Lanthanum Titanium Oxide Research Articles

(Keynote) Perovskite Lanthanum Titanium Oxides for Solar Water Splitting

Perovskite lanthanum titanium oxides are very stable but have large band gap and poor charge mobility. This talk presents our effort to tune lanthanum titanium oxides to enhance solar water splitting. Anion doping can result band narrowing while cation doping can increase charge mobility. Incorporation of lanthanum titanium oxides with the reduce graphene oxide sheets to significantly improve the charge extraction from the perovskite oxide. Also, transient absorption spectroscopy has been sued to track the charge dynamics.

Lanthanum–titanium oxide composite from a single molecular cluster: Non-enzymatic mesoporous electrochemical nitrite ion sensor

In the present investigation, lanthanum–titanium [La3Ti6O4(OH)6(C2F3O2)13(H2O)2(C4H8O)6] (1) was successfully used as single source precursor to fabricate electrodes of LTO 600 (La4Ti9O24-La2O3-LaTiO3-TiO2(rutile)) and LTO 700 (La4Ti9O24-La2O3) at sintering temperature of 600 and 700 °C, respectively. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been used to determine the phase purity and oxidation states of the elements present in the samples. Nitrogen adsorption/desorption isotherms are used to investigate the Brunauer, Emmett, and Teller (BET) surface area and the Barrett–Joyner–Halenda (BJH) pore size distribution of LTO 600 and LTO 700. The BET analysis revealed pore sizes of 8.7 and 9.9 nm for LTO 600 and LTO 700, respectively, transmission electron microscopy (TEM) revealed the particles are irregular in shape with size range of 55–150 and 145–155 nm for LTO 600 and LTO 700, respectively. The LTO 700 modified glassy carbon electrode (GCE) was used for the elecrtrochemical oxidation of NaNO2 and it showed a better electrocatalytic performance towards the oxidation of NaNO2 than LTO 600. The larger pore size found at the higher sintering temperature could enhance the sensing performance with the limit of detection (LoD) of 0.0151 µM. Furthermore, the composite modified electrode (LTO 700) showed high selectivity towards the detection of nitrite ions in the presence of the common salts. Therefore, the fabricated LTO 700 electrode is a potential candidate for monitoring the toxic nitrite ions levels in edibles, additives and drinking water.

Characterization of thin film Li0.5La0.5Ti1−xAlxO3 electrolyte for all-solid-state Li-ion batteries

Since addition of Al in Li0.5La0.5TiO3 has enhanced ionic conductivity in bulk materials, it is important to apply this material on all solid state thin film batteries. Because some of the good ionic conductors such as Lithium Phosphorus Oxynitride (LiPON) are sensitive to oxygen and moisture and their application is limited, so amorphous Li0.5La0.5Ti1−xAlxO3 (LLTAlO) is a most promising candidate because of its stability. In this study, the crystalline LLTAlO targets were prepared changing the amount of x content by conventional solid state reactions. Using these targets, lithium lanthanum titanium oxide (LLTO) thin film electrolytes were deposited on ITO/SLG substrates by radio frequency magnetron sputtering system in Ar atmosphere. The structural and compositional properties of targets and thin films were characterized by SEM, XRD, Raman spectroscopy and XPS. It was found that all targets are crystalline while the thin films are amorphous. To understand the effect of Al doping on ionic conductivity, electrical measurements were done at room temperature by AC impedance spectroscopy forming ITO/LLTAlO/Al structure like capacitor. Highest ionic conductivity result, 0.96 × 10−6 S·cm−1, is obtained from the nominal thin film composition of Li0.5La0.5Ti1−xAlxO3 (x = 0.05) at room temperature measurements. Heat treatment is also conducted to investigate to understand its effect on ionic conductivity and the structure of the thin films. It is found that ionic conductivity enhances with annealing. Also, temperature dependent ionic conductivity measurements from 298 K to 385 K are taken in order to evaluate activation energy for Li-ion conduction.

Wet-Chemical Synthesis of 3D Stacked Thin Film Metal-Oxides for All-Solid-State Li-Ion Batteries.

By ultrasonic spray deposition of precursors, conformal deposition on 3D surfaces of tungsten oxide (WO3) negative electrode and amorphous lithium lanthanum titanium oxide (LLT) solid-electrolyte has been achieved as well as an all-solid-state half-cell. Electrochemical activity was achieved of the WO3 layers, annealed at temperatures of 500 °C. Galvanostatic measurements show a volumetric capacity (415 mAh·cm−3) of the deposited electrode material. In addition, electrochemical activity was shown for half-cells, created by coating WO3 with LLT as the solid-state electrolyte. The electron blocking properties of the LLT solid-electrolyte was shown by ferrocene reduction. 3D depositions were done on various micro-sized Si template structures, showing fully covering coatings of both WO3 and LLT. Finally, the thermal budget required for WO3 layer deposition was minimized, which enabled attaining active WO3 on 3D TiN/Si micro-cylinders. A 2.6-fold capacity increase for the 3D-structured WO3 was shown, with the same current density per coated area.

Correlation of Photocatalytic Activity with Band Structure of Perovskite Lanthanum Titanium Oxide

This talk deals with the relationship between the photocatalytic activity and the band structure of perovskite lanthanum titanium oxide (La2Ti2O7). Nitrogen doping results in shift of the valence band, leading to band gap narrowing. This renders the visible-light responsive photocatalytic activity of lanthanum titanium oxide. Transient absorption spectroscopy has been used to investigate the charge dynamics in both the pristine and the N-doped perovskite lanthanum titanium oxide.

Long-term time dependence of internal stress in lanthanum titanium oxide (H4) optical thin films.

The time variation in the internal stress of optical thin films composed of lanthanum titanium oxide (H4) deposited by ion-beam assisted deposition (IAD) and electron beam deposition was observed over a period of 10 years after deposition, and it was found that the internal stresses in the optical thin films can be controlled by optimizing the IAD conditions. Both tensile stress and compressive stress could be created by IAD, and the chemical bonding state of Ti may affect the stress behavior. The network size of the chemical bonds may affect the stress direction.

Protonated Oxide, Nitrided, and Reoxidized K2La2Ti3O10 Crystals: Visible-Light-Induced Photocatalytic Water Oxidation and Fabrication of Their Nanosheets

Protonated lanthanum titanium oxide H2La2Ti3O10 and oxynitride H2La2Ti3O10–3/2xNx crystals were synthesized from the oxide, nitrided, and reoxidized layered K2La2Ti3O10 crystals prepared by solid-state reaction through proton exchange. Here, we investigated the holding time of nitridation of oxide K2La2Ti3O10 crystals influencing their crystal structure, shape, and absorption wavelength and band gap energy. The XRD and SEM results confirmed that the crystal structure and plate-like shape of the parent oxide were maintained after nitridation at 800 °C for 10 h, and the color of crystals was changed from white to dark green. However, no clear absorption edges were observed in the UV–vis diffuse reflectance spectra of the nitrided crystals due mainly to the reduced titanium species (Ti3+), which act as the recombination center of the photogenerated charge carriers. To decrease the amount of the reduced titanium species, the nitrided crystals were further reoxidized at 400 °C for 6 h. After partial reoxidatio...

Obtention of Li3xLa2/3−xTiO3 ceramics from amorphous nanopowders by spark plasma sintering

ABSTRACTIn this work, Li3xLa2/3−xTiO3 powder with nominal lithium content (x = 0.08) was synthesized by mechano synthesis method. Spark plasma sintering (SPS) was employed to prepare lithium lanthanum titanium oxide solid-state ceramic. The techniques of X-ray diffraction, high resolution scanning electron microscopy, and Raman spectroscopy were used to characterize the composition and microstructure of samples. The results showed that fine-grained ceramics with relative density of 95.5% were obtained by sintering the oxide powders at 1100°C for only 5 min.

Sol-gel-processed amorphous lithium ion electrolyte thin films: Structural evolution, theoretical considerations, and ion transport processes

Amorphous lithium lanthanum titanium oxide (LLTO) is a promising inorganic solid electrolyte for all-solid-state lithium ion batteries. However, preparation of amorphous LLTO by sol-gel process is rare. There is a pressing need for experimental and theoretical investigation for sol-gel-processed amorphous LLTO. In this study, amorphous LLTO thin films were successfully prepared by sol-gel process with a partially hydrolyzed sol. Microstructure evolution from dried gel film to fired one to annealed one was examined. The microstructure of the annealed film, amorphous or crystalline, depends on annealing temperature and time. Theoretical analysis based on nucleation and growth theory was carried out to understand the microstructure evolution at various annealing temperatures. Induction time determines the longest annealing time without transformation from amorphous to crystalline state. The induction time decreases with annealing temperature until the time approach a minimum, and after that, the time increases with the temperature. The frequency and temperature dependence of the ac conductivity of amorphous LLTO thin film was analyzed by the jump relaxation model. The plateau at low frequencies results from lithium ion long-range diffusion which contributes to dc conductivity, while the observed frequency dispersion at high frequencies is attributed to short-range forward–backward hopping motion of lithium ions.

Li-ion conducting Li0.35La0.55TiO3 electrolyte thick films fabricated by aerosol deposition

Lithium lanthanum titanium oxide (Li0.35La0.55TiO3, LLT) films with thickness of 5 ∼ 30 μm were fabricated on a stainless-steel substrates by using aerosol deposition with a micron-sized powder at room temperature, and their Li-ion conductivity values were analyzed and compared with bulk ceramics sintered using the same powder. The crystalline size of the film was controlled by controlling the initial particle size of the LLT powder. The phase formation and the microstructural evolution of the films for different deposition conditions were observed by X-ray diffraction and electron microscopy. The lithium-ion conductivity of the film at room temperature was analyzed by the impedance measurement technique. The LLT bulk ceramic sintered at 1200 °C and LLT film deposited at room-temperature showed total lithium ion conductivity of 8.37 × 10−6 and 6.38 × 10−7 S/cm, respectively.

Luminescence properties of lanthanide and ytterbium lanthanide titanate thin films grown by atomic layer deposition

Lanthanide based luminescent materials are highly suitable as down conversion materials in combination with a UV-absorbing host material. The authors have used TiO2 as the UV-absorbing host material and investigated the energy transfer between TiO2 and 11 different lanthanide ions, Ln3+ (Ln = La, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb) in thin films grown by atomic layer deposition. They have also investigated the possibility to improve the overall energy transfer from TiO2 to Yb3+ with a second Ln3+, in order to enhance down conversion. The films were grown at a substrate temperature of 300 °C, using the Ln(thd)3/O3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) and TiCl4/H2O precursor pairs. The focus of the work is to explore the energy transfer from TiO2 to Ln3+ ions, and the energy transfer between Ln3+ and Yb3+ ions, which could lead to efficient down conversion. The samples have been characterized by x-ray diffraction, x-ray fluorescence, spectroscopic ellipsometry, and photoluminescence. All films were amorphous as deposited, and the samples have been annealed at 600, 800, and 1000 °C in order to investigate the correlation between the crystallinity and luminescence. The lanthanum titanium oxide samples showed a weak and broad emission centered at 540 nm, which was absent in all the other samples, indicating energy transfer from TiO2 to Ln3+ in all other lanthanide samples. In the amorphous phase, all samples, apart from La, Tb, and Tm, showed a typical f-f emission when excited by a 325 nm HeCd laser. None of the samples showed any luminescence after annealing at 1000 °C due to the formation of Ln2Ti2O7. Samples containing Nd, Sm, and Eu show a change in emission spectrum when annealed at 800 °C compared to the as-deposited samples, indicating that the smaller lanthanides crystallize in a different manner than the larger lanthanides. Energy transfer from Ln3+ to Yb3+ was observed neither in the amorphous or annealed samples. On the other hand, Yb3+ was found to be an efficient sensitizer for Ho3+'s 1200 nm emission.

Patterning of lithium lanthanum titanium oxide films by soft lithography as electrolyte for all-solid-state Li-ion batteries

The combination of sol–gel processing and soft-lithographic patterning presents a promising route towards three-dimensional (3D) micro Li-ion electrodes, and may offer a viable approach for the fabrication of all-solid-state 3D Li-ion batteries. The methods are relatively simple and therefore cheap and moreover easy to scale up. In this paper, micro-patterned films of the Li-ion conducting perovskite-type phase with nominal composition Li0.29La0.57TiO3 (LLT) were prepared on silicon, using sol-gel synthesis in combination with micro-molding. After thermal annealing at 700°C, the phase formation, morphology, chemical composition and LLT film thickness were investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Analysis of X-rays (EDAX) and Atomic Force Microscopy (AFM). The ionic conductivity of the LLT powder prepared during this study, determined by impedance spectroscopy, was 2.68·10−6S/cm at 25°C.

Electrochemical characterization of sodium and potassium doped lanthanum–titanium mixed oxides prepared by sol–gel method

Varying amounts of Na and K doped lanthanum–titanium oxides were synthesized by gel entrapment technique. These ceramics were characterized by X-ray diffraction. Microstructural investigations revealed grain growth in the doped material compared to undoped sample. Dielectric relaxations of these compounds were investigated in the temperature range 250–900 °C. A high degree of dispersion of the permittivity of un-doped lanthanum–titanium oxide and K and Na doped lanthanum–titanium oxide was observed in the frequency range <100 kHz which was attributed to oxygen vacancies. An increase in the permittivity values were observed with 1 % Na and K doped samples. The permittivity values further deteriorated with the dopant concentration. Using the Cole–Cole model, an analysis of the dielectric loss with frequency was performed, assuming a distribution of relaxation time. The dielectric loss was found to decrease by doping K in lanthanum–titanium oxide matrix. The dc conductivity studies showed that a temperature dependent hopping type mechanism is responsible for electrical conduction in the system.

Miniaturized notch antenna based on lanthanum titanium perovskite oxide thin films

This paper presents the integration of a dielectric lanthanum titanium oxide compound as thin film in a discrete capacitive component operating at microwaves. The integration in a notch antenna of a MIM (Metal/Insulator/Metal) structure based on this oxide material is numerically and experimentally studied. Oxide films are deposited by reactive magnetron RF sputtering of an La2Ti2O7 target. The films are composed of an unusual phase: the orthorhombic La2Ti2O7 compound, with a textured growth on Pt/Si and Pt/SrTiO3 substrates. Moderate dielectric constant values (Epsilon around 60) and low loss (Tan Delta lower than 0.005) are obtained at 1GHz. Inserting this original MIM capacitor in the antenna structure results in a shift to a lower value of its operating frequency. This shift, from 885MHz to 317MHz, corresponds to a significant size reduction of 64.2%. The measured values are confronted with simulation obtained by numerical software.

Lanthanum titanium perovskite compound: Thin film deposition and high frequency dielectric characterization

Perovskite lanthanum titanium oxide thin films were deposited on (001) MgO, (001) LaAlO3 and Pt(111)/TiO2/SiO2/(001)Si substrates by RF magnetron sputtering, using a La2Ti2O7 homemade target sputtered under oxygen reactive plasma. The films deposited at 800°C display a crystalline growth different than those reported on monoclinic ferroelectric La2Ti2O7 films. X-ray photoelectron spectroscopy analysis shows the presence of titanium as Ti4+ ions, with no trace of Ti3+, and provides a La/Ti ratio of 1.02. The depositions being performed from a La2Ti2O7 target under oxygen rich plasma, the same composition (La2Ti2O7) is proposed for the deposited films, with an unusual orthorhombic cell and Cmc21 space group. The films have a textured growth on MgO and Pt/Si substrates, and are epitaxially grown on LaAlO3 substrate. The dielectric characterization displays stable values of the dielectric constant and of the losses in the frequency range [0.1–20]GHz. No variation of the dielectric constant has been observed when a DC electric field up to 250kV/cm was applied, which does not match a classical ferroelectric behavior at high frequencies and room temperature for the proposed La2Ti2O7 orthorhombic phase. At 10GHz and room temperature, the dielectric constant of the obtained La2Ti2O7 films is ε~60 and the losses are low (tanδ<0.02).

All-solid-state sensors used in drilling muds to prevent H2S gas evolution on oil wells

During oil or water drilling, the evolution of gaseous hydrogen sulfide (H 2 S) may occur. A better solution would be to prevent the evolution of the gas by simultaneously measuring the presence of sulfide ions (S 2- ) in the drilling mud and the pH, sulfide ions being predominantly under gaseous H 2 S form when pH is smaller than 7. We proposed then to perform in situ measurements, using a potentiometric technique, to simultaneously record the presence of sulfide and the pH of the mud. In case of a rapid decrease of pH, human action could be done to rapidly increase the pH and to prevent H 2 S evolution. A new type of all-solid-state reference electrode based on thick films of lithium lanthanum titanium oxide (LLTO) has therefore been developed. This reference electrode is associated with a solid state pH electrode and an ionic selective electrode for the detection of sulfide ions. • New sensors have been proposed for detection of sulfide ions. • Preventing hydrogen sulfide exhaust is possible. • The all solid state sensors can be used in oil drilling rigs.

Encapsulation of LiNi0.5Co0.2Mn0.3O2 with a thin inorganic electrolyte film to reduce gas evolution in the application of lithium ion batteries

Emission of gas at charged states of lithium ion batteries (LIBs) is a significant problem because it causes swelling and deformation of LIBs. In this study, the gas generation mechanism is investigated and preventative measures are developed. Decomposition of the electrolyte solution related to residual lithium compounds on the surface of LiNi0.5Co0.2Mn0.3O2 (NCM523) and to the structural change in the cathode active material is investigated as two main mechanisms of gas generation in LIB cells. NCM523 particles are encapsulated in a continuous lithium lanthanum titanium oxide (LLTO) thin layer to inhibit gas-generating reactions. The LLTO layer fixes free lithium of the cathode surface and effectively suppresses side reactions between the charged cathode active material and the electrolyte solution, resulting in substantial reduction of the gas generation. In addition, LLTO-coated NCM523 shows improved capacity retention without any loss of capacity or rate performance because LLTO is a good conductor of Li ions.

New concept of an all-solid-state reference electrode using a film of lithium lanthanum titanium oxide (LLTO)

A new type of all-solid-state reference electrode based on thick films of lithium lanthanum titanium oxide (LLTO) was developed for electrochemical measurements in harsh environments where robustness, no clogging and resistance to high temperatures and high pressures are required. These reference electrodes do not need any filling solution and any porous junction between them and the analyte. The characteristics, namely stability and impedance of the all-solid-state reference electrode, are studied in different pH buffer aqueous solutions. This reference electrode is then used during cyclic voltammetric experiments in different aqueous media. The recorded voltammograms are compared to those obtained with a classical liquid reference electrode, i.e. a saturated calomel electrode. Finally, this reference electrode is associated to an antimony pH indicating electrode to prepare an all-solid-state pH sensor able to measure the pH of muds and to follow its variations during addition of acid or alkaline solutions. This all-solid-state potentiometric sensor can then be used in oil or geothermic drilling muds in order to prevent hydrogen sulphide evolution when sulphide ions are present in the muds.

Photocatalytic generation of hydrogen with visible-light nitrogen-doped lanthanum titanium oxides

In order to generate hydrogen by splitting water under visible-light irradiation, nitrogen-doped La2Ti2O7 (LTO) nanosheets loaded with the Pt nanoparticles have been synthesized by hydrothermal processing, followed with wet impregnation and subsequent heat treatment in a NH3 flow. The light absorption of the pristine LTO nanosheets is cut off at 330nm while the N-doped LTO nanosheets exhibit the extended light absorption up to 560nm. Nitrogen doping has not only resulted in the visible-light-responsive photocatalytic water splitting but also enhanced the ultraviolet-light-responsive photocatalytic activity. Loading the Pt nanoparticles on the LTO surface further improved the photocatalytic activity due to the enhanced separation of charge carriers.

Lithium Lanthanum Titanium Oxides: A Fast Ionic Conductive Coating for Lithium-Ion Battery Cathodes

This work introduces Li–La–Ti–O (LLTO), which is a fast lithium-ion conductor, as an effective coating material for cathode materials used in rechargeable lithium-ion batteries. This fast Li-ion conductor is characterized by first-principles calculations showing low activation barrier for lithium diffusion at various different lithium concentrations. The morphology and the microstructure of the pristine electrode and coated electrode materials are characterized systematically, and we show clear evidence of the presence of the coating after electrochemical cycling. The coated electrodes show significantly improved rate capabilities and cycling performance, compared to the pristine electrodes. The possible reasons for such enhancements are explored experimentally using potentiostatic intermittent titration technique (PITT), electrochemical impedance spectroscopy (EIS). Because of the high lithium conductivity in the LLTO coating material, the chemical Li+ diffusion coefficient is one magnitude of order high...