Pb[（Zn1／3Nb2／3）0.91Ti0.09]O3压电单晶的驰豫反常

对用改进的Bridgman法生长的Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3（PZNT91／9）单晶用Laue衍射法和XRD衍射曲线定向，取（001）晶片研究材料的电学性能，结果表明，材料的介电性能呈现出明显的频率色散现象，随着测试频率的升高，介电常数的峰值温度出现反常，峰的位置向低温方向移动。用扫描电子显微镜和正交偏光显微镜研究了PZNT91／9单晶的电畴结构，发现规则排列的带状畴与杂乱分布的细畴并存，X射线荧光分析结果表明，在PZNT91／9单晶中存在着由成分分凝引起的组分变化。成分发凝引起的组分波动和电畴结构的复杂性导致了材料性能的不均匀性，并与材料铁电相变的弥散性特征相关。     

Pb(Mg1/3Nb2/3)O3-PbTiO3晶体组分对结构与性能的影响

用熔体Modified Brdgman法生长出尺寸直径40 mm长度80 mm的弛豫铁电单晶PMNT90/10,表明该方法不仅适合在准同型相界(MPB)附近生长PMNT单晶,也适合生长PT含量很低的PMNT单晶.在生长出的PMNT90/10晶体中,铁电相与顺电相两相共存,并呈现亚微畴结构特征.随着晶体组分由PMN组元变化到MPB组分附近,PMNT的电畴结构呈现微畴-亚微畴-不规则宏畴-规则宏畴演化系列,而介电弛豫特性则逐步弱化.PMNT固熔体的电学性能依赖于晶体组分,(001)切型PMNT90/10晶体的压电常数d33约80 pC/N,显著低于MPB附近组分,但其介电常数ε达到12600,明显高于后者.     

PMN-PT弛豫铁电单晶畴结构的压电响应力显微术研究

利用压电响应力显微术开展了PMN-PT弛豫铁电单晶铁电畴结构的三维极化取向成像、畴结构的不均匀性及极化状态稳定性机理的研究.揭示了纳米尺度畴结构的不均匀性源于纳米尺度极性微区的相互作用和无规场之间的共同调制,而单晶表面屏蔽电荷机制主要源于大气环境下水的溶解性吸附,该机制对PMN-PT单晶中畴状态的稳定性及材料最佳性能的发挥起着重要作用.     

BaTiO3单晶的正方形电畴翻转模型

大量实验已经证实电畴翻转是铁电材料非线性和迟滞性本构行为的根本原因。研究者已经对BaTiO3单晶的微观电畴翻转行为进行了详细的研究,给出了电畴纵向长大和横向扩张的速度公式。依据这些关系,结合电畴翻转是一渐变过程提出了正方形电畴翻转模型,目的是为了从微观上建立电畴翻转体积分数的演化方程。进一步,应用模型对轴向应力和轴向电...     

分凝对Pb(Mg1/3Nb2/3)O3-38%PbTiO3单晶的成分及介电、压电性能的影响

研究了用改进的Bridgman法生长的PMNT62/38单晶在其生长过程中的分凝现象,研究了分凝导致的成分不均匀及其对介电和压电性能的影响.XRFA分析表明,PMNT62/38单晶底部的PbTiO3(PT)含量为x=35.2mol％,而顶部的PT含量为43mol％.底部晶体(001),(110)和(111)三种切型的晶片加电场极化后,其介电和压电性能出现了异常的现象.(110)切型的压电模量最大,为1200pC/N;(111)次之,为789pC/N;(001)最低,为371pC/N.极化后的(110)和(111)晶片在室温、1kHz频率下的相对介电常数(两种切型的εr都在10000左右),约为(001)晶片(ε_r-5000)的1倍,并且介电常数在低温端有上升的趋势.     

近化学计量比LiNbO3晶体电畴结构观察和机理探讨

采用双坩埚提拉法(DCCZ)生长了各种不同成分的近化学计量比LiNbO3晶体,并用腐蚀法观察了其电畴结构.结果表明,化学成分对未经极化处理晶体的电畴结构起决定性作用,当Li2O含量处于49.4mol%附近时,晶体z面电畴呈现特殊的三次对称反畴;当晶体中Li2O含量为49.7mol%时,晶体为完全单畴.本文对其形成机理进行了探讨,认为在由顺电相向铁电相转变时,局部铁电畴的极性方向与该处沿z轴方向的温度梯度正负密切相关,z轴生长晶体时,由于相变发生所处位置离生长界面的距离受LiNbO3晶体计量比影响,所处温场固有温梯也随之不同,在此基础上解释了不同成分晶体的电畴结构形成原因.最后讨论了控制铁电畴结构的工艺措施.     

近化学计量比LiNbO3晶体电畴结构观察和机理探讨

采用双坩埚提拉法(DCCZ)生长了各种不同成分的近化学计量比LiNbO₃晶体, 并用腐蚀法观察了其电畴结构. 结果表明, 化学成分对未经极化处理晶体的电畴结构起决定性作用, 当Li₂O 含量处于49.4mol%附近时, 晶体z面电畴呈现特殊的三次对称反畴; 当晶体中Li₂O含量为49.7mol%时, 晶体为完全单畴. 本文对其形成机理进行了探讨, 认为在由顺电相向铁电相转变 时, 局部铁电畴的极性方向与该处沿z轴方向的温度梯度正负密切相关, z轴生长晶体时, 由于相变发生所处位置离生长界面的距离受LiNbO₃晶体计量比影响, 所处温场固有温梯也 随之不同, 在此基础上解释了不同成分晶体的电畴结构形成原因. 最后讨论了控制铁电畴结构的工艺措施.     

67Pb(Mg1/3Nb2/3)O3-33PbTiO3单晶的微结构与铁电畴

用偏光显微镜(PLM)和透射电镜(TEM)观察了67Pb(Mg1/3Nb2/3)O3-33PbTiO3单晶的畴结构.在PLM下,光学质量不同的晶体具有不同的畴结构,透明晶体具有毫米尺度的大畴,透明性差的晶体的带状孪生畴宽约为0.1mm;在TEM下,雾状晶体中存在着复杂的微米尺度的孪生畴,而均匀晶体中存在着不规则的微米尺度的180°畴.原位EDS分析表明,在孪生晶体中存在Nb-Ti-Mg-Pb-O非晶相.透明晶体的介电和压电常数显著地高于雾状晶体.讨论了化学不均性对畴结构的影响.     

PMNT单晶电畴结构随组分与结构的变化

利用多种方法观察了弛豫型铁电单晶ＰＭＮＴ中电畴结构随组分与结构的演变过程与特征．观察发现,在ＰＭＮ－ＰＴ的三方相区内,随ＰＴ含量的增加,电畴结构表现出微畴一（亚微畴）－不规则宏畴一规则宏畴转变历程;在三方－四方相变中,非１８０°电畴发生７１°（或１０９°）宏畴－９０°宏畴的转化,同时电畴图像变得更为规则．根据不同组分ＰＭＮＴ电畴的显示特征,提出晶体的最大双折射率可以作为度量其弛豫性强弱的光学参数．观察到了电畴的分布不均匀与多级结构现象,前者与组分或结构的起伏有关,后者与多期式马氏体转变有关．本文还分析了偏光显微镜、ＤＩＣ、ＳＥＭ、ＳＥＡＭ等观察方法中电畴的成像特征．     

Sol-gel制备PLCT薄膜的结晶特性与电畴结构研究

运用sol-gel技术制备了(Pb,La,Ca)TiO3(简写为PLCT)铁电薄膜;利用XRD、SEM、AFM和EDAX分析了PLCT薄膜的结构、表面形貌和组分。XRD衍射结果表明,PLCT薄膜呈钙钛矿结构。随着退火时间的增加,PLCT薄膜的XRD衍射峰的强度也随之增加。SEM、AFM分析表明,PLCT铁电薄膜表面平整、致密、无裂缝。EDAX分析表明,PLCT薄膜的实际组分十分接近设计组分。利用PFM分析了PLCT薄膜的电畴结构,发现随着退火时间的增加,PLCT薄膜的电畴由细小圆点状逐渐增大并形成片状电畴。     

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)/3Fex/3)O3体系磁电阻行为的研究

通过系统地测量(La     

(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．     

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.     

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.     

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.     

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.     

Liquid-vapor equilibria in the binary systems AsCl3-1,1,1-C2H3Cl3, AsCl3-1,1,2-C2H3Cl3, and AsCl3-C2HCl3O

Experimental data are presented on the liquid-vapor equilibria in the binary systems AsCl₃-1,1,1-trichloroethane, AsCl₃-1,1,2-trichloroethane, and AsCl₃-dichloroacetyl chloride.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 503–507.Original Russian Text Copyright © 2005 by Potolokov, Nikolashin, Menshchikova, Fedorov.     

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。