Vacancy-enhanced cycle life and electrochemical performance of lithium-rich layered oxide Li2RuO3

Int J of Quantum Chemistry

Lin

2020

Although ZrB 12 is a promising advanced material because of the boron cuboctahedron cages, the hardness of ZrB 12 remains controversy. Here, we apply first-principles calculations to study the influence of transition metals (4d-and 5d-) on the hardness and thermodynamic properties of ZrB 12 . The calculated hardness of ZrB 12 is 32.9 GPa, which is in good agreement with the previous theoretical result. Importantly, the calculated hardness of Re-doped ZrB 12 is up to 40.0 GPa, which is a potential superhard material. The essential reason is that the alloying element of Re enhances the localized hybridization of B B and Zr B atoms, and then forms the strong B B covalent bond and Zr B bond. The result is well demonstrated by the chemical bonding and lattice parameter. Here, our work shows that the alloying elements of Nb, Mo, and Re enhance the thermodynamic properties of ZrB 12 . The Debye temperature of Re-doped ZrB 12 is 1225.2 K, which is larger than that of the parent ZrB 12 (1213.5 K). K E Y W O R D S borides, elastic modulus, first-principles calculations, hardness, thermodynamic properties, ZrB 12 1 | INTRODUCTION Hard and superhard materials (≥40 GPa) are very important industrial materials, which are widely used in various industrial applications because of their high hardness, ultracompressibility, high melting point, and excellent thermal stability etc. [1-10] In comparison to diamond and boron nitride (c-BN), the transition metal borides (TMBs) are attractive potential superhard materials because of the network and shorter covalent bonding such as B B covalent bond and TM B bond. [11][12][13][14][15][16][17][18][19] Diborides (TMB 2 ) and transition metal tetraborides (TMB 4 ) have been widely investigated over the last years. [20][21][22][23][24] However, the reported Vickers hardness of TMB 2 or TMB 4 is difficult to meet the requirement of superhard material. [25][26][27][28][29] Naturally, the Vickers hardness of TMBs mainly relies on the shorter and network covalent bonds. In other words, the high concentration of boron plays a crucial role in Vickers hardness of TMBs. Among these TMBs, it is obvious that the transition metal dodecaborides (TMB 12 ) are potential superhard materials in comparison to TMB 2 and TMB 4 .Recently, ZrB 12 has evoked great interest because of the high concentration of boron and the network B B covalent bonds. [30] This dodecaboride is composed of the boron cuboctahedron cage (24 atoms) and 12-coordinate transition metals at the center of cubic structure. This structural feature is possible to enhance the Vickers hardness of TMBs. However, the Vickers hardness of ZrB 12 remains controversy. Korozlu et al. have found that the calculated Vickers hardness of ZrB 12 is 40.1 GPa, which is believed to a potential superhard material. [31] However, the recent works have shown that the Vickers hardness of ZrB 12 is 35.4 GPa by Chen et al. [32] and 29.3 GPa by Li et al., [33] which are different from Korozlu's result. On the other hand, even if the Vickers hardness of ZrB 12 remains...

Section: Theoretical Methodsmentioning

confidence: 99%

Influence of alloying elements on the mechanical and thermodynamic properties of ZrB₁₂ceramics from first‐principles calculations

Int J of Quantum Chemistry

Lin

2020

“…[44][45][46] To study their structural stability, Figure 2 shows the calculated formation enthalpy of ReB 12 and RuB 12 as a function of pressure. Generally speaking, the negative value of formation enthalpy indicates the thermodynamic stability at the ground state.…”

Section: Resultsmentioning

confidence: 99%

“…Generally speaking, the negative value of formation enthalpy indicates the thermodynamic stability at the ground state. [44][45][46] To study their structural stability, Figure 2 shows the calculated formation enthalpy of ReB 12 and RuB 12 as a function of pressure. It can be seen that the calculated formation enthalpy of ReB 12 and RuB 12 is lower than zero.…”

Section: Resultsmentioning

confidence: 99%

The influence of high pressure on the structural stability, Vickers hardness and mechanical properties of Re and Ru dodecaborides

Int J of Quantum Chemistry

Jia

2019

We apply the first-principles approach to study the structural stability, Vickers hardness, and elastic modulus of ReB 12 and RuB 12 . In particular, we further investigate the influence of high pressure on the structural stability and mechanical properties of ReB 12 and RuB 12 . The calculated results show that ReB 12 and RuB 12 are thermodynamic stability under high pressure. Here, ReB 12 is more thermodynamic stability than that of the RuB 12 . The calculated Vickers hardness of ReB 12 and RuB 12 is 16.25 and 16.55 GPa, respectively. It is found that the calculated elastic constants and elastic modulus of ReB 12 and RuB 12 increase with increasing pressure. In particular, the calculated elastic constants and elastic modulus of ReB 12 are larger than that of the RuB 12 . The calculated electronic structure shows that the high hardness and elastic modulus of ReB 12 and RuB 12 are attributed to the 3D network B-B covalent bonds. K E Y W O R D Sfirst-principles calculations, hardness, mechanical properties, ReB 12 , RuB 12 , superhard materials

“…It is well known that the metal dihydrides are attractive hydrogen storage materials because of their renewable, low cost, excellent deformation resistance, etc . Some noble metal hydrides have been investigated due to the good chemical stability and excellent catalytic activity . For example, the Pt‐Ru catalyst shows high hydrogen generation rate .…”

Section: Introductionmentioning

confidence: 99%

“…[9][10][11][12][13][14][15] Some noble metal hydrides have been investigated due to the good chemical stability and excellent catalytic activity. [16][17][18][19][20] For example, the Pt-Ru catalyst shows high hydrogen generation rate. 21 Ir-dopant can double enhance the hydrogen storage capacity of Pd nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

Exploring the novel structure, transportable capacity and thermodynamic properties of TiH ₂ hydrogen storage material

Chen

2020

Int J Energy Res

Summary We apply the first‐principles calculations to study the structure, elastic modulus, Debye temperature and heat capacity of four TiH2. The results show that one new orthorhombic (Pnma) TiH2 is predicted. The tetragonal (I4mmm) TiH2 is more stable than the cubic (Fm‐3m) TiH2. Compared to MgH2, TiH2 shows the strong deformation resistance. TiH2 dihydrides exhibit the strong bulk modulus compared to MgH2. The electronic structure shows that the high elastic modulus of TiH2 is determined by the Ti‐H bonds. The Debye temperature of cubic (Fm‐3m) and tetragonal (I4mmm) TiH2 is larger than the orthorhombic TiH2. The heat capacity follows the order of orthorhombic > cubic > tetragonal.