Zeilinger Michael, Fässler Thomas F
Department Chemie, Technische Universität München, Lichtenbergstraße 4, 85747 Garching b. München, Germany.
Dalton Trans. 2014 Oct 28;43(40):14959-70. doi: 10.1039/c4dt00743c. Epub 2014 Jun 5.
A reinvestigation of the lithium-rich section of the Li-Ge phase diagram reveals the existence of two new phases, Li17Ge4 and Li4.10Ge (Li16.38Ge4). Their structures are determined by X-ray diffraction experiments of large single crystals obtained from equilibrated melts with compositions Li95Ge5 and Li85Ge15. Excess melt is subsequently removed through isothermal centrifugation at 400 °C and 530 °C, respectively. Li17Ge4 crystallizes in the space group F4[combining macron]3m (a = 18.8521(3) Å, V = 6700.1(2) Å(3), Z = 20, T = 298 K) and Li4.10Ge (Li16.38Ge4) in Cmcm (a = 4.5511(2) Å, b = 22.0862(7) Å, c = 13.2751(4) Å, V = 1334.37(8) Å(3), Z = 16, T = 123 K). Both phases are isotypic with their Si counterparts and are further representative of the Li17Pb4 and Li4.11Si structure types. Additionally, the solid solutions Li17Si4-xGex follows Vegard's law. A comparison of the GeLin coordination polyhedra shows that isolated Ge atoms are 13- and 14-coordinated in Li17Ge4, whereas in Li16.38Ge4 the Ge atoms possess coordination numbers 12 and 13. Regarding the thermodynamic stability, Li16.38Ge4 is assigned a high-temperature phase existing between ∼400 °C and 627 °C, whereas Li17Ge4 decomposes peritectically at 520-522 °C. Additionally, the decomposition of Li16.38Ge4 below ∼400 °C was found to be very sluggish. These findings are manifested by differential scanning calorimetry, long-term annealing experiments and the results from melt equilibration experiments. Interestingly, the thermodynamic properties of the lithium-rich tetrelides Li17Tt4 and Li4.1Tt (Li16.4Tt4) are very similar (Tt = Si, Ge). Besides Li15Tt4, Li14Tt6, Li12Tt7, and LiTt, the title compounds are further examples of isotypic tetrelides in the systems Li-Tt.
对锂 - 锗相图中富锂部分的重新研究揭示了两个新相Li17Ge4和Li4.10Ge（Li16.38Ge4）的存在。它们的结构通过对从成分分别为Li95Ge5和Li85Ge15的平衡熔体中获得的大单晶进行X射线衍射实验来确定。随后分别在400℃和530℃通过等温离心去除多余的熔体。Li17Ge4在空间群F4[组合宏]3m中结晶（a = 18.8521(3) Å，V = 6700.1(2) Å(3)，Z = 20，T = 298 K），Li4.10Ge（Li16.38Ge4）在Cmcm中结晶（a = 4.5511(2) Å，b = 22.0862(7) Å，c = 13.2751(4) Å，V = 1334.37(8) Å(3)，Z = 16，T = 123 K）。这两个相与其硅对应物同型，并且进一步代表Li17Pb4和Li4.11Si结构类型。此外，固溶体Li1 ^ { 7 } Si _ { 4 - x } Ge _ { x }遵循维加德定律。对GeLin配位多面体的比较表明，在Li17Ge4中孤立的Ge原子是13配位和14配位的，而在Li16.38Ge4中Ge原子的配位数为12和13。关于热力学稳定性，Li16.38Ge4被认为是存在于约400℃至627℃之间的高温相，而Li17Ge4在520 - 522℃发生包晶分解。此外，发现Li16.38Ge4在约400℃以下的分解非常缓慢。这些发现通过差示扫描量热法、长期退火实验以及熔体平衡实验的结果得以体现。有趣的是，富锂的IV族元素化合物Li17Tt4和Li4.1Tt（Li16.4Tt4）的热力学性质非常相似（Tt = Si，Ge）。除了Li15Tt4、Li14Tt6、Li12Tt7和LiTt之外，标题化合物是Li - Tt体系中同型IV族元素化合物的进一步实例。
