Mössbauer study of the modulated magnetic structure of FeVO<Subscript>4</Subscript>

Mössbauer spectroscopy is used to study the FeVO₄ multiferroic, which undergoes two magnetic phase transitions at T _N1 ≈ 22 K and T _N2 ≈ 15 K. The first transition (T _N1) is related to transformation from a paramagnetic state into a magnetically ordered state of a spin density wave, and the second transition (T _N2) is associated with a change in the type of the spatial magnetic structure of the vanadate. The electric field gradient tensor at ⁵⁷Fe nuclei is calculated to perform a crystal-chemical identification of the partial Mössbauer spectra corresponding to various crystallographic positions of Fe³⁺ cations. The spectra measured in the range T _N2 < T < T _N1 are analyzed on the assumption about amplitude modulation of the magnetic moments of iron atoms μ_Fe. The results of model intersection of the spectra recorded at T < T _N2 point to a high degree of anharmonicity of the helicoidal magnetic structure of the vanadate and to elliptic polarization of μ_Fe. These features are characteristic of type-II multiferroics. The temperature dependences of the hyperfine interaction parameters of ⁵⁷Fe nuclei that were obtained in this work are analyzed in terms of the Weiss molecular field model on the assumption of orbital contribution to the magnetic moments of iron cations.     

Doping strategies for increased performance in BiFeO3

Investigation of crystal structure, dielectric, magnetic and local ferroelectric properties of the diamagnetically substituted Bi_1−xA_xFeO_3−x/2 (A=Ca, Sr, Pb, Ba; x=0.2, 0.3) polycrystalline samples has been carried out. It has been shown that the heterovalent A²⁺ substitution result in the formation of oxygen vacancies in the host lattice. The solid solutions have been found to possess a rhombohedrally distorted perovskite structure described by the space group R3c. Piezoresponse force microscopy has revealed signs of existence of the ferroelectric polarization in the samples at room temperature. Magnetization measurements have shown that the magnetic state of these compounds is determined by the ionic radius of the substituting elements. A-site substitution with the biggest ionic radius ions has been found to suppress the spiral spin structure of BiFeO₃ giving rise to the appearance of room-temperature weak ferromagnetism.     

光谱法表征蛋白酶K的热变性过程

用不同温度处理蛋白酶K,以变性酪蛋白底物法测定酶活力,稳态/瞬态荧光光谱法和圆二色谱法测定空间构象和二级结构,研究温度对蛋白酶K酶活力和构象的影响。温度由25 ℃升高至65 ℃过程中,蛋白酶K的酶活力逐渐降低,半衰期缩短;发射光谱荧光强度降低,峰位由335 nm红移至354 nm;色氨酸残基同步荧光强度降低,酪氨酸残基同步荧光强度增大;色氨酸残基荧光寿命由4.427 1 ns降低至4.032 4 ns;α-螺旋百分含量降低。结果表明：采用稳态/瞬态荧光光谱法和圆二色谱法能较简便、准确的描述蛋白酶K的热稳定性变化;蛋白酶K的热变性过程符合三态模型,存在一个中间态;蛋白酶K分子内部存在酪氨酸残基对色氨酸残基的共振能量转移作用;α-螺旋是维系蛋白酶K活性中心构象稳定性的主要结构。     

Spectra of characteristic losses and the electronic structure of sodium nitrite

The complete sets of optical functions for a NaNO₂ crystal are calculated in the energy range of 4 to 24 eV using the integral Kramers-Kronig relations, experimental reflectivity spectra, and theoretical spectra of permittivity. The main distinguishing features and patterns of optical properties are determined as functions of the direction of the light polarization vector. An analysis of the participation of electrons in the formation of optical spectra is presented.     

热交换器中氦气流量对生长蓝宝石温场影响的研究

采用热交换法生长蓝宝石晶体,通过数值模拟与实验研究了晶体生长过程中热交换器中氦气流量对温场的影响.结果表明:晶体生长过程中固液界面为近弧面;随氦气流量增大,晶体与熔体的温度下降,温度梯度增大;加热器功率缓慢上升.     

Crystal growth and defect crystal structure of CdF2 and nonstoichiometric phases Cd1 − x R x F2 + x (R = rare earth element or in). 5. Crystal structure of as-grown Cd0.9R0.1F2.1 (R = La-Nd) single crystals: Nanoclusters of structural defects

As-grown Cd_0.9 R _0.1F_2.1 (R = La-Nd) crystals were assigned to the CaF₂ structure type and their structure was determined by X-ray diffraction. A new octacubic cluster of structural defects in Cd_0.9 R _0.1F_2.1 phases is proposed. The changes in the anionic motif of the Cd_0.9 R _0.1F_2.1 phase can be explained as a result of the formation of tetrahedral [Cd_{4 ? n} R _n F₂₆] and inverse octacubic [Cd_{14 ? n} R _n F₆₈] clusters with, respectively, tetrahedral and cuboctahedral anionic groups as cores. It is established that fluctuations of the La concentration in the cross section of a Cd_0.9La_0.1F_2.1 crystal boule do not exceed 2.7%.     

Electric Hyperfine Interactions of 57Fe Impurity Atoms in ACrO3 Perovskite-Type Chromites (A = Sc,In, Tl,Bi)

Journal of Experimental and Theoretical Physics - Perovskite-type chromites ACr0.9557Fe0.05O3 (A = Sc, In, Tl, Bi) have been studied by probe Mössbauer spectroscopy on 57Fe nuclei. The spectra...     

Electrokinetic properties of methylated quartz capillaries

Electrokinetic (zeta)-potentials of methylated (trimethylchlorosilane) quartz capillaries (5-6 microm in radius) were determined in 10(-4) M KCl solution. Over the course of time, the absolute values of the zeta-potential decrease, as a result of the formation of small bubbles on the rough methylated surface, generated from the flowing, nitrogen gas-saturated solution. This decrease is attributed to screening of a part of the solid surface. After the passage of time, a sharp increase in the zeta-potentials was observed, as the pressure was increased and the initial potential values were recovered. Sometimes, oscillations in the zeta-potentials were observed. This behaviour was explained by detachment of bubbles from the methylated surfaces by the flowing solution. Addition of non-ionic surfactant, which made the methylated surface hydrophilic, decreased the measured zeta-potentials. This was attributed to suppression of water slippage, an effect known to occur for hydrophobic solid surfaces. A mixed mechanism of charge formation is characteristic for these methylated quartz surfaces and is connected with presence of hydrophobic and hydrophilic areas. The ratio between these areas controls both the formation of surface charge as well as the contact angles.     

Reflection Spectra of Single Crystals of La2CuO4−x ‐Type Metal‐Oxide Compounds

We have investigated the reflection spectra in polarized light at 80 and 295 K in an energy region of 1.0–4.8 eV for the single crystals of ternary and quaternary copperoxide systems with the participation of rareearth elements (La₂CuO_4–x , LaCuO₄, Pr₂CuO_4–x , GdBa₂Cu₃O_7–x , and LaSrCaCuO).     

Reflection and Absorption Spectra of Fluorite in the UV Spectral Region

We have calculated the R(E) and ₁(E) spectra from the theoretical ₂(E) spectra of five models in the region 8–27 eV and the ₂(E) and ₁(E) spectra from the experimental R(E) spectrum in the region 6–35 eV. The results are compared with the known theoretical ₂(E) spectra of five models. The basic features of all of the R(E), ₂(E), and ₁(E) spectra have been revealed. It is established that the experimental R(E) spectrum and the ₂(E) and ₁(E) spectra calculated with the use of experimental data are in good agreement with the results of theoretical calculations for the models of ₂(E). On the basis of the known theoretical calculations of the fluorite zones, a scheme of the nature of the principal maxima of R(E) and ₂(E) is suggested.