Nature of conductivity of Perovskites La1 ? x Sr x ScO3 ? α (x = 0.01–0.15) under oxidative and reducing conditions

Transport numbers of ions and protons are measured on ceramic samples of La_{1 ? x} Sr _x ScO_{3 ? ??} (x = 0.01?C0.15); partial conductivities (hole, proton, and oxygen-ion) are determined in the temperature range of 500?C900°C at pH₂O = 0.04?C2.35 kPa and pO₂ from air to 10^?15 Pa.     

Phase Transitions in the BaCe1–x Nd x O3–δ System (x = 0–0.15)

Phase transitions in BaCe_{1 – x} Nd _x O_3– (x = 0–0.15) are studied on ceramic samples by dilatometry (at 370–1100 K) and by measuring electroconductivity (at 750–1220 K). Ion transport numbers are measured by an EMF method at 850–1240 K. All measurements are done in dry air (₂ 40 Pa). By treating the obtained temperature dependences of linear expansion with a difference method (difference between first-degree polynomial approximating the dependence and experimental points), the position and the sort of the phase transitions are determined. High-temperature phase transitions are confirmed by measuring the electroconductivity and ion transport numbers. Second-order phase transitions in pure BaCeO₃ are discovered at 480 ± 10, 530 ± 10, 900 ± 10, 1030 ± 20, and 1170 ± 10 K and a first-order transition, at 665 ±10 K. Phase transitions at 900 and 1030 K are discovered for the first time ever.     

Electrical, electrochemical, and thermomechanical properties of perovskite-type (La1?x Sr x )1?y Mn0.5Ti0.5O3?δ (x?=?0.15–0.75, y?=?0–0.05)

Strontium additions in (La_1?x Sr _x )_1?y Mn_0.5Ti_0.5O_3?δ (x?=?0.15–0.75, y?=?0–0.05) having a rhombohedrally distorted perovskite structure under oxidizing conditions lead to the unit cell volume contraction, whilst the total conductivity, thermal and chemical expansion, and steady-state oxygen permeation limited by surface exchange increase with increasing x. The oxygen partial pressure dependencies of the conductivity and Seebeck coefficient studied at 973–1223?K in the p(O₂) range from 10^?19 to 0.5?atm suggest a dominant role of electron hole hopping and relatively stable Mn³⁺ and Ti⁴⁺ states. Due to low oxygen nonstoichiometry essentially constant in oxidizing and moderately reducing environments and to strong coulombic interaction between Ti⁴⁺ cations and oxygen anions, the tracer diffusion coefficients measured by the ¹⁸O/¹⁶O isotopic exchange depth profile method with time-of-flight secondary-ion mass spectrometric analysis are lower compared to lanthanum–strontium manganites. The average thermal expansion coefficients determined by controlled-atmosphere dilatometry vary in the range 9.8–15.0?×?10^?6?K^?1 at 300–1370?K and oxygen pressures from 10^?21 to 0.21?atm. The anodic overpotentials of porous La_0.5Sr_0.5Mn_0.5Ti_0.5O_3?δ electrodes with Ce_0.8Gd_0.2O_2-δ interlayers, applied onto LaGaO₃-based solid electrolyte, are lower compared to (La_0.75Sr_0.25)_0.95Cr_0.5Mn_0.5O_3?δ when no metallic current-collecting layers are introduced. However, the polarization resistance is still high, ~2 Ω?×?cm² in humidified 10?% H₂–90?% N₂ atmosphere at 1073?K, in correlation with relatively low electronic conduction and isotopic exchange rates. The presence of H₂S traces in H₂-containing gas mixtures did not result in detectable decomposition of the perovskite phases.     

Phase equilibriums, oxygen exchange kinetics and diffusion in oxides CaZr1 ? x Sc x O3 ? x/2 ? δ

Oxides CaZr_{1 ? x} Sc _x O_{3 ? x/2 - ??} (x = 0.00?C0.20) were synthesized according to the ceramic technology. The solubility boundary of scandium with formation of solid solutions on the basis of calcium zirconate CaZrO_{3 ? ??} corresponds to x = 0.07?C0.08. The second phase of CaSc₂O₄ is present in the samples with scandium content of x = 0.10, 0.15, 0.20. Its fraction grows at an increase in x. The method of full-profile Rietveld analysis was used to calculate the structure parameters for oxides CaZr_0.99Sc_0.01O_{2.995 ? ??} and CaZr_0.95Sc_0.05O_{2.975 ? ??}. The method of isotopic exchange with gas phase analysis was used to study the kinetics of gas-phase oxygen interaction with the CaZr_0.95Sc_0.05O_{2.975 ? ??} oxide in the temperature range of 700?C850°C and at oxygen pressures of 0.13?C6.67 kPa. The values of effective activation energies of the oxygen exchange and diffusion processes were 1.36 ± 0.32 and 1.92 ± 0.21 eV, accordingly. The dependence of the interphase exchange rate on the pressure of oxygen corresponds to the power law with the exponent of 0.31 ± 0.04 at the temperature of 750°C.     

Phase composition and conductivity of La1 ? x Sr x ScO3 ? α (x = 0.01?0.20) under oxidative conditions

The phase composition was studied and overall conductivity of oxides La_{1 ? x} Sr _x ScO_{3 ? ??} (x = 0.01?0.20) was measured as dependent on air humidity (pH₂O = 0.04?2.35 kPa) in the temperature range from 100 to 900°C. The samples were synthesized in air at 1600°C. They are single-phase, with a perovskitetype structure with orthorhombic distortions and the density of 94?C99%. The conductivity measurements were carried out using the impedance technique and four-probe dc technique. The contributions of bulk and grain boundary resistances were determined, effective conductivity activation energies were calculated.     

Hydrogen content in proton-conducting perovskites CaZr1 − x Sc x O3 − x /2 (x = 0.0–0.2)

The hydrogen content in CaZr_{1 ? x} Sc _x O_{3 ? x/2} (x = 0.00–0.20) and BaZr_0.9Y_0.1O_3-α (for comparison) was studied by powder nuclear microanalysis. The samples were saturated with heavy water (D₂O) vapors at 350 and 400°C in air. The chemical expansion of the CaZr_0.95Sc_0.05O_3-α and BaZr_0.95Y_0.05O_3-α samples at 700°C was measured at different water vapor pressures. A model was suggested to explain the lowered hydrogen content in oxides based on CaZrO₃.     

Synthesis and crystal structure of Mo6−x Nb x I11 (x = 1–1.5)

A solid solution Mo_{6 ? x} Nb _x I₁₁ (x = 1.1–1.5) containing cluster cores {Mo₅NbI₈} is obtained by the high-temperature reaction of molybdenum, niobium, and iodine (550°C, 70 h, quartz ampule). According to the X-ray diffraction data, heating at 800°C in a molybdenum container results in the decomposition of the solution to Mo₆I₁₂ and Nb₆I₁₁. According to the X-ray structure analysis data, the compounds are isostructural to the high-spin modification Nb₆I₁₁ (space group Pccn). The presence of Nb atoms in the structure changes the structural type from the layered (Mo₆I₁₂) to framework structure, noticeably increases the metalmetal distances (2.661–2.716 Å, 2.695 Å) Mo₆ octahedron with the retention of the distance from the metal (M) to the μ₃-“capped” I atoms, and strongly elongates the M₆-I-M₆ bridges almost to the value observed in Nb₆I₁₁.     

Determination of the stability constants of Pb–(DIPSO)x–(OH)y and Pb–(AMPSO)x–(OH)y systems

In this work, complexation between lead ion and the ligands 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) and N-(1,1-dimethyl-2-hydroxyethyl)-3-amino-2-hydroxypropanesulfonic acid (AMPSO), which are commercial pH buffers, is presented. Both ligands form complexes with lead in their pH buffer range (between pH 6.5 and 8.5 for DIPSO and between pH 8.0 and 9.0 for AMPSO). The final models and the overall stability constants, which are reported here, were determined by direct current polarography and glass electrode potentiometry [only for the Pb–(DIPSO)_x–(OH)_y system] at 25.0 °C and 0.1 M KNO₃ ionic strength. For the Pb–(DIPSO)_x–(OH)_y system, the proposed final model contains PbL, PbL₂, PbL₂(OH), and PbL₂(OH)₂ with stability constants, as log β, of 3.4 ± 0.1, 6.35 ± 0.15, 12.8 ± 0.2, and 18.0 ± 0.3, respectively. For the Pb–(AMPSO)_x–(OH)_y system, the species observed are PbL, PbL(OH), and PbL(OH)₂ with stability constants, as log β, of 2.9 ± 0.5, 9.4 ± 0.1, and 14.5 ± 0.2, respectively. For AMPSO, the possible adsorption of the ligand at the mercury electrode surface was evaluated by alternating current polarography through calculation of the capacitance of the double layer.     

Electrochemical studies of LiCr x Fe x Mn2?2x O4 in an aqueous electrolyte

In this paper, LiCr _x Fe _x Mn_2−2x O₄ (x = 0, 0.05, 0.1) electrode materials were prepared by sol–gel technique and characterized by X-ray diffraction (XRD) and transmission electron microscopy or high-resolution transmission electron microscopy techniques. XRD results reveal that the Cr–Fe-co-doped LiCr _x Fe _x Mn_2−2x O₄ materials are phase-pure spinels. The electrochemical properties of the LiMn₂O₄, LiCr_0.05Fe_0.05Mn_1.9O₄, and LiCr_0.1Fe_0.1Mn_1.8O₄ electrodes in 5 M LiNO₃ aqueous electrolyte were investigated using cyclic voltammetry, AC impedance, and galvanostatic charge/discharge methods. In the current range of 0.5–2 A g⁻¹, the specific capacity of the LiCr_0.05Fe_0.05Mn_1.9O₄ electrode is close to that of the LiMn₂O₄ electrode, but the specific capacity of the LiCr_0.1Fe_0.1Mn_1.8O₄ electrode is obviously lower than that of the LiMn₂O₄ electrode. When the electrodes are charge/discharge-cycled at the high current rate of 2 A g⁻¹, the LiCr_0.05Fe_0.05Mn_1.9O₄ electrode exhibits an initial specific capacity close to that of the LiMn₂O₄ electrode, but its cycling stability is obviously prior to that of the LiMn₂O₄ electrode.     

Synthesis of garnet structured Li7+x La3Y x Zr2-x O12 (x = 0–0.4) by modified sol–gel method

Preparation of lithium garnet Li₇La₃Zr₂O₁₂ (LLZ) in cubic phase by solid state method requires high temperature sintering around 1,200 °C for 36 h in Al₂O₃ crucible with intermittent grinding. Synthesis of LLZ in cubic phase at lower temperatures by wet chemical methods was reported earlier, however that decompose at high temperature around 850 °C. In this work we report the systematic studies on synthesis of garnet structured electrolytes by modified sol–gel method by the simultaneous substitution of Li⁺ and Y³⁺ for Zr⁴⁺ according to the formulae Li_7+x La₃Y _x Zr_2-x O₁₂ (x = 0, 0.1, 0.2, 0.3 and 0.4). The present investigation revealed that the cubic garnet phase is obtained at much lower temperature for Li₇La₃Zr₂O₁₂ and the simultaneous increase of both Li⁺ and Y³⁺ in Li_7+x La₃Y _x Zr_2-x O₁₂ requires slightly higher sintering temperatures for the formation of cubic garnet phase. SEM micrographs of the Li_7+x La₃Y _x Zr_2-x O₁₂ (x = 0, 0.1, 0.2, 0.3 and 0.4) annealed at minimum sintering temperature required for the formation of cubic garnet phase revealed the increase in grain size and relatively dense structure with increase of x in Li_7+x La₃Y _x Zr_2-x O₁₂.     

Characteristics of nanosized LiNi x Fe1−x PO4/C (x = 0.00–0.20) composite material prepared via sol–gel-assisted carbothermal reduction method

Pure LiFePO₄ and LiNi _x Fe_1?x PO₄/C (x?=?0.00–0.20) nanocomposite cathode materials have been synthesized by cheap and convenient sol–gel-assisted carbothermal reduction method. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy, and inductively coupled plasma have been used to study the phase, morphology, and chemical composition of un-doped and Ni-doped materials. XRD patterns display the slight shrinkage in crystal lattice of LiFePO₄ after Ni²⁺ doping. The SEM images have revealed that Ni-doped particles are not agglomerated and the particle sizes are practically homogeneously distributed. The particle size is found between 50 and 100 nm for LiNi_0.20Fe_0.80PO₄/C sample. The discharge capacity at 0.2 C rate has increased up to 155 mAh g^?1 for the LiNi_0.05Fe_0.95PO₄/C sample and good capacity retention of 99.1 % over 100 cycles, while that of the unsubstituted LiFePO₄/C and pure LiFePO₄ has showed only 122 and 89 mAh g^?1, respectively. Doping with Ni has a noticeable effect on improving its electrical conductivity. However, serious electrochemical declension will occur when its doping density is beyond 0.05 mol LiNi_0.20Fe_0.80PO₄/C electrode shows only 118 mAh g^?1, which is less than un-doped LiFePO₄/C sample at 0.2 C. The cycling voltammogram demonstrates that Ni-doped LiNi_0.05Fe_0.95PO₄/C electrode has more stable lattice structure, enhanced conductivity, and diffusion coefficient of Li⁺ ions, in which Ni²⁺ is regarded to act as a column in crystal lattice structure to prevent the collapse during cycling process.     

Sol–gel synthesized high anisotropy magnetic nanoparticles of NiCr x Fe2−x O4

The nanoparticles of NiCr _x Fe_2?x O₄ were synthesized through sol–gel reactions involving nitrates of Ni, Cr and Fe in an aqueous medium containing citric acid. The cubic spinel structure in single phase with nanometric crystallite size of ~5 nm, the spherical morphology and magnetic relaxations were examined through XRD, TEM and Mössbauer techniques. The abnormal occurrence of finite remanance (M _r ) and coercivity (H _c ) resulted in the room temperature dc magnetization measurements for the small particles authenticate the ferrimagnetic regime, as proposed by the room temperature Mössbauer results of the samples, with a proximate superparamagnetic regime still at lower particle volumes. This could be attributed to the antiferromagnetic spin interactions of chromium ions at octahedral sites and subsequently the over-occupancy of the rest of the cations at tetrahedral sites. In justification to this, the magnetocrystalline anisotropy constant, K, is estimated to have value relatively high of the order of 10⁷ erg/cm³ at room temperature for all studied concentrations.     

Synthesis and magnetic properties of Cu0.5Fe0.5 ? x In x Cr2S4 (x = 0?0.4) solid solutions

Multistep synthesis with X-ray diffraction monitoring of the phase composition has been carried out, optimal synthesis parameters have been determined, and the magnetic properties of solid solutions between thiospinels with ordered tetrahedral A lattices (ferrimagnet Cu_0.5Fe_0.5Cr₂S₄ (T _C = 347 K) and anti-ferromagnet Cu_0.5In_0.5Cr₂S₄ (T _N = 35 K) have been studied. Both compounds crystallize in F $\bar 4$ 3m (T _d ² ) structure. Measurements over wide ranges of fields (0.05?C40 kOe) and temperatures (5?C300 K) highlighted the nature of magnetism in the samples; new magnetic species have been discovered.     

Synthesis and characterization of nano-structured Th1?x Ce x O2 mixed oxide

GEL combustion technique was applied to obtain oxides of thorium and cerium from their respective nitrate solutions using citric acid as the gelating agent. The dried samples were characterized by IR and TG studies. Intermediate and final products during TG studies have been isolated and characterized by XRD studies. All the TG runs during heating of thorium and cerium nitrate with citric acid dried Gels showed a two step process. The weight loss at each step and the X-ray data of the product at each step, helped in suggesting a possible mechanism. Kinetic study was carried out independently for each step. The reaction mechanism as observed during interactive procedure was found to be diffusion controlled. The kinetic parameters (activation energy and pre-exponential factor) for each step in all reactions have been calculated. Observations from XRD studies show that with increase in cerium concentration in the oxides, the lattice parameter values have shown a decreasing trend for all the five compositions studied. It was observed that in TG studies with increase in cerium concentration, the final temperature of the reactions have shown a decreasing trend. SEM studies of the powders reveal that synthesized oxides have a tendency to form agglomerate of varying size ranging from 50 to 100 μm in case of mixed oxides but the size of thorium oxide powder so synthesized have pore size 10–100 μm. SEM images shows that GEL combustion may result in agglomeration, if the temperature is not properly controlled to the desired value. SEM studies also reveal that each agglomerate contains approximately 10–100 individual particles. Surface area of the mixed oxide powders were determined using Gas adsorption technique. The surface area was found to be in the range of 3–17 m²/g in all cases. Specific surface area of thorium oxide was found to be lesser than cerium oxide but in case of mixed oxides surface area decreases with increase in cerium content. Majority of pores, indicating the particle size are in the range of 0.01–0.04 cm³/g.     

Formation of (C x H2x+1)4NBr·nH2O (x = 1–3) hydrate

The phase diagram of the binary system tetramethylammonium bromide-water was studied by the differential thermal analysis. In the stable region two phases, ice and the salt itself, were detected, and in the metastable region, three tetramethylammonium bromide hydrates (bromide-water, 1 : 4, mp 68.8°C, 1 : 5, mp 36.0°C, 1 : 7.5, mp ?19.5°C) were found. Formation of (C _x H_2x+1)₄NBr·nH₂O (x = 1–3, n = 4, 5, 7.5) hydrates was revealed.     

Structures and optical properties of Zn1?x Ni x O nanoparticles by coprecipitation method

Nanocrystals of undoped and nickel-doped zinc oxide (Zn_1?x Ni _x O, where x?=?0.00?C0.05) were synthesized by the coprecipitation method. Crystalline size, morphology, and optical absorption of prepared samples were determined by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and UV?Cvisible spectrometer. XRD and SEM studies revealed that Ni-doped ZnO crystallized in hexagonal wurtzite structure. Doping of ZnO with Ni²⁺ was intended to enhance the surface defects of ZnO. The incorporation of Ni²⁺ in place of Zn²⁺ provoked an increase in the size of nanocrystals as compared to undoped ZnO. Crystalline size of nanocrystals varied from 10 to 40?nm as the calcination temperature increased. Enhancement in the optical absorption of Ni-doped ZnO indicated that it can be used as an efficient photocatalyst under visible light irradiation. Optical absorption measurements indicated a red shift in the absorption band edge upon Ni doping. The band gap value of prepared undoped and Ni-doped ZnO nanoparticles decreased as annealing temperature was increased up to 800?°C.     

Study of ceramic pigments based on Er2Ce2?x Mo x O7

This contribution is focused on the synthesis, characterization and optical properties of new inorganic pigments which are environment friendly and can substitute some toxic metals in interesting colour compounds. Pyrochlores belong to the group of high-temperature pigments, and are a variety of actual and potential applications for several materials. Examples include catalysts, thermal barrier coatings, solid electrolytes, nuclear waste forms and host materials for luminescence centers. The pigments were prepared by the solid state reaction and also by method of suspension mixing of materials in the series with increasing content of molybdenum. The pigments were applied into organic matrix and ceramic glaze. The colour properties of these applications were investigated depending on content of Mo, method of preparation and temperature of calcination (1350?C1550?°C after step 50?°C). The optimum conditions for their synthesis were determined. The pigments were evaluated from standpoint of their structure, colour and particle sizes. Characterization of Er₂Ce_2?x Mo _x O₇ pigments (x?=?0.1, 0.3, 0.5 and 0.7) suggests that they have a potential to be alternative yellow or orange colourants for paints, plastics, ceramics and building materials.     

High-pressure densities and P–T–x–y diagrams for carbon dioxide+linalool and carbon dioxide+limonene

Liquid and vapor densities for carbon dioxide+linalool, and carbon dioxide+limonene were measured by using a system consisting of two vibrating tube densimeters. The P–T–x–y diagrams and saturated liquid and vapor densities for these two binary mixtures were determined at 313, 323 and 333 K, respectively, as well as at pressures up to 11 MPa. The density of the saturated CO₂ phase increased with increasing pressure. At higher pressure, the density of the liquid phase decreased with increasing pressure, corresponding to an increasing amount of carbon dioxide.     

Synthesis and magnetic properties of CuCr1.5Sb0.5S4 ? x Se x solid solutions

CuCr_1.5Sb_0.5S_{4 ? x} Se _x (x = 0, 0.5, 3.5, 4) metal chalcogenides with spinel structure have been synthesized for the first time. Unit cell parameters have been calculated and magnetic properties have been measured for the samples prepared. These samples are nonuniform antiferromagnets having Neel temperatures of T _N = 21?C30 K.     

Magnetic properties of Cu0.5Fe0.5 ? x Ga x Cr2S4 solid solutions

Solid solutions between ferrimagnet Cu_0.5Fe_0.5Cr₂S₄ (T _C = 347 K) and antiferromagnet Cu_0.5Ga_0.5Cr₂S₄ (T _N = 31 K) have been synthesized, and their magnetic properties studied. Both compounds belong to the A _0.5 ⁺ A _0.5 ³⁺ Cr₂X₄ group with the 1 : 1 order of A⁺ and A³⁺ ions in the tetrahedral spinel sites. Measurements on a SQUID magnetometer over wide ranges of fields (0.05?C40 kOe) and temperatures (5?C300 K) provided a deeper insight into the nature of magnetism and cation distribution in the studied samples.