Characterization of MgxM2 − xP2O7 (M = Cu and Ni) solid solutions

In this study, Mg_xM_2 − xP₂O₇ (M = Cu, Ni; 0 ≤ x ≤ 2) and Mg_3 − yNi_y(PO₄)₂ (0 ≤ y ≤ 3) compositions were synthesized by the chemical coprecipitation method and characterized by X-ray diffraction, UV-vis-NIR spectroscopy and CIE L* a* b* (Commission Internationale de l’Eclairage L* a* b*) parameters measurements.Solid solutions with α-Cu₂P₂O₇ and α-Ni₂P₂O₇ structures and solid solutions with Ni₃(PO₄)₂ structure were obtained from diphosphate and orthophosphate compositions respectively. Isostructurality of α-Ni₂P₂O₇ and α-Mg₂P₂O₇ structures enlarges the compositional range of solid solution formation respect to the Mg_xCu_2 − xP₂O₇ solid solutions one.The CIE L* a* b* parameters in Mg_xNi_2 − xP₂O₇ samples were obtained comparable with these parameters in others yellow materials suitable for ceramic pigments. Mg_0.5Ni_1.5P₂O₇ composition fired at 800 °C or 1000 °C is the optimal composition to obtain yellow materials with α-diphosphate structure in conditions of this study.     

Improvement of electrochemical properties of Li[Ni0.4Co0.2Mn(0.4−x)Mgx]O2−yFy cathode materials at high voltage region

Spherical Li[Ni_0.4Co_0.2Mn_(0.4−x)Mg_x]O_2−yF_y (x = 0, 0.04, y = 0, 0.08) with phase-pure and well-ordered layered structure have been synthesized by heat-treatment of spherical [Ni_0.4Co_0.2Mn_0.4−xMg_x]₃O₄ precursors with LiOH·H₂O and LiF salts. The average particle size of the powders was about 10-15 μm and the size distribution was quite narrow due to the homogeneity of the metal carbonate, [Ni_0.4Co_0.2Mn_(0.4−x)Mg_x]CO₃ (x = 0, 0.04) precursors. Although the Li[Ni_0.4Co_0.2Mn_0.36Mg_0.04]O_1.92F_0.08 delivered somewhat slightly lower initial discharge capacity, however, the capacity retention, interfacial resistance, and thermal stability were greatly enhanced comparing to the Li[Ni_0.4Co_0.2Mn_0.4]O₂ and Li[Ni_0.4Co_0.2Mn_0.36Mg_0.04]O₂.     

Study on phase structure and electrochemical properties of Ml1−xMgxNi2.80Co0.50Mn0.10Al0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) hydrogen storage alloys

Phase structure and electrochemical properties of the Ml_1−xMg_xNi_2.80Co_0.50Mn_0.10Al_0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) (Ml = La-rich mixed lanthanide) alloys were studied. X-ray diffraction (XRD) analysis and Rietveld refinement show that the alloys consist mainly of LaNi₅ and (La,Mg)Ni₃ phase. Due to variation in phases of the alloys, the maximum discharge capacity, the high rate dischargeability (HRD), and the low temperature dischargeability increase first and then decrease. The maximum discharge capacity increases from 322 mAh g⁻¹ (x = 0.08) to 375 mAh g⁻¹ (x = 0.12), and then decreases to 351 mAh g⁻¹ (x = 0.28) with increasing x. As the case of x = 0.20, HRD at 1200 mA g⁻¹ and discharge capacity at 233 K reaches 41.7% and 256 mAh g⁻¹, respectively. The cycling stability is improved by substituting La with Ml and B-site multi-alloying, and the capacity retention of Ml_0.72Mg_0.28Ni_2.80Co_0.50Mn_0.10Al_0.10 at the 200th cycle is 71%.     

Preparation and characterization of novel spinel Li4Ti5O12−xBrx anode materials

Br-doped Li₄Ti₅O₁₂ in the form of Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) compounds were successfully synthesized via solid state reaction. The structure and electrochemical properties of the spinel Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) materials were investigated. The Li₄Ti₅O_12−xBr_x (x = 0.2) presents the best discharge capacity among all the samples, and shows better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂, especially at high current rates. When the discharge rate was 0.5 C, the Li₄Ti₅O_12−xBr_x (x = 0.2) sample presented the excellent discharge capacity of 172 mAh g⁻¹, which was very close to its theoretical capacity (175 mAh g⁻¹), while that of the pristine Li₄Ti₅O₁₂ was 123.2 mAh g⁻¹ only.     

Evolution of the local structure and electrochemical properties of spinel LiNixMn2−xO4 (0 ≤ x ≤ 0.5)

A series of Ni substituted spinel LiNi_xMn_2−xO₄ (0 ≤ x ≤ 0.5) have been synthesized to study the evolution of the local structure and their electrochemical properties. X-ray diffraction showed a few Ni cations moved to the 8a sites in heavily substituted LiNi_xMn_2−xO₄ (x ≥ 0.3). X-ray photoelectron spectroscopy confirmed Ni²⁺ cations were partially oxidized to Ni³⁺. The local structures of LiNi_xMn_2−xO₄ were studied by analyzing the and A_1g Raman bands. The most compact [Mn(Ni)O₆] octahedron with the highest bond energy of Mn(Ni)O was found for LiNi_0.2Mn_1.8O₄, which showed a Mn(Ni)O average bond length of 1.790 Å, and a force constant of 2.966 N cm⁻¹. Electrolyte decomposition during the electrochemical charging processes increased with Ni substitution. The discharge capacities at the 4.1 and 4.7 V plateaus obeyed the linear relationships with respect to the Ni substitution with the slopes of −1.9 and +1.9, which were smaller than the theoretical values of −2 and +2, respectively. The smaller slopes could be attributed to the electrochemical hysteresis and the presence of Ni³⁺ in the materials.     

Sintering behavior and microwave dielectric properties of a new low-permittivity ceramic system Ca(Mg1−xAlx)(Si1−x/2Alx/2)2O6

The diopside ceramics with a formula of Ca(Mg_1−xAl_x)(Si_1−x/2Al_x/2)₂O₆ (x=0.01–0.3) were synthesized via a traditional solid-state reaction method, and their solid solubility, sintering behavior and microwave dielectric properties were investigated. The results revealed that the solubility limit of Al₂O₃ in Ca(Mg_1−xAl_x)(Si_1−x/2Al_x/2)₂O₆, which is defined as x, was between 0.15 and 0.2, and a second phase of CaAl₂SiO₆ presented when the x value reached 0.2. Appropriate Al³⁺ substitution for Mg²⁺ and Si⁴⁺ could promote the sintering process and lower the densification temperature, and a broadened densification temperature range of 1250–1300 °C was obtained for the compositions of x=0.08–0.15. With the increase of the x value, the dielectric constant (ε_r) increased roughly linearly, and the temperature coefficient of frequency (τ_f) showed a rising trend. The Q×f values increased from 57,322 GHz to 59,772 GHz as the x value increased from 0.01 to 0.08, and then they were saturated in the range of x=0.08–0.2. Further increase of the x value (x≥0.25) deteriorated the microwave dielectric properties. Good microwave dielectric properties of ε_r=7.89, Q×f=59,772 GHz and τ_f=−42.12 ppm/°C were obtained for the ceramics with the composition of x=0.08 sintered at 1275 °C.     

Combustion synthesis of Ca1−xCuxAl2O4 (x = 0.0, 0.4 and 0.8) copper doped calcium aluminate

We report the effect of Cu²⁺ ion on CaAl₂O₄ with different molar concentrations of 0.0, 0.4 and 0.8 M prepared by simple combustion method. The materials have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR) and scanning electron microscopy (SEM). DC electrical conductivity has also been measured to study the electrical behavior of the materials. The XRD patterns confirm the formation of single-phase CaAl₂O₄ along with some impurity phases like CaAl₄O₇, CaAl₁₂O₁₉ and Ca₁₂Al₁₄O₃₃. The FT-IR spectra show the stretching and bending vibrations of the synthesized compounds. DC electrical conductivity of the Ca_1−xCu_xAl₂O₄ is found to vary from 26.46 × 10⁻⁴ to 515.68 × 10⁻⁴ S cm⁻¹ for x = 0.0 to x = 0.8 at the measuring temperature of 1000 °C. SEM images show the morphological features of the compounds.     

Influence of the tetravalent cation on the high-voltage electrochemical activity of LiNi0.5M1.5O4 spinel cathode materials

The electrochemical properties of substituted LiNi_0.5Mn_1.5−xM_xO₄ spinels at high potential (>4 V vs Li⁺/Li) have been investigated for M = Ti and Ru, in order to determine the role of the tetravalent cation in such systems where nickel is a priori the only electroactive species. These systems are found to form extended solid solutions (up to x = 1.3 and x = 1.0 for Ti and Ru, respectively) that were characterized by X-ray diffraction and Raman spectroscopy. Titanium substitution induces a drastic decrease in high potential electrochemical capacity, whereas the capacity is maintained and the kinetics are even improved in the presence of ruthenium. These results are completed by new results on the Li_4−2xNi_3xTi_5−xO₁₂ spinel system, which shows not any high potential activity in spite of the presence of up to 0.5 Ni²⁺ per spinel formula unit on the octahedral site. Taking into account previous data on LiNi_0.5Ge_1.5O₄, we clearly show that even if the tetravalent cation does not participate in the overall redox reaction, electrochemical activity is only possible when nickel is surrounded by tetravalent cations able to accept a local variation of valence (Mn, Ru), whereas full-shell cations such as Ti⁴⁺ and Ge⁴⁺ block the necessary electron transfer pathways in the spinel oxide electrode.     

Comparative study of Li[Co1−zAlz]O2 prepared by solid-state and co-precipitation methods

Li[Co_1−zAl_z]O₂ (0 ≤ z ≤ 0.5) samples were prepared by co-precipitation and solid-state methods. The lattice constants varied smoothly with z for the co-precipitated samples but deviated for the solid-state samples above z = 0.2. The solid-state method may not produce materials with a uniform cation distribution when the aluminum content is large or when the duration of heating is too brief. Non-stoichiometric Li_x[Co_0.9Al_0.1]O₂ samples were synthesized by the co-precipitation method at various nominal compositions x = Li/(Co + Al) = 0.95, 1.0, 1.1, 1.2, 1.3. XRD patterns of the Li_x[Co_0.9Al_0.1]O₂ samples suggest the solid solution limit is between Li/(Co + Al) = 1.1 and 1.2. Electrochemical studies of the Li[Co_1−zAl_z]O₂ samples were used to measure the rate of capacity reduction with Al content, found to be about −250 ± 30 (mAh/g)/(z = 1). Literature work on Li[Ni_1/3Mn_1/3Co_1/3−zAl_z]O₂, Li[Ni_1−zAl_z]O₂ and Li[Mn_2−yAl_y]O₄ demonstrates the same rate of capacity reduction with Al/(Al + M) ratio. These studies serve as baseline characterization of samples to be used to determine the impact of Al content on the thermal stability of delithiated Li[Co_1−zAl_z]O₂ in electrolyte.     

Combustion synthesis of (Ti1−xNbx)2AlC solid solutions from elemental and Nb2O5/Al4C3-containing powder compacts

Preparation of the (Ti_1−xNb_x)₂AlC solid solution (formed from the M_n+1AX_n or MAX carbides, where n = 1, 2, or 3, M is an early transition metal, A is an A-group element, and X is C) with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS). Nearly single-phase (Ti,Nb)₂AlC was produced through direct combustion of constituent elements. Due to the decrease of reaction exothermicity, the combustion temperature and reaction front velocity decreased with increasing Nb content of (Ti_1−xNb_x)₂AlC formed from the elemental powder compacts. In addition, the samples composed of Ti, Al, Nb₂O₅, and Al₄C₃ were adopted for the in situ formation of Al₂O₃-added (Ti,Nb)₂AlC. The SHS process of the Nb₂O₅/Al₄C₃-containing sample involved aluminothermic reduction of Nb₂O₅, which not only enhanced the reaction exothermicity but also facilitated the evolution of (Ti,Nb)₂AlC. Based upon the XRD analysis, two intermediates, TiC and Nb₂Al, were detected in the (Ti,Nb)₂AlC/Al₂O₃ composite and their amounts were reduced by increasing the extent of thermite reduction involved in the SHS process. The laminated microstructure characteristic of the MAX carbide was observed for both monolithic and Al₂O₃-added (Ti,Nb)₂AlC solid solutions synthesized in this study.     

Effect of TiO2 on phase evolution and microstructure of MgAl2O4 spinel in different atmospheres

The effect of TiO₂ on the formation and microstructure of magnesium aluminate spinel (MgAl₂O₄) at 1600 °C in air and reducing conditions were investigated. Under reducing conditions, stoichiometric MgAl₂O₄ spinel shifted toward alumina-rich types owing to volatilization of MgO, resulting in an increase in the porosity of fired samples. Addition of graphite to mixtures of MgO and Al₂O₃ intensified the reducing conditions and accelerated the formation of non-stoichiometric MgAl₂O₄. For TiO₂-containing samples on addition of MgAl₂O₄, magnesium aluminum titanium oxide (Mg_xAl_2(1−x)Ti_(1+x)O₅, x = 0.2 or 0.3) was detected as a minor phase. Under reducing conditions, XRD peak shifts were smaller for TiO₂-containing samples than for samples without TiO₂ owing to the formation of a solid solution of TiO₂ in MgAl₂O₄ and establishment of alumina-rich spinel, which have opposite effects on increasing the lattice parameter. In bauxite-containing samples, MgAl₂O₄ spinel, corundum, magnesium orthotitanate spinel (Mg₂TiO₄) and amorphous phases were identified. Mg₂TiO₄ spinel formed a complete solid solution with MgAl₂O₄ spinel but Mg₂TiO₄ remained as a distinct phase owing to the heterogeneous microstructure of bauxite-containing samples. Also dense microstructure established in air fired TiO₂ containing samples. The results are discussed with emphasis on the application and design of alumina-magnesia-carbon refractory materials, which are used in the steel industry.     

A novel layered Li [Li0.12NizMg0.32−zMn0.56]O2 cathode material for lithium-ion batteries

Layered Li[Li_0.12Ni_zMg_0.32−zMn_0.56]O₂ oxide cathodes containing lithium atoms in the transition metal layers were synthesized and characterized using X-ray diffraction (XRD), galvanostatic cycling, and differential scanning calorimetry (DSC). The Li[Li_0.12Ni_zMg_0.32−zMn_0.56]O₂ cathodes deliver a specific discharge capacity of about 190 mAh/g at room temperature and 236 mAh/g at 55 °C when cycled between 2.7 and 4.6 V versus Li/Li⁺. Excellent capacity retention and smooth potential profiles at room and elevated temperatures over extended cycles suggest that this material does not convert into a spinel structure.     

Preparation and cycling performance of Aland F co-substituted compounds Li4AlxTi5−xFyO12−y

Li₄Al_xTi_5−xF_yO_12−y compounds were prepared by a solid-state reaction method. Phase analyses demonstrated that both Al³⁺ and F⁻ ions entered the structure of spinel-type Li₄Ti₅O₁₂. Charge-discharge cycling results at a constant current density of 0.15 mA cm⁻² between the cut-off voltages of 2.5 and 0.5 V showed that the Al³⁺ and F⁻ substitutions improved the first total discharge capacity of Li₄Ti₅O₁₂. However, Al³⁺ substitution greatly increased the reversible capacity and cycling stability of Li₄Ti₅O₁₂ while F⁻ substitution decreased its reversible capacity and cycling stability slightly. The electrochemical performance of the Al³⁺-F⁻-co-substituted specimen was better than the F⁻-substituted one but worse than the Al³⁺-substituted one.     

Effective factor on antibacterial characteristics of Mg1−XNiXO solid solution

Mg_1−XNi_XO solid solution powder samples with different chemical compositions were prepared by heating MgO–NiO mixtures at 1300 °C for 12 h in air. From XRD measurement, all powder samples were indexed as a single phase of cubic structure, of which the diffraction peaks shifted to high-angle side with the increase of doping amount of NiO. The pH values of the solution dispersed with the powder samples decreased when the doping amount of NiO in solid solution was increased. Antibacterial activity of the powder samples was examined by colony count method. In the result, the antibacterial activity of Mg_1−XNi_XO was remarkably weaker than original MgO powders, irrespective of the kind of bacteria. In addition, it was found that the antibacterial activity of Mg_1−XNi_XO reduced with increasing the doping amount of NiO. Two factors, the generated amount of O₂⁻ and the eluted amount of Ni²⁺ ions affected the antibacterial activity of Mg_1−XNi_XO solid solution. Especially, the stability of O₂⁻ in aqueous solution is dependent on pH value. Therefore, the strength of antibacterial activity was associated with the pH values in the dispersed solution of Mg_1−XNi_XO.     

Structural and magnetic properties of NiFe2−xBixO4 (x = 0, 0.1, 0.15) nanoparticles prepared via sol-gel method

NiFe_2−xBi_xO₄ (x = 0, 0.1, 0.15) nanopowders were synthesized via sol-gel method. The precursor gels were calcined at 773 K in air for 1 h to obtain the pure nanostructured NiFe_2−xBi_xO₄ spinel phase. The crystal structure and magnetic properties of the substituted spinel series of NiFe_2−xBi_xO₄ have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy, transmission electron microscopy and alternating gradient force magnetometry. Mössbauer spectroscopic measurements revealed that Bi³⁺ cations tend to occupy octahedral positions in the structure of the substituted ferrite, i.e., the crystal-chemical formula of the as-prepared nanoparticles may be written as: (Fe)[NiFe_1−xBi_x]O₄ (x = 0, 0.1, 0.15), where parentheses and square brackets enclose cations on sites of tetrahedral and octahedral coordination, respectively. Selective area electron diffraction studies provided evidence that the samples of the NiFe_2−xBi_xO₄ series, independently of x, exhibit the cubic spinel structure. The values of the saturation magnetization and the coercive field of NiFe_2−xBi_xO₄ nanoparticles were found to decrease with increasing degree of bismuth substitution.     

Preparation and microstructural characterization of (Nd1−xGdx)2(Ce1−xZrx)2O7 solid solutions

(Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ (0 ≤ x ≤ 1.0) powders with an average particle size of 100 nm were synthesized with chemical-coprecipitation and calcination method, and were characterized by X-ray diffractometry and scanning electron microscopy. The sintering behaviour of (Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ powders was studied by pressureless sintering at 1600–1700 °C for 10 h in air. The relative densities of (Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ solid solutions increase with increasing the sintering temperature, and gradually decrease with increasing the content of neodymium and cerium at identical temperature levels. (Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ solid solutions have a single phase of defect fluorite-type structure among all the composition combinations studied. The lattice parameters of (Nd_1−xGd_x)₂(Ce_1−xZr_x)₂O₇ solid solutions agree well with the Vegard's rule.     

Synthesis and negative thermal expansion property of Y2−xLaxW3O12 (0≤x≤2)

Y_2−xLa_xW₃O₁₂ solid solutions were successfully synthesized by the solid state reaction method. The microstructure, hygroscopicity and thermal expansion property of the resulting samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and thermal mechanical analysis (TMA). Results indicate that the structural phase transition of the Y_2−xLa_xW₃O₁₂ changes from orthorhombic to monoclinic with increasing substituted content of lanthanum. The pure phase can form for 0≤x≤0.4 with orthorhombic structure and for 1.5≤x≤2 with monoclinic one. High lanthanum content leads to a low relative density of Y_2−xLa_xW₃O₁₂ ceramic. Thermal expansion coefficients of the Y_2−xLa_xW₃O₁₂ (0≤x≤2) ceramics also vary from −9.59×10⁻⁶ K⁻¹ to 2.06×10⁻⁶ K⁻¹ with increasing substituted content of lanthanum. The obtained Y_0.25La_1.75W₃O₁₂ ceramic shows almost zero thermal expansion and its average linear thermal expansion coefficient is −0.66×10⁻⁶ K⁻¹ from 103 °C to 700 °C.     

Phase transition and negative thermal expansion properties of Sc2−xCrxMo3O12

The crystal structure, phase transition and thermal expansion behaviors of solid solutions Sc_2−xCr_xMo₃O₁₂ (0≤x≤2) were investigated using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). At room temperature, samples with x≤0.7 and x≥0.8 crystallize in orthorhombic and monoclinic structures, respectively. DSC result indicates that the phase transition of Sc_0.5Cr_1.5Mo₃O₁₂ from monoclinic to orthorhombic structure occurs at 203.66 °C. The linear thermal expansion coefficient of orthorhombic phases varies from −2.334×10⁻⁶ °C⁻¹ to 0.993×10⁻⁶ °C⁻¹ when x increases from 0.0 to 1.5. The near-zero linear thermal expansion coefficients of −0.512×10⁻⁶ °C⁻¹ and −0.466×10⁻⁶ °C⁻¹ are observed for compounds with x=0.5 and 0.7, respectively.     

CoAl2O4 spinel catalyst for soot combustion with NOx/O2

Mesoporous and nanosized cobalt aluminate spinel with high specific surface area was prepared using microwave assisted glycothermal method and used as soot combustion catalyst in a NO_x + O₂ stream. For comparison, zinc aluminate spinel and alumina supported platinum catalysts were prepared and tested. All samples were characterised using XRD, (HR)TEM, N₂ adsorption–desorption measurements. The CoAl₂O₄ spinel was able to oxidise soot as fast as the reference Pt/Al₂O₃ catalyst. Its catalytic activity can be attributed to a high NO_x chemisorption on the surface of this spinel, which leads to the fast oxidation of NO to NO₂.     

Effect of La/Ce ratio on the structure and electrochemical characteristics of La0.7−xCexMg0.3Ni2.8Co0.5 (x = 0.1-0.5) hydrogen storage alloys

The effect of La/Ce ratio on the structure and electrochemical characteristics of the La_0.7−xCe_xMg_0.3Ni_2.8Co_0.5 (x = 0.1, 0.2, 0.3, 0.4, 0.5) alloys has been studied systematically. The result of the Rietveld analyses shows that, except for small amount of impurity phases including LaNi and LaNi₂, all these alloys mainly consist of two phases: the La(La, Mg)₂Ni₉ phase with the rhombohedral PuNi₃-type structure and the LaNi₅ phase with the hexagonal CaCu₅-type structure. The abundance of the La(La, Mg)₂Ni₉ phase decreases with increasing cerium content whereas the LaNi₅ phase increases with increasing Ce content, moreover, both the a and cell volumes of the two phases decrease with the increase of Ce content. The maximum discharge capacity decreases from 367.5 mAh g⁻¹ (x = 0.1) to 68.3 mAh g⁻¹ (x = 0.5) but the cycling life gradually improve. As the discharge current density is 1200 mA g⁻¹, the HRD increases from 55.4% (x = 0.1) to 67.5% (x = 0.3) and then decreases to 52.1% (x = 0.5). The cell volume reduction with increasing x is detrimental to hydrogen diffusion D and accordingly decreases the low temperature dischargeability of the La_0.7−xCe_xMg_0.3Ni_2.8Co_0.5 (x = 0.1-0.5) alloy electrodes.