Cationic transport mechanism in α-Ag<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>I(0 < <Emphasis Type="Italic">x</Emphasis> < 0.25): Molecular-dynamics simulation

The structural and transport characteristics of an Ag_{1 ? x} Cu _x I(0 < x < 0.25) solid solution have been simulated by the molecular-dynamics method. It is found that the cation diffusion coefficient decreases with increasing copper concentration; this correlation is in agreement with the experimentally observed decrease in ionic conductivity. It is shown that the cationic transport in disordered Ag_{1 ? x} Cu _x I phases is mainly due to the migration of silver cations, whereas the mobility of copper cations is much lower. Cu⁺ cations are found to reside in the 8c positions in a bcc cell; this finding suggests the existence of nanoscale α-CuI regions.     

Growth of ZnSe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solution crystals from vapor phase

Partially faceted ZnSe_{1 − x} S _x solid solution crystals have been grown from a vapor phase in a closed stationary horizontal system. The growth has been performed in cylindrical quartz ampoules—∼10 mm in diameter and evacuated to a residual pressure of less than ∼10⁻³ Pa-at a temperature of 1050°C and a temperature drop between the source and growth zones of 10–16°C. The crystal structure, optical absorption, and composition inhomogeneity along the ingot length have been investigated by X-ray diffractometry and optical spectroscopy in the wavelength range of 300–3000 nm. The solid-solution composition range corresponding to cubic polymorphs is determined. The concentration dependences of the lattice parameter and band gap are presented.     

Crystal nucleation of high-temperature Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> multiferroics in bismuth trimolybdate-borate fluxes

Crystallization of the orthorhombic phase of variable Fe _x Ga_{2 − x} O₃ composition in fluxes based on the Bi₂Mo₃O₁₂-B₂O₃ system with monitoring of the Néel temperature of this phase has been investigated. The data obtained are used to choose the flux composition for growing single crystals with Néel temperatures T _N > 0°C in order to investigate their properties as multiferroics. The method of group growth of single crystals on seeds and the regime of their subsequent heat treatment (which increases T _N) are described.     

Local symmetry breaking for negatively charged impurity centers in SrTi<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>

First-principles calculations of the geometry and electronic structure of the impurity center in SrTi_{1 − x} Mn _x O₃ have been performed. Neutral and negatively charged defects are considered. It is found that the doubly charged impurity center is polar; it has C _4v symmetry and electronic state ⁴ B ₁ with electron polaron localized at one of the neighboring titanium atoms. It is shown that this state is due to the spontaneous breaking of the defect local symmetry: O _h (⁴ A _1g ) → D _4h (⁴ B _1g ) → C _4ν(⁴ B ₁).     

Refinement of the composition and structure of YBaCo<Subscript>4−<Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>7+δ</Subscript> crystals

YBa(Co_{4 ? x} Al _x )O_{7 + δ} (114Y) crystals have been grown in the Y-Ba-Co-O system by spontaneous crystallization from a slowly cooled nonstoichiometric melt. To change the oxygen content, the crystals were isothermally annealed in air in the range of 280–490°C. The crystals grown were characterized by scanning electron microscopy and powder X-ray diffraction. According to the data of an X-ray spectroscopic quantitative microprobe analysis, the average compositions of “as-grown” and oxygen-saturated crystals were Y_1.04Ba₁Co_3.54Al_0.50O_7.8 and Y_1.02Ba₁Co_3.55Al_0.51O_8.4, respectively. The refinement of the crystal structure after saturation on an automatic Bruker X8APEX diffractometer with a CCD detector (MoKα radiation, graphite monochromator, θ_max = 32.54°, sp. gr. P6₃ mc, a = 6.2746(9), c = 10.257(3) Å, V = 349.71(13) ų, Z = 2, d _calcd = 5.220 g/cm³) reveals the location of Al in two independent positions of Co atoms and yields the general formula of the compound as YBaCo_3.26Al_0.74O₇. Problems related to the difference in the compositions obtained by different methods are discussed.     

Structure and magnetism of low-doped monoclinic crystals of (Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>Se<Subscript>3</Subscript>

The influence that doping with Mn³⁺ ions has on the fine crystal structure of the monoclinic compound Ga₂Se₃ was studied by single-crystal neutron diffraction and the measurements of magnetic properties. It was found that the structural state of the crystals changes even at relatively low doping levels (x = 0.04). Local Jahn-Teller distortions were shown to be responsible for the formation of the fine structure and magnetism in this type of compounds.     

X-ray imaging of structural defects in Si<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> single crystals using a white synchrotron beam

Nonmonochromatic (white) synchrotron radiation with a high spatial coherence makes it possible to use different types of interaction of X-rays with matter simultaneously: diffraction, refraction, absorption, and fluorescence. In this case, the structure of materials is studied by the real-time recording of high-resolution images of different types under the same conditions. The use of X-ray images for studying the structural quality is demonstrated by the example of Czochralski-grown Si_{1 −x} Ge _x single crystals. The effect that the germanium content has on the formation and evolution of the defect structure is analyzed and the relationship between the structure and properties is investigated. The experiments were performed on the Pohang Light Source (Pohang, Republic of Korea).     

Growth and dielectric properties of KTiOPO<Subscript>4</Subscript> and K<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Rb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiOPO<Subscript>4</Subscript> crystals

Methods of growth of KTiOPO₄ and K_{1 ? x} Rb _x TiOPO₄ crystals of high optical quality have been optimized. The dielectric properties (permittivity and conductivity) of the crystals grown have been investigated at frequencies from 10² to 10⁶ Hz in the temperature range from 100 to 350 K, along the [001] crystallographic direction. It is established that partial substitution of K⁺ ions with Rb⁺ ions leads to a decrease in the permittivity and conductivity.     

Study of the solid-state amorphization of (GaSb)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> semiconductors by real-time neutron diffraction and electron microscopy

The spontaneous amorphization of high-pressure quenched phases of the GaSb-Ge system has been studied by neutron diffraction while slowly heating the phases at atmospheric pressure. The sequence of changes in the structural parameters of the initial crystalline phase and the final amorphous phase is established. The behavior of the phases and the correlation in the structural features of the phase transitions and anomalous thermal effects exhibit signs of the inhomogeneous model of solid-state amorphization.     

Study of structural properties of In<Subscript>x</Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As/In<Subscript>y</Subscript>Al<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>As heterosystems on InP substrates

The structural properties of In_xGa_1?xAs/In_yAl_1?yAs samples on InP substrates are studied as functions of growth conditions by the method of high-resolution diffractometry. The results obtained and the photoluminescence spectroscopy data are used to optimize the technology of preparation of high-quality heterostructures with sharp interfaces. The parameters of the two-dimensional electron gas of such heterostructures measured at 77 and 300 K are comparable with the best world standards in this field, so these heterostructures may be used to manufacture transistors and integral amplifiers operating at the frequency 40 GHz and even higher.     

Behavior of ammonium ion in β-LiRb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(NH<Subscript>4</Subscript>)<Subscript>x</Subscript>SO<Subscript>4</Subscript> mixed crystals (0.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1.0)

The influence of replacement of an ammonium ion by rubidium on the x-T phase diagram in the concentration range 0.50 ≤ x ≤ 1.0 has been studied by X-ray and neutron powder diffraction over a wide temperature range. It is shown that a decrease in the ammonium concentration is accompanied by an increase in the temperature of the II ? I phase transition and stabilization of phase II up to low temperatures (20 K). The changes occurring in the dynamics of mixed crystals are studied by inelastic incoherent neutron scattering. The spectra of the generalized vibrational density of states obtained allowed one to establish the difference in the phonon modes corresponding to phase III of β-LiNH₄SO₄ and phase II of β-LiRb_1?x(NH₄)_xSO₄ mixed crystal with x = 0.91 and x = 0.77 at 20 K. It is shown that a mixed crystal with x = 0.77 at 20 K is in the orientational glass state.     

Growth of ultrathin twin-free <Emphasis Type="Italic">b</Emphasis>-oriented YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7 – <Emphasis Type="Italic">x</Emphasis></Subscript> films

Twin-free b-oriented YBa₂Cu₃O_{7 – x} films with a thickness less than 40 nm have been epitaxially grown on (100)SrLaGaO₄ crystals. Based on the temperature dependence of resistance, the onset temperature of the transition to the superconducting state is found to be 90 K; the transition width is 4 K. The film growth has been performed in two stages. A (100)PrBa₂Cu₃O_{7 – x} buffer layer was previously grown on a (100)SrLaGaO₄ substrate by rf magnetron sputtering in an Ar–O₂ gas mixture at a continuous and monotonic increase in temperature from 660 to 830°C. The main YBa₂Cu₃O_{7 – x} film was grown on the buffer layer surface by pulsed laser deposition in an oxygen medium at a fixed temperature (800°C). The above processes were implemented in different chambers, which were connected by a vacuum channel for transporting samples. Both films were grown in situ, without contacting atmosphere in all growth stages. An X-ray diffraction study has shown that the YBa₂Cu₃O_{7 – x} films are single-crystal and free of precipitates of other phases and domains of other orientations.     

Solid-state Spectroscopic and Structural Investigation of <Emphasis Type="Italic">cis</Emphasis>-(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>Au(<Emphasis Type="Italic">O</Emphasis>,<Emphasis Type="Italic">O</Emphasis>′-acac)

Abstract  The structure of cis-(CH₃)₂Au(O,O′-acac) was investigated by single-crystal X-ray diffraction. It crystallizes in the orthorhombic space group Cmca with unit cell dimensions a = 6.7831(13) ?, b = 15.080(3) ?, c = 18.073(3) ? and α = β = γ = 90°. The molecule is planar but lacks a C₂ axis in the solid-state, with two Au–C bond lengths that differ by 0.078(21) ? due to crystal packing effects. The inequivalence of the crystallographic carbon positions is evident in the solid-state ¹³C CP-MAS NMR spectrum, which was recorded at low temperature due to the thermal sensitivity of the compound during magic-angle spinning. Head-to-tail stacking, which creates short intermolecular paths, was reproduced computationally in a dimer model. Graphical Abstract   Solid-state Spectroscopic and Structural Investigation of cis -(CH ₃ ) _Au 2 ( O , O ′-acac) Miyako Hisamoto • Swarup Chattopadhyay • Juergen Eckert • Guang Wu • Susannah L. Scott In the solid state, cis-(CH₃)₂Au(O,O′-acac) has no C₂ axis, two different Au–C bond lengths (1.960, 2.038 ?; Δd = 0.078(21) ?) and a close Au–C…C–Au contact; these features give rise to additional features in the ¹³C CP-MAS NMR spectrum.     

Structural and magnetic phase transformations in La<Subscript>0.88</Subscript>MnO<Subscript>3 − <Emphasis Type="Italic">x</Emphasis></Subscript> crystals

The crystal structure and elastic, magnetic, and transport properties of the La_0.88MnO_{3 ? x} system are studied. It is established that, depending on the oxygen content at x > 0.13, the system is orbitally ordered by the LaMnO₃ type and consists of a mixture of orbitally ordered and disordered orthorhombic phases (0.11 ≤ x ≤ 0.13); at x < 0.11, the system is monoclinically distorted. The orbitally ordered samples show properties inherent in both antiferro-and ferromagnetics, whereas the orbitally disordered samples are ferromagnetics and possess extremely high magnetic resistance. Analysis of the structure and properties of the samples showed that no oxygen vacancies are formed in the La_0.88MnO_{3 ? x} system. It is assumed that the excessive Mn³⁺ is incorporated into interstitials in the vicinity of lanthanum vacancies.     

Synthesis and Crystal Structure of Bis (<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′,<Emphasis Type="Italic">N</Emphasis>′-tetramethylethylendiammonium) Octaiodo Pentachloroantimonate (III)

Abstract  

The synthesis and Crystal structure are given for the bis (N,N,N′,N′-tetramethylethylendiammonium) octaiodo pentachloroantimonate (III) salt. An X-ray investigation has shown that the title compound crystallizes in a monoclinic system, space group P2₁/m with the following lattice parameters a = 9.786(2) Ǻ, b = 14.024(5) Ǻ, c = 14.336(3) Ǻ, β = 91.35(2)° and Z = 2. The structure was solved from 3085 independent reflections with R ₁ = 0.0402 and wR ₂ = 0.0952 and refined with 152 parameters. The structure shows a layer arrangement perpendicular to the [(b)\vec] \vec{b} -axis: planes of [SbCl₅]²⁻, I₃ ⁻ and I₅ ⁻ anions alternate with planes of [(CH₂)₂(NH(CH₃)₂)₂]²⁺ cations. The [SbCl₅]²⁻ square pyramids present an active lone electron pair (LEP) on the Sb atoms and they are interconnected by means of N–H···Cl hydrogen bond originating from [(CH₂)₂(NH(CH₃)₂)₂]²⁺ entities. The polyiodides (I₃ ⁻ and I₅ ⁻) anions form a planer zigzag polymeric chains via I···I linking interactions. These chains are linked to the [SbCl₅]²⁻ anions by a long range contact.     

Molecular Dynamics Simulation of the Structure and Ion Transport in the Ce<Subscript>1 – <Emphasis Type="Italic">x</Emphasis></Subscript>Gd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2 – δ</Subscript>|YSZ Heterosystem

Molecular dynamics simulation has been used to develop a realistic atomistic model of two-layer Ce_{1 – x}Gd _x O_{2 – δ}|YSZ heterosystem. It is shown that Ce_{1 – x}Gd _x O_{2 – δ} and YSZ layers (about 15 and 16 Å thick, respectively) retain their crystal structure on the whole. The main structural distortions are found to occur near the Ce_{1 – x}Gd _x O_{2 – δ}|YSZ geometric interface, within a narrow interfacial region of few angstroms thick. Both the generalized diffusion characteristics of the system as a whole and the oxygen diffusion coefficients in the layers are calculated, and the diffusion activation energies are determined.     

Crystal structure of Сu<Subscript>2–<Emphasis Type="Italic">m</Emphasis></Subscript>Te (<Emphasis Type="Italic">m</Emphasis> = 0.25)

The Сu₂Te compound has been synthesized by alloying Сu and Te taken in stoichiometric ratios. A Сu₂Te sample has been homogenized by annealing at 773 K for 100 h. A pure copper phase in the form of thin filaments is found to segregate from the synthesized product (4 g) by the end of annealing. It is established by X-ray diffraction analysis that the copper-deficient sample is crystallized into the trigonal system with lattice parameters а = 8.328(1) Å, с = 7.196(1) Å, V = 432.2(1) ų, sp. gr. \(P\overline 3 m1\), Z = 8. The crystal structure is determined and the sample composition Сu_2–m Te (m = 0.25) is refined by the Rietveld method. The three independent copper atoms in the lattice are found to have different coordination numbers: 3, 4, and 5.     

Boundary conditions for the formation of a ferromagnetic phase during the deposition of Ti<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2-δ</Subscript> thin films

The conditions and the mechanism of the formation of a ferromagnetic phase in a Ti_1-xCo _x O_2-δ oxide semiconductor are studied. It is found that the ferromagnetism manifests itself at room temperature in the films of Co-doped TiO_2-δ oxide deposited on SrTiO₃ (100) substrates only within a limited range of charge carrier densities: 2 × 10¹⁸?3 × 10²² cm^?3. The minimum concentration of charge carriers corresponding to the formation of the ferromagnetic phase increases with a decrease in the cobalt content in the material under study. The ferromagnetism in Ti_1-xCo _x O_2-δ thin films can be attributed to Co-enriched clusters with above critical sizes.     

Investigation of the possibility of obtaining homogeneous Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>In<Subscript>x</Subscript>Sb crystals under weak flow conditions

The possibility of growing macrohomogeneous Ga_{1 ? x}In_xSb crystals with x = 0.2 was studied using the axial heating process close to the melt/crystal interface. The grown ingots were analyzed by a JSM-5300 scanning electron microscope and the experimental results were compared with the results of numerical simulation. It was shown that, as a whole, the mathematical model adequately describes the processes of the steady-state heat and mass transfer. It was found that, at the crystallization of Ga_{1 ? x}In_xSb by the axial heating process under conditions of weak laminar flows, longitudinal homogeneity is observed when a dead zone is formed in the melt and that the crystallization regime is similar to diffusion. It was shown that the composition of the grown crystals strongly depends on the structure of a melt flow and its dynamics.     

Crystal and molecular structures of [Co(<Emphasis Type="Italic">D</Emphasis>H)(<Emphasis Type="Italic">o-phen</Emphasis>)<Subscript>2</Subscript>][BF<Subscript>4</Subscript>]<Subscript>2</Subscript> · 2H<Subscript>2</Subscript>O

The crystal structure of a new mixed-ligand complex [Co(DH)(o-phen)₂][BF₄]₂ · 2H₂O is determined by X-ray diffraction. The crystal is monoclinic, a = 12.2081(11) Å, b = 14.3474(9) Å, c = 17.7393(16) Å, β = 104.95(1)°, and space group P2₁/c. The coordination octahedron of Co³⁺ is formed by two nitrogen atoms of the dimethylglyoxime molecule and four nitrogen atoms of o-phenanthroline molecules. The dimethylglyoxime molecule is singly deprotonated and acts as DH^?. The mean Co-N distances for dioxime and o-phenanthroline are 1.911 and 1.964 Å, respectively. The key role in the formation of the crystal structure is played by [BF₄]^? outer-sphere anions and crystallization water molecules, which form an extended hydrogen-bond system.