四方相Fe:KTa1-xNbxO3晶体电致应变分布特性

采用顶部籽晶助熔法制备0.15%（摩尔分数）Fe掺杂的KTa_1–xNb_xO₃晶体,测试了晶体介电性能、电致应变性能分布、组分分布和电畴结构。结果表明：数字全息是一种有效表征材料应变空间分布的方法,Fe:KTN晶体电致应变性能呈现不均匀分布的特性,室温下外加电场为435 V/mm时,晶体应变最大值为0.05%,有3/4区域应变在0.02%附近。Fe:KTN晶体的应变分布与组分分布、电畴结构之间存在联系,室温低于晶体Curie温度时,晶体Nb元素含量少的区域电畴结构小,具有更大的电致应变。     

PLZT驰豫铁电陶瓷偏压压电效应的研究

本文研究了铌掺杂的ＰＬＺＴ驰豫铁电陶瓷在不同直流偏压及温度下的介电常数ε３３,平面机电耦合系数ｋ和等效横向压电常数ｄ３１。实验表明,铌掺杂的ＰＬＺＴ驰豫铁电陶瓷ｄ３１值可由直流偏压控制及ｄ３１值的温度系数远小于ＰＭＮ－ＰＴ系陶瓷。室温上２ｍｏｌ％和３ｍｏｌ％的铌掺杂的ＰＬＺＴ１０／６５／３５驰豫铁电陶瓷在１０ＫＶ／ｃｍ的偏压下│ｄ３１│分别为２０５ｐＣ／Ｎ和１６０Ｃ／Ｎ。     

铌酸钾钠基无铅压电陶瓷的掺杂

采用传统陶瓷制备方法制备KNN-STO陶瓷,研究了SrTiO3对KNN陶瓷材料晶体结构和介电性能的影响。SrTiO3的加入极大地改善了KNN压电陶瓷的烧结性能,在常压条件下得到的陶瓷的实际密度占理论密度的97%以上。随着立方相SrTiO3的加入,KNN基陶瓷的相结构由正交相转变为假立方相,同时压电也使得KNN基压电陶瓷的介电性能大大提高,介电损耗降低,频率稳定性增强,并表现出驰豫性铁电体的特征。     

残余内应力对大各向异性陶瓷材料性能的影响

采用传统工艺制备了一种新型B位联合取代的、性能得到改善的钙改性钛酸铅陶瓷(Pb 0.76Ca0.24)[(Zn1/2W1/2)0.03(Ni1/3Nb2/3) 0.03Ti0.94]O3+1.3%(mol) MnCO3.在不同极化电场下对样品的性能变化进行研究, TEM观察发现晶体内存在有比90°畴更精细的畴结构;XRD发现陶瓷在强极化电场下90°畴基本没有转向, 并观察到强极化电场下陶瓷体内存在的宏观内应力和微观应力的变化.精细的畴结构重新取向可能是微观内应力增加的主要原因;强电场下陶瓷体内出现的微裂纹是残余内应力得到释放的主要原因;径向机电耦合系数kp存在极小值是电畴重新取向和残余内应力共同作用的结果.     

A/B位离子掺杂BiFeO3纳米薄膜的微结构与铁电性能

采用化学溶液法结合层层旋涂退火工艺,在掺氟氧化锡导电玻璃基片上制备了BiFe_0.95Mn_0.05O₃和Bi_0.9Nd_0.1FeO₃纳米晶铁电薄膜,并分析比较了其微结构和铁电性能。结果表明:2组分样品均为单相多晶钙钛矿结构,晶粒细小均匀,表面平整,结构致密。两薄膜均获得了饱和电滞回线,且BiFe_0.95Mn_0.05O₃薄膜具有向上的择优取向极化和更优异的铁电性能,其剩余极化强度(Pr)达60mC·cm^–2,在1~50 k Hz频率范围与25~200℃温度区间内铁电极化响应稳定,保持时间长达1′10³ s工作与反复极化翻转高达1′10⁹次表现出优异的电荷保持力和抗疲劳稳定性。     

新型弛豫铁电单晶(1-x)Pb(Zn_(1/3)Nb_(2/3))O_(3-x)PbTiO_3生长的技术创新

(1-x)Pb(Zn_(1/3)Nb_(2/3))O_(3-x)PbTiO_3(PZNT)晶体是弛豫铁电体Pb(Zn_(1/3)Nb_(2/3)O_3与普通铁电体PbTiO_3组成的具有钙钛矿结构的固溶体,其准同型相界成分(x=0.09)附近表现出极其优异的压电性能,在医用超声成像、声纳、微位移器等方面具有广阔的应用前景,分析了PZNT-PbO赝二元系的析晶行为和相关系,总结了PZNT晶体的压电性能,讨论了生长工艺和成分对晶体性能的影响。针对PZNT晶体生长中存在的问题,发展了助熔剂-坩埚下降法、通气诱导成核技术、两步法生长工艺、区熔凝固技术、底部籽晶高温溶液法等多种生长技术,生长出大尺寸的PZNT晶体,并比较了这些生长技术的特点。     

PMnS-PZN-PZT压电纤维的制备与铁电性能

采用固相法制备了0.8Pb(Mn1/3Sb2/3)0.05(Zr1/2Ti1/2)0.95O3–0.2Pb(Zn1/3Nb2/3)0.28(Zr1/2Ti1/2)0.72O3(PMnS–PZN–PZT)粉末,然后用塑性聚合物方法制备了PMnS–PZN–PZT压电纤维。研究了纤维夹持状态对其铁电性能的影响。结果表明:塑性聚合物法制备的PMnS–PZN–PZT压电纤维具有良好的铁电性能,压电纤维处于自由状态时,剩余极化强度和矫顽场分别为85.4μC/cm2和8.5kV/cm,但电滞回线很难饱和。将纤维采用环氧树脂固化后,剩余极化强度变成39.2μC/cm2,电滞回线呈饱和状态,说明夹持状态对纤维的铁电性能产生很大的影响。高压下压电纤维浇铸前后的漏电流测试结果表明,压电纤维浇铸后剩余极化强度变小主要与漏电流有关。     

Li2CO3掺杂对0.2PMN-0.8PZT陶瓷的影响

利用铌铁矿预产物合成法,研究不同温度烧结下Li2CO3掺杂对0.2 PMN-0.8PZT压电陶瓷(简称PLC)的相结构和电性能的影响。X射线衍射(XRD)和扫描电镜(SEM)的分析结果表明,掺杂LiCO3的0.2PMN-0.8PZT压电陶瓷经不同温度煅烧后,所有陶瓷样品的相组成均为纯钙钛矿相,并随着烧结温度的升高,PLC的相结构有由四方相向菱方相转变的趋势。通过0.2PMN-0.8PZT压电陶瓷掺杂LiCO3煅烧后的微观形貌、介电常数、压电性能、铁电性能的分析,发现经1200℃烧结的样品的介电和压电性能最佳:介电常数(εr)为38512,室温压电常数(d33)为300 pC/N,剩余极化强度(Pr)为31.3 C/cm2,矫顽电场(Ec)为7.5 kV/cm。     

Pb用量对锆钛酸铅薄膜微观结构和铁电性能的影响

在Pt/Ti/SiO2/Si基片上,通过多次匀胶旋涂-预热处理工艺制备了PbTiO3(PT)无机薄层夹心的锆钛酸铅(lead zirconate titanate,PZT)薄膜,然后经650℃退火处理得到了所需的具有钙钛矿结构的PZT铁电薄膜.用X射线衍射、原子力显微镜表征了PZT铁电薄膜微观结构,并测试铁电性能.结果表明:制备PT层时的Pb用量对得到的PZT铁电薄膜的微观结构和铁电性能有重要影响.当Pb过量15%(摩尔分数)左右时,得到的PZT铁电薄膜不仅晶界清晰,晶粒尺寸分布均匀,具有纯钙钛矿结构,而且铁电性能优异,剩余极化强度Pr=21μC/cm2,矫顽场Ec=37kV/cm.     

三方/四方相共存铌锑锆钛酸铅压电陶瓷极化的研究

研究了极化条件对三方 /四方相共存 (即准同型相界 ,简称MPB)的铌锑锆钛酸铅 (PNSZT)压电陶瓷性能和结构的影响 .利用XRD探讨了三方、四方相共存PNSZT压电陶瓷极化过程中畴转向、相变、晶格常数的变化、应变 ,分析讨论了极化作用机理 .XRD结果分析表明 :两相共存压电陶瓷极化过程中畴转向的同时伴随着相变 (四方相→三方相 )、应变、晶格常数变化 ;随着极化程度的提高 ,试样的应变量和 90°畴转向率不断增加 ;当达到极化饱和状态时 ,它们也达到最大值 ,其中应变的最大值为 0 .4% ,90°畴的转向率最大值为 41.6 % ,此时样品的介电常数和机电耦合系数也达到最大值 .当 90°畴转向率高和应变大时 ,材料的机电耦合系数和介电常数也大 .90°畴转向率和应变是表征极化程度的微观结构物理量 .最优极化条件是得到最佳压电性能陶瓷的关键之一     

Ferroelectric Ceramics in the PbMg1/3Nb2/3O3-PbCd1/3Nb2/3O3 System

Solid solutions (1-x)PbMg_1/3Nb_2/3O₃ + xPbCd_1/3Nb_2/3O₃ with x = 0-0.30 are investigated with purpose to work out a capacitor ceramics with good dielectric properties and low sintering temperature. It is found that the perovskite phase forms at sintering near to 980°C and begins to decompose at higher temperatures. When x grows from 0 to 0.30, the Curie temperature linearly grows from -10°C to +25°C, the dielectric permittivity ε_m in the Curie point T_C decreases from 18000 to 6800 and the phase transition becomes more diffused. The dielectric permittivity at room temperature is rather high and the temperature stability is improved. The system is of interest, because it can serve as a base for working out some ceramic materials for capacitors with low sintering temperature, which needs of no special atmosphere at burning.     

Structure Evolution from Pb(Mg1/3Nb2/3)O3 to La(Mg2/3Nb1/3)O3

The crystal structure of lanthanum-modified lead magnesium niobates having composition (Pb_{1− x} La _x ) (Mg_{(1+ x )/3}-Nb_{(2− x )/3})O₃ with X = 0 to 1 was investigated by X-ray powder diffraction. It was found that the fundamental reflections from perovskite structure remain in the whole range of composition. The superlattice reflections from the A(B'_1/2-B"_1/2)O₃ ordered structure are also well preserved for La content greater than 50 at.%; however, a series of extra peaks of mixing indices appears, with intensities gradually enhanced with the increase of La content. For the complete substitution of Pb by La, a splitting of some reflections can be observed in the diffraction pattern. The results indicate that the crystal structure evolves continuously with the La content, from disordered cubic perovskite of space group Pm 3 m for X = 0, to ordered cubic perovskite of space group Fm 3 m for X = 0.5, distorted cubic perovskite of space group Pa 3 for 0.5 < X < 0.9, and finally to a rhombohedral perovskite, possibly belonging to the space group R 3 , for X ≥ 0.9. In the evolution of structure, a linear reduction of the lattice constant of the perovskite cell from 4.048 to 3.964 Å was observed.     

Cation Ordering Transformations in the Ba(Zn1/3Nb2/3)O3-La(Zn2/3Nb1/3)O3 System

Single-phase perovskites were formed in the (1−_x)Ba(Zn_1/3Nb_2/3)O₃-( _x )La(Zn_2/3Nb_1/3)O₃ system for compositions with 0.0≤ x ≤0.6. Although the stability of the trigonal "1:2" ordered structure of the Ba(Zn_1/3Nb_2/3)O₃ end member is very limited (0.0≤ x ≤0.05), low levels of lanthanum induce a transformation to a cubic, "1:1" ordered structure that has a broad range of homogeneity (0.05≤ x ≤0.6). Samples with x > 0.6 were comprised of La₃NbO₇, ZnO, and a perovskite with x = 0.6. The cubic 1:1 phases were fully ordered and no evidence was found for a compositionally segregated microstructure. These observations could not be reconciled in terms of a "space-charge" model; rather, they supported a charge-balanced, "random-site" structure for the 1:1 cation-ordered Ba(β_1/2'β_1/2")O₃ phases.     

Morphotropic Phase Boundary in the Pb(Zn1/3Nb2/3O3)-BaTiO3-PbTiO3 System

The morphotropic phase boundary (MPB) in the relaxor ferroelectric system Pb(Zn_1/3Nb_2/3O₃)-BaTiO₃-PbTiO₃ (PZN-BT-PT) with 15 mol% BT was investigated through dielectric permittivity and high-temperature X-ray diffraction measurements. It was revealed that MPB is a broad composition region extending from 12 to 18 mol% PT, within which the temperatures of the permittivity maximum are close to the ending temperatures for the phase transformation from coexisting rhombohedral and tetragonal phases to cubic phase on heating. When the specimen is cooled, the starting temperatures for the rhombohedral-to-tetragonal phase transition increase with increasing PT content. The large thermal hysteresis observed by X-ray diffraction is caused by the phase transformation between rhombohedral and tetragonal phases. On cooling, the MPB curves toward the PT-rich side, so that ceramics within this composition range undergoe successive phase transitions from cubic to rhombohedral and from rhombohedral to tetragonal phase. The diffuseness of the paraelectric-to-ferroelectric phase transition is remarkably decreased by the addition of PT. The enhanced dielectric permittivity peak values for the MPB compositions are correlated with the reduced lattice distortion and phase coexistence.     

Sintering of glass-added BaZn1/3Nb2/3O3 ceramics

The complex perovskite oxide Ba(Zn_1/3Nb_2/3)O₃ (BZN) has been studied for its attractive dielectric properties which place this material interesting for applications as multilayer ceramics capacitors or hyperfrequency resonators. This material is sinterable at low temperature with combined glass phase–lithium salt additions, and exhibits, at 1 MHz very low dielectric losses combined with relatively high dielectric constant and a good stability of this later versus temperature. The 2 wt.% of ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of LiF-added BZN sample sintered at 900 °C exhibits a relative density higher than 95% and attractive dielectric properties: a dielectric constant ?_r of 39, low dielectrics losses (tan(δ) < 10⁻³) and a temperature coefficient of permittivity τ_? of 45 ppm/°C⁻¹. The 2 wt.% ZnO–SiO₂–B₂O₃ glass phase and 1 wt.% of B₂O₃-added BZN sintered at 930 °C exhibits also attractive dielectric properties (?_r = 38, tan(δ) < 10⁻³) and it is more interesting in terms of temperature coefficient of the permittivity (τ_? = −5 ppm/°C). Their good dielectric properties and their compatibility with Ag electrodes, make these ceramics suitable for L.T.C.C applications.     

Electromechanical Testing and Modeling of a Pb(Mg1/3Nb2/3)O3-PbTiO3-BaTiO3 Relaxor Ferroelectric

Compressive prestress effects on the electrical and mechanical properties of relaxor ferroelectric materials were studied as a function of temperature for several formulations of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃-BaTiO₃ (PMN-PT-BT) ceramics. Experimentally measured polarization and strain, induced by an ac electric field, decreased as compressive stress increased. Effective Young's moduli also were measured under constant dc electric fields. A significant decrease in modulus was observed with increasing field. The prestress and modulus experiments were modeled analytically using a proposed relaxor ferroelectric constitutive law. In general, excellent agreement between the model and experiments was obtained, indicating that the model accurately predicted the coupled behavior of this relaxor ferroelectric material.     

Dielectric and Piezoelectric Properties of Pb(Co1/3Nb2/3)O3-PbTiO3-PbZrO3 Solid Solution Ceramics

Ceramic and piezoelectric properties of the Pb(Co_1/3Nb_2/3)O₃-PbTiO₃-PbZrO₃ system were investigated. The system contains rhombohedral, tetragonal, and pseudocubic phases at room temperature. The triple point is at 0.07Pb(Co_1/3Nb_2/3)O₃-0.43PbTiO₃-0.50PbZrO₃. High dielectric constants (750 to 1500) and radial coupling coefficients (40 to 45%) and low average temperature coefficients of resonant frequency (of the order of 10^-6°C) were obtained for compositions near the morphotropic phase boundary.     

Sintering Behavior and Surface Microstructure of PbO-Rich PbNi1/3Nb2/3O3–PbTiO3–PbZrO3 Ceramics

The sintering behavior and surface microstructure of PbNi_1/3Nb_2/3O₃–PbTiO₃–PbZrO₃ (PNiNb-PT-PZ) ceramics were investigated. The PNiNb-PT-PZ ceramics with the stoichiometric composition and the addition of excess lead oxide (PbO-rich ceramics) were sintered by liquid-phase sintering in accordance with the solution-reprecipitation mechanism at temperatures below the melting point of PbO. The temperature at which the liquid phase forms fell to near the eutectic point of the PbO–Nb₂O₅ and the PbO–TiO₂ system (868°C) with the addition of 5 mol% PbO. As the calcination temperature influenced the sinterability of the stoichiometric PNiNb-PT-PZ ceramic, unreacted PbO was considered to be the source of the liquid phase in the sintering of the stoichiometric powder. The secondary phase was observed at the surface of PbO-rich ceramics and was suggested to be a liquid phase expelled from inside the ceramic. A sintering scheme of PNiNb-PT-PZ ceramics was proposed, and the high sinterability of PNiNb-PT-PZ ceramics was attributed to the low formation temperature of the liquid phase.     

Effect of the hydrogen spillover on the selectivity of dibenzothiophene hydrodesulfurization over CoSx/γ-Al2O3, NiSx/γ-Al2O3 and MoS2/γ-Al2O3 catalysts

Dibenzothiophene (DBT) hydrodesulphurization (HDS) reaction at 3 MPa and 325–375 °C on Mo/γ-Al₂O₃ single-bed and Me/γ-Al₂O₃//SiO₂//Mo/γ-Al₂O₃ (Me = Co or Ni) double-bed catalysts were investigated. Results indicate that ratio cyclohexylbenzene (CHB)/biphenyl (BP) or selectivity is higher when using double-beds rather than a single-bed. Synergy in dibenzothiophene hydrodesulphurization on Co//Mo and Ni//Mo double-beds is also detected. Changes in selectivity and conversion are attributed to the action of spillover hydrogen (Hso) formed in the first bed that reaches the second bed.     

Low-Temperature Synthesis of 0.65 PbMg1/3Nb2/3O3–0.35PbTiO3 Ceramics

Nanocrystalline 0.65 PbMg_1/3Nb_2/3O₃–0.35PbTiO₃ powders were synthesized by citrate gel method. The gel was prepared using citrate (titanium and niobium) and nitrate (lead and magnesium) salts. The hard gel obtained after completion of the reaction was treated to get the desired phase. Thermal analysis of the gel was done to optimize the calcination temperature. The calcined powders were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The crystallite size and the effective strain were found to be 50 nm and 0.03584 N, respectively.