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arXiv 1005.4253cond-mat.str-el
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Li $_x$ CoO $_2$单晶的磁性和电子性质

Magnetic and Electronic Properties of Li$_x$CoO$_2$ Single Crystals

K. Miyoshi, C. Iwai, H. Kondo, M. Miura, S. Nishigori, J. Takeuchi

摘要:

用单晶样品测量了层状氧化物Li $_x$ CoO $_2$(0.25 $\leq$ $x$ $\leq$ 0.99)的电阻率($ρ$)、直流磁化强度($M$)和比热($C$)。发现$x$ =0.90和0.99的$ρ$对温度($T$)曲线是绝缘的,但对于0.25 $\leq$ $x$ $\leq$ 0.71观察到金属行为。在$T_{\rm S}$ $\sim$ 155 K时,$ρ$ $-$ $T$,$M$ $-$ $T$和$C$ $/$ $T$ $-$ $T$曲线中观察到一个尖锐的异常,当$x$ =0.66时,有热滞,表明转变的一级特征。在$T_{\rm S}$ $\sim$ 155 K的转变观察到的$x$ =0.46 $-$ 0.71的宽范围。发现在低于$T_{\rm F}$(对于$x$ =0.46 $-$ 0.71,$\sim$为$\sim$ 130 K)的温度下,快速冷却后测量的$M$ $-$ $T$曲线变得不同于缓慢冷却后测量的$T$曲线。发现$T_{\rm F}$与观察到$^7$ Li NMR谱线宽度中的运动变窄的温度一致,表明Li离子停止扩散并在低于$T_{\rm F}$的规则位点有序。低于$T_{\rm F}$ $\sim$ 130 K的Li离子的有序化可能由低于$T_{\rm S}$的CoO $_2$层中的电荷有序化触发和稳定。

英文摘要:

Measurements of electrical resistivity ($ρ$), DC magnetization ($M$) and specific heat ($C$) have been performed on layered oxide Li$_x$CoO$_2$ (0.25$\leq$$x$$\leq$0.99) using single crystal specimens. The $ρ$ versus temperature ($T$) curve for $x$=0.90 and 0.99 is found to be insulating but a metallic behavior is observed for 0.25$\leq$$x$$\leq$0.71. At $T_{\rm S}$$\sim$155 K, a sharp anomaly is observed in the $ρ$$-$$T$, $M$$-$$T$ and $C$$/$$T$$-$$T$ curves for $x$=0.66 with thermal hysteresis, indicating the first-order charactor of the transition. The transition at $T_{\rm S}$$\sim$155 K is observed for the wide range of $x$=0.46$-$0.71. It is found that the $M$$-$$T$ curve measured after rapid cool becomes different from that after slow cool below $T_{\rm F}$, which is $\sim$130 K for $x$=0.46$-$0.71. $T_{\rm F}$ is found to agree with the temperature at which the motional narrowing in the $^7$Li NMR line width is observed, indicating that the Li ions stop diffusing and order at the regular site below $T_{\rm F}$. The ordering of Li ions below $T_{\rm F}$$\sim$130 K is likely to be triggered and stabilized by the charge ordering in CoO$_2$ layers below $T_{\rm S}$.

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