Sol–gel derived nanocrystalline multiferroic BiFeO3 and R (R=Er and Tm) doped therein: Magnetic phase transitions and enhancement of magnetic properties

Nanocrystalline BiFeO₃ and rare earth ion doped BiFeO₃ (Bi_0.9R_0.1FeO₃, R=Er and Tm) were prepared by sol–gel method. Rietveld analysis of the X-ray diffractograms of the samples revealed that small amount of impurity phase of Bi₂Fe₄O₉ was formed together with the desired phase. In the thermal variation of magnetic mass susceptibility (χ_m) of the samples, one sharp transition below T_M (T_M∼100 K, 50 K and 30 K for BiFeO₃, Bi_0.9Er_0.1FeO₃ and Bi_0.9Tm_0.1FeO₃, respectively) was observed, which clearly hint the change of the domination of the ferromagnetic exchange interaction over the usual antiferromagnetic exchange interaction. Also, static magnetization (M) and susceptibility of each doped sample have been drastically enhanced compared to that of BiFeO₃. The values of χ_m and M measured at different temperatures confirmed that the magnetic behavior of the doped systems has been dominated by the paramagnetic/ferromagnetic clusters below ∼T_M. Another phase transition were observed in the χ_m vs. T curve of the samples at relatively higher temperature T_B (∼260 K for BiFeO₃, ∼220 K for Bi_0.9Er_0.1FeO₃ and ∼180 K for Bi_0.9Tm_0.1FeO₃), which may be attributed to the charge ordering transition. Ferroelectric hysteresis loops of the samples observed at 100 Hz confirmed the presence of ferroelectric ordering of the samples. Measured values of dielectric constants at 1 kHz of each sample in presence and absence of magnetic field confirmed a substantial magnetoelectric coupling of all the samples.     

Li2K(IO3)3与Li2NH4(IO3)3的晶体结构

本文用X射线粉末法测定了Li₂K(IO₃)₃与Li₂NH₄(IO₃)₃的晶体结构和原子参数。发现Li₃K(IO₃)₃,Li₂NH₄(IO₃)₃与Li₂Rb(IO₃)₃同晶型,属单斜晶系,空间群为P2₁/α,每个单胞含有四个化合式量。室温的点阵常数分别为α=11.198?,b=11.046?,c=8.254?,β=111.53°,及α=11.327?,b=11.078?,c=8.341?,β=111.87°。讨论了二元化合物的形成与离子半径的关系。 关键词：     

Observation of simultaneous ν1(SF6) + ν3(NF3) and ν2(SF6) + ν3(NF3) transitions enhanced by the resonance dipole-dipole interaction with the ν1 + ν3 and ν2 + ν3 states of the SF6 molecule

IR spectra of the solution of SF₆ molecules in liquid NF₃ at 84 K have been recorded. In a solvent transmission window of 1500–1750 cm⁻¹, two wide absorption bands with pronounced peaks in the high-frequency part are observed. The profile of these bands is explained by the influence of the resonance dipole-dipole (RDD) interaction of the states of the simultaneous transition ν₁(SF₆) + ν₃(NF₃) and ν₂(SF₆) + ν₃(NF₃) with the states (ν₁ + ν₃) and (ν₂ + ν₃) of the SF₆ molecules, respectively. The use of three isotopic modifications ³²SF₆, ³³SF₆, and ³⁴SF₆ has allowed us to vary the resonance detuning and thus to change the strength of the RDD interaction. With the liquid near the melting point being represented as a close-packed cubic crystal, the profile was calculated and its spectral characteristics were determined. The frequencies of the main peaks coincide with the experimental values accurate to the error.     

A new analysis of the ν4(E) rovibrational band of the symmetric top molecule PF3

The high-resolution Fourier transform infrared spectrum of phosphorus trifluoride PF₃ have been reinvestigated in the ν₄ perpendicular band region around 347 cm⁻¹. Thanks to recent pure rotational measurements, 595 new infrared transitions of the ν₄ band have been assigned extending the rotational quantum number values up to K_max = 66 and J_max = 67. As a consequence of this extension, a sophisticated model containing a large number of parameters and interaction constants was adopted for the analysis of the IR transitions of the ν₄ fundamental band of PF₃. A merge of the IR transitions and the reported MW/MM/RF data within the v₄ = 1 excited level yielded an accurate rotational ground state C₀ value, 0.159970436 (69) cm⁻¹, which was used to determine an improved GS structure, r₀(P-F) = 1.56324405 (11) Å and ?(FPF) = 97.752232 (29)°. All experimental data have been refined applying various reduction forms of the effective rovibrational Hamiltonian developed for an isolated degenerate state of a symmetric top molecule. The v₄ = 1 excited state of the PF₃ oblate molecule was treated with models taking into account ?- and k-type intravibrational resonances. Parameters up to sixth order have been accurately determined and the unitary equivalence of the derived parameter sets in different reductions was demonstrated.     

Effect of elevated concentrations of strontium and iron on the structural and dielectric characteristics of Ba(1−x−y)Sr(x)Ti Fe(y)O3 prepared through sol–gel technique

Nano-composite Ba_1−xSr_(x)TiO₃ (BST), where x=0.01–0.50 and doped with different concentrations of iron Ba_(1−x−y)Sr_(x)TiFe _(y)O₃ (BSTF), where x=0.01 and y=0.01–0.05 powders were prepared by sol–gel method.     

Structural and electrical investigation of (Ag3AsS3)x(As2S3)1?x superionic glasses

Structural studies of (Ag₃AsS₃) _x (As₂S₃)_1−x chalcogenide superionic glasses in the compositional range x = 0.3–0.9 were performed by scanning electron microscopy. Temperature and compositional dependences of transmission coefficient, electrical conductivity, and activation energy were investigated     

希夫碱配合物M3L3(NO3)6(H3O)2的合成与光谱性质

以4-氨基-1,2,4-三氮唑与对二甲氨基苯甲醛为原料, 在冰醋酸催化下合成了配体4-氨基-1,2,4-三氮唑缩对二甲氨基苯甲醛（L）。 然后利用L与过渡金属硝酸盐［M(NO3)2·xH2O(M=Cu,　Co,　Zn,　Cd; x=3～6)］在无水乙醇中反应, 制得固态配合物M3L6(NO3)6(H2O)2。 通过元素分析、 红外光谱、 紫外光谱、 荧光光谱等手段对合成的配体及配合物进行了表征。 实验结果表明, 该物质是一种多晶粉末状的发光材料,　在紫外光的激发下,　在乙醇溶液体系中的荧光发射峰在416 nm处,　为蓝色荧光, 色纯度高,　荧光量子效率高, 而配合物M3L6(NO3)6(H2O)2的荧光发射峰则红移至445 nm左右, 同时荧光强度显著增强。　M3L6(NO3)6(H2O)2中与M(Ⅱ)发生配位作用的基团是配体中三氮唑环上的氮原子。     

正磷酸盐晶体Ba3(PO4)2和Sr3(PO4)2高温拉曼光谱研究

测量了碱土金属正磷酸盐Ba₃(PO₄)₂和Sr₃(PO₄)₂常温及高温拉曼光谱, 对拉曼振动模式进行指认, 并分析了晶体拉曼振动光谱及晶体结构在高温下的变化. 在温度升高的过程中, 拉曼振动频率向低频移动且振动峰宽度展宽, 晶体中的P-O平均键长随温度升高而变长, 但O-P-O的键角并未发生变化. 晶体在900 ℃以下无结构相变发生. 关键词： 3(PO₄)₂和Sr₃(PO₄)₂')" href="#">Ba₃(PO₄)₂和Sr₃(PO₄)₂ 高温拉曼光谱 振动模式 高温结构     

Luminescence studies of Nd- and Yb-doped α-Y(IO3)3 and β-Y(IO3)3, transparent host matrix in the mid- and beginning of the far-infrared

α-Y(IO₃)₃ and β-Y(IO₃)₃ are transparent until 12.8 and 13.4 μm, respectively; thus they are interesting as a potential laser matrix in the mid- and beginning of the far-infrared. So, in order to investigate the properties of lanthanides- doped anhydrous yttrium iodate, polycrystalline samples of α-Y_1−xNd_x(IO₃)₃ (0.01?x?0.05), β-Y_1−xNd_x(IO₃)₃ (0.001?x?0.1), α-Y_1−xYb_x(IO₃)₃ (0.01?x?0.33) and β-Y_1−xYb_x(IO₃)₃ (0.01?x?0.25) were synthesized. For Nd³⁺ ions, fluorescent emissions from the ⁴F_3/2 multiplet were observed at 300 K under pulsed laser excitations at 750 nm and for Yb³⁺, fluorescent emissions from the ²F_5/2 multiplet were observed at 300 K under pulsed laser excitations at 980 nm. The decays of all these emissions were measured. They are exponential and the fluorescence lifetimes are in the range 0.093-0.193 ms for Nd³⁺ and 0.370-0.541 ms for Yb³⁺, depending on the nature of the host and the concentration of doping.     

(La0.7Sr0.3MnO3 )m(BiFeO3)n 超晶格结构的导电机理

利用射频磁控溅射的方法在SrTiO₃(001) 基片上制备了(La_0.7Sr_0.3MnO₃)_m(BiFeO₃)_n超晶格结构.对所制备的超晶格结构进行了50—150℃温度范围内的电流-电压测试分析.结果表明,随着BiFeO₃薄膜的厚度减小,温度的升高,(La_0.7Sr_0.3MnO₃)_m(BiFeO₃)_n超晶格结构的电流变大.进一步根据介质导电模型对(La_0.7Sr_0.3MnO₃)_m(BiFeO₃)_n超晶格结构的导电特性做了分析.在温度较低或者电场较弱时,所制备的(La_0.7Sr_0.3MnO₃)_m(BiFeO₃)_n超晶格结构表现为欧姆导电,而在高温,高电场的情况下,其导电行为由空间电荷限制电流机理主导. 关键词： 超晶格薄膜 多铁 空间电荷限制电流     

(Sb2Te3)0.75(1－x)(Bi2Te3)0.25(1－x)(Sb2Se3)x机械合金化粉体的制备及其冷压烧结样品的热电性能研究

采用机械合金化法制备了p型赝三元(Sb₂Te₃-Bi₂Te₃-Sb₂Se₃)合金粉体，对其进行XRD分析表明Te，Bi，Sb，Se单质粉末，经100h球磨后实现了合金化；SEM分析表明所得机械合金化粉体材料颗粒均匀、细小，颗粒尺寸在10nm到100nm量级.使用这种粉体制备了冷压烧结块体样品，在室温下测量了温差电动势率(α)和电导率(σ)，研究了烧结温度对材料热电性能的影响，结果表明在低于300℃的烧结温区，样品室温下的热电性能随烧结温度的升高不断提高，功率因子(α²σ)由未烧结样品的0.59μW cm^-1K^-2升高到在300℃下烧结样品的15.9μW cm^-1K^-2，这一结果对确定材料的最佳烧结温度具有重要意义. 关键词： 赝三元热电材料 机械合金化 冷压 烧结     

Optical properties of (In2Se3)1–x·(CuIn5Se8)x solid solutions

Single crystals of In₂Se₃ and CuIn₅Se₈ compounds and (In₂Se₃)_1–x·(CuIn₅Se₈)_x solid solutions have been grown from the melt using the Bridgman method and their composition and structure determined. It is shown that the crystals have n-type conductivity. Their transmission spectra were studied in the self-absorption edge region at 80 and 295 K. Based on the spectral measurements, the band gap width (E_g) was determined and the band gap concentration dependences were plotted. It is found that E_g varies with the x composition nonlinearly. Using the dielectric model of Van Vechten–Bergstresser and the Hill–Richardson pseudo potential model, E_g(x) was calculated theoretically.     

Magnetostriction of TbxHo0.75−xPr0.25(Fe0.9B0.1)2 (x=0–0.3) compounds

The Tb_xHo_0.75−xPr_0.25(Fe_0.9B_0.1)₂ (x=0, 0.1, 0.15, 0.2, 0.25, and 0.3) compounds are found to stabilize in a cubic Laves phase structure. The lattice parameter, magnetostriction (at 10 kOe), and Curie temperature are found to increase with increasing Tb content. The compound with x=0.15 exhibits a possible anisotropy compensation between the Tb and (Ho/Pr) sublattices. The easy magnetization direction rotates towards the 〈1 1 1〉 from the 〈1 0 0〉 direction, with increasing Tb content. The splitting of the (4 4 0) peak accompanied by the spontaneous magnetostriction-induced rhombohedral distortion is observed for compounds with x?0.15 and the spontaneous magnetostriction (λ_1 1 1) is found to increase with Tb content.     

Crystal field study and magnetic properties of [TbCu6(μ3OH)3(HL)2(L)4](ClO4)2·25H2O (H2L=imino-diacetic acid)

A crystal field (CF) investigation of the magnetic properties of [TbCu₆(μ₃-OH)₃(HL)₂(L)₄](ClO₄)₂·25H₂O (H₂L=imino-diacetic acid) has been carried out. An enhancement of the average magnetic susceptibility (defined by =(χ_||+2χ_⊥)/3, where χ_|| and χ_⊥ are the magnetic susceptibilities parallel and perpendicular to the symmetrical axis of the cluster) with respect to the Tb³⁺ free ion value has been noticed and is attributed to the Tb-Cu interaction. The CF parameters obtained for the system for the first time have been exploited to find the Stark splitting of the ⁷F manifold of Tb³⁺, paramagnetic resonance g-values, and the heat capacity. Two anomalies are obtained in the heat capacity at 40 and 5 K; the peak values are 3.1 and 5.98 J mol⁻¹ K⁻¹, respectively.     

Structure and magnetic properties of magnetostrictive compounds Tb0.36Dy0.64(Fe0.85Co0.15)2−xBx (0⩽x⩽0.15)

Crystal structure and magnetic properties of magnetostrictive compounds Tb_0.36Dy_0.64(Fe_0.85Co_0.15)_2−xB_x (0?x?0.15) have been investigated at room temperature. The matrix of these compounds keeps a cubic MgCu₂-type structure. Lattice parameter a of the Laves phase decreases to reach a minimum at x=0.10, then increases with increasing boron content. Through analyzing the Mössbauer spectra, the easy magnetization direction (EMD) for all samples is confirmed to lie along 〈111〉 direction at room temperature, suggesting the presence of the giant magnetostriction. The mean hyperfine field H_hf and the deduced iron moment μ_Fe increase with increasing boron content, resulting in the enhancement of both Curie temperature T_C and spin reorientation temperature T_r. Although the addition of B enlarges the magnetocrystalline anisotropy constant K₁, the composition dependence of the ratio λ/K₁ for Tb_0.36Dy_0.64(Fe_0.85Co_0.15)_2−xB_x, however, reaches a maximum value at x=0. 05 under high magnetic fields.     

Vibration-Torsion-Rotation Study of the ν5 State of CH3CF3

An investigation of the torsion-rotation-vibration energies in the ν₅ vibrational state in CH₃CF₃ has been carried out using infrared and mm-wave spectroscopy. The lowest frequency parallel fundamental band ν₅ near 600 cm⁻¹ has been measured at a resolution of 0.00125 cm⁻¹ with Fourier transform spectroscopy for the two lowest torsional states v₆=0 and 1. The cold band (v₅=1, v₆=0)←(v₅=0, v₆=0) showed no torsional splittings and looked much like a parallel band in a C_3v molecule. The hot band (v₅=1, v₆=1)←(v₅=0, v₆=1) consisted of three distinct subbands, one for each torsional sublevel σ=0, +1, and −1. For the state (v₅=1, v₆=1), the torsional splitting was increased from ∼0.001 cm⁻¹ to ∼0.022 cm⁻¹ by torsion-mediated Fermi-type interaction primarily with the dark state (v₅=0, v₆=5). The effects of this coupling on the spectrum are striking in spite of the fact that the two interacting states are ∼100 cm⁻¹ apart and differ by four units in v₆. The large amplitude character of the state (v₅=0, v₆=5) is seen to be largely responsible for the unusual (k, σ) dependence of the energies in the state (v₅=1, v₆=1). The pure rotational spectrum in the state (v₅=1, v₆=0) has been measured between ∼50 and 370 GHz with Doppler-limited resolution; no σ-splitting was detected. The 3590 infrared and mm-wave frequencies measured here have been analyzed together with the 1494 measurements reported earlier by Wang et al. in an analysis of the vibrational ground state (2001, J. Mol. Spectrosc.205, 146-163). A good fit was obtained here by varying 36 parameters in a Hamiltonian which takes into account the interaction between the torsional stacks of levels for v₅=0 and 1, as well as the (A₁−A₂) splittings measured earlier for v₅=0. The explicit treatment of the interstack interactions is shown to lead to significant changes in the parameters (V_0,3, V_0,6) that characterize the torsional potential for v₅=0. These changes have been explained quantitatively by examining the contact transformation that is implicitly applied when the interstack coupling is neglected.     

Magnetoelectric effect in laminates of polymer-based pseudo-1–3 (Tb0.3Dy0.7)0.5Pr0.5Fe1.55 composite and?0.3Pb(Mg1/3Nb2/3)O3–0.7PbTiO3 single crystal

We report an extrinsic magnetoelectric effect in composite laminates made by sandwiching one thickness-polarized 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN–PT) piezoelectric single crystal plate between two length-magnetized, polymer-based pseudo-1–3 (Tb_0.3Dy_0.7)_0.5Pr_0.5Fe_1.55 magnetostrictive composite plates. The laminates exhibit large magnetoelectric voltage coefficients (α _V ) of ∼0.17 V/Oe with a flat response for frequencies in excess of 40 kHz and of ∼2.97 V/Oe at the natural resonance frequency of ∼65 kHz. The distinct advantages of the laminates include high magnetic field sensitivity, low Joule heating loss, wide operating bandwidth, and low cost.     

Profile of the refractive index distribution over the depth of (HfO2)x(Al2O3)1 ? x films

Capabilities of the method of laser null ellipsometry for the study of optical parameters of thin films of multicomponent alloys are demonstrated. Films of alloys (HfO₂) _x (Al₂O₃)_{1 − x} on single-crystal silicon are obtained by the chemical vapor deposition with the use of the following volatile compounds: hafnium dipivaloylmethanate (IV) and aluminum acetylacetonate (III). The selection of initial sets for their optical parameters is justified. The selected model is shown to correspond to experimental data. In films deposited from the mixture of precursors, the refractive index increases from a substrate to a film surface. Due to the separation of sources, films described by a single-layer model were deposited. This fact is indicative of the homogeneous distribution of components over the film thickness.