Inhibition of Jahn–Teller cooperative distortion in LiMn2O4 spinel by transition metal ion doping

Abstract

The aim of this study is to determine the minimum amount of dopant that prevents the occurrence, near room temperature, of a JahnÈTeller (JÈT) transition in the M-doped lithium manganese spinel of composition with 0.00 \ x O 0.06 and M \ Ni2`, Co3`, Cr3`or Ti4`. EPR spectra and magnetic Li 1.02 M x Mn 1.98~x O 4 susceptibility data are related to the valence state of M and Mn, and the homogeneous distribution of the dopant. We Ðnd that the spinel framework is remarkably sensitive to displaying low electronic and magnetic changes in its cationic sublattice due to cation substitution. The JÈT distortion, which is associated with a sudden drop in conductivity with decreasing temperature, is suppressed by substituting 3% of Mn with Co3ò r Cr3`, or by adding an even smaller amount of Ni2`(x \ 0.02, or 1% substitution). However, this inhibition occurs only in samples with a ratio r \ [Mn4`]/[Mn3`] P 1.18, i.e., a value larger than the ratio r \ 1.106 we have with no doping (x \ 0). As a consequence, doping with the tetravalent cation Ti4`, which always decreases the r value, does not suppress the JÈT transition. We suggest that both the dopant ion and the Li`in excess over the stoichiometric composition are located in 16d sites. The removal of the JÈT transition in the Co3`(x \ 0.06) sample is also due to local disorder.

Mn4+ environment in layered Li[Mg0.5−xNixMn0.5]O2 oxides monitored by EPR spectroscopy

“…However, it has been shown that analysis of the EPR line width (determined at X-band EPR) of Mn 4+ in ordered LiMg x Ni 0.5Àx Mn 1.5 O 4 (0pxp0.5) spinels allows differentiating between the contributions of the density of paramagnetic species and the strength of the exchange interactions [18]. Moreover, lithium-transition metal oxides containing more than one paramagnetic ions have been studied by EPR: non-stoichiometric Li 1Àd Ni 1+d O 2 [19][20][21][22] [24][25][26][27][28][29].…”

Nanosized LiMn2O4 from mechanically activated solid-state synthesis

“…In other words, for Tp723 K Cr 2 O 3 phase does not completely participate in the spinel formation and a nonstoichiometric Li-rich spinel must be considered. For such phase, we should consider a charge distribution on the octahedral frame represented by [10] ½Li þ y Cr 3þ…”

“…The transition, depending on Mn 3+ concentration, can be inhibited by reducing the Mn 3+ amount. Recent studies showed that the inhibition of the JT distortion can be reached both by suitable cationic substitution on Mn site [9][10][11][12][13], such as Cr 3+ ions, and by stoichiometry deviations induced by Li excess with respect to 0.333 cationic fraction [14][15][16][17].…”

Excellent stability of Al-doped LiMn2O4 prepared by a sol - gel method

“…To a certain extent, the introduction of more Al improved the cycle performance availably. Al -doped LiMn 2 O 4 with better cycleability has great correlation with enhanced structural stability and reduced the Jahn-Teller distortion [11].…”