Structure - Electrode Activity Relationship in Triphyllite - Related Compounds

在优化的条件下，通过化学氧化法合成了一系列（Mn_yFe_（1-y））PO_4（y&lt;0.8）相<1-y>。所有样品都表现出反铁磁性，但（Mn_yFe_）PO_4的Neel温度下降<1-y>幅度是Li（Mn_yFe_）PO_4的7倍多<1-y>。通过Jahn-Teller畸变和PO_4四面体共边互连的协同效应，从非对称超交换相互作用的角度对这一现象进行了讨论，并提供了实验证据，证明室温下的Li_xFePO_4可以描述为Fe^&lt;3+&gt;/Fe^&lt;2+&gt;混合价中间体Li_αFePO_4和Li_&lt;1-β&gt; FePO_4的混合物。4相，具有令人惊讶的大的α和β值。利用粉末中子衍射，锂在每个相中的占位数被细化为α=0.05和1-β=0.89。通过构型异常检测到了在可混性间隙（0&lt;x&lt;α，1-β&lt;x&lt;1）之外的相应固溶体区域 关于我们 熵以及开路电压与恒定平衡电位的偏差。这些发现鼓励了这类重要化合物在室温下的进一步改进。对LiFePO_4的粉末中子衍射轮廓进行了Rietveld分析。各向异性热因子的张量元表明锂振动的主轴朝向面共享的四面体空位。这与理论预测一致;锂离子沿着弯曲的一维链沿着b轴扩散。粒径大于200 nm的LixFePO_4在200 ℃左右的非混合线以下，温度对相图的影响较小。而颗粒尺寸减小至&lt;100 nm似乎对室温相容性间隙具有显著影响。讨论了在较小颗粒中扩展溶液的热力学概念，随后观察到小于80 nm的小球形颗粒具有非常高的倍率性能。少

A series of synthetic (Mn_yFe_<1-y_)PO_4(y<0.8) phases were obtained by chemical oxidation of crystallized isotypic Li(Mn_yFe_<1-y>)PO_4 under optimized conditions. All samples exhibit antiferromagnetism but the decrease in Neel temperature is more than 7 times larger in (Mn_yFe_<1-y>)PO_4 than in Li(Mn_yFe_<1-y>)PO_4. This was discussed in terms of the asymmetric superexchange interaction by an unusual synergetic effect of Jahn-Teller distortion and edge-shared interconnection with PO_4 tetrahedra.We provide firm experimental evidence that Li_xFePO_4 at room temperature can be described as a mixture of the Fe^<3+>/Fe^<2+> mixed-valent intermediate Li_αFePO_4 and Li_<1-β>FePO_4 phases with surprisingly large values of α and β. Using powder neutron diffraction, the site occupancy numbers for lithium in each phase were refined to be α=0.05 and 1-β=0.89. The corresponding solid solution ranges outside the miscibility gap (0<x<α, 1-β<x<1) were detected by the anomaly in the configurational … More entropy and also by the deviation of the open-circuit voltage from the constant equilibrium potential. These findings encourage further improvement of this important class of compounds at ambient temperatures.Rietveld analysis for the powder neutron diffraction profile for LiFePO_4 was performed. Tensor elements of the unisotropic thermal factor showed the principal axis of the lithium vibration is toward the face shared vacant tetrahedral space. This is consistent with the theoretical prediction ; lithium ions diffuse along curved one-dementional chain along b-axis. Impact of temperature on the phase diagram of LixFePO_4 with > 200nm particle size was slight under the unmixing line around 200 C. While the reduction in particle size down to <100 nm seems to have significant effect to the room temperature miscibility gap. The thermodynamic concepts for the extended solution in smaller particles are discussed, followed by a very high rate capability observed for the small spherical particles <80nm. Less