Decay of the homogeneous state in Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiSe<Subscript>2</Subscript>

The stability of a homogeneous state in materials with a more than half-filled polaron band has been investigated for the Fe _x TiSe₂ system used as an example. It has been demonstrated that the factor limiting the stability of the homogeneous state of these materials is a change in the degree of filling of the conduction band due to the thermal broadening of the polaron band. This factor becomes substantial when the top of the polaron band intersects the Fermi level. It has been revealed that the decay of the homogeneous state leads to the precipitation of the intercalant. The morphology and structure of the precipitates formed in this decay in Fe _x TiSe₂ single crystals have been studied by transmission electron microscopy.     

Kinetics of reactions in interlayer space of titanium diselenide intercalated with iron

Decomposition of a homogeneous intercalation compound with the formation of inclusions in the interlayer space of a matrix lattice has been directly observed. In full compliance with previously advanced theoretical concepts, it has been shown that the decomposition is accompanied by metallic iron extraction, which then gradually transforms into iron selenide due to the interaction with gaseous selenium.The hierarchy of diffusion mobilities of various defects in Fe_xTiSe₂ intercalation compound has been determined. It has been found that the largest mobility is inherent to intrinsic defects of the TiSe₂ lattice, i.e., vacancies in Ti and Se sublattices. The phenomenon of dissociation pressure oscillations as a function of time has been detected. This phenomenon has been explained by the existence of a slow decomposition stage, i.e., intercalated iron diffusion during the formation and dissolution of its inclusions as an individual phase.     

插层化合物Ag1/4TiSe2电子结构的第一性原理研究

采用基于密度泛函理论的平面波赝势方法,选用局域密度近似对Ag_1/4TiSe₂及TiSe₂的几何结构进行了优化和总能量计算.计算得到的晶格常量与实验结果符合较好,负的形成能表明有序Ag_1/4TiSe₂系统的稳定性.布居数、键长、能带结构和态密度的计算结果显示：Ag以较强的离子性结合于Ag_1/4TiSe₂中.Ag的插入使得半金属性的TiSe_{2关键词： 1/4}TiSe₂')" href="#">Ag_1/4TiSe₂ 电子结构 插层化合物 第一性原理计算     

Determination of the polaron shift in titanium diselenide-based intercalation compounds

A study is reported of the dependence of the TiSe₂ lattice constants on the concentration of an intercalated metal in various valence states and external pressure. The strain energy and the polaron shift created in the intercalation of TiSe₂ with metals in various valence states have been determined. The position of the polaron band is shown to decrease linearly with the increasing intercalant ionization potential.     

The pressure effect on the CDW-transition and the transport properties of TiSe2

The transport properties of TiSe₂ have been measured under hydrostatic pressure up to about 5 kbar. It is found that the Hall coefficient at 77 K is insensitive to pressure, which suggests the possibility that the whole Fermi surface is gapped at 77 K by the CDW-instability. The pressure dependence of the CDW-transition temperature in TiSe₂ has also been investigated. The pressure effect on TiSe₂ is compared with those on the metallic dichalcogenides of group Vb transition metals.     

利用扫描隧道显微镜在溶液中直接观测过渡族金属硫属化合物

本文利用自制的溶液扫描隧道显微镜在溶液环境下直接观测到TiSe₂、MoTe₂和TaS₂样品的原子分辨率图像. 通过将单晶样品在溶液中直接解理,可以保护解理过的新鲜样品表面在几个小时内不会被严重污染. 利用自行搭建的溶液扫描隧道显微镜,首先观察到了TiSe₂活泼样品的原子分辨率图像,并观察到了TiSe₂表面所特有的点缺陷和三角形缺陷结构. 此外,还观察到了MoTe₂的原子分辨率超结构和TaS₂表面的电荷密度波结构. 结果表明：在室温、溶液环境下能更高效的研究过渡族金属硫属化合物等活泼样品的表面电子态结构,同样适用于溶液环境下的电催化和电化学研究.     

Shift of the Fermi level during cointercalation of copper and iron into TiSe<Subscript>2</Subscript>

The influence of copper intercalation into the TiSe₂ compound on the Fermi energy has been investigated using two independent methods. The first method is based on the analysis of the amplitude of the deformation (induced by impurity intercalation and providing the formation of polarons) as a function of the binding energy of the band of polaron states. For this purpose, the Fe _x Cu _y TiSe₂ system has been synthesized for the first time by cointercalation of copper and iron into the TiSe₂ lattice and studied. The second method consists in measuring the electromotive force of an open-circuit electrochemical cell with respect to a metal reference electrode. Both methods lead to consistent results in the range of moderate copper contents. However, considerable discrepancies have been observed in the copper concentration range that corresponds to the beginning of filling of Cu/Ti hybrid states. These discrepancies are explained by the softening of the lattice due to an increase in the density of states at the Fermi level.     

Structure and properties of Ti1 − x CrxSe2 substitutional solid solutions

Titanium diselenide TiSe₂ is doped for the first time with an acceptor impurity through substitution of Cr³⁺ ions for Ti⁴⁺ ions in the host lattice. The structure and electrical resistivity of the TiSe₂-based solid solutions are investigated in the vicinity of the compensation point, and the influence of the compensation point on the stability of the charge-density-wave state is analyzed. It is demonstrated that disorder in the guest sublattice does not lead to Anderson localization of charge carriers.     

Magnetic state and properties of the Fe0.5TiSe2 intercalation compound

The Fe_0.5TiSe₂ compound with a monoclinic crystal structure has been prepared by intercalation of Fe atoms between Se-Ti-Se sandwiches in the layered structure of TiSe₂. The crystal and magnetic structures, electrical resistivity, and magnetization of the Fe_0.5TiSe₂ compound have been investigated. According to the neutron diffraction data, the Fe_0.5TiSe₂ compound has a tilted antiferromagnetic structure at temperatures below the Néel temperature of 135 K, in which the magnetic moments of Fe atoms are antiferromagnetically ordered inside layers and located at an angle of approximately 74.4° with respect to the layer plane. The magnetic moment of Fe atoms is equal to (2.98 ± 0.05)μ_B. The antiferromagnetic ordering is accompanied by anisotropic spontaneous magnetostrictive distortions of the crystal lattice, which is associated with the spin-orbit interaction and the effect of the crystal field.     

Physical properties of n-CdGeAs2 single crystals prepared by low-temperature crystallization

The first results obtained in studies of the temperature dependences of electrical conductivity and Hall constant of n-CdGeAs₂ single crystals prepared by low-temperature crystallization are reported. It has been established that the method developed permits growing single crystals with a free-electron concentration ⋍(1−2)×10¹⁸ cm⁻³ and a Hall mobility ⋍10000 cm²/(Vs) at T=300 K. It is shown that the temperature dependence of Hall mobility exhibits a behavior characteristic of electron scattering by lattice vibrations, whereas below 150 K a deviation from this law is observed to occur evidencing an increasing contribution of static lattice defects to scattering. The Hall mobility in the crystals prepared was found to reach ⋍36000 cm²/(Vs) at 77 K. Photosensitive heterojunctions based on n-CdGeAs₂ single crystals were prepared. The spectral response of the photosensitivity of these structures is analyzed. It is concluded that this method is promising for preparation of perfect CdGeAs₂ crystals. Fiz. Tverd. Tela (St. Petersburg) 41, 1190–1193 (July 1999)     

Bi2Sr2CaCu2Oy单晶调制结构的X射线衍射研究

用Ｘ射线转靶衍射仪，详细地观察和分析了Bi₂Sr₂CaCu₂O_y单晶的调制结构．指出布喇格反射的卫星峰是沿ｃ^*拉长的，与Ｂ心正交对称结构不相符的宽化峰正是由于这种拉长的结果，且导致卫星峰强度的不对称性．Ｂｉ-Ｏ层和钙钛矿层晶格失配形成的超晶格为非正交而是单斜的，并可能存在超晶格孪晶     

The influence of intercalation on the phonon spectrum of titanium dichalcogenides

A systematic investigation of the inelastic neutron scattering spectra is carried out for intercalation titanium diselenide compounds of the general formula M _x TiSe₂ (M = Cr, Fe, Ni, Ag). It is shown that the effect of intercalation on the phonon spectrum of the material is determined primarily by the modification of the host lattice due to the formation of Ti-M-Ti covalent centers. It is established that the lattice can undergo a substantial softening when the impurity band coincides with the Fermi level.     

Vortex structure in FeTeSe single crystals

Vortex structure in FeTe_0.66Se_0.44 and FeTe_0.6Se_0.4 single crystals with T _c ∼ 11.7 and 14.5 K, respectively, has been studied using the decoration technique. It has been found that in single crystals with the simplest crystalline structure of 11-family iron-containing superconductors (without interlayers), no regular vortex lattice is observed, similar to the case of the previously studied 122 and 1111 families. Using transmission electron microscopy, the dislocation structure with a density of ∼10⁹ cm⁻² has been observed. The problem of pinning in iron-containing superconductor single crystals is discussed.     

Thermo-optical response of VxTi1-xSe2 in the plasmon reion

It is shown that some structure growing on the high energy side of the plasmon when cooling TiSe₂ crystals through the transition temperature is smeared out with vanadium concentrations of the order of 1% and that the plasmon lifetime is considerably affected both by temperature and vanadium content.     

Erholungsvorgänge in UV-bestrahltem Silberchlorid

The formation of defects in AgCl single crystals under UV and X-ray exposure and their thermal annealing are studied by measuring the optical density, the lattice parameter change, the X-ray Ag-reflection and by electronmicroscopical observations. Specks of crystalline silver are found to be produced at the surface of the crystals as well as in the interior. According to surface and volume darkening the isochronal annealing curves exhibit two stages. The activation energy for stage I, (0,59±0,08) eV, is suggested to be the energy for the thermal formation of electrons and Ag ₀ ⁺ -ions from Ag-aggregates. Stage II appears when the crystal is annealed in chlorine at above 523 °K. It is due to the regeneration of silver at the surface, where chlorine was able to leave the crystal during exposure.     

On the nature of state with a charge-density wave in TiSe<Subscript>2</Subscript> from data of scanning tunneling microscopy

The surface of a fresh cleavage of TiS₂, TiSe₂, and TiTe₂ crystals has been investigated using scanning tunneling microscopy with atomic resolution. All materials are characterized by triangular defects coinciding in shape with those supposedly formed as a result of the local change in the titanium atom coordination from octahedral to trigonal-prismatic by the chalcogen due to the Jahn-Teller effect. The conclusion has been drawn that the Jahn-Teller effect exists in these materials, but it is responsible for the formation of nanodefects rather than for the transition to a charge-density wave state. It has been shown that this interpretation of defects allows one to understand the evolution of the stability boundary of a charge-density wave upon donor and acceptor doping.     

Structural features of the system of cubic crystals Zn0.999Fe0.001S1 ? x Se x (x = 0, 0.2)

The structural state of cubic single crystals Zn_0.999Fe_0.001S_{1 ? x} Se _x (x = 0, 0.2) obtained by the chemical transport method has been investigated using thermal neutron diffraction for the first time. It has been found that the diffraction patterns of these crystals contain the previously unknown effects of diffuse scattering caused by local statistic atomic displacements in the metastable fcc lattice.     

Preparation and properties of spray-deposited ZnIn2Se4 nanocrystalline thin films

Zinc indium selenide (ZnIn₂Se₄) thin films have been deposited onto amorphous and fluorine doped tin oxide (FTO)-coated glass substrates using a spray pyrolysis technique. Aqueous solution containing precursors of Zn, In, and Se has been used to obtain good quality deposits at different substrate temperatures. The preparative parameters such as substrate temperature and concentration of precursors solution have been optimized by photoelectrochemical technique and are found to be 325 °C and 0.025 M, respectively. The X-ray diffraction patterns show that the films are nanocrystalline with rhombohedral crystal structure having lattice parameter a=4.05 Å. The scanning electron microscopy (SEM) studies reveal the compact morphology with large number of single crystals on the surface. From optical absorption data the indirect band gap energy of ZnIn₂Se₄ thin film is found to be 1.41 eV.     

Solution of selfconsistent equations for superconducting glasses: a new universal ratio,critical exponent β=1, and behaviour in magnetic fields

A new two step oxidation model is proposed that describes the mechanism of internal oxidation of the non-noble impurities antimony and indium in silver. We have found that internal oxidation at 550 K leads to the formation of isolated SbO₂ or InO₂ molecules, respectively. The commonly used model of Wagner treats the oxidation as a one step process, which means that in the case of antimony and indium two oxygen atoms must be trapped effectively in one step. Assuming a trapping radius of one lattice constant this model predicts an oxidation front that is much steeper than observed experimentally. The two step oxidation model assumes that first one oxygen atom is trapped at the non-oxidized impurity to form a relatively unstable complex. If within the lifetime of this complex a second oxygen atom is trapped, a stable and completely oxidized complex is formed in the silver matrix. The two step oxidation model predicts the shape of the oxidation front during internal oxidation at 550 K of antimony or indium in silver single crystals correctly, when a dissociation energy of 0.60(5) eV for the unstable complex is taken.