Specific features of the structural and magnetic states of a Zn1 ? x Ni x Se crystal ( x = 0.0025) at low temperatures

The magnetic state and the structure of a Zn_{1 − x} Ni _x Se (x = 0.0025) bulk crystal were studied at low temperatures. It is revealed that the magnetic and crystal structures below T ≅ 15 K are dependent on the cooling rate of this dilute semiconductor. For example, on fast cooling to 4.2 K, about 10% hexagonal ferromagnetic phase is formed in the crystal. During heating, the phase disappears at T ≅ 15 K. The results obtained are discussed with allowance for the specific features of the Jahn-Teller distortions in this compound. Original Russian Text ? S.F. Dubinin, V.I. Sokolov, V.D. Parkhomenko, S.G. Teploukhov, N.B. Gruzdev, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 12, pp. 2188–2191.     

Low-frequency lattice dynamics in Ba1−x KxBiO3 oxides according to 39K NMR data

The spin-lattice relaxation times T ₁ in Ba_1−x K_xBiO₃ (x=0.3, 0.4, 0.5) were measured in the normal temperature range (20–300 K).A substantial contribution to the spin-lattice relaxation rate from dynamic local distortions of the crystal lattice near potassium atoms is found. The activation energy of this process increases with decreasing potassium concentration, and the frequency of lattice excitations decreases. The nature of the low-frequency lattice dynamics is discussed. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 344–349 (10 September 1999)     

Dynamic Deformations of the Crystal Lattice of Sphalerite in the Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se(<Emphasis Type="Italic">x</Emphasis>=0.01) Compound

Local distortions of the crystal lattice of the semiconductor compound Zn_{1 − x} Co _x Se (x = 0.01) have been investigated using thermal neutron diffraction. It has been found that the diffraction patterns of the crystal contain regions of diffuse scattering in the vicinity of strong Bragg peaks at 300 K. As the temperature decreases, the intensity of diffuse scattering effects substantially decreases. Arguments in favor of the assumption that the origin of the diffuse scattering is caused by the Jahn-Teller vibronic effect are presented.     

Structure and magnetism of semiconductor crystals of the (Ga1 ? xMnx)2Se3 (x = 0?0.04) compounds

Neutron diffraction and magnetic measurements have been used to study the effect of doping with Mn³⁺ ions on the fine crystal structure of the Ga₂Se₃ monoclinic compound. It has been established that the structural state of the crystals is changed even at a relatively low doping level (x = 0.04). Arguments in favor of the fact that local Jahn-Teller distortions are responsible for the formation of the fine structure and magnetism in compounds of this class are presented.     

Crystal structure and properties of Bi1 ? x Ca x FeO3 and Bi1 ? x Ca x FeO1 ? x Ti x O3 solid solutions

Systems of solid solutions Bi_{1 − x} Ca _x FeO₃ (I) and Bi_{1 − x} CaxFeO_{1 − x} Ti _x O₃ (II) have been obtained and their properties have been studied using neutronography and M?ssbauer spectroscopy; magnetization and permittivity have been measured. It is shown that an increase in the concentration of calcium ions in system I for x > 0.2 changes rhombohedral distortions of a unit cell (space group R3c) to tetragonal distortions (space group I4/mcm), while rhombohedral distortions in system II for x > 0.2 are replaced by orthorhombic distortions (space group Pnma). Analysis of the crystal structure has revealed strong anisotropy in vibrations of Bi and O ions in system I compounds. Systems I and II are characterized by G-type antiferromagnetic ordering of magnetic moments. In system II, spontaneous magnetization associated with the Dzyaloshinskii-Moriya interaction has been detected. According to M?ssbauer spectroscopy data, iron ions in compounds I and II are in the trivalent state and charge compensation occurs due to the formation of oxygen vacancies. The permittivity increases with the calcium concentration. Original Russian Text ? I.O. Troyanchuk, D.V. Karpinsky, M.V. Bushinskii, O. Prokhnenko, M. Kopcevicz, R. Szymczak, J. Pietosa, 2008, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2008, Vol. 134, No. 1, pp. 105–112.     

Experimental and theoretical studies of Si/P substituted orthorhombic Fe2P

A Mössbauer spectroscopic study of orthorhombic Fe₂P_1–x Si _x withx 0.35 was performed. A large spread in magnetic hyperfine fields was found at the six Fe positions ranging from 10–26 T at 4.2 K. Small rearrangements in the crystal positions as compared to the hexagonal phase cause large changes in the magnetic field. Large changes in Fe magnetic moments have also been obtained in a spin-polarized LMTO band calculation performed on orthorhombic Fe₂P as compared to a similar calculation of hexagonal Fe₂P.     

镁含量和热处理对Zn1-xMgxO薄膜结构和发光性能的影响

采用溶胶-凝胶工艺在玻璃衬底上制备了Zn_1-xMg_xO(x=0.1,0.2,0.3, 0.4,0.5,0.6,0.7)薄膜.X射线衍射谱(XRD)测试结果发现,在 0.1<x<0.3 范围内,薄膜仍然保持氧化锌六角纤锌矿结构,(002)面衍射峰位向大角度方向移动,超过0.3时出现氧化镁立方相.对镁含量为0.1,0.2,0.3薄膜的光致发光谱研究表明：紫外发光峰随镁含量的增加向短波方向移动.对于Zn_0.9Mg_0.1O薄膜,在5,5.5和6℃/min的升温速率下,升温速率越快结晶程度越好.在相同升温速率下,随着退火温度从500 ℃升高到560 ℃,样品的结晶程度变好,当退火温度达到590 ℃时,结晶质量下降. 关键词： 氧化锌 结构 禁带宽度 光致发光谱     

Effects of hydrostatic pressure on CdxHg1−xTe alloys

The hydrostatic pressure effects on Cd_xHg_1−xTe alloys have been investigated. In the relatively low pressure region, we find an anomaly in each Hall coefficient vs. pressure curve for the alloys (x<0.09), which is attributed to the inversion of the Γ₈/Γ₆ energy bands. In the relatively high pressure region, the electrical resistivities of the alloy crystals (x>0.09) show changes of three stages with increase of pressure. The crystal structures corresponding to the three stages are studied by an X-ray diffraction analysis. It is found that the crystal structure of the alloys exhibits transitions from the zinc-blende to the rock salt type and at last to the hexagonal cinnabar type.     

Lattice,electrical, and magnetic effects in lanthanum manganites La1−x Sr x MnO3 (x = 0.125, 0.150, 0.175)

The temperature dependences of the velocities of transverse and longitudinal hypersound in lanthanum strontium manganites of the composition La_1−x Sr _x MnO₃ (x = 0.125, 0.150, 0.175) have been measured at frequencies of 0.5–0.7 GHz. The structural phase transitions have been revealed, and their positions have been confirmed by data on the electrical resistance and magnetic measurements performed using the same samples. The results obtained have been analyzed in the framework of the model of competing Jahn-Teller distortions and magnetic ordering. The anomalies observed in the behavior of the velocities of longitudinal hypersound have been attributed to the local Jahn-Teller distortions, and their suppression due to the magnetic ordering has been considered a possible factor responsible for the colossal magnetoresistance.     

Oleylamine‐Assisted Phase‐Selective Synthesis of Cu2−xS Nanocrystals and the Mechanism of Phase Control

Environmentally friendly Cu_2?x S compounds exist in many different mixed phases in nature, while their nanoscale counterparts can be pure phase with interesting localized surface plasmon resonance properties. Because of the complexity of composition and phase, controllable synthesis of Cu_2?x S nanocrystals becomes an important scientific issue in colloidal chemistry. In this work, a hot‐injection method is developed to synthesize Cu_2?x S nanocrystals by injecting a sulfur precursor into a copper precursor using oleylamine and octadecene as solvents. By varying the reaction parameters (temperature, volume ratio of oleylamine/octadecene, molar ratio of Cu/S in the precursors), hexagonal CuS, monoclinic Cu_1.75S, and rhombohedral Cu_1.8S, nanocrystals can be selectively synthesized, providing a platform to illustrate the mechanism of crystal phase control. The crystal phase control of Cu_2?x S nanocrystals is oleylamine‐determined by controlling the molar ratio of Cu/S in the reaction precursors as well as the ratio of Cu_2?x S clusters/Cu⁺ in the subsequent reaction. More importantly, temperature plays an important role in varying the molar ratio of Cu/S and Cu_2?x S clusters/Cu⁺ in the reaction system, which significantly influences the crystal phase of the resulting Cu_2?x S nanocrystals. The understanding into crystal control provides a guideline to realize reproducible phase‐selective synthesis and obtain well‐defined high‐quality materials with precise control.     

Ab initio simulation of the influence of zirconium impurity ions on the atomic and electronic structure of BaTiO<Subscript>3</Subscript>

The influence of zirconium impurity ions on the atomic and electronic structure of cubic barium titanate is studied theoretically by the electronic density functional theory and pseudopotential theory. It is shown that Zr ions induce local distortions in the BaTiO₃ lattice, although neither zirconium nor titanium ions shift from their ideal positions, so that the structure of BaTi_{1 − x} Zr _x O₃ compounds remains cubic. The introduction of zirconium in an amount of 37.5 at % broadens the energy gap by 0.18 eV.     

Synthesis and high-resolution study distinguishing between very similar interstitial iron nitride structures

Angle-dispersive X-ray diffraction and microfluorescence together with precession electron diffraction (PED) and scanning electron microscopy measurements on iron nitride prepared at 15?GPa and 1800?K from iron and sodium azide starting materials reveal synthesis of both hexagonal P6₃22 and trigonal P312 Fe₃N_1+x modifications (a?=?4.745 (1) Å, c?=?4.403 (1) Å, Z?=?2). Nitrogen access to vacant interstitial sites, repulsions between nitrogen ions and metal nitride thermal stability are the factors relating iron nitride-phase relations to those of other early (Hf, Zr, Ti)-N and late (Ni-N) transition metal nitrides subjected to similar pressure and temperature conditions. Here, Fe₃N_1+x can accommodate pressure and x variability by situating nitrogen in a broader range of interstitial crystallographic sites in the intimately related hexagonal and trigonal crystal structures.     

The influence of local distortions on the static and dynamic properties of copper and silver eightfold-coordinated Jahn-Teller complexes in mixed crystals with a fluorite-type structure

The influence of local distortions on the structure and properties of copper and silver impurity Jahn-Teller complexes in mixed crystals, namely, Ca_xSr_1?x F₂: Me ²⁺ and Sr_1?x Ba_xF₂: Me ²⁺ (0≤x≤1, Me ²⁺=Cu²⁺ or Ag²⁺), is investigated using electron paramagnetic resonance (EPR) spectroscopy at frequencies of 9.3 and 37 GHz in the temperature range 4.2–250 K. Local distortions of the tensile and compressive types are induced by Ca²⁺, Sr²⁺, and Ba²⁺ impurity ions incorporated into the first or second coordination sphere of the cationic environment of the Me ²⁺ impurity ion during crystal growth.     

Features of the Percolation Scheme of Vibrational Spectrum Reconstruction in the Ga1 – xAl x P Alloy

Specific features of the properties of Ga–P lattice vibrations have been investigated using the percolation model of a mixed Ga_{1 – x}Al _x P crystal (alloy) with zero lattice mismatch between binary components of the alloy. In contrast to other two-mode alloy systems, in Ga_{1 – x}Al _x P a percolation splitting of δ ~ 13 cm^–1 is observed for the low-frequency mode of GaP-like vibrations. An additional GaP mode (one of the percolation doublet components) split from the fundamental mode is observed for the GaP-rich alloy, which coincides in frequency with the gap corresponding to the zero density of one-phonon states of the GaP crystal. The vibrational spectrum of impurity Al in the GaP crystal has been calculated using the theory of crystal lattice dynamics. Upon substitution of lighter Al for the Ga atom, the calculated spectrum includes, along with the local mode, a singularity near the gap with the zero density of phonon states of the GaP crystal, which coincides with the mode observed experimentally at a frequency of 378 cm^–1 in the Ga_{1 – x}Al _x P (x < 0.4) alloy.

     

Structural phase transitions in Cu2–x Te crystals (x = 0.00, 0.10, 0.15, 0.20, 0.25)

Structural phase transitions in Cu_2–x Te crystals have been investigated by high-temperature X-ray diffraction.

At room temperature Cu₂Te and Cu_1.90Te specimens are two-phased, i.e. they consist of an orthohombic phase with a = 7.319, b = 22.236, c = 36.458 Å and a hexagonal phase with a = 4.150, c = 7.188 Å. The changes in both compounds take place generally in the hexagonal phase with increasing temperature. At 821, 873 K they transform to a FCC phase. Monocrystals of the other compounds at room temperature crystallize in the hexagonal system and at 673, 773, 723 K, respectively, they transform to a FCC phase. It is determined that as the cation deficiency increases the crystal quality becomes better.     

Compositional and structural characterization of strained Si/Si x Ge1−x multilayers and interfaces by high-resolution transmission electron microscopy

A method is described for the quantitative characterization of strained Si/Si _x Ge_1–x multilayers and interfaces by high-resolution transmission electron microscopy (HRTEM) in [110] and [100] crystal projections. The method relies on systematic variations of the image contrast with variations of the local composition x for certain ranges of objective lens defocus f and specimen thickness t and takes tetragonal lattice distortions fully into account. From an extensive study of the image formation process for Si _x Ge_1–x alloys and coherent Si/Si _x Ge_1–x interfaces, ranges of f and t were identified by Bloch-wave and multi-slice image simulations at 400 keV for which a quasi-linear functional relationship between the composition x and the first-order Fourier coefficients of the image intensity exists. By application of a novel image-processing algorithm, which allows a precise measurement of image Fourier coefficients in geometrically distorted lattice images, local composition values x can be determined at near-atomic resolution with an accuracy of x ±0.1 and interface sharpness can be detected at the atomic level. Recent applications of the method to the characterization of interfaces of strained Si _x Ge_1–x layers and short-period Si _m Ge _n superlattices fabricated by different deposition techniques will be presented.     

Spatial topology of local nano scale inhomogeneity of crystal structure Zn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> = 0.001)

The method of thermal neutron diffraction is used to study a structural state of crystal Zn_{1 − x} Fe _x Se (x = 0.001) obtained in the sphalerite modification. It was found that the diffractive pictures of a cubic crystal contain the regions of diffuse scattering in the vicinity of Bragg reflections of an initial crystal lattice. It was shown that the diffuse scattering effects were caused by the local transverse displacements of atoms in a crystal lattice induced by Fe²⁺ ions. It is concluded that a static tetragonal-type Jahn-Teller effect exists in a ZnSe alloy doped by magnetoactive iron ions.     

Inhomogeneous lattice distortions in a Zn1 − x CrxSe crystal

The structure of a Zn_1?x Cr_xSe semiconductor crystal with x = 0.0029 was studied using thermal neutron diffraction. It was detected that the diffraction patterns of the crystal contain regions of diffuse scattering concentrated in the vicinity of the strong Bragg reflections. It was shown that the diffuse scattering was caused by transverse displacements of lattice atoms induced by chromium impurities, which undergo static tetragonal Jahn-Teller distortions in ZnSe.     

制备工艺对Zn1-xMgxO薄膜结构及光学性能的影响

采用脉冲激光沉积（PLD）方法在单晶Si（100）衬底上沿c轴方向生长单晶Zn_1-xMg_xO薄膜,通过X射线衍射（XRD）、原子力显微镜（AFM）、扫描电镜（SEM）和荧光光谱（PL）研究了膜厚、Mg含量、退火温度及氧气氛等制备工艺对Zn_1-xMg_xO薄膜的结构、形貌和光学性质的影响.实验结果表明,Mg含量x≤0.15时, Zn_{关键词： 1-x}Mg_xO薄膜')" href="#">Zn_1-xMg_xO薄膜 制备工艺 结构 光学性质     

Correlation of magnetic properties with the local features of the electronic and crystal structure in the Ce2Fe17 ? xMnx intermetallide: XAFS data analysis

The rearrangement of the local environment of cerium has been examined using extended X-ray absorption fine structure spectroscopy above the K-Ce absorption edge for various manganese contents and temperatures in Ce₂Fe_{17 − x} Mn _x intermetallics (x = 0, 1, 2). The valence state of cerium has been studied simultaneously by X-ray absorption near-edge structure spectroscopy above the L ₃-Ce absorption under the same conditions. A correlation has been revealed between the changes observed in the local electronic and crystal structure of Ce₂Fe_{17 − x} Mn _x compounds and the types of magnetic states in them.