Piezoelectric and dielectric properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Ba0.77Ca0.23TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5(Na_0.84K_0.16)_0.5TiO₃–xBa_0.77Ca_0.23TiO₃ (BNKT–xBCT, x = 0–0.04) were synthesized by conventional solid-state reaction method. The piezoelectric, dielectric, and ferroelectric characteristics of the ceramics are investigated and discussed. The XRD results show that Ba_0.77Ca_0.23TiO₃ (BCT) has diffused into Bi_0.5(Na_0.84K_0.16)_0.5TiO₃ (BNKT) lattices to form a new solid solution. It is shown that moderate additive of BCT (x ≤ 0.025) in BNKT–xBCT ceramics can enhance their piezoelectric and ferroelectric properties. Three dielectric anomalies are observed in BNKT–xBCT (x ≤ 0.03) ceramics. The piezoelectric measurements and P–E hysteresis loops reveal that BNKT–0.025BCT ceramic has the highest piezoelectric performance and strongest ferroelectricity in all the samples. Piezoelectric constants d ₃₃, k _p, and k _t of 175 pC/N, 29.1, and 54% are, respectively, achieved. Remnant polarization P _r and coercive field E _c reach 28.3 μC/cm² and 24.2 kV/cm, respectively.     

Structure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiCoO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ (x = 0.12–0.24, y = 0–0.04) have been fabricated by a conventional solid-state reaction method, and their structure and electrical properties have been investigated. The XRD analysis shows that samples with y ≤ 0.03 exhibit a pure perovskite phase and very weak impurity reflections can be detected in the sample with y = 0.04. With x increasing from 0.12 to 0.24 and y increasing from 0 to 0.04, the ceramics transform gradually from a rhombohedral phase to a tetragonal phase and rhombohedral–tetragonal phase coexistence to a pseudocubic phase, respectively. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18–0.21, y = 0–0.03. The ceramics near the composition of the MPB have good performances with piezoelectric constant d ₃₃ = 156 pC/N and electromechanical coupling factor k _p = 0.34 at x = 0.21 and y = 0.01, which attains a maximum value in this ternary system. Adding content of BiCoO₃ leads to a disappearance of the response in the curves of dielectric constant-temperature to the ferroelectric–antiferroelectric transition. The temperature dependence of dielectric properties suggests that the ceramics are relaxor ferroelectrics. The results show that (1 − x − y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiCoO₃ ceramics are good candidate for use as lead-free ceramics.     

Bi0.5Na0.5TiO3和Bi0.5K0.5TiO3含量对三元固溶体系无铅PTC热敏陶瓷性能的影响

PTC热敏陶瓷的无铅化是绿色智能加热及电路智能保护元件研制的重要前提。为了获得可在空气气氛下烧结且兼具高居里温度和高升阻比的无铅化PTC热敏陶瓷,本工作采用固相法制备了(1-x)BaTiO₃-0.5xBi_0.5Na_0.5TiO₃-0.5xBi_0.5K_0.5TiO₃和0.98BaTiO₃-0.02yBi0_.5Na_0.5TiO₃-0.02(1-y)Bi_0.5K_0.5TiO₃三元固溶体系无铅PTC热敏陶瓷材料,研究了不同含量的Na和K元素对无铅PTC热敏陶瓷材料的烧结特性和电学性能的影响。结果表明,BNT和BKT均与BaTiO₃形成固溶体,随着BNT含量的增加,PTC陶瓷平均晶粒尺寸减小;当BNT和BKT含量相同时,PTC陶瓷可以在较宽的烧结温度范围内实现半导化,且在...     

Structure and electrical properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Bi0.5(Na0.82K0.18)0.5TiO3–BiAlO3 lead free piezoelectric ceramics

0.09(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–(0.01 − x) Bi_0.5(Na_0.82K_0.18)_0.5TiO₃–x BiAlO₃ (BNBKT–xBA) lead-free piezoelectric ceramics were synthesized by conventional solid-state reaction processes. Structure, ferroelectric and piezoelectric properties of BNBKT–xBA ceramics were investigated. X-ray diffraction data shows that BNBKT–xBA ceramics form the pure perovskite phases and the ceramics have the morphotropic phase boundary when x ≤ 0.030. At room temperature, the BNBKT–xBA ceramics at x = 0.030 have better electrical properties, the piezoelectric constant d₃₃ and planar coupling factor k_p of BNBKT–xBA ceramics reaches peak values at x = 0.030: d₃₃ = 217 pC N⁻¹, k_p = 0.308. The remnant polarization P_r, mechanical quality factor Q_m and relative dielectric constant ?_r of BNBKT–xBA ceramics at x = 0.030 attains 33.8 μC cm⁻², 133 and 928 (100 KHz), respectively. As BA content increase, the depolarization temperature T_d shift toward lower temperature, and T_d of BNBKT–xBA ceramics with x = 0.030 decreased to 55 °C.     

Na0.5Bi0.5TiO3纳米纤维的制备及形成机理研究

以Bi(NO3)3 5H2O、板状钛酸(H1.07Ti1.73O4 nH2O)、NaOH为原料,采用水热法合成了具有钙钛矿结构的Na0.5Bi0.5TiO3纳米纤维.利用X射线衍射仪(XRD)、场发射扫描电镜(FESEM)、透射电镜(TEM)和X射线能谱仪(EDS)对产物进行表征.通过考察在200℃下水热反应不同时间的产物的相结构、微观形貌及化学组成,对Na0.5Bi0.5TiO3纳米纤维的形成机理进行了探讨.结果表明:钛酸H1.07Ti1.73O4 nH2O是一类具有层板结构的化合物,在水热反应过程中,板状钛酸的层间H3O+可与Na+、Bi3+进行离子交换,通过原位生长的方式形成了板状Na0.5Bi0.5TiO3颗粒,随着水热反应的进行,板状Na0.5Bi0.5TiO3颗粒裂解形成纳米纤维.所得的Na0.5Bi0.5TiO3纳米纤维分散性好,具有钙钛矿结构,直径为30~150 nm,长度为几个微米到十几个微米.     

Structure and piezoelectric properties of new (Bi0.5Na0.5)1?x?yBax(Yb0.5Na0.5)yTiO3 lead-free ceramics

New lead-free ceramics (Bi_0.5Na_0.5)_1−x−yBa_x(Yb_0.5Na_0.5)_yTiO₃ (x = 0.02–0.10 and y = 0–0.04) have been prepared by an ordinary sintering technique and their structure and piezoelectric properties have been studied. X-ray diffraction shows that Ba²⁺ and Yb³⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure and a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases is formed at 0.04 < x < 0.10. The partial substitutions of Ba²⁺ and Yb³⁺ for A-site ions of Bi_0.5Na_0.5TiO₃ decrease effectively the coercive field E _c and improve significantly the remanent polarization P _r. The ceramics with x = 0.06 and y = 0–0.02 situate within the MPB and possess the lower E _c and larger P _r, and thus exhibit optimum piezoelectric properties: d ₃₃ = 155–171 pC/N and k _p = 29.2–36.7%. The temperature dependences of the dielectric and ferroelectric properties suggest that the ceramics may contain both the polar and non-polar regions at temperatures near/above T _d.     

Li0.5La0.5TiO3包覆LiNil/3Co1/3Mnl/3O2材料的研究

以Li0.5La0.5TiO3为包覆物,制备了固体电解质包覆的LiNil/3Co1/3Mnl/3O2正极材料。采用XRD、SEM对材料进行了表征:XRD显示未包覆的材料具有α-NaFeO2层状结构,粒径在200～300nm之间,包覆后材料粒径略有增大,包覆层具有ABO3型固体电解质结构。包覆层的致密程度及材料的循环稳定性与热处理温度有关。包覆后400℃热处理得到的材料首次放电比容量为185mAh/g,较未包覆材料容量有所提高,50次循环后其容量仍能达到156.5mAh/g,表明包覆物Li0.5La0.5TiO3对LiNil/3Co1/3Mnl/3O2具有保护作用。     

Sr、Nb掺杂(Bi0.5Na0.5)0.94Ba0.06TiO3陶瓷的介电性能研究

采用固相反应法制备Sr、Nb掺杂BNBT无铅压电陶瓷,利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)和介电谱仪表征了样品的晶体结构,表面形貌及介电性能,研究了陶瓷的相结构,微观形貌和介电响应。结果表明,BNBT陶瓷为单一的钙钛矿结构,而BNBT-3SN、BNBT-3SN-3Sr和BNBT-3SN-1Nb陶瓷除了主相钙钛矿结构,存在少量第二相。形貌结构显示出样品相对比较致密,晶粒尺寸分布均匀。SrNb₂O₆的引入使介电峰T_s向低温方向移动,增强弛豫相变程度从而提高了陶瓷基体的介电温度稳定性,BNBT-3SN陶瓷在40～406℃内表现出良好的温度稳定性。通过阻抗图谱分析可知,所有样品主要为晶界传导机制。而且研究表明Sr、Nb掺杂可通过对BNBT-3SN陶瓷氧空位浓度的作用,实现对电导率的调控。随着Sr²⁺的增加,样品的氧空位浓度增加,电导率增大;而Nb⁵⁺的增加,填充了氧空位导致氧空位浓度减小促使电导率降低。     

微波可调BaSrZnSi2O7-Ba0.5Sr0.5TiO3复合陶瓷的结构与介电性能关系

采用传统电子陶瓷工艺制备出BaSrZnSi₂O₇-Ba_0.5Sr_0.5TiO₃复合陶瓷,系统研究了其相结构、微观结构和介电性能。研究表明：随着BaSrZnSi₂O₇的加入,样品的居里峰向低温方向移动;但BaSrZnSi₂O₇加入量达到一定程度后,居里峰在一定的温度下保持稳定。调制特性变化规律类似于居里峰的移动。品质因数（Q值）的变化主要取决于微波材料加入后的"掺杂"和"复合"效果。当BaSrZnSi₂O₇质量分数为60wt% 时,复合材料表现出良好的综合特性：介电可调率为 16%（10 kHz）,介电常数为152,Q值达到417（2.720 GHz）,表明BaSrZnSi₂O₇-Ba_0.5Sr_0.5TiO₃复合陶瓷是电可调微波器件很好的潜在应用材料。     

溶胶-凝胶法制备(Na0.85K0.15)0.5Bi0.5TiO3铁电薄膜晶化行为研究

利用溶胶-凝胶法在(111)Pt/Ti/SiO2/Si衬底上成功制备了无铅(Na0.85K0.15)0.5Bi0.5TiO3(NKBT)铁电薄膜。利用XRD和原子力显微镜(AFM)分别对薄膜的晶化行为和表面形貌进行了表征。结果表明,在一定温度范围内,随着热分解温度和退火温度的升高,薄膜的晶化程度变得越来越完全,晶粒变得更加均匀致密。当热分解温度为450℃、退火温度为700℃时,薄膜表现出最优的晶化行为,其铁电性能良好,剩余极化强度(Pr)和矫顽场强(Ec)分别为10.37μC/cm2和78.2kV/cm。     

溶胶-凝胶法制备K0.5Bi0.5TiO3陶瓷的晶格结构和介电特性研究

采用溶胶-凝胶工艺成功制备出K0.5Bi0.5TiO3微细粉料,并利用此微粉烧结出成瓷良好的K0.5Bi0.5TiO3陶瓷.用X射线衍射法测定了K0.5Bi0.5TiO3陶瓷粉末室温和高温(600℃)时的点阵常数,确定K0.5Bi0.5TiO3的高温相为立方结构(点群m3m)指标化其衍射线,给出了K0.5Bi0.5TiO3陶瓷粉末的多晶X射线衍射数据.以此X射线衍射方法研究了K0.5Bi0.5TiO3陶瓷粉末的铁电-顺电相变,测定了k0.5Bi0.5TiO3的介电特性.所作测量表明K0.5Bi0.5TiO3可能是一种有序-无序型弛豫铁电体,呈现一级弥散相变特征.这可采用极性微区理论阐释,弛豫特性是由此类材料非均衡性产生的极性微区在逐渐冻结过程中引起的.     

Phase diagram and electric properties of the (Mn, K)-modified Bi0.5Na0.5TiO3–BaTiO3 lead-free ceramics

In this study, the phase diagram and electric properties were demonstrated for a (Mn, K)-modified Bi_0.5Na_0.5TiO₃ (BNT)-based solid solution. (0.935−x) Bi_0.5Na_0.5TiO₃−xBi_0.5K_0.5TiO₃−0.065BaTiO₃ with 0.5% mol Mn doping was prepared by a conventional solid-state reaction method. A morphotropic phase boundary (MPB) formed between the ferroelectric rhombohedral and tetragonal phases around x of 0.04 with the MPB tolerance factor t of 0.984–0.986. The temperature and composition dependence of the dielectric, piezoelectric, ferroelectric properties along with the strain characteristics were investigated in detail and a phase diagram was presented. Around the MPB region, the maximum values of piezoelectric constant d₃₃^* d_{33}^{*} of 290 pC/N, d ₃₃ of 155 pC/N, dielectric constant e₃₃^T /e₀ \varepsilon_{33}^{T} /\varepsilon_{0} of 1059 and low dielectric loss tangent tan δ of 0.017 were obtained. In addition, the authors also suggest that the solid solution with composition x of 0.24, exhibiting both high-depolarization temperature T _d of 182 °C, d₃₃^* d_{33}^{*} of 156 pC/N, d ₃₃ of 130 pC/N, will be favorable for high-temperature actuator and sensor applications.     

Densification behavior, microstructure, and electrical properties of sol–gel-derived niobium-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics

Superfine powders (~100 nm) with compositions of (1 − x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + xNb⁵⁺ (BNTBT6 + xNb) with x from 0 to 0.02 were synthesized by an improved citrate sol–gel method using Nb₂O₅ as Nb⁵⁺ source. The sintering behavior, microstructure, and various electrical properties of BNTBT6 + xNb ceramics were investigated. The results indicated that the addition of a small amount of Nb⁵⁺ has no remarkable effect on the crystal structure and grain morphology, but the electrical properties of the ceramics are obviously influenced. The BNTBT6 + 0.005Nb compositions exhibit enhanced densification behavior and improved electrical properties of a piezoelectric constant d ₃₃ ~ 205 pC/N and a planar electromechanical coupling factor k _p ~ 33%.     

Effects of ball milling on microstructure and electrical properties of sol–gel derived (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoelectric ceramics

A citrate sol–gel method was investigated for synthesizing lead-free piezoelectric compositions of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNT) and the effect of ball milling on the sintering, microstructure and electrical properties of BNT ceramics was emphasized. The thermal analysis and X-ray diffraction results show that crystalline powders with a single perovskite structure can be obtained when calcined at 600 °C for 3 h. The average particle size of as-calcined powder and electrical properties of sintered samples were obviously dependent on an additional ball milling. Because of well-dispersed superfine powders (∼100 nm), the BNT ceramics can be well densified at temperature 50 °C lower than that by mixed-oxide method and conventional sol–gel method and as a result exhibit enhanced electrical properties of a piezoelectric constant d₃₃ ∼ 180 pC/N and a planar electromechanical coupling factor k_p ∼ 0.29.     

Synthesis and electrical characteristics of (1 − x)BaTiO3–xK0.5Bi0.5TiO3 PTCR ceramics

Solid solutions of (1 − x)BaTiO₃–xK_0.5Bi_0.5TiO₃ were prepared by the solid state reaction technique. Samples were sintered in reducing atmosphere of N₂/H₂ in the temperature range 1100–1240 °C with subsequent oxidation at 700 °C. Phase composition and crystal structure were investigated by X-ray powder diffractometry (XRPD). It was shown that all samples of (1 − x)BaTiO₃–xK_0.5Bi_0.5TiO₃ (0 ≤ x < 0.4) exhibit a tetragonal structure at room temperature, the parameters a and c decrease with increasing x. With increasing x the Curie temperature of solid solutions (1 − x)BaTiO₃–xK_0.5Bi_0.5TiO₃ (0.1 ≤ x < 0.4) increases from 150 to 220 °C. The values of potential barriers at grain boundaries were calculated on the basis of Heywang model. With increasing x, the potential barrier at grain boundaries increases. It was shown that the grain size decreases with increasing the bismuth–potassium titanate content. The complex impedance results indicate that the grain boundary and the outer layer region, located between the boundary and the core of the grain, make a contribution to the positive temperature coefficient of resistance (PTCR) effect in (1 − x)BaTiO₃–xK_0.5Bi_0.5TiO₃ solid solutions. With increasing x ρ_max increases due to an increase in potential barrier at grain boundaries.     

La0.5Y0.5Ni4.8Mn0.1Al0.1和La0.5Y0.5Ni4.8Al0.2合金的储氢性能研究

针对两种新型稀土型储氢合金La0.5Y0.5Ni4.8Mn0.1Al0.1和La0.5Y0.5Ni4.8Al0.2的储氢特性进行研究分析。实验表明,相同温度下,La0.5Y0.5Ni4.8Mn0.1Al0.1和La0.5Y0.5Ni4.8Al0.2合金的PCT曲线基本重合,且都具有优良的吸氢动力学性能;相比之下,后者的滞后系数要小于前者,吸氢量较大,吸氢速率也较快,故其储氢性能较优。300次吸放氢循环实验结果表明,La0.5Y0.5Ni4.8Al0.2合金的吸氢动力学性能虽然略有下降,但抗粉化性能较好。     

Oxidation state of chromium in (Na0.5Bi0.5TiO3)(1?x)(BiCrO3)x solid solution; investigated by XAS and impedance spectroscopy

X-ray absorption spectroscopy (XAS) and impedance spectroscopy have been used to study the oxidation state of chromium in (Na_0.5Bi_0.5TiO₃)_(1−x)(BiCrO₃) _x solid solution. XAS measurements reveal that chromium ion occupies the octahedral site in Na_0.5Bi_0.5TiO₃ (NBT). The increase in chromium content increases the distortion in chromium-oxygen octahedral. No shift in the Cr–K edge was observed with increase in chromium content. The XAS measurements suggest that chromium exists either as +3 or +5 state in (Na_0.5Bi_0.5TiO₃)_(1−x)(BiCrO₃) _x . The impedance measurements show a considerable increase in the electrical conductivity with increase in chromium content. The activation energy for conduction mechanism was found to lie between 0.50 and 0.7 eV for all the samples. These measurements indicate that main contribution to the conductivity is because of oxygen defects generated by the incorporation of chromium at B-site of NBT.     

Pr掺杂Sm0.5Sr0.5CoO3阴极的性能研究

固体氧化物燃料电池(SOFC)因能量转换效率高,绿色无污染而备受关注。研究发现,钙钛矿结构的Sm_0.5Sr_0.5CoO_3-δ(SSC)是电子-离子混合导体,具有良好的氧还原活性,以及电导率高、极化电阻低等优点。为了探究镧系元素Pr掺杂对SSC阴极性能的影响,采用溶胶-凝胶法制备Pr_xSm_0.5-xSr_0.5CoO₃(x=0.1,0.2,0.3,0.4,0.5)阴极粉体,对其进行一系列表征和电化学性能测试。电化学阻抗谱(EIS)测试表明,当Pr掺杂量为0.3时,PSSC-30阴极在550～750℃范围内的极化电阻均小于其他掺杂量;在700℃时,全电池的功率密度达到最大,为311.06mW/cm²。     

La掺杂Hf0.5Zr0.5O2薄膜铁电性能研究

铪基氧化物薄膜在超薄膜厚下仍具有优良的铁电性能,非常适用于高密度集成的铁电存储。La掺杂铪基薄膜拥有极为优异的循环写擦特性,但其剩余极化强度(2Pr≤35μC/cm²)还有待进一步提高。本研究采用原子层沉积(ALD)制备La掺杂的Hf_0.5Zr_0.5O₂薄膜(HZLO),通过快速热退火(RTA)对样品进行500℃、550℃和600℃的热处理,研究La掺杂及退火温度对TiN/HZLO/TiN/W结构铁电性能的影响。研究表明,La掺杂促进薄膜四方相转变为正交相,剩余极化强度(49.8μC/cm²)获得极大提高。此外,La掺杂还降低了器件矫顽场(～1.25 MV/cm)并改善矫顽电场对称性。随着退火温度升高至550℃,正交相占比升高至～77%,剩余极化强度高达49.8μC/cm²,而进一步升高退火温度至600℃,正交相、四方相和立方相朝着单斜相转变,器件剩余极化强度降低。     

Preparation and properties of ceramics based on (Na0.5Bi0.5)1 ? xAxTiO3 (A = Sr, Cd) solid solutions

This paper describes the preparation and properties of (Na_0.5Bi_0.5)_{1 − x} A _x TiO₃ (A = Sr, Cd) lead-free ferroelectric ceramics. The (0.63–0.66)Na_0.5Bi_0.5TiO₃ · (0.37–0.34)Sr_0.7Bi_0.2TiO₃ ceramics are shown to have the best dielectric and piezoelectric properties: tanδ = 0.013–0.009, ɛ_RT = 1200–1500, d ₃₁ = (370–400) × 10⁻¹² C/N, and k _ρ = 0.4–0.58. The cadmium-containing ceramics offer low dielectric losses and high dielectric permittivity at room temperature.