面内场和静态偏磁场作用下条畴和泡畴的稳定性

实验研究面内场H_in和静态偏磁场H_b作用下,(111)面磁泡膜内条畴的消失过程。保持H_b恒定,增加H_in,测量条畴消失场H_s^*和泡畴消失场H_k^*与面内场方向β的变化关系。计及立方磁晶各向异性的影响,建立H_in和H_b共同存在时的条畴稳定性理论。定性解释了实验的主要特点。导出黑、白条畴同时消失时的角度 β_n=1/3(2nπ±arc cos│3/(2^1/2)(M_sH_b)/K₁│)(n=0,±1,±2,…)与实验基本符合。 关键词：     

LiNbO3晶体中缺陷的X射线形貌研究

用X射线透射扫描形貌方法观察了直拉法生长LiNbO₃晶体中各种类型点阵缺陷,诸如铁电畴壁、生长层、位错、亚晶界和胞状组织等;用不同衍射矢量对[001]和[210]方向生长的晶体的形貌消象规律,结合X射线铁电异常散射效应和光学显微观察,讨论了晶体中180°铁电畴和生长层的衬度及其分布,并研究了LiNbO₃晶体中180°畴壁形成及其相互关系。 关键词：     

(Pb0.85Sm0.10)(Ti0.98Mn0.02)O3压电陶瓷超高各向异性机电耦合性能的X射线衍射研究

本文用X射线衍射技术研究了具有典型超高各向异性机电耦合性能的Sm改性PbTiO₃压电陶瓷。通过引入面网取向密度指数ρ_(hkl)和建立90°电畴转向畴壁平移模型,就改性PbTiO₃陶瓷圆片经不同电压极化后材料内部电畴结构变化作了定量的分析与讨论。结果表明,在改性PbTiO₃陶瓷结构中,90°畴壁空间取向分布具有高度的择优性;极化处理使材料中90°电畴壁显著平移,但其取向分布变化甚少;材料的纵向机电耦合系数K_t与(002)面网取向密度指数增量△ρ₍₀₀₂₎具有基本平行的电场依赖关系。 关键词：     

KTa1-xNbxO3晶体的同步辐射X射线白光形貌术研究

利用北京同步辐射光源，对居里点在室温附近的掺铁钽铌酸钾光折变晶体进行了Ｘ射线白光形貌术研究．观察显示，晶体内部除了杂质偏析物和一组沿［０１０］方向的生长层外，还有一组与之正交的畴组态，后者被发现不满足一般面缺陷的衬度消光规律，仅有异常散射效应揭示其衬度．利用同步辐射波长的可调谐性，揭示了该组畴随波长改变其衍时衬度变化的规律，而且畴的衍射强度被发现违背Ｆｒｉｅｄｅｌ定律．依据实验证据，这组畴被确认为１８０°铁电畴．对畴形成原因和晶体生长特性进行了讨论． 关键词：     

PT/PZT/PT铁电薄膜的铁电畴和畴壁

用sol-gel法制备出了具有良好铁电性、纯钙钛矿结构的PbTiO₃/Pb(Zr_0.3Ti_0.7)O₃/PbTiO₃(PT/PZT/PT)新型夹心结构铁电薄膜.用扫描力显微镜(SFM)的压电响应模式获得了薄膜铁电畴的垂直于膜平面方向(OPP)、膜平面内(IPP)及OPP的相位和幅度图像，结合理论分析指出薄膜的电畴主要由c畴和偏离垂直于膜平面方向上的c畴构成，薄膜取向的复杂性导致了复杂的畴结构.对于［111］取向的薄膜，当偏离垂直于膜平面方向上的c畴在垂直膜平面方向和面内方向都相反时构成180°的畴壁，在垂直膜平面方向上相同、面内方向相反或由垂直膜平面方向上相反、面内方向相同时构成90°畴壁. 关键词： 铁电薄膜 PT/PZT/PT 电畴和畴壁 扫描力显微镜(SFM)     

无扩散相变中界面动力学的唯象理论及其应用

固态相变中相界面或畴界面的平均运动速度V与有效相变驱动力△G＇(相变驱动力△G与相界面运动阻力△G_R之差)之间的关系可表示为V=φ(△G—△G_R)。当有单向变化的外场(场强为ξ,变化速率为ξ)作用于相变系统并能诱导相界面运动时,就会产生母相/新相间的转变。在相变过程中同时叠加一个交变应力时,则可计算得界面动力学关系V=φ(△G—△G_R)与相变过程内耗Q^-1、相关的模量亏损(△M/M)、相变速率dF/dξ、相变应变ε₀间的关系为 [d lnφ(△G-△G_R)/d(△G-△G_R)]= Q^-1ω/n²M(dF/dξ)ξ = (△M/M)ω/nMε₀(dF/dξ)ξ, 以及 (△M/M)/Q^-1=ε₀/n。此处ω为交变应力的圆频率,M为与振动模式有关的弹性模量,n为应力与界面运动的耦合因子。因此,界面动力学关系式的通解为 V = ∑(±n)/(α≠-1) A_α exp{[(△G-△G_R)/△G_α^*]^{α+ 1}/(α+ 1)} +∑(m)/(β₀) A_β[(△G-△G_R)/△G_β^*]^β 此处n,m为正整数。上式中的各项参数可由实验数据确定。此外,(△M/M)/Q^-1的等式还可用于判别相变过程的模量亏损中有无声子模软化的贡献。 关键词：     

RbIO3-HIO3和CsIO3-HIO3两个赝二元系的研究

用X射线衍射及差热分析法研究了两系统的相平衡。确定了RbH₂(IO₃)₃的结构(三斜晶系,点阵常数:a=8.338?,b=8.244?,c=8.254?,α=60.66°,β=85.58°,γ=66.01°,z=2)。密度D_m=4.61g/cm³。CsIO₃-HIO₃系中有两个化合物:CsH(IO₃)₂(为质子导体)和3CsIO₃·17HIO₂。 关键词：     

镍铬合金中不全位错的透射电子显微镜观察

对镍铬合金(20％Cr,1％Al,2.5％Ti)中层错边界处及共格孪晶界面上的不全位错进行了观察和分析,结果是:1.用g·b_p=±2/3或±1/3作为不全位错是否显示衍衬是可行的,但不够严格。为此,应尽量选择{220}或{311}类型衍射成像,这时g·b_p或者等于零,或者等于整数,比较容易确定不全位错的柏氏矢量。2.共格孪晶界面上有不全位错,大多数是全位错分解的产物,成对出现。3.平行滑移面上的层错在运动中可以相互重迭。重迭层错中内禀层错与外禀层错之间的不全位错,在g·b_p=±2/3时无衍衬(在层错条纹的较强背景下是亮线),而在g·b_p=±1/3时显示衍衬(暗线)。 关键词：     

密环菌甲素晶体结构研究

密环菌甲素(C₂₄H₃₀O₆)属正交晶系,空间群为P2₁ 2₁ 2₁,晶胞参数为a=18.784(9)?,b=14.002(7)?,c=8.598(5)?,z=4,计算密度D_c=1.216g·cm^-1。使用菲利浦PW-1100四圆衍射仪收集衍射强度。该结构是在MULTAN-78求解失败以后,使用MULTAN-80,在正切修正时选择统 关键词：     

Nd2Fe14B单晶磁畴结构随厚度的变化

观察了Nd₂Fe₁₄B单晶磁畴结构随试样厚度的变化。发现试样厚度存在某个临界值L₀,小于此值时,在垂直于e轴表面上的畴纹呈迷宫形,大于此值时,迷宫形条状畴在加宽的同时,其表面出现按一定间隔分布的斑点,此即与基畴反向的锥形畴底部,随试样厚度的进一步增加,基畴宽度和锥形反向畴尺寸也随之增大,后者的数目也增多,甚至出现多重锥形畴结构,本文着重讨论了锥形畴的形成机制,并估算了锥形畸形成所对应的临界厚度L₀。此外,根据实验结果,计算了Nd₂Fe₁₄B相的畴壁能。 关键词：     

Magnetization reversal process and intrinsic coercivity of sputtered Sm2Co17-based films

The Sm₂Co₁₇-based intermetallic films with additives of Fe, Cu, and Zr have been deposited on Si(1 0 0) substrates by dc magnetron sputtering process. Subsequent thermal treatment and the film thickness are found to have significant contribution to the crystal structure and grain structure, which determines the magnetization reversal process and intrinsic coercivity (H_C) of these films. The conventional thermal annealing (CTA) treatment almost failed to crystallize the as-deposited films, leading to a very low H_C. Continuous and homogeneous domain walls cannot form in this deteriorated microstructure, so that the pinning mechanism can be excluded. Contrarily, the films with thickness exceeding 0.8 μm treated by rapid recurrent thermal annealing (RRTA) show an improved H_C, which is attributed to the observed completed crystallization and compact microstructure. It is suggested that this film structure is responsible for providing continuous and homogeneous domain walls, leading to a magnetization reversal process controlled by domain wall pinning model. In special, the H_C of the RRTA-treated film with thickness of 1.8 μm shows a good temperature dependence from 25 to 300 °C, with intrinsic coercivity temperature coefficient β of −0.23%/°C.     

A variable temperature structural study of the Jahn-Teller distortion in Ba2CuUO6

The structure of the ordered double perovskite Ba₂CuUO₆ has been investigated between room temperature and 800 °C using synchrotron X-ray powder diffraction. At room temperature Ba₂CuUO₆ is tetragonal, space group I4/m, a=8.82331(13) c=8.82330(13) Å, the structure being characterized by a large Jahn-Teller distortion of the CuO₆ octahedra and small out-of-phase tilts of the BO₆ octahedra. This Jahn-Teller distortion is also evident in the UV-Vis spectra. Analysis of the spontaneous tetragonal strain reveals a continuous ferroelastic phase transition near 420 °C. This appears to be related to the loss of the tilts whilst maintaining the Jahn-Teller distortion, so that the high temperature structure is in space group I4/mmm.     

The domain structure of ferroelastic BiVO4 crystal studied by Gd EPR

The domain structure of ferroelastic BiVO₄ single crystal has been investigated using the electron paramagnetic resonance (EPR) of the Gd³⁺ ions existing as an impurity in the crystal. Two sets of Gd³⁺ EPR signals were obtained in the crystallographic ca-plane. These two sets of signals originated not from the two kinds of substitutional sites but from the twin-domain structure in the host crystal. It is found that the BiVO₄ crystal investigated with Gd³⁺ EPR has the prominent (W-plane) domain wall. The domain structure is stable in contrast with a previous report by Baran et al. From the observed W-plane of the domain wall, it is suggested that a ferroelastic transition in BiVO₄ is 4/mmm F 2/m instead of 4/m F 2/m. The model of twinning mechanism improved in a previous report by Mn²⁺ EPR is confirmed by Gd³⁺ EPR.     

Nonplanar domain walls in ferroelastic Gd2(MoO4)3 and Pb3(PO4)2

A new stable, mobile zigzag-shaped domain wall configuration has been discovered in the Gd₂(MoO₄)₃ and Pb₃(PO₄)₂ structures. Previous work on these materials had not predicted this type of domain wall. The zigzag walls have mobilities 30–40 times that of planar walls in the same material. This increased mobility can be explained as a geometrical effect.     

Ferroelastic domains in lead phosphate-arsenate: An afm,X-ray diffraction,tem and Raman study

Ferroelastic domain patterns in lead phosphate-type crystals depend on their chemical composition. The intersection of ferroelastic W domain walls with the (100) surface of lead phosphate-arsenate mixed crystals has been imaged using tapping mode atomic force microscopy. Dilution of the strain leads to characteristic surface deformations which deviate from those in pure lead phosphate. In highly twinned lead phosphate-arsenate X-ray diffraction was used to show renormalization effects and scattering phenomena stemming from the twin walls. Raman-active hard modes show wall-related profile changes and low-frequency tails. Symmetry mode analysis is used to describe the displacive modes characterizing the structural distortion in lead phosphate-arsenate for the sequence K m → P2₁/c.     

Y2O3·Cr2O3复合氧化物热力学性质的研究

在1182—1386K温度范围内,用固体电解质氧浓差电池:Mo|Cr,Y₂O₃,Y₂O₃·Cr₂O₃|ZrO₂(+MgO)|Cr,Cr₂O₃|Mo测定了复合氧化物Y₂O₃·Cr₂O₃的热力学性质。对于反应Y_{2关键词：}     

Domain wall orientations in ferroelastics and ferroelectrics

This paper concerns the problem of orientations of domain walls in ferroelastic and/or ferroelectric single crystals. They are specified on the basis of elastic compatibility of the neighbouring domains. Results are presented in form of tables, which make it possible to find spontaneous tensors (i.e. strain and polarization) for each domain state in any ferroelastic and/or ferroelectric species. Domain wall orientations are listed in tables for all combinations of domain states. For each domain wall orientation, their charge or neutrality is indicated. Results are summarized in comprehensive table including numbers of possible domain states, domain wall types (W _∞, W _f , S) and their charge or neutrality. Domain pairs with non-permissible domain walls (R case) are also specified.     

Structure and phase transitions in chloroantimonate(V) crystals: [(C2H5)3NH]SbCl6 and [(C2H5)3NH]SbCl6·1/2[(C2H5)3NH]Cl

New triethylammonium salts: [(C₂H₅)₃NH]SbCl₆ (TCA) and [(C₂H₅)₃NH]SbCl₆·1/2[(C₂H₅)₃NH]Cl (TCAT) have been synthesized. The compounds crystallise in monoclinic symmetry: space groups P2₁/n and P2₁/c, for TCA at 293 K and TCAT at 100 K, respectively. The crystal structure of [(C₂H₅)₃NH]SbCl₆ consists of discrete ionic pairs—triethylammonium cations and hexachloroantimonate anions—linked via the bifurcated N-H?Cl hydrogen bonds. The crystal structure of [(C₂H₅)₃NH]SbCl₆·1/2[(C₂H₅)₃NH]Cl is composed of three symmetrically independent triethylammonium cations, chlorine anion and two symmetrically independent hexachloroantimonate anions. TCA undergoes a structural phase transition at 336 K (on heating) into the orthorhombic C222 space group, whereas TCAT reveals a structural phase transition at 332 K. The phase transitions are of the first order type. TCA shows a ferroelastic domain structure below 336 K. Differential scanning calorimetry, dilatometric, dielectric dispersion and Raman scattering measurements have been used to study the phase transition mechanisms in these triethylammonium salts.     

Polarized light microscopy of the ferroelastic domains of YBa2Cu3O7−x

A short overview is given on recent polarized light microscopy studies of the orthorhombic ferroelastic domains and domain structures of YBa₂Cu₃O_7-x . The optical characteristics of large domains and lamellar domains with a high density of twin walls are pointed out, both for reflected and transmitted light. The polarizing microscope has allowed to observe the ferroelastic detwinning in situ and to determine the activation energy of the ferroelastic wall movements. The question of a potential ferroelectric phase transition is also discussed.