Single crystal growth of apatite-type Al-doped neodymium silicates by the floating zone method

An, Tao; Baikie, Tom; Wei, Fengxia; Li, Henan; Brink, Frank; Wei, Jun; Ngoh, S.L.; White, Timothy John; Kloc, Christian

doi:10.1016/j.jcrysgro.2011.08.010

Cited by 9 publications

(22 citation statements)

References 16 publications

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“…Our recent success in growing large hexagonal single crystals of pure and Al‐doped neodymium silicate apatite (Nd 9.33+ x /3 Al x Si 6− x O 26 , x = 0, 0.5, 1.0, 1.5) and their evaluation by impedance spectroscopy confirmed the anisotropic character of oxygen migration and the tandem role of Ln 3+ vacancies and O 2− interstitials in facilitating ion diffusion. In general, interstitial transport is the greatest along the crystallographic c axis, but this anisotropic character decreases with Al‐doping as basal plane percolation becomes more favorable .…”

Section: Introductionmentioning

confidence: 77%

“…As the Al 3+ ion is 50% larger than Si 4+ , the unit cell progressively dilated in the more aluminous materials. However, similar to the single crystals, Vegard's is not obeyed because at the low Al content (0 ≤ x ≤ 0.5), charge balance is achieved by the filling of Nd vacancies:

\begin{matrix} ({Nd}_{9.33 □ 0.67}) {Si}_{6} O_{26} + x {Al}^{3 +} \to \\ ({Nd}_{9.33 + x / 3 □ 0.67 - x / 3}) {Al}_{x} {Si}_{6 - x} O_{26} \end{matrix}

while at higher Al content (1.0 ≤ x ≤ 2.0) vacancy creation is also significant:

O^{2 -} + 2 {Si}^{4 +} \to □_{O} + 2 {Al}^{3 +}

All samples were over 90% relative density, and those for x ≥ 1.0 were particularly well consolidated (Table ).…”

Section: Resultsmentioning

confidence: 97%

“…Comparing the ionic conductivity in these dense ceramics with single crystals of similar composition provides insights into the relative contribution of grain boundaries and intrinsic defects to oxygen mobility in apatites. For this study, Nd‐apatite was chosen, rather than the common La–Si–Al analog, because as described elsewhere, colored apatites are more easily grown as large crystals in the optical mirror furnace …”

Section: Introductionmentioning

confidence: 99%

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Oxygen Migration in Dense Spark Plasma Sintered Aluminum‐Doped Neodymium Silicate Apatite Electrolytes

Baikie

Herrin

et al. 2013

J. Am. Ceram. Soc.

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Neodymium silicate apatites are promising intermediate temperature (500°C-700°C) electrolytes for solid oxide fuel cells. The introduction of Al promotes isotropic percolation of O 2− , and at low levels (0.83-2.0 wt% Al) enhances bulk conductivity. To better understand the effect of Al-doping on intrinsic conductivity, and the impact of grain boundaries on the transport, dense Nd 9.33+x/3 Al x Si 6−x O 26 (0 ≤ x ≤ 2) pellets were prepared by spark plasma sintering. Phase purity of the products was established by powder X-ray diffraction and the microstructure examined by scanning electron microscopy. The ionic conductivity measured by AC impedance spectroscopy for the spark plasma sintered ceramics were compared with transport in single crystals of similar composition. Intermediate Al-doping (0.5 ≤ x ≤ 1.5) delivered superior overall conductivity for both the polycrystalline and single crystal specimens. W.-C. Wei-contributing editor Manuscript No. 32730.

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Section: Introductionmentioning

confidence: 77%

\begin{matrix} ({Nd}_{9.33 □ 0.67}) {Si}_{6} O_{26} + x {Al}^{3 +} \to \\ ({Nd}_{9.33 + x / 3 □ 0.67 - x / 3}) {Al}_{x} {Si}_{6 - x} O_{26} \end{matrix}

while at higher Al content (1.0 ≤ x ≤ 2.0) vacancy creation is also significant:

O^{2 -} + 2 {Si}^{4 +} \to □_{O} + 2 {Al}^{3 +}

All samples were over 90% relative density, and those for x ≥ 1.0 were particularly well consolidated (Table ).…”

Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Oxygen Migration in Dense Spark Plasma Sintered Aluminum‐Doped Neodymium Silicate Apatite Electrolytes

Baikie

Herrin

et al. 2013

J. Am. Ceram. Soc.

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“…38) The next successful single crystal growth was reported in 2011 by An et al, who used the floating zone method to grow Al-doped Nd 9.33+x/3 Si 6¹x Al x O 26 (0¯x¯1). 39) Single crystals of approximately 5 mm in diameter and more than 20 mm in length were obtained. These crystals were grown along the c-axis, similar to the single crystals reported by Higuchi et al 18),34) With respect to the conductivity of the crystals, 40) An et al reported four important results; however the explanations in the text and figures were inconsistent.…”

Section: Single Crystal Growth and Discovery Of High Conductivitymentioning

confidence: 99%

Research progress in nondoped lanthanoid silicate oxyapatites as new oxygen-ion conductors

Kobayashi

Sakka

2014

J. Ceram. Soc. Japan

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The discovery of oxygen-ion conductivity and changes in the crystal-structure model of nondoped lanthanum silicate oxyapatites are reviewed from the researches which led to the discovery to current work. The oxygen-ion conductivity of lanthanoid silicate oxyapatites was discovered by Nakayama et al., during development of new oxide lithium-ion conductors. Although samples with compositions of LiRESiO 4 (RE = La, Nd, Sm, Gd, Dy) were initially reported to be single phases with the same crystal structure, the accurate crystal structure of LiRESiO 4 was not clarified until later. The crystal structure determined from X-ray diffraction patterns of LiLnSiO 4 was revised as oxyapatite by another group. The chemical composition of the crystal phases in LiRESiO 4 was also revised to RE 10 Si 6 O 25 and/or RE 9.33 Si 6 O 24 . The discovery of oxygen-ion conductivity in these materials was confirmed when researchers noted that samples of RE 10 Si 6 O 25 , specifically, the samples without lithium, are electrically conducting. Furthermore, very high oxygen-ion conductivity in the direction parallel to c-axis was discovered after single crystals of RE 9.33 (SiO 4 ) 6 O 2 (RE = Nd, Pr, and Sm) were successfully grown. The crystal structure and defect models were also altered after the discovery of oxygen-ion conductivity. Although numerous reports related to the electrical conductivity of La 9.33+x (SiO 4 ) 6 O 2+3x/2 ceramics have appeared in the literature, clear dependences of the total conductivity on the cation nonstoichiometry (x) as well as the sintering temperature are still unclear because of large discrepancies in the reported data. Furthermore, the composition region, where the lanthanum silicate oxyapatite single phase is formed, is also still unclear because of the inconsistencies in the reported results.

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“…This apatite compositional pair was selected to most directly examine the heavy cation (Nd/Sr) distribution and correlate crystal chemistry with oxygen mobility measured by impedance spectroscopy. 18 Polycrystalline feed rods were prepared by conventional solid state sintering. Nd 2 O 3 (Alfa Aesar, 99.9%), SrCO 3 (99.9%, Alfa Aesar), and SiO 2 (Alfa Aesar, 99.9%) were thoroughly mixed in stoichiometric metal ratios in an agate mortar with manual grinding for 1 h, followed by preheating (1200°C/10 h) to decarbonize SrCO 3 .…”

Section: ■ Introductionmentioning

confidence: 99%

Crystal Chemical Analysis of Nd_9.33Si₆O₂₆ and Nd₈Sr₂Si₆O₂₆ Apatite Electrolytes Using Aberration-Corrected Scanning Transmission Electron Microscopy and Impedance Spectroscopy

Baikie

Weyland

et al. 2015

Chem. Mater.

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Lanthanoid silicate apatite solid electrolytes contain one-dimensional channels. These materials display substantial oxygen mobility at temperatures lower than conventional zirconia-based ionic conductors because interstitial oxygen displacements, mediated by Ln cation vacancies, have a lower activation energy. For these nonstoichiometric apatites, crystal structure solutions derived from X-ray and neutron powder diffraction yield the average atomic arrangement, but these techniques also average over local lattice disorders. Large apatite single crystals permit the evaluation of oxygen migration anisotropy using impedance spectroscopy and the correlation of this behavior to atomic scale domain formation or defect cluster aggregation if present. Aberration-corrected scanning transmission electron microscopy, in both high angle annular dark field (HAADF) and bright field (BF) modalities, was applied to characterize the local atomic structure of Nd 9.33 Si 6 O 26 and Nd 8 Sr 2 Si 6 O 26 apatite electrolytes. Quantitative image analysis found the distribution of metal vacancies and dopant metal in apatites to be remarkably homogeneous at the unit cell scale. This is distinct from other oxide electrolytes including fluorites, perovskites, and melilites, where domain and superstructure formation are a consequence of interstitial oxygen incorporation and prescribe the mode of ionic transport. In the present case, the unexpectedly high perfection of silicate apatites arises from the flexible topological response of one-dimensional channels penetrating the structure, which, in turn, allows robust chemical tailoring of these electrolytes. ■ INTRODUCTIONLanthanoid silicate apatites are one-dimensional tunnel structures that adopt hexagonal (P6 3 /m) or pseudohexagonal crystal symmetry and are candidate electrolytes for next generation solid oxide fuel cells (SOFC) (Figure 1). These materials show significant ionic conductivity at intermediate temperatures (500−700°C) 1 that reduces mechanical stress in the cell assemblages and extends their serviceable lifetimes. The general composition of the apatite prototype is Ln 9.33 □ 0.67 Si 6 O 26 (Ln = La) with Ln 3+ vacancies (□) required for charge balance. More completely, two distinct Ln sites occupy the tunnel (Ln T ) and framework (Ln F ) of apatite and the formula can be recast as [Ln F 3.33 □ 0.67 ][Ln T 6 ][SiO 4 ] 6 O 2 . 2 Extrastoichiometric Ln 3+ can be introduced with an accompanying interstitial oxygen (2Ln 3+ + 3O i 2− ), and both atomistic modeling 3,4 and neutron diffraction 5,6 suggest this substitution creates an [001] 7 conduction path for O 2− . However, intratunnel transport only accounts for two-thirds of the conduction, with the balance by cross-tunnel migration, which is less well understood. In any event, ionic mobility in apatites is quite distinct from the extensively studied yttria-stabilized zirconia 8 electrolytes and other ionic conductors, such as dopedceria 9 and La−Sr−Ga−Mg perovskites, 10 whose O 2− conduction is based on vacancy transport. 11

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Single crystal growth of apatite-type Al-doped neodymium silicates by the floating zone method

Cited by 9 publications

References 16 publications

Oxygen Migration in Dense Spark Plasma Sintered Aluminum‐Doped Neodymium Silicate Apatite Electrolytes

Oxygen Migration in Dense Spark Plasma Sintered Aluminum‐Doped Neodymium Silicate Apatite Electrolytes

Research progress in nondoped lanthanoid silicate oxyapatites as new oxygen-ion conductors

Crystal Chemical Analysis of Nd_9.33Si₆O₂₆ and Nd₈Sr₂Si₆O₂₆ Apatite Electrolytes Using Aberration-Corrected Scanning Transmission Electron Microscopy and Impedance Spectroscopy

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Single crystal growth of apatite-type Al-doped neodymium silicates by the floating zone method

Cited by 9 publications

References 16 publications

Oxygen Migration in Dense Spark Plasma Sintered Aluminum‐Doped Neodymium Silicate Apatite Electrolytes

Oxygen Migration in Dense Spark Plasma Sintered Aluminum‐Doped Neodymium Silicate Apatite Electrolytes

Research progress in nondoped lanthanoid silicate oxyapatites as new oxygen-ion conductors

Crystal Chemical Analysis of Nd9.33Si6O26 and Nd8Sr2Si6O26 Apatite Electrolytes Using Aberration-Corrected Scanning Transmission Electron Microscopy and Impedance Spectroscopy

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Crystal Chemical Analysis of Nd_9.33Si₆O₂₆ and Nd₈Sr₂Si₆O₂₆ Apatite Electrolytes Using Aberration-Corrected Scanning Transmission Electron Microscopy and Impedance Spectroscopy