Ragavendran K, Xia H, Mandal P, Arof A K
Condensed Matter Physics Division, Saha Institute of Nuclear Physics, Kolkata 700064, India.
School of Materials Science and Engineering, Nanjing University of Science and Technology, Xiaolingwei 200, Nanjing, Jiangsu 210094, China.
Phys Chem Chem Phys. 2017 Jan 18;19(3):2073-2077. doi: 10.1039/c6cp07289e.
The phase transition near room temperature in LiMnO was 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 T ∼ 220 K for the nearly half-doped material, with [Mn]/[Mn] ≈ 1. The T shifts 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 Mn in LiMnO is increased, i.e., [Mn]/[Mn] > 1. These studies show that the first-order phase transition near room temperature in LiMnO is 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 LiMnO. Electrochemical measurements show that both materials, either with a T ∼ 220 K or T ∼ 290 K, exhibit capacity fading to almost the same extent. Electrochemical capacity retention is observed only in nanosized LiMnO, for which the phase transition anomalies are completely absent.
通过热膨胀测量研究了LiMnO中接近室温的相变，并将其与该材料的电化学性能直接进行了比较。基于热膨胀的研究表明，对于接近半掺杂的材料（[Mn]/[Mn]≈1），在T ∼ 220 K时开始出现一级相变。当LiMnO中 Jahn-Teller Mn的比例增加，即[Mn]/[Mn] > 1时，T移至更高温度 ∼290 K，并且在290 K处可以观察到Verwey型电荷有序的特征。这些研究表明，LiMnO中接近室温的一级相变与电荷有序有关，而电荷有序最终是Jahn-Teller效应的结果。此外，Jahn-Teller效应被证明是LiMnO中磁电阻和电化学容量衰减的重要原因。电化学测量表明，这两种材料，无论是T ∼ 220 K还是T ∼ 290 K，都表现出几乎相同程度的容量衰减。仅在纳米尺寸的LiMnO中观察到电化学容量保持，而该材料完全不存在相变异常。
