A Modal of Twin Domains in YBa2(Cu1?xCox)3Oy

The existence of twin domains in YBa₂(Cu_1–x Co _x )₃O _y samples was confirmed by many experiments. However, the physical picture of the twin domains has not been reported up to now. By analyzing oxygen content, Cu and Co valences, and Co coordination in those samples, we propose a domain model, which consists of two pairs of parallel zigzag Co-O chains surrounding orthorhombic cells, one along (110) direction and the other along (110) direction. The zigzag Co-O chains are the twin walls, with neighboring walls perpendicular and the opposite ones parallel. The distance between parallel walls (i.e., zigzag Co-O chains) depends upon Co concentration of sample. The twin domain model predicts the geometry, size, and absence of systematic symmetry of the domains. The model also predicts the modulation periodicity of electron diffraction patterns, which depends on Co concentration. All the predictions by the model agree well with the experimental results reported in literatures. Furthermore, the model indicates the possible existence of two domains, which have incommensurable modulation periodicity.     

Synthesis, Structure, and Superconductivity of (La1.5Pb0.5?xSrx)CuOz

The substitution of strontium for lead in the material (La_1.5Pb_0.5–x Sr _x )CuO _z , x = 0–0.15 has been carried out. A stable and reproducible single phased superconducting materials can be obtained inside an evacuated quartz tube. The X-ray diffraction pattern shows that the superconducting phase can be indexed on the basis of an orthorhombic symmetry (F _mmm) for x = 0 and on the basis of tetragonal symmetry (I _4/mmm) for x > 0. The transition temperature T _c increases as the strontium substitution parameter x increases. We observed the maximal T _c around x = 0.15 with 38 K with fairly large Meissner volume fraction of 38% (FC).     

(2?x)MgO · x(MnO, FeO) · 2Al2O3 · 5SiO2 (x = 0–2) ceramic materials and heat effects of their formation

We have determined the main characteristics of ceramic materials prepared by modifying 2MgO · 2Al₂O₃ · 5SiO₂ with MnO and FeO. The formation of the ceramics was analyzed by detailed thermal analysis, X-ray diffraction, IR spectroscopy, and differential scanning calorimetry. We have determined the heat effects of formation of Mg_{1 − x} M _x Al₂O₄ (0.25 < x < 0.75) and Mg_{2 − y} M _y Al₄Si₅O₁₈ (0.5 < y < 1.5) solid solutions with M = Mn(II) and Fe(II) and calculated the standard heats of formation of the Mg_{1 − x} M _x Al₂O₄ and Mg_{2 − y} M _y Al₄Si₅O₁₈ solid solutions.     

Structure and Diamagnetic Properties of (Pb0.6SnyCu0.4 ? y)Sr2(Y1 ? xCax)Cu2Oz

The effect of Sn doping in (Pb_0.6Sn _y Cu_{0.4 – y} )Sr₂(Y_{1 – x} Ca _x )Cu₂O _z with 0 y 0.3 and 0 x 0.7 was investigated. It was established that a nearly pure 1212 phase can be obtained at 0 y 0.1 and 0 x 0.3. The obtained XRD patterns as well as the results of the EDX and ICP-AES analyses showed that Sn substitution is possible in the (Pb,Cu)-1212 phase. Superconductivity was observed at 0.4 x 0.7. The onset of the diamagnetic transitions varied from 10 to 30 K. The influence of the strong Pb deficiency on the superconducting properties of the samples was discussed.     

Oxygen Configuration in the Superconductor (Hg0.7Mo0.3)Sr2(Ca1?xRx)Cu2Oz (R = Nd and Pr)

Two series of Hg-based oxides (Hg_0.7Mo_0.3)Sr₂(Ca_1–x R _x )Cu₂O _z (R = Nd and Pr, 0.2 x 0.7) have been synthesized. Electrical-resistivity measurements show that these compounds are superconductors with maximum onset T _c of 107 and 102 K for Nd- and Pr-containing samples, respectively. The neutron powder diffraction experiments on both as-prepared and O₂-annealed samples of R = Nd revealed that the O(3) site at the HgO sheets are fully occupied and shifted towards the Hg/Mo site to form Mo–O bonds.     

Electrical conductivity and thermal stability of (1 ? x )CsH2PO4/ x SiP y O z ( x = 0.2–0.7) composites

The physicochemical properties of (1 − x)CsH₂PO₄/xSiP _y O _z (x = 0.2–0.7) composites containing fine-particle silicon phosphates as heterogeneous additives have been studied at different humidities. The introduction of silicon phosphates suppresses the superionic phase transition of CsH₂PO₄ and increases the low-temperature conductivity of the materials, which depends significantly on humidity. The CsH₂PO₄-SiP _y O _z materials offer high conductivity (∼3 × 10⁻³ to 10⁻² S/cm at ∼110–230°C) at low water vapor pressures (3 mol % H₂O). Amorphization of the CsH₂PO₄ in the composites markedly changes its thermodynamic properties. The effect of long-term isothermal holding (210°C, 3 mol % H₂O) on the conductivity of the composites has been studied. Original Russian Text ? V.G. Ponomareva, E.S. Shutova, G.V. Lavrova, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 9, pp. 1131–1136.     

Excitation of transitions of singly charged ytterbium ions terminating on levels 4 f 13(2 F °7/2)5 d 6 s (3 D ) 3[ L 2]°

The excitation of transitions of singly charged ytterbium ions terminating on odd levels 4f ¹³(² F°_7/2)5d6s(³ D) ³[L ₂]° is experimentally studied. The generation of excited ytterbium ions occurs as the process of simultaneous excitation and ionization under single electron-atom collisions. Eighty five excitation cross sections are measured at an electron energy of 50 eV. Fifteen optical excitation functions are recorded with the energy of exciting electrons varying from zero to 200 eV. Original Russian Text ? Yu.M. Smirnov, 2008, published in Teplofizika Vysokikh Temperatur, Vol. 46, No. 2, 2008, pp. 197–205.     

Solid-phase extractant with dipicolinic acid N,N’-diethyl-N,N’-di(p-tolyl)diamide for preconcentration and separation of actinides and lanthanides

The sorption ability of a solid-phase extractant with dipicolinic acid N,N’-diethyl-N,N’-di(p-tolyl) diamide groups on fibrous polyacrylonitrile (PAN) matrix was studied. The conditions for immobilization of the reagent on PAN disks were determined, and the possibility of sorption preconcentration and separation of U(VI), Pu(IV), Am(III), and Eu(III) from 2–6 M HNO₃ solutions was examined. The solid-phase extractant obtained exhibits good kinetic properties and can be used for separation of Am(III) + EU(III).     

Neutron Structural Studies of the Superconducting (Nd1?yCay)Ba2(Cu0.94Ga0.06)3Oz System

We investigate the influence of Ca ions on the structural and superconducting properties of (Nd_1–y Cay)Ba₂(Cu_0.94Ga_0.06)₃O _z system by Rietveld refinement of the neutron diffraction patterns of three samples with y = 0.0 (A₁), y = 0.18 (A₂), and y = 0.36 (A₃) along with X-ray diffraction, resistivity, and ac susceptibility measurements. Samples A₂ and A₃ are superconducting with T _c values of 37 K and 76 K, respectively, whereas sample A₁ is semiconducting to 20 K. Neutron diffraction data confirms (a) the occurrence of a single-phase tetragonal structure (space group Pmmm) for all three samples; (b) Ca ions substitute at the Nd site; and (c) increasing y from 0.0 to 0.36 decreases Cu(1)-O(1), Cu(2)-O(2), and Nd-Cu(2) bond lengths, whereas Cu(2)-O(4) bond length increases with corresponding increase in T _c to 76 K due to increasing occupancy of Ca ions at Nd site. A correlation exists between the Cu(1)-O(1), Cu(2)-O(2), Cu(2)-O(4), and Nd-Cu(2) bond lengths and the measured T _c values of three samples.     

Effect of the frequency and temperature on the complex impedance spectroscopy (C–V and G–V) of p-ZnGa2Se4/n-Si nanostructure heterojunction diode

X-ray diffraction pattern and AFM results confirm the nanostructure of p-ZnGa₂Se₄/n-Si. The unit cell lattice parameters, the crystallite size L, the dislocation density δ, and the main internal strain ε were calculated. The temperature and frequency-dependent electrical characteristics of the Al/p-ZnGa₂Se₄/n-Si/Al heterojunction diode (HJD) have been investigated to determine the interface states which are responsible for the non-ideal behavior of the characteristics of the diode. The capacitance–voltage (C–V), conductance–voltage (G–V), and series resistance–voltage (R _s–V) characteristics of the diode have been analyzed in the frequency range of 5 kHz–1 MHz and temperature range of 303–423 K. The interfaces states of the diode were determined using conductance–voltage technique. The interface state density profile for the diode was obtained as a function of temperature and frequency. The values of the built-in potential V _bi, the doping concentration N _d and the barrier height φ _b(C–V) of the diode were calculated at different temperatures and frequencies. Our experimental results revealed that both the series resistance and interface state density values must be taken into account in studying the impedance spectroscopy of HJD to stand up their performance for electronic applications characteristics.     

Structural and superconducting properties of single-crystal Bi2Sr2Can ? 1CunO2n + 4 + δ (n = 1–3) whiskers grown in gas-filled cavities

Using growth inside gas-filled cavities in KCl-fluxed melts, we have obtained free-standing phasepure Bi₂Sr₂Ca _{n − 1}Cu _n O_{2n + 4 + δ} (n = 1–3) whiskers possessing superconducting properties in the as-grown state. Bi-2212 whiskers have been prepared in a wide range of doping levels, from underdoped (T _c = 76.5 K) to optimally doped (T _c = 84 K). The whiskers possess high structural perfection, as shown by X-ray diffraction. Annealing under optimal conditions raises the superconducting transition temperature of the underdoped Bi-2212 whiskers to T _{c max} = 85.5 K (ΔT _c = 1.8 K), without impairing their structural perfection. Original Russian Text ? M.V. Golubkov, Yu.I. Gorina, G.A. Kalyuzhnaya, V.V. Rodin, N.N. Sentyurina, V.A. Stepanov, S.G. Chernook, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 6, pp. 731–737.     

FTIR Spectra of the M(EDTA)n? Complexes in the Process of Sol-Gel Technique

Sol-gel is one of the effective techniques for preparing YBa₂Cu₃O_{7 –} (YBCO) coatings at relatively low cost. Its process from gel to oxide coatings, however, was not yet fully understood. This is one of the obstacles for achieving YBCO coatings with good superconducting properties. In this paper, we chose EDTA as the complexant to prepare gels with different kinds of M(EDTA)^n– complexes, where M is any combination of Y, Ba, and Cu cations, in order to investigate the decomposition process of the gels with the help of Fourier transform infrared (FTIR) spectra. Comparing the FTIR spectra of the gel powders with those of the calcined powders, we found that the decomposed temperatures were different for different M(EDTA)^n– complexes. We considered this was the cause of the Ba segregation (as BaCO₃) in the coatings at low heating temperature, which in turn blocked the formation of high quality YBa₂Cu₃O_7–.     

LiNi1 ? x ? yCoxMnyO2 (x = y = 0.1, 0.2, 0.33) cathode materials prepared using mechanical activation: Structure, state of ions, and electrochemical performance

We have investigated LiNi_{1 − x − y} Co _x Mn _y O₂ (x = y = 0.1, 0.2, 0.33) cathode materials synthesized from mechanically activated mixtures of lithium hydroxide and nickel cobalt manganese hydroxide. The materials have a layered structure (sp. gr. ). Their unit-cell volume and the degree of disordering in their structure decrease with decreasing nickel content. According to x-ray photoelectron spectroscopy data, the major states of the transition-metal ions in the surface layer of the materials are Ni²⁺, Co³⁺, and Mn⁴⁺. With increasing nickel content, the Ni 2p _3/2 and Co 2p _3/2 binding energies increase, attesting to changes in M-O bond covalence. The highest specific electrochemical capacity, ∼170 mA h/g, is offered by LiNi_0.6Co_0.2Mn_0.2O₂. The position of redox peaks in the differential capacity curves of the three materials depends on composition: with increasing nickel content, the peaks shift to lower voltages. Original Russian Text ? N.V. Kosova, E.T. Devyatkina, V.V. Kaichev, 2007, published in Neorganicheskie Materialy, 2007, Vol. 43, No. 2, pp. 227–235.     

Systematic investigation of electronic structure in BEDT-TTF based organic superconductors withTc above 10 K; κ-(BEDT-TTF)2X (X=Cu(NCS)2, Cu[N(CN)2]Br, and Cu(CN)[N(CN)2])

The electronic structure of the title superconductors has been investigated by electrical resistivity, complex susceptibility, and electron paramagnetic resonance (EPR) measurements. The superconducting properties (pressure dependence ofT _c , magnetic penetration depth, upper critical field, and so on) of these three salts are similar to each other, while transport properties in the normal state have shown a large variety in the temperature dependence. In order to clarify the electronic structure in the normal state, the EPR parameters, the spin susceptibility ( _spin), and the linewidth (H _pp), are compared. An anomalous temperature dependence of theg-value has been observed below 150 K in the Cu(NCS)₂ and Cu(CN)[N(CN)₂] salts.     

Density functional study of structural and electronic properties of GaPn (2?≤?n?≤?12) clusters

Low-lying equilibrium geometric structures of GaP _n (n = 2–12) clusters obtained by an all-electron linear combination of atomic orbital approach, within spin-polarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied within the local spin density approximation (LSDA) and the three-parameter hybrid generalized gradient approximation (GGA) due to Becke–Lee–Yang–Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static dipole polarizabilities are calculated for the ground-state structures within the GGA. It is observed that the gallium atoms of the symmetric ground-state structures prefer to occupy the peripheral positions. It is found that the relative ordering of the isomers is influenced by the nonlocal exchange-correlation effects for small clusters. Generalized gradient approximation extends bond lengths and widens the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), as compared to the LSDA gap. The odd–even oscillations in the dissociation energy, the second differences in energy, the HOMO–LUMO gaps, the ionization potential, the electron affinity, and the hardness are more pronounced within the GGA. The stability analysis based on the energies clearly shows the GaP₅ and GaP₇ clusters to be endowed with special stabilities.     

Study of the electron structure of Mn, Sr, La, Ce, and Sm cations in Ln1 ? x Sr x MnO3 (Ln = La, Ce, Sm) manganites by the X-ray line shift method

The X-RayK _α line shifts of all cations in Ln_{1 − x} Sr _x MnO₃ (Ln = La, Ce, Sm) manganites have been measured using crystal diffraction spectrometers. The Mn K _αline shifts have been found in the Sm_{1 − x} Sr _x MnO₃ system correspond to an increase in the valence from Mn³⁺ to Mn⁴⁺. In the Ce_{1 − x} Sr _x MnO₃ system, in addition to this, the valence of cerium have been found also increases to almost 4. It is shown that the dependence of the valence of manganese on the content of strontium does not correspond to a simple model of the local mixture of Mn³⁺ and Mn⁴⁺ ions, which is usually applied to these systems. It is also demonstrated that the bonds of Sr, La, and Sm in the manganites studied exhibit a significant covalent character. In cation-deficient Sm_{1 − y} Mn_{1 − z} O₃, an increase in the valence of Mn is found accompanied by a decrease in the covalence of Sm.     

Frequency effect on the electrical and dielectric properties of (TlGaS2) 1 ? x(TlInSe2)x (x = 0.005, 0.02) single crystals

The electrical properties (loss tangent (tanδ), real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity, and ac conductivity across the layers (σ_ac)) of (TlGaS₂)_{1 − x} (TlInSe₂) _x (x = 0.005, 0.02) layered single crystals have been studied in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. Almost throughout the frequency range studied, their ac conductivity follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level. The Fermi-level density of states (N _F ), the spread of their energies, the mean hop time τ and distance R, and the concentration of deep traps determining the ac conductivity of the crystals (N _t ) have been estimated. With increasing x in (TlGaS₂)_{1 − x} (TlInSe₂) _x , N _F and N _t increase, while τ and R decrease.     

Effects of additional elements (M) on the thermal stability and structure of (Zr52.2Cu39.1Al8.7)100?xMx (M?=?Ag, Be, Gd, x?=?8, 7, 2) amorphous alloys

The effects of Ag (8 at.%), Be (7 at.%), and Gd (2 at.%) addition on structure and thermal stability, as well as bulk glass forming ability, in (Zr_52.2Cu_39.1Al_8.7)_100−x M _x (M = Ag, Be, Gd) alloys are investigated by means of X-ray diffraction and differential scanning calorimetry. The alloy containing Ag and Be have a critical diameter of more than 10 mm, with larger supercooled liquid region and atomic packing efficiency than Zr_52.2Cu_39.1Al_8.7 alloy, while the (Zr_52.2Cu_39.1Al_8.7)₉₈Gd₂ alloy only has a critical diameter of up to 5 mm and shows smaller supercooled liquid region and atomic packing density. CuZr is the main competing crystal phase with amorphous phase in the present Zr-Cu-based alloys. Ag and Be atoms in Zr_52.2Cu_39.1Al_8.7 alloy decrease the long range diffusion of Cu atoms and hinder the crystallization process under rapid solidification conditions. As a result, the glass forming ability of (Zr_52.2Cu_39.1Al_8.7)₉₂Ag₈ and (Zr_52.2Cu_39.1Al_8.7)₉₃Be₇ alloys are effectively enhanced.     

Impact of Silver Addition on Room Temperature Magneto-Resistance in La0.7Ba0.3MnO3 (LBMO): Ag x ?( x =0.0,?0.1, 0.2, 0.3, 0.4)

La_0.7Ba_0.3MnO₃ (LBMO): Ag _x (x=0.0, 0.1, 0.2, 0.3, and 0.4) composites are synthesized by a solid-state reaction route, the final sintering temperatures are varied from 1300 °C (LBMO1300Ag) to 1400 °C (LBMO1400Ag), and their physical properties are compared as a function of temperature and Ag content. All samples are crystallized in single phase accompanied by some distortion in main structural phase peaks at higher angles with an increase in silver content. Though the lattice parameters (a,c) decrease, the b increases slightly with an increase in Ag content. The scanning electron micrographs (SEM) showed better grains morphology in terms of size and diffusion of grain boundaries with an increase in Ag content. In both LBMO1300Ag and LBMO1400Ag series, the metal insulator transition (T ^MI) and accompanied paramagnetic-ferromagnetic transition (T _C) temperatures are decreased with an increase in Ag content. The sharpness of MI transition, defined by temperature coefficient of resistance (TCR), is improved for Ag added samples. At a particular content of Ag(0.3), the T ^MI and T _C are tuned to 300 K and maximum magneto-resistance at 7 Tesla applied field (MR^{7 T}) of up to 55% is achieved at this temperature, which is more than double to that as observed for pure samples of the both 1300 and 1400 °C series at same temperature. The MR^{7 T} is further increased to above 60% for LBMOAg(0.4) samples, but is at 270 K. The MR^{7 T} is measured at varying temperatures of 5, 100, 200, 300, and 400 K in varying fields from ±7 Tesla, which exhibits U and V type shapes. Summarily, the addition of Ag in LBMO improves significantly the morphology of the grains and results in better physical properties of the parent manganite system.     

The electrochemical properties of MgNi–x?wt% TiNi0.56Co0.44 (x?=?0, 10, 30, 50) composite alloys

The effect of ball milling time and different content of the TiNi_0.56Co_0.44 alloy on the structure and electrochemical properties of MgNi–x wt% TiNi_0.56Co_0.44 (x = 0, 10, 30, 50) alloys were studied systematically. The results indicated that the cycle durability of the alloy was improved with addition of the TiNi_0.56Co_0.44 alloy. By cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis, it was shown that the introduction of the TiNi_0.56Co_0.44 alloy could significantly improve the catalytic activity of the electrode, decrease the charge-transfer reaction resistance and the diffusion impedance of H atoms. Potentiodynamic polarization curves revealed that anti-corrosion performance of the composite electrodes was enhanced, which was responsible for the ameliorative cycle stability of composite alloys. A high discharge capacity and good cycle stability had been observed for the x = 10 (10 h) composite electrode with a maximum discharge capacity of 397 mAh/g and capacity retaining rate (S ₅₀) of 62%.