Synthesis and electrochemical behavior of layered Li(Ni0.5−xCo2xMn0.5−x)O2 (x = 0 and 0.025) materials prepared by solid-state reaction method

Layered Li(Ni_0.5−xCo_2xMn_0.5−x)O₂ (x=0 and 0.025) materials were prepared by conventional solid state reaction method combined with high energy ball milling (HEBM). The Li(Ni_0.5−xCo_2xMn_0.5−x)O₂ electrodes delivered discharge capacity of 142-185 mAh/g depending on upper cut-off voltage limit with excellent cycleability. The charge/discharge and differential capacity versus voltage studies show that only one phase reaction occurs and no phase transition takes place during the electrochemical cycling.     

Microstructure and martensitic transformation of Ti49Ni51 − xHfx high temperature shape memory alloys

In present work, the microstructure and martensitic transformation of Ti₄₉Ni_51 − xHf_x (x = 3-15) alloys were studied. The microstructure of Ti₄₉Ni_51 − xHf_x alloys consists of B19′ martensite and (Ti,Hf)₂Ni phase at room temperature. The martensitic transformation behavior is characterized by a single-stage transformation. With increasing Hf content, the transformation temperature increases from 75 to 279 °C resulting from the reduced valence electron concentration, indicating that the replacement of Hf for Ni is effective in increasing the transformation temperatures. The results suggest that the Ti₄₉Ni_51 − xHf_x shape memory alloy is one of potential candidates for high temperature applications.     

Oxide-ion conductivity in CuxCe1−xO2−δ (0 ≤ x ≤ 0.10)

Up to 10 at.% of copper readily substitutes for cerium in ceria. It is found that at oxygen partial pressures between 0.21 atm and 10⁻⁵ atm, Cu_xCe_1−xO_2−δ (0 ≤ x ≤ 0.10) solid solution behave as an oxide-ion electrolyte. Interestingly, Cu_0.10Ce_0.90O_2−δ exhibits the oxide-ion conductivity of ca. 10⁻⁴ Ω⁻¹ cm⁻¹ at 600 °C at an oxygen partial pressure of 10⁻⁵ atm.     

Structural and electrical properties of La2−xBaxMo2O9−x/2 (x = 0-0.18)

La_2−xBa_xMo₂O_9−x/2 (x ≤ 0.18) have been prepared by solid state reaction method. The lattice parameter of La_2−xBa_xMo₂O_9−x/2 (x ≤ 0.18) determined by XRD data refinement shows a linear dependence on the dopant Ba content x. For the specimen with a La/Ba molar ratio of 0.18-0.2, additional reflection of secondary phase exists in the XRD pattern, so the value of solubility limit for Ba in La₂Mo₂O₉ is defined in range of 0.18 < x < 0.2. As the replacement degree of La³⁺ by Ba²⁺ increases, the bulk conductivity of La_2−xBa_xMo₂O_9−x/2 (x ≤ 0.18) decreases initially and then increases, a minimum value at La_1.9Ba_0.1Mo₂O_8.95 exists. Hebb-Wagner studies in argon atmosphere, which use an oxide-ion blocking electrode, show that La_2−xBa_xMo₂O_9−x/2 (x ≤ 0.18) are predominantly oxide-ion conducting in the temperature ranging from 773 to 1173 K. The average thermal expansion coefficient of La_1.84Ba_0.16Mo₂O_8.92 determined by high-temperature XRD was deduced as great as 17.5 × 10⁻⁶ K⁻¹ between 298 and 1173 K.     

Synthesis of perovskite-type (La1−xCax)FeO3 (0 ≤ x ≤ 0.2) at low temperature

Gel formation was realized by adding citric acid to a solution of La(NO₃)₃·5H₂O, Ca(NO₃)₂·4H₂O, and Fe(NO₃)₂·9H₂O. Perovskite-type (La_1−xCa_x)FeO₃ (0 ≤ x ≤ 0.2) was synthesized by firing the gel at 500 °C in air for 1 h. The crystallite size (D_1 2 1) decreased with increasing x, while the specific surface area was 6.8-9.4 m²/g and independent of x. The XPS measurement of the (La_1−xCa_x)FeO₃ surface indicated that the Ca²⁺ ion content increased with increasing x, while the Fe ion content was independent of x. Catalytic activity for CO oxidation increased with increasing x.     

Order-disorder phase transitions and high-temperature oxide ion conductivity of Er2+xTi2−xO7−δ (x = 0, 0.096)

The Er_2+xTi_2−xO_7−δ (x = 0.096; 35.5 mol% Er₂O₃) solid solution and the stoichiometric pyrochlore-structured compound Er₂Ti₂O₇ (x = 0; 33.3 mol% Er₂O₃) are characterized by X-ray diffraction (phase analysis and Rietveld method), thermal analysis and optical spectroscopy. Both oxides were synthesized by thermal sintering of co-precipitated powders. The synthesis study was performed in the temperature range 650-1690 °C. The amorphous phase exists below 700 °C. The crystallization of the ordered pyrochlore phase (P) in the range 800-1000 °C is accompanied by oxygen release. The ordered pyrochlore phase (P) exists in the range 1000−1200 °C. Heat-treatment at T ≥ 1600 °C leads to the formation of an oxide ion-conducting phase with a distorted pyrochlore structure (P2) and an ionic conductivity of about 10⁻³ S/cm at 740 °C. Complex impedance spectra are used to separately assess the bulk and grain-boundary conductivity of the samples. At 700 °C and oxygen pressures above 10⁻¹⁰ Pa, the Er_2+xTi_2−xO_7−δ (x = 0, 0.096) samples are purely ionic conductors.     

Rietveld refinements of the solid solution Li(1−2x)NixTiO(PO4) (0 ≤ x ≤ 0.50)

Li_(1−2x)Ni_xTiO(PO₄) oxyphosphates with 0 ≤ x ≤ 0.10 crystallize in the orthorhombic system with the space group Pnma, those with 0.10 < x ≤ 0.25 crystallize in the monoclinic system with the space group P2₁/c and compositions with 0.25 < x < 0.50 present a mixture of the limit of the solid solution Li_0.50Ni_0.25TiO(PO₄) and Ni_0.50TiO(PO₄). The structure of the compositions 0 ≤ x ≤ 0.25 is based on a three-dimensional anionic framework constructed of chains of alternating TiO₆ octahedra and PO₄ tetrahedra, with the lithium and nickel atoms in the cavities in the framework. The dominant structural units in the compositions are chains of tilted corner-sharing TiO₆ octahedra running parallel to one of the axis. The oxygen atoms of the shared corners, not implied in (PO₄) tetrahedra, justify the oxyphosphate designation. Titanium atoms are displaced from the geometrical center of the octahedra resulting in alternating long (≈2.25 Å) and short (≈1.71 Å) TiO(1) bonds. The four remaining TiO bond distances have intermediate values ranging from 1.91 to 2.06 Å.     

Structure and magnetism in the oxygen-deficient perovskites Ce1−xSrxCoO3−δ (x ≥ 0.90)

We have examined the structure and phase behaviour of strontium-doped Ce_1−xSr_xCoO_3−δ and found that the perovskite form is stabilised over a relatively narrow solid solution range (x > 0.85). A combination of electron, powder X-ray and neutron diffraction has revealed tetragonal superstructures of the basic perovskite unit; (I4/mmm) 2a_p × 2a_p × 4a_p (x = 0.90) and (P4/mmm) a_p × a_p × 2a_p (x = 0.95). Magnetisation measurements show ferromagnetic behaviour under applied magnetic fields. Low temperature neutron diffraction of Ce_0.10Sr_0.90CoO_2.80 in zero field reveals a magnetic cell of dimension 2a_p × 2a_p × 4a_p with an ordered cobalt moment of 1.7 B.M. at 25 K.     

Basic properties of Sr1 − xBaxSi2

Basic properties, such as the phase relationship, crystal structure, and energy gap E_g, have been investigated in Sr-rich Sr_1 − xBa_xSi₂. Sr_1 − xBa_xSi₂ (0 ≤ x ≤ 1.0) has two phases: one with the SrSi₂-type structure and another with the BaSi₂-type structure. The SrSi₂ phase exists at x ranging from 0 to 0.13, and the BaSi₂ phase exists at x ranging from 0.24 to 1.0. The volume increases with x in both the SrSi₂ and BaSi₂ phases. A volume jump of 13.7% appears at the structural phase transition from the SrSi₂ phase to the BaSi₂ phase. E_g increases with x in SrSi₂-phase Sr_1 − xBa_xSi₂ but E_g decreases with x in the BaSi₂-phase Sr_1 − xBa_xSi₂. In Sr-rich BaSi₂-phase Sr_1 − xBa_xSi₂, Ba atoms at a specific crystallographic site, the A1 site, are preferentially substituted by Sr atoms, as well as in Ba-rich BaSi₂-phase Sr_1 − xBa_xSi₂.     

Electrochemical behaviors of Li[Li(1−x)/3Mn(2−x)/3Nix/3Cox/3]O2 cathode series (0 < x < 1) synthesized by sucrose combustion process for high capacity lithium ion batteries

A mixed cathode material between Li₂MnO₃ and Li[Mn_1/3Ni_1/3Co_1/3]O₂ for high capacity lithium secondary batteries was introduced in this study. It was prepared using the sucrose combustion process because this is a simple process. The oxidation states of Mn, Co and Ni ions in the pristine Li[Li_(1−x)/3Mn_(2−x)/3Ni_x/3Co_x/3]O₂ compounds were confirmed to be tetravalent, trivalent and divalent, respectively, via XANES measurements. Electrochemical charge/discharge studies showed that the highest first discharge capacity of 224 mAh/g was obtained in composition of x = 0.5 at a 0.2 C rate. The oxidation state of the Co and Ni ions in the Li[Li_1/6Mn_1/2Ni_1/6Co_1/6]O₂ changed to higher oxidation states, but that of the Mn ions did not change.     

Impurity induced band-gap narrowing in p-type CuIn1 − xGax(S,Se)2

Green's functions modelling of the impurity induced effects in p-type CuIn_1 − xGa_xS₂ and CuIn_1 − xGa_xSe₂ (x = 0.0, 0.5, and 1.0) reveals that: (i) the critical active acceptor concentration for the metal non-metal transition occurs at N_c ≈ 10¹⁷-10¹⁸ cm^− 3 for impurities with ionization energy of E_A ≈ 30-60 meV. (ii) For acceptor concentrations N_A > N_c, the hole gas of the metallic phase affects the band-edge energies and narrows the energy gap E_g = E_g⁰ − ΔE_g. The energy shift of the valence-band maximum ΔE_v1 is roughly twice as large as the shift of the conduction-band minimum ΔE_c1. (iii) ΔE_v1 depends strongly on the non-parabolicity of the valence bands. (iv) Sulfur based compounds and Ga-rich alloys have the largest shifts of their band edges. (v) A high active acceptor concentrations of N_A = 10²⁰ cm^− 3 implies a band-gap narrowing in the order of ΔE_g ≈ 0.2 eV, thus E_g = E_g⁰ − 0.2 eV, and an optical band gap of E_g^opt ≈ E_g⁰ − 0.1 eV.     

Synthesis and electrochemical properties of Ti doped Li3 − xFe2 − xTix(PO4)3/C cathode materials

Li_3 − xFe_2 − xTi_x(PO₄)₃/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li₃Fe₂(PO₄)₃/C (x = 0) and Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C (x = 0.2) possess two plateau potentials of Fe³⁺/Fe²⁺ couple (around 2.8 V and 2.7 V vs. Li⁺/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C has higher reversibility and better capacity retention than that of the undoped Li₃Fe₂(PO₄)₃/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.     

Preparation and characterization of La-doped Ba(1 − x)SrxTiO3 powders and thin films

Ba_(1 − x)Sr_xTiO₃ powders with different Ba/Sr ratios (x = 0.10, 0.25, 0.40, 0.55, 0.70) and La-doped Ba_0.9Sr_0.1TiO₃·yLa powders (y = 0.002, 0.004, 0.006, 0.008, 0.010) have been prepared by sol-gel technology using dehydrated barium-acetate, strontium-carbonate, lanthanum-nitrate, and titanium-isopropoxide as raw materials. The experimental results show that the dielectric properties of Ba_(1 − x)Sr_xTiO₃ powders depend on the Ba/Sr ratios. When the Sr fraction is 0.10, the dielectric constant is relatively higher and the dielectric loss is relatively lower, which are more than 2000 and less than 2.0 × 10^− 2 at 1000 Hz, respectively, the most important is that this kind of powder has better frequency stability. La-doping can increase the dielectric constant distinctly, but the dielectric loss can also be increased. Their dielectric properties at 1.0 × 10³ Hz are better than those at 1.0 × 10⁵ Hz. At 1.0 × 10³ Hz the dielectric constant is much higher, while the dielectric loss is much lower. The dielectric constant of different La-doping contents is nearly 3.5 × 10⁴ and the dielectric loss is less than 0.20 when La fraction is 0.008. The La-doped BST sample also has better frequency stability, especially at high frequency. La-doped BST thin films are successfully deposited on mild steel substrates by using plasma spray system with suspension precursors of Ba_0.90Sr_0.10TiO₃·0.8La powders. The XRD patterns of Ba_0.90Sr_0.10TiO₃ and Ba_0.90Sr_0.10TiO₃·0.8La powders are almost the same. No new peaks appear after La-doping, but the peaks move slightly to a larger degree, which indicates that the element La has entered the lattice of the Ba_0.90Sr_0.10TiO₃ and has made the constant of the crystal cell reduce. The XRD pattern of the thin films is just like that of the Ba_0.90Sr_0.10TiO₃·0.8La powders except a peak corresponding to Fe substrate. The SEM results show that the thin films have a uniform and smooth surface. The morphology of cross-section shows a columnar grain structure indicating smooth surface and uniform thickness of the film. The thickness of the film is about 15 um. The thin films obtained are expected to be prospective material for applications in tunable microwave devices.     

Synthesis, low-temperature sintering and the dielectric properties of the ZnO-(1 − x)TiO2-xSnO2 (x = 0.04-0.2)

ZnO-(1 − x)TiO₂-xSnO₂ (x = 0.04-0.2) ceramics were prepared by conventional mixed-oxide method combined with a chemical processing. Fine particle powders were prepared by chemical processing to activate the formation of compound and to improve the sinterability. One wt.% of V₂O₅ and B₂O₃ with the mole ratios of 3:1 were used to lower the sintering temperature of ceramics. The effect of Sn content on phase structure and dielectric properties were investigated. The results show that the substituting Sn for Ti accelerates the hexagonal phase transition to cubic phase, and an inverse spinel structure Zn₂(Ti_1−xSn_x)O₄ solid solution forms. The best dielectric properties obtained at x = 0.12. The ZnO-0.88TiO₂-0.12SnO₂ ceramics sintered at 900 °C exhibit a good dielectric property: ?_r = 29 and tan δ = 9.86 × 10⁻⁵. Due to their good dielectric properties, low firing characteristics, ZnO-(1 − x)TiO₂-xSnO₂ (x = 0.04-0.2) can serve as the promising microwave dielectric capacitor.     

Synthesis of spherical nanostructured LiMxMn2−xO4 (M = Ni, Co, and Ti; 0 ≤ x ≤ 0.2) via a single-step ultrasonic spray pyrolysis method and their high rate charge-discharge performances

LiM_xMn_2−xO₄ (M = Ni²⁺, Co³⁺, and Ti⁴⁺; 0 ≤ x ≤ 0.2) spinels were prepared via a single-step ultrasonic spray pyrolysis method. Comparative studies on powder properties and high rate charge-discharge electrochemical performances (from 1 to 15 C) were performed. XRD identified that pure spinel phase was obtained and M was successfully substituted for Mn in spinel lattice. SEM and TEM studies confirmed that powders had a feature of ‘spherical nanostructural’, that is, powders consisted of spherical secondary particles with the size of about 1 μm, which were developed from close-packed primary particles with several tens of nanometers. Substitutions enhanced density of second particles to different extents, depending on M and its content. Charge-discharge tests showed that as-prepared LiMn₂O₄ could deliver excellent rate performance (around 100 mAh/g at 10 C). Ni substitution contributed to improving electrochemical performances. In the voltage range of 4.95-3.5 V, the materials showed much better electrochemical performances than LiMn₂O₄ in terms of capacity, cycleability and rate capability.     

All-solid-state cells based on solid electrolyte systems Cu1−xAgxI-Ag2O-Y, where x = 0.05-0.25; Y = MoO3, B2O3, SeO2, V2O5 and CrO3

All-solid-state cells of the configuration (−)Ag + SE//SE//I₂-phenothiazine + C(+) using the best conducting compositions of the solid electrolyte systems, namely, Cu_1−xAg_xI-Ag₂O-Y where x = 0.05, 0.1, 0.15, 0.2 and 0.25, Y = MoO₃, B₂O₃, SeO₂, V₂O₅ and CrO₃, as the electrolytes were fabricated. Discharge, polarization and power characteristics of these cells were also evaluated. The open circuit voltage values of these cells were in the range 620-635 mV. The stability of these cells has been indicated by the constancy of their OCV over a period of 6 months. The polarization and discharge studies on these cells have shown that typical cells based on the electrolytes with Y = B₂O₃, SeO₂ and V₂O₅ would possess discharge capacities of 12.84, 3.76 and 5.05 mA h and specific energy of 6.55, 1.81 and 2.77 W h kg⁻¹, respectively. The solid electrolytes have good electrochemical stability and compatibility with the Ag/Phenothiazine-I₂ electrode couple thus offering their suitability of application in microwatt power sources.     

Structural and transport properties of stoichiometric Mn-doped magnetite: Fe3−xMnxO4

The polycrystalline samples of Fe_3−xMn_xO₄ (0.10 ≤ x ≤ 0.50) were prepared by a solid-state route reaction method. X-ray diffraction pattern shows that Mn²⁺ doped magnetites are in single phase and possess cubic inverse spinel structure. The resistivity measurements (10 < T < 300 K) for x = 0.0 and 0.01 confirms the first order phase transition at the Verwey transition T_V = 123 K and 117 K, respectively. No first order phase transition was evidenced for Fe_3−xMn_xO₄ (0.10 ≤ x ≤ 0.50). Small polaron model has been used to fit the semiconducting resistivity behavior and the activation energy ?_a, for samples x = 0.10 and 0.50 is about 72.41 meV and 77.39 meV, respectively. The Raman spectra of Fe_3−xMn_xO₄ at room temperature reveal five phonons modes for Fe_3−xMn_xO₄ (0.01 ≤ x ≤ 0.50) as expected for the magnetite (Fe₃O₄). Increased Mn²⁺ doping at Fe site leads to a gradual changes in phonon modes. The Raman active mode for Fe_3−xMn_xO₄ (x = 0.50) at ≅641.5 cm⁻¹ is shifted as compared to parent Fe₃O₄ at ≅669.7 cm⁻¹, inferring that Mn⁺² ions are located mostly on the octahedral sites. The laser power is fixed to 5 mW causes the bands to broaden and to undergo a small shift to lower wave numbers as well as increase in the full width half maxima for A_1g phonon mode with the enhancement of Mn²⁺ doping. Mössbauer spectroscopy probes the site preference of the substitutions and their effect on the hyperfine magnetic fields confirms that Mn⁺² ions are located mostly on the octahedral sites of the Fe_3−xMn_xO₄ spinel structure.     

Thermal, spectroscopic and magnetic properties of the CoxNi1−x(SeO3)·2H2O (x = 0, 0.4, 1) phases: Crystal structure of Co0.4Ni0.6(SeO3)·2H2O

The Co_xNi_1−x(SeO₃)·2H₂O (x = 0, 0.4, 1) family of compounds has been hydrothermally synthesized under autogeneous pressure and characterized by elemental analysis, infrared and UV-vis spectroscopies and thermogravimetric and thermodiffractometric techniques. The crystal structure of Co_0.4Ni_0.6(SeO₃)·2H₂O has been solved from single-crystal X-ray diffraction data. This phase is isostructural with the M(SeO₃)·2H₂O (M = Co and Ni) minerals and crystallizes in the P2₁/n space group, with a = 6.4681(7), b = 8.7816(7), c = 7.5668(7) Å, β = 98.927(9)° and Z = 4. The crystal structure of this series of compounds consists of a three-dimensional framework formed by (SeO₃)²⁻ selenite oxoanions and edge-sharing M₂O₁₀ dimeric octahedra in which the metallic cations are coordinated by the oxygens belonging to both the selenite groups and water molecules. The diffuse reflectance spectra show the essential characteristics of Co(II) and Ni(II) cations in slightly distorted octahedral environments. The calculated values of the Dq and Racah (B and C) parameters are those habitually found for the 3d⁷ and 3d⁸ cations in octahedral coordination. The magnetic measurements indicate the existence of antiferromagnetic interactions in all the compounds. The magnetic exchange pathways involve the metal orbitals from edge-sharing dimeric octahedra and the (SeO₃)²⁻ anions which are linked to the M₂O₁₀ polyhedra in three dimensions.     

Synthesis and magnetic properties of layered MnPSxSe3−x (0 < x < 3) and corresponding intercalation compounds of 2,2′-bipyridine

In this work, we synthesize a series of new MnPS_xSe_3−x (0 < x < 3) compounds by high temperature solid-state reaction and also obtain the corresponding intercalation compounds (Mn_1−yPS_xSe_3−x(bipy)_4y, x = 1.2, 1.8 and 2.4) via the intercalation of 2,2′-bipyridine with MnPS_xSe_3−x. XRD results confirm that MnPS_xSe_3−x compounds show the layered structure and can be regarded as the solid solution of MnPS₃ and MnPSe₃. Magnetic measurements indicate that MnPS_xSe_3−x compounds exhibit paramagnetism with negative Weiss constant in the paramagnetic temperature region, and an antiferromagnetic phase transition occurs at the Neel temperature. It is found that the magnetic properties of MnPS_xSe_3−x slab are dramatically changed after the intercalation of 2,2′-bipyridine, which is close related to the relative ratio of S and Se atom as well as the intralayered Mn²⁺ vacancies of MnPS_xSe_3−x slab.     

Tantalum influence on physical properties of (K0.5Na0.5)(Nb1−xTax)O3 ceramics

Lead-free (K_0.5Na_0.5)(Nb_1−xTa_x)O₃ ceramics with x = 0.00-0.30 were prepared by the solid-state reaction technique. The effects of Ta on microstructure, crystallographic structure, phase transition and piezoelectric properties have been investigated. It has been shown that the substitution of Ta decreases Curie temperature T_C and orthorhombic-tetragonal phase transition temperature T_O-T, while increasing the rhombohedral-orthorhombic phase transition temperature T_R-O. In addition, piezoelectric activity is enhanced with the increase of Ta content. The ceramics with x = 0.30 have the high value of piezoelectric coefficient d₃₃ = 205 pC/N. Moreover, k_p shows little temperature dependence between −75° C and 75 °C, and d₃₃ exhibits very good thermal stability over the range from −196 °C to 75 °C in the aging test.