Magnetic and transport properties of layered LixCoO2 single crystals
Magnetic and transport properties of layered LixCoO2 single crystals
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层状LixCoO2单晶的磁性和输运特性
DOI：
10.1088/1742-6596/150/4/042129
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
J. Takeuchi
中科院分区：
文献类型：
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作者：
K. Miyoshi;H. Kondo;M. Miura;C. Iwai;K. Fujiwara;J. Takeuchi
本文测量了LixCoO2 （x = 0.92, 0.47和0.42）层状单晶的电阻率（ρ）和直流磁化强度(M)随温度(T)的变化规律。LixCoO2单晶是由浮区炉生长的单晶在NO2BF4/CH3CN溶液中浸出Li脱嵌得到的。发现x = 0.92时ρ-T曲线是绝缘的，但x = 0.47和0.42时观察到金属行为。当x = 0.47和0.42时，M-T曲线在Ts~170 K以下均出现突然下降。x = 0.47和0.42时的ρ-T曲线在Ts~170 K处出现跳变异常，存在热滞后现象，表明存在一阶相变。这些M-T和ρ-T曲线的行为表明，Co+4在~170 K时发生了自旋态跃迁。此外，在TF以下，快速冷却后的M-T曲线与缓慢冷却后的M-T曲线有所不同。TF取决于x，并且似乎对应于观察到7Li核磁共振谱线宽度运动变窄的温度，这表明Li离子从刚性晶格的规则位置释放出来，并开始在TF上方扩散。
Electrical resistivity (ρ) and DC magnetization (M) have been measured as a function of temperature (T) for layered LixCoO2 (x = 0.92, 0.47 and 0.42) single crystals, which are obtained by deintercalating Li from single crystals grown in a floating-zone furnace through immersion in NO2BF4/CH3CN solution. The ρ—T curve for x = 0.92 is found to be insulating but a metallic behavior is observed for x = 0.47 and 0.42. The M—T curve both for x = 0.47 and 0.42 exhibits a sudden decrease below Ts~170 K. Also, the ρ—T curve both for x = 0.47 and 0.42 shows a jump-like anomaly at Ts~170 K with thermal hysteresis, indicating a first-order phase transition. These behaviors of the M—T and ρ—T curve suggest an occurrence of spin state transition of Co+4 at ~170 K. Furthermore, the M—T curve after rapid cooling becomes different from that after slow cooling below TF. TF depends on x and appears to correspond to the temperature at which the motional narrowing of the 7Li NMR line width is observed, suggesting that the Li ions are released from the regular site of the rigid lattice and begin to diffuse above TF.