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.     

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.     

Roles of lithium ions and La/Li-site vacancies in sinterability and total ionic conduction properties of polycrystalline Li3xLa2/3−xTiO3 solid electrolytes (0.21 ≤ 3x ≤ 0.50)

The Li_0.33La_0.55TiO₃ solid electrolyte has a maximum grain ionic conductivity of 1.13 × 10⁻³ S cm⁻¹ among the Li_3xLa_2/3−xTiO₃ oxides (0.21 ≤ 3x ≤ 0.50), but the total ionic conductivity of its polycrystalline phase is not the highest. Owing to the grain-boundary resistances controlling the total resistances of bulk samples, an excellent solid electrolyte is mainly characterized by the grain-boundary resistances. With regard to the role of lithium ions, the substitution of La³⁺ ions by the Li⁺ ions weakens the strength of inter-ionic forces, leading to the decrease in the sintering temperature. The presence of La³⁺/Li⁺-site vacancies promotes the densification and grain growth and further results in rapid decreases in porosity and grain-boundary resistances. Li_0.21La_0.60TiO₃ with a larger amount of La³⁺/Li⁺-site vacancies can therefore exhibit the highest total ionic conductivity through rapidly decreasing its grain-boundary resistances by changing its microstructure, and it becomes a better polycrystalline solid electrolyte than Li_0.33La_0.55TiO₃ in the Li_3xLa_2/3−xTiO₃ system studied, in spite of its lower grain ionic conductivity.     

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.     

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).     

Subsolidus phase relation and crystal structure of the PrBa2−xSrxCu3O7±δ system

The PrBa_2−xSr_xCu₃O_7±δ solid solution was investigated by means of X-ray powder diffraction in combination with Rietveld analysis. The Sr-doped Pr123 single phase could be synthesized at 950 °C in air. The solubility of PrBa_2−xSr_xCu₃O_7±δ solid solution is 0.2≤x≤0.6. The structure of PrBa_2−xSr_xCu₃O_7±δ is orthorhombic for x=0.2. The structure transforms into tetragonal for 0.3≤x≤0.6. In the PrBa_2−xSr_xCu₃O_7±δ structure, Sr ions can replace Ba ions, the highest value is x=0.6 under our experimental condition. But Sr ions could not replace Pr ions. Furthermore Pr ions could not occupy the sites of Ba ions in the PrBa_2−xSr_xCu₃O_7±δ system. Both ionic radii and chemical properties play an important role in the mutual substitution of Pr, Ba and Sr ions in the Pr123 structure of the PrBa_2−xSr_xCu₃O_7±δ system.     

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.     

Effect of TiO2 on high-temperature thermoelectric properties of ZnO

The as-sintered Zn_1−xTi_xO (0.01 ≤ x ≤ 0.05) samples contained a solid solution of Zn_1−xTi_xO with a wurtzite structure and a small amount of the cubic spinel Zn₂TiO₄. The amount of Zn₂TiO₄ increased with an increase in TiO₂ content. The density and grain size increased with the small TiO₂ content (≤0.01), and then they decreased gradually by further increasing the TiO₂ content. The addition of TiO₂ to ZnO led to a significant increase in the electrical conductivity and a decrease in the absolute value of the Seebeck coefficient, resulting in an increase in the power factor. The highest value of power factor (7.6 × 10⁻⁴ W m⁻¹ K⁻²) was attained for Zn_0.98Ti_0.02O at 1073 K. It is demonstrated that the TiO₂ addition is fairly effective for enhancing thermoelectric properties.     

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.     

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.     

Composition-dependent electrical transport properties of Pb50Te52 doped with PbI2 prepared by HPHT

Cubic (Pb₅₀Te₅₂)_100−x(PbI₂)_x (0 ≤ x ≤ 0.065) bulk thermoelectric (TE) materials with enhanced power factor were prepared by high-pressure and high-temperature (HPHT) method. The mean grain size of the samples was about 10 μm. The dependence of electrical transport properties on composition was studied at room temperature. With an increase of x, the Seebeck coefficient in absolute value and the electrical resistivity firstly increase slightly and then decrease dramatically. The maximum power factor reaches 24.2 μW cm⁻¹ K⁻² at x = 0.015, which is much higher than that reported previously for the PbTe doped with PbI₂ prepared at normal pressure. The results indicate that HPHT combined with trace quantity doping is an effective method to enhance the thermoelectric properties for PbTe.     

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.     

Thermoelectric properties of A-site doped perovskites (Sr0.6Ba0.4)1−xMxPbO3 (M = La, K)

La- and K-doped perovskite-type ceramics, (Sr_0.6Ba_0.4)_1−xLa_xPbO₃ with x = 0.0−0.1 and (Sr_0.6Ba_0.4)_1−xK_xPbO₃ with x = 0.00−0.15, were prepared to modify thermoelectric properties of semi-metallic Sr_0.6Ba_0.4PbO₃ via the doping of electrons and holes, respectively. The electrical conductivity σ and Seebeck coefficient S for the ceramics were measured at temperatures of 373–1073 K in air. With the La doping, electron carriers were successively doped and the material changed from a semi-metal for the undoped Sr_0.6Ba_0.4PbO₃ to a metal for the (Sr_0.6Ba_0.4)_0.9La_0.1PbO₃. With the K doping, the thermoelectric properties were essentially unchanged probably due to the carrier compensation effect by the generation of oxygen deficiencies. The thermoelectric power factor S²σ was maximized to a value of 3.1 × 10⁻⁴ Wm⁻¹ K⁻² at 773 K for the undoped Sr_0.6Ba_0.4PbO₃ ceramic.     

Microstructure and tribological properties of LaxCeyO1 − x − y composite nanofilms

A series of La_xCe_yO_{1 − x − y} films (x = 0–0.54, y = 0–0.58) with thickness of 35–45 nm was deposited by unbalanced magnetron sputtering. High-resolution transmission electron microscope observation shows that La_0.24Ce_0.34O_0.42 film has polycrystalline structure. La₂O₃ and CeO₂ are formed within the La_xCe_yO_{1 − x − y} films confirmed by the X-ray diffraction and X-ray photoelectron microscopy. The friction coefficient and residual compressive stress of five kinds of three-element compound films exhibit symmetric distribution with the relative equilibrium of La and Ce atomic concentration within the films. The critical load of all deposited films is between 28 and 33 mN. The friction coefficient of two kinds of rare earth complex oxide films is in the range of 0.08–0.09, which is lower than that of only one kind of rare earth oxide films, and the friction mechanism is discussed.     

Preparation and structures of the La1−xKxCo1−xNbxO3 (x = 0–l) system

The La_1−xK_xCo_1−xNb_xO₃ system was performed by conventional solid state reaction technique using metal oxides. By DSC analysis, the activation energy of crystallization of the powders with x = 0.3 is 388.4 kJ/mol. The crystal structure of the compound reveals a transition from rhombohedral to cubic, and then to orthorhombic structure as the amount of the potassium niobate (KNbO₃) increases. It is found that the structure of the samples with x < 0.3 is similar to that of lanthanum cobaltate (LaCoO₃), while at the compositions with 0.7 ≥ x ≥ 0.3, the structure transforms to cubic. Finally, with x ≥ 0.7, the structures were similar to that of KNbO₃. According to the results of selected-area-diffraction (SAD) patterns and X-ray diffraction (XRD) identifications, the lattice parameters were calculated. The direction of superlattice structure along [2 1 0] was found for x = 0.5 as identified from SAD patterns. The dielectric constants were measured with cubic structure. Dielectric constant (K) decreases with increasing x.     

Corrosion resistance of (Nd,Dy)16(Fe,Co)76−xTixB8 mechanically alloyed magnets

Nanocrystalline (Nd,Dy)₁₆(Fe,Co)_76−xTi_xB₈ magnets were prepared by mechanical alloying and respective heat treatment at 973–1073 K/30–60 min. An addition of 0.5 at.% of Ti results in increase of coercivity from 796 to 1115 kA/m. Partial substitution of Nd by Dy results in an additional increase of coercivity up to 1234 kA/m. The highest corrosion resistance have magnets with 0.5–0.75 at.% of Ti. Beside the Ti, the Co and Dy content significantly improve the corrosion resistance, too. It was found, that for Ti content smaller than x ≤ 1, the (Nd,Dy)₁₆(Fe,Co)_76−xTi_xB₈ powders are single phase. For higher Ti contents (x > 1) the mechanically alloyed powders heat treated at 973 K are no more single phase, and the coercivity as well as corrosion resistance decreases due to the presence of an amorphous phase and -Fe. A heat treatment at a higher temperature (1073 K/30 min) or at 973 K for longer time (1 h) results in the full recrystallisation of the powders. The obtained homogenized structure results in higher corrosion resistance.     

Electrical, magnetic and elastic properties of La1.2(Sr1−xCax)1.8Mn2O7 (0.0 ≤ x ≤ 0.4)

Polycrystalline bulk samples of double layered manganite system La_1.2(Sr_1−xCa_x)_1.8Mn₂O₇ (0.0 ≤ x ≤ 0.4) were prepared by sol–gel method. After characterizing the samples using XRD and SEM, their electrical, magnetic and elastic properties were investigated. The lattice parameters and cell volume show a monotonous decrease with increase of Ca content, whereas the grain size is found to increase with increasing Ca content. The value of T_IM is found to decrease with Ca content up to x = 0.3 and then a slight increase of T_IM is observed. The low temperature upturn of resistivity is attributed to the spin-glass-like behavior, which is also evidenced by the irreversibility observed between ZFC and FC magnetizations. The conduction mechanism above T_IM can be explained by Mott VRH model. The present magnetization and ultrasonic studies indicate that the system shows a secondary transition at T^*, which decreases with increasing Ca content. Further, the T^* seems to be intrinsic to the present double layered manganite system.     

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.     

Physical properties of Mo6−xRuxTe8 and Mo6Te8−xSx

A series of the Chevrel phases, Mo_6−xRu_xTe₈ and Mo₆Te_8−xS_x (x=0, 1, 2), has been prepared and the various physical properties, such as the elastic modulus, Debye temperature, and electrical resistivity, have been evaluated. The relationships between several properties of the compounds have also been studied. Young’s modulus and Debye temperature of Mo_6−xRu_xTe₈ and Mo₆Te_8−xS_x increase with increasing x value. The relationship between the Vickers hardness and Young’s modulus shows ceramic characteristics for Mo_6−xRu_xTe₈, while they show glass-like characteristics for Mo₆Te_8−xS_x. The electrical resistivities of Mo_6−xRu_xTe₈ and Mo₆Te_8−xS_x increase with increasing x value.     

Magnetocrystalline anisotropy of Nd3(Fe1−xCox)27.7Ti1.3Ny compounds

The effect of Co substitution for Fe in Nd₃(Fe_1−xCo_x)_27.7Ti_1.3N_y (0 ≤ x ≤ 0.4) compounds on the magnetocrystalline anisotropy has been investigated. The anisotropy constants K's and the anisotropy field H_A have been deduced from the magnetization curves measured on magnetically aligned powder (4–7 μm) samples. The obtained results show that at RT the anisotropy is uniaxial and H_A (about 10 T) does not change substantially upon the substitution. At 5 K the results for K's give evidence for the presence of easy-cone-type anisotropy. The cone angle as well as the anisotropy field decrease upon the substitution from 21.6° to 11.8° and from 22.8 to 18.6 T, respectively.