Evaluation on the effect of gadolinium-doping for niobium on the morphology and ionic conductivity of garnet-like [Li.sub.5][La.sub.3][Nb.sub.2][O.sub.12]

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Date: Apr. 2016
From: Canadian Journal of Chemistry(Vol. 94, Issue 4)
Publisher: NRC Research Press
Document Type: Report
Length: 4,454 words
Lexile Measure: 1710L

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Abstract :

There is a great interest in gaining a deeper understanding of the lithium ion conductivity of Li-stuffed garnets that result from the substitution at either the La or M sites in [Li.sub.5][La.sub.3][M.sub.2][O.sub.12] (M = Nb, Ta), since these materials can be used as potential electrolytes in all solid-state batteries. Here, we investigate the effect of replacing [Nb.sup.5+] with [Gd.sup.3+] and stuffing two [Li.sup.+] per [Gd.sup.3+] in [Li.sub.5][La.sub.3][Nb.sub.2][O.sub.12] on the structure and ionic conductivity of the new family of garnet-type compounds with the nominal formula [Li.sub.5+2x][La.sub.3][Nb.sub.2-x][Gd.sub.x][O.sub.12] (0 [less than or equal to] x [less than or equal to] 0.45). The samples were prepared via conventional solid-state synthesis in air at elevated temperatures. Powder X-ray diffraction studies confirmed the formation of the garnet-type structure for [Li.sub.5+2x][La.sub.3][Nb.sub.2-x][Gd.sub.x][O.sub.12] (0 [less than or equal to] x [less than or equal to] 0.45). Elemental mapping obtained using energy dispersive X-ray analysis showed no evidence of a secondary phase being formed in [Li.sub.5+2x][La.sub.3][Nb.sub.2-x][Gd.sub.x][O.sub.12] (0 [less than or equal to] x [less than or equal to] 0.45). Archimedes' density measurements confirmed that the density of the samples with x [less than or equal to] 0.25 is not improved. The porosity of the samples with x [greater than or equal to] 0.3 was found to be in the 8%-16% range. Among the samples investigated in this work, the x = 0.45 member of [Li.sub.5+2x][La.sub.3][Nb.sub.2-x][Gd.sub.x][O.sub.12] showed the highest ionic conductivity of 1.91 x [10.sup.-5] S [cm.sup.-1] at room temperature, which is an order of magnitude higher than that of the parent compound [Li.sub.5][La.sub.3][Nb.sub.2][O.sub.12]. The activation energy of this material was calculated to be 0.38 eV at 25-225[degrees]C and 0.28 eV at 225-325[degrees]C. The change in the activation energy at the high temperature regime can be explained using the Li site occupation model in the garnet-type structure. Key words: Li-stuffed garnets, solid Li ion electrolytes, [Li.sub.5+2x][La.sub.3][Nb.sub.2-x][Gd.sub.x][O.sub.12] (0 [less than or equal to] x [less than or equal to] 0.45), conductivity. Une comprehension plus approfondie de la conductivite des ions Li dans les grenats surcharges de lithium resultant de la substitution des sites La ou M dans les composes de formule [Li.sub.5][La.sub.3][M.sub.2][O.sub.12] (M = Nb, Ta) suscite un grand interet, etant donne que ces substances peuvent eventuellement etre employees comme electrolytes dans toutes les batteries a l'etat solide. Dans le cadre des presents travaux, nous avons etudie les effets du remplacement dans le [Li.sub.5][La.sub.3][Nb.sub.2][O.sub.12] des ions [Nb.sup.5+] par des ions [Gd.sup.3+] et de la surcharge de deux ions de Li+ par ion de [Gd.sup.3+] sur la structure et la conductivite ionique de la nouvelle classe de composes de type grenat, de formule moleculaire [Li.sub.5+2x][La.sub.3][Nb.sub.2-x][Gd.sub.x][O.sub.12] (0 [less than or equal to] x [less than or equal to] 0,45). Nous avons prepare les echantillons par synthese en phase solide classique a l'air libre et a temperature elevee. Des analyses de diffraction des rayons X sur poudre ont permis de confirmer la formation de la structure de type grenat des composes de formule [Li.sub.5+2x][La.sub.3][Nb.sub.2- x][Gd.sub.x][O.sub.12] (0 [less than or equal to] x [less than or equal to] 0,45). La cartographie elementaire obtenue par spectroscopie de rayons X a dispersion d'energie n'a revele aucun signe de formation d'une phase secondaire dans les composes [Li.sub.5+2x][La.sub.3][Nb.sub.2-x][Gd.sub.x][O.sub.12] (0 [less than or equal to] x [less than or equal to] 0,45). Des mesures de la densite d'Archimede ont permis de confirmer que la densite des echantillons oU x Mots-cles : grenats surcharges de Li, electrolytes solides au Li ion, [Li.sub.5+2x][La.sub.3][Nb.sub.2- x][Gd.sub.x][O.sub.12] (0 [less than or equal to] x [less than or equal to] 0; 45), conductivite.

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Gale Document Number: GALE|A452157134