Water vapor absorption and proton conductivity of (Ba1−x La x )2In2O5+x

The proton conductivity of (Ba_1−x La _x )₂In₂O_5+x system has been investigated as a function of the La content, temperature and amount of absorbed water. The proton conductivity increased with La content up to x = 0.10, to reach a maximum of 1.12 × 10⁻⁵ (S/cm) at 400 °C. From that point on, it decreased. From the results of thermogravimetry and mass spectra, we confirmed that the water was absorbed in the (Ba_1−x La _x )₂In₂O_5+x system, in a maximum quantity of 0.14 mol/mol (sample). The proton conductivity increased monotonically with the quantity of water uptake, suggesting that this variable is one of the dominant parameter of proton conductivity in this system.     

Incorporation of bismuth into Ba6− x R8+2/3x Ti18O54(R = Nd, Gd)

Microstructural investigations and microanalyses of a series of Ba_6–x R _8+2/3x Ti₁₈O₅₄ ceramics (R = Nd, Gd) revealed that the solid-solubility limit for the isovalent substitution of R ³⁺ by Bi³⁺ depends on the composition of the Ba_6–x R _8+2/3x Ti₁₈O₅₄ phase. For the Nd analogue the solid-solubility limit (y in Ba_6–x (Nd_1–y Bi _y )_8+2/3x Ti₁₈O₅₄) decreases with a decrease in x from y = 0.16 for x = 2.0 to y = 0.10 for x = 0.8. An even lower solid-solubility limit (y = 0.06) was found for the Ba_4.5(Gd_1–y Bi _y )₉Ti₁₈O₅₄ compound (x = 1.5). All substituted Nd compositions exhibit higher permittivities (93–99), lower temperature coefficients of permittivity (11–15 ppm/K) and higher dielectric losses (Q · f = 1300–5500 GHz) than the parent compositions. By exceeding the solid-solubility limit, abrupt changes in the microstructural and dielectric characteristics are induced.     

The effect of Ba2+ doping on the structure of SrBi4Ti4O15

In this paper, bi-layered structural ferroelectric materials Sr_1–x Ba _x Bi₄Ti₄O₁₅(SBBT) (x=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) were prepared using sol–gel method. The stable precursors were fabricated by mixing the salts of strontium (Sr), barium (Ba), bismuth (Bi) and titanium butoxide in acetic acid together with ethanolamine as a catalyzer and acetylacetone as a stable agent. The structural evolution of SBBT after Ba²⁺ doping was studied. The experimental results confirm that complete solid solutions of SrBi₄Ti₄O₁₅ and BaBi₄Ti₄O₁₅ are formed. The perovskite lattice will expand after the doping of Ba²⁺ because of the difference of ionic radii of strontium and barium cations, which will lead to increasing of the lattice spacing. With the increase of the content of Ba cations the grain size of SBBT powder increases, the granularity distribution widens and average particle size of SBBT powder also increases. The average particle size of SrBi₄Ti₄O₁₅ and BaBi₄Ti₄O₁₅ is 82.5 and 165.2 nm, respectively.     

Preparation, characterization and conductivity studies of AgI-Ag2O-(TeO2 + P2O5) fast ionic conducting glasses

Silverphosphotellurate (SPT) quaternary fast ionic conducting (FIC) glasses of compositions AgI-Ag₂O-[(1 – x)P₂O₅ + xTeO₂], x = 0.0 to 1.0 in steps of 0.1, were prepared by melt quenching. All SPT compounds were characterized by X-ray diffraction and the amorphous nature of the samples was confirmed. The structure of all compositions was examined by Fourier Transform Infrared Spectroscopy. The glass transition temperature (T _g) was determined for all SPT samples, using differential scanning calorimetry. Complex impedance measurements were made on all glasses in the frequency range 40 Hz to 100 kHz. Impedance data were analyzed using Boukamp equivalent circuit software and the bulk conductivity was obtained. The highest conductivity ( = 1.59*10^–2 S/cm) was shown by the composition 60%AgI – 26.67%Ag₂O – 13.33% (0.3P₂O₅ + 0.7TeO₂).     

Anomalous High-Temperature Properties of BaPbO3-Based Solid Solutions

The thermal expansion, thermal stability, and electrical resistivity of the Ba_{1 – x} M _x Pb_{1 + y} O_{3 +} (M = Sr, Ca; 0 x 1.0, 0 y 0.2) and Ba_{1 – x} M" _x Pb_{1 – y} M" _y O_{3 +} (M" = K, La; M" = Sc, Sb; x, y= 0.01) ceramic materials were studied between 293 and 1073 K in air. The linear thermal expansion coefficient of the ceramics was found to increase abruptly at 700 K, from (10–14) × 10^–6K^–1in the range 300–600 K to (13–18) × 10^–6K^–1in the range 800–1000 K. The electrical resistivity of the ceramics passes through a sharp maximum near 750 K, with the largest jump in resistivity at the compositions Ba_0.6Sr_0.4PbO₃and Ba_0.9Ca_0.1PbO₃. The anomaly in thermal expansion is likely associated with the rearrangement of the lead–oxygen polyhedra in the structure of the solid solutions, and the jump in resistivity is attributable to changes in the average oxidation state of Pb ions in the surface layer of the ceramics.     

High-temperature thermoelectric properties of the sintered Bi2Sr2Ca1 − xYxCu2Oy (x = 0 – 1)

Electrical conductivity and Seebeck coefficient were measured in a temperature range of 320–1073 K for sintered samples of Bi₂Sr₂Ca_{1 – x} Y _x Cu₂O _y (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). It has been found that the conduction behavior changes from n-type metallic to p-type semiconducting with increasing yttrium concentration. The power factors were in a range of 1.7–3.0 × 10^–5 Wm^–1 K^–2 for the sample with x = 0.8, being maximized by the optimization of the yttrium concentration. The thermal conductivity for the sample with x = 0.8 was 0.73 Wm^–1 K^–1 at 310 K, and decreased with increasing temperature. The values of thermoelectric figure of merit were estimated to be in a range of 3.4–4.8 × 10^–5 K^–1 at temperatures of 320–673 K for the sample with x = 0.8.     

Investigations of Bi substitution in NdBa2Cu3Oy

Attempts to substitute Bi for Nd in orthorhombic NdBa₂Cu₃O _y , prepared in air or oxygen at about 950°C led instead to formation of Ba₂NdBiO₆, a new cubic compound witha=0.8703 nm. The possibility was then explored of preparing superconducting (Nd_1–x Bi _x )Ba₂Cu₃O _y , by first forming the tetragonal phase at 880–950°C in nitrogen or argon followed by reheating in oxygen or air at 250–500°C in order to insert the additional oxygen required to yield the orthorhombic form while avoiding oxidation of Bi³⁺ to Bi⁵⁺. X-ray diffraction studies, electrical conductivity measurements, and thermogravimetric analysis of products indicate that Bi does not enter the NdBa₂Cu₃O _y , lattice in either the tetragonal or the orthorhombic phase. Ba₂NdBiO₆ clearly forms on reheating in oxygen or air even at low temperatures, and evidence is presented that a poorly crystallized oxygen-deficient form of this compound is already present prior to the reheating.     

Water Degradation of Thallium-2212 Ceramics

Water degradation of Tl₂Ba₂CaCu₂O_{8 – x} , Tl₂Ba₂CaCu₂O_{8 – x} + 0.2ZrO₂, and Tl_1.8Pb_0.2Ba₂CaCu₂O _x high-T _c ceramics is studied. The results demonstrate that the introduction of PbO and ZrO₂ improves the resistance of the Tl-based high-T _c ceramic to corrosion in water and humid air. The degradation products are identified by x-ray diffraction.     

Electrochemical characteristics of Ba0.5Sr0.5Co0.8Fe0.2O3−δ–Sm0.2Ce0.8O1.9 composite materials for low-temperature solid oxide fuel cell cathodes

In this paper, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ–xSm_0.2Ce_0.8O_1.9 (BSCF–xSDC, x = 0–60 wt.%) composite cathodes were prepared by soft chemical methods, and then examined for potential applications in lower temperature solid oxide fuel cells. Both DC polarization and AC impedance spectroscopy measurements indicated that the addition of SDC electrolyte into BSCF remarkably improved the electrochemical properties. The optimum composition was found to be BSCF–30SDC, which exhibited 5.5 times higher polarization current density and 15.1% polarization resistance, compared with the pure-phase BSCF cathode at 550 °C.     

Doping-induced microstructural, textural and optical properties of In2Ti1−xVxO5+δ semiconductors and their role in the photocatalytic splitting of water

The physicochemical properties of V-doped indium titanates (In₂Ti_1−xV_xO_5+δ, 0.0 ≤ x ≤ 0.2) were investigated by using XPS, powder XRD, UV–vis, SEM and luminescence spectroscopy techniques. The Rietveld refinement of XRD data revealed that even though the V-containing samples were isostructural with In₂TiO₅ (orthorhombic space group Pnma), a systematic x-dependent variation was noticeable in the Ti–O bond lengths in [TiO₆] octahedral units, cell parameters and in the value of δ. XPS results confirmed the coexistence of V⁵⁺ and V⁴⁺ states, leading thereby to an enhancement in oxygen non-stoichiometry in the doped samples. A loading-dependent progressive shift from 400 to 750 nm was also observed in the onset of the absorption edge, indicating a significant narrowing of the band gap. Furthermore, the samples with higher V-content were comprised of the grain clusters having larger size and an irregular shape. The UV–vis, photoluminescence and thermoluminescence studies indicate that the doping-induced lattice defects may give rise to certain closely spaced acceptor/donor energy levels in between the band gap of host matrix. The indium titanates are found to serve as stable photocatalysts for water splitting under visible light, where oxygen was the major reaction product. The role of microstructural and morphological properties in the photocatalytic activity is discussed.     

Fabrication of dense LaCrO3-based interconnect thin membrane on anode substrates by co-firing

In order to develop cost-effective method to prepare ceramic interconnect membrane for solid oxide fell cell stacks, the triple-phase composites of NiO/Sm_0.2Ce_0.8O_2−δ/La_0.7Ca_0.3Cr_0.97O_3−δ with the weight ratios of 6:4:x (x = 0, 2, 3, 4, 5) were, respectively prepared, and then examined as novel anode supports. The sintering character, microstructure, electrical conductivity, fracture strength, and thermal expansion coefficient of the anodes were, respectively investigated in detail as a function of La_0.7Ca_0.3Cr_0.97O_3−δ content. Results indicate the above-mentioned performances of NiO/Sm_0.2Ce_0.8O_2−δ/La_0.7Ca_0.3Cr_0.97O_3−δ anode at x ≤ 3 have no significant reduction, and are still acceptable for the practical requirements for solid oxide fell cells. Furthermore, by using a simple and cost-effective drop-coating/co-firing process, dense La_0.7Ca_0.3Cr_0.97O_3−δ interconnect membrane was successfully prepared on the anode support of NiO/Sm_0.2Ce_0.8O_2−δ/La_0.7Ca_0.3Cr_0.97O_3−δ at x = 3. This work presents a simple technical route for developing dense interconnect membranes for Sm_0.2Ce_0.8O_2−δ-based fuel cell stacks.     

Single-crystal growth of La2−2x Sr1+2x Mn2O7 under pressure

Large single crystals of La_2–2x Sr_1+2x Mn₂O₇ (x=0.3 to 0.525) have been prepared under controlled atmospheric conditions. The crystals were grown by the floating-zone technique in an image furnace under a mixed oxygen/argon atmosphere pressurized to 6–8×10⁵ Pa. Rectangular single crystals with sizes up to 50×9×4 mm³ have been obtained. The phase-purity, composition, and quality of the crystals were analyzed by X-ray diffraction and electron probe microanalysis. The magnetic behavior is found to be sensitive to the composition of the atmosphere during growth.     

Oxidation of reduced Y-doped semiconducting barium titanate ceramics

Oxidation-induced microstructural changes in reduced yttrium-doped barium titanate (Ba_{1 – x}Y_xTi_{1 – x}⁴⁺Ti_x³⁺ O₃) are studied using samples sintered in a reducing atmosphere ( = 10^–4Pa) and then oxidized in air at 1150 and 1350°C. The results indicate that oxidation leads to precipitation of Ba₆Ti₁₇O₄₀ and, at relatively high doping levels, Y₂Ti₂O₇. These phases increase the electrical resistance of the outer layer of the grains in the ceramics.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 93–100.Original Russian Text Copyright © 2005 by Vyunov, Kovalenko, Belous, Belyakov.     

Effect of M and M-Ca Substitution on the Structure and Superconductivity of GdBa2Cu3O7?δ [M = Mo, Hf ]

The structural and superconducting properties of (Gd_1–x–y Ca _y M _x )Ba₂Cu₃O _z with M = Mo, Hf are investigated using X-ray diffraction, electrical resistivity, and oxygen content measurements. The effect of increasing the Mo concentration in (Gd_1–x Mo _x )Ba₂Cu₃O _z changes the structure from orthorhombic to tetragonal accompanied by a large increase in resistivity and a fast decrease in T _c at the rate of 1.9 K per at.% of Mo, unlike that of Hf substitution in (Gd_1–x Hf _x )Ba₂Cu₃O _z , which maintains the orthorhombic structure and decreases T _c very slowly at the rate of 0.6 K per atm.% of Hf with nearly no change in resistivity. The suppression of T _c by M = Mo, Hf can be counterbalanced by hole doping by Ca which increases T _c with increasing Ca content showing maximum compensation for Mo. A comparative study of M = Mo, Hf doped samples in (Gd_1–x–y Ca _y M _x )Ba₂Cu₃O _z indicates that the valence of the dopant M = Mo^4+,6+, Hf⁴⁺ and its ionic radius play an important role in controlling the structural and superconducting properties of the systems.     

Preparation of Tl2Ba2Ca1 − y CeyCu2O8 − x/2Fx Ce-and F-substituted superconductors

High-T _c superconducting ceramics with the compositions Tl₂Ba₂CaCu₂O_{8 ? x/2} (0 ≤ x ≤ 0.3), Tl₂Ba₂(Ca_{1 ? y} Ce_y)Cu₂O_x (0 ≤ y ≤ 0.2), and Tl₂Ba₂(Ca_0.9Ce_0.1)(Cu_1.98Fe_0.02)F_0.2O_8.01 are synthesized. Partial fluorine substitution for oxygen in Tl₂Ba₂CaCu₂O_{8 ? x/2} (0 ≤ x ≤ 0.1) alters the carrier density in the Cu-O planes of the material, raising its superconducting transition temperature from 106 to 110 K. Partial cerium substitution for calcium in Tl₂Ba₂(Ca_{1 ? y} Ce_y)Cu₂O_x (0 ≤ y ≤ 0.2) reduces T _c. The combined substitution in Tl₂Ba₂(Ca_0.9Ce_0.1)(Cu_1.98Fe_0.02)F_0.2O_8.01 has an insignificant effect on T _c.     

X-ray, IR and bulk magnetic properties of Cu1 + x Mn x Fe2–2x O4 ferrite system

The structural, IR and magnetic properties of the mixed spinel Cu_{1 + x} Mn _x Fe_2-2x O₄ (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) system have been investigated by means of X-ray diffraction, Infrared spectroscopy, magnetization and a.c. susceptibility measurements. X-ray results confirm single-phase spinel structure for all the concentrations. The structure of CuFe₂O₄ is tetragonal and changes to cubic for x = 0.1 to 0.4. For x = 0.5 and 0.6 the structure become tetragonal. The lattice parameter and X-ray density are deduced and their variation with Mn⁴⁺ concentration is studied. The cation distribution derived from the X-ray diffractometry data was found to agree very well with the cation distribution obtained from magnetization measurements. X-ray intensity calculations indicate that Mn⁴⁺ occupy only octahedral [B] sites and Cu²⁺ and Fe³⁺ ions occupy both octahedral [B] and tetrahedral (A) sites. The infrared spectra obtained at room temperature in the range 200–800 cm^–1 showed two absorption bands. The force constants have been obtained from IR data. The variation of the saturation magnetization per formula unit as a function of Mn⁴⁺ content x has been satisfactorily explained on the basis of Neel's collinear spin ordering model for all values of x. The Curie temperature T _C determined from a.c. susceptibility data decreases with increase of Mn⁴⁺ concentration x, suggesting decrease in ferrimagnetic behaviour.     

Microscopic and Macroscopic Magnetic Properties of the MgAl x Cr x Fe2 − 2x O4 Spinel Ferrite System

To determine the influence of the substitution of Al³⁺ and Cr³⁺ for Fe³⁺ in MgFe₂O₄ ferrites on the structural and magnetic properties, the MgAl _x Cr _x Fe_{2 – 2x} O₄ (x = 0.0–0.8) spinel systems were studied by using the X-ray diffraction analysis, magnetization in strong fields, magnetic susceptibility in weakly variable electric fields, and Mössbauer spectroscopy. Unlike previous investigations, it was discovered that a half of Al³⁺ occupies tetragonal positions. The system forms a noncollinear spin structure and a central paramagnetic doublet is superimposed over the magnetic sextet in the Mössbauer spectrum (0.5 > x > 0.2). The dependence of the magnetic susceptibility on temperature reveals the normal ferromagnetic properties of the material.     

Kinetics and thermodynamics of intracrystalline Fe-Ga distribution in Y3(Fe,Ga)5O12

Garnets of composition Y₃Fe_5–x Ga _x O₁₂, withx=0–5, were synthesized from oxides. Samples with various Ga content were annealed at temperatures between 700–1290° C; the heating duration varied between 90 s and 1350 h. Cation distribution was measured by Mössbauer spectroscopy at room temperature. The standard free energy change for the exchange reaction Fe³⁺ (tet)+ Ga³⁺ (oct)Fe³⁺ (oct)+Ga³⁺ (tet) is about 20 kJ mol^–1, and decreases slightly with increasing Fe content. The specific rate constants for the ordering process were determined according to the Mueller model for order-disorder kinetics. The activation energies for the ordering process between 200–250 kJ mol^–1 were calculated from the temperature dependence of the specific rate constants.     

Effects of Al2O3 addition on the sinterability and ionic conductivity of nasicon

The effects Al₂O₃ doping on the sintering behaviour and ionic conductivity of nasicon have been investigated using formulations of Na_3+2x Zr₂Si₂Al _x P_1–x O₁₂ where Al³⁺ ions were substituted to P⁵⁺ sites within the range 0x0.2. The density of Na_3+2x Zr₂Si₂Al _x P_1–x O₁₂ was increased with increasing amount of Al₂O₃ doping due to the enhanced liquid-phase sintering. The relative density of Na_3.4Zr₂Si₂Al_0.2P_0.8O₁₂ reached a maximum value of 96% when sintered at 1200°C for more than 7 h. The maximum conductivity of 0.24 ^–1 cm^–1 at 300°C was obtained for the composition with x=0.1 when sintered at 1200°C for 10 h.     

M?ssbauer and magnetic investigation of scandium and indium substituted PbFe12O19 hexagonal ferrite

Magnetic and Mössbauer measurements have been performed on polycrystalline substituted M-type hexagonal ferrites of compositions PbFe_12–x Sc _x O₁₉ (x = 0, 0.5, 1, 1.5) and PbFe_12–x In _x O₁₉ (x = 0, 1, 2). The substitution of the Fe³⁺ by Sc³⁺ and In³⁺ ions perturbs the axial magnetic order giving rise to angled magnetic structures. From the values of the quadrupole splitting of the Fe⁵⁷ 14.4 keV level, measured above and below the Curie temperatures, the angle between the magnetic moment of the Fe³⁺ ions in various sublattices and the hexagonal c-axis have been deduced. At 77 K the measured angles do not exceed 20° and depending on x are different for different sublattices. The dependence of x on the saturation magnetisation at 0 K, expressed in Bohr magnetons, differs markedly in Sc and In containing compounds, partly due to the different substitution probability of iron in the spin up and spin down sublattices, and also due to the different spin canting angles.