Apatite-type Lanthanum Research Articles

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.

Preparation and Conductivity Research of Zinc Ions Doped La9.33(SiO4)6O2 Electrolyte

Solid electrolyte as a conductive medium has a good application prospect in the field of fuel cells. In order to improve the conductivity at low and medium temperature. The electrolyte of apatite type lanthanum silicateLa9. 33(SiO4)6O2 (ATLS) was doped with Zn at position of Si using urea nitrate combustion method. And XRD, SEM, IR were performed for ATLS electrolytes doped with Zn. The results showed that the combustion synthesis of zinc doped ATLS powders have apatite crystal structure after calcined 12 hours. Zn doping into the ATLS lattice has little impact on the crystal structure and morphology. Analysis of samples determine the best sintering temperature at 1250 for the La9. 33Si6-xZnxO26-x electrolyte. The electrolyte has good resistance stability by AC impedance test. When the amount of zinc ions doped x = 1. 0, the La9. 33Si6-xZnxO26-x has the highest ionic conductivity. Doping a moderate amount of ion at Si can enhance the conductivity of the ATLS electrolyte.

Synthesis and Conductivity Investigation of Cu Doped Apatite Type Lanthanum Silicate Electrolyte

In this paper, Cu-doped lanthanum silicate electrolyte (La9.33Si6-xCuxO26-x) precursor was synthesized by urea-nitrate combustion method using La2O3, CuO and TEOS as raw materials. The as-prepared precursor was lighted at 600 °C and sintered at 800 °C. The sintered powder samples were grinded and mixed absolutely by ball milled. Finally, we preformed and sintered powder samples to synthesis Cu-doped lanthanum silicate ceramics. Ac impedance method and analysis was used to test conductivity of as-prepared electrolyte, investigated the influence of balling time, sintering temperature and doping content on conductivity property of LSO sintered product. The final result shows that best balling time is 3 h, secondary sintering temperature is 1500 °C and the doping content is 0.3. Under this condition, the conductivity of Cu-doped lanthanum silicate electrolyte could reach 7.28×10-3 s/cm at 700 °C.

Structural and electrical characterization of Sr- and Al- doped apatite type lanthanum silicates prepared by the pechini method

The subject of this work regards the synthesis of La9.83−xSrxSi6−yAlyO26+δ (0≤x,y≤0.5) via a modified Pechini method. The compounds where characterized by XRD and SEM. Pure La9.83Si6O26+δ, La9.38Sr0.45Si6O26+δ and La9.38Sr0.45Si5.70Al0.30O26+δ were prepared after sintering at 1400°C for 20h while La9.38Sr0.45Si5.55Al0.45O26+δ and La9.38Sr0.45Si5.50Al0.50O26+δ contained traces (<8%) of La2SiO5 as secondary phase. Rietveld analysis showed that La9.83−xSrxSi6−yAlyO26+δ (0≤x,y≤0.5) compounds crystallize in the P63/m space group. Al doping on Si site exhibits more pronounced effect upon structural parameters in comparison to Sr doping on La site. Interstitial oxygen accommodates a position at the periphery of the hexagonal channels in the vicinity of the SiO4 groups. Ion conduction is close related with the size of the hexagonal channels and the interstitial oxygen content. The ion conductivity is promoted when an optimum balance between the aforementioned magnitudes is reached. The LS and LsSa4530 compounds exhibit the highest values of ionic conductivity at 700°C with 11 and 14mS/cm and activation energy of 0.47 and 0.46eV, respectively.

Compositional effect of Cr contamination susceptibility of La9.83Si6−x−yAlxFeyO26±δ apatite-type SOFC electrolytes in contact with CROFER 22 APU

Apatite type lanthanum silicate (ATLS) electrolytes in contact with CROFER 22 APU exhibit a compositional effect on their Cr contamination susceptibility.

Synthesis of Pure La10-XSrxSi6O27-0.5x Apatites Using an Optimized Sol-Gel Process

Apatite-type lanthanum silicates draw researcher’s attention due to their good performances as electrolyte materials for IT-SOFC (intermediate temperature solid oxide fuel cells) [1-5]. In this paper we present the synthesis and characterisation of Sr-doped La10Si6O27 prepared through an optimized, water-based sol-gel [6] process. The parameters involved in this process have been investigated to obtain high purity, high crystallinity powders. The mechanisms of the sol-gel reactions that underlie the quality of the sol are discussed. The optimized sol gel process enables obtaining pure apatite structures through a calcination step for 2 hours at a temperature as low as 800℃. They were characterized by scanning electron microscopy, X-ray diffraction and Energy-dispersive X-ray spectroscopy. Ionic conductivities have been measured after sintering at 1500℃ in order to investigate the effect of the Sr-doping. The electrical properties were measured as a function of temperature by complex impedance spectroscopy, using a Solartron 1260A frequency response analyzer (FRA) in the frequency range 5 Hz - 15 MHz, under static air. The measurements were performed at the open circuit voltage as well as with an applied AC voltage of 100 mV. The impedance diagrams were recorded from 673 K to 1273 K with thermal steps and stabilization times of about 25 K and 20 minutes respectively. The results show that the ionic conductivity is thermally activated and its value lies between 3×10-5 and 1×10-6 S.cm-1 at 873 K as function of the composition and powder preparation conditions. Keywords: Sol-gel processes; SOFC; apatite type lanthanum silicates; Sr doping

Chemical solution deposition of the highly c-axis oriented apatite type lanthanum silicate thin films.

Highly c-axis oriented apatite-type lanthanum silicate (LSO) thin films were fabricated by a simple solution coating method. In the solution coating method, LSO thin films are obtained by crystallization of initially deposited amorphous LSO precursor thin films. The degree of orientation was influenced by the precursor morphologies and a dense LSO precursor led to a high c-axis orientation perpendicular to the substrate. The oriented LSO thin films were composed of columnar grains with a single crystal orientation over the entire film thickness. In-plane orientation was not detected, which indicates that the c-axis orientation of the LSO thin films can be attributed to self-orientation.

Oxygen self-diffusion and conductivity measurements in apatite type electrolyte materials for SOFCs

Abstract Dense apatite type lanthanum silicate LSO (La 9.33 Si 6 O 26 ) electrolyte and the Al-, Fe- and Mg-doped compositions LASO (La 9.83 Al 1.5 Si 4.5 O 26 ), LFSO (La 9.83 Fe 1.5 Si 4.5 O 26 ), and LMSO (La 9.93 Mg 0.9 Si 5.1 O 26 ) have been prepared and investigated in this work in terms of their oxygen self-diffusion and total conductivity. Oxygen self-diffusivities and surface exchange coefficients and the respective activation enthalpies have been estimated and discussed. All samples exhibit a typical Arrhenius behaviour of the surface exchange coefficients meaning that the surface incorporation reaction is thermally activated. The doped samples exhibit higher surface concentrations as well as higher surface exchange coefficients as compared to the undoped sample. This indicates that doping has a direct influence to the oxygen incorporation reaction. It has been found that doping enhances the self-diffusion in all cases as compared to the undoped material. The trend found in this study is LSO «LFSO

Electrophoretic deposition of apatite type lanthanum silicates for SOFC half cell production

Apatite type lanthanum silicates (ATLS) are a new class of electrolyte materials exhibiting good oxygen ion conductivity in the intermediate temperature range. Electrophoretic deposition of aluminium doped ATLS powders from a non-aqueous solvent on a conductive polymer substrate was assessed by carefully adjusting the charging agent and polyelectrolyte addition. A modified electrode was built to be able to deposit on the non-conductive substrate. The optimised suspension was used to assess the feasibility of depositing a thin ATLS electrode powder layer directly on a precompacted non-conductive porous mixed ATLS-NiO anode. The combined use of optimised suspension along with the modified electrode configuration enabled successful production of green half cells.

Synthesis and Impedance Spectroscopy of Ga-Doped La&lt;sub&gt;9.33&lt;/sub&gt;(SiO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;6&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; Apatite Oxide Ion Conductor

Apatite materials are interesting alternative solid oxide fuel cell (SOFC) electrolytes because of their open structure including tunnels for the diffusion of oxide ions and their good chemical stability. However, the conductivity was still relative low when it was used as SOFC in the intermediate operating temperature range. So the apatite-type lanthanum silicates/germanates and doping were widely researched for enhancing conductivity recently. This study reports the influence of Ga doping on conductivity of the apatite phase La9.33(SiO4)6O2 according to the formula La9.33+x/3(SiO4)6-x(GaO4)xO2 where 0  x  2. Samples were prepared by a sol-gel process. The conductivities of all compositions have been obtained by impedance spectroscopy analysis. The conductivity enhancement observed for moderate x values and illustrates further influenced by the tetrahedral cation sublattice and the La vacancies in optimizing the conductivity.

Water-Based Soft Chemical Synthesis of Apatite Type Lanthanum Silicate Powder in Nano-Scale

The low temperature synthesis route of lanthanum silicate oxyapatite was investigated by x-ray diffraction and by carrying out thermal analyses using a precursor prepared by a water-based sol-gel method. The precursor was heated at 873 K, and it was found to consist of a lanthanum oxycarbonate (type IA-La2O2CO3), which has a layered stacked structure consisting of two-dimensional (La2O2)n2+ and two (CO3)n2- layers, and amorphous silica. Lanthanum silicate oxyapatite was found to be formed both by the in-situ chemical pulverization of La2O2CO3 into a nano-sized La2O3 powder and a solid-state reaction between the nano-sized powders of La2O3 and amorphous SiO2.

Electrophoretic Deposition as Preparation Method for Intermediate Temperature SOFC Half Cells

In this study we present the preparation of SOFC half cells by electrophoretic deposition. The cathode is deposited from a methyl ethyl ketone (MEK) suspension on dense apatite type lanthanum silicate (ATLS) pellets using a constant voltage. ATLS are a new class of electrolytes, which provides good oxygen permeability even at temperatures below 800°C. As cathode materials we used La2Ni0.8Cu0.2O4+δ (LNC) and La0.8Sr0.2Ni0.6Fe0.4O3 (LSNF). A conductive layer on the ATLS material was used to provide the necessary conductivity for electrophoretic deposition (EPD) process. For the preparation of suitable suspensions the charging behaviour and particle size of the different powders were investigated by means of zeta-potential and laser scattering measurements. When the electrophoretic mobility of the suspended particles was not sufficient iodine was added. Deposition kinetics were determined prior to preparation of the half cells. EPD parameters as well as sintering conditions were optimized in order to gain well adhering porous cathode layers.

Water-based Soft Chemical Synthesis of Apatite Type Lanthanum Silicate Powder in Nano-scale

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Synthesis of hexagonal lanthanum germanate apatites through site selective isovalent doping with yttrium

Apatite-type lanthanum silicates/germanates have been attracting considerable interest as a new class of oxide ion conductors, whose conductivity is mediated by oxide ion interstitials. For the germanates, it has been shown that, depending on composition, the cell can be either hexagonal or triclinic, with evidence for reduced low-temperature conductivities for the latter, attributed to increased defect trapping in this lower symmetry cell. In this paper we show that site selective doping of Y into the triclinic apatite-type oxide ion conductors, La 9.33+ z (GeO 4) 6O 2+3 z/2 (0.33 ≤ z ≤ 0.67) results in a hexagonal lattice for the complete series with correspondingly enhanced low-temperature conductivity.