CoFe2O4/Ba0.9Ca0.1Ti0.9Zr0.1O3双层复合薄膜的磁电性能研究

通过脉冲激光沉积法(PLD)在(001)-SrRuO3/SrTiO3(SRO/STO)衬底上生长了CoFe2O4/Ba0.9Ca0.1Ti0.9Zr0.1O3(CFO/BCZT)双层磁电复合薄膜.采用X射线衍射仪(XRD)、原子力显微镜(AFM)和扫描电子显微镜(SEM)测试样品的晶体结构及形貌.XRD结果显示:单相BCZT铁电薄膜、CFO铁磁薄膜及CFO/BCZT磁电复合薄膜均为(00l)择优取向结构.物理性能测试结果表明:CFO/BCZT复合薄膜具有良好的铁电性能(剩余极化值,Pr=15.1μC/cm2)、铁磁性能和磁电耦合性能(磁电耦合系数,αE～82.4 mV·cm-1·Oe-1).这种无铅的磁电复合薄膜为设计新型多铁电子器件提供了一种选择.     

Relation between the real structure and optical inhomogeneity of lithium niobate single crystals

Crystallography Reports - A real structure of lithium niobate single crystals has been studied by the etching method. A relationship between the real structure and the optical inhomogeneity...     

Nano-particles of La0.9Ca0.1MnO3 manganite: Size-induced change of magnetic ground state and interplay between surface and core contributions to its magnetism

The structure, dc and ac magnetic properties of sonochemically prepared nano-particles of La_0.9Ca_0.1MnO₃ compound were studied as compared to those of the bulk sample of the same composition. It is shown that transition to the nanometer sized scale results in a change of the magnetic order from a mixed antiferro + ferromagnetic to a pure ferromagnetic one due to the improvement of crystallinity and suppression of chemical/magnetic disorder in nano-particles. The surface contribution to its magnetism leads to a super-paramagnetic-like ordering supposedly due to the interfacial exchange coupling via surface tunneling of carriers above the Curie point (T_C). Below T_C ∼ 90 K, a notable contribution of surface spin disorder reduces the spontaneous magnetization of the nano-sample as compared to the bulk-one.     

Microscopic investigations of morphological structures on the pyramidal faces of KDP and DKDP single crystals

Studying a number of {101} faces of KDP and DKDP single crystals in the as-grown state we found in most cases one, rarely few, clearly stepped growth hillocks covering the whole face. The geometry of these growth hillocks was determined from photomicrographs; the step heights were measured with a profilometer. To prove our results we carried out X-ray topographic investigations and in-situ observations on KDP crystals. In addition we studied the as-grown faces of ADP and LiJO₃ single crystals.     

On the relations between surface structures and morphology of crystals

Some general structural rules concerning the stability of stepped and kinked faces in relation with reconstructed flat faces are given. These rules have been mainly deduced from our experiments on stepped faces of fcc metals, using ultra-vacuum techniques and low energy electron diffraction. Other examples (on Si diamond structure for example) are presented and discussed.     

Synthesis and Crystal Structure of Fluoride K2(Ta0.9I0.1)F7 with the Micro-Isomorphic Substitution in the Ta Cationic Position

Crystallography Reports - Fluoride crystals K2(Ta0.9I0.1)F7 (sp. gr. Р21/c) complementary to the K2TaF7 and K2NbF7 fluoride family have been obtained by hydrothermal synthesis. Their...     

烧结温度对(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3无铅压电陶瓷结构和电学性能的影响研究

采用固相反应法成功制备出具有ABO3型钙钛矿结构的锆钛钡钙(Ba0.85Ca0.15) (Zr0.1Ti0.9) O3无铅压电陶瓷,研究了粉体预烧温度和陶瓷片烧结温度对(Ba0.85Ca0.15) (Zr0.1Ti0.9) O3陶瓷结构和电学性能的影响.结果表明:当预烧温度为1200oC、烧结温度为1400oC可获得具有优异电学性能的(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3无铅压电陶瓷,其电学性能分别为居里温度Tc＝97 ℃,最大介电常数εmax＝14920,剩余极化强度为Pr＝9.96 μC/cm2,矫顽场Ec＝7.20 kV/cm,压电常数d33＝543 pC/N,机电耦合系数kp＝52;,其高的电学性能可以和铅基压电材料相媲美,表明(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3陶瓷有望实现压电陶瓷的无铅化应用.     

Discovery of difference in the diffuse scattering from nonstoichiometric Ca0.87La0.13F2.13 and Ca0.92Er0.08F2.08 crystals with different types of clusters of structural defects

A new approach to application of diffuse scattering (DS) for studying the defect structure of crystals on laboratory radiation sources is implemented. The basic principles of this approach are as follows: (i) choice of crystals with a high concentration of structural defects (highly nonstoichiometric Ca_{1 ? x} R _x F_{2 + x} phases), (ii) application of intermeasurement minimization method (experimental comparison) to select a weak desired DS signal from a superposition of signals of different nature, and (iii) choice of the basic model proceeding from the reliable information provided by accurate analysis of the contribution of structural defects to Bragg reflections. Significantly different DS diffraction patterns have been recorded for Ca_0.87La_0.13F_2.13 and Ca_0.92Er_0.08F_2.08 crystals, characterized by different types of structural-defect clusters, determined from the Bragg diffraction data. Experiments performed at 90–100 K proved that DS is caused by clusters with stable atomic configurations rather than cooperative thermal atomic vibrations. A set of methods is proposed which can efficiently be used in diagnostics of nanomaterials.     

(Na0.9K0.1)0.5Bi0.5TiO3-(Ba0.7Ca0.3)TiO3无铅压电陶瓷的结构与性能

采用固相法制备了(1-x)(Na0.9 K0.1)05Bi0.TiO3-xBa0.7Ca0.3 TiO3[(1-x)NKBT-xBCT]无铅压电陶瓷.研究了不同BCT含量(x=0,0.02,0.04,0.05,0.06,0.07)对NKBT陶瓷结构与电性能的影响.结果表明:所有样品均形成纯的钙钛矿结构,体系陶瓷的准同行相界(MPB)位于0.04≤x≤0.06.随着BCT掺量的增加,样品的退极化温度Td逐渐向低温方向移动,压电常数d33和平面机电耦合系数kp均先升高后降低.系列陶瓷电性能较佳:x=0.05时,kp最大,为0.29.当x=0.06时,样品的综合性能较好,其中d33=168 pC/N,kp=0.26,相对介电常数εr=1280,介质损耗tanδ =3.7;,剩余极化强度Pr=37 μC/cm2,矫顽场Ec =18.8 kV/cm.变温电滞回线和介电温谱表明体系陶瓷在Td以上可能存在极性相与非极性相共存.     

Er3+:NaY(Wo.9Moo.1O4)2晶体的生长及光谱性能

采用提拉法(CZ法),生长出质量良好的Er3+:NaY(W0.9Mo0.1O4)2晶体.通过X射线粉末衍射,红外光谱分析,并与NaY(WO4)2相比较,得到Er3+:NaY(W0.9Mo0.1O4)2晶体的结构与NYW类似,仍为四方晶系的白钨矿结构,I4(1)/α空间群.测定了晶体的实际组成,得到晶体中各元素均按理论值进行掺杂,计算了掺杂离子的分凝系数约为1.15.在光谱性质上,测试了晶体的吸收光谱,及晶体在50～1000cm-1波数范围内的拉曼光谱,并计算了各吸收峰的半峰宽及吸收系数A.     

Structural inhomogeneity and properties of Y3Fe5O12 crystals with allowance for their crystallographic orientation

The character of nonuniform distribution of the main cations Y and Fe in the plane of samples of yttrium garnet Y₃Fe₅O₁₂ and the nonstatistical incorporation of process impurities along the crystallographic directions [110], [111], and [100] are investigated. The structural inhomogeneity revealed in the samples is discussed with allowance for the difference in the growth rates of the garnet crystal faces under study, specific features of the incorporation of dominant impurities, and the relationship between this inhomogeneity and the optical and kinetic properties of the crystals.     

SnO2掺杂对(Ba0.85Ca0.15)(Ti0.9Zr0.1-xSnx)O3无铅压电陶瓷介电弛豫与电性能的影响

采用固相烧结法制备了(Ba0.85Ca0.15)(Ti09Zr0.1-xSnx) O3(BCZTS)无铅压电陶瓷.研究了不同含量SnO2(x=0,0.02,0.04,0.06,0.08)对BCZT无铅压电陶瓷相结构、压电性能、介电性能和铁电性能的影响,并利用XRD、SEM、准静态d33测试仪等表征样品.结果表明,所有样品均为单一钙钛矿结构.当掺杂x=0.02时,(Ba0.ss Ca0.1s)(Ti0.9 Zr0.1-xSnx) O3无铅压电陶瓷材料的综合性能优异:d33 =553 pC/N,kp=49;,εr～ 7474(l kHz),tanδ～1.5; (lkHz),Pr=6.06 μC/cm2,Ec=2 kV/cm,利用Curie-Weiss定律对该实验结果进行拟合,发现x=0.02的样品的介电弛豫特征更为明显.     

Ordering of tysonite structure in an as-grown Er0.715Ca0.285F2.715 crystal and in a component of annealed two-phase crystal of the Er0.67Ca0.33F2.67 composition

The structures of the as-grown tysonite phase (TP) Er_0.715Ca_0.285F_2.715 as grown and the tysonite component in a crystal of the Er0.67Ca0.33F2.67 composition annealed at 760°C have been determined by X-ray diffraction methods from the main reflections in the sp. gr. P6₃/mmc, Z = 2. Ca²⁺ cations in the Er_0.715Ca_0.285F_2.715 structure occupy the 2c site on the 6₃ axis, thus confirming the conclusion about the symmetrizing effect of alkaline earth cation, which was made previously for the Y_0.715Ca_0.285F_2.715 compound. Er³⁺ cations are disordered over 6h sites around this axis. The Er_0.67Ca_0.33F_2.67 composition contains Er_0.67+δCa_0.33?δF_2.67+δ TP and inclusions of distorted fluorite phase rhβ-Ca₈Er₅F₃₁. The tysonite and two fluorite lattices have no “correct” relationship. Ca²⁺ cations and a half of TP Er³⁺ cations are fixed in the 2c sites, while the other Er³⁺ cations are disordered over the 6h sites. Superstructural ordering occurs in Er_0.715Ca_0.285F_2.715 crystals; however, the process is not completed, as follows from the character of the diffraction pattern. Weak satellite reflections in the diffraction pattern of the Er_0.67Ca_0.33F_2.67 composition are indicative of the development of TP ordering processes but remain unfit for structural calculations.     

Study of the domain structure of GASH single crystals and its correlation with their dielectric and switching behaviour

The domain structure topography of GASH single crystals is investigated by electron microscope decoration technique. A large variety of domain shapes was found in “young” crystals immediately after growth, whereas after one or more years of ageing the domain structure became coarse. The domain structure of the samples is related with their dielectric and switching behaviour.     

Defect structure and the nature of the obstacles for dislocations in NaCl(Ca) crystals

On the basis of the investigation of the influence of Ca concentration on yield point at different strain rates it is revealed the nature of the obstacles for dislocations overcomed with and without thermal activation.     

Development of methods of X-ray diffraction analysis for determining the composition and structure of sillenite-family crystals

A methodology for refining the crystal structure of sillenites of nominal composition Bi₂₄ M ₂O₄₀ based on the choice of the correct initial model and thermal atomic parameters is reported. The validity of the approach proposed is demonstrated by examples of crystals with M = Si, Fe, or V, for which the real composition is found with allowance for the composition of each structural site. Individual structural details are confirmed by IR and Raman spectroscopy data.     

0.6(Na0.5Bi0.5)TiO3-0.4(Bi0.1Sr0.9)TiO3无铅压电陶瓷的铁电性和阻抗谱研究

采用传统固相法制备了0.6(Na0.5Bi0.5)TiO3-0.4(Bi0.1Sr0.9)TiO3陶瓷(即6BNT-4BST-9),研究了其相结构、铁电性能和储能特性;且利用复阻抗谱和电模量谱分析了其电性能.结果表明:(1)6BNT-4BST-9陶瓷在室温时具有三方和四方共存的相结构;P-E回线和S-E曲线分析表明陶瓷中由非极性四方相占据主导.(2)6BNT-4BST-9陶瓷具有较大Pmax～18.2μC/cm2,和较小的Pr～1.0μC/cm2;它在低场下的储能特性为W1=0.313 J/cm3,η=85.3;(@40kV/cm).(3)M″-f和(-Z″)-f曲线在同一位置的特征峰表明对于6BNT-4BST-9陶瓷只有一种材料微区对电性能起主导.6BNT-4BST-9陶瓷具有负温度系数的电阻-温度特性;根据Arrhenius Law计算的激活能Ea=1.48 eV,表明该陶瓷具有电子导电特征.     

Magnetovolume effects and effect of pressure on the temperature dependence of sublattice magnetization in Ho(Co<Subscript>0.9</Subscript>Ga<Subscript>0.1</Subscript>)<Subscript>2</Subscript> compounds

The temperature dependence of the magnetic moments of cobalt and holmium ions in the temperature range of 5–300 K at pressures of P = 0 and 5 kbar was determined based on neutron diffraction data on Ho(Co_0.9Ga_0.1)₂ intermetallide. The temperature dependence of the lattice parameter was established, and the spontaneous bulk magnetostriction was determined. These quantities were calculated using the exchange striction model of a ferrimagnet, and good agreement with the experiment was obtained. The parameters of the exchange interaction between pairs of atoms of this compound and the magnetoelastic coupling constant were estimated. An original interpretation of the nature of the first-order magnetic phase transition in HoCo₂ is proposed.     

Growth and characterization of isotopically enriched 40Ca100MoO4 single crystals for rare event search experiments

Calcium molybdate is considered as a very promising scintillator material for experimental studies of rare processes. This paper reports on the production and characterization of a ⁴⁰Ca¹⁰⁰MoO₄ scintillator. Using the Czochralski technique, a crystal of high optical quality with total mass 0.55 kg, 42 mm diameter (minimum) and 53 mm 1ength of the cylindrical section was produced from isotopically enriched raw materials, containing 96.1% of ¹⁰⁰Mo and 99.964% of ⁴⁰Ca. To satisfy the requirement of low intrinsic radioactivity the purity of the materials was monitored at different stages of the production process and it is shown that the concentration of ²³⁸U and ²³²Th in the final crystal does not exceed 0.05 ppb. The scintillation properties of ⁴⁰Ca¹⁰⁰MoO₄ were measured over the 8 – 300 K temperature range and it is found that the light yield of the ⁴⁰Ca¹⁰⁰MoO₄ crystal is very similar to that of the CaMoO₄ reference scintillator. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)