Structural, magnetic and electrical transport properties for a series of La1−xSrxFe1−xMnxO3 (0.3 ≤ x ≤ 0.7) compounds

The structural, electrical transport and magnetic properties have been studied for compounds: La_1−xSr_xFe_1−xMn_xO₃ (0.3 ≤ x ≤ 0.7). The lattice parameter, a, first decreases with x, and followed by an increase when Sr²⁺ and Mn⁴⁺ was continuously doped. The cell parameters, b and c, slightly decrease with coupled substitution of Sr²⁺ for La³⁺ and Mn⁴⁺ for Fe³⁺. In the paramagnetic temperature range, formation of magnetic clusters is suggested; the sizes of clusters decrease with x up to 0.5, following that they increase sharply with continuing doping. The electrical behaviors of all specimens demonstrate insulators and the electrical resistivity increases with content of Mn⁴⁺ and Sr²⁺ ions doped. A variable range hopping model is suitable to describe electrical transport process for the compounds at low temperature. At high temperature the electrical transport process can be described by bipolaron model for all compounds.     

Characterization of hydrothermally prepared BaTi1−xZrxO3

BaTiO₃ (BTO) and BaTi_0.8Zr_0.2O₃ (BZT) powders were prepared using the hydrothermal method, starting from BaO, TiO₂ and Zr(NO₃)₂, 7H₂O. X-ray diffraction analysis showed that the cubic phase is stable at room-temperature and the pure perovskite phase is obtained after heating the powders for 2 h at 1280 °C. The temperature dependence of the dielectric constant points to ferroelectric behavior. This ferroelectric behavior can likely be due to the presence of a possible quadraticity gradient in the grains since the cubic phase may not be ferroelectric. The diffuse character of the transition is attributed to this quadraticity gradient, to grain size distribution and (for BZT) to spatial fluctuations in the concentrations of the substituted ion (Zr) leading to the coexistence of regions of different Curie temperatures.     

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).     

Nanocrystalline LaNi4−xMn0.75Al0.25Cox electrode materials prepared by mechanical alloying (0≤x≤1.0)

Polycrystalline hydrogen storage alloys based on lanthanum (La) are commercially used as negative electrode materials for the nickel–metal hydride (Ni–MH_x) batteries. In this paper, mechanical alloying (MA) was used to synthesize nanocrystalline LaNi_4−xMn_0.75Al_0.25Co_x (x=0, 0.25, 0.5, 0.75 and 1.0) hydrogen storage materials. XRD analysis showed that, after 30 h milling, the starting mixture of the elements decomposed into an amorphous phase. Following the annealing in high purity argon at 700 °C for 0.5 h, XRD confirmed the formation of the CaCu₅-type structures with a crystallite sizes of about 25 nm. The nanocrystalline materials were used as negative electrodes for a Ni–MH_x battery. Cobalt substituting nickel in LaNi₄Mn_0.75Al_0.25 greatly improved the discharge capacity and cycle life of the LaNi₅ material. For example, in the nanocrystalline LaNi_3.75Mn_0.75Al_0.25Co_0.25 powder, discharge capacities up to 258 mA h g⁻¹ (at 40 mA g⁻¹ discharge current) were measured. Mechanical alloying is a suitable procedure to obtain LaNi₅-type alloy powders for electrochemical energy storage.     

Structural, electrical and magnetic properties of Cu1−xZnxFe2O4 ferrites (0 ≤ x ≤ 1)

Copper–zinc ferrites bearing chemical formula Cu_1−xZn_xFe₂O₄ for x ranging from 0.0 to 1.0 with the step increment of 0.2 were prepared by the standard solid-state technique. The variation of Zn substitution has a significant effect on the structural, electrical and magnetic properties. Lattice parameters ‘a’ increased from 8.370 to 8.520 Å. Dielectric constant decreased up to 311 with the increase in frequency from 80 Hz to 1 MHz at room temperature. All the samples follow the Maxwell–Wagner's interfacial polarization. Saturation magnetization, magnetic moment and Yafet–Kittel angles were also determined. The possible reasons responsible for the change in density related, electrical and magnetic properties with the increase in Zn concentration are undertaken.     

Preparation of NaV1−xAlxPO4F cathode materials for application of sodium-ion battery

The effects of Al doping on the electrochemical properties of NaVPO4F as a cathode material for sodium-ion batteries were investigated. Al-doped NaV1-xAlxPO4F （x=0, 0.02） samples were prepared by a simple high temperature solid-state reaction involving VPO4 and NaF for the application of cathode material of sodium-ion batteries. The crystal structure and morphology of the material were studied by Flourier-infrared spectrometry（FT-IR）, X-ray diffractometry（XRD） and scanning electron microscopy（SEM）. The results show that NaV1-xAlxPO4F （x=0, 0.02） has a typical monoclinic structure. The effects of Al doping on the performance of the cathode material were analyzed in terms of the crystal structure, charge-discharge curves and cycle performance. It is found that NaV0.98Al0.02PO4F shows an improved cathodic behavior and discharge capacity retention compared with the undoped samples in the voltage range of 3.0-4.5 V. The electrodes prepared from NaV0.98Al0.02PO4F deliver an initial discharge capacity of 80.4 mA.h/g and an initial coulombic efficiency of 89.2%, and the capacity retention is 85% after 30th cycle. Though the Al-doped samples have lower initial capacities, they show better cycle performance than Al-free samples.     

一步固相合成Nb掺杂LiFePO4/C及其电化学性能

用廉价的三价铁离子化合物为铁源,以聚丙烯为还原剂和碳源,在一步固相法合成Nb掺杂LiFePO4的同时实现颗粒表面碳导电膜的原位包覆。结果表明:一步固相合成的Nb掺杂LiFePO4/C具有完整的橄榄石型LiFePO4晶体结构和近似球状的颗粒形貌,颗粒尺寸为100~500 nm;聚丙烯分解后在颗粒表面和颗粒之间形成连通的网络状碳膜。电化学测试结果表明,当Nb的掺入量为1.0%(摩尔分数)时具有最好的倍率放电性能和循环性能;在2C充放电时具有130 mA.h/g的放电容量,循环100次容量无衰减,在4C充放电时仍具有105 mA.h/g的放电容量。     

Thermoelectric properties of Sn1−x−yTiySbxO2 ceramics

Thermoelectric properties of Sn_1−x−yTi_y Sb_xO₂ ceramics were investigated in detail. The addition of Sb into SnO₂ matrix increased the electric conductivity, σ. The increase in the σ value should be caused by the increase in the carrier concentration. The Seebeck coefficients of all the samples were negative, which means that these samples have n-type conduction. The samples of this study have porous structure. The maximum Z value of all the samples measured in this study was 2.4 × 10⁻⁵ K⁻¹.     

Structural and thermodynamic properties of the pseudo-binary TiCr2−xVx compounds with 0.0≤x≤1.2

The TiCr_2−xV_x compounds with 0.0≤x≤1.2 series have been synthesised and characterised by X-ray powder diffraction. X-Ray qualitative and quantitative phase analysis has been carried out on the as-cast alloys using the Rietveld method. The refinements of the structure shows that the materials crystallise either in the hexagonal or in the cubic Laves phase type for low V contents. For x>0.6, the system is found of b.c.c.-type structure only. The pressure–composition–temperature (P–C–T) isotherms measured at 298 K show that the as-cast alloys absorb large amounts of hydrogen, from 4 to 5.2 H/f.u. The P–C–T diagrams reveal also the presence of a relatively flat plateau, and a large hysterisis effect, and correspondingly the hydride cannot be completely dehydrogenated.     

Magnetic properties of Ce3−xGdxCo11B4 borides

The structure and magnetic properties of Ce_3−xGd_xCo₁₁B₄ borides have been studied by X-ray powder diffraction (XRPD), magnetization and differential scanning calorimetry (DSC) measurements. X-ray analysis reveals that the compounds crystallize in the hexagonal Ce₃Co₁₁B₄-type structure with P6/mmm space group. The substitution of Gd for Ce leads to an increase of the unit-cell parameter a and the unit-cell volume V, while the unit-cell parameter c decreases linearly. Magnetic measurements indicate that all samples are ordered magnetically below the Curie temperature. The Curie temperatures increase as Ce is substituted by Gd. The saturation magnetization at 4 K decreases upon the Gd substitution up to x = 1, and then increases.     

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.     

Influence of simultaneous addition of Sb2O3 and SnO2 on thermoelectric properties of Zn1−x−ySbxSnyO prepared by tape casting

Solid aluminum hydride, AlH₃, has been proposed and studied for applications in hydrogen storage. In some samples, a comparatively narrow feature in the proton NMR spectrum is observed; we demonstrate here that this peak is due to molecular hydrogen (H₂) trapped within the solid, presumably from earlier processing procedures or partial decomposition. Static and magic-angle spinning NMR show that the responsible species is highly mobile, even at 11 K. Neutron-energy-gain spectra obtained at 3.5 K yield a feature at or near the free-rotor H₂ energy difference between the J = 1 and J = 0 states. Both NMR and neutron scattering demonstrate ortho–para conversion at low temperatures. Similar NMR signatures in other hydrogen-storage solids such as NaAlH₄ may also be due to trapped H₂.     

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.     

Thermoelectric performance of Mg2−xCaxSi compounds

Thermoelectric materials Mg_2−xCa_xSi (x = 0, 0.01, 0.03, 0.05, 0.07, 0.1) compounds have been prepared by vacuum melting followed by hot-pressing. Effects of the substitution of Ca for Mg on phase structures and the thermoelectric properties of the hot-pressed compounds were investigated. It was found that the alloying of Ca in Mg₂Si based compounds increases the electrical conductivity and decreases the Seebeck coefficient of the compounds, due to the electronegativity difference between Ca and Mg. The dimensionless figures of merit of Mg₂Si and Mg_1.99Ca_0.01Si reach, respectively, 0.41 and 0.34 at 660 K.     

Electrochemical performances of Co-doped LiFePO4/C obtained by hydrothermal method

LiFePO₄, C-coated LiFePO₄ (LiFePO₄/C), and Co-doped LiFePO₄/C as cathode materials for lithium ion batteries are synthesized by a hydrothermal method. The electrochemical properties of the three samples are investigated and compared by galvanostatic cycling, rate capability and cyclic voltammetry (CV) measurements. LiFePO₄, LiFePO₄/C, and Co-doped LiFePO₄/C exhibit initial discharge capacities of 88, 90 and 116 mAh g⁻¹ at 0.1 C, respectively. After annealing at 400 °C, the initial discharge capacities of the three corresponding samples increase to 115, 125 and 132 mAh g⁻¹ at 0.1 C. In both cases, Co-doped LiFePO₄/C shows the best rate performance among the three samples. CV measurements indicate that the improvement of dynamic behavior could be attributed to Co doping. All experimental observations indicate that the preparation of Co-doped LiFePO₄/C offers a way to combine the common methods to improve the performance of LiFePO₄: particle size reduction, intimate conducting phase coating and metal supervalent doping, which explain the enhanced electrochemical properties.     

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.     

The role of valence electron concentration in the cohesive properties of YBxN1−x, YCxN1−x and YNxO1−x compounds

The mechanical properties are not yet understood at basic levels. Previous works shows that the greatest hardness for rock-salt structures (such as TiC_xN_1−x) is attained for a valence electron concentration (VEC) of 4.2 electrons per atom. The present work is aimed to explore this concept for yttrium-based compounds. By means of first principles calculations we did a systematical investigation where nitrogen in YN (VEC = 4) was supplanted by either of B, C or O to reduce or increase its VEC, forming YB_xN_1−x, YC_xN_1−x and YN_1−xO_x ternary compounds. We have calculated the cohesive energy (E_O), cell volume (V_O), bulk modulus (B_O) and density of states (DoS) as a function of VEC. The Fermi level (E_f,) is shifted toward the valence band by substituting B or C in YN, and toward the conduction band by means of O. It is concluded that the optimal position for E_f (maximum B_O) is linked to the saturation of electronic states with e_g-symmetry. At this point the excess of electrons provided by O starts filling antibonding states with t_2g-symmetry. That is, B_O increases monotonically as a function of VEC until VEC  4.1, after that point B_O decrease.     

Glass-forming ability and magnetic properties of mechanically solid-state reacted Co100−xTix alloy powders

A high-energy ball milling technique using the mechanical alloying method has been employed for fabrication of glassy Co_100−xTi_x (25≤x≤67) alloy powders at room temperature. The fabricated glassy alloys in the Co-rich (33≥x) side exhibit good soft magnetic properties. The binary glassy alloys for which the glass transition temperatures (T_g) have rather high temperatures (above 800 K), show large supercooled liquid regions before crystallization (ΔT_x larger than 50 K). The reduced glass transition temperature (ratio between T_g and liquidus temperatures, T_l (T_g/T_l)) was found to be larger than 0.56. We have also performed post-annealing experiments on the mechanically deformed Co/Ti multilayered composite powders. The results show that annealing of the powders at 710 K leads to the formation of a glassy phase (thermally enhanced glass formation reaction), of which the heat of formation was measured directly. The similarity in the crystallization and magnetization behaviors between the two classes of as-annealed and as-mechanically alloyed glassy powders implies the formation of the same glass state.     

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.     

Synthesis and properties of lithium ion conductors Li3−2x(Sc1−xZrx)2(PO4)3

Lithium ion conductors, Li_3−2x(Sc_1−xZr_x)₂(PO₄)₃ (0 x 0.3), were prepared by a solid-state reaction. TG–DTA analysis indicated no phase transition in the samples with x superior to 0.05. X-ray powder diffraction analysis of these samples clearly showed the stabilization of a superionic conduction phase at room temperature with an orthorhombic system Pbcn. The highest conductivity was observed for the sample with x=0.05, and ascribed to the stabilization of the superionic conduction phase and the introduction of vacancies on the Li⁺ sites by substituting Zr⁴⁺ for Sc³.