Nanocrystalline LiMn2O4 thin film cathode material prepared by polymer spray pyrolysis method for Li-ion battery

Nanocrystalline cubic spinel lithium manganese oxide thin film was prepared by a polymer spray pyrolysis method using lithium acetate and manganese acetate precursor solution and polyethylene glycol-4000 as a polymeric binder. The substrate temperature was selected from the thermogravimetric analysis by finding the complete crystallization temperature of LiMn₂O₄ precursor sample. The deposited LiMn₂O₄ thin films were annealed at 450, 500 and 600 °C for 30 min. The thin film annealed at 600 °C was found to be the sufficient temperature to form high phase pure nanocrystalline LiMn₂O₄ thin film. The formation of cubic spinel thin film was confirmed by X-ray diffraction study. Scanning electron microscopy and atomic force microscopy analysis revealed that the thin film annealed at 600 °C was found to be nanocrystalline in nature and the surface of the films were uniform without any crack. The electrochemical charge/discharge studies of the prepared LiMn₂O₄ film was found to be better compared to the conventional spray pyrolysed thin film material.     

Fabrication of LiMn2O4 thin film cathode from chitosan-containing solution

Thin film of spinel LiMn₂O₄ was obtained by spin coating the chitosan-containing precursor solution on a platinumized Si substrate, followed by a two-step annealing procedure at 300 and 700 °C, respectively. It was demonstrated that the addition of the appropriate amount of chitosan to the precursor solution enhanced the deposition of LiMn₂O₄ films. The thickness of the deposited film from chitosan-containing precursor solution is about 5.2 μm after five-time spin coating under a spinning speed of 2500 rpm. Without the addition of chitosan in precursor solution, the deposited film was as thin as 0.16 μm under the same processing parameters. Furthermore, the electrochemical behavior for the deposited LiMn₂O₄ film calcined at 700 °C for 1 h was characterized by the charge–discharge test. The result shows that the 1st discharge capacity is 56.31 μAh cm⁻² μm⁻¹ at a discharge rate of C/2 and the fading rate of the discharge capacity is only 0.19% cycle⁻¹ after 50 cycles.     

Ferroelectric properties of dysprosium-doped Bi4Ti3O12 thin films crystallized in various atmospheres

Dysprosium-doped Bi4Ti3O12 （Bi3.4Dy0.6Ti3O12, BDT） ferroelectric thin films were deposited on Pt（111）/Ti/SiO2/Si（111） substrates by chemical solution deposition （CSD） and crystallized in nitrogen, air and oxygen atmospheres, respectively. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were used to identify the crystal structure, the surface and cross-section morphology of the deposited ferroelectric films. The results show that the crystallization atmosphere has significant effect on determining the crystallization and ferroelectric properties of the BDT films. The film crystallized in nitrogen at a relatively low temperature of 650 ℃, exhibits excellent crystallinity and ferroelectricity with a remanent polarization of 2Pr = 24.9 ℃/cm^2 and a coercive field of 144.5 kV/cm. While the films annealed in air and oxygen at 650 ℃ do not show good crystallinity and ferroelectricity until they are annealed at 700 ℃. The structure evolution and ferroelectric properties of BDT thin films annealed under different temperatures （600-750 ℃） were also investigated. The crystallinity of the BDT films is improved and the average grain size increases when the annealing temperature increases from 600 ℃ to 750 ℃ at an interval of 50 ℃. However, the polarization of the films is not monotonous function of the annealing temperature.     

The influence of the transformation of electronic structure and micro-structure on improving the thermoelectric properties of zinc antimonide thin films

Measurements of electronic structure, microstructure and thermoelectric properties of zinc antimonide thin films prepared by direct current magnetron co-sputtering were carried out. The as-deposited zinc antimonide thin film had a very high resistivity similar to insulating ceramics, which was due to a low binding energy of both zinc and antimony, with the electron scattering increases and impedes the current transport. With the increase in annealing temperature, the films became more crystalline and the thermoelectric properties were also improved. The resistivity of the film decreased rapidly with its crystallinity when the annealing temperature was above 350 °C. The Seebeck coefficients of the thin films were positive, indicating that the films were P-type. The Seebeck coefficient of those samples increased with increasing annealing temperature. The thin film annealed at 400 °C has an optimal power factor of 1.87 × 10⁻³ Wm⁻¹ K⁻² with a Seebeck coefficient of 300 μVK⁻¹ and a resistivity of 4.82 × 10⁻⁵ Ωm at 573 K.     

Effect of annealing temperature on ferroelectric properties of （Bi, Nd）4（Ti, V）3O12 thin films

Thin films of Nd^3＋/V^5＋-cosubstituted bismuth titanate, （Bi3.sNd0.5）（ Ti2.96V0.04）O12 （BNTV）, were fabricated on the Pt（111）/Ti/SiO2/Si（100） substrates by a chemical solution deposition technique and annealed at different temperatures of 650, 700, 750 and 800 ℃. The surface morphology and ferroelectric properties of the samples were studied in detail. The result shows that the film annealed at 800 ℃ indicates excellent ferroelectricity with a remanent polarization of 2Pr=40.9 i.tC/cm^2, a coercive field （Ec） of 114 kV/cm at an applied electrical field of 375 kV/cm. The substitution of Ti-site ion by V^5＋ ions could improve the upper limit of the optimal annealing temperature by decreasing the space charge density in BNT thin film. Additionally, the mechanism concerning the dependence of ferroelectric properties of BNTV thin films on the annealing temperature was discussed.     

Effect of annealing temperature on structure and electrochemical properties of LiCoO2 cathode thin films

LiCoO2 thin films, which can be used as a cathode material in microbatteries, were deposited using radio frequency (r.f.) magnetron sputtering system from a LiCoO2 target and in an O2+Ar atmosphere.The films were characterized by various methods such as XRD, SEM and AFM.The LiCoO2 films were annealed in air at 300, 500, 700 and 800 ℃ respectively.The effect of the annealing temperature on the structure, the surface morphology and the electrochemical properties of the films were investigated.The LiCoO2 thin film deposited at room temperature is amorphous and has smaller grain size.With increasing of annealing temperature, the crystallinity of the films is promoted.When the annealing temperature increases to 700 ℃, the films have a perfect crystalline LiCoO2 phase.The LiCoO2 thin film without annealing has no discharge plateau and small discharge capacity (about 27 μAh·cm-2μm).The discharge capacity increases with the increasing of annealing temperature and reaches 47 μAh·cm-2μm for the film annealed with 700 ℃, which also shows the typical discharge plateau of 3.9 V.The cycle performance of LiCoO2 thin films of as grown and annealed at different temperatures were studied.In the case of the film without thermal treatment, the capacity fading is much faster than that of the film annealed at different temperature, showing about 40% capacity loss only after 25 cycles.However, in the case of the film annealed at 700 ℃, the capacity reaches to steady state gradually and maintained constantly with cycling.After 25 times cycling, the discharge capacity of the film annealed at 700 ℃ decreases to about 36.9 μAh·cm-2·μm, only 0.8% capacity loss per cycle.     

Effect of crystallization temperature on microstructure and ferroelectric property of Bi3.25 Eu0.75 Ti3O12 thin films prepared by MOD method

1 Introduction Many researches have been done on candidates in ferroelectric material for non-volatile random access memories applications. Among them, lead zirconate titanate(PZT) thin films have been widely studied because they have many advantages such…     

Effects of annealing temperature and time on microstructure and magnetic properties of Pr-Co thin films

A series of Pr-Co thin films were deposited on the Si (100) substrates with Cr underlayer by magnetron sputtering. The effects of both the post-annealing temperature and the annealing time on the microstructure and magnetic properties for the Pr-Co films were studied systemati- cally. The as-deposited Pr-Co thin films are mostly amorphous and tend to crystallize after annealing at temperatures above 600 C. When the annealing time is increased, the films show a complicated structure with various phases coexisting. Accordingly, the as-deposited film and low temperature annealed films are soft magnets and films annealed at temperatures beyond 600 C tend to be hard magnets. When the annealing time is increased from 5 min to 2 h, the films transfer from hard magnets to soft again. The sample annealed at 600 C for 10 min shows the largest coercivity of 0.59 T.     

Dependence of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> coating thickness and annealing conditions on microstructural and electrochemical properties of LiCoO<Subscript>2</Subscript> film

We studied the dependence of Al₂O₃ coating thickness and annealing conditions on the surface morphology and electrochemical properties of Al₂O₃ coated LiCoO₂ films. The optimum coating thickness allowing for the highest capacity retention was about 24 nm. A sample consisting of Al₂O₃ coated on annealed LiCoO₂ film with additional annealing at 400 °C had a uniform coating layer between the coating materials and cathode films. This sample showed the best capacity retention of ∼91 % with a charge-cut off of 4.5 V after 30 cycles, while the bare cathode film showed a capacity retention of ∼32 % under the same conditions. The formation of second phases such as Co-Al-O was observed in the coating films by X-ray photoelectron spectroscopy (XPS). The Co-Al-O containing samples showed a higher initial capacity because of their smaller grain size, but less capacity retention than the Al₂O₃ containing samples.     

Microstructural Investigation of CoCrFeMnNi High Entropy Alloy Oxynitride Films Prepared by Sputtering Using an Air Gas

Microstructural properties of as-grown and annealed CoCrFeMnNi high entropy alloy (HEA) oxynitride thin films were investigated. The CoCrFeMnNi HEA oxynitride thin film was grown by magnetron sputtering method using an air gas, and annealed under the argon plus air flow for 5 h at 800 °C. The as-grown film was homogeneous and uniform composed of nanometer-sized crystalline regions mixed with amorphous-like phase. The crystalline phase in the as-grown film was face centered cubic structure with the lattice constant of 0.4242 nm. Significant microstructural changes were observed after the annealing process. First, it was fully recrystallized and grain growth happened. Second, Ni-rich region was observed in nanometer-scale range. Third, phase change happened and it was determined to be Fe₃O₄ spinel structure with the lattice constant of 0.8326 nm. Hardness and Young’s modulus of the as-grown film were 4.1 and 150.5 GPa, while those were 9.4 and 156.4 GPa for the annealed film, respectively.     

Synthesis and characterization of Li<Subscript>1.3</Subscript>Al<Subscript>0.3</Subscript>Ti<Subscript>1.7</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-coated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> by wet chemical route

Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ was prepared by wet chemical route. The phase, surface morphology, and electrochemical properties of the prepared powders were characterized by X-ray diffraction, scanning electron micrograph, and galvanostatic charge-discharge experiments. Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ has similar X-ray diffraction patterns as LiMn₂O₄. The corner and border of Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ particles are not as clear as the uncoated one. The two powders show similar values of lithium-ion diffusion coefficient. When cycled at room temperature and 55°C for 40 times at the charge-discharge rate of 0.2C, Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ shows the capacity retentions of 98.2% and 93.9%, respectively, which are considerably higher than the values of 85.4% and 79.1% for the uncoated one. Both the capacity retention differences between Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ and LiMn₂O₄ cycling at room temperature and 55°C become larger with the increase of charge-discharge rate. When the charge-discharge rate reaches 2C, the capacity retention of LATP-coated LiMn₂O₄ becomes 8.4% higher than the uncoated LiMn₂O₄ for room temperature cycling, and it becomes 11.1% higher than the latter when cycled at 55°C.     

Annealing behaviors of vacancy in varied neutron irradiated Czochralski silicon

The difference of annealing behaviors of vacancy-oxygen complex (VO) in varied dose neutron irradiated Czochralski silicon: (S1 5×10¹⁷ n/cm³ and S2 1.07×10¹⁹ n/cm³) were studied. The results show that the VO is one of the main defects formed in neutron irradiated Czochralski silicon (CZ-Si). In this defect, oxygen atom shares a vacancy, it is bonded to two silicon neighbors. Annealed at 200 °C, divacancies are trapped by interstitial oxygen(O_i) to form V₂O (840 cm⁻¹). With the decrease of the 829 cm⁻¹ (VO) three infrared absorption bands at 825 cm⁻¹ (V₂O₂), 834 cm⁻¹ (V₂O₃) and 840 cm⁻¹ (V₂O) will rise after annealed at temperature range of 200–500 °C. After annealed at 450–500 °C the main absorption bands in S1 sample are 834 cm⁻¹, 825 cm⁻¹ and 889 cm⁻¹ (VO₂), in S2 is 825 cm⁻¹. Annealing of A-center in varied neutron irradiated CZ-Si is suggested to consist of two processes. The first is due to trapping of VO by O_i in low dose neutron irradiated CZ-Si (S1) and the second is due to capture the wandering vacancy by VO, etc, in high dose neutron irradiated CZ-Si (S2), the VO₂ plays an important role in the annealing of A-center. With the increase of the irradiation dose, the annealing behavior of A-center is changed.     

Dielectric properties of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films deposited onto Ti and TiO<Subscript>2</Subscript> layer

The present study describes the dielectric properties of RF sputtered Ta₂O₅ thin films as a function of the buffer layer and annealing condition. The buffer layers were Ti or TiO₂. And the thin film was annealed in various conditions. The X-ray pattern results showed that the phase of the RF sputtered Ta₂O₅ thin films was amorphous and this state was kept stable to RTA (rapid thermal annealing) even at 700°C. Measurements of the electrical and dielectric properties of the reactive sputtered Ta₂O₅ fabricated in two simple metal insulator semiconductor (MIS) structures, (Cu/Ta₂O₅/Ti/Si/Cu and Cu/Ta₂O₅/TiO₂/Si/Cu) indicated that the amorphous Ta₂O₅ grown on Ti possesses a high dielectric constant (30–70) and high leakage current (10⁻¹–10⁻⁴ A/cm²), whereas a relatively low dielectric constant (−10) and low leakage current (−10⁻¹⁰ A/cm²) were observed in the amorphous Ta₂O₅ deposited on the TiO₂ buffer layer. In addition, the leakage current mechanisms of the two amorphous Ta₂O₅ thin films were investigated by plotting the relation of current density (J) vs. applied electric field (E). The Ta₂O₅/Ti film exhibited three dominant conduction mechanism regimes contributed by the Ohmic emission at low electrical field, by the Schottky emission at intermediate field and by the Poole-Frenkel emission at high field. In the case of Ta₂O₅/TiO₂ film, the two conduction mechanisms, the Ohmic and Schottky emissions, governed the leakage current density behavior. The conduction mechanisms at various electric fields applied were related to the diffusion of Ta, Ti and O, followed by the creation of vacancies, in the rapid thermal treated capacitors.     

Physicochemical Properties of Spray-Deposited CoFe2O4 Thin Films

Cobalt ferrite thin films are deposited onto quartz glass substrates by chemical spray pyrolysis technique at different substrate temperatures using ferric nitrate and cobalt nitrate as precursors. Thermogravimetric analysis (TGA) study indicates the formation of CoFe₂O₄ by decomposition of cobalt and ferric nitrates after 800 °C. X-ray diffraction studies reveal that annealed films are polycrystalline in nature and exhibit spinel cubic crystal structure. Crystallite size varies from 39 to 44 nm with the substrate temperatures. Direct optical band gap energy of CoFe₂O₄ thin films is found to be 2.57 eV. The AFM images show that roughness and grain size of the CoFe₂O₄ thin film are about 9 and 138 nm, respectively. The measured DC resistivity of the deposited thin films indicates that as temperature increases the resistivity decreases indicating the semiconductor nature of the films. Decrease in dielectric constant (ε′) and loss tangent (tanδ) has been observed with frequency and attains the constant value at higher frequencies. The AC conductivity of cobalt ferrite thin films increases with increase in frequency. Thus, the prepared films show normal dielectric performance of the spinel ferrite thin film. Room-temperature complex impedance spectra show the incomplete semicircles as films exhibit high resistance values at lower frequencies.     

Preparation and property of spinel LiMn2O4 material by co-doping anti-electricity ions

1 Introduction At present, LiCoO2 is almost the only cathode material of Li-ion batteries, which can be used in large-scale commercialization, because such material possesses high specific capacity, ease of preparation, high discharging flat and favorable…     

Synthesis,Fabrication and Characterization of ZnO-Based Thin Films Prepared by Sol–Gel Process and H<Subscript>2</Subscript> Gas Sensing Performance

In this paper, an attempt is made to deposit ZnO thin films using sol–gel process followed by dip-coating method on p-silicon (100) substrates for intended application as a hydrogen gas sensor owing to the low toxic nature and thermal stability of ZnO. The thin films are annealed under annealing temperatures of 350, 450 and 550 °C for 25 min. The crystalline quality of the fabricated thin films is then analyzed by field-emission scanning electron microscopy and transmission electron microscope. The gas sensing performance analysis of ZnO thin films is demonstrated at different annealing temperatures and hydrogen gas concentrations ranging from 100 to 3000 ppm. Results obtained show that the sensitivity is significantly improved as annealing temperature increases with maximum sensitivity being achieved at 550 °C annealing temperature and operating temperature of 150 °C. Hence, the modified ZnO thin films can be applicable as H₂ gas sensing device showing to the improved performance in comparison with unmodified thin-film sensor.     

Elaboration and characterization of nanocrystalline TiO2 thin films prepared by sol–gel dip-coating

Nanocrystalline TiO₂ thin films were deposited on a ITO coated glass substrate by sol–gel dip coating technique, the layers undergo a heat treatment at temperatures varying from 300 to 450 °C. The structural, morphological and optical characterizations of the as deposited and annealed films were carried out using X-ray diffraction (XRD), Raman spectroscopy, Atomic Force Microscopy (AFM), visible, (Fourier-Transform) infrared and ultraviolet spectroscopy, Fluorescence and spectroscopic ellipsometry. The results indicate that an anatase phase structure TiO₂ thin film with nanocrystallite size of about 15 nm can be obtained at the heat treatment temperature of 350 °C or above, that is to say, at the heat treatment temperature below 300 °C, the thin films grow in amorphous phase; while the heat treatment temperature is increased up to 400 °C or above, the thin film develops a crystalline phase corresponding to the titanium oxide anatase phase. We have accurately determined the layer thickness, refractive index and extinction coefficient of the TiO₂ thin films by the ellipsometric analysis. The optical gap decreases from 3.9 to 3.5 eV when the annealing temperature increases. Photocatalytic activity of the TiO₂ films was studied by monitoring the degradation of aqueous methylene blue under UV light irradiation and was observed that films annealed above 350 °C had good photocatalytic activity which is explained as due to the structural and morphological properties of the films.     

Electric and dielectric behavior of CaCu3Ti4O12-based thin films obtained by soft chemical method

CaCu₃Ti₄O₁₂ (stoichiometric) and Ca_1.1Cu_2.9Ti₄O₁₂ (non-stoichiometric) thin films have been prepared by the soft chemical method on Pt/Ti/SiO₂/Si substrates, and their electrical and dielectric properties have been compared as a function of the annealing temperature. The crystalline structure and the surface morphology of the films were markedly affected by the annealing temperature and excess calcium. The films show frequency-independent dielectric properties at room temperature which is similar to those properties obtained in single-crystal or epitaxial thin films. The room temperature dielectric constant of the 570-nm-thick CCTO thin films annealed at 600 °C at 10 kHz was found to be 124. The best non-ohmic behavior (α = 12.6) presented by the film with excess calcium annealed at 500 °C. Resistive hysteresis on the I-V curves was observed which indicates these films can be used in resistance random access memory (ReRAM).     

Optical spectroscopic and electrochemical characterization of oxide films on a ferritic stainless steel

Colored oxide films that form on ferritic stainless steel in a high-temperature, oxidizing environment and correspond to different chemical compositions can cause a deterioration of pitting resistance and corrosion performance. Herein, optical spectroscopic and electrochemical techniques have been used to reveal the relationship between color, chemical composition, and corrosion resistance of oxide films formed in the temperature range from 400°C to 800°C for 30 min and at 800°C for 10, 20, 30, and 60 min. The substrate with a thin and dense passivation film leads to a low pitting potential but high corrosion resistance. Oxide films of yellowish or brownish color formed below 600°C are mainly iron oxides, which correspond to low corrosion resistance. No passivation characteristics can be observed for polarization curves of oxide films formed at 500°C and 600°C. The color of oxide films varies from blue to dark gray with the increase of oxidation time at 800°C. Corrosion resistance changes with different proportions of Fe₃O₄, Cr₂O₃, and FeCr₂O₄. The gray oxide films formed at 800°C for 30 min exhibit the lowest pitting susceptibility and the highest corrosion resistance.     

Reaction Time and Film Thickness Effects on Phase Formation and Optical Properties of Solution Processed Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> Thin Films

Copper-zinc-tin-sulfide (Cu₂ZnSnS₄ or CZTS) is a promising p-type semiconductor material as absorber layer in thin film solar cells. The sulfides of copper and tin as well as zinc and sulfur powders were dissolved in hydrazine. The effect of chemical reaction between precursor species, at room temperature, was assessed for 6 to 22 h. For 22 h reaction time, the effect of spin coated film thickness on the resulting composition, after annealing under N₂ flow at 500 °C for 1 h, was investigated. The morphology, composition, and optical properties of the annealed films were determined by means of x-ray diffraction, scanning electron microscope, and spectrophotometer studies. It was found that, for less than optimal reaction time of 22 h or film thickness below 1.2 µm, other ternary phases namely Cu₄SnS₄, Cu₅Sn₂S₇, and ZnS co-exist in different proportions besides CZTS. Formation of phase-pure CZTS films also exhibited a tendency to minimize film cracking during annealing. Depending on the processing conditions, the band gap (E _g) values were determined to be in the range of 1.55 to 1.97 eV. For phase-pure annealed CZTS film, an increase in the E _g value may be attributed to quantum confinement effect due to small crystallite size.