title: Jahn-Teller effect in LiMn2O4: influence on charge ordering, magnetoresistance and battery performance.
abstract: The phase transition near room temperature in LiMn2O4was studied using thermal expansion measurements, and directly compared with the electrochemical performance of the material. Studies based on thermal expansion indicate the onset of a first-order phase transition at Tc∼ 220 K for the nearly half-doped material, with [Mn3+]/[Mn4+] ≈ 1. The Tcshifts to a higher temperature, ∼290 K, and signatures for Verwey-type charge ordering at 290 K can be observed when the fraction of Jahn-Teller Mn3+in LiMn2O4is increased, i.e., [Mn3+]/[Mn4+] > 1. These studies show that the first-order phase transition near room temperature in LiMn2O4is associated with charge ordering, which ultimately is a consequence of the Jahn-Teller effect. In addition, the Jahn-Teller effect is proven to be an important cause of magnetoresistance and electrochemical capacity fading in LiMn2O4. Electrochemical measurements show that both materials, either with a Tc∼ 220 K or Tc∼ 290 K, exhibit capacity fading to almost the same extent. Electrochemical capacity retention is observed only in nanosized LiMn2O4, for which the phase transition anomalies are completely absent.
authors.affiliation: Condensed Matter Physics Division, Saha Institute of Nuclear Physics, Kolkata 700064, India. raguphys@gmail.com.
authors.forename: K
authors.identifier: http://orcid.org/0000-0002-7888-7479
authors.initials: K
authors.lastname: Ragavendran
authors.affiliation: School of Materials Science and Engineering, Nanjing University of Science and Technology, Xiaolingwei 200, Nanjing, Jiangsu 210094, China.
authors.forename: H
authors.initials: H
authors.lastname: Xia
authors.affiliation: Condensed Matter Physics Division, Saha Institute of Nuclear Physics, Kolkata 700064, India. raguphys@gmail.com.
authors.forename: P
authors.initials: P
authors.lastname: Mandal
authors.affiliation: Center for Ionics, Department of Physics, University of Malaya, Kuala Lumpur 50603, Malaysia.
authors.forename: A K
authors.initials: AK
authors.lastname: Arof