Lead-free piezoelectric ceramics manufactured from tantalum-substituted potassium sodium niobate nanopowders

Nanopowders of lead-free (K_0.5Na_0.5)(Nb_0.9Ta_0.1)O₃ (KNNT) system were prepared by high-energy ball milling at different milling times keeping the milling speed fixed at 250 rpm. The particle size first decreases from 35 nm to 3 nm and then increases to 98 nm as the milling time increases in steps of 5 h from 10 h to 30 h. Without using any sintering aid, dense ceramics were formed by sintering the powders at 1050 °C for 1 h. With decreasing particle size of the starting nanopowders, the ceramics exhibit gradual increase in density from 93.1% to 95.8%, coercive field (E_c) from 10.9 kV/cm to 15.1 kV/cm, electromechanical coupling factor (k_p) from 35% to 48%, and piezoelectric charge constant (d₃₃) from 80 pC/N to 128 pC/N. The systematic changes observed in these parameters corroborate the observed increase in particle size as the milling time increases from 25 h to 30 h.     

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.     

一种改性铌酸盐系无铅压电陶瓷的合成与特性研究

K0.5Na0.5NbO3(KNN)系铌酸盐是一类可能替代铅基压电陶瓷的无铅压电陶瓷.利用Ta和Sb掺杂或者取代KNN中的相关离子,在陶瓷的准同型相界(MPB)处显现出高的压电和介电性能.利用传统技术制作出一种新的致密度较高的无铅压电陶瓷(1-x)(K0.5Na0.5)(Nb0.96Sb0.04)O3-xLiTaO3(简记为KNNS-LT).所有的组分在MPB处都存在纯的钙钛矿结构,主要压电性能在MPB处达极大值,其机电耦合系数kp为40%,压电常数d33为225pC/N,居里温度Tc为355℃.     

Structure and piezoelectric properties of Cu-doped potassium sodium tantalate niobate ceramics

The Cu-doped (K_0.5Na_0.5)(Nb_0.95Ta_0.05)O₃ (KNNT) ceramics were prepared by the solid state reaction ceramic technique. The phase structure and the micro-morphology were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). There exhibits a single phase in perovskite structure, even the grain sizes increase with copper addition. The dielectric constant (ε), the planar mode electromechanical coupling factor (k_p), the piezoelectric coefficient (d₃₃), and the mechanical quality factor (Q_m) of KNNT ceramics with copper additive are 320–450, 0.21–0.41, 70–110 pC/N, 105–979, respectively.     

Growth of lithium doped silver niobate single crystals and their piezoelectric properties

Lithium doped silver niobate (Ag_1−xLi_xNbO₃, 0 < x < 0.1) is one of the candidate materials for lead-free piezoelectric materials. In this study, Ag_1−xLi_xNbO₃ single crystals were successfully grown by a slow cooling method. Crystal structure was assigned to perovskite-type orthorhombic (monoclinic) phase. Dielectric properties were measured as a function of temperature. As a result, with increasing lithium contents, the phase transition at around 60 °C was shifted to lower temperature while the phase transition at around 400 °C was shifted to higher temperature. On the basis of these peak shifts, the lithium contents in Ag_1−xLi_xNbO₃ single crystals were determined. Moreover, P–E hysteresis measurement revealed that pure silver niobate crystal was weak ferroelectrics with P_r of 0.095 μC/cm² while Ag_0.9Li_0.1NbO₃ (ALN10) crystal was normal ferroelectrics with P_r of 10.68 μC/cm². About this ALN10 crystal, polling treatment was performed and finally piezoelectric properties were measured. As a result, high electromechanical coupling coefficient k₃₁ over 70% was observed.     

Barium titanate nanoparticles produced by planetary ball milling and piezoelectric properties of corresponding ceramics

Barium titanate (BaTiO₃) nanocrystalline powders were prepared by solid state reaction route starting from BaCO₃ and TiO₂ powders accompanied by high-energy ball milling. Different samples were prepared by varying the milling time from 1 h to 30 h, keeping the milling speed fixed at 250 rpm. All the milled powders were examined with TEM. The particle size first decreases from 105 nm to a minimum of 28 nm as the milling time increases from 1 h to 20 h and then increases to 38 nm with further increase of milling time to 30 h. Dense ceramics were formed by sintering the nanopowders at 1350 °C for 4 h. With decreasing particle size of the starting nanopowders, the ceramics exhibit gradual increase in density from 5.65 g/cc to 5.84 g/cc, coercive field (E_c) from 2.25 kV/cm to 4.77 kV/cm and piezoelectric charge constant (d₃₃) from 99pC/N to 121pC/N.     

Structural integrity and ferroelectric–piezoelectric properties of PbTiO3 coating prepared via supersonic plasma spraying

In order to prepare the PbTiO₃ coating with high density and excellent piezoelectric properties on all kinds shape surface, the PbTiO₃ coating was prepared by supersonic plasma spraying. The microstructure and mechanical properties were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectrograph (XPS). The dielectric constant and dissipation constant of the PbTiO₃ coating were tested. The results show that the coating has a single ferroelectric phase with perovskite structure, and its surface is smooth and dense. In the course of spraying, about 50% PbTiO₃ is decomposed into PbO and TiO₂ at high temperature. The ferroelectric hysteresis is weak and the ferroelectric hysteresis loop is not completely closed, which indicates that the defects, such as pores and cracks, exist in the coating. Although the defects are inevitable, the PbTiO₃ coating with ferroelectric and piezoelectric properties is successfully prepared.     

Lead-free ceramics based on alkaline niobate tantalate antimonate with excellent dielectric and piezoelectric properties

This paper reports lead-free (Na_0.52K_0.48−x)(Nb_0.94−xSb_0.06)O₃-xLiTaO₃ compositions with significantly enhanced piezoelectric properties. The 6% Sb substituted Na_0.52K_0.48NbO₃ was modified by a small amount of LiTaO₃, leading to the formation of a morphotropic phase boundary between orthorhombic and tetragonal phases in the range of x = 0.035-0.04 where the materials show a strong compositional dependence of various electrical properties. Excellent properties of d₃₃ = 335 pC/N, k_p = 53%, , Q_m = 41 and T_c = 291 °C were obtained in the composition with x = 0.04, indicating that the ceramics studied are promising as a lead-free piezoelectric candidate.     

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.     

Sintering behavior and dielectric properties of Ce doped strontium barium niobate ceramics with silica sintering additive

Sr_0.5Ba_0.5Nb₂O₆ ceramics with and without CeO₂ dopant were prepared by a partial co-precipitation method and a liquid phase sintering process. The cooperative effects of Ce doping and silica sintering additive on the sintering behaviors and the dielectric properties of Sr_0.5Ba_0.5Nb₂O₆ ceramics was investigated. It was observed that the lattice parameters of a-axis and c-axis of Sr_0.5Ba_0.5Nb₂O₆ ceramics decrease with the increase of Ce dopant, namely contraction of crystal cell volume occurs. Amorphous silica used for sintering additive can effectively restrain abnormal grain growth and prevent the rise of sintering activation energies caused by Ce doping, but Ce doping has more effect on the average size of the grains and the dielectric properties than the silica sintering additive when the Ce dopant and the silica sintering additive are introduced. Both the Curie temperatures and the maximum of dielectric constant at Tc decrease as the Ce³⁺ concentration increases.     

Microstructure and Thermal Diffusivity of Ceramic Powders

For the first time, the thermal diffusivity (α) in red clay samples has been determined as a function of the annealing time, for a furnace temperature above 900°C. The thermal diffusivity measurements on the samples were obtained by means of the photoacoustic technique in a heat transmission configuration. A complementary microstructure analysis using X-ray diffraction (XRD) and energy dispersion spectroscopy (EDS) has been performed. The ceramic material used in this work is widely used in the fabrication of several kinds of building materials such as bricks and roof tiles in the north oriental region of Colombia (Cúcuta). The importance of these results is in the determination of conditions to obtain manufactured products with the desired heat transport capacity. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

High electrical properties of W-additive Mn-modified PZT–PMS–PZN ceramics for high power piezoelectric transformers

The ceramics were prepared successfully by the addition of WO₃ to the Mn-modified Pb(Zr_0.52Ti_0.48)O₃–Pb(Mn_1/3Sb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃ (PZT–PMS–PZN) for high power piezoelectric transformers application. XRD analysis indicated that the ceramics were mainly composed of a tetragonal phase in the range of 0–1.0 wt.% WO₃ addition. The grain size of the ceramics significantly decreased from 10.0 to 2.9 μm by addition of WO₃. Moreover, the addition of WO₃ promoted densification of the ceramics and increased mechanical quality factor (Q_m), planar coupling factor (K_p) and piezoelectric constant (d₃₃) kept high values, whereas, dielectric loss (tan δ) was low. Δf (=f_a − f_r) slightly changed when WO₃ addition was above 0.5 wt.%. The ceramics with 0.6 wt.% WO₃ addition, sintered at 1150 °C showed the optimized piezoelectric and dielectric properties with Q_m of 1852, K_p of 0.58, d₃₃ of 243 pC/N and tan δ of 0.0050. The ceramics are promising candidates for high power piezoelectric transformers application.     

Fabrication and characterization of potassium-sodium niobate piezoelectric ceramics by spark-plasma-sintering method

High density (Na_1−xK_x)NbO₃ (x = 0.5, 0.6, and 0.7) ceramics were successfully prepared by spark-plasma-sintering (SPS) method. The dielectric and piezoelectric properties of the SPS samples were investigated and compared to that of hot-pressed samples. It is found that, the SPS-sintered (Na_1−xK_x)NbO₃ samples show higher room temperature dielectric constant, higher coercive fields, lower remnant polarizations and lower electromechanical coefficients than that of the hot-pressed (Na_1−xK_x)NbO₃ samples. The dielectric and piezoelectric property differences between the SPS-sintered and hot-pressed samples have been attributed to grain size effects.     

Effect of Fe and Fe-Ba substitution on the piezoelectric and dielectric properties of lead zirconate titanate ceramics

Polycrystalline samples of Fe and Fe-Ba doped lead zirconate titanate (PZT) ceramics near the morphotrophic phase boundary have been synthesized by a solid-state reaction technique. Preliminary X-ray analysis of the compound confirms that there is no change in the crystal structure of PZT on co-doping with Fe and Ba. The maximum mechanical quality factor Q_m was found to be 1000 for Fe doped material and 880 for Fe-Ba doped material. The electromechanical coupling factor for Fe and Fe-Ba doped samples were 0.535 and 0.495 respectively. The corresponding values for the piezoelectric charge constant d₃₃ were 135 and 250 pC/N respectively. These results are discussed in terms of position occupied by dopants in to the lattice and their corresponding microstructures. These Fe-Ba doped PZT materials could be likely candidates for high power ultrasonic and underwater SONAR transducer systems.     

Novel piezoelectric ceramics and composites for sensor and actuator applications

 Novel piezoelectric ceramic, and ceramic /polymer composite structures were fabricated by solid freeform fabrication (SFF) for sensor and actuator applications. SFF techniques including: Fused Deposition of Ceramics (FDC), and Sanders Prototyping (SP) were utilized to fabricate a variety of complex structures directly from a computer aided design (CAD) file. Many novel and complex composite structures including volume fraction gradients (VFG), staggered rods, radial and curved composites, and actuator designs such as tubes, spirals and telescoping were made using the flexibility provided by the above processes. Radial composites with various connectivities in the radial direction were made for towed array applications. VFG’s were incorporated into some of these designs, with the ceramic content decreasing from the center towards the edges. Many new designs are also being used to manufacture high authority actuators utilizing the FDC technique. The telescoping actuation of the device is the summation of actuation of all individual tubes making of the actuator, therefore, increasing the number of the tubes which are the driving component of the actuator will further enhance the displacement. The design, fabrication and electromechanical properties of these sensor and actuator structures are discussed in this paper. Received: 2 November 1998 / Reviewed and accepted: 2 November 1998     

Effects of sintering aid CuTa2O6 on piezoelectric and dielectric properties of sodium potassium niobate ceramics

In this study, the effects of a sintering aid CuTa₂O₆ (CT) on (Na_0.5K_0.5)NbO₃ (NKN) ceramics were investigated. The diffracted angles in XRD profiles decreased because the Nb-sites were replaced by Cu and Ta ions, causing the expansion of lattice volume. SEM images showed smaller grain sizes at a low concentration of CuTa₂O₆, and grain sizes increased as the concentration of CuTa₂O₆ doping increased because of a liquid phase formed. When CuTa₂O₆ dopants were doped into NKN ceramics, the T_O–T and T_c phase transitions decreased because the replacement of Ta⁵⁺ ions in the B-site. A high bulk density (4.595 g/cm³) and electromechanical coupling factor (k_p, k_t) were enhanced when CT dopants were doped into NKN ceramics. Moreover, the mechanical quality factor (Q_m) also increased from 67 to 1550. NKN ceramics with sintering aid CuTa₂O₆ doping showed excellent piezoelectric properties: k_p: 42.5%; k_t: 49.1%; Q_m: 1550; and d₃₃: 96 pC/N.     

Sintering, microstructure and piezoelectric properties of CuO and SnO2 co-modified sodium potassium niobate ceramics

The CuO and SnO₂ co-modified Na_0.52K_0.48NbO₃ ceramics were prepared by a conventional mixed oxide method. Densification can be further improved but the grain growth is inhibited as a small amount of SnO₂ is added into 1% CuO doped Na_0.52K_0.48NbO₃. The results indicate that the physical and various electrical properties of CuO and SnO₂ doped Na_0.52K_0.48NbO₃ ceramics significantly depend on sintering conditions and the content of dopants. The ceramics doped with 1 mol% CuO and 1 mol% SnO₂ sintered at 1070 °C for 3 h show improved dielectric and piezoelectric properties: d₃₃ = 120 pC/N, k_p = 0.38, Q_m = 1040, ?_r = 710 and tanδ = 0.013 (1 kHz), in comparison with un-doped or CuO doped compositions.     

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.     

Microstructural characteristics,porosity and strength development in ceramic-laterized concrete

Interfacial bonding between constituent materials and pore sizes in a concrete matrix are major contributors to enhancing the strength of concrete. In a bid to examine how this phenomenon affects a laterized concrete, this study explored the relationship between the morphological changes, porosity, phase change, compressive, and split tensile strength development in a ceramic-laterized concrete. Varying proportions of ceramic aggregates, sorted from construction and demolition wastes, and lateritic soil were used as substitutes for natural aggregates. Strength properties of the concrete specimens were evaluated after 7, 14, 28 and 91 days curing, but morphological features, using secondary electron mode, were examined only at 7 and 28 days on cured specimens, using Scanning electron microscope (SEM). From all the mixes, selected samples with higher 28 day crushing strength, and the reference mix, were further characterized with more advanced analysis techniques, using the mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA), X-ray Diffractometer, and SEM (backscatter electron mode-for assessment of the interfacial transition properties between aggregates and paste).The reference mix yielded higher mechanical properties than the concrete containing secondary aggregates, this was traced to be as a result of higher peaks of hydration minerals of the concrete, coupled with its low tortuosity and compactness. However, a laterized concrete mix containing both 90% of ceramic fine and 10% of laterite as fine aggregate provided the optimal strength out of all the modified mixes. Although, the strength reduction was about 9% when compared with the reference case, however, this reduction in strength is acceptable, and does not compromise the use of these alternative aggregates in structural concrete.     

Fabrication and properties of highly transparent Er:YAG ceramics

Highly transparent Er:YAG ceramics with different Er doping concentrations were fabricated by a reactive sintering method under vacuum. The optical properties and the microstructures of the Er:YAG ceramics were investigated. For 3 mm thickness samples, the in-line transmittances of the as-fabricated Er:YAG ceramics at the wavelength of 1100 nm and 400 nm were about 84% and 82%, respectively. The micrograph of the Er:YAG transparent ceramics exhibited a pore-free structure and the average grain size was about 10 μm. The grain boundary of the ceramics was clean and no secondary phase was detected. The absorption and emission spectra, the fluorescence decay traces of the Er:YAG ceramics were measured and discussed. The ceramics obtained may have potential use for eye-safe solid-state lasers partly replacing Er:YAG single crystals.