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.     

Effect of heat treatment in sulfur and mercury vapors on the magnetic susceptibility of Hg1 ? x Mn x Te1 ? y S y crystals

We have studied the effect of heat treatment in mercury and sulfur vapors on the magnetic susceptibility of Hg_{1 − x} Mn _x Te_{1 − y} S _y crystals. Measurements were performed by the Faraday method in the temperature range 77–300 K at H= 318 kA/m before and after heat treatments. The results demonstrate that the behavior of the magnetic susceptibility can be understood in terms of Mn-S-Mn-S, Mn-Te-Mn-Te, and (mixed) Mn-Te-Mn-S clusters of different sizes with indirect antiferromagnetic exchange interaction between the Mn atoms through the chalcogen atoms. Heat treatment in sulfur and mercury vapors leads to the formation of new clusters or changes (increases or decreases) the size of already existing clusters. Original Russian Text ? P.D. Maryanchuk, E.V. Maistruk, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 5, pp. 549–554.     

(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.     

Effect of cobalt substitution on magnetic and transport properties of Nd0·5Sr0·5Mn1?xCoxO3 (x = 0·1, 0·3 and 0·5)

The magnetic and transport properties of the compounds Nd_0·5Sr_0·5Mn_1-x_{{\rm 1}-{x}}Co_x_{{x}}O₃ (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn^3 +–O^2 −–Mn^4 + as compared to Co^3 +–O^2 −–Co^4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile e_g{e}_{\rm g} electrons).     

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.     

Phase composition and structure of La1 ? x Ca x MnO3 + δ (0 ≤ x ≤ 0.2) solid solutions

A structural phase diagram of La_{1 − x} Ca _x MnO_{3 + δ} (0 ≤ x ≤ 0.2) solid solution in air has been constructed for the first time, and the equilibrium T-x fields of the monoclinic, orthorhombic, and rhombohedral phases in this system have been outlined. The transitions between these phases are accompanied by sharp changes in lattice parameters, suggesting that they are first-order. Original Russian Text ? S.Kh. Estemirova, A.M. Yankin, S.G. Titova, V.F. Balakirev, Yu.E. Turkhan, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 11, pp. 1387–1392.     

Structure of Sr1 ? xPbxFeO3 ? δ (0 < x < 0.5) perovskite-like materials

We have synthesized Sr_{1 − x} Pb _x FeO_{3 − δ} (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.5) perovskite-like materials and studied their structure by X-ray diffraction, M?ssbauer spectroscopy, and electron microscopy. According to the X-ray diffraction data, the Pb solubility limit in the perovskite structure is x ≈ 0.15. The materials with x = 0.05 and 0.1 contained Pb_1.33Sr_0.67Fe₂O₅ inclusions 10–30 nm in size. Using chronopotentiometry and temperature-programmed desorption, we have estimated oxygen mobility in the materials with x = 0.05 and 0.1. The results demonstrate that Pb doping increases oxygen mobility in the strontium-ferrite-based materials.     

The effect of Sm substitution on properties of Bi1.6Pb0.4Sr2Ca2? x Sm x Cu3O y superconductors

The effect of the partial substitution of Ca by Sm in the Bi-2223 superconducting samples have been investigated in terms of X-ray diffraction (XRD), EDXRF (Energy Dispersive X-ray Fluorescent), magnetoresistivity, critical temperature, transport critical current density, and ac susceptibility measurements. The samples were prepared by the conventional solid-state reaction method. XRD patterns are used to calculate lattice parameters and phase ratio of the Bi-2223 samples. The volume fraction was determined from the intensities of Bi-2223 and Bi-2212 peaks. The room temperature XRD patterns of the samples showed the presence of Bi-2223 phase decreases with increasing the Sm content. We estimated the transition temperature of the samples from the resistivity versus temperature measurements in dc magnetic fields up to 0.6 T. We observed that transition temperature, T _c , and transport critical current density, , depend on the Sm substitution. They both decrease with increasing the Sm substitution. We extracted the peak temperature, T _p , and the pinning force density from our previous ac susceptibility measurements. The pinning force density decreased with increasing the Sm content. The possible reasons for the observed decreases in critical temperature and critical current density due to Sm substitution were discussed.     

Normal state and superconductivity of ErBa2(Cu1?xCrx)O7?δ(x=0–0.1)

The effects of Cr in ErBa₂(Cu_1–x Cr _x )O_7– (x=0–0.1) superconductor have been investigated. The critical temperature, which was determined by DC electrical resistance measurements, showed no suppression of the onset temperature (T _{c onset}) within the substitution range. The transition width (T _c ) broadened as the Cr content is increased. The normal state changes from the metal-like to semimetal/semiconductor-like for x0.03. Micrographs from the scanning electron microscope, X-ray diffraction pattern, and energy dispersive X-ray analysis results are used to describe the superconducting properties of these materials. The orthorhombic structure was preserved throughout the substitution range. Some possible roles of Cr in the system are discussed.     

Electrical conductivity and dielectric permittivity of Bi5Nb3 ? 3 x M3 x O15 ? δ (M = Cr, Cu, Ni) solid solutions

Bi₅Nb_{3 − 3x} M_3x O_{15 − δ} (M — Cr, Cu, Ni) (M = Cr, Cu, Ni) layered perovskite-like solid solutions have been prepared by solid-state reactions. Increasing the solute content of the solid solutions gives rise to solute-dependent monoclinic distortion of their tetragonal cell. The electrical conductivity and dielectric permittivity of the Bi₅Nb_{3 − 3x} M_3x O_{15 − δ} solid solutions and bismuth niobate, Bi₅Nb₃O₁₅, have been measured at temperatures from 300 to 750 K and frequencies from 1 to 200 kHz. Original Russian Text ? N.A. Zhuk, I.V. Piir, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 12, pp. 1504–1509.     

Preparation and characterization studies of metaborates, Cu1?xMxB2O4 (M = Ni, Co and Mn; x = 0, 0·1 and 0·5)

Copper metaborates of Cu_1−x M _x B₂O₄ (M = Ni, Co and Mn; x = 0, 0·1 and 0·5) compositions are prepared using B₂O₃ flux. Powder XRD studies showed them all to belong to the tetragonal system with space group I $ \bar 4 $ \bar 4 2d. Their infrared spectra exhibit characteristic vibrational bands of BO₄ tetrahedron. The room temperature powder electron spin resonance (ESR) spectrum of copper metaborate gave a single peak at g ∼ 2·15. The diffuse reflectance spectra (DRS) of Cu_1−x M _x B₂O₄ (M = Ni, Co and Mn; x = 0, 0·1 and 0·5) are consistent with ligand to metal ion charge transfer and square planar symmetry of Cu²⁺ ion. The ligand field parameters Dq _xy , D _s and D _t are obtained.     

Role of Calcium in the Evolution of Superconductivity in a (La2?xRx)Ba2(CayCu4+y)Oz (R = Y, Er, Gd) System

It has been reported that, by adding equal amounts of CaO and CuO to non superconducting La₃Ba₃Cu₆O _z (La-336), a series of superconductors with nominal compositions La₃Ca _y Ba₃Cu_6+y O _z were prepared with maximum T^on _c 80K. Similar studies on addition of CaO and CuO in nonsuperconducting LaBaCu₂O _z (La-112) resulted into superconducting LaCaBaCu₃O _z (La-1113). To date no attempt has been made to synthesize La₂CaBa₂Cu₅O _z (La-2125) superconducting phase by addition of CaO and CuO to non superconducting La₂Ba₂Cu₄O _z (La-224) system. Also no reports are published to study the effect of replacing larger La³⁺-ions (1.01Å) by smaller rare earth ions viz Y³⁺(0.89Å), Er³⁺(0.91Å), Gd³⁺(0.91Å) on the structural and superconducting properties of (La_2–x R _x )Ba₂(Ca _y Cu_4+y )O _z (LRBCaC); 0.0 x 0.5; y=2x system. In this paper, we report the method of synthesis, structural and superconducting property characterization using X-ray diffraction, oxygen content measurements using iodometry, resistivity measurements using d.c. four probe technique and a.c. susceptibility measurements in the temperature range RT to 15K. Also a comparative study, on the evolution of superconducting phase with Ca-concentration for different rare earth substitutions for LRBCaC system in the context of hole doping mechanism, is carried out.     

Low temperature synthesis of Ba1?xSrxSnO3 (x = 0–1) from molten alkali hydroxide flux

Perovskite structured stannates (Ba_1−x Sr _x SnO₃, x = 0·0–1·0) powders have been synthesized for the first time by molten salt synthesis (MSS) method using KOH as the flux at lower temperature (400°C) compared to other methods. The phase formation was confirmed by FT-IR spectroscopy, powder X-ray diffraction (XRD) and the microstructure was analysed by scanning electron microscopy. XRD patterns reveal the formation of single phasic products for parent and substituted products with good crystallinity throughout the range (x = 0·0–1·0). The morphology of the particles of BaSnO₃ and SrSnO₃ is spherical and rod shaped, respectively. Effect of soaking periods on the grain growth is observed clearly in SrSnO₃. Ba_0·5Sr_0·5SnO₃ (BSS5) crystallizes in flake like morphology.     

Magnetic susceptibility of (Bi2 ? xSbx)Te3 (0 < x < 1) crystals from 2 to 400 K

The magnetic susceptibility (χ) of crystals of (Bi_{2 − x} Sb _x )Te₃ (0 < x < 1) solid solutions has been measured at temperatures from 2 to 400 K. The χ of the crystals containing 10 and 25 mol % Sb₂Te₃ increases with temperature in the range 50 to 220 K, where the Hall coefficient of Bi₂Te₃ increases anomalously. The increase in diamagnetic susceptibility and Hall coefficient with temperature is shown to be caused by a reduction in light-hole concentration, accompanied by a decrease in light-hole effective mass. With increasing Sb₂Te₃ content, the shape of the χ(T) curve changes as a consequence of changes in band structure, which increase the influence of heavy, paramagnetic holes.     

Potassium ion conducting K2 ? 2 x Fe2 ? x P x O4 solid electrolytes

Potassium ion conducting solid electrolytes based on potassium monoferrite have been prepared by substituting pentavalent phosphorus cations for Fe³⁺. The highest conductivity of K_{2 − 2x} Fe_{2 − x} P _x O₄ is achieved in the range x = 0.05−0.10: 7.1 × 10⁻³ S/cm at 300°C and 1.6 × 10⁻¹ S/cm at 700°C. The rise in the conductivity of KFeO₂ upon phosphorus doping is due to the formation of potassium vacancies. Original Russian Text ? E.I. Burmakin, G.Sh. Shekhtman, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 8, pp. 995–998.     

Structural and electrical properties of fritless Ni(1?x)CuxMn2O4 (0?≤?x?≤?1) thick film NTC ceramic

Spinel structured NTC thermistor Ni_(1−x)Cu _x Mn₂O₄ (0 ≤ x ≤ 1) ceramics was prepared by oxalic precursor method and fritless thick films screen printed on alumina. The composition dependent structural and electrical properties are reported in this paper. The results show that with increasing copper ion substitution both Cu²⁺ and Mn⁴⁺ predominantly occupy the octahedral site. The concentration of Cu²⁺ ions in octahedral site increases while that of Ni²⁺ ions decreases linearly. The thick film Ni_(1−x)Cu _x Mn₂O₄ ceramic comply with Arrhenius equation. A thermistor constant of ~1,200 K has been obtained for fritless thick film NTC ceramics using inorganic binders in the RT/90 thermal range.     

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%.     

Electrical properties of (K0.5Na0.5)1? x Ag x NbO3 lead-free piezoelectric ceramics

(K_0.5Na_0.5)_1−x Ag _x NbO₃ lead-free piezoelectric ceramics have been fabricated by an ordinary ceramic technique. The results of XRD reveal that Ag⁺ diffuses into the K_0.5Na_0.5NbO₃ lattices to form a new solid solution with an orthorhombic perovskite structure and the solubility of Ag⁺ into A-sites of K_0.5Na_0.5NbO₃ is about 0.20. The ceramics can be well-sintered at 1,100–1,110 °C. The partial substitution of Ag⁺ for A-site ion (K_0.5Na_0.5)⁺ decreases slightly both paraelectric cubic-ferroelectric tetragonal (T _C) and ferroelectric tetragonal-ferroelectric orthorhombic phase transition temperatures (T _O−T). The ferroelectricity of the ceramics becomes weak at high Ag⁺ concentration. The ceramic with x = 0.10 possesses optimum electrical properties: d ₃₃ = 135 pC/N, k _P = 0.43, k _t = 0.46, ε _r = 470, tanδ = 3.39%, and T _C = 394 °C.     

Spin Gap Effects on Bulk R1+xba2?x Cu3O7?δ (R=Eu or Nd and 0≤x≤0.4)

Spin gap effects on the underdoping states of the bulk system of R_1+x Ba_2–x Cu₃O_7– (R = Eu or Nd and 0 x 0.4) were investigated through transport property measurements. The underdoping states were achieved by, alternatively substituting R³⁺ for Ba²⁺ ions in the system rather than adjusting the oxygen deficiency. The excess R³⁺ ions were to occupy the Ba sites of the crystalline lattice as revealed from Rietveld analysis for powder X-ray diffraction. The underdoped materials were observed to first undergo spin pairing transition in the temperature range well above T _c, and come across with superconducting transition at T _c. The increasing feature observed for spin gap temperature and the decreasing one for T _c, as the concentration of holes decreases, are in qualitatively good agreement with theoretical predictions from the mean-field RVB model.     

Structural and luminescent property of gallium chalcogenides GaSe1? x S x layer compounds

Structural and luminescence properties of GaSe_1−x S _x (0 ≤ x ≤ 1) series optical materials have been studied by X-ray diffraction, photoluminescence (PL), and piezoreflectance (PzR) measurements. Powder X-ray diffraction patterns showed the whole series layers present three different kinds of stacking formula with respect to the compositional change of sulfur from x = 0 to x = 1. The comparison of PL and PzR spectra reveals that the GaSe_1−x S _x layers have three different kinds of stacking phase from x = 0 to x = 1. The PL results show the whole series GaSe_1−x S _x layers emit the luminescences from red to blue visible region. The PL and PzR spectra of the GaSe_1−x S _x are analyzed. The structural variation in between the layers is discussed.