Apatite-type Lanthanum Silicate Research Articles

Highly c-axis-oriented apatite-type lanthanum silicate thin films fabricated by magnetron sputtering under bias

The development of apatite-type lanthanum silicate (LSO) thin films with enhanced c-axis orientation has received attention because highly c-axis oriented LSO is an attractive electrolyte for lowering the operating temperature of solid oxide cells. In this study, the effect of thin-film conditions in magnetron sputtering on the c-axis orientation of LSO thin films after crystallization were investigated. X-ray diffraction and X-ray reflectivity measurements revealed that the c-axis orientation of LSO thin films after crystallization is correlated with the density of the amorphous thin films deposited by magnetron sputtering. Bias application during magnetron sputtering effectively increased the c-axis orientation of crystallized LSO thin films, which showed extremely high c-axis orientation (Lotgering factor of 0.99). This thin film consisted of columnar grains, most of which were c-axis oriented, as confirmed by direct observation using scanning transmission electron microscopy.

Enhanced electrical conductivity of P-doped apatite-type lanthanum silicate solid electrolytes and analysis of the mechanism

Enhanced electrical conductivity of P-doped apatite-type lanthanum silicate solid electrolytes and analysis of the mechanism

Synthesis and Densification of Mo/Mg Co-Doped Apatite-type Lanthanum Silicate Electrolytes with Enhanced Ionic Conductivity.

Apatite-type lanthanum silicate (LSO) electrolyte is one of the most promising candidates for developing intermediate-temperature solid oxide electrolysis cells and solid oxide full cells (IT-SOECs and SOFCs) due to its stability and low activation energy. However, the LSO electrolyte still suffers from unsatisfied ionic conductivity and low relative density. Herein, a new co-doped method is reported to prepare highly purified polycrystalline powders of Mg-Mo co-doped LSO (Mg/Mo-LSO) electrolytes with high excellent densification properties and improved ionic conductivity. Introducing the Mo6+ and Mg2+ ions into the LSO structure can increase the number of interstitial oxide ions and improve the degree of densification at lower sintering temperatures, more importantly, expand the migration channel of oxide ions to enhance the ionic conductivity. As a result, the relative density of the fabricated Mo/Mg-LSO electrolytes pellets could achieve more than 98 % of the theoretical density after sintering at 1500 °C for 4 h with a grain size of about 1-3 μm and the EIS results showed the ionic conductivity increased from 0.782 mS ⋅ cm-1 for the pristine LSO to 33.94 mS ⋅ cm-1 for the doped sample La9.5 Si5.45 Mg0.3 Mo0.25 O26+δ at 800 °C. In addition, the effect of different Mo6+ doping contents was investigated systematically, in which La9.5 Si5.45 Mg0.3 Mo0.25 O26+δ possessed the highest ionic conductivity and relative density. The proposed Mo/Mg co-doped method in this work is one step forward in developing apatite-structured electrolytes offering excellent potential to address the common issues associated with the fabrication of dense, highly conductive, and thermochemically stable electrolytes for solid oxide electrolysers and fuel cells.

Preparation of Al and Sm Co-doped Apatite-Type Lanthanum Silicate Electrolyte and analysis of the conductivity mechanism

The contradiction between the increasing demand for energy and the scarcity of traditional fossil energy sources is becoming increasingly acute, and it is urgent to accelerate the development and use of new, more efficient, and environmentally friendly energy sources. Apatite-type lanthanum silicate solid oxide electrolyte materials (La9.33Si6O26, LSO) are widely used in the field of fuel cell electrolytes due to their high ionic conductivity and high density. In this paper, Al and Sm co-doped LSO solid electrolytes were successfully prepared by the urea-nitrate combustion method. SEM images, relative density, and linear shrinkage of Al and Sm co-doped lanthanum silicate electrolytes sintered at different temperatures were compared. The results show that the best sintering temperature is 1500°C. The electrical conductivity of La9.33SmxSi5.5Al0.5O25.75+1.5x was analyzed by EIS. The conductivity of La9.33Sm0.2Si5.5Al0.5O26.05 is 2.56 × 10−4 S·cm−1 when measured at 600°C. The reason Al and Sm co-doping enhances the conductance is that Al doping generates oxygen vacancies and increases the interstitial oxygen (Oi) concentration. Doping of Sm not only increases the concentration of Oi but also reduces the concentration of cation vacancies, thus improving the conductivity of the electrolyte.

Enhancing conductivity of apatite-type lanthanum silicate by Li and Cu co-doping

Solid oxide fuel cells (SOFC) are all-solid power generation devices that directly convert chemical energy stored in fuel gases and oxidizers to electrical energy efficiently and without pollution at medium to high temperatures. Recognized as the green energy technology of the 21st century, it is of great significance to alleviating the energy crisis, meeting electricity demand, and reducing environmental pollution. Using the urea-nitrate combustion method, the solid electrolyte powder (LLSCO) of lanthanum silicate of apatite type La9.33LixSi5.5Cu0.5O25.5 + 0.5x (x = 0.1, 0.2, 0.3, 0.4) was successfully prepared by igniting 6-8 mins at 600 °C. According to XRD analysis, LLSCO has a typical P63/m apatite structure and high purity. The volume of LLSCO lattice increases further than that of LSO and LSCO and increases with the increase of Li+ doping. This is because when Li and Cu are doped simultaneously, Li+ enters the empty space in the LSO lattice that occupies the LaII position, which causes the lattice to expand. At the same time, Cu2+ enters the LSO lattice to replace the partial Si4+, which will also cause lattice expansion. The IR analysis shows that Cu2+ replaces Si4+ and enters the [SiO4] tetrahedron to form the [Si(Cu)O4] tetrahedron, while Li+ occupies the vacancy of the LaII position. The optimal sintering temperature of Li and Cu co-doped LLSCO was determined to be 1575 °C based on shrinkage rate, relative density with temperature, and microscopic morphology analysis. The conductivity of La9.33LixSi5.5Cu0.5O25.5+0.5x (x=0.1, 0.2, 0.3, 0.4) was significantly higher than that of LSO and LSCO. With the increase of Li doping, the impedance of the doping sample was lowest when x = 0.3, and the conductivity reached the highest of 9.27 × 10−4 S · cm ·−1 at 600°C.

Defects and disorder in apatite-type silicate oxide ion conductors: implications for conductivity

Extensive diffuse scatter observed by single crystal neutron diffraction was modelled to gain insight into structural distortions in apatite-type lanthanum silicate.

Crystal Growth Mechanism of Highly c-Axis-Oriented Apatite-Type Lanthanum Borosilicate Using B2O3 Vapor.

Apatite-type lanthanum silicate (LSO) exhibits high oxide-ion conductivity and has recently garnered attention as a potential solid electrolyte for high-temperature solid oxide fuel cells and oxygen sensors that operate in the low- and intermediate-temperature ranges (300–500 °C). LSO exhibits anisotropic oxide-ion conduction along with high c-axis-oriented oxide-ion conductivity. To obtain solid electrolytes with high oxide-ion conductivity, a technique for growing crystals oriented along the c-axis is required. For mass production and upscaling, we have thus far focused on the vapor-phase synthesis of c-axis-oriented apatite-type LSO and successfully grew polycrystals of highly c-axis-oriented boron-substituted apatite-type lanthanum silicate (c-LSBO) using B2O3 vapor. Here, we investigated the mechanism of c-LSBO crystal growth to determine why the utilization of B2O3 vapor resulted in such a strong c-axis crystal orientation. The synthesis of c-LSBO by the B2O3 vapor-phase method results in crystal growth accompanied by the diffusion of B2O3 supplied from another new compound that formed on the surface of the La2SiO5 disk, LaBO3. In addition, c-LSBO crystals are formed not only by vapor–solid reactions but also by solid–solid and liquid–solid reactions. The increase in the c-axis orientation degree might be due to the increase in the amount of the liquid-phase interface.

Noble-metal-free catalysts based on apatite-type lanthanum silicate for complete toluene combustion

Noble-metal-free LaCoO3/La[Formula: see text]Si5CoO[Formula: see text]/[Formula: see text]-Al2O3 catalysts were developed for complete toluene combustion, and their catalytic activities were investigated. The active oxygen supply from the apatite-type La[Formula: see text]Si5CoO[Formula: see text] promoter successfully improved the oxidation ability of the LaCoO3 activator, and the highest catalytic activity was obtained for the 10 wt.% LaCoO3/20 wt.% La[Formula: see text]Si5CoO[Formula: see text]/[Formula: see text]-Al2O3 catalyst, which oxidized toluene completely at the temperature as low as 300[Formula: see text]C.

Morpho-structural and electrical characterization of Bi-doped apatite-type lanthanum silicates prepared by gel-combustion

La10−xBix(SiO4)6O3 ceramics (x = 0; 0.1; 0.15; 0.2; 0.3) were obtained from precursors prepared by gel combustion using l-aspartic acid as fuel. This study presents the effect of Bi3+ doping level and sintering temperature on the morpho-structural and electrical properties of apatites. Processes involved in the apatite formation same as crystallization temperature were examined through TGA. The XRD patterns have showed that all samples adopt the apatite structure and crystallize in the hexagonal space group P-3(147). Samples crystallite size varies between ~ 58 and ~ 118 nm depending on the Bi3+ doping level and the sintering temperature. In order to explain the conduction in apatite, the preferential position of Bi3+ in lattice and the occupancy factors of O5, O6 were calculated by Rietveld refinement. ICP-OES and XPS measurements give the bismuth amount accommodated in apatite lattice and its oxidation states. The morphology, homogeneity and compactness of the ceramics at different Bi doping level were examined through SEM. The relative density of the material is enhanced by the sintering temperature up to 1500 °C, reaching 91.63% for sample doped with 1.5% Bi. Through EIS investigations, the conductivities at 500 °C, for sample doped with 1.5% Bi, are: 9.22 × 10−5 Scm−1 (sintered at 1400 °C) and 1.02 × 10−3 Scm−1 (sintered at 1500 °C), respectively, values which are higher than that of un-doped apatite (6.46 × 10−5 Scm−1).

Preparation of zinc and alkaline earth metal co-doped apatite-type lanthanum silicate electrolyte ceramics by combustion method and mechanism of co-doping enhanced conductivity

The amorphous and high purity apatite-type lanthanum silicate La9.33A0.2Si5ZnO25.2 (LASZO, A=Ca, Sr and Ba) co-doped with zinc and alkaline earth metal has been successfully prepared at 600 °C in 7-9 min by employing the combustion method, along with revealing the combustion thermochemical mechanism. The LASZO ceramics were sintered at 1400-1500 °C after pressing molding. The XRD, IR, SEM and EIS analyses confirm that Zn2+ replaces Si4+ and A2+ replaces LaⅡ3+, along with the lattice volume increasing with the A2+ radius. The conductivity of co-doped La9.33Sr0.2(Si5ZnO24)OiOi*0.2VO·· at 1073 K is noted as 5.43 × 10-3 S·cm-1, which is higher than undoped, Zn2+ single-doped and A2+ single-doped ceramics. It is due to the generation of the oxygen vacancy VO·· by the Zn2+ doping, formation of an oxygen vacancy VO·· and increased lattice volume leading to a reduced space drag of the oxygen ion transport and A2+ doping increasing the concentration of the interstitial oxygen ions by introducing the additional interstitial oxygen ions Oi*. Therefore, the mechanism of co-doping driven increment in the conductivity is the oxygen vacancy defect-interstitial oxygen concentration-lattice volume composite enhancement.

Correction to: Structure and ionic conductivity of cerium doped La9.33−xCexSi6O26 apatite-type lanthanum silicates

Correction to: Structure and ionic conductivity of cerium doped La9.33−xCexSi6O26 apatite-type lanthanum silicates

Structure and ionic conductivity of cerium doped La9.33-xCexSi6O26 apatite-type lanthanum silicates

In this work, the effect of cerium doping on the structure and ionic conductivity of the apatite-type lanthanum silicates is presented. Ceramic samples with nominal composition of La9.33-xCexSi6O26 (x = 0, 0.1, and 0.2) are synthesized via a solid-state reaction process. They are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and complex impedance measurements. The study shows that the samples, having small amount of secondary phases of La2SiO5 and La2Si2O7, crystallize in the hexagonal apatite type structure with P63/m space group. The doping increases first the cell parameters for x = 0.1 before decreasing for x = 0.2. It also increases the grain size of the samples and reduces their porosity. The complex impedance measurements have been carried out in the temperature range 625–769 °C. The results are treated by separating the grain from the grain boundaries components and show that the ionic conductivity is remarkably improved by this kind of doping.

Improving conductivity of apatite-type lanthanum silicate by Nd and Zn co-doping

The electrical properties of apatite-type lanthanum silicate co-doped with Nd and Zn has been investigated. The Nd and Zn co-doped lanthanum silicate, La9.33NdxSi6-yZnyO26+(3x/2)-y (0 ≤ x ≤ 1, y = 0,1), are successfully synthesized by the urea nitrate combustion method. The phase, morphology and electrical properties are characterized by X-ray diffraction, scanning electron microscopy and electrochemical impedance spectra, respectively. La9.33NdxSi6-yZnyO26+(3x/2)-y ceramics has good apatite structure and high purity. The conductivity of La9.33NdxSi5ZnO25+(3x/2) first increases and then decreased accompanying with Nd content increasing, which higher than that of undoped La9.33Si6O26. The increase of the conductivity, which is attributed to Zn doped introduces oxygen vacancies and expands oxygen ions migration channel as well as Nd doped decreases the defect centers and increases the amount of interstitial oxygen ions. The decrease in conductivity is due to excess Nd blocking the oxygen ions migration channel. La9.33Nd0.8Si5ZnO26.2 exhibited the highest conductivity which values equal to 8.11 × 10−4 S cm−1 at 650 °C.

Effect of Boron Substitution on Oxide-Ion Conduction in c-Axis-Oriented Apatite-Type Lanthanum Silicate

Apatite-type lanthanum silicate (LSO) is a material with high oxide-ion conductivity in the low- and intermediate-temperature range (573–873 K) and is, therefore, a promising solid electrolyte for ...

Synthesis and characterization of Ba2+ and W6+ co-doped apatite-type lanthanum silicate electrolytes

Ba2+ and W6+ co-doped apatite-type lanthanum silicate solid electrolytes La9.4Ba0.6Si6-xWxO27-δ (x = 0, 0.05, 0.1, 0.15, 0.2) were successfully synthesized by high-temperature solid state method. The crystal structure, phase composition, microstructure, and electrical performance of samples were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy, respectively. The dense co-doped solid electrolyte materials sintered at 1550 °C for 5.5 h have good crystallinity and apatite-type crystal structure. The influences of the co-doped W6+ content on the properties of La9.4Ba0.6Si6-xWxO27-δ were investigated. The grain structure gradually changes from equiaxed and columnar grains to equiaxed grains. After Ba2+ and W6+ are co-doped, the lattice constant and cell volume are larger than those of La10Si6O27. The conductivities of the apatite lanthanum silicates are improved. La9.4Ba0.6Si5.9W0.1O26.8 exhibits the highest conductivity of 8.11 × 10−3 S cm−1 at 800 °C, whereas the conductivity of La10Si6O27 is only 3.91 × 10−3 S cm−1.

Use of waste water glass as silica supplier in synthesis of pure and Mg-doped lanthanum silicate powders for IT-SOFC application

Water glass in alkali solution (Na2SiO3/NaOH) an abundant effluent, generated in the alkaline fusion of zircon sand, represents a potential silica source to be converted in useful silica technological application. Actually, the generation of energy by environmental-friendly method is one of the major challenges for researchers. Solid Oxide Fuel Cells (SOFC) is efficient and environmentally clean technique to energy production, since it converts chemical energy into electrical power, directly. Apatite-type lanthanum silicates are promising materials for application as an electrolyte in intermediate temperature SOFC (IT-SOFC) because of their higher ionic conductivity, in temperatures of range 600–700 °C, than conventional zirconia electrolytes. In this work, pure (La9,56(SiO4)6O2,34) and Mg-doped (La9,8Si5,7Mg0,3O26,4) lanthanum silicate were synthesized, from that rich effluent. Using the sol-gel followed by precipitation method, the single crystalline apatite phase of both silicates was obtained by thermal treatment at 900 °C of their precursors. Sintered ceramic samples reached density of higher than 90%.

Preparation and Study of La9.33(SiO4)6O2 Solid Electrolyte Materials Doped with Ba and Zn

In this paper, apatite-type lanthanum silicate (hereinafter referred to as ATLS) electrolytes were doped with Ba and Zn at La and Si levels by gel sol method at a lower temperature. The doped La9.33BaxSi5ZnO25-x electrolytes were characterized by XRD, SEM analysis. The addition of Ba and Zn into the lattice of ATLS did not destroy the apatite crystal structure of the substance itself. SEM test showed that La9.33BaxSi5ZnO25-x electrolyte had the best sintering effect when Ba doping amount x=0.3.

Synthesis and conductivities of the Ti-doped apatite-type phases La9.33Si6-xTixO26

Solid oxide fuel cell is one of the alternative energy sources with high efficiency and low emissions. Solid oxide electrolyte is an important component of this fuel cell. A new electrolyte that suitable at medium temperature is needed to be developed. Apatite type lanthanum silicate is one of the electrolytes, which can operate at medium temperature. Increasing performance of apatite lanthanum silicate such as ionic conductivity can be achieved by doping. The purpose of the present study was to synthesize the electrolyte of Lanthanum silicates oxide with hydrothermal method and to investigate the effect of Ti4+ dopant on apatite electrolyte characteristics such as crystal lattice parameter and conductivity. The results showed that samples of La9.33Si6-xTixO26 with x = 0.1, 0.2, 0.3 were successfully synthesized. The value of c on the crystal lattice parameter increases with increasing the doping content of Ti4+. Increasing c value on the crystal lattice parameter is directly proportional to the conductivity. Apatite La9.33Si5.7Ti0.3O26 showed the highest conductivity of 2.4 × 10-4 S/cm at 700°C.

Doped apatite-type lanthanum silicates in CO oxidation reaction

Apatite-Type Lanthanum Silicate materials are reported as successful CO oxidation catalysts for the first time. A composition related activity is observed. Doping by Fe in the form La9.83Si4.5Fe1.5O26±δ enhanced remarkably activity versus the respective La9.83Si4.5Al1.5O26±δ compound resulting a lower shift by 109 °C in T50. In a composite 5%wt NiO/apatite catalytic system the catalytic performance was further improved by a synergistic effect. O2-TPD, H2-TPR and XPS studies revealed great variations in O2 desorption profiles, reducibility of materials and nickel species among catalytic samples in relation to their chemical composition.

High oxide-ion conductivity in Si-deficient La9.565(Si5.826□0.174)O26apatite without interstitial oxygens due to the overbonded channel oxygens

Overbonding of the channel oxygens in the apatite-type lanthanum silicates was found to be a key for the high oxide-ion conductivities by the present single-crystal neutron and X-ray diffraction studies.