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On the Synthesis of Ramsdellite LiTiMO 4 (M = Ti, V, Cr, Mn, Fe): An Experimental and Computational Study of the Spinel–Ramsdellite Transformation
Author(s) -
Kuhn Alois,
DíazCarrasco Pilar,
Arroyo y de Dompablo María Elena,
GarcíaAlvarado Flaviano
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200600993
Subject(s) - spinel , chemistry , transformation (genetics) , inverse , enthalpy , thermodynamics , manganese , crystallography , transition metal , inorganic chemistry , materials science , metallurgy , physics , catalysis , geometry , mathematics , organic chemistry , biochemistry , gene
The LiTiMO 4 (spinel) ↔ LiTiMO 4 (ramsdellite) transformation has been investigated by combining computational and experimental techniques, for M = Ti, V, Cr, Mn, and Fe, in order to understand the characteristics of this transformation and the influence of the metal M on the relative stability of the ramsdellite polymorph. The calculations predict that all the aforementioned LiTiMO 4 spinels are thermodynamically stable with respect to the ramsdellite polymorph, with the calculated enthalpy variation of the transformation being less than 40 kJ mol –1 . In the case of normal spinels [Li] t [TiM] o O 4 we estimated a transformation temperature in the range 900–1600 °C, whereas the polymorphic transformation for inverse spinels [Li 0.5 M 0.5 ] t [TiM 0.5 Li 0.5 ] o O 4 is accompanied by a lower entropy gain, hence a much higher temperature would be needed to overcome the enthalpy of the transformation. The transformation is thus entropically controlled. Accordingly, experimental results show that normal [Li] t [TiM] o O 4 spinels (M = Ti, V, Cr) readily transform into ramsdellites at temperatures between 900 and 1400 °C, whereas this transition is hindered for spinels LiTiMO 4 (M = Fe, Mn), which possess a high degree of inversion. Based on a possible mechanism for the transformation, we infer that the impossibility of transforming the Mn and Fe inverse‐spinels into their ramsdellite forms is also due to the high energy barriers that must be overcome during the transformation. The obtained LiTiMO 4 (M = Ti, V, and Cr) ramsdellites, which contain Ti IV and M III , display a twofold electrochemical application, namely that one lithium ion per formula unit can be inserted into these compounds at about 1.4 V vs. Li (reduction of Ti IV to Ti III ). The oxidation of M III ions to M IV enables lithium deinsertion from LiTiMO 4 (M = Ti, V, and Cr) at potentials of 1.9 V (M = Ti), 3.1 V (M = V), and 4.2 (M = Cr) vs. Li. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)