不同镁源反应物对反应烧结制备Pb（Mg1/3Nb2/3）O3陶瓷的影响

采用MgO和(MgCO3)4·Mg(OH)2·5H2O为不同镁源反应物,通过高温反应烧结工艺制备Pb(Mg1/3Nb2/3)O0.(PMN)陶瓷,研究不同Mg源反应物对PMN陶瓷物相组成、相对密度及组织形貌的影响.结果表明:以MgO为前驱体时.由于其反应活性差,扩散和反应不均匀,导致烧结样品中有焦绿石相残留,且焦绿石相对晶界的钉扎阻碍作用使得致密化过程进行相对较慢,所得PMN样品致密度相对较低;而以(MgCO3)4·Mg(OH)2·5H2O为前驱体时,因其受热分解可以得到大比表面积、高反应活性的MgO,从而可以制得高致密度且具有单一钙钛矿相组成的PMN陶瓷材料.     

烧结温度对粉末冶金铁基材料组织与性能的影响

目的 利用粉末冶金工艺制备了Fe-Ni-Cu-Cr-Si-C(石墨)材料,并且研究烧结温度对材料显微组织、硬度、致密度、耐磨性的影响.方法 在1050,1100,1150℃烧结温度下烧结2 h后得到了3组样品,并利用光学显微镜、扫描电子显微镜、X射线衍射仪对样品进行组织结构分析.采用布氏硬度计和电子天平分别对样品进行硬度和密度测试,采用球盘磨损实验机对样品进行耐磨性分析.结果 随着烧结温度的升高,晶粒尺寸逐渐变大.当烧结温度从1050℃增大到1100℃时,奥氏体量增加,表明奥氏体的转变在进行,且硬度和致密度也逐渐增加.烧结温度从1100℃增大到1150℃时,硬度的增速放缓,且在1150℃时硬度达到最大值,烧结温度在1150℃时耐磨损性能最好.随着烧结温度的升高,摩擦因数逐渐减小,由于材料的硬度增大,基体更有能力支撑表面润滑膜,从而表现出更加优越的耐磨损性能.结论 在1050～1150℃范围内,烧结温度的提高可以改善显微组织,提高组织的硬度、致密性、耐磨性.     

多孔铝基陶瓷型芯的制备及其性能

为了解决铝基陶瓷型芯难于烧结和不易脱芯的难题, 在样品中加入了一定量的SiO₂. 利用干压法制备了多孔氧化铝基陶瓷型芯样品, 研究了不同SiO₂的添加量、烧结温度和保温时间对样品性能的影响. 研究结果表明: 经1500℃烧结保温2 h和1600℃烧结降温2 h的样品, 其线收缩率变化不大. 经1700℃烧结保温2 h的样品, 由于SiO₂的挥发导致样品的气孔率升高, 抗弯强度明显降低. 经1500℃烧结保温2 h的样品综合性能最好, 当SiO₂添加量为10wt%时, 样品的线收缩率为1.1%, 抗弯强度为63 MPa, 气孔率为35.5%, 体积密度为2.29 g/cm³; 当保温时间≥4 h时, 其线收缩率、抗弯强度、气孔率和体积密度变化不大, 有望成为高温型芯的候选材料.     

快速烧结制备纳米Y-TZP材料

研究了快速热压烧结和放电等离子快速烧结（ＳＰＳ）制备纳米Ｙ－ＴＺＰ材料．利用快速热压烧结和 ＳＰＳ快速烧结,可在烧结温度为 １２００℃、保温９～１０ｍｉｎ条件下,制得相对密度超过９９％的 Ｙ－ＴＺＰ材料．研究发现：虽然快速热压烧结和 ＳＰＳ烧结都可使Ｙ－ＴＺＰ在相同温度下的密度高于普通热压烧结,但两种快速烧结所得Ｙ－ＴＺＰ的晶粒都大于无压烧结所得;另外,快速热压烧结所得样品的结构不够均匀,而ＳＰＳ烧结的样品的均匀性较好．文章对产生这些现象的原因进行了理论探讨．     

莫来石一氧化锆复相陶瓷材料原位反应烧结机理的研究

通过测定试样真密度、烧成收缩率、相对密度以及ＸＲＤ分析，系统地研究了原位反应结法制备莫来石一氧化锆复相陶瓷的反应烧结机理，研究结果表明，ＺｒＳｉＯ４在１３５０℃开始分解，生成ｔ－ＺｒＯ２和非晶相ＳｉＯ２随着温度升高，非晶相含量增加，并在１４２０℃形成莫来石。ＺｒＯ２的分解物莫来石晶相的生成有一定时间间隔，该化学反应在１４２０～１４８０℃之间迅速进行，并对致密化产生不利影响，可采和分段烧结或阶段笥保     

放电等离子快速烧结纳米3Y-TZP材

本文采用放电等离子烧结技术（ＳＰＳ）快速烧结结纳米３Ｙ－ＴＺＰ材料,利用ＳＰＳ技术快速烧结,可制备出完整、致密的３Ｙ－ＴＺＰ材料,在烧结温度为１３００℃,保温３ｍｉｎ条件下,相对密度达９８．２％,晶粒仅１００￣１３０ｎｍ,研究发现,材料的密度随烧结温度的变化趋势与一般快速烧结有明显区别;材料的晶粒随烧结温度的提高而长大,但长大幅度小于其他一些烧结方法所得的３Ｙ－ＴＺＰ材料,本研究对这些现象进行了理     

无铅压电陶瓷K0.5Na0.5NbO3-BiFeO3的烧结工艺与压电性能研究

采用传统常压固相烧结工艺制备了掺杂0.8at%BiFeO₃(BF)的K_0.5Na_0.5NbO₃(KNN) 无铅压电陶瓷,着重研究了烧结温度与保温时间对陶瓷的晶体结构、相转变、致密度与压电、介电性能的影响. 研究结果表明, 所有陶瓷样品都为单一的钙钛矿结构, 烧结温度与保温时间对陶瓷样品的室温晶体结构与相转变温度几乎没有影响, 但对陶瓷的表面形貌、密度和压电性能有较大的影响. 当保温时间为3h,在1100℃至1150℃范围内, 随烧结温度的升高,陶瓷的压电常数d33、平面机电耦合系数Kp及机械品质因数Qm均一直升高, 介电损耗tanδ则显著降低. 当烧结温度为1150℃时, 随保温时间的增加, 陶瓷的压电性能先显著提高后基本保持不变. 1150℃保温2h烧结的陶瓷获得良好的性能：密度ρ=4.50g/cm³（致密度为95.63%）, d₃₃=132pC/N, K_p=45%, Q_m=333.73, tanδ=2.39%.     

聚合物前驱体法制备(Ce,Cu)-SnO2纳米粉体及其烧结行为

采用聚合物前驱体法制备了CeO2-CuO-doped SnO2纳米粉体,并研究了掺杂SnO2纳米粉体的无压烧结行为.结果表明乙二醇、柠檬酸与金属离子的摩尔比为631时制得的掺杂SnO2粉体为分散良好的球形颗粒,大小为～15nm,粒度分布范围窄;CuO掺杂可显著提高SnO2的烧结性能,CeO2-CuO复合掺杂可进一步降低SnO2陶瓷的致密化温度;1.0%CeO2-1.5%CuO-doped SnO2可在1050℃烧结致密,相对密度达96%以上;两步法(先升温到1050℃保温15min,然后降到980℃烧结5h)烧结的1.0%CeO2-1.5%CuO-doped SnO2陶瓷相对密度为96.1%,其晶粒＜800nm.     

SPS烧结参数对Ti3Al2Mo5Nb室温及低温力学性能的影响

目的 研究SPS烧结温度、保温时间等工艺参数对Ti3Al2Mo5Nb在不同温度下力学性能的影响规律.方法 利用放电等离子烧结(SPS)技术快速烧结,得到致密度较高的Ti3Al2Mo5Nb低温钛合金,通过设置不同的烧结温度及保温时间,结合室温及77 K低温力学性能测试,对不同参数得到的合金的室温及低温性能进行表征,探究SPS烧结过程中工艺参数对Ti3Al2Mo5Nb合金室温及低温力学性能的影响规律.结果 随着烧结温度的升高,合金的致密度、硬度逐渐提高,室温条件下的抗拉强度逐渐提高,伸长率逐渐降低,而77 K条件下合金的抗拉强度逐渐增加,伸长率先增加后减少.随着保温时间的增加,合金的致密度及硬度变化不大,无论在室温还是在77 K低温条件下,合金的强度均先减小后增加,伸长率逐渐减少.微观组织显示,随着烧结温度的增加,β相含量逐渐减少,与伸长率的变化相同,这可能是由于β相的存在促进了室温变形过程中晶界滑移及低温条件下产生孪晶;随着保温时间的增加,析出的强化相含量先减少后增加,这可能是导致合金强度变化的原因,同时β相含量减少,从而导致合金在273 K及77 K条件下的塑性均降低.结论 对低温条件下使用的钛合金而言,在50 MPa压力下,当温度为1050℃时,保温5 min得到的样品力学性能最好,过高的烧结温度及保温时间会减少合金中β相含量,降低低温塑性.     

钛酸钡陶瓷烧结动力学曲线的研究

以超重力反应沉淀法(HGRP)制备的纳米钛酸钡粉体为原料,以热膨胀仪为测试手段,对钛酸钡陶瓷的烧结动力学曲线特征进行了研究.结果表明,烧结温度和成型坯片密度都会对钛酸钡陶瓷的烧结过程产生影响,所表现出的烧结动力学曲线特征也不相同,而升温速率几乎不对坯片的烧结动力学曲线特征产生影响.随着烧结温度的升高,坯片收缩率增大,当烧结温度由1150℃升到1300℃时,收缩率由6.7%增大到23.2%;坯片的密度增大,收缩率减小,当成型坯片相对密度由61.08%增大到64.42%时,收缩率由17.5%减少到14.4%;升温速率增大,坯片开始收缩的温度及收缩率几乎不变.     

(La2/3Ca1/3)(Mn(3-x)/3Fex/3)O3体系磁电阻行为的研究

通过系统地测量(La     

Influence of Layer-Thickness Ratio on Magnetic Properties in F-La2/3Ca1/3MnO3/AF-La1/3Ca2/3MnO3 Bilayers

Magnetic properties were investigated in ferromagnetic/antiferromagnetic bilayers based on a Ca-doped lanthanum manganite system via hysteretic loops, La_1?x Ca _x MnO₃ grown in?situ on (001) oriented SrTiO₃ crystalline substrates by using a dc sputtering technique at high-pressure (3.5?mbar) pure oxygen as sputter gas and at a substrate temperature of 850?^°C. We grew the antiferromagnetic layer La_1/3Ca_2/3MnO₃ (AF-LCMO) with a given thickness, t _AF, and the ferromagnetic layer La_2/3Ca_1/3MnO₃ (F-LCMO) with a given thickness, t _F. We produced two series of samples: the first one with thickness ratio, t _F/t _AF, of 1/6 and 6/1, maintaining constant the total thickness of the bilayer to 70?nm, and the second one with t _F/t _AF of 3/25, 9/25, 15/25, maintaining constant the antiferromagnetic thickness to 25?nm. Magnetization versus applied field loop was strongly dependent on the t _F/t _AF ratio, which was influenced by both the strains presented in very thin films originated during the growth of the bilayer and the magnetic moment interaction at the ferromagnetic/antiferromagnetic interface due to changes of the electronic structure in this strongly correlated system.     

(La2/3Ca1/3)(Mn(3-x)/3)Fex/3)O3体系磁电阻行为的研究

通过系统地测量（La2/3Ca1/3）（Mn（3-x）／3Fex／3）O3（x＝0、0.1、0．2、0．3的体系样品的电阻率-温度关系以及一定温度下磁电阻率与磁场的关系,发现随x的变化其磁电阻率峰和电阻率峰均发生位移,磁电阻率峰值增大,并伴生磁电阻率峰展宽效应．作者认为由于Fe的替代,引起体系中Mn3 ／Mn4 比率及磁矩的变化,加之外场对磁有序结构的调制作用,从而影响了Mn3 －O－Mn4 的双交换作用,最终导致磁电阻行为发生变化．     

Grain boundary effects on the electrical and magnetic properties of Pr2/3Ba1/3MnO3 and La2/3Ca1/3MnO3 manganites

Electrical and magnetic properties of orthorhombic Pr_2/3Ba_1/3MnO₃ (PBMO) and La_2/3Ca_1/3MnO₃ (LCMO) manganites with considerable difference in variance factors (σ²) are reported here. PBMO with higher variance exhibits distinct intrinsic (due to grains) and extrinsic (due to grain boundaries) transitions in the resistivity behaviour. Extrinsic effects, however, are not observed in the lower σ² LCMO system. Low field magnetoresistivity (LFMR) data also substantiate these results. Increase in the density of states obtained through Mott's 3-D variable range hopping mechanism in the paramagnetic insulating regime indicates the suppression of magnetic domain scattering with applied magnetic field. Ferromagnetic metallic regime below the extrinsic transition in PBMO seems to emanate from the electron-magnon scattering process. LFMR at 77 K also points towards the higher canting of spins in the vicinity of grain boundary regions in PBMO compared to that in LCMO.     

Influence of BaZrO3, MnCO3 additives on dielectric properties and microstructure of Ba(Zn1/3Nb2/3)O3 ceramics and Ba(Zn1/3Nb2/3)O3-Sr(Zn1/3Nb2/3)O3 solid solutions

The effect of BaZrO₃, MnCO₃ additives on the dielectric properties, sintering temperature and microstructure of Ba(Zn_1/3Nb_2/3)O₃ (BZN) and Ba(Zn_1/3Nb_2/3)O₃-Sr(Zn_1/3Nb_2/3)O₃ (BSZN) ceramics was studied in this paper. It indicates that both BaZrO₃ and MnCO₃ can lower the sintering temperature of the ceramics and accelerate the crystallization of BZN and BSZN. The dielectric constant ɛ _r increases after MnCO₃ added, but decreases when BaZrO₃ added alone. The existence of MnCO₃ can modulate the temperature coefficient of capacitance τ _c toward positive, while BaZrO₃, can make c more negative. MnCO₃ and BaZrO₃ can restrain the appearance of the second phase; while BaZrO₃, can prevent the appearance of the superstructure. In the BSZN system, when 1 mass % MnCO₃ added, sintering temperature(t _s ) is lowered to 1240°C. In this study, the best sample that has the excellent properties is sample 5 with dielectric properties of ɛ _r = 43.6, τ _c = −8 × 10⁻⁶ °C⁻¹ and tan δ = 0.6 × 10⁻⁴ (1 MHz). The sintering temperature of BZN and BSZN system can be lowered to less than 1300°C.     

Electrical properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics modified with WO3

Ferroelectrics 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) + x mol% WO₃ (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties of WO₃-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃+2 mol% WO₃. Dielectric peak temperature decreased with WO₃ doping, indicating that W⁶⁺ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of K_max. Both piezoelectric constant (d₃₃) and electromechanical coupling factors (k_p) were enhanced by doping 0.1 mol% WO₃, which results from the introduction of “soft” characteristics into PMN-PT, while further WO₃ addition was detrimental. We consider that the two factors, introduction of “soft” characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO₃.     

Dielectric Relaxation and Conductivity of Ba(Mg1/3Ta2/3)O3and Ba(Zn1/3Ta2/3)O3

The frequency dependent dielectric properties of barium magnesium tantalate(BMT),Ba(Mg_(1/3)Ta(2/3))O_3 and barium zinc tantalate(BZT),Ba(Zn_(1/3)Ta_(2/3))O_3 synthesized by solid state reaction technique have been investigated at various temperatures by impedance spectroscopy.BMT and BZT possess cubic structure with lattice parameter a = 0.708 and 0.451 nm,respectively.The resonance peaks due to dielectric relaxation processes are observed in the loss tangent of these oxides.The relaxation in the samples is polydispersive in nature.The temperature dependence of dc conductivity,the most probable relaxation frequency(ω_m) obtained from tanδ vs logw plots and ω_m obtained from imaginary parts of the complex electrical modulus vs logw plots follow the Arrhenius behavior.According to these Arrhenius plots the activation energies of BMT and BZT are about 0.54 and 0.40 eV,respectively.Thus the results indicate that samples are semiconducting in nature.The frequency-dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms.Both these formalisms show qualitative similarities in relaxation time.Our study points that for complex perovskite oxides with general formula A(B'B")O_3,the dielectric properties significantly depend on the atomic radii of both A and B type cations.BMT and BZT exhibit enhancement in dielectric property compared to their niobate counterparts.They may find several technological applications such as in capacitors,resonators and filters owing to their high dielectric constant and low loss tangent.     

Structural order in Ba(Zn1/3Ta2/3)O3, Ba(Zn1/3Nb2/3)O3 and Ba(Mg1/3Ta2/3)O3 microwave dielectric ceramics

The process and nature of structural ordering and the factors that influence them have been investigated in the microwave dielectric perovskites, barium zinc tantalate (BZT), barium zinc niobate (BZN), and barium magnesium tantalate (BMT), sintered at various temperatures. The samples were characterized mainly by X-ray powder diffraction and transmission electron microscopy. The results show that short-range 1 : 1 B-site order features strongly in the early stages of ordering in BZT and BZN, but it is extremely rare in BMT, for which most grains commence with 1 : 2 order. As sintering progresses, 1 : 1 order is replaced by 1 : 2 long-range order in BZT and by disorder in BZN. Orientational variants of the ordered domains within grains occur in similar numbers when order is fine-scale, but their distribution is less homogeneous in well-ordered samples. Local inhomogeneities in the degree of order within grains, which will affect dielectric properties, correlate with both residual non-stoichiometry and the presence of dislocations. Incompletely reacted starting materials which may persist to late stages of sintering can also strongly influence order. Anomalously large ordered domains at grain boundaries are attributed to grain-boundary migration accompanied by enhanced diffusion. The results indicate that with starting materials that are well-mixed and homogeneous at the nanoscale, tailoring of physical properties should be possible by controlling the type and degree of order through chemical composition. This revised version was published online in November 2006 with corrections to the Cover Date.     

碳酸盐前躯体Ni_(1/3)Co_(1/3)Mn_(1/3)CO_3合成条件的研究

以碳酸盐为沉淀剂,采用共沉淀法合成Ni1/3Co1/3Mn1/3CO3前驱体,再按照一定的锂配比将其烧结合成层状Li(Ni1/3Co1/3Mn1/3)O2。通过SEM及电性能测试仪等方法研究了碳酸盐前躯体的合成条件,考察了碳酸盐前躯体的振实密度与合成的pH值、溶液浓度以及反应时间的关系。经过实验分析,在pH=8、溶液浓度为2mol·L-1,反应时12～13h时合成的碳酸盐前躯体Ni1/3Co1/3Mn1/3CO3振实密度达到最高值0.98g·cm-3。     

多铁性BaTiO3/La2/3Sr1/3MnO3复合薄膜的制备及其强磁电效应的研究

使用脉冲激光沉积技术,在(001)取向的LaAlO3(LAO)单晶基片上外延生长了BaTiO3/La2/3Sr1/3MnO3(BTO/LSMO)双层复合薄膜.电学和磁学性能的研究显示复合薄膜具有较低的相对介电常数(εr=263),优良的铁电和铁磁性能以及高于室温的铁磁居里温度(Tc=317 K).复合薄膜的磁电电压系数(αE)为176 mV/A,高于同类结构磁电系统一个数量级,相应的界面耦合系数k值为0.68,表明铁磁层和铁电层界面之间存在较大程度的耦合.