZN–PMS ceramics prepared by molten salt synthesis method

Piezoelectric powders and ceramics with the composition of Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Mn_1/3Sb_2/3)O₃ (PZT–PZN–PMS) were prepared by molten salt synthesis (MSS) and conventional mixed-oxide (CMO) methods, respectively. The influence of synthesis process on the properties of powders and ceramics were investigated in detail. The results show that the MSS method significantly improved the sinterability of PZT–PZN–PMS ceramics, resulting in an improvement of dielectric and piezoelectric properties compared to the CMO method. The optimum values of MSS samples are as follows: _r = 1773; tan δ = 0.0040; T_c = 280 °C; d₃₃ = 455 pC/N; k_p = 0.70; Q_m = 888; E_c = 10.3 kV/cm; and P_r = 28.2 μC/cm², at calcination of 800 °C and sintering of 1120 °C temperature.     

Effects of ZnO on piezoelectric properties of 0.01PMW–0.41PNN–0.35PT–0.23PZ ceramics

The microstructure and piezoelectric properties of the 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃ + 0.1 and 0.3 wt.% Y₂O₃ + x ZnO ceramics were investigated. The crystal structure changed from psudocubic to tetragonal when ZnO added. The average grain size increased from 4 μm to 8 μm with the addition of ZnO by oxygen diffusion, even if the growth rate was low. When ZnO added until 0.5 wt.%, the , k_p and d₃₃ values of specimens were slightly increased regardless Y₂O₃ contents. The curie point of PMW–PNN–PT–PZ ceramics were increased from 162 °C to 232 °C, as increasing the ZnO contents. When ZnO added, the k_p of specimens slightly was increased regardless Y₂O₃ contents. The mechanical quality factors were abruptly decreased regardless Y₂O₃ contents, when ZnO added until 0.75 wt.%. The optimized piezoelectric properties were obtained; d₃₃ = 730 (pC/N), k_p = 60, Q_m = 50, and  = 4750, when PMW–PNN–PT–PZ + 0.3 wt.% Y₂O₃ + 0.5 wt.% ZnO sintered at 1200 °C for 1 h.     

Structure and electrical properties of strontium barium niobate ceramics

SBN, x=0.25, 0.35, 0.50, 0.60 and 0.75 series of ceramics prepared by traditional sintering method have been studied systematically. The impact of composition and sintering temperature on structures, microstructures, and electrical properties of SBN ceramics was characterized of X-ray diffraction, scanning electron microscopy, and electrical measurements. It is found that the composition and temperature play an important role on the fabrication of single phase tetragonal TTB SBN ceramics. At x=0.5, TTB SBN ceramics can be obtained at 1200°C. For x<0.5, it consists of a mixture of TTB structure SBN and orthorhombic phase BaNb₂O₆ even at 1300°C; TTB structure SBN and orthorhombic phase SrNb₂O₆ for x>0.5. The complete TTB phase is produced at 1350°C. With Sr content increasing, the electrical performances show a regular change, strongly conforming to the reducing of the Curie temperature. SBN with the Sr composition of x=0.60-0.75 is a promising candidate for electro-optics device applications.     

Fabrication and properties of PYN-PMN-PZT quaternary piezoelectric ceramics for high-power, high-temperature applications

xPb(Yb_1/2Nb_1/2)O₃ - 0.05Pb(Mn_1/3Nb_2/3)O₃ - (0.95 - x)Pb(Zr_0.48Ti_0.52)O₃ (PYN-PMN-PZT) quaternary piezoelectric ceramics were prepared by a traditional ceramics process. The effects of Pb(Yb_1/2Nb_1/2)O₃ (PYN) content on the phase structure, electrical properties and Curie temperature of the quaternary system were investigated in detail. The phase structure of PYN-PMN-PZT ceramics changed from tetragonal to rhombohedral with increasing PYN content. The piezoelectric coefficient (d₃₃), the electromechanical coupling factor (K_p) and the dielectric constant (ε₃₃^T/ε₀) reach maximum values near the morphotropic phase boundary (MPB), whereas the mechanical quality factor (Q_m) decreases. The sintered PYN-PMN-PZT ceramics exhibit high T_C, and as the PYN content increases, T_C decreases slightly. The MPB of the tetragonal and rhombohedral phase coexist and are located at a PYN composition of 0.12 ≤ x ≤ 0.14.The composition of PYN-PMN-PZT around the MPB showed high d₃₃ (> 300pC/N), K_p (> 0.50), Q_m (> 1000) and T_C (> 350 °C), meaning it is a very promising piezoelectric material for high-power and high-temperature applications.     

Dielectric response of piezoelectric ceramics at low voltage excitations

An improved model is proposed for the interpretation of the dielectric response of a piezoelectric lead zirconate titanate (PZT) ceramic at low voltage excitations appropriate for microdevices by considering multiple relaxation processes. The model parameters are optimised in order to achieve a satisfactory agreement between the predicted values and experimental data obtained from room temperature measurements on a commercially available PZT-805 ceramic sample.     

Bismuth-modified BiScO3-PbTiO3 piezoelectric ceramics with high Curie temperature

New piezoelectric ceramics, 0.15BiScO₃-0.85(Pb_{1 − 3x / 2}Bi_x)(Ti_0.98Mn_0.02)O₃ (x = 0.04~0.10), were prepared by using conventional solid phase processing. The results of X-ray diffraction (XRD) show that the ceramics have a single phase tetragonal perovskite structure. The ceramics, poled by normal poling process, have piezoelectric coefficient d₃₃, planar electromechanical coupling factor kp and thickness electromechanical coupling factor k_t of 50~60 pC/N, ~ 11% and ~ 30%, respectively. An extremely high mechanical quality factor Q_m of 1540 was obtained at the composition x = 0.08. The Curie temperature (T_C) is in the range of 520-550 °C, higher than 490 °C of pure PbTiO₃. The combination of good piezoelectric properties and high T_C makes these ceramics suitable for elevated temperature piezoelectric devices.     

Sintering behavior and electrical properties of the (Li, Ta, Sb) modified (K, Na)NbO3 lead-free ceramics with KNbO3 as sintering aid

Highly dense KNbO₃ (KN) doped (Li, Ta, Sb) modified (K, Na)NbO₃ ceramics (NKLNST) were prepared by normal sintering at reduced temperature of 1060 °C. The XRD study indicates that KN diffuses into the NKLNST lattice to form a new homogenous solid solution. It was found that the presence of KNbO₃ greatly enhances the densification of the ceramic, providing a dense ceramic at a lower sintering temperature due to the formation of a suitable amount of liquid phase around the optimal temperature. The 0.95(Na_0.52 K_0.44Li_0.04)(Nb_0.88Sb_0.08Ta_0.04)O₃ − 0.05KNbO₃ ceramics show a dense microstructure of ρ = 4.56 g/cm³, with a high piezoelectric d₃₃ up to 350 pC/N and k_p up to 0.49.     

Dielectric and piezoelectric properties of alkaline-earth titanate doped (K0.5Na0.5)NbO3 ceramics

(K_0.5Na_0.5)NbO₃ (KNN) and 0.995(K_0.5Na_0.5)NbO₃-0.005AETiO₃ (AE = Mg, Ca, Sr, Ba) were successfully prepared by conventional ceramic processing and without the cold-isostatic-pressing (CIP) process. The effects of low AETiO₃ (AET) concentration on crystal structure, density, dielectric and piezoelectric properties of the KNN based ceramics were evaluated. The results show that adding MgTiO₃(MT) and BaTiO₃(BT) to KNN can lead to the appearance of a trace amount of second phase(s), reduced density and deteriorated electrical properties. Adding CaTiO₃(CT) and SrTiO₃(ST) to KNN can promote densification and optimize electrical properties. Two phase transitions at T_t-o ( the temperature at which the phase transition from orthorhombic to tetragonal occurs) and T_c (the Curie temperature) were observed in KNN and all KNN-AET ceramics, by using differential scanning calorimetry (DSC) analysis and dielectric characterization. Adding AET to KNN caused the variations of T_t-o and T_c.     

Enhanced piezoelectric and mechanical properties of ZnO whiskers and Sb2O3 co-modified lead zirconate titanate composites

ZnO whiskers and Sb₂O₃ co-modified lead zirconate titanate (denoted as PZT/ZnO_w/Sb₂O₃) piezoelectric composites were fabricated using a solid state sintering technique. The characteristic diffraction peaks of the PZT perovskite and ZnO phases were identified from all the composites, suggesting the retention of these individual phases. The grain size of PZT was found to be reduced with Sb₂O₃ addition. A high relative density of 96.5%-99.1% was achieved in PZT co-doped with ZnO_w and Sb₂O₃. Both the piezoelectric and mechanical properties of the PZT/ZnO_w/Sb₂O₃ composites showed significant improvement over the monolithic PZT. The intrinsic effects of ZnO_w and Sb₂O₃ on the electrical and mechanical properties of the PZT/ZnO_w/Sb₂O₃ composites were discussed.     

Effects of lanthanum modification on electrical and dielectric properties of Pb(Zr0.70,Ti0.30)O3 ceramics

Lanthanum modified lead zirconate titanate ceramics with lanthanum content changing from 7.6 to 9.0 at.% La and a Zr/Ti ratio of 70/30 (PLZT 100x/70/30) have been prepared by conventional high temperature solid-state reaction technique. The studies of the ferroelectric, electromechanical and dielectric properties of the ceramics were carried out. The results showed the enhanced antiferroelectricity stability when the lanthanum content increases. The polarization and strain decreased with the increasing La content. The dielectric spectra of all the PLZT samples show a dispersive behavior. With increasing La concentration, the maximum dielectric constants ε_m and the transition temperatures T_m were reduced.     

Extraordinary role of Ce–Ni elements on the electrical and magnetic properties of Sr–Ba M-type hexaferrites

The structural, electrical and magnetic behavior of Sr_0.5Ba_0.5−xCe_xFe_12−yNi_yO₁₉ (where x = 0.00–0.10; y = 0.00–1.00) hexaferrite nanomaterials are reported in this paper. The structural analysis indicates that the Ce–Ni doped Sr–Ba M-type hexaferrite samples synthesized by the co-precipitation method are stoichiometric, single magnetoplumbite phase with crystallite sizes in the range of 35–48 nm. The dc-electrical resistivity of the pure Sr–Ba hexaferrite is enhanced to almost 10² times by doping with Ce–Ni contents of x = 0.06; y = 0.60. The dielectric constant and dielectric loss tangent decrease to values 14 and <0.2, respectively, by increasing the frequency up to 1 MHz. Small relaxation peaks at frequencies >10⁵ Hz are observed for the samples with Ce content of x > 0.06. The values of saturation magnetization increase from 66.32 to 84.33 emu/g and remanance magnetization from 42.64 to 56.01 emu/g but coercivity decreases from 2.85 to 1.59 kOe by substitution of Ce–Ni. Sharp ferri-paramagnetic transition is observed in the samples, which is confirmed by DSC results. Ce–Ni substitution acts to reduce the electron-hopping between Fe²⁺/Fe³⁺ ions and also improves the magnetic properties. These characteristics are desirable for their possible use in microwave and chip devices.     

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 sintering temperature on microstructure and electrical properties of ZVMCDN ceramics

The microstructure and electrical properties of ZnO-V₂O₅-MnO₂-Co₃O₄-Dy₂O₃-Nb₂O₅ (ZVMCDN) ceramics were investigated in accordance with sintering temperature (850-950 °C). The microstructure of the samples consisted of mainly ZnO grain as a main phase, and Zn₃(VO₄)₂, ZnV₂O₄, and DyVO₄ as the minor secondary phases. The sintered density decreased from 5.69 to 5.52 g/cm³ due to the volatility of V₂O₅ in accordance with increasing sintering temperature. The maximum nonlinear coefficient (57) was obtained at 925 °C. The donor concentration increased from 1.15 × 10¹⁸/cm³ to 11.1 × 10¹⁸/cm³ in accordance with increasing sintering temperature and the barrier height exhibited the maximum value (1.03 eV) at 925 °C.     

Structural, electrical and optical properties of TiO2-WO3 polycrystalline ceramics

Mixed oxides from the TiO₂-WO₃ system were prepared as polycrystalline materials. Their phase composition and electrical conductivity were investigated using X-ray diffraction (XRD) and dc electrical measurements. The energy gap, evaluated on the basis of optical measurements, was presented as a function of W concentration. The influence of chemical composition on structural, semiconducting and optical properties of the TiO₂-WO₃ polycrystalline ceramics was discussed.     

Improvement of electrical properties of V2O5 modified ZnO ceramics by Mn-doping for varistor applications

The dependence of microstructure, electrical properties, dielectric characteristics, and stability of conduction characteristics in ternary ZnO–V₂O₅–Mn₃O₄ system on the amount of Mn₃O₄ present in them was investigated. For all compositions studied, the microstructure of the ternary ZnO–V₂O₅–Mn₃O₄ system consisted of mainly ZnO grains and Zn₃(VO₄)₂ as a secondary phase. The incorporation of Mn₃O₄ to the binary ZnO–V₂O₅ system was found to restrict abnormal grain growth of ZnO. The breakdown field in the electric field–current density characteristics increased from 175 to 4,635 V/cm with the increase of Mn₃O₄ amount. The ternary system doped with 0.5 mol% Mn₃O₄ exhibited the highest non-ohmic properties, in which the non-ohmic coefficient is 22.4 and the leakage current density is 0.22 mA/cm². Furthermore, the sample doped with 0.5 mol% Mn₃O₄ was found to possess 0.43 × 10¹⁸/cm³ in donor density and 2.66 eV in barrier height.     

Substitution of Nb doping on the structural, microstructural and electrical properties in PZT films

Undoped and niobium (Nb) doped Pb_1−y(Zr_0.54Ti_0.46)_1−yNb_yO₃ have been deposited by sputtering on Pt metallized silicon substrates. The niobium concentration, y, was varied from 1 to 7 at.% by 1 at.%. The Zr/Ti ratio was fixed to 54/46 corresponding to the Morphotropic Phase Boundary. Structural, microstructural, and electrical properties were evaluated depending on Nb content. The films (doped and undoped) present a (1 1 1)-preferred orientation. The Nb doping induces an increase of the grain size and as it was observed in bulk materials the dielectric constant (ε_r) and the piezoelectric coefficients (e₃₁ and d₃₃) reach their maximum for low Nb concentration (2 at.%). The remnant and the maximum polarizations increase as the coercive field decreased slightly with the Nb concentration. The internal electric field increases with Nb content; as a result, the ‘self-polarization’ of the films (polarization measured without poling treatment) is enhanced with niobium substitution. In term of fatigue behavior, it was found that switching endurance characteristics are maximum for low Nb doping level.     

不同粉体制备工艺对铌酸钠钾无铅压电陶瓷性能的影响

铌酸钠钾(KNN)基无铅压电陶瓷性能的提高可通过掺杂、取代和添加烧结助剂等方法来实现,还可通过适当改变陶瓷制备工艺来达到.为了探索可实用化的KNN陶瓷制备工艺,以纯KNN陶瓷的制备为例,考察了3种不同粉体制备工艺(包括传统固相反应法、原料中添加活性炭的固相反应法、以及粉体经分批预烧处理后再混合的固相反应法)对KNN元铅压电陶瓷的晶相、微观结构和电学性能的影响.实验结果表明:采用原料中添加活性炭的固相反应法制得的纯KNN陶瓷,其表面晶粒尺寸相对均一,晶界清晰,样品致密性好;所得的陶瓷样具有较好的介电、压电性能,其中d33=116pC/N,κP=0.37,e=630,tanδ=0.034,Pr=22.40μC/cm2,Ec=0.675kV/mm,Tc=405℃.     

The effect of high-temperature annealing on the structure and electrical properties of well-aligned carbon nanotubes

Systematic work has been performed on the effect of high-temperature annealing on structural defects and impurities of well-aligned carbon nanotubes (ACNTs) in this paper. ACNTs had been prepared by CVD process with ferrocene as catalyst and then the as-grown samples were experienced heat treatment (HT) from 1800 to 3000 °C. X-ray diffraction, Raman spectroscopy and electron dispersive spectroscopy (EDS), etc., have been used to analyze the effect of annealing. Results indicate that some impurities can be removed once annealing temperature exceeds vaporization point of corresponding metal or non-metal. Desorption of O should be attributed to reduced active sites of dangling covalent bonds after heat treatment. Specious discrepancy about interlayer spacing resulted from XRD and Raman tests show that although high-temperature heat treatment can remove in-plane defects of carbon nanotubes greatly, interlayer spacing between graphene shells could not be reduced effectively because of the special concentric cylindrical structure of nanotubes. Electrical resistivity of ACNTs block is about three orders higher than that of copper even after HT at 3000 °C, and the anisotropy of electrical properties increased once experienced heat treatment at increased temperature.     

Enhanced ferro- and piezoelectric properties in (100)-textured Nb-doped Pb(ZrxTi1 − x)O3 films with compositions at morphotropic phase boundary

To develop high-performance piezoelectric films on conventional Pt(111)/Ti/SiO₂/Si(100) substrates, sol-gel-derived highly [100]-textured Nb-doped Pb(Zr_xTi_1 − x)O₃ (PNZT) thin films with different Zr/Ti ratios ranging from 20/80 to 80/20 were prepared and characterized. The phase structure, ferroelectric and piezoelectric properties of the PZNT films were investigated as a function of Zr/Ti ratios, and it was confirmed that there was distinct phase transition of the PNZT system from tetragonal to rhombohedral when the Zr/Ti ratio varied across the morphotropic phase boundary (MPB). The Nb-doped PZT films showed enhanced remanent polarization but reduced coercive field, whose best values reached 75 μC/cm² and 82 kV/cm, respectively at the composition close to MPB. In addition, the [100]-textured PNZT film at MPB also shows a high piezoelectric coefficient up to 161 pm/V. All these properties are superior to those for undoped PZT films.     

On the Lewis–Nielsen model for thermal/electrical conductivity of composites

Several models have been proposed in the literature to describe the thermal and electrical conductivities of particulate composites. Among the proposed models, the Lewis–Nielsen model appears quite attractive as it is simple to use and it predicts the correct behavior when filler concentration () approaches the maximum packing concentration (_m). In this paper, the Lewis–Nielsen model is evaluated in light of a vast amount of experimental data available on thermal and electrical conductivities of particulate composites. The Lewis–Nielsen model is found to describe the experimental data for both thermal and electrical conductivities reasonably well.