BaCu0.5W0.5O3掺杂改性Li0.04Na0.52K0.44Nb0.86Ta0.140Sb0.04O3无铅压电陶瓷

以传统固相法制备了(1-x)Li0.04Na0.52K0.44Nb0.86Ta0.10Sb0.04O3-xBaCu0.5O3[简称(1-x)LF4-xBCW]无铅压电陶瓷,研究了不同BCW掺杂量(x=0%,0.1%,O.2%,O.5%,1%,摩尔分数)对LF4陶瓷的显微结构和电性能的影响.结果表明:引入BCW后,材料仍为钙钛矿结构,当x≥1%时,样品由四方相向正交相转变,出现To-t,Tc则随BCW掺入量的增加向低温区移动.BCW掺杂量对LF4的电性能起到"硬性"掺杂作用,其压电常数d33,平面机电耦合系数kp,介电损耗tan δ和介电常数εr均随着BCW含量的增加而降低,而机械品质因素Qm整体提高.此外,BCW的掺入降低了陶瓷的烧结温度并提高了其密度.     

(K_(0.5)Na_(0.5))NbO_3-CaZrO_3基无铅压电陶瓷的相结构和压电性能研究

采用传统陶瓷工艺制备了(1-x)(K0.5Na0.5)NbO3-xCaZrO3(简称KNN-CZ)无铅压电陶瓷。分析了陶瓷样品的相结构组成。测试结果表明:所有陶瓷样品均为钙钛矿相,未发现其它晶相。随着CaZrO3含量的增加,(1-x)KNNxCZ陶瓷的相结构由正交相转变为四方相,最后变为立方相。研究了不同CaZrO3含量对压电性能的影响,实验表明:当CaZrO3含量为0.05mol时,压电常数d33和径向机电耦合系数kp分别达到了最大值196pC/N和0.35。(1-x)KNNxCZ(x=0.05)陶瓷的压电性能展现了良好的温度稳定性和经时稳定性,这些结果表明(1-x)KNN-xCZ(x=0.05)陶瓷是一种优良的无铅压电备选材料。     

BiFeO_3掺杂改性铌酸钾钠无铅压电陶瓷

采用传统固相法制备了(1–x)(K0.5Na0.5)NbO3-xBiFeO3[(1–x)KNN-xBF]无铅压电陶瓷,研究了不同BF含量(x=0,0.175%,0.5%,1%,2%,3%,摩尔分数)样品的物相组成、显微结构及电性能。结果表明:当x≤3%时,得到了纯钙钛矿结构的(1–x)KNN-xBF陶瓷。与纯KNN相比,在0x≤1%时,(1–x)KNN-xBF样品的密度(ρ)、压电常数(d33)、平面机电耦合系数(kp)和机械品质因子(Qm)都显著增大;当1%x≤3%时,ρ,d33,kp和Qm又迅速降低;在x=1%时达到最大值。x=1%时,(1-x)KNN–xBF材料的综合性能最好,其中ρ=4.42g/cm3,d33=172pC/N,kp=0.45,介电损耗tanδ=0.021,相对介电常数εr=759和Qm=138;同时表现出较好的抗老化性能。     

Bi_(0.5)K_(0.5)TiO_3掺杂对0.945K_(0.5)Na_(0.5)NbO_3-0.045LiSbO_3无铅压电陶瓷结构性能的影响

采用传统固相合成法合成(1-x)(0.945K0.5Na0.5NbO3-0.045LiSbO3)-x(Bi0.5K0.5TiO3)(简记为(KNN-LS)(1-x)-BKTx))无铅压电陶瓷,研究不同BKT掺入量(x=0.000,0.005,0.010,0.015,0.020,0.025,0.030)对该体系陶瓷的微观结构和压电介电性能。结果表明:x≤0.025时,均可形成单一钙钛矿结构;与KNN-LS相比,体积密度(ρ)、机械耦合系数kp、kt显著提高;d33、介电损耗tanδ、机械品质因数Qm和次级相变温度降低;当x=0.020时,样品的整体性能达到最佳值:ρ=4.239g/cm3,d33=94pC/N,kp=30.9%,kt=20.7%,tanδ=0.024,相对介电常数εT33/ε0=2468,Qm=53.95,次级相变温度降至室温以下,温度稳定性好。     

Na0.5Bi0.5TiO3-Ba0.5Sr0.5Nb2O6无铅压电陶瓷的研究

采用固相法制备了(1-x)(Na0.5Bi0.5)TiO3-xBa0.5Sr0.5Nb2O6(0≤x≤1.0％)(简称(1-x)NBT-xBSN)无铅压电陶瓷,研究了不同BSN含量(x=0,0.1％,0.3％,0.5％,0.7％,1.0％,摩尔分数)样品的物相组成、显微结构及电性能.结果表明:所有样品均为纯钙钛矿结构,随掺杂量x的增加,陶瓷的相对密度pr、压电常数d33和机电耦合系数kp均先增大后降低,机械品质因子Qm和退极化温度Td则逐渐下降.该体系陶瓷具有弥散相变特征,弥散指数介于1.6～1.7.当x=0.5％时,陶瓷获得最佳性能:d33=92pC/N,kp=0.164,Qm=89,εr=650,tanδ=5.47％,pr=96.5％.     

(K0.5Na0.5)(TaxNb1-x)O3无铅压电陶瓷的性能特征

采用传统电子陶瓷制备工艺制备了(K0.5Na0.5)(TaxNb1-x)O3无铅压电陶瓷。研究了不同Ta含量下(K0.5Na0.5)(TaxNb1-x)O3陶瓷的晶相组成及性能特征。结果表明,(K0.5Na0.5)(TaxNb1-x)O3陶瓷在低Ta含量时形成单一斜方相固溶体,但Ta含量达到0.08mol后则有K6Ta10.8O30次晶相产生。随着Ta的加入,陶瓷的体积密度逐渐增大,居里温度(Tc)逐渐降低。当Ta含量为0.08mol时陶瓷具有良好的铁电、压电性能和介电稳定性能,其压电常数d33为76pC/N。     

CaZrO3改性KNN基无铅压电陶瓷结构与电学性能研究

通过固相反应法制备(1-x)(K0.48Na0.52)0.96Li0.04(Nb0.96Sb0.04) O3-xCaZrO3(KNN-xCaZrO3)无铅压电陶瓷,获得了正交-四方(O-T)多晶共存相.结果 表明:未经改性的KNN基陶瓷为正交相,CaZrO3引入后出现了四方相,体系的压电性能也得到了改善;随着CaZrO3含量的增加,四方相含量增加.在x=0.03 ～0.04范围内,O-T两相共存,并且在x=0.03时陶瓷具有优异的压电性能:d33=252 pC/N,kp=0.55.当x=0.06时,陶瓷为贋立方相结构,性能急剧恶化.CaZrO3的引入使KNN正交-四方相变温度(To-T)向室温偏移,同时也降低了居里温度(Tc),室温附近O-T相界共存,促进畴壁运动,是压电性能得以提高的根本原因.     

K0.5Na0.5NbO3-BaCu0.5W0.5O3无铅压电陶瓷的结构与性能

以传统固相法工艺制备(1-x)K0.5Na0.5NbO3-xBaCu0.5W0.5O3[(1-x)KNN-xBCW]无铅压电陶瓷,研究不同BCW掺量(x=0％,0.1％,0.25％,0.5％,1.0％,摩尔分数,下同)对KNN陶瓷的晶体结构和电性能的影响,结果表明:x＜0.5％时,KNN陶瓷的相结构没有改变,仍为正交相...     

(K_(0.44)Na_(0.52)Li_(0.04))(Nb_(0.86)Ta_(0.10)Sb_(0.04))O_3陶瓷的压电性能

采用传统固相法制备Li、Ta和Sb共同掺杂铌酸钾钠(KNN)的(K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3(KNLNTS)无铅压电陶瓷。研究不同烧结温度对该陶瓷的结构、形貌、致密度以及电学性能的影响。结果表明:不同温度下烧结的陶瓷样品均为钙钛矿相结构;在1 050~1 150℃之间烧结均可获得性能良好的陶瓷样品;1 050℃烧结的样品表现出最佳的综合电学性能,即相对介电常数和压电系数均较大,分别为1 120pC/N和193pC/N,介电损耗较小为2.55%,机械品质因子较大为85,密度较大为4.65g/cm3,且该样品具有饱和的电滞回线。随着烧结温度的升高,陶瓷样品电学性能下降和晶粒增大均与样品中存在着碱金属离子挥发有关。KNLNTS陶瓷样品的Curie温度由不掺杂的KNN陶瓷样品的420℃下降为301℃。     

(K_(0.485)Na_(0.485)Li_(0.03))NbO_3-Pb(Zr_(0.53)Ti_(0.47))O_3压电陶瓷的压电性能与微观结构

采用传统电子陶瓷制备技术和工业原料制备了新型(1-x)(K0.485Na0.485>Li0.03)NbO3-Pb(Zr0.53Ti0.47)O3少铅压电陶瓷,研究了该体系陶瓷的压电性能及微观结构.X射线衍射分析表明:在1250℃烧结3h的条件下,所有陶瓷样品都具有纯的钙钛矿结构和高致密性,并且在室温下形成了正交相和四方相共存的结构.x=0.75时,陶瓷的压电性能达到最佳:压电常数d33=363 pC/N,机电耦合系数kp=63%,相对介电常数εr=1 590,介质损耗tanδ=1.70%.     

Dielectric and impedance spectroscopy analysis of lead-free (1-x)(K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3-xBaTiO3 ceramics

(1-x)(K_0.44Na_0.52Li_0.04)(Nb_0.86Ta_0.10Sb_0.04)O₃-xBaTiO₃ (labeled as (1-x)KNLNTS- xBT, x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) lead-free ceramics were prepared by a solid-state sintering method. As the BT content increased, the phase of ceramics changed from orthorhombic (0.00 ≤ x ≤ 0.02) to orthorhombic-tetragonal (0.02 < x < 0.06) structure, and finally turned into tetragonal (0.06 ≤ x ≤ 0.10) structure. The Curie-Weiss law and modified Curie-Weiss law were applied to analyzing dielectric properties. With the increase of BT content, the relaxation degree increased, which indicated that the ceramics shown a excellent relaxation behavior. For 0.9KNLNTS- 0.1BT ceramics, the dispersion coefficient γ reached the maximum of 1.73, which is hugely attractive for lead-free relaxor ferroelectrics. From its variation of impedance spectroscopy with temperature, it was found that the relaxation and conduction behavior were associated with the thermal activation, and the oxygen vacancies were the potential ionic carriers. Moreover, through Arrhenius fitting, the activation energy of 0.9KNLNTS- 0.1BT ceramic was 0.82(6) eV, indicating that the oxygen vacancy concentration for the ceramics was high.     

Temperature Dependence of Energy Storage in Pb0.90La0.04Ba0.04[(Zr0.7Sn0.3)0.88Ti0.12]O3 Antiferroelectric Ceramics

The temperature‐dependent energy storage and dielectric properties of Pb_0.90La_0.04Ba_0.04[(Zr_0.7Sn_0.3)_0.88Ti_0.12]O₃ were investigated in this work. With the phase transition from antiferroelectric to paraelectric induced by temperature rise, the releasable energy density decreases from 0.74 J/cm³ (20°C) to 0.29 J/cm³ (140°C), whereas the discharge efficiency increases from 75.0% to 93.4%. The pulsed discharge current indicates that the stored energy can be released in less than 1 μs. The temperature has little impact on the amplitude of the current but influences the discharge duration time greatly. In addition, with the comprehensive analysis of hysteresis loops, the DC‐bias character of dielectric constant and the discharge current, the transition from strong nonlinearity to linearity of the dielectric along with the phase switching was confirmed. It proves that the vanishment of high‐electric‐field nonlinear polarization contributions causes the declination of releasable energy with the temperature rise.     

Influence of B-site compositional homogeneity on properties of (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3-based piezoelectric ceramics

The effect of B-site compositional homogeneity on microstructure, piezoelectric properties and dielectric behaviour of lead-free piezoelectric ceramics, (K_0.44Na_0.52Li_0.04) (Nb_0.86Ta_0.10Sb_0.04)O₃, is investigated. The B-site compositional homogeneity is evaluated by using an intermediate precursor obtained by solid state reaction between adequate amounts of Nb₂O₅, Ta₂O₅ and Sb₂O₅, calcined at 1350 °C and attrition milled. The B-site precursor powder is mixed with alkaline carbonates to synthesize perovskite powders and, finally, sinter piezoceramics. X-ray diffraction and Raman spectroscopy reveal the formation of a perovskite phase, although tetragonal tungsten-bronze structure is detected as minor secondary phase. Ceramics processed by using B-site precursor show different crystalline structure as a function of sintering conditions or K/Na ratio. The B-site precursor route produces thus lower piezoelectric properties, but the control of alkali volatilization by using sintering powder bed resulted in a relevant decrease of dielectric losses that favours the d₃₃ enhancement.     

Investigation of the Structure and Electrical Properties of (KxNa0.96−xLi0.04)(Nb0.96−yTaySb0.04)O3 Piezoelectric Ceramics Modified with Manganese

The effect of high doping levels of manganese (Mn) on the structure and electrical properties of (K_xNa_1?x)NbO₃ (KNN) ceramics containing Li, Ta, and Sb has been investigated. The samples were measured using synchrotron X‐ray diffraction whereas Rietveld refinement with Fullprof was used to determine the structural information as a function of temperature. Temperature‐dependent dielectric measurement was used to compare the phase transition temperatures. The results show that Mn decreases the temperature range of phase coexistence between the orthorhombic and tetragonal phase from ~180°C to ~120°C. The Curie temperature remained unchanged with Mn addition while the dielectric constant and dielectric loss increased with Mn addition. High amounts of Mn led to a reduction in both piezoelectric and ferroelectric properties. The remnant polarization, remnant strain, and piezoelectric coefficient values decreased from 24 μC/cm², 0.000824, 338 ± 37 pm/V to 13 μC/cm², 0,00014 and 208 ± 27 pm/V, respectively for the undoped and 5 mol% Mn‐doped sample.     

Synthesis of fine-grain Ba0.96La0.04TiO3 dielectric ceramics by different routes for multilayer ceramic capacitors

Spherical Ba_0.96La_0.04TiO₃ powders were synthesized by a wet chemical method-based on a precipitation process, able of controlling uniformity and particle size. After sintering, fine-grain Ba_0.96La_0.04TiO₃ ceramics with good dielectric properties were obtained. Different synthesis routes of Ba_0.96La_0.04TiO₃ ceramics were used, and their effects on microstructure and dielectric properties were examined. Results showed that the ceramics samples prepared by La³⁺ and Ba²⁺ added together (abbreviated as, BLT-T) resulted in a mixture of large and small grains, sharp permittivity peaks, and high dielectrics loss. By comparison, another ceramics samples prepared by La³⁺ and Ba²⁺ added separately (BLT-S) exhibited uniform grain size and broadened/flattened permittivity peaks. The high value of ε_r (3255) and low tan δ (0.01) at room temperature and negligible temperature coefficient of capacitance from − 35 to 85 °C suggested the suitability of the above materials for multilayer capacitor applications.     

A-site mixed-valence co-doping to optimize room-temperature TCR of polycrystalline La0.8K0.04Ca0.16-xSrxMnO3 ceramics

Herein, polycrystalline La_0.8K_0.04Ca_0.16-xSr_xMnO₃ ceramics (A-site = La, K, Ca and Sr, 0.00 ≤ x ≤ 0.16) are successfully synthesized via the sol-gel process and the influence of Sr content on microstructural and electrical transport properties is investigated in detail. The results reveal that the replacement of Ca-ions by Sr-ions resulted in a decreased resistivity and enhanced temperature coefficient of resistance (TCR) peak temperature (T_k). The influence of A-site mixed-valence co-doping, where A-site is occupied by monovalent alkali-metal, divalent alkaline-earth element and trivalent rare-earth element, on electrical transport properties can be explained by using different conduction mechanisms in different temperature regions. At optimal doping content of 0.12, peak TCR of the resistivity was found to be 12.04% K⁻¹ at 290.38 K, which is the best reported TCR for A-site mixed-valence co-doped perovskite manganese oxides. These results confirm that high room-temperature TCR values can be achieved by optimizing A-site mixed-valence co-doping and demonstrate the potential of polycrystalline La_0.8K_0.04Ca_0.04Sr_0.12MnO₃ ceramic in uncooling infrared bolometers.     

Phase transition behavior and electrical properties of (1 − x)Bi0.5Na0.5TiO3–x(Na0.53K0.44Li0.04)(Nb0.88Sb0.08Ta0.04)O3 lead-free ceramics

(1 ? x)Bi_0.5Na_0.5TiO₃–x(Na_0.53K_0.44Li_0.04)(Nb_0.88Sb_0.08Ta_0.04)O₃ (BNT–xNKLNST) with x = 0–0.10 lead-free piezoelectric ceramics were prepared by a solid state method, and the structure and electrical properties were investigated in this study. It is found that a morphotropic phase boundary (MPB) of rhombohedral (R) and tetragonal (T) phase exists in the range of 0.03 ≤ x ≤ 0.05 and the structure changes to paraelectric phase when x > 0.07. The samples with x = 0.05 exhibit improved electrical properties owing to the formation of MPB, which are as follows: piezoelectric constant d₃₃ = 120 pC/N, remnant polarization P_r = 39.4 μC/cm² and coercive field E_c = 3.6 kV/mm. These results indicate that the enhanced piezoelectric properties for BNT can be achieved by forming the coexistence of R and T phase.     

On the origin of grain size effects in Ba(Ti0.96Sn0.04)O3 perovskite ceramics

Over the last 50 years, the study of grain size effects in ferroelectric ceramics has attracted great research interest. Although different theoretical models have been proposed to account for the variation in structure and properties of ferroelectrics with respect to the size of structural grains, the underlying mechanisms are still under debate. Here, we report the results of a study on the influence of grain size on the structural and physical properties of Ba(Ti_0.96Sn_0.04)O₃ (BTS), a ferroelectric compound that represents a model perovskite system, where the effects of point defects, stoichiometry imbalance and phase transitions are minimized by chemical substitution. It was found that different microscopic mechanisms are responsible for the different grain size dependences observed in BTS. High permittivity is achieved in fine-grained BTS ceramics due to high domain wall density and polar nanoregions; high d₃₃ is obtained in coarse-grained ceramics due to a high degree of domain alignment during poling; large electric field-induced strain in intermediate-grained ceramics is an outcome of a favorable interplay between constraints from grain boundaries and reversible reorientation of non-180° domains and polar nanoregions. These paradigms can be regarded as general guidelines for the optimization of specific properties of ferroelectric ceramics through grain size control.     

(Ba0.85Ca0.15)(Ti0.90Zr0.06Sn0.04)O3-Fe2O3无铅压电陶瓷的性能研究

采用固相法制备了(Ba0.85Ca0.15) (Ti0.90Zr0.06Sn0.04)O3-xmol％Fe2O3(简写为BCTZS-xFe)无铅压电陶瓷.研究了不同掺杂量对该陶瓷的显微结构、介电、铁电及压电性能的影响.结果表明,所有样品均具有单一的钙钛矿结构,少量掺杂能使晶粒长大,提高电性能.在x=0.025时,具有最佳的综合电性能,压电常数d33 =515 pC/N,机电耦合系数kp=48.2％,机械品质因数Qm =182,2Pr=18.2 μC/cm2,2Ec =4.3 kV/cm,介电常数εr=5175.