Proton conduction and chemical stability of (La0.5Sr0.5)(Mg0.5+yNb0.5−y)O3−δ

Electrical conduction properties of complex perovskite-type oxides in the (La_0.5Sr_0.5)(Mg_0.5+yNb_0.5−y)O_3−δ (y = 0.02-0.06) series at intermediate-high temperatures were investigated; introduction of protons by hydration of oxide-ion vacancies was expected by increasing the Mg/Nb ratio from unity. The conductivity depended on y and a maximum conductivity was obtained at y = 0.04: σ = 4.9 × 10⁻⁶ S cm⁻¹ at 400 °C in wet H₂ atmospheres. From electromotive force measurements of hydrogen and water vapor concentration cells, electrical conduction in wet H₂ atmospheres can be attributed to ionic conduction, and proton conduction is dominant below 700 °C. Unlike other perovskite-type proton conductors, (La_0.5Sr_0.5)(Mg_0.54Nb_0.46)O_3−δ was stable in CO₂ atmospheres even in the low-intermediate temperature region due to dilution of reactive strontium by lanthanum.     

Properties of superconducting, polycrystalline dysprosium-doped Bi1.6Pb0.5Sr2−xDyxCa1.1Cu2.1O8+δ (0 ≤ x ≤ 0.5)

The structural and superconducting properties of dysprosium (Dy) doped (Bi,Pb)-2212 superconductor have been studied. Dy concentration is varied from x = 0.0 to 0.5 in a general stoichiometry of Bi_1.6Pb_0.5Sr_2−xDy_xCa_1.1Cu_2.1O_8+δ. It is found that the Dy atoms enter into the crystal structure by replacing Sr atoms and induce significant change in lattice parameter, microstructure, hole-concentration and normal state conductivity of the system. The critical temperature (T_C) and critical current density (J_C) at self-field of the Dy-doped samples enhance considerably at optimum doping levels. Maximum T_C of 92.3 K (for x = 0.4) and J_C of 1390 A/cm² at 64 K (for x = 0.2) are observed for doped samples as against 79.4 K and 127 A/cm², respectively, for the pure sample. The results are discussed on the basis of the change in hole-concentration due to Dy-doping at Sr-site of (Bi,Pb)-2212 superconductor.     

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。     

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.     

Effect of Cu doping and oxygen-annealing on the magnetic properties of Nd0.5Sr0.5Mn1−xCuxO3−δ (x = 0.0, 0.01, 0.03, 0.05 and 0.10)

The polycrystalline samples with nominal compositions Nd_0.5Sr_0.5Mn_1−xCu_xO₃ (x = 0.0, 0.01, 0.03, 0.05 and 0.10) have been synthesized with the aim to study the change in the structural, magnetic and electrical properties due to substitution of Cu for Mn and oxygen-annealing. The temperature dependence magnetization measurement shows a charge ordering transition (T_CO) at 240 K in Nd_0.5Sr_0.5Mn0₃ sample. The Neel temperature (T_N) increases with increasing the Cu doping content but changes induced by even 0.1 Cu doping are quite small. As compared to the air sintered samples, higher values of T_N are observed for the oxygen annealed samples. Furthermore, oxygen annealing enhances the magnetization of the samples. It is also found that T_C increases and T_N decreases with increase in the applied magnetic-?eld. The value of resistivity decreases with the increasing Cu content from x = 0.0 to x = 0.03 and afterwards it increases with increasing value of x up to 0.10 for both air and oxygen sintered samples. It is also found that oxygen annealed samples exhibit higher resistivity than the air sintered samples. In the present paper the results are discussed according to the change of magnetic exchange interaction caused by Cu-doping. It is also found that the amount of Mn⁴⁺ appears to be the main variable which in?uences the physical properties.     

Crossover of magnetoresistance from positive to negative in La0.5Sr0.5CoO3 − σ/Si heterostructure

The magnetoresistance (MR) properties of a heterostructure fabricated by depositing a La_0.5Sr_0.5CoO_3 − σ film on an n-type Si substrate have been studied. The heterostructure exhibits a good rectifying behavior. A negative MR at T = 210 K and a positive MR at T = 300 K are observed for all bias currents whereas; for temperatures ranging from 240 to 280 K the MR changes from being positive to negative with the increase of the bias current. The observed behavior of the MR effect is discussed in terms of current-induced ferromagnetic spin order.     

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.     

Fabrication of LiNi0.5 + δMn0.5 − δO2 nanofibers by electrospinning

Polycrystalline tetranary LiNi_0.5 + δMn_0.5 − δO₂ nanofibers have been successfully fabricated by a sol-gel assisted electrospinning technique. The structures and properties of fabricated nanofibers were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA). After heat treatment of the electrospun fibers at a temperature of 800 °C, the LiNi_0.5 + δMn_0.5 − δO₂ phase was found without other trace phases. Multilayered nanoparticles with a grain size of 50 nm or less within a single fiber are notable from TEM. In this study, it was shown that the sol-gel assisted electrospun LiNi_0.5 + δMn_0.5 − δO₂ fibers could be formed with the α-NaFeO₂ type crystal structure at a temperature lower than that in a typical solid-state or sole sol-gel process and possess good thermal stability as high as 800 °C.     

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.     

Dielectric properties,thermal expansion and heat capacity of (1 − x)Na0.5Bi0.5TiO3–xBaTiO3 single crystals (x = 0, 0.02, 0.025, 0.0325 and 0.05)

High-quality and large-size lead-free (1 − x)Na_0.5Bi_0.5TiO₃–xBaTiO₃ single crystals (x = 0, 0.025, 0.0325 and 0.05) were grown using Czochralski method. The obtained samples were of pure perovskite structure with rhombohedral symmetry at room temperature. Thermal expansion, heat capacity, ferroelectric and dielectric properties were measured in a wide temperature range. The broad anomalies observed in thermal expansion and heat capacity were corresponded to structural, ferroelectric and dielectric anomalies, related to temperature features of polar regions and formation of a long-range order ferroelectric phase. The Burns temperature was found to increase with increasing BaTiO₃ content. At low-frequency (100 Hz–100 kHz) the samples showed diffuse phase transitions. The obtained results were discussed in terms of local electric and strain fields caused by a difference in ionic radii between (Na,Bi) and Ba ions.     

Significant improvement of the oxygen permeation flux of tubular Ba0.5Sr0.5Co0.8Fe0.2O3 − δ membranes covered by a thin La0.6Sr0.4Ti0.3Fe0.7O3 − δ layer

We present a new method to improve the oxygen flux properties and stability of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ tube membrane using a thin layer of La_0.6Sr_0.4Ti_0.3Fe_0.7O_3 − δ as protective coatings. The first relevant result is that the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3 − δ protective layer had an extraordinary positive effect on improving the oxygen permeation flux of the tubular Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ membranes. La_0.6Sr_0.4Ti_0.3Fe_0.7O_3 − δ-coated Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ tubular membrane showed the highest oxygen permeability with the flux reaching ~ 3 ml cm⁻² min⁻¹ (oxygen purity > 99%) at 950 °C in static atmospheric pressure through a 1.0 mm thick membrane.     

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...     

Nd3+A位置换对(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷微波介电性能的影响

研究了Nd3+离子A位置换改性(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷的微波介电性能.[(Pb0.5Ca0.5)1-xNdx](Fe0.5Nb0.5)O3(PCNFN)陶瓷的微波介电性能得到改善是由于少量过剩的Nd3+与(Pb,Ca)2+的固溶能够消除氧空位.当x=0.02时,能够形成单相的钙钛矿相,随着Nd3+置换量的增加,过剩的Nd3+将导致第二相焦绿石的形成,焦绿石会恶化PCNFN的微波介电性能.PCNFN介电性能随x的增加而下降是由于焦绿石相随x增加的结果.当x=0.02-0.05,PCNFN陶瓷有很好的微波介电性能,介电常数K>100,Qf值为5385-5797GHz,频率温度系数TCF随Nd3+含量的增加从正的变为负的.     

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。     

聚吡咯/Ni0.5Zn0.5Fe2O4复合物的合成与表征

采用超声场下原位聚合法制备聚吡咯/Ni0.5Zn0.5Fe2O4(PPy/NZFO)复合物。分别采用X射线衍射仪(XRD)、扫描电镜(SEM)、四探针测试仪和矢量网络分析仪对其结构、形貌、电性能和吸波性能进行研究。结果表明:APS/Py摩尔比为0.75的条件下可获得团聚程度较小、粒径大小比较均匀的聚吡咯颗粒。随着超声聚合反应时间的延长,聚吡咯颗粒的粒径呈现增大趋势。PPy/NZFO复合物的电导率与PPy含量成正比。复合物的吸波性能较纯PPy有很大提高,在5~20GHz频率范围内,NZFO含量为40%(质量分数)的复合物反射损耗都在-12dB以上,在18.15GHz处具有最大的反射损耗-16.76dB,-15dB有效带宽为1.65GHz。     

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%.     

阴极材料Ba0.5Sr0.5Co0.8Fe0.2O3-σ合成工艺优化

为了在较低温度下合成具有高纯度的阴极材料Ba0.5Sr0.5Co0.8Fe0.2O3-σ(BSCF),采用X射线、扫描电镜以及能谱分析等方法,研究了共沉淀合成法中溶液pH值和煅烧温度等工艺条件对产物的相结构、组成成分和颗粒形貌的影响.结果表明,pH值的升高使前驱体由草酸盐沉淀向氢氧化物沉淀转化,在pH=10条件下,前驱体1100℃煅烧2 h后形成了单一的立方型钙钛矿型结构,比在pH=6条件下的前驱体煅烧温度降低了约100℃,而且成分配比更为准确.研究认为前躯体溶液的pH值对煅烧产物的组成和形貌影响至关重要,这主要是由于pH值的不同改变了前驱体的组成和颗粒形貌造成的.     

La0.5Ca0.5MnO3中Ca位上Ba掺杂效应研究

用固态反应法制备了具有单相的Ｌａ０．５Ｃａ０．５－ｘＢａｘＭｎＯ３系列样品,其结构随Ｂａ含量增加由立方晶系转变为典型的正交晶系。零场下运输性质实验表明,在较低掺杂量时,系统在整个温区显示半导体型导电特征,而当掺杂量超过０．１４时,系统发生由半导体到金属的转变,且转变的温度随掺杂量增加而移向高温端,基于对实验结果的分析,就Ｃａ位上Ｂａ的掺杂所起的作用进行了初步探讨。     

不同烧结工艺对K0.5Na0.5NbO3陶瓷微结构的影响

采用普通烧结方法和热压烧结方法制备了K0.5Na0.5NbO3(KNN)无铅压电陶瓷.着重研究了两种烧结工艺对陶瓷的微观结构、晶粒形貌及致密度的影响.研究结果表明,两种烧结方法制备的陶瓷样品都具有单一的正交钙钛矿结构,与普通烧结工艺相比,利用热压烧结工艺制备的样品呈现较高的相对密度(大于98%)、较小的晶粒尺寸(0.6μm左右)及较低的介电损耗(1 kHz,tanδ≤2.8%).实验中发现对于热压烧结的样品,通过改变后期退火温度,样品的晶粒尺寸,致密度可以有规律地变化.