Ferroelectricity of Pb(Zn1/3Nb2/3)O3-BaTiO3-PbTiO3 ceramics in the vicinity of morphotropic phase boundary

The morphotropic phase boundary (MPB) in the (0.85 – x)Pb(Zn_1/3Nb_2/3)O₃ – 0.15BaTiO₃ – xPbTiO₃(0 < x < 0.2) ceramic system was delineated by x-ray diffraction analysis. Polarization hysteresis loop measurements at room temperature were performed for compositions in the vicinity of the MPB. Experimental results demonstrate that the MPB, by its definition the rhombohedral and tetragonal phase coexist in the present system, is a broad composition region where the value of x ranges from 0.12 to 0.18. The remanent polarization, P _r, increases with PbTiO₃(PT) reaching a maximum value of 18 C/cm² at 15 mol%PT, then decreases remarkably with further PT addition, whereas the variation of coercive field, E _c, with PT content shows the opposite trend. The effect of PT incorporation on P _r is more pronounced than on E _c. Correlation between the degree of lattice distortion, instead of the maximization of the polarization orientations inherent to both phases, and P _r is attained to account for the observed phenomenon. The dependence of E _c upon PT content, however, reflects the transition from typical relaxor ferroelectrics to weak normal ferroelectrics, as confirmed by the results of the dielectric measurement.     

Microstructure and dielectric and piezoelectric properties of PbFe0.5Nb0.5O3 ceramics modified with Li2CO3 and MnO2

Unmodified lead ferroniobate (PFN) and samples modified with 1 wt % Li₂CO₃ (PFNL) and 1 wt % MnO₂ (PFNM) have been prepared by solid-state reactions followed by sintering by a conventional ceramic processing technique. The modifiers have been shown to change the nature of the recrystallization sintering process, reduce the optimal sintering temperature of the material, increase its average grain size, stabilize its dielectric properties, and improve its piezoelectric performance. The observed effects are interpreted in terms of the crystal-chemical specifics of the modifiers and their location in the structure of the parent compound.     

Bi(Mg_(1/2)Ti_(1/2))O_3-PbTiO_3压电陶瓷体系介电与居里温度特性研究

采用传统固相法工艺制备了(1-x)Bi(Mg1/2Ti1/2)O3-x Pb Ti O3(BMT-x PT,0.34≤x≤0.44)陶瓷。研究发现,随着PT含量增加,试样结构由三方相逐渐转变为四方相结构,当0.36x0.40时,试样结构处于准同型相界(MPB)区。研究表明BMT组元是一种具有非铁电体特征的组分,随着PT含量减少,BMT-PT体系的居里温度减小,介电峰变得越来越不明显。通过研究BMT-PT体系组分与居里温度(TC)的关系可以看出:(1)PT含量为0.34~0.44时,TC随BMT含量变化实验值和Stringer的经验值差异较小,变化趋势一致;(2)BMT-PT体系居里温度最大值可能在x=0.73的附近,其居里温度最大值TC max约为550℃。     

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.     

Sintering and piezoelectric properties of Pb(Ni1/3Sb2/3)O3-PbZrO3-PbTiO3 ceramics

The sintering and piezoelectric properties of Pb(Ni_1/3Sb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics have been investigated. When the powders contain 48 mol% PbTiO₃ and less than 10 mol% Pb(Ni_1/3Sb_2/3)O₃ followed by calcination at 850°C for 2 h, the calcine only contains the perovskite structure; but if the Pb(Ni_1/3Sb_2/3)O₃ content is between 12 mol% and 14 mol%, both tetragonal and rhombohedral phases are obtained. The composition of the morphotropic phase boundary(MPB) in the Pb(Ni_1/3Sb_2/3)O₃-PbZrO₃-PbTiO₃ system is Pb(Ni_1/3Sb_2/3)O₃ = 12 mol%, PbZrO₃ = 40 mol% and PbTiO₃ = 48 mol%. As the composition at the MPB is sintered at 1260°C and 1280°C for 2 h, respectively, the maximum density (7.8 g/cm³) is obtained. The SEM micrographs indicate that a decrease in porosity with increasing sintering temperature is attained at 1280°C, which is due to a decrease in the number and size of pores. When the sintering temperature is higher than 1280°C, the porosity increases due to PbO evaporation leading to an increase of the number of pore sites and in enlargement of the pore diameter. When the compact composition at MPB is sintered at 1280°C for 2 h, the planar coupling coefficient (K _p) and mechanical quality coefficient (Q _m) tend to approach the maximum (0.488) and minimum values (292.5), respectively.     

Structure and properties of LiNbO3 doped Bi(Mg1/2Ti1/2)O3–PbTiO3 ceramics with the morphotropic phase boundary composition

(1?x){0.62Bi(Mg_1/2Ti_1/2)O₃–0.38PbTiO₃}–xLiNbO₃ (BMT–0.38PT–xLN, 0.00 ≤ x ≤ 0.06) ceramics were prepared by the conventional mixed oxide method. It showed that all compositions belong to the pseudocubic phase when LN doped into BMT–0.38PT ceramics, meanwhile piezoelectric properties declined. With LN content increasing, a change from a ferroelectric behavior to an abnormal diffuse behavior was observed. Furthermore, stable dielectric permittivity (1,300–3,800) and low losses were obtained in the temperature range 100–400 °C for 0.02 ≤ x ≤ 0.06 samples, indicating a potential for high-temperature applications.     

Temperature stable dielectric properties for Pb(Mg1/3Nb2/3)O3-BaTiO3-PbTiO3 system ceramics

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Dielectric properties of BaBi2Nb2O9 ceramics

The crystal structure and dielectric properties as a function of temperature for Ba-based with Bi-layered structure BaBi₂Nb₂O₉ (BBN) ceramics were investigated. The obtained results confirmed the relaxor ferroelectric behavior of the studied ceramics, including a strong frequency dispersion of the permittivity maximum and a visible shift of its temperature with frequency. Analysis of the real and imaginary part of permittivity allowed us to determine the values of Burn’s temperature and of the freezing temperature characterizing the relaxor ferroelectrics. The physical processes, responsible for the relaxor behavior of the studied ceramics are discussed. The additional low frequency dielectric dispersion at high temperatures in the paraelectric phase range was also observed. Correlation between this dispersion and the thermally stimulated depolarization current was ascertained.     

Dielectric properties of low-fitting Pb(Mg1/3Nb2/3)1−xTixO3-Bi2O3/Li2O ceramics

Dielectric properties of low-firing Pb(Mg_1/3Nb_2/3)_1–x Ti _x O₃-Bi₂O₃/Li₂O ceramics are studied in this work. With the addition of Bi₂O₃/Li₂O eutectic composition, the sintering temperature of PMN_1–x PT _x could be lowered to 900° C. Relaxor behaviour of PMN_1–x PT _x is enhanced by the incorporation of Bi₂O₃/Li₂O due to the substitution of Bi⁺³/Li⁺ into the PMN_1–x PT _x framework. Bi₂O₃/Li₂O eutectic composition is used as a fluxing agent, Curie shifter and depressor. Evaporation of Bi₂O₃/Li₂O and PbO during firing is checked and examined via energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) is used to clarify the Curie shifting and depressing effect of Bi₂O₃/Li₂O.     

Dielectric and piezoelectric properties of Pb(Ni1/3Nb2/3)O3–PbTiO3–PbZrO3 ceramics modified with bismuth and zinc substitutions

The dielectric and piezoelectric properties of the (Pb_0.985Bi_0.01)(Ni_1/4Zn_1/12Nb_2/3)_x- (Zr_σTi_1-σ)_1-xO₃ piezoelectric ceramic system (0.2 ≤ x ≤ 0.7, 0.1 ≤ σ ≤ 0.9) were systematically investigated. The results showed that, after poling, the dielectric constant, ε ₃₃ ^T , increased for the tetragonal compositions but decreased for the rhombohedral compositions. Furthermore, high values of ε ₃₃ ^T and piezoelectric modulus, d ₃₁ were found for the compositions along the extension of the morphotropic phase boundary. The highest values of the planar electromechanical coupling factor, K _p, and the piezoelectric modulus, d ₃₁, were found to be 0.70 and − 274 × 10^-12 C N^-1, respectively. The Curie temperature, remanent polarization, coercive field and the lattice constants of the a and c axes in relation to the Pb(Ni_1/3Nb_2/3)O₃ content and the Zr/Zr + Ti ratio were also determined. This revised version was published online in November 2006 with corrections to the Cover Date.     

Quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 transparent ceramics under both DC and AC bias

The basic quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) transparent ceramics have been studied under both DC and AC electric field bias. The contribution of piezoelectric resonance to electro-optic effect for this quadratic electro-optic ceramics material has been experimentally demonstrated and theoretically analyzed. It is found that, at the piezoelectric resonance frequencies, the piezoelectric induced electro-optic effect dominates and leads to a dramatically high sensitivity for weak electric signal detection. About 20 dB signal-to-noise ratio is attained when detecting AC electric field strength of 1 V/m with optimized DC bias. Besides, the effects of AC frequency and amplitude on halfwave voltage V(π) of PMN-PT are investigated.     

Dielectric properties of Pb(Zn1/3, Nb2/3)O3 ceramics modified by Ba(Zn1/3, Nb2/3)O3 and BaTiO3

Dielectric properties of lead zinc niobate (PZN) ceramics modified by barium zinc niobate (BZN) and BaTiO₃ (BT) were investigated. By adding the modifier of BT and BZN, the stabilization of perovskite phase of PZN increased, but its Curie temperature decreased linearly with the amount of added modifier. Room temperature dielectric constant of PZN increased by addition of stabilizers up to 12 and 15 mol% of BZN and BT, respectively. The maximum room temperature dielectric constant was observed to be 7800 at 12 mol% of BZN, and 9800 at 15 mol% of BT, respectively.     

The substitution-site of Cd2+ in Pb(Ni1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

三元陶瓷Pb(In1/2Nb1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3准同型相界附近组分的介电、铁电和压电性能

铅基复合钙钛矿铁电材料广泛应用于机电传感器、致动器和换能器。二元铁电固溶体Pb(Ni_1/3Nb_2/3)O₃- PbTiO₃(PNN-PT)由于其在准同型相界(MPB)区域具有优异的压电、介电性能而备受关注。然而较大的介电损耗和较低的居里温度限制了其在高温高功率器件方面的应用。本研究通过引入Pb(In_1/2Nb_1/2)O₃ (PIN)作为第三组元改善PNN-PT的电学性能, 提高其居里温度; 通过两步法合成了MPB区域的三元铁电陶瓷Pb(In_1/2Nb_1/2)O₃- Pb(Ni_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PNN-PT), 研究了其结构、介电、铁电和压电性能。制备的所有组分陶瓷具有纯的钙钛矿结构。随着PT含量的增加, 陶瓷结构从三方相转变为四方相。通过XRD分析得到了室温下PIN-PNN-PT体系的MPB相图。体系的居里温度由于PIN的加入得到了很大的提高, 更重要的是PIN的引入降低了PNN-PT体系的介电损耗和电导。MPB处的组分展现出了优异的电学性能, 室温下, 性能最优组分为0.30PIN-0.33PNN-0.37PT: d₃₃=417 pC/N, T_C=200 ℃, ε′= 3206, tanδ=0.033, P_r=33.5 μC/cm², E_C=14.1 kV/cm。引入PNN-PT的PIN第三组元使得体系的居里温度和压电性得到提高的同时降低了的介电损耗和电导率, 因此, PIN-PNN-PT三元铁电陶瓷在高温高功率换能器等方面具备一定的应用潜力。     

Dielectric and impedance properties of LiCa2Nb5O15 ceramics

Polycrystalline sample of LiCa₂Nb₅O₁₅ was prepared by a high-temperature solid-state reaction technique. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscope (SEM). X-ray studies reveal that the material has orthorhombic structure at room temperature. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (31–500 °C) and frequency (10²–10⁶ Hz) ranges. The complex impedance plots reveal the main contribution of bulk effects in it. The bulk resistance, evaluated from complex impedance spectrum, has been observed to decrease with rise in temperature showing a typical negative temperature coefficient of resistance (NTCR) behavior. Variation of dc conductivity (bulk) with temperature demonstrates that the compound exhibits Arrhenius type of electrical conductivity.     

Perovskite phase formation in the PbMg1/3Nb2/3 O3-PbZrO3-PbTiO3 system by the columbite route

The reaction mechanism of PbMg_1/3Nb_2/3O₃-PbZrO₃-PbTiO₃ (PMN-PZT) perovskite phase prepared by the columbite route has been studied in the temperature range from 600 to 800 °C. The effects of heating and cooling rate during the calcination of 3PbO +MgNb₂O₆+PZT powder mixtures have also been investigated. Nearly pure perovskite phase, 0.9 PMN-0.1 PZTsolid solution with no pyrochlore phase, as determined by X-ray diffraction, could be prepared at 800 °C for 2 H. From DTA/TGA, dilatometry and XRD data the reaction mechanism of PMN-PZT solid solution formation could be divided into three steps: (i) decomposition of columbite (MgNb₂O₆) by reacting with PbO at 350 to 600 °C (ii) the formation of a B-site-deficient pyrochlore phase Pb₂Nb_1.33Mg_0.17O_5.50 at close to 650 °C, and (iii) the formation of perovskite phase PMN-PZT solid solution from the reaction of Pb₂Nb_1.33Mg_0.17O_5.50 pyrochlore phase with MgO and PZT above 650 °C.     

Processing and properties of Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramic relaxors

The shrinkage phenomenon during the reaction-sintering of PMN-PZT from low-temperature pre-reacted 3PbO + MgNb₂O₆ + PZT powder mixtures has been studied. It was assumed that the pre-reaction treatment leads to the formation of a pyrochlore phase containing very active MgO small particles, and that the strong shrinkage occurring up to 800 °C took place by the diffusion of Mg²⁺ cations into the pyrochlore phase particles, thus controlling the reaction-sintering shrinkage phenomenon. Above that temperature the densification was enhanced by a liquid-phase sintering process. The ceramics sintered at 1050 °C for 2 h showed 96% of the theoretical density, and the dielectric constant of such a sintered ceramic showed a maximum value of 17 000 at 1 kHz. It was also found that the dielectric constant decreased with increasing grain size. Although the role of PZT in enhancing the dielectric constant of otherwise low-purity PMN ceramics is not clear, the increase in K is assumed to be a solid-solution effect. The presence of impurities and the PbO stoichiometry could be influencing the not too high dielectric constant value of PMN-PZT ceramics.