Mn掺杂(K 0.5 Na 0.5 ) 0.96 Sr 0.02 NbO3无铅压电陶瓷的研究

采用常压烧结方法制备了Mn掺杂的（K0.5Na0.5）0.96Sr0.02Nb1-xMnxO3无铅压电陶瓷.研究了Mn含量对该体系材料的相组成、微观结构、介电、压电和热稳定性能的影响.XRD表明随着Mn含量的增加,体系由正交相过渡到赝四方相;而且,富Na的第二相消失,得到纯净的钙钛矿相结构.在Mn含量为x=0.03和0.04时,观察到了两个温度（200和390℃）处的介电反常,这和晶格畸变引起的复晶胞结构有关.Mn含量为x=0.02时,得到综合性能优良的压电超声换能器用材料：介电常数ε^T33/ε0=479,压电常数d33=121pC/N,机电耦合系数Kp=41%,机械品质因子Qm=298,介电损耗tanδ=1.6%,居里温度Tc=391℃,谐振频率αfr和机电耦合系数Kp随温度的变化率αfr（80℃）和αKp（80℃）分别为-1.85%和1.19%.     

A位复合铁电陶瓷Bi0.5(Na0.82K0.18)0.5TiO3-BiCrO3的介电弛豫

采用固相反应法制备了A位复合铁电陶瓷(1-x)Bi_0.5(Na_0.82K_0.18)_0.5TiO₃-xBiCrO₃(BNKT-BCx). 研究了该陶瓷在室温至500℃温度范围内的介电性能. 结果表明该陶瓷的介电温谱存在两个介电反常峰和一个介电损耗峰, 低温介电反常峰温度附近具有明显的介电常数频率依赖性, 但居里峰随频率增加基本不变, 与典型弛豫铁电体的特征不同. 将弛豫铁电体分为本征弛豫和非本征弛豫铁电体, 通过分析极化前和极化后陶瓷的介电温谱, 发现该体系低温介电反常峰温度附近的介电频率依赖性为空间电荷和缺陷偶极子极化引起的非本征弛豫.     

无铅压电陶瓷Bi0.5(Na0.90-xKxLi0.10)0.5TiO3-KNbO3的微结构与电学性能

采用传统陶瓷工艺制备了Bi0.5(Na0.90-xKxLi0.10)0.5TiO3-KNbO3无铅压电陶瓷,利用XRD,SEM 等测试技术分析表征了陶瓷的结构、表面形貌、介电、压电与铁电性能.结果表明:该体系陶瓷具有单相钙钛矿结构,KNbO3的引入使体系的居里温度和铁电-反铁电相变温度降低;随着钾含量的增加,KNbO3对体系性能的影响越明显.在室温下,该体系表现出良好的压电与铁电性能:压电常数d33和机电耦合系数kp分别达到195pC/N和31.9%,陶瓷样品表现出明显的铁电体特征,剩余极化强度Pr达到34.8μC/cm2,矫顽场强Ec为3.2kV/mm.     

Na0.5 Bi0.5 TiO3-K0.5 Bi0.5 TiO3系铁电体的相变研究

研究了(Na1-xKx)0.5Bi0.5TiO3体系x分别为0、0.08、0.16和0.20时陶瓷不同频率下的介电温谱,发现材料为弛豫型铁电体,材料的介电谱在室温到500℃的温度范围内存在一个介电常数-温度"台阶",一个介电常数-温度峰和一个介电损耗-温度峰,通过分析陶瓷不同温度下的电滞回线验证陶瓷在升温过程中产生了铁电-反铁电-顺电相变,采用铁电体成分起伏理论和内电场理论解释了这类弛豫型铁电体相变的原因.     

A位复合铁电陶瓷Bi0.5(Na0.82K0.18)0.5TiO3-BiCrO3的介电弛豫

采用固相反应法制备了A位复合铁电陶瓷(1-x)Bi_0.5(Na_0.82K_0.18)_0.5TiO₃-xBiCrO₃(BNKT-BCx). 研究了该陶瓷在室温至500℃温度范围内的介电性能. 结果表明该陶瓷的介电温谱存在两个介电反常峰和一个介电损耗峰, 低温介电反常峰温度附近具有明显的介电常数频率依赖性, 但居里峰随频率增加基本不变, 与典型弛豫铁电体的特征不同. 将弛豫铁电体分为本征弛豫和非本征弛豫铁电体, 通过分析极化前和极化后陶瓷的介电温谱, 发现该体系低温介电反常峰温度附近的介电频率依赖性为空间电荷和缺陷偶极子极化引起的非本征弛豫.     

LiTaO3掺杂对K0.5Na0.5NbO3基无铅压电陶瓷性能的影响

采用传统陶瓷工艺制备了LiTaO3掺杂的K0.5Na0.5NbO3基无铅压电陶瓷(记为KNN xLT,x=0～8%(摩尔分数)),并研究了陶瓷的晶相、显微结构和压电、铁电等性能.研究结果表明,KNN xLT陶瓷的正交相-四方相准同型相界(MPB)位于4%＜x＜6%处.随着LiTaO3含量的增加,陶瓷的正交→四方结构相变温度(TO-T)向低温方向移动,而四方→立方结构相变温度(Tc)向高温方向移动.陶瓷的压电常数d33和机电耦合系数kp随LiTaO3含量的增加均先增大后减小,而剩余极化强度Pr则随之逐渐减小,矫顽场Ec逐渐增大.当x=6%时,陶瓷具有较好的压电和铁电性能:d33=190pC/N,kp=40.0%,Pr=22.0μC/cm2,Ec=1.78kV/mm,Tc=440℃.该体系陶瓷具有较高的压电常数和比较大的平面机电耦合系数,是一种应用前景良好的压电铁电材料.     

Bi3NbTiO9的结构与电学性能

用传统固相法成功制备出了致密的、相对密度超过95％的BiaNbTiO9(BNT)压电陶瓷；采用XRD和SEM对陶瓷的结构和晶粒形貌进行了表征；测出了BNT陶瓷在居里温度点附近的介电特性，同时确定了该陶瓷的居里温度Tc为914℃。电滞回线的测试显示了该材料典型的硬铁电性，经过高温极化，测出材料的压电常数d33=7pC／N。     

NBT-KBT-LBT系无铅陶瓷的弛豫相变与介电性能研究

采用传统电子陶瓷制备工艺获得无铅压电陶瓷(1-x)(0.8Na0.5Bi0.5TiO3-0.2K0.5Bi0.5TiO3)-xLi0.5Bi0.5TiO3(NBT-KBT-xLBT),研究了该材料的相结构、介电、铁电及压电性能。结果表明,NBTKBT中引入LBT形成了单相钙钛矿固溶体,LBT的引入量为0.08≤x≤0.10时,该体系处于准同型相界处;随着LBT的引入量增加,陶瓷的烧结温度显著降低,介电温度异常峰对应的退极化温度Tf向高温方向移动,而铁电-顺电相变峰Tm则向低温方向移动,弛豫铁电相变特征也表现得更为明显,对弛豫相变与A位离子的局域分布不均匀及其在原子尺度上的有序无序排布之间的关联进行了初步探讨;在NBT-KBT体系中引入LBT有助于改善其铁电性能,提高压电活性,矫顽场Ec从14.5kV/cm(x=0.06)降低至12.3kV/cm(x=0.12),在准同型相界处(x=0.10),压电常数d33达到了145pC/N。LBT组分引入到NBT-KBT体系中可获得高压电常数及低矫顽场的无铅压电材料。     

锰掺杂Sr2-xCaxNaNb5O15（x=0.05～0.35）无铅压电陶瓷微观结构与电学性能的研究

采用传统陶瓷制备工艺制备了Mn掺杂的钨青铜结构无铅压电陶瓷Sr2-xCaxNaNb5O15+ywt%MnO2(x=0.05～0.35,y=0,0.3,0.5)(SCNN-M),并对SCNN-M陶瓷相组成、微观结构及介电、压电、铁电性能进行了研究.分析表明:Ca2+已进入Sr2NaNb5O15晶格之中形成固溶体;掺杂适量的锰,能够得到致密、单一的钨青铜结构陶瓷,有效降低烧结温度,促进晶粒长大,显著提高陶瓷的介电、压电、铁电性能.当x=0.05,添加0.5wt%的MnO2时,陶瓷具有较好的介电、压电和铁电性能:介电常数εr=2123,介电损耗tanδ=0.038,压电系数d33=190pC/N,机械品质因数Qm=1455,平面伸缩振动机电耦合系数Kp=13.4%,厚度伸缩振动机电耦合系数Kt=36.5%,剩余极化强度Pr=4.76μC/cm2,自发极化强度Ps=9.36μC/cm2,矫顽场Ec=12.68kV/cm,居里温度Tc=260℃.     

(0.84-x)Na_(0.5)Bi_(0.5)TiO_3-0.16K_(0.5)Bi_(0.5)TiO_(3-x)SrTiO_3系无铅压电陶瓷结构与电性能

采用固相法制备了Bi补偿的(0.84-x)Na0.5Bi0.5TiO3-0.16K0.5Bi0.5TiO3-x SrTiO3(简称NBTKBT-xST)无铅压电陶瓷,研究不同ST掺量对体系陶瓷的结构与电性能的影响规律。结果表明,在掺杂范围内(0≤x≤0.06),材料均能形成单一的钙钛矿固溶体结构。随着x的增加,陶瓷晶体结构逐渐由三方相向四方相过渡,且该体系的三方-四方准同型相界(MPB)位于0.03≤x≤0.04。在此组成区域内,体系陶瓷的铁电与压电性能较好,其中x=0.04时,材料的电性能较好:压电常数d33=156 pC/N,平面机电耦合系数k p=0.29,相对介电常数εr=1116,介质损耗tanδ=4.1%,剩余极化强度P r=30.5μC/cm2,矫顽场E c=23.9 kV/cm。介电温谱和变温电滞回线表明体系陶瓷在T d以上可能存在极性相与非极性相共存。     

Enhancement of electrical resistivity of Sr0.5Ba0.5Fe12O19 nanomaterials by doping with lanthanum and nickel

From the viewpoint of electronic and telecommunication devices, the electrical resistivity is required to be high to curb the eddy current losses for efficient performance at high frequencies. In the present work, Sr_0.5Ba_0.5Fe₁₂O₁₉ hexaferrite has been doped with a binary mixture of lanthanum and nickel using chemical co-precipitation method of synthesis. The crystallite size of the synthesized samples is estimated in the range of 36–58 nm and their structural analyses have confirmed a single magnetoplumbite phase. The magnitude of the dc-electrical resistivity is enhanced, by almost 100 times, but Curie temperature (T_C) is reduced by doping with La–Ni, which has been explained on the basis of the exchange interactions. In addition, the doped samples exhibit very low dielectric constant (έ = 11–13) and low dielectric loss tangent (tan δ = 0.07–0.10) determined at a frequency of 1 MHz. These characteristics may be suitable for their potential application in electromagnetic attenuation materials and microwave devices.     

Piezoelectric and dielectric properties of K0.5Na0.5NbO3-LiSbO3-BiScO3 lead-free piezoceramics

(1 − x) (0.95K_0.5Na_0.5NbO₃-0.05LiSbO₃)-xBiScO₃ lead-free piezoceramics have been fabricated by an ordinary pressure-less sintering process. The relationship between the BS content, phase structure, density, and piezoelectric properties and their temperature stability was discussed particularly. All compositions show a main perovskite structure, showing room-temperature symmetries of orthorhombic at x = 0, of tetragonal at 0.002 ≤ x ≤ 0.01. When 0.002 ≤ x ≤ 0.008, the ceramics have excellent electrical properties of d₃₃ = 265-305 pC/N, k_p = 45-54%, ?_r = 1346-1638, Curie temperature T_c = 315-370 °C and depolarizing temperature T_d = 315-365 °C, comparable to that of other KNN-based piezoceramics. The results indicate that the ceramics are promising lead-free piezoelectric materials.     

Effects of reduction treatment on the photorefractive properties of Pb0.5Ba0.5Nb2O6

Lead barium niobate is a new photorefractive material of high interest for a variety of applications including holographic storage. Pb_0.5Ba_0.5Nb₂O₆ crystals have been grown by the Bridgman method, and the effects of heat treatments on their photorefractive properties were investigated using Ar ion laser at λ=514.5 nm. The color and absorption spectrum of the crystals varied depending on the oxygen partial pressure during heat treatment. The oxygen diffusivity was estimated to be in the order of 10⁻⁶ and 10⁻⁵ cm²/h at 425 and 550 °C, respectively. Reduction treatment at an oxygen pressure of 215 mTorr increased the effective density of photorefractive charges about three times from 8.0×10¹⁵ to 2.2×10¹⁶ cm⁻³ and made the charge transport more electron-dominant. As a result, the maximum gain coefficient improved from 5.5 to 13.8 cm⁻¹. A diffraction efficiency as high as 70% was achieved in a reduced crystal.     

Structural engineering of Ba0.5Sr0.5TiO3 epitaxial films

Ba_0.5Sr_0.5TiO₃ single-layered and multilayered films were epitaxially grown on a (001) LaAlO₃ substrate using single target and dual target pulsed laser deposition, respectively. Compared to the single-layered films, the multilayered films exhibited broader phase transition and improved thermo-stability. The microstructure of these epitaxial films was investigated using high-resolution transmission electron microscopy in details. Misfit and threading dislocations were observed in the single-layered film, while the threading dislocations were dramatically decreased and no misfit dislocations were found in the multilayered film. It is suspected that the difference in dislocation densities is responsible for the different behaviors of the permittivity with temperature.     

The effect of Bi1.5Zn0.5Nb0.5Ti1.5O7 cover layer on the dielectric and tunable properties of Ba0.6Sr0.4TiO3/Bi1.5Zn0.5Nb0.5Ti1.5O7 bilayered thin films

Bi_1.5Zn_0.5Nb_0.5Ti_1.5O₇ (BZNT) thin films with different thicknesses as cover layers were deposited on the Ba_0.6Sr_0.4TiO₃ (BST) thin films on the Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering method. The microstructure, surface morphology, dielectric and tunable properties of BST/BZNT heterogeneous bilayered films were investigated as a function of the thickness of BZNT films and the effect of BZNT films on the asymmetric electrical properties of BST/BZNT bilayered films was discussed. It was found that BZNT cover layer significantly improved the leakage current and the dielectric loss, and the dielectric constant and tunability of BST/BZNT bilayered thin films simultaneously decreased with the increasing thickness of BZNT films. The BST/BZNT bilayered thin film with a 50 nm BZNT cover layer gave the largest figure of merit (FOM) of 33.48 with the upper tunability of 55.38%. The asymmetric electrical behavior of BST/BZNT bilayered films is probably related to an internal electric field caused by built-in voltages at Pt/BST and BZNT/Au interfaces.     

Preparation, characterization and microwave absorption properties of polyaniline/Co0.5Zn0.5Fe2O4 nanocomposite

The polyaniline (PAni)/Co_0.5Zn_0.5Fe₂O₄ nanocomposite was prepared by an in situ polymerization in an aqueous solution. The products were characterized by Fourier transform infrared (FT-IR) spectrometer, ultraviolet-visible (UV-vis) spectrometer, X-ray diffraction (XRD) and transmission electron microscope (TEM). The average particle size of the PAni/Co_0.5Zn_0.5Fe₂O₄ was estimated to be about 70 nm by TEM. The reflection loss (dB) of the nanocomposite was measured at different microwave frequencies in X-band (8.2-12.4 GHz), U-band (12.4-18 GHz) and K-band (18-26.5 GHz) by radar cross-section (RCS) method according to the national standard GJB-2038-94. The results showed the reflection loss of the PAni/Co_0.5Zn_0.5Fe₂O₄ nanocomposite was higher than that of the PAni. The maximum reflection loss of the PAni/Co_0.5Zn_0.5Fe₂O₄ nanocomposite was about −39.9 dB at 22.4 GHz with a bandwidth of 5 GHz (full frequency width at about a half of the peak response). In conclusion, this sample is a good microwave shielding and absorbing materials at higher frequency.     

Modified (K0.5Na0.5)(Nb0.9Ta0.1)O3 ceramics with high Qm

Lead-free ceramics (K_0.5Na_0.5)(Nb_0.9Ta_0.1)O₃ (KNNT) + x mol% K₄CuNb₈O₂₃ (KCN) + y mol% MnO₂ have been prepared using the conventional solid-state reaction technique. Crystalline structures and Microstructures were analyzed by X-ray diffraction and scanning electron microscope (SEM) at room temperature. The low dielectric loss tanδ and relatively high piezoelectric properties were obtained when KCN and MnO₂ were added into KNNT ceramics. The ceramics with x = 1.0, y = 0.50 exhibited excellent piezoelectric properties: high mechanical quality factor Q_m = 1563, piezoelectric coefficient d₃₃ = 96pC/N, electromechanical coupling coefficient k_p = 42.2%, k_t = 44.5%, k₃₃ = 58.4%, relative dielectric constant ε′ = 308, tanδ = 0.4%. This material is a promising candidate for the lead-free piezoelectric transformer applications.     

Crystal and magnetic study of the disordered perovskites Ca(Mn0.5Sb0.5)O3 and Ca(Fe0.5Sb0.5)O3

We have investigated the double perovskites Ca₂MSbO₆ (M = Mn, Fe) that have been prepared by solid-state reaction (M = Fe) and wet chemistry procedures (M = Mn). The crystal and magnetic structures have been studied from X-ray (XRD) and neutron powder diffraction (NPD) data. Rietveld refinements show that the crystal structures are orthorhombic (space group Pbnm) with complete disorder of M and Sb cations, so the formula should be rewritten as Ca(M_0.5Sb_0.5)O₃. Due to this disorder no evidences of Jahn-Teller distortion can be observed in the MnO₆ octahedra of Ca(Mn_0.5Sb_0.5)O₃, in contrast with the ordered double perovskite Sr₂MnSbO₆. Ca(Fe_0.5Sb_0.5)O₃ behaves as an antiferromagnet with an ordered magnetic moment for Fe³⁺ of 1.53(4)μ_B and a propagation vector k = 0, as investigated by low-temperature NPD. The antiferromagnetic ordering is a result of the high degree of Fe/Sb anti-site disorder of the sample, which originates the spontaneous formation of Fe-rich islands, characterized by the presence of strong Fe-O-Fe antiferromagnetic couplings with enough long-range coherence to produce a magnetic contribution perceptible by NPD. By contrast, the magnetic structure of Ca(Mn_0.5Sb_0.5)O₃ cannot be observed by low-temperature NPD because the magnitude of the ordered magnetic moments is below the detection threshold for neutrons.     

Effects of BiAlO3 on structure and electrical properties of K0.5Na0.5NbO3-LiSbO3 lead-free piezoceramics

(1−x)(0.948 K_0.5Na_0.5NbO₃-0.052LiSbO₃)-xBiAlO₃ (KNNLS-xBA) lead-free piezoceramics were synthesized by conventional solid state reaction method. The compositional dependence of phase structure and electrical properties of the ceramics was systemically studied. XRD patterns revealed that all the ceramic samples possessed pure perovskite structure. In addition, polymorphic phase transition (PPT) for the ceramics with BA doping could not be observed in the measuring range from room temperature to 500 °C. Within the studied range of BA addition, the ceramics with x = 0.002 represented a relatively desirable balance between the degradation of the piezoelectric properties, improvement in temperature stability and mechanical quality factor. It was found that the KNNLS-0.002BA ceramics exhibited optimum overall properties (d₃₃ = 233 pC/N, k_p = 35%, tanδ = 0.047, P_r = 27.3 μC/cm², Q_m = 56 and T_c = 349 °C), suggesting that this material should be a promising lead-free piezoelectric candidate for piezoelectric applications.     

Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol–gel route was investigated for preparation of epitaxial La_0.5Sr_0.5CoO₃ (LSCO) films on 100 SrTiO₃ (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min^− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al₂O₃ substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of a_c = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.