Power factor of La1−xSrxFeO3 and LaFe1−yNiyO3

The electrical conductivity (σ), Seebeck coefficient (S), and power factor (σS²) of perovskite-type LaFeO₃, La_1−xSr_xFeO₃ [0.1 ≤ x ≤ 0.4] and LaFe_1−yNi_yO₃ [0.1 ≤ y ≤ 0.6] were investigated in the temperature range of 300–1100 K to explore their possibility as thermoelectric materials. The electrical conductivity of LaFeO₃ showed semiconducting behavior, and its Seebeck coefficient changed from positive to negative around 650 K with increasing temperature. The electrical conductivity of LaFeO₃ increased with the substitutions of Sr and Ni atoms, while its Seebeck coefficient decreased. The Seebeck coefficient of La_1−xSr_xFeO₃ was positive, whereas that of LaFe_1−yNi_yO₃ changed from positive to negative with increasing Ni content. The substitutions of Sr and Ni were effective in increasing the power factor of LaFeO₃; 0.0053 × 10⁻⁴ Wm⁻¹ K⁻² for LaFeO₃ (1050 K), 1.1 × 10⁻⁴ Wm⁻¹ K⁻² for La_1−xSr_xFeO₃ (x = 0.1 at 1100 K) and 0.63 × 10⁻⁴ Wm⁻¹ K⁻² for LaFe_1−yNi_yO₃ (y = 0.1 at 1100 K).     

Ba4In2−x(CO3)1+xO6−2.5x and Ba4In0.8Cu1.6(CO3)0.6O6.2—new indium oxycarbonates closely related to n=3 Ruddlesden–Popper phases

Investigations of phase relations in the Ba-rich part of the In₂O₃–BaO(CO₂)–CuO pseudo-ternary system at 900 °C have revealed the existence of new indium–copper oxycarbonate – Ba₄In_0.8Cu_1.6(CO₃)_0.6O_6.2. Rietveld refinement of the X-ray powder diffraction data combined with infrared studies gives evidence that this phase is a oxycarbonate crystallising in the tetragonal structure (space group I4/mmm) with unit cell parameters: a=4.0349(1) Å and c=29.8408(15) Å. In the binary part of the In₂O₃–BaO(CO₂) system we have identified the occurrence of Ba₄In_2−x(CO₃)_1+xO_6−2.5x oxycarbonate solid solution showing a crystal structure also described by I4/mmm space group, but with the unit cell parameters: a=4.1669(1) Å and c=29.3841(11) Å for x=1. The existence range of this phase, −0.153<x<0.4, includes chemical compositions of earlier found phases: Ba₅In_2+xO_8+0.5x with 0≤x≤0.45 (known as the -solid solution), as well as the binary Ba₄In₂O₇ phase. The crystal structures of both new oxycarbonates are isomorphic and related to n=3 member of the Ruddlesden–Popper family.     

Solid solution Pb1−xSrxTiO3 and its thermal expansion

The solid solution limit of Pb_1−xSr_xTiO₃ was determined in the composition range of 0≤x≤1.0 at room temperature (RT). The phases were isolated and indexed in a tetragonal system with x<0.5 and in a cubic one with x≥0.5. The cell parameters of Pb_1−xSr_xTiO₃ continuously, but nonlinearly, change with solubility x. The intrinsic thermal expansions of the solid solution compounds Pb_1−xSr_xTiO₃ (x=0, 0.15, 0.20, 0.50, 0.90, 1.0) were obtained in the temperature range from RT to 1173 K with high-temperature X-ray powder diffraction. Negative thermal expansion coefficients of Pb_1−xSr_xTiO₃ (x=0, 0.15, 0.20) were found below the Curie points. The thermal expansions of these titanate ceramics were highly correlated with the solubility in the solid solution Pb_1−xSr_xTiO₃.     

Synthesis and characterization of proton conducting Sr(Ce1−xZrx)0.95Yb0.05O3−δ by the citrate method

The citrate method was used to synthesize Sr(Ce_1−xZr_x)_0.95Yb_0.05O_3−δ (x = 0.1, 0.2, 0.3, 0.4) and to avoid the drawbacks of the conventional solid state reaction method. The products were characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe X-ray microanalyzer (EPMA). The results indicate that the citrate method is an advantageous route in producing Sr(Ce_1−xZr_x)_0.95Yb_0.05O_3−δ materials. Sr(Ce_0.9Zr_0.1)_0.95Yb_0.05O_3−δ powders are composed of nanoscaled crystallites with the average grain size in the range of 60–70 nm. Single phase is confirmed over the whole x range. In addition, chemical stability against CO₂ and electrical conduction behavior of the sintered Sr(Ce_1−xZr_x)_0.95Yb_0.05O_3−δ ceramics were investigated. The chemical stability of the ceramics against CO₂ is certified to increase with the increase in zirconium content. Impedance spectroscopy was used to study the electrical conduction behavior of Sr(Ce_0.9Zr_0.1)_0.95Yb_0.05O_3−δ ceramic.     

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Oxygen release behaviour of Ce(1−x)ZrxO2 powders and appearance of Ce(8−4y)Zr4yO(14−δ) solid solution in the ZrO2–CeO2–CeO1.5 system

To clarify the existence of metastable phases in the ZrO₂–CeO₂–CeO_1.5 system, evolved-oxygen gas analyses, (EGA), by heating a single phase of t′ and t″ (Ce_(1−x)Zr_xO₂) with various compositions, x, in a reducing gas and successive oxidation were carried out repeatedly. The oxygen release behaviour of the t′ and t″ phases was very complicated. The single κ phases, (Ce_(1−x)Zr_xO₂) with the composition, x=0.5 and 0.6, which were obtained by oxidizing the resulting pyrochlore as a precursor in O₂ gas at 873 K, exhibited a sharp oxygen release at the lowest temperature; the composition range of κ phase may be x=0.450.65. A new tetragonal phase t*, (Ce_(1−x)Zr_xO₂), which was attained by cyclic redox process together with annealing in O₂ gas at 1323 or 1423 K, exhibited a sharp oxygen release at the highest temperature; the composition range of t* phase may be as wide as x=0.200.65. A metastable solid solution expressed by a chemical formula of Ce_(8−4y)Zr_4yO_(14−δ) (y=01) possessing a CaF₂-related structure appeared on deoxidation of the t* phase. A ternary phase diagram containing the t* and Ce_(8−4y)Zr_4yO_(14−δ) solid solution was proposed.     

Bulk and lattice thermal expansion in Ce1−xSrxO2−x (0.0≤x≤0.10)

In this communication, we report on the bulk and lattice thermal expansion studies on a number of compounds, within the homogeneity range of solid solutions, in a series with the general composition Ce_1−xSr_xO_2−x (0.0≤x≤0.10). The XRD pattern of each product was refined to determine the solid solubility of SrO into the lattice of CeO₂, and the homogeneity range. The composition with maximum solid solubility limit of SrO in CeO₂ lattice, under the slow cooled conditions, was delineated as Ce_0.91Sr_0.09O_1.91 (i.e. 9 mol.% of SrO). The bulk thermal expansion measurements from ambient to 1123 K, as investigated by a dilatometer, revealed that the _l (293 to 1123 K) values for the compositions within the homogeneity range increase from 11.58×10⁻⁶ to 12.13×10⁻⁶ K⁻¹ on increasing the Sr²⁺ content from 0 mol.% (i.e. CeO₂) to 9 mol.%, i.e. the upper solubility limit of SrO into the lattice of CeO₂. A similar trend was observed in the lattice thermal expansion coefficients _a (293 to 1473 K) as obtained by a high temperature-XRD.     

Crystal structure, magnetic behaviour and valence state of ytterbium in the Yb4Ni10+xGa21−x phase

The ternary phase Yb₄Ni_10+xGa_21−x has been synthesised from the elements by high frequency melting in argon atmosphere. The homogeneity region has been established from X-ray powder data and confirmed by EDX analysis for 0.3≤x≤1. The crystal structure of Yb₄Ni_10+xGa_21−x has been estimated from X-ray single crystal data: space group C2/m (no. 12), Z=2, a=20.6815(9) Å, b=4.0560(4) Å, c=15.3520(7) Å, β=124.800(3)°, R(F)=0.023 for 1701 symmetry independent reflections with F(hkl)>4σ(F). A special feature of the structure is the local disorder within the gallium/nickel network. Neglecting atomic disorder in the region of the Ga9 and Ga11 positions, the Yb₄Ni_10+xGa_21−x structure is an occupation variant of the Ho₄Ni₁₀Ga₂₁ type with nickel atoms partially replacing the Ga atoms in the 2d sites at the centers of distorted icosahedra. From magnetic susceptibility and from L_III-XAS spectra, the valence state of ytterbium is near 3+.     

Synthesis and characterization of LiGaxMn2−xO4 (0 ≤ x ≤ 0.05) by triethanolamine-assisted sol–gel method

Spinel LiGa_xMn_2−xO₄ (0 ≤ x ≤ 0.05) cathode materials with phase-pure particles and nano-sized distribution were synthesized by sol–gel method using triethanolamine as the chelating agent. The effects of heat treatment on the physicochemical properties of the spinel LiGa_xMn_2−xO₄ powders were examined with thermogravimetric and differential thermal analysis (TG/DTA), powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). The LiGa_xMn_2−xO₄ (0 ≤ x ≤ 0.05) electrodes were characterized electrochemically by charge/discharge experiments under a current rate of 0.5C at 55 °C. Although the Ga-doped spinel electrode showed smaller initial discharge capacity, it exhibited better cycling performance than the undoped-LiMn₂O₄ electrode. The dQ/dV versus potential plots at 55 °C revealed that the improvement in cycling performance of the Ga-doped spinel electrode is attributed to stabilization of the spinel structure by the presence of gallium ion.     

The characteristics of Li(CoxNi1 − x)O2 cathode powders formed from the fine-sized Co3O4/NiO precursor powders

Li(Co_xNi_1 − x)O₂ (0 ≤ x ≤ 1) cathode powders were prepared by solid state reaction method using Co₃O₄/NiO precursor powders obtained by spray pyrolysis. The effect of the ratios of cobalt and nickel components on the characteristics of Co₃O₄/NiO precursor and Li(Co_xNi_1 − x)O₂ cathode powders were investigated. The Co₃O₄/NiO precursor powders with the ratios of cobalt and nickel components as 1/0, 0.75/0.25 and 0.5/0.5 had submicron size and regular morphologies. On the other hand, the Co₃O₄/NiO powders with the high contents of nickel component had aggregated morphologies of submicron size primary powders. The fine-sized precursor powders formed the fine-sized LiCoO₂ and Li(Co_0.75Ni_0.25)O₂ cathode powders by solid state reaction with LiOH powders. However, the high contents of the nickel component of the Co₃O₄/NiO precursor powders formed the Li(Co_xNi_1 − x)O₂ (0 ≤ x ≤ 0.5) cathode powders with aggregated morphologies and large sizes. The discharge capacities of the powders increased with increasing the nickel content into the Li(Co_xNi_1 − x)O₂ cathode powders up to 188 mAh/g.     

Phase behavior and some properties of LaMn1−xRhxO3 solid solution

Structure and magnetic and electrical properties of the polycrystalline compounds LaMn_1−xRh_xO₃ (0 < x ≤ 1) have been investigated. The samples were characterized by X-ray diffraction and Rietveld refinement which confirmed the space group Pnma (No. 62) for all compositions at room temperature. A transformation from O′- to O-type orthorhombic structure is seen near x = 0.6 tending to make the phase unstable. The electrical conductivity measurement shows semiconducting property above room temperature with a rather low activation energy for Mn-rich compositions. Compounds in the region 0.1 ≤ x ≤ 0.9 show ferromagnetic property but the substitution of Rh³⁺ ion for Mn³⁺ ion suppresses the ferromagnetism that results in reducing the Curie temperature, T_C.     

Hydrogen-induced decomposition in Pr(Co1−xCux)5 intermetallic compounds

Quasi-binary Pr(Co_1−xCu_x)₅ intermetallics with 0≤x≤1 were hydrogenated at elevated temperatures to precipitate Co and Cu and to study their mutual solubility. Low temperature hydrogenation was found to form a CaCu₅-type hydride containing about 1.6 hydrogen atoms per formula unit. Above 500 °C, the samples decompose into PrH_2.6, Cu and h.c.p.-Co. In the temperature range 330–450 °C, the CaCu₅-type hydrides coexist with the decomposed phases. Structural and magnetic measurements indicate that no solid solution are formed in Co-Cu decomposed phases. The magnetoresistance on both parent and hydrogenated samples does not exceed 0.5%.     

Preparation and structural characterization of perovskite-type LaxLn1−x″CoO3 by the thermal decomposition of heteronuclear complexes, LaxLn1−x″| Co(CN)6| · nH2O (Ln″ = Sm and Ho)

Perovskite-type La_xLn_1−x″CoO₃ oxides are prepared by the thermal decomposition of La_xLn_1−x″ [Co(CN)₆] · nH₂O hetero-nuclear complexes. Except for LaCoO₃ (hexagonal), the structures observed for La_xSm_1−xCoO₃ are othorhombic. While the perovskite-type oxide HoCoO₃ is not formed by decomposition at 1000°C of the corresponding hexacyano complex, the partial replacing of Ho with La is effective in forming the pervoskite-type oxide having an orthorhombic structure containing Ho even at 800°C. A monotonous correlation (quasi-linear relationship) was found between the b- and c-lattice constants of the orthorhombic structures of the perovskite-type oxides and the effective radii of Ln ions, defined as r_eff = xr_1.a + (1 − x)r_1.0″. The distortion parameter for the orthorhombie cell (3″a/b−1) increaseswith decrease in r_eff and is expected to be 0.270 for perovskite-type HoCoO₃. The crystal structure of the La_xLn_1−x″, CoO₃ oxides is mainly controlled by the effective radii of Ln ions.     

HfFe6Ge6-type YbMn6Ge6−xGax compounds (0.07≤x<0.72) with large magnetocrystalline anisotropy

The HfFe₆Ge₆-type YbMn₆Ge_6−xGa_x solid solution (0.07≤x≤0.72) has been studied by X-ray diffraction, microprobe analysis and powder magnetization measurements. All the compounds order antiferromagnetically between T_N=481 K for x=0.07 and T_N=349 K for x=0.72 and display more or less pronounced spontaneous magnetization at lower temperature. The corresponding Curie points increase from 40 K for x=0.07 to 319 K for x=0.72. The maximum magnetization values of the Ga-rich compounds (M≈5 μ_B/f.u. at 6 K) is compatible with a ferrimagnetic order of the Mn and Yb sublattices whereas the smaller values measured in the Ga-poor compounds suggest the stabilization of non-colinear magnetic structures. All the studied compounds are characterized by rather large coercive fields at low temperature (4.0≤H_c≤8.2 kOe).     

Large-scale synthesis of Pb1−xLaxTiO3 ceramic powders by molten salt method

The ferroelectric perovskite type lanthanum doped lead titanate (PLT) ceramic powders were synthesized in one step with the starting materials of PbC₂O₄, La₂O₃ and TiO₂ in NaCl–KCl molten salts in the temperature range of 700–950 °C. It was found that molten salt method was a large scale and easy preparation way to produce PLT powders with high dispersity. Tetragonal phase Pb_1−xLa_xTiO₃ ceramic powders were identified by XRD in the composition range 0 ≤ x ≤ 0.3 and mono-dispersed particles with spheric shape and less than 100 nm size were observed by SEM. The grain sizes of Pb_1−xLa_xTiO₃ ceramic powders increased with the increase of La content and decreased with calcination temperature. The grain growth progress and the possible reaction mechanism in molten salts and its influencing factors were discussed in this work. The grain growth process was the main influencing factor of the grain size, which depended on the solubility in the flux.     

The effect of f-ion valence on superconductivity in the series Pb2Sr2RCu3O8 (R=Ce, Pr, Tb and Am)

The magnetic properties and valences of the rare earth ions are probed in the superconducting series Pb₂Sr₂R_1−xCa_xCu₃O₈ (R=Ce, Pr, Tb and Am). The R=Pr and Tb samples are superconducting for x≈0.5 below 61 and 72 K, respectively, whereas the Ce and Am samples could not be made superconducting for any single phase sample, irrespective of x. X-ray absorption near edge spectroscopy (XANES), used to probe the valence of R, reveals that Pr and Tb are trivalent whereas the Ce and Am are tetravalent. This direct correlation of R valence and the observation of superconductivity is discussed.     

Tailoring of misfit along interfaces between ZnxMn3−xO4 and Ag

This work is aimed at examining how the tetragonality of Zn_xMn_3−xO₄ spinel structures depends on the chemical composition when Zn_xMn_3−xO₄ is embedded in a metal matrix. The paper focuses on a wide range of Zn_xMn_3−xO₄ precipitates in a Ag matrix with x varying between 0 and 1.5. This variation of x has been obtained by internal oxidation of Ag–2at.%Mn–4at.%Zn in air followed by annealing in vacuo at different temperatures. It will be demonstrated that the Zn concentration x in Zn_xMn_3−xO₄ has a major influence on the interfacial misfit and orientation relation between Ag/Zn_xMn_3−xO₄. The degree of mismatch of 10.4% of 1 1 1 Ag–Mn₃O₄ and 2.4% of Ag–Zn_1.5Mn_1.5O₄ was visualized using the Bragg filtering technique on HRTEM micrographs of those interfaces. It was possible to identify misfit dislocations qualitatively with this technique at 1 1 1 Ag–Zn_xMn_3−xO₄ interfaces with different degree of mismatch.     

Evolution of magnetic hardness in the HfFe6Ge6-type RMn6Sn6−xGax and RMn6Sn6−xInx compounds (R=Tb, Dy; 0.2≤x≤1.4)

The HfFe₆Ge₆-type RMn₆Sn_6−xX_x′ solid solutions (R=Tb, Dy, X′=Ga, In; x≤1.4) have been studied by powder magnetization measurements. All the series are characterized by ferrimagnetic ordering and by a decrease in Curie temperatures with the substitution (ΔT_c/Δx≈−39 K for X′=Ga and ΔT_c/Δx≈−75 K for X′=In). The RMn₆Sn_6−xGa_x systems are characterized by a strong decrease in the spin reorientation temperature with substitution (ΔT_t/Δx≈−191 K and −78 K for R=Tb and Dy, respectively) while this transition almost does not change in systems containing indium. The coercive fields drastically decrease with the substitution in the TbMn₆Sn_6−xGa_x system while the substitution of In for Sn has a weaker effect. The coercive fields of the Dy compounds do not vary greatly with the substitution in both series. The behaviour of the TbMn₆Sn_6−xGa_x is compared with the evolutions observed in the TmMn₆Sn_6−xGa_x series. This comparison strongly suggests that the replacement of Sn by Ga changes the sign of the A₀² crystal field parameter.     

Synthesis, crystal structure, oxygen stoichiometry, and electrical conductivity of La1−aCaaCr0.8Ti0.2O3−δ solid solutions

Series of perovskite-type compounds La_1−aCa_aCr_0.8Ti_0.2O_3−δ (a=0–1.0) were synthesized by the ceramic technique in air (final heating 1350 °C). The crystal structure of the compounds after cooling in air to room temperature was characterized as orthorhombic in space group Pbnm. Analysis of the lattice constants shows a noticeable decrease with increasing Ca content. All compounds prepared were stable in air and in a stream of Ar/1 Pa O₂ at 20–1400 °C, as also in Ar/5% H₂ (pH₂O/pH₂=0.01) at 850–1000 °C. Oxygen stoichiometry and electrical conductivity of the solid solutions with a=0.0–1.0 are investigated. Increasing Ca contents decrease the stability of the oxides in respect to the thermal dissociation of oxygen. All compounds are p-type semiconductors in the temperature range 20–1000 °C at oxygen partial pressures of 10⁻¹⁵ to 0.21×10⁵ Pa. A maximum conductivity of about 30 S/cm in air at 1000 °C is observed for the composition with a=0.6 corresponding to a ratio of Cr³⁺/Cr⁴⁺=1 at an oxygen stoichiometry near 3.0, and oxidation states of La, Ca, Ti, and O ions of 3+, 2+, 4+, and 2−, respectively.     

Existence, structure and valence properties of the skutterudites CeyFe4−xCoxSb12

We report on sample preparation, annealing effects, electron microprobe analysis in the series Ce_yFe_4−xCo_xSb₁₂ which shows that a phase separation occurs for substituted samples (0<x<4) annealed at 650 and 550 °C. Single phase samples are obtained for either Ce_yFe₄Sb₁₂ or Ce_yCo₄Sb₁₂ samples annealed at 650 °C and for all compositions when annealed at 700 °C. The valence state of Ce in homogeneous samples has been studied using X-ray absorption spectroscopy (XAS). Ce ions are trivalent throughout the series and the XAS spectra does not show effect of the crystal field on the 5d-final state.