Lanthanum–silicon system

Bulanova, M.; Zheltov, P.N.; Meleshevich, K. A.; Saltykov, P. A.; Effenberg, G.; Tédenac, J. C.

doi:10.1016/s0925-8388(01)01686-3

Cited by 55 publications

(41 citation statements)

References 11 publications

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“…The as-deposited film has a quasi-amorphous structure as it can be concluded from the broad diffraction peaks detected by X-ray diffraction around 2θ ≈ 36 and 57°. Annealing the film at 873 K promotes its crystallization and the formation of the LaSi 2 phase [15] which is thermodynamically stable at this temperature [16]. However, the LaSi phase, which is also predicted by the equilibrium La-Si phase diagram [16] is not formed upon annealing of the coating containing 59.3 at.% Si.…”

Section: Resultsmentioning

confidence: 91%

“…Annealing the film at 873 K promotes its crystallization and the formation of the LaSi 2 phase [15] which is thermodynamically stable at this temperature [16]. However, the LaSi phase, which is also predicted by the equilibrium La-Si phase diagram [16] is not formed upon annealing of the coating containing 59.3 at.% Si. LaSi 2 remains the only phase detected after annealing at 973 K. The sharpening of the diffraction peaks indicates that the crystallization process progresses while increasing the annealing temperature.…”

Section: Resultsmentioning

confidence: 91%

“…The quite similar broad diffraction peaks already observed for the film with Si/(Si + La) ratio of 53.2 at.% are also detected by X-ray diffraction. Even if the film chemical composition lies in the LaSi + La 5 Si 4 phase mixture compositional range of the La-Si phase diagram [16], no equilibrium phases were detected by X-Ray diffraction after annealing up to 1073 K. Instead, a broad peak centred around 2θ = 33°appears in the diffraction pattern at 873 K along with weak diffraction peaks corresponding to the LaSi 2 phase. The broad diffraction peak is the only feature present in the diffraction pattern after annealing up to 1073 K. Once again, annealing at 1173 K leads to the formation of the lanthanum silicate apatite-like phase.…”

Section: Resultsmentioning

confidence: 98%

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Oxidation of magnetron sputtered La-Si thin films for solide oxide fuel cell electronlytes

et al. 2009

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La-Si thin films were deposited on stainless steel substrates by magnetron sputtering from pure La and Si targets. The Si/(Si + La) atomic ratio in the films was varied from 43.2 to 59.3% by adjusting the discharge current on the La target. The films had a homogeneous chemical composition down to the substrate and sharp interfaces. Annealing the films in air at 1173 K promotes the formation of apatite-structure La 9.33 Si 6 O 26 and the diffusion of different species from the film to the substrate and vice-versa, resulting in broadening the interfaces. X-Ray diffraction showed that all the as-deposited films had an amorphous structure. The formation of the LaSi 2 phase at intermediate temperatures was observed for the films deposited with higher Si contents while the films deposited with lower Si contents remained amorphous up to the start of the apatite structure crystallization process. The lanthanum silicate apatite-like phase (La 9.33 Si 6 O 26 ) was obtained only after annealing at 1173 K, excepted for the film with the lower Si content which is already partially crystallized after annealing at 1073 K. Quite pure La 9.33 Si 6 O 26 was obtained only after annealing the film with the highest Si content (Si/(Si + La) = 59.3%) although the theoretical Si/(Si + La) atomic ratio for apatite structure lanthanum silicate is 39%. For the other films, La 2 O 3 was always detected when the lanthanum silicate phase was formed. Both phenomena clearly resulted from the strong diffusion of silicon excess towards the stainless steel substrate.

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Section: Resultsmentioning

confidence: 91%

Section: Resultsmentioning

confidence: 91%

Section: Resultsmentioning

confidence: 98%

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Oxidation of magnetron sputtered La-Si thin films for solide oxide fuel cell electronlytes

et al. 2009

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“…[18]. Among these, the superconductivity was found in three tetragonal systems, LaSi 2 with α-ThSi 2 crystal structure (T c = 2.3 K) [19], La 3 Si 2 with U 3 Si 2 crystal structure (T c 2.1 K) [18,20] and La 5 Si 3 with Cr 5 B 3 crystal structure (T c = 1.6 K) [18,21]. However, none of these superconducting La-Si phases was detected through electron microprobe analysis in our sample.…”

Section: Resultsmentioning

confidence: 99%

Inhomogeneous Superconducting Behaviour in $$\hbox {La}_{5}\hbox {Ni}_{2}\hbox {Si}_{3}$$ La 5 Ni 2

et al. 2017

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The superconducting phase transition at T c = 2.3 K was observed for the electrical resistivity ρ(T ) and magnetic susceptibility χ(T ) measurements in the ternary compound La 5 Ni 2 Si 3 that crystallizes in the hexagonal-type structure. Although a single-phase character with the nominal stoichiometry of the synthesized sample was confirmed, a small trace of the La-Ni phase was found, being probably responsible for the superconducting behaviour in the investigated compound. The magnetization loop recorded at T = 0.5 K resembles a star-like shape which indicates that the density of the critical current can be strongly suppressed by a magnetic field. The low-T ρ (T ) and specific heat C p (T ) data in the normal state reveal simple metallic behaviour. No clear evidence of a phase transition to any long-or short-range order was found for C p (T ) measurements in the T -range of 0.4-300 K.

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“…Recently, lanthanum silicates with an apatite-like structure (La 9,33 Si 6 O 26 ) have attracted considerable interest as potential materials for low cost electrolyte [2]. Some of these materials show conductivities at 875 K comparable to, or better than, YSZ; their high level of oxide ion mobility was related to the presence of oxygen channels along the c axis which facilitate the diffusion of the anionic species (O 2-for SOFCs applications) [3]. Another way to fulfil IT-SOFCs requirements is to decrease the electrolyte thickness to the micrometer range and, therefore, the ohmic drop at the electrolyte.…”

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confidence: 99%

Morphological and structural characterization of oxidized La-Si sputtered thin films

Oliveira

Cavaleiro

2008

Microsc Microanal

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High temperatures in Solid Oxide Fuel Cells (SOFCs) place stringent requirements on the cell components materials which result in high material costs for interconnects and insulation and cause the degradation of the system. The development of Intermediate Temperature SOFCs (IT-SOFCs) will require electrolyte materials with higher ionic conductivity at moderate temperatures than the conventional yttria-stabilised zirconia (YSZ) [1]. Recently, lanthanum silicates with an apatite-like structure (La 9,33 Si 6 O 26 ) have attracted considerable interest as potential materials for low cost electrolyte [2]. Some of these materials show conductivities at 875 K comparable to, or better than, YSZ; their high level of oxide ion mobility was related to the presence of oxygen channels along the c axis which facilitate the diffusion of the anionic species (O 2-for SOFCs applications) [3]. Another way to fulfil IT-SOFCs requirements is to decrease the electrolyte thickness to the micrometer range and, therefore, the ohmic drop at the electrolyte. Magnetron sputtering has already been used to synthesize thin film electrolytes for SOFCs owing to its versatility for depositing complex materials as well as its ability to control their composition and morphology [4]. The manufacturing of thin film lanthanum silicate electrolytes by magnetron sputtering, with thicknesses in the micrometer range, can be achieved through the previous deposition of La-Si films and subsequent thermal oxidation [5]. The present study focuses on the characterization of the morphological and structural changes upon oxidation of La-Si films deposited by magnetron sputtering.The La-Si films were deposited by magnetron sputtering from pure La and Si targets (200 mm of diameter). The La target power was maintained constant at 1000 W in all depositions whereas the Si target power was varied from 400 to 750 W. All films were deposited on Al 2 O 3 pellets. The substrate bias voltage was kept constant at -50 V. An Ar (99.99%) flow rate of 20 sccm, which resulted in a total pressure of about 0.4 Pa, was used in all experiments. The La-Si films were oxidised at 1175 K for 1 h in industrial air (99.995% purity) flowing through a dehumidificator. The chemical composition of the coatings was determined by electron probe microanalysis (EPMA). The cross section, surface topography and morphological features of the La-Si films were examined on a scanning electron microscope (SEM) equipped with an EDAX energy dispersive spectrometer (EDS). The structure of the coatings was studied by X-ray diffraction (XRD) in Bragg-Brentano configuration with Co(Kα) radiation and by Micro-Raman spectroscopy. Figure 1 shows the surface and cross-section SEM micrographs of a La-Si film deposited with 49 at. % Si after thermal oxidation in industrial air for one hour at 1175 K. Besides the substrate induced features, the film surface is covered by fine grains with angular shapes (compare both halves in figure 1a) which indicate that a crystalline phase was formed as a result of the oxidatio...

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Lanthanum–silicon system

Cited by 55 publications

References 11 publications

Oxidation of magnetron sputtered La-Si thin films for solide oxide fuel cell electronlytes

Oxidation of magnetron sputtered La-Si thin films for solide oxide fuel cell electronlytes

Inhomogeneous Superconducting Behaviour in $$\hbox {La}_{5}\hbox {Ni}_{2}\hbox {Si}_{3}$$ La 5 Ni 2

Morphological and structural characterization of oxidized La-Si sputtered thin films

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