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2017

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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/106554

Structures and thermal stability of the [alpha]-LiNH4SO4 polytypes doped with Er3+ and Yb3+

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https://doi.org/10.1107/S2052520616019028

Resum

In order to clarify the polymorphism in the lithium sulfate family, LiREx(NH4)1 - xSO4 (0.5 [less-than or equal to] x [less-than or equal to] 4.0 mol%, nominal value; RE = Er3+, Yb3+ and Dy3+) crystals were grown from aqueous solution by slow evaporation between 298 and 313 K. The doping of the samples allowed us to obtain two polymorphic forms, [alpha] and [beta], of LiNH4SO4 (LAS). By means of X-ray diffraction (XRD) in single crystals, we determined the crystal structures of two new [alpha]-polytypes, which we have named [alpha]1- and [alpha]2-LAS. They present the same space group P21/c and the following relation among their lattice parameters: a2 = -c1, b2 = -b1, c2 = -2a1 - c1. In order to evaluate the stability of the new [alpha]-polytypes, we performed thermal analysis, X-ray diffraction and dielectric spectroscopy on single crystals and polycrystalline samples over the cyclic temperature range: 190 [rightwards arrow] 575 [rightwards arrow] 190 K. The results obtained by all the techniques used in this study demonstrate that [alpha]-polytypes are stable across a wide range of temperatures and they show an irreversible phase transition to the paraelectric [beta]-phase above 500 K. In addition, a comparative study of [alpha]- and [beta]-polytypes shows that both polymorphic structures have a common axis, with a possible intergrowth that facilitates their coexistence and promotes the reconstructive [alpha] [rightwards arrow] [beta] transition. This intergrowth was related to small anomalies detected between 240 and 260 K, in crystals with an [alpha]-habit.

Matèries

Sulfats, Liti, Polimorfisme (Cristal·lografia)

Matèries (anglès)

Sulfates, Lithium, Polymorphism (Crystallography)

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Articles publicats en revistes (Química Inorgànica i Orgànica)

Citació

SABALISCK, Nanci Prado, et al. Structures and thermal stability of the [alpha]-LiNH4SO4 polytypes doped with Er3+ and Yb3+. Acta Crystallographica Section B: Structural Science. Crystal Engineering and Materials. Vol.  2017, num. B73, pags. 122-133. ISSN 2052-5192. [consulted: 4 of August of 2026]. Available at: https://hdl.handle.net/2445/106554

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