电池材料LiFePO $_4$中的反位无序
Antisite disorder in the battery material LiFePO$_4$
摘要：
我们报告了详细的磁力测量和高频电子自旋共振（HF-ESR）测量，这些测量允许详细研究单晶LiFePO $_4$中的Li-Fe反位无序，即，Fe $^{2+}$ -和Li $^+$ -离子的交换。结果表明，Li位Fe $^{2+}$ -离子的磁矩不参与LiFePO $_4$中的长程反铁磁有序，而是形成准自由磁矩.反位缺陷处磁矩的各向异性轴与主晶向有关。这些时刻的本地字符被确认由HF-ESR研究检测相关的线性共振分支。磁各向异性表现为$Δ= 220(3)$ ~GHz、$Δ'\sim50$ ~GHz的显著零场分裂和高度各向异性的$g$因子，即，$g_\mathrm{a} = 1.4$、$g_\mathrm{b} = 2.0$和$g_\mathrm{c} = 6.3$。我们展示了一个通用的方法来精确地确定铁反位无序LiFePO $_4$从磁性研究，这意味着在锂位置的顺磁性Fe $^{2+}$ -离子的密度为0.53\%。
英文摘要：
We report detailed magnetometry and high-frequency electron spin resonance (HF-ESR) measurements which allow detailed investigation on Li-Fe antisite disorder in single-crystalline LiFePO$_4$, i.e., exchange of Fe$^{2+}$- and Li$^+$-ions. The data imply that magnetic moments of Fe$^{2+}$-ions at Li-positions do not participate in long-range antiferromagnetic order in LiFePO$_4$ but form quasi-free moments. Anisotropy axes of the magnetic moments at antisite defects are attached to the main crystallographic directions. The local character of these moments is confirmed by associated linear resonance branches detected by HF-ESR studies. Magnetic anisotropy shows up in significant zero-field splittings of $Δ= 220(3)$~GHz, $Δ'\sim50$~GHz and a highly anisotropic $g$-factor, i.e., $g_\mathrm{a} = 1.4$, $g_\mathrm{b} = 2.0$, and $g_\mathrm{c} = 6.3$. We demonstrate a general method to precisely determine Fe-antisite disorder in LiFePO$_4$ from magnetic studies which implies a density of paramagnetic Fe$^{2+}$-ions at Li-positions of 0.53\%.
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