Balijapelly Srikanth, Sandineni Prashanth, Adhikary Amit, Gerasimchuk Nikolay N, Chernatynskiy Aleksandr V, Choudhury Amitava
Department of Chemistry, Missouri University of Science and Technology, Rolla, MO 65409, USA.
Department of Chemistry, Missouri State University, Springfield, MO 65897, USA.
Dalton Trans. 2021 Jun 1;50(21):7372-7379. doi: 10.1039/d1dt00766a.
Two new ternary thiogallates in the A5GaS4 (A = Li (i) and Na (ii)) series have been synthesized for the first time employing a gas passing route using oxide precursors and a high temperature solid state route using stoichiometric combinations of elements, respectively. Li5GaS4 crystallizes in the P21/m space group and the structure is built up of layers of corner sharing tetrahedra of LiS4 and GaS4 stacked along the a-axis and the octahedrally coordinated Li ions residing in the interlayer space. Na5GaS4 crystallizes in the Pbca space group and the structure consists of isolated (GaS4)5- tetrahedra held together by charge balancing sodium ions in distorted tetrahedral and octahedral coordination geometries. Measurements of ionic conductivity of the compounds showed room temperature ionic conductivities of 1.8 × 10-7 and 4.0 × 10-7 S cm-1 with activation energies of 0.54 and 0.28 eV, respectively, for I and II. Density functional theory calculations show close agreement in structural parameters with the measured data and predict band gaps of 2.75 eV (I) and 2.70 eV (II). Single point hybrid functional calculations result in band gaps of 3.95 and 3.65 eV correspondingly, in better agreement with the experimental value of ∼4.1 eV for both. Bond valence energy landscape maps suggest the absence of any suitable diffusion path for Li in Li5GaS4. On the other hand, BVEL maps of Na5GaS4 confirm that the tetrahedrally coordinated Na ions are responsible for ionic conduction, whereas the involvement of octahedrally coordinated Na ions in the conduction process could not be discerned.
首次分别采用使用氧化物前驱体的通气路线和使用元素化学计量组合的高温固态路线，合成了A5GaS4（A = Li (i) 和Na (ii)）系列中的两种新型三元硫代镓酸盐。Li5GaS4晶体属于P21/m空间群，其结构由沿a轴堆叠的LiS4和GaS4角共享四面体层组成，八面体配位的Li离子位于层间空间。Na5GaS4晶体属于Pbca空间群，其结构由孤立的 (GaS4)5-四面体组成，电荷平衡的钠离子以扭曲的四面体和八面体配位几何结构将它们连接在一起。对这些化合物的离子电导率测量表明，I和II在室温下的离子电导率分别为1.8×10-7和4.0×10-7 S cm-1，活化能分别为0.54和0.28 eV。密度泛函理论计算表明，结构参数与测量数据吻合良好，并预测带隙为2.75 eV（I）和2.70 eV（II）。单点杂化泛函计算相应地得出带隙为3.95和3.65 eV，与两者约4.1 eV的实验值更吻合。键价能景观图表明Li5GaS4中不存在任何适合Li的扩散路径。另一方面，Na5GaS4的BVEL图证实，四面体配位的Na离子负责离子传导，而八面体配位的Na离子在传导过程中的作用无法辨别。
