Lanthanum Silicate Research Articles

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.

Flux growth of doped lanthanum silicate oxyapatite crystals with hexagonal tabular morphology

Flux growth of doped lanthanum silicate oxyapatite crystals with hexagonal tabular morphology

Effects of LaSiO<italic>x</italic> Thickness and Forming Gas Anneal Temperature on Threshold Voltage Instability of 4H-SiC MOSFETs With LaSiO<italic>x</italic>

We report the effects of lanthanum-rich layer thickness and forming gas anneal (FGA) conditions on mobility and threshold voltage ( ${V} _{{\text {T}}}$ ) instability of high-mobility 4H-SiC MOSFETs using lanthanum silicate (LaSiO x ) interface engineering. MOSFETs with LaSiO x after high-temperature FGA show significantly improved ${V} _{\text {T}}$ reliability under positive gate bias. It is found that both the thickness of the initial lanthanum-rich layer and the FGA temperature profoundly influence MOSFET mobility and ${V} _{\text {T}}$ instability under positive bias. There is a tradeoff between mobility and ${V} _{\text {T}}$ shift under positive bias.

Oxygen pumping based on <i>c</i>-axis-oriented lanthanum silicate ceramics: challenge toward low operating temperature

Oxygen pumping based on <i>c</i>-axis-oriented lanthanum silicate ceramics: challenge toward low operating temperature

Interface dominated conductivity change in Ce0.8Sm0.1Nd0.1O2−δ/La9.33Si6O26 composite electrolyte

Samarium and neodymium co-doped ceria (Ce0.8Sm0.1Nd0.1O2−δ abbreviated SNDC) and lanthanum silicate (La9.33Si6O26 abbreviated LSO) composite electrolytes with different mixing ratio were prepared at 1500 and 1550 °C. The composite obtained were all with high density, and no chemical reaction between two phases was observed during sintering according to the XRD result. The addition of LSO has a great influence on the suppression of grain growth of SNDC, and brought about the change in conduction behavior of composite. High distortion at hetero interface has been observed by TEM. The composite with 30 wt% LSO exhibits the highest conductivity (0.0036 S/cm at 500 °C) with an improvement of 37% compared with SNDC. The measurement at low oxygen partial pressure demonstrated the high chemical stability of composite electrolyte, making it a promising candidate for intermediate temperature SOFCs or oxygen sensors.

Stability and compatibility of lanthanum silicates electrolyte with standard cathode materials

Lanthanum silicate (LSO) electrolytes doped with different valence cations are successfully synthesized by solid state reaction. Crystal structure, electrical properties, stability and compatibility with cathode materials are characterized. The measured total conductivities of LSO electrolytes doped with In3+, Nb5+ and W6+ are relatively high compared with that of undoped La10Si6O27, which is attributed to more carriers including either excessive oxygen vacancies generated when doping with In3+ or more interstitial oxide-ion O (5) generated when doping with Nb5+ and W6+. The thermal expansion coefficients of La10Si5.9A0.1O27±δ (A = In3+, Si4+, Nb5+, W6+) electrolytes vary from 8.48 to 8.83 × 10–6 K–1 at 1073 K. The doped LSO electrolytes match well with (La0.75Sr0.25)0.95MnO3±δ cathode at temperatures below 1573 K, which is highly stable, to some extent, in various atmospheres of CO2 or H2O vapour.

A new family of Cu-doped lanthanum silicate apatites as electrolyte materials for SOFCs: Synthesis, structural and electrical properties

La9.67Si6-xCuxO26.5-x (LSC, x = 0, 0.1, 0.3 and 0.5) are synthesized by a citric-nitrate method. Substitution Si with Cu promotes the densification process of silicate apatite. Unit cell parameters and volume increase linearly with Cu content. The Rietveld refinement reveals a much more distorted (Si,Cu)O4 tetrahedra in the oxygen stoichiometric La9.67Si5.5Cu0.5O26 sample. The structural observation from high temperature XRD implies a second-order phase transition in La9.67Si5.5Cu0.5O26. Cu-doping decreases the activation energy of oxygen ion conduction and increases the conductivity of LSC materials in the temperature range of 550–800 °C. La9.67Si5.5Cu0.5O26 shows the conductivity values of 29.3 and 12.3 mS cm−1 at 800 °C and 650 °C, respectively. The oxygen ion transference number of La9.67Si5.5Cu0.5O26 is higher than 0.99. These attractive properties make the La9.67Si5.5Cu0.5O26 a promising oxygen ion conducting electrolyte for applications of solid oxide fuel cells, oxygen sensors, oxygen separation membranes, etc.

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.

Lanthanum–silicate–substituted apatite synthesized by fast mechanochemical method: Characterization of powders and biocoatings produced by micro–arc oxidation

Lanthanum–silicate substituted apatite with equal concentrations of the substituents in the range of 0.2–6.0 mol were produced by a fast method – mechanochemical synthesis. This method makes it possible to synthesize a nanosized single–phase product by activating reaction mixtures containing CaHPO4, CaO, La(OH)3 and SiO2·H2O for 25–30 min in AGO–2 and AGO–3 planetary mills. The structure of the apatites was investigated by the FTIR and XRD methods. It was found that the synthesized samples with substituent concentrations up to 2 mol are substituted oxy–hydroxyapatites, at higher concentrations, they are substituted oxyapatites. The mechanochemically synthesized apatite with a substituent concentration of 0.5 mol was used for depositing biocoatings on titanium substrates by the micro-arc oxidation method. The structure of the coatings is mainly amorphous. In vitro biological tests demonstrated high biocompatibility of the coatings and the absence of cytotoxic action on mesenchymal stem cells.

Hydrothermal Synthesis and Characterization of an Apatite‐Type Lanthanum Silicate Ceramic for Solid Oxide Fuel Cell Electrolyte Applications

AbstractApatite‐type lanthanum silicate (La10Si6O27; LS) nanopowders are synthesized using a hydrothermal process and used for the electrolyte applications in solid oxide fuel cells (SOFCs). The synthesized nanopowders are characterized by Rietveld refinement of the X‐ray diffraction (XRD) data, SEM–energy‐dispersive X‐ray spectroscopy (EDS), TEM, and dialotometry. The prepared nanopowders can be sintered to near theoretical density at sintering temperature of 1500 °C. Reactivity studies between the synthesized La10Si6O27 material and cathode materials such as La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF), Nd2NiO4 (NNO), and Pr2NiO4 (PNO), are carried out by XRD analysis revealing that they do not react. Symmetric cells are fabricated and characterized electrochemically. The area specific resistances for LSCF, NNO, PNO, and PNO‐LS (1:1 (wt %)) measured at 900 οC, are 100, 2.2, 1.8, and 0.5 Ω cm2, respectively. EDS analysis shows that interdiffusion of cations at the cathode–electrolyte interface is not detected for LS/PNO, which is attributed to the low area‐specific resistance values. The results demonstrate that Pr2NiO4 and the composites are promising cathode materials for the apatite‐type lanthanum silicate electrolyte for SOFC applications.

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.

Effect of High Temperature Forming Gas Annealing on Electrical Properties of 4H-SiC Lateral MOSFETs with Lanthanum Silicate and ALD SiO<sub>2</sub> Gate Dielectric

We investigated the impact of an initial lanthanum oxide (La2O3) thickness and forming gas annealing (FGA) conditions on the MOSFET performance. The FGA has been shown to dramatically improve the threshold voltage (VT) stability of 4H-SiC MOSFETs. The FGA process leads to low VT shift and high field effect mobility due to reduction of the interface states density as well as traps by passivating the dangling bonds and active traps in the Lanthanum Silicate dielectrics. By optimizing the La2O3 interfacial layer thickness and FGA condition, SiC MOSFETs with high threshold voltage and high mobility while maintaining minimal VT shift are realized.

Influence of the porosity caused by incomplete sintering on the mechanical behaviour of lanthanum silicate oxyapatite

Lanthanum silicate oxyapatite (LSO) is an encouraging material for its use as an electrolyte in intermediate temperature solid oxide fuel cells. There is a vacancy in knowledge respecting to LSO's mechanical properties, and thus they are the scope of research of the present work.Isostatically pressed bars were sintered at temperatures from 1200 °C to 1500 °C. The dependence of Young's modulus with porosity was fitted using three different modeling curves, and extrapolated for a fully dense material. The fitting of these equations give an E0 between 144 GPa and 169 GPa. This is the first time that LSO's Young's modulus is reported.Flexural strength,Vickers hardness, fracture toughness (KIC) from microindentation cracks and nanohardness were also measured. Scanning electron micrography was performed on both a sub-sintered and the most sintered sample, and the microstructure and fracture mechanism were analyzed.In general, the mechanical behaviour is similar to other intermediate temperature solid oxide electrolytes. The fracture mechanism of the most sintered sample makes it well-suited for future SOFC applications.

Effect of lanthanum silicate interface layer on the electrical characteristics of 4H-SiC metal-oxide-semiconductor capacitors

The effect of La-silicate interface layer (IL) on the electrical characteristics of 4H-SiC metal-oxide-semiconductor (MOS) capacitors with atomic-layer-deposited SiO2 (ALD-SiO2) gate dielectrics was investigated. In addition to a slight reduction in the interface state density (Dit), the surface potential fluctuation was greatly reduced due to the reduction in the fixed charges (Qfix) with La-silicate IL. Moreover, two orders of magnitude reduction in the oxide trap density in the ALD-SiO2 layer adjacent to the La-silicate IL was confirmed. Physical analysis revealed the reduction in carbon concentration and incorporation of La atoms adjacent to the La-silicate IL.

Preparation of lanthanum silicate electrolyte with high conductivity and high chemical stability

Effects of dopant content and synthesis temperature on phase relations and conducting behavior of lanthanum silicate, La9.33+xSi6O26+1.5x (LSO) electrolytes were investigated. The La-excess-type Fe-doped LSO, La10(Si5.5Fe0.5)O26.75 synthesized at 1973 K showed lower grain boundary as well as grain interior resistances, and then, had high total conductivity (6.9 × 10−3 S cm−1 at 873 K and 3.6 × 10−5 S cm−1 at 573 K). In addition, the chemical instability owing to a high lanthanum activity in the La-excess-type LSO (x = 0.67) specimen could be eliminated by incorporating iron into the specimen. The synchrotron radiation microbeam X-ray diffraction technique revealed that this specimen contains a small amount of new secondary phase, which differs from the situation found in a highly conductive but chemically unstable Al-doped LSO specimen with the same x value and the same synthesis temperature.

Synergetic enhancement of mechanical and electrical properties in Ce0.8Sm0.1Nd0.1O2−δ/La10Si6O27 composite electrolytes

AbstractIt has been demonstrated that the samarium and neodymium codoped ceria (Ce0.8Sm0.1Nd0.1O2−δ abbreviated SNDC) shows high ionic conductivity at intermediate operating temperature (0.012 S/cm at 500°C. However, the poor mechanical properties limited its applications in solid fuel cells and oxygen sensors. Present research reports an approach to improve the mechanical properties of SNDC by adding another kind of oxide solid electrolyte, the apatite‐type lanthanum silicate (La10Si6O27 abbreviated LSO). The SNDC/LSO composites were prepared by mixing the powders with different proportion, and sintered at 1600°C. Their structure, morphology, mechanical, and electrical properties were characterized. It was found that with the 5wt%‐7wt% LSO addition, both the flexural strength and the fracture toughness were improved. The improvement of flexural strength for the SNDC reached as high as 71%. It is also seen that the ionic conductivity of SNDC was enhanced with the adding of 5wt% LSO. The enhanced mechanical properties and electrical conductivity of SNDC/LSO composites make them a promising candidates for high‐performance SOFCs and oxygen sensors.

Improvement of Threshold Voltage Reliability of 4H-SiC MOSFETs With Lanthanum Silicate by High Temperature Forming Gas Anneal

We report the effect of a high-temperature forming gas anneal (FGA) on the electrical characteristics and threshold voltage (VT) instability of high-mobility Si-face (0001) 4H-SiC metal oxide semiconductor field effect transistors (MOSFETs) with lanthanum silicate (LaSiOx). The MOSFET with LaSiOx after 800 °C FGA in 5% H2 and 95% N2 mixture shows significantly reduced VT shift under 3-MV/cm positive bias stressing from 2.78 to 1.65 V, while maintaining high field-effect mobility of 122.7 cm2/Vs and sufficiently positive VT of 2.76 V.

Effect of the temperature on the sintering behavior of CeO2 -La2 O3 doped with silicate

This paper evaluates the sintering behavior of CeO2-La2O3-silicate at different temperatures. The sintered compact of this system may be a candidate to be used as a refractory lining for biomass (sugarcane bagasse) gasifier. The raw material (CeO2-La2O3-silicate powder) was characterized by granulometric distribution, differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and dilatometry. Cylindrical compacts of this powder were heat treated at 1200 oC, 1300 oC and 1400 oC for 1 h and characterized by X-ray diffraction (XRD), micro Raman spectroscopy, SEM/EDS, shrinkage and apparent porosity. The results show that the sintering degree of the samples increases with temperature, reaching shrinkage of about 16 % and apparent porosity of 3.5 % at 1400 oC. The XRD and Raman spectroscopy results revealed that a cerium/ lanthanum silicate was formed which is stable against melting at temperature as high as 1400 oC. The study of the reactivity of the bagasse ash and the CeO2-La2O3-silicate refractory will be presented in a future publication.

Dense lanthanum silicate oxyapatite ceramics obtained by uniaxial pressing and slip casting

Lanthanum silicate oxyapatite (LSO) is a promising ion conductive ceramic material, which has higher oxygen ion conductivity at intermediate temperatures (600-800?C) compared to yttria-stabilized zirconia. Its mechanical properties, though important for any of its applications, have been scarcely reported. In this study, we compare apparent densification, open porosity and Vickers hardness of samples conformed by uniaxial pressing and slip casting and fired up to 1600?C. Colloidal processing was optimized for slip casting in order to get high green densities. At sintering temperatures higher than 1400?C, both processing routes yielded comparable densities, although uniaxially pressed samples show slightly better mechanical properties, evidencing that slip cast ones already underwent a grain growth process.

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.