钇掺杂对BSPT高温压电陶瓷铁电性能的影响

利用传统固相法制备了(1-x)Bi(Sc1-yYy)O3-xPbTiO3(BSYPT-x/y)压电陶瓷,采用XRD、SEM、压电工作站等技术表征了体系的晶体结构、微观组织及其铁电性能.发现随着PbTiO3含量的增加,BYSPT-x/y陶瓷相结构由三方结构逐渐转变为四方结构.体系的准同型相界(MPB)位置随BiYO3含量的增加而移向PbTiO3含量更低的一端.在准同型相界附近的BSYPT0.58/0.15陶瓷的电滞回线出现"束腰"现象,这种现象来源于BSYPT0.58/0.15陶瓷内部产生的正极为O2-,负极为Y3+的缺陷偶极子.     

铌镁酸铋-钛酸铅压电陶瓷准同型相界附近的性能和相变温度研究

利用传统固相烧结法制备了Bi(Mg_2/3Nb_1/3)O₃-PbTiO₃(BMN-PT)压电陶瓷, 分析了不同PbTiO₃含量对BMN-PT压电陶瓷的晶体结构、介电、压电及铁电性能的影响. XRD结果表明: 合成的BMN-PT陶瓷具有纯钙钛矿结构, 并且在PbTiO₃含量为x=0.60时, 其组分的XRD图谱在衍射角2θ=45°出现明显的分峰, 说明该组分相结构中存在三方和四方相的共存. 压电铁电性能显示, BMN-0.60PT有最大的压电常数d₃₃(~170pC/N)和平面机电耦合系数k_p(0.35), 最小的矫顽场E_c(29.4 kV/cm)及最大的剩余极化P_r(31.4 μC/cm²). 确定了BMN-PT压电陶瓷的准同型相界(MPB)为PbTiO₃含量x=0.60的组分. 介电系数温谱表明介电系数峰值温度(Tm)随着PbTiO₃含量的增大而升高, MPB组分的Tm约为276℃.     

Domain Structure and Phase Symmetry of Multiferroic BiFeO3-PbTiO3 Single Crystals Studied by Piezoresponse Force Microscopy

Piezoresponse force microscopy (PFM) was used to investigate the domain structure of multiferroic BiFeO₃- PbTiO₃ single crystals with morphotropic phase boundary (MPB) compositions. The PFM data demonstrate the piezoelectricity and the PFM domain responses under the designed experimental setup reveal the coexistence of a rhombohedral, a tetragonal, and an orthorhombic phases in the MPB crystals, which is consistent with the results of structural refinements based on X-ray diffraction data.     

新型钙钛矿型铁电陶瓷BSPT研究进展

(1-x)BiScO3-xPbTiO3(BSPT)是一种新型钙钛矿型结构的铁电体.BSPT体系在x=0.64附近有三方相和四方相的准同型相界(MPB).BSPT陶瓷的制备主要采用传统的电子陶瓷制备方法,包括常压法和高压法.BSPT陶瓷具有优良的介电和压电性能,居里温度Tc比Pb(Zr,Ti)O3(PZT)的高.综述了近年来对BSPT陶瓷的研究进展,重点介绍了邻近MPB的0.36BiScO3-0.64PbTiO3铁电陶瓷的性能.同时还介绍了掺杂对BSPT陶瓷的影响.     

Dielectric and ferroelectric properties of Bi(Zn1/2Ti1/2)O3-PbTiO3-PbZrO3 ternary ceramics

Ceramics of a new ternary solid solution system, xBi(Zn(1/2)Ti(1/2))O(3-yPbTiO(3)z)PbZrO(3) (xBZT-yPT-zPZ), with compositions along the solubility limit curve are prepared by solid-state reaction and sintering technique. Two morphotropic phase boundaries (MPBs) separating the orthorhombic and tetragonal (MPB(O-T)) phases and the tetragonal and rhombohedral (MPB(T-R)) phases, respectively, are observed with increasing z (0.10 ≤ x ≤ 0.21; 0 ≤ y ≤ 0.49). It is found that the transition from the ferroelectric to paraelectric phase becomes more diffuse with the addition of BZT into the PZT solid solution. Enhanced dielectric and ferroelectric properties appear at MPB(R-T), which exists over a wide composition region (0.45 ≤ z ≤ 0.6), as revealed by X-ray diffraction and dielectric measurements. The dielectric constant reaches a maximum value (ε' = 1250) on the tetragonal majority side of the MPB. The highest remnant polarization (P(r) = 34.2 μC/cm(2)) is found in the composition at the center of the MPB, where the rhombohedral and tetragonal phases coexist in almost equal quantities.     

(Na0.5K0.5)NbO3–LiTaO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics were prepared in the system (1−x)(Na_0.5K_0.5)NbO₃–xLiTaO₃ following the conventional mixed oxide route. The effect of cationic substitution of lithium for sodium and potassium in the A sites and tantalum for niobite in the B sites in (Na_0.5K_0.5)NbO₃ (NKN) perovskite lattice on symmetry and physical properties were investigated. The materials with perovskite structure are in orthorhombic phase when x<5 mol.% and transform to tetragonal phase when x>6 mol.%; when x≥8 mol.%, a K₃Li₂Nb₅O₁₅ phase with tetragonal tungsten bronze structure begins to appear and becomes dominant with increasing content of LiTaO₃. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases appears at x=5–6 mol.%. Analogous to Pb(Zr,Ti)O₃, the piezoelectric and electromechanical properties are enhanced for compositions near the morphotropic phase boundary. Piezoelectric constant d₃₃ values reach ∼200 pC/N. Electromechanical coefficients of planar mode reach ∼36%, respectively. Our results show that (Na_0.5K_0.5)NbO₃ with small amount of LiTaO₃ (x=7 mol.%) is a good lead-free piezoelectric ceramic.     

In3+、Ga3+掺杂BSPT高温压电陶瓷的研究

将BiGaO3和BiInO3分别引入BiScO3-PbTiO3(BSPT)体系,并通过氧化物合成法制备了0.075BiGaO3-(0.925-x)BiScO3-xPbTiO3(SPTx, x=0.58～0.62)和0.075BiInO3-(0.925-x)BiScO3-xPbTiO3(BISPTx, x=0.61～0.65)压电陶瓷.X射线衍射分析表明,BiGaO3和BiInO3的替换掺杂均不影响BSPT体系的钙钛矿结构.随着PbTiO3含量的增加,SPTx和BISPTx陶瓷由三方钙钛矿结构逐渐变到四方结构,其三方-四方准同型相界分别位于x=0.60和x=0.62附近.在准同型相界附近,SPTx陶瓷的压电常数d33,机电耦合系数kp为分别为350pC/N和52.0%,而BISPTx的d33高达475pC/N,kp为52.3%.介电常数的温度特性测试表明,掺入Ga3+可以有效地提升BSPT体系的居里温度,其MPB组分(x=0.60)居里温度高达472℃,而掺入In3+对BSPT体系的居里温度影响则不明显.     

相组成对PMN-PT陶瓷压电性能的影响

研究了ＰＭＮ－ＰＴ陶瓷在准同型相界（ＭＰＢ）区域、不同烧结温度下,化学组成、相组成对陶瓷压电性能的影响．发现对于同一化学组成的陶瓷,随着烧结温度的上升,发生了菱方相→四方相的相转变,同时随着菱方相、四方相相比例的接近,陶瓷的压电性能有显著的提高．而在不同烧结温度下,最佳压电性能所对应的化学组成有微小的变化．据此认为,陶瓷的压电性能不仅与化学组成有关,而且与相组成也密切相关,随着烧结温度的变化,发生了准同型相界的微小移动     

Toughening due to domain switching in single crystal ferroelectric materials

In this paper Mode I steady state crack growth in single crystal ferroelectric materials is investigated. Specifically, the fracture toughness enhancement due to domain switching near a steadily growing crack tip is analyzed. For this purpose, an incremental phenomenological constitutive law for single crystal ferroelectric materials is implemented within a finite element model to calculate the stress and remanent strain fields around the crack tip. Also, the ratio of the far field applied energy release rate to the crack tip energy release rate, i.e. the toughening, is calculated. The numerical computations are carried out for single crystal ferroelectric materials of tetragonal or rhombohedral structure with different switching hardening and irreversible remanent strain levels. Toughening levels for crack growth along different crystallographic directions and planes are obtained and compared. Results from numerical computations for the toughening anisotropy for both tetragonal and rhombohedral crystals are presented and discussed.     

Piezoelectric properties in (K0.5Bi0.5)TiO3-(Na0.5Bi0.5)TiO3-BaTiO3 lead-free ceramics.

Lead-free piezoelectric ceramics with compositions around the morphotropic phase boundary (MPB) x(Na0.5Bi0.5)TiO3-y(K0.5Bi0.5)TiO3-zBaTiO3 [x + y + z = 1; y:z = 2:1] were synthesized using conventional, solid-state processing. Dielectric maximum temperatures of 280 degrees C and 262 degrees C were found for tetragonal 0.79(Na0.5Bi0.5)TiO3-0.14(K0.5Bi0.5)TiO3-0.07BaTiO3 (BNBK79) and MPB composition 0.88(Na0.5Bi0.5)TiO3-0.08(K0.5Bi0.5)TiO3-0.04BaTiO3 (BNBK88), with depolarization temperatures of 224 degrees C and 162 degrees C, respectively. Piezoelectric coefficients d33 were found to be 135 pC/N and 170 pC/N for BNBK79 and BNBK88, and the piezoelectric d31 was determined to be -37 pC/N and -51 pC/N, demonstrating strong anisotropy. Coercive field values were found to be 37 kV/cm and 29 kV/cm for BNBK79 and BNBK88, respectively. The remanent polarization of BNBK88 (approximately 40 microC/cm2) was larger than that of BNBK79 (approximately 29 microC/cm2). The piezoelectric, electromechanical, and high-field strain behaviors also were studied as a function of temperature and discussed.     

Relations between single-domain and multidomain piezoelastic properties in single crystals

This paper presents a new method to compute the piezoelastic properties of multidomain single crystals from the single-domain constants. Based on a quasi static assumption, a PMN-chiPT multidomain is defined as a periodic medium with a lattice composed of layers of two domains in a twin structure. Such a structure is assumed to have charged domain walls that imply specific lattice media and boundary conditions. A numerical computation has been performed for a PMN-33PT single crystal in the rhombohedral phase. The effective elastic, piezoelectric, and dielectric constants of the macroscopic structure have been calculated, as well as the wave velocities in different configurations of domain patterns.     

R-curve behaviour of PZT ceramics near the morphotropic phase boundary

The mechanical failure of PZT ceramics was characterized by measuring R-curves for compositions near and at the morphotropic phase boundary (MPB) where tetragonal and rhombohedral phases coexist in equal quantities. The R-curve behaviours (an increasing fracture toughness with crack extension) were identified by indentation-fracture testing and they were analysed to determine the key parameters. The fracture toughness of the PZT ceramics consisted of three different terms, representing particular microstructural processes in front of advancing cracks, that is, intrinsic cleavage, 90° domain switching and microcracking. Their relative contributions to an overall crack-extension resistance varied with the length of the advancing crack and, more importantly, with the compositions of the PZT. In the compositional range where the tetragonal phase was dominant, the R-curves were determined by domain switching and microcracking. However, the compositional dependency of the fracture toughness was due to the microcracking mechanism. On the other hand, in regions rich in rhombohedral phases, the R-curves were essentially determined by domain switching in the crack-tip area. The R-curves characterized by the domain-switching mechanism were insensitive to the compositional variation near the MPB. Our results also demonstrated that R-curve analysis could be used to probe further into the microstructural responses of materials in front of advancing cracks and to quantify them particularly in systems like PZT where several different toughening processes compete with each other.     

Morphotropic phase boundary (MPB) effect in Pb (Zr,Ti)O3 rhombohedral/tetragonal multilayered films

Alternating rhombohedral/tetragonal Pb(Zr_xTi_1−x)O₃ (P_x) multilayered films were prepared via a chemical solution method. It has been found that the P45/P55 multilayers show significant dielectric enhancement comparing with the uniform P45 and P55 films, and this dielectric enhancement increases as the decrease of the layer periodicity. However, the dielectric constant of the Pb(Zr,Ti)O₃ rhombohedral/tetragonal multilayered films decreases when the layer compositions are away from morphotropic phase boundary (MPB), and no remnant polarization enhancement was observed in all the multilayered films. After comparing the dielectric and ferroelectric properties of the multilayers with the corresponding single-phase films, the dielectric enhancement in P45/P55 multilayers was ascribed to the formation of the MPB region around the interfaces between the P45 and P55 layers.     

弛豫铁电材料在准同型相界附近结构和性能研究的最新进展

铅系钙钛矿结构弛豫铁电材料在准同型相界区域的单晶,因为具有优异的介电、压电性能及潜在的应用前景,近年来已经引起了广泛的重视,本文较详细地介绍了其反常性能的一些特征,以及对其起源在理论及实验观察上的最新进展,重点介绍了自发极化在外场下进行偏转的理论,以及近年来用同步辐射的Ｘ射线衍射实验研究结果,发现在原先以为只有菱方相和四方相的准同型相界区域存在着单斜相．     

Phase-transition temperatures and piezoelectric properties of (Bi1/2Na1/2)TiO3-(Bi1/2Li1/2)TiO3-(Bi1/2K1/2)TiO3 lead-free ferroelectric ceramics.

The phase-transition temperatures and piezoelectric properties of x(Bi(1/2)Na(1/2))TiO3-y(Bi(1/2)Li(1/2))TiO3-z(Bi(1/2)K(1/2))TiO3 [x + y + z = 1] (abbreviated as BNLKT100(y)-100(z)) ceramics were investigated. These ceramics were prepared using a conventional ceramic fabrication process. The phase-transition temperatures such as depolarization temperatures T(d), rhombohedraltetragonal phase transition temperature T(R-T), and dielectric-maximum temperature T(m) were determined using electrical measurements such as dielectric and piezoelectric properties. The X-ray powder diffraction patterns of BNLKT100(y)-100(z)) show the morphotropic phase boundary (MPB) between rhombohedral and tetragonal at approximately z = 0.20, and the piezoelectric properties show the maximum at the MPB. The electromechanical coupling factor k(33), piezoelectric constant d(33) and T(d) of BNLKT4-20 and BNLKT8-20 were 0.603, 176 pC/N, and 171 degrees C, and 0.590, 190 pC/N, and 115 degrees C, respectively. In addition, the relationship between d33 and Td of tetragonal side and rhombohedral side for BNLKT4-100z and BNLKT8-100z were presented. Considering both high Td and high d(33), the tetragonal side of BNLKT4-100z is thought to be the superior composition. The d(33) and T(d) of BNLKT4-28 were 135 pC/N and 218 degrees C, respectively. Moreover, this study revealed that the variation of T(d) is related to the variation of lattice distortion such as rhombohedrality 90-alpha and tetragonality c/a.     

Crystal chemistry and domain structure of relaxor piezocrystals

The major recent advances in the crystal chemistry and domain properties of relaxor piezoelectric single crystals include: (i) A better understanding of the phase nature and components near the morphotropic phase boundary; (ii) The establishment of high temperature phase diagrams and development of improved growth techniques that provide piezocrystal resources for characterization and applications; (iii) A deeper insight into the mesoscopic domain structures of the morphotropic rhombohedral, tetragonal and monoclinic phases.     

Low-temperature synthesis of chemically homogeneous lead zirconate titanate (PZT) powders by a semi-wet method

A semi-wet procedure for the synthesis of single-phase Pb(Zr _x Ti_1–x )O₃ powders at 600 °C is described. The ultrafine powders so obtained do not exhibit tetragonal/rhombohedral distortions until they are sintered at higher temperatures. The morphotropic phase boundary (MPB) for these powders, which are chemically homogeneous, lies between x=0.52 and 0.53. For x=0.525, the rhombohedral and tetragonal phases coexist.     

Depolarization temperature and piezoelectric properties of Na1/2Bi1/2TiO3-Na1/2Bi1/2(Zn1/3Nb2/3)O3 ceramics by two-stage calcination method

A new group of NBT-based lead-free piezoelectric ceramics, Na_1/2Bi_1/2TiO₃-Na_1/2Bi_1/2(Zn_1/3Nb_2/3)O₃, was synthesized using the two-stage calcination method and depolarization temperatures and piezoelectric properties were also investigated. The XRD analysis showed that the ceramics system had a morphotropic phase boundary (MPB) between the rhombohedral and the tetragonal structure. The highest piezoelectric properties of d ₃₃ = 97 pC/N and k _t = 0·46 were obtained near MPB compositions. Furthermore, the depolarization temperatures near MPB compositions were slightly decreased and the lowest T _d was maintained at 210°C.     

Phase transition,ferroelectric and piezoelectric properties of Bi(Mg0.5Zr0.5)O3-modified BiFeO3–BaTiO3 lead-free ceramics

(0.725 ? x)BiFeO₃–0.275BaTiO₃–xBi(Mg_0.5Zr_0.5)O₃ + 1 mol% MnO₂ lead-free ceramics (x = 0–0.08) were synthesized by a conventional solid state reaction method and the effects of Bi(Mg_0.5Zr_0.5)O₃ on phase transition, piezoelectric and ferroelectric properties of the ceramics were investigated. After the addition of Bi(Mg_0.5Zr_0.5)O₃, the crystal structure of the ceramics is transformed from rhombohedral to tetragonal phase and the morphotropic phase boundary (MPB) of rhombohedral and tetragonal phase is formed at x = 0.01. The grain size of the ceramics increases with x increasing from 0 to 0.02 and then decreases with x further increasing. The dielectric peak of the ceramics becomes diffusive with x increasing after the addition of Bi(Mg_0.5Zr_0.5)O₃. The ceramics with x = 0–0.08 exhibit much better electric insulation with the resistivity of 1.0 × 10⁹–5.0 × 10⁹ Ω·cm than pure BiFeO₃ ceramic with the resistivity of ~5 × 10⁷ Ω·cm. Due to the formation of the MPB, the ceramics with x = 0–0.02 possess good densification with the relative densities ρ _r of 94.9–96.3 %, strong piezoelectricity with the d ₃₃ of 129–135 pC/N and very high Curie temperature with the T _C of 559–610 °C.     

Piezoelectric properties of [Bi<Subscript>0.5</Subscript>(Na<Subscript>0.7</Subscript>K<Subscript>0.25</Subscript>Li<Subscript>0.05</Subscript>)<Subscript>0.5</Subscript>]TiO<Subscript>3</Subscript>−Ba(Ti,Zr)O<Subscript>3</Subscript> binary system ceramics

Dense lead-free binary system piezoelectric ceramics (1 − x)[Bi_0.5(Na_0.7K_0.25Li_0.05)_0.5]TiO₃−xBa(Ti_0.95Zr_0.05)O₃ (BNKLT–BZT) were prepared by a two-step sintering process. A phase transition from rhombohedral to tetragonal was observed with increasing BZT fraction in the range x = 0.06–0.1 and the morphotropic phase boundary (MPB) between rhombohedral and tetragonal appears in this range. Ceramics containing 10 mol% BZT with tetragonal phase near the MPB region has the maximum piezoelectric constant d ₃₃(151pC/N).