Structure and Properties of Hot-Pressed Pb(Lu1/2Nb1/2)O3-PbTiO3 Binary System Ceramics*

Solid solution series of the (1 - x)Pb(Lu_1/2Nb_1/2)O₃ - x PbTiO₃ binary system ceramics (PLuNT) were synthesized and hot-pressed (temperature 950°C to 1130°C, pressure 25 MPa); its structure, dielectric and piezoelectric properties were studied. Pure lutecium niobate PLuN (x = 0) has a pronounced long-range order in the B-sublattice and an antiferroelectric to paraelectric phase transition at ～258°C. The phase structure of the PLuNT system, at room temperature, changes from a pseudomonoclinic (psd-M, space group Bmm2) to tetragonal (T, space group P4mm). The pseudomonoclinic phase extends over the 0 ≤ x ≤ 0.38 interval within which the monoclinic angle β proceeds a minimum near to 90° at x ? 0.2. The morphotropic region covers the interval x = 0.38 - 0.49, the concentration ratio psd-M:T? 1 (the morphotropic phase boundary—MPB) corresponds to x = 0.41. Within the morphotropic region, a rather strong distortion of the unit cell—(c/a - 1)≥ 0.02, β ≥ 90.37º, characteristic of “hard” piezoelectrics is maintained. Dielectric dispersion and broadening of the phase transition, features typical to relaxors, are observed within the concentration interval of 0.1 ≤ x ≤ 0.3. The highest electromechanical coupling coefficients: k_p = 0.66, k_t = 0.48, k₃₁ = 0.34 of (1 - x) PLuN?xPT ceramics are attained in compositions near the MPB at x ≈ 0.41. Non-isovalent doping of PLuNT with La³⁺ in Pb sublattice shifts the MPB to lower values of x.     

Study of the Electrical Properties of Pb(Mg,Ni)1/3Nb2/3O3-PbTiO3 System Across the Morphotropic Phase Boundary

Phase transitional behavior and electrical properties of (1 – x)Pb(Mg,Ni)_1/3Nb_2/3O₃-xPbTiO₃ ceramics (PMNN-PT with Mg/Ni = 1:1, x = 0.20–0.40) across the morphotropic phase boundary (MPB) were examined. X-ray diffraction and dielectric measurement reveal that two phases, pseudocubic and tetragonal phases, coexist in the composition range x = 0.30–0.36. The maximum d ₃₃ (about 570 pC/N) was observed at the composition x = 0.32–0.34. Dielectric and ferroelectric properties exhibit abnormal high near the MPB. An unusual peak shoulder occurred in the dielectric measurement upon thermal cycling for poled samples. This phenomenon was considered to be associated with the macro to micro domain transition and depolarization.     

Substituent Effects in 0.65Pb(Mg1/3Nb2/3O30.35PbTiO3 Piezoelectric Ceramics

Pb(Mg_1/3Nb_2/3O₃–-PbTiO₃ (PMN-PT) ceramics with base compositions close to the morphotropic phase boundary are potential materials for many applications such as transducers and actuators due to their high dielectric constants and electromechanical coupling factors. However, their dielectrical and mechanical losses are too high for high-power applications. In this paper, the dielectric and electromechanical properties of piezoelectric PMN-PT ceramics were investigated in specimens containing various A-site and B-site substituents with the goal of developing lower loss materials for wider applications. Emphasis was placed on various transition metal cation substituents of both lower and higher valences. Mn substituent was found to be the most promising substituent investigated for developing high power low loss piezoelectric PMN-PT ceramics.     

Processing and Electrical Properties of 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 Ceramics

Pb(Yb_1/2Nb_1/2)O₃-PbTiO₃ ceramics at the morphotropic phase boundary (50:50) were sintered by conventional and reactive methods to 95% theoretical density and grain sizes <10 m. Excess PbO, added to enhance the densification, resulted in PbO-based non-ferroelectric phases that degraded the electrical properties. Volatilization of excess PbO by annealing the samples after sintering resulted in dense, perovskite samples and excellent electrical properties. The best electrical properties, obtained via reactive sintering, were a remanent polarization, P _r, of 0.36 C/m², a maximum dielectric constant of 31,000 (at the T _c = 371°C and 1 kHz), a piezoelectric charge coefficient, d ₃₃, of 508 pC/N, and an electromechanical coupling coefficient, k ₃₃, of 0.61.     

Bi0.5(Na0.82-xK0.18Lix)0.5TiO3无铅压电陶瓷的微结构与电性能

采用传统陶瓷制备工艺制备了[Bi0.5(Na0.82-xK0.18Lix)0.5]TiO3(x=0.01~0.07)无铅压电陶瓷.研究了该体系陶瓷的微结构以及应力对平面机电耦合系数kp和压电常数d33的影响.结果表明,[Bi0.5(Na0.82-xK0.18Lix)0.5]TiO3无铅压电陶瓷具有单一钙钛矿结构,Li+有抑制晶粒长大的作用.当x=0.03时,压电陶瓷样品表现出优良的压电性能:压电常数d33和平面机电耦合系数kp分别为154 pC/N和0.296.同时发现,退火可消除内应力,有利于提高d33,但会使kp减小;极化会引起介电常数εr减小,电畴转向过程中产生的应力对d33影响较为明显     

Processing and properties of nanocrystalline Pb(Sc0.5Ta0.5)O3, Pb(Sc0.5nb0.5)O3 and Pb(Mg1/3Nb2/3)O3 films produced by RF-sputtering from ceramic targets

Abstract

Nanocrystalline thin films of different relaxor materials, namely Pb(Sc_0.5Ta_0.5)O₃ (PST), Pb(Sc_0.5Nb_0.5)O₃(PSN), Pb(Mg_1/3Nb_2/3)O₃(PMN) have been produced by RF-sputtering to investigate whether it will affect their dielectric properties if their grain size is reduced to the dimensions known from their nanodomains. The XRD shows that the amorphous film crystallizes in pyrochlore structure at lower temperatures and short times. Annealing at higher temperatures and far longer time intervals leads to an increasing amount of perovskite phase with a grain size in the nanometer range. These results including dielectric measurements will be presented and discussed.     

Studies on Electrical Properties and Magnetoelectric Effect of (x)Ni0.8Cu0.2Fe2O4 + (1?x)Ba0.8Pb0.2Ti0.8Zr0.2O3 Composites

Materials consisting of piezomagnetic and piezoelectric phases viz. Ni_0.8Cu_0.2Fe₂O₄ and Ba_0.8Pb_0.2 Ti_0.8Zr_0.2O₃ have been prepared by standard ceramic method. The presence of two phases in the composites has been confirmed by XRD. Variation of the dielectric constant with frequency in the range 100–1 MHz has been studied at room temperature and the variation of dielectric constant with temperature at set frequencies (1 kHz, 10 kHz, 100 kHz and 1 MHz) has been studied. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure. All the samples have shown linear magnetoelectric conversion in the presence of a static magnetic field. The dc resistivity (ρ_DC) was studied as a function of temperature in the range 300–773^∘K. The variation of resistivity with temperature shows metal/seconductor behaviour.     

Piezoelectric properties of the Pb(Sc1/2Nb1/2) O3-Pb(Mg1/3Nb2/3) O3-PbTiO3 ternary ceramic materials near the morphotropic phase boundary

Abstract

The physical and electrical properties of xPb(Sc_1/2Nb_1/2)O₃-yPb(Mg_1/3Nb_2/3)O₃-zPbTiO₃(PSMNT 100x/100y/100z) ternary ceramic materials near the morphotropic phase boundary (MPB) were investigated. The MPB follows on almost linear region between the PSMNT 58/00/42 and PSMNT 00/68/32 MPB compositions of the binary systems. The maximum piezoelectric constant, d ₃₃ = 680 pC/N, were found at PSMNT 29/33/38, where ε^T ₃₃/ε₀ = 3,800, and electromechanical coupling factors, (k _p = 70%, k₃₁ = 43%, and k ₃₃ = 76%) and T _c = 207°C were obtained. The maximum electromechanical coupling factors, (k _p = 72%, k ₃₁ = 45%, and k ₃₃ = 77%) were found at PSMNT 29/34/37, where ε^T ₃₃/ε₀ = 3,000, d ₃₃ = 640 pC/N, and T _c = 205°C were obtained. These values are better than those of PZT.     

IR detectors using Pb(Mg1/3Nb2/3)O3 and Pb(Sc1/2Ta1/2)O3 ceramics under DC bias

Recently, one type of thermal-type IR detector, the pyroelectric sensor, has become of great interest in commercial applications, because of its ability to operate without cooling, its constant detectivity independent of wavelength, and its low cost. The conventional pyroelectric materials are usually normal ferroelectric materials with a first and second phase transition. The working temperatures are sufficiently below the Curie temperature T_c for stable responsivity to temperature. Electric field induced-type pyroelectric sensors have also been proposed. Relaxor ferroelectric materials such as Pb(Mg_1/3Nb_2/3)O₃ (PMN) and Pb(Sc_1/2Ta_1/2)O₃ (PST), which have a glassy Curie temperature near room temperature, are used in this type of sensor. This paper describes the sensor properties of electric field induced-type pyroelectric sensors prepared by using PMN and PST ceramics as compared with the conventional type sensors. Material evaluations of PMN and PST ceramics were made to determine their dielectric and pyroelectric properties. PMN shows excellent induced pyroelectric properties for the sensors over a wide range of temperatures. On the other hand, PST seems to be inadequate for an IR detector because of a very narrow high-response temperature range. The sensors with PMN and PST ceramics show enhanced pyroelectric activities under dc bias field. The measured sensor voltage responsivities agree with the calculated values for the PMN case. The electric field induced-type infrared sensor with thick or thin film materials seems to be satisfactory as linear array IR detectors for thermal imaging, with application of a higher electric field.     

Ferroelectricity in Aurivillius-Type Structure Ceramics with n = 2 and (SrBi2Nb2O9)0.35(Bi3TiNbO9)0.65 Composition

Aurivillius-type structure compounds are good candidates for their use as high temperature piezoelectrics, due to their high ferro-paraelectric phase transition temperature. However, this characteristic correlates with a high coercive field that makes difficult the poling process, necessary to have piezoelectric activity. The electric properties, specially conductivity, limit the maximum poling field. On the other hand, piezoelectric properties are directly related to the ferroelectric remanent polarization. Thus, the study of both characteristics is towards improving the piezoelectric properties of these materials. In this work, ceramics with nominal composition (SrBi₂Nb₂O₉)_0.35(Bi₃TiNbO₉)_0.65 (T_C∼ 760^∘C), prepared by hot pressing of mechanically activated precursors, have been studied. The electrical properties (permittivity, dielectric loss factor and d.c. conductivity) as a function of frequency and temperature have been measured, up to temperatures higher than the ferro-paraelectric phase transition, and their anisotropy explained in terms of the ceramic texture. Well-saturated ferroelectric hysteresis loops at 250^∘C have been obtained, with values of P_r = 21.4 μ C/cm² and E_c = 70.4 kV/cm.     

Random-Site Cation Ordering and Dielectric Properties of PbMg1/3Nb2/3O3-PbSc1/2Nb1/2O3

(1 ? x)PbMg_1/3Nb_2/3O₃-(x)PbSc_1/2Nb_1/2O₃ (PMN-PSN) solid solution crystals have been grown by the flux method in the whole concentration range. X-ray supercell reflections due to B-cation ordering were observed for as-grown crystals from the 0.1 ≤ x ≤ 0.65 compositional range. Though the ordered domains are rather large (～50 nm) the relaxor-like dielectric behavior is observed for compositions with x < 0.6. The diffusion of the dielectric permittivity maximum in as-grown crystals is the lowest at x = 0.6 and increases towards the end members of solid solution. Such behavior is explained within a Bragg-Williams approach by employing the random layer model. At x ～ 0.6 the excitation energy determined from the Vogel-Fulcher relation exhibits a jump which we regard to changing the kind of the polar regions from PbMg_1/3Nb_2/3O₃ to PbSc_1/2Nb_1/2O₃ related type.     

Li(Ni1/3Co1/3Mn1/3)O2正极材料的电化学性能

用共沉淀法制备出(Ni1/3Co1/3Mn1/3)(OH)2,与LiOH·H2O混合后,在900℃下焙烧12 h,得到锂离子电池正极材料Li(Ni1/3Co1/3Mn1/3)O2.在2.70～4.35 V,电流为40 mA/g时,循环性能稳定.当截止电压升高到4.60 V时,容量可达190 mAh/g.循环伏安实验表明,材料的结构在循环过程中保持稳定.     

Surface acoustic wave properties in 0.955Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 multidomain single crystal poled along [001]c

Surface acoustic wave propagation in a 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ multidomain single crystal poled along [001]_c has been analyzed theoretically using Christoffel wave equations. From the measured experimental data, the orientational dependence of surface acoustic wave phase velocities, electromechanical coupling coefficients and power flow angles was calculated. The results showed that surface acoustic wave propagations of 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ are poor than 0.93Pb(Zn_1/3Nb_2/3)O₃-0.07PbTiO₃ crystal slightly. However, the 0.955Pb (Zn_1/3Nb_2/3)O₃-0.045PbTiO₃ single crystals have higher rhombohedral-tetragonal phase transition temperature and much stabler electromechanical properties. This may expand applications range of SAW devices.     

Structural, Electrical and Dielectric Behavior of Pb(Mg1/4 Ni1/4 W1/2)O3 Ceramics

Polycrystalline samples of Pb(Mg_1/4 Ni_1/4 W_1/2)O₃ (PMNW) have been prepared by a conventional solid-state reaction. Preliminary room temperature X-ray study shows the formation of single-phase compound with cell parameters a = 9.8045 (28) Å, b = 13.1280 (28) Å and c = 14.42072 (28) Å. Dielectric anomaly and ferroelectric phase transition observed at 76°C was supported by our polarization study. The variation of dc resistivity of the material with temperature shows its semiconducting behaviour.     

Epitaxial thin film heterostructures of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3

Abstract

We have grown stoichiometric pure perovskite phase Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) thin films and PMN-PT/SrRuO₃ heterostructures on miscut (100) SrTiO₃ substrates by pulsed laser deposition. X-ray diffraction θ–2θ scans show that the PMN-PT films are purely c-axis oriented. The off-axis Φ scans show that the heterostructures grow “cube-on-cube” with an in-plane epitaxial arrangement of PMN-PT[100], [010] // SrRuO₃[001] // SrTiO₃[100] and PMN-PT[010], [100] // SrRuO₃[110] // SrTiO₃[010]. The crystalline quality of the films found to be comparable to that of bulk single crystals. The AFM images show that the SrRuO₃ and PMN-PT layers have smooth surfaces with root mean square roughness of 9Å. These epitaxial heterostructures can be used for the fabrication of piezoelectric devices.     

Phase Formation,Dielectric, Ferroelectric and Magnetic Properties of Cr2O3 Doped (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Ceramics

Abstract

In this paper, we studied the effect of Cr₂O₃ doping (0–0.8?wt%) on the phase formation, dielectric, ferroelectric and magnetic properties of (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ (BCTZ) ceramics prepared by the solid state combustion method. All samples were prepared with a calcined and sintered temperature of 1050?°C and 1450?°C, respectively, for 2?h. The results of the XRD patterns showed the coexistence between the tetragonal (T) and orthorhombic (O) phases for all samples, and the tetragonal phase increased with increasing amounts of Cr₂O₃. The dielectric constant decreased when Cr₂O₃ increased. The P-E hysteresis loops of the BCTZ ceramics doped with Cr₂O₃ between 0 and 0.2?wt% showed slim and saturated loops. By increasing Cr₂O₃ doping from 0.4 to 0.8?wt%, the P-E loops were unsaturated and a leakage current was produced. The undoped BCTZ ceramics exhibited diamagnetic behavior. The sample with 0.2?wt% Cr₂O₃ showed ferromagnetic behavior. Increasing Cr₂O₃ doping from 0.4 to 0.8?wt%, caused the ceramics to exhibit paramagnetic behavior. Doping with Cr₂O₃ led to improper ratios between the tetragonal and orthorhombic phases, decreased density and increased porosity which caused a decrease in the electric properties.     

Electromechanical Properties and Morphotropic Phase Boundary of Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3-BaTiO3 Lead-free Piezoelectric Ceramics

The crystal structure and electromechanical properties of two ternary ceramic Na_0.5Bi_0.5TiO₃- K_0.5Bi_0.5TiO₃-BaTiO₃ (NBT-KBT-BT) systems were investigated. A gradual change in crystalline structure and microstructure with the increase of KBT and BT concentrations were observed. It was ascertained that the rhombohedral-tetragonal morphtropic phase boundary (MPB) lies in the range of 0.024 ≰ x ≰ 0.030 for (1–5x) NBT-4x KBT-x BT system and 0.025 ≰ y ≰ 0.035 for (1 − 3y) NBT—2y KBT—y BT system at room temperature. The piezoelectric constant d₃₃ and electromechanical coupling factor k_p of the ceramics attain a maximum value of 150 pC/N and 0.298, respectively. The MPB phase diagram of NBT-KBT-BT ternary system was determined by phase analysis of XRD patterns from calcined specimens. The ferroelectric properties of the (1 − 5x) NBT—4x KBT—x BT system have been characterized. The ternary system ceramics have relatively high Curie temperature T_c.     

Microstructures and Piezoelectric Properties of Microwave-Sintered Pb(Mn1/3Nb2/3)0.1Zr0.52Ti0.38O3 Ceramics

In this work, we study the microstructural modifications and the electrical properties of Pb(Mn_1/3Nb_2/3)_0.1Zr_0.52Ti_0.38O₃ + 1.5 wt% PbO (PMNZT) ceramics processed using microwave sintering (MS) and conventional sintering (CS) techniques. Dielectric and piezoelectric properties were evaluated via an impedance/gain phase analyzer and the corresponding microstructures were examined using transmission electron microscopy (TEM). The experimental results imply that smaller grain size and less loss of PbO obtained for specimens using MS process. The MS specimens (1200°C-15 min) show the remanent polarization (P_r) of 24.1 μC/cm², coercive field (E_c) of 15.2 kV/cm, dielectric constants (?_r) of 432 and electromechanical coupling coefficient (k_p) of 0.47, which are superior to CS specimens (1200°C-2 h) with P_r = 19.5 μC/cm², E_c = 16.1 kV/cm, ?_r = 395 and k_p = 0.45. The results revealed that the MS process shows capability of fabrication of good quality PMNZT ceramics with advantages of lowing process temperature and shorten process time. TEM investigations of MS specimens show that smaller grain size and simpler domain arrangements exist inside the specimens. From the energy aspect, the domain structure in piezoelectric ceramics below the temperature of a ferroelectric structural phase transformation is a result of energy minimization. Homogeneous elastic strain energy is reduced at the expense of domain boundary energy during the phase transformation. Density of domain boundaries, 71° (109°) domains in particular, depends on and increases with the grain size. Base on the above argument, therefore, CS specimens exhibit more complicated domain arrangements because they possess larger grain size than MS specimens do. The microstructural investigations suggest that the electrical property difference is intimately related to different sintering methods since the complicated domain arrangements could hinder domain moving and deteriorate electrical performance. In addition, the microstructural characteristics in both MS and CS specimens will be discussed further in the context.     

掺杂少量Co对Li(Li1/9Ni1/3Mn5/9)O2电化学性能的影响

改进共沉淀法合成层状电极材料Li(Li1/9Ni1/3Mn5/9)O2和Li(Li1/9Ni1/3Mn5/9)0.95Co0.05O2.分别用X射线粉末衍射(XRD)、扫描电镜(SEM)、X射线光电子能谱(XPS)表征材料结构、形貌和电化学循环过程中过渡金属离子价态的变化,用恒电流充放电研究材料的电化学性能.实验结果显示在3.0～4.2 V(vs.Li+/Li)电势范围内,以25 mA/g恒流充放电,Li(Li1/9Ni1/3Mn5/9)O2和Li(Li1/9Ni1/3Mn5/9)0.95Co0.05O2初始放电比容量分别为159 mAh/g和186.8 mAh/g,Li(Li1/9Ni1/3Mn5/9)0.95Co0.05O2经过50次循环后容量仍保持在183.9 mAh/g,高倍率放电效果较Li(Li1/9Ni1/3Mn5/9)O2有很大的改善.实验证明掺杂少量的Co可在很大程度上改善电极材料的电化学性能.     

Li(Ni0.4Co0.2Mn0.4)O2包覆Al2O3对隔膜形貌及结构的影响

以Al2O3包覆前后的Li(Ni0.4Co0.2Mn0.4)O2为正极活性物质,中间相炭微球(MCMB)为负极活性物质,与聚丙烯(PP)-聚乙烯(PE)-PP三层隔膜组装成18650型锂离子电池,在循环不同次数后,用SEM观察隔膜形貌,XRD分析其精细结构.在电池的循环过程中,隔膜出现微孔闭合及微观结构改变;包覆抑制了隔膜中微孔的闭合,同时提高了结构稳定性.