4 research outputs found
Role of Lithium Ordering in the Li<sub><i>x</i></sub>TiO<sub>2</sub> Anatase → Titanate Phase Transition
The mechanism of the tetragonal ↔ orthorhombic phase separation of Li-intercalated anatase TiO<sub>2</sub> has previously been proposed to be a cooperative Jahn–Teller distortion due to occupation of low-lying Ti 3d<sub><i>xz</i>,<i>yz</i></sub> orbitals. Using density functional calculations, we show that the orthorhombic distortion of Li<sub>0.5</sub>TiO<sub>2</sub> is not a purely electronic phenomenon and that intercalated Li plays a critical role. For a 2 × 1 × 1 expanded supercell for 0 ≤ <i>x</i>(Li) ≤ 1, the intercalation voltage is minimized for <i>x</i>(Li) = 0.5. The low-energy structures display a common structural motif of edge-sharing pairs of LiO<sub>6</sub> octahedra, which allows all Li to adopt favorable oxygen coordination. Long-ranged disorder of these subunits explains the apparent random Li distribution seen in experimental diffraction data
Conductivity Limits in CuAlO<sub>2</sub> from Screened-Hybrid Density Functional Theory
CuAlO<sub>2</sub> is a prototypical delafossite <i>p</i>-type transparent conducting oxide (TCO). Despite this, many fundamental questions about its band structure and conductivity remain unanswered. We utilize the screened hybrid exchange functional (HSE06) to investigate defects in CuAlO<sub>2</sub> and find that copper vacancies and copper on aluminum antisites will dominate under Cu-poor/Al-poor conditions. Our calculated transitions levels are deep in the band gap, consistent with experimental findings, and we identify the likely defect levels that are often mistaken as indirect band gaps. Finally, we critically discuss delafossite oxides as TCO materials
Cooperative Mechanism for the Diffusion of Li<sup>+</sup> Ions in LiMgSO<sub>4</sub>F
Extensive molecular dynamics simulations are performed
on tavorite-structured
LiMgSO<sub>4</sub>F, in order to analyze the diffusion mechanism of
the Li<sup>+</sup> ions. In a first step, an interaction potential,
including polarization effects, is parametrized from density functional
theory calculations. This is then tested by reproducing experimental
properties of the material, such as structural parameters (lattice
constants and interatomic distances) and ionic conductivity to a high
degree of accuracy. Next, the conduction mechanism is studied: the
diffusion of the Li<sup>+</sup> ions occurs via correlated hops inside
diffusion channels, which reflects in the much larger values calculated
for their <i>collective</i> diffusion coefficient compared
to the <i>individual</i> ones (by 1 order of magnitude on
average). The consequences (both scientific and technical) of this
finding are discussed
Cooperative Mechanism for the Diffusion of Li<sup>+</sup> Ions in LiMgSO<sub>4</sub>F
Extensive molecular dynamics simulations are performed
on tavorite-structured
LiMgSO<sub>4</sub>F, in order to analyze the diffusion mechanism of
the Li<sup>+</sup> ions. In a first step, an interaction potential,
including polarization effects, is parametrized from density functional
theory calculations. This is then tested by reproducing experimental
properties of the material, such as structural parameters (lattice
constants and interatomic distances) and ionic conductivity to a high
degree of accuracy. Next, the conduction mechanism is studied: the
diffusion of the Li<sup>+</sup> ions occurs via correlated hops inside
diffusion channels, which reflects in the much larger values calculated
for their <i>collective</i> diffusion coefficient compared
to the <i>individual</i> ones (by 1 order of magnitude on
average). The consequences (both scientific and technical) of this
finding are discussed