Akrouchi A, Benzidi H, Al-Shami A, El Kenz A, Benyoussef A, El Kharbachi A, Mounkachi O
Laboratory of Condensed Matter and Interdisciplinary Sciences (LaMCScI), B.P. 1014, Faculty of Science, Mohammed V University in Rabat, Morocco.
Univ Rennes, INSA Rennes, CNRS, Institut FOTON -UMR 6082, F-35000 Rennes, France.
Phys Chem Chem Phys. 2021 Dec 8;23(47):27014-27023. doi: 10.1039/d1cp03215a.
-dodecaborates MBH are considered among the potential candidates for solid-state electrolyte materials due to their high ionic conductivities. It has been demonstrated that the reorientation of the icosahedral anion BH plays a key role in high cation motion. However, this category of BH materials is still not well established with respect to their structural, thermodynamic and diffusion properties. In the present work, the electronic, vibrational and thermodynamic properties of MBH (M = Li, Na, K) structures are reported using first-principles calculations. The results of structural and electronic properties show that these structures have an insulator character with a large band gap of 5.75, 5.63 and 5.59 eV, respectively, for LiBH, NaBH and KBH. The thermodynamic stabilities of these systems are confirmed by their phonon calculation results. The primary quantities, such as heat capacity, vibrational entropy and volume variation at finite temperatures, are determined using the quasi-harmonic approximation in order to provide an input for the Gibbs free energy assessment. The calculated enthalpy of formation of the LiBH structure at 0 K and the proposed one at 300 K are found to be -127.31 and -740.44 kJ mol per H, respectively. The migration energy barrier of various cations in each system is calculated to be 0.7 (Li), 1.16 (Na) and 1.25 eV (K), where the lowest energy barrier corresponds to the lithium ion migration in LiBH. Additionally, the molecular dynamics simulation of MBH (M = Li, Na, K) structures demonstrated that these structures are stable above room temperature, except for the LiBH structure at 600 K, where the most stable is NaBH. Finally, the temperature effect on icosahedral anion reorientation in each structure is elucidated as a function of temperature and cation type.
十二硼酸盐MBH因其高离子电导率而被视为固态电解质材料的潜在候选物。已证明二十面体阴离子BH的重新取向在阳离子的快速移动中起关键作用。然而，就其结构、热力学和扩散性质而言，这类BH材料仍未得到充分研究。在本工作中，使用第一性原理计算报道了MBH（M = Li、Na、K）结构的电子、振动和热力学性质。结构和电子性质的结果表明，这些结构具有绝缘特性，LiBH、NaBH和KBH的带隙分别为5.75、5.63和5.59 eV。这些体系的热力学稳定性通过其声子计算结果得到证实。为了为吉布斯自由能评估提供输入，使用准谐近似确定了诸如热容量、振动熵和有限温度下的体积变化等主要量。计算得出LiBH结构在0 K时的生成焓和在300 K时的生成焓分别为每H -127.31和-740.44 kJ/mol。计算得出每个体系中各种阳离子的迁移能垒为0.7（Li）、1.16（Na）和1.25 eV（K），其中最低能垒对应于LiBH中锂离子的迁移。此外，MBH（M = Li、Na、K）结构的分子动力学模拟表明，除了600 K时的LiBH结构外，这些结构在室温以上是稳定的，其中最稳定的是NaBH。最后，阐明了温度对各结构中二十面体阴离子重新取向的影响与温度和阳离子类型的函数关系。
