The ionic conductivity in lithium-boron oxide materials and its relation to structural, electronic and defect properties: Insights from theory

Mazharul M. Islam, Thomas Bredow, Paul Heitjans

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We review recent theoretical studies on ion diffusion in (Li 2 O) x (B 2 O 3 ) 1x compounds and at the interfaces of Li 2 O :B 2 O 3 nanocomposite. The investigations were performed theoretically using DFT and HF/DFT hybrid methods with VASP and CRYSTAL codes. For the pure compound B 2 O 3 , it was theoretically confirmed that the low-pressure phase B 2 O 3 I has space group P3 1 21. For the first time, the structure, stability and electronic properties of various low-index surfaces of trigonal B 2 O 3 I were investigated at the same theoretical level. The (101) surface is the most stable among the considered surfaces. Ionic conductivity was investigated systematically in Li 2 O, LiBO 2 , and Li 2 B 4 O 7 solids and in Li 2 O:B 2 O 3 nanocomposites by calculating the activation energy (E A ) for cation diffusion. The Li + ion migrates in an almost straight line in Li 2 O bulk whereas it moves in a zig-zag pathway along a direction parallel to the surface plane in Li 2 O surfaces. For LiBO 2 , the migration along the c direction (E A =0.55eV) is slightly less preferable than that in the xy plane (E A =0.430.54eV). In Li 2 B 4 O 7 , the Li + ion migrates through the large triangular faces of the two nearest oxygen five-vertex polyhedra facing each other where E A is in the range of 0.270.37eV. A two-dimensional model system of the Li 2 O :B 2 O 3 interface region was created by the combination of supercells of the Li 2 O (111) surface and the B 2 O 3 (001) surface. It was found that the interface region of the Li 2 O :B 2 O 3 nanocomposite is more defective than Li 2 O bulk, which facilitates the conductivity in this region. In addition, the activation energy (E A ) for local hopping processes is smaller in the Li 2 O :B 2 O 3 nanocomposite compared to the Li 2 O bulk. This confirms that the Li 2 O :B 2 O 3 nanocomposite shows enhanced conductivity along the phase boundary compared to that in the nanocrystalline Li 2 O.

Original languageEnglish
Article number203201
JournalJournal of Physics Condensed Matter
Issue number20
Publication statusPublished - 27 Apr 2012

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics

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