4'1 Introduction to CASTEP 1

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4.1 Introduction to CASTEP (1)

• CASTEP is a state-of-the-art quantum
  mechanics-based program designed specifically for
  solid-state materials science. CASTEP employs the
  density functional theory plane-wave
  pseudo-potential method, which allows you to
  perform first-principles quantum mechanics
  calculations that explore the properties of
  crystals and surfaces in materials such as
  semiconductors, ceramics, metals, minerals, and
  zeolites.
• Typical applications involve studies of surface
  chemistry, structural properties, band structure,
  density of states, and optical properties. CASTEP
  can also be used to study the spatial
  distribution of the charge density and wave
  functions of a system.

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4.1 Introduction to CASTEP (2)

• CASTEP can be used effectively to study
  properties of both point defects (vacancies,
  interstitials, and substitutional impurities) and
  extended defects (e.g., grain boundaries and
  dislocations) in semiconductors and other
  materials.
• Furthermore, the vibrational properties of solids
  (phonon dispersion, total and projected density
  of phonon states, thermodynamic properties) can
  be calculated with CASTEP using either the linear
  response methodology or the finite displacements
  technique. The results can be used in various
  ways, for instance, to investigate the
  vibrational properties of adsorbates on surfaces,
  to interpret experimental neutron spectroscopy
  data or vibrational spectra, to study phase
  stability at high temperatures and pressures,
  etc. The linear response method can also be used
  to calculate the response of a material to an
  applied electric field - polarizability for
  molecules and dielectric permittivity in solids -
  and to predict IR spectra.

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4.2 Modeling

• Figure 4.1. Model for the motion energy
  calculation.
• Supercell with an extra oxygen vacancy.
• Supercell with a oxygen ion located at the saddle
  point.

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4. 3 Choosing Parameters

• The structural parameters were calculated by
  geometry optimization with high accuracy from
  first principles.
• Calculations of the total energy of the systems
  were carried out using the pseudo-potential
  method.
• All static calculations were performed using the
  CASTEP code with ultra soft pseudo-potentials and
  the Perdew-Burke-Ernzerhof (PBE) GGA exchange
  correlation term.
• The ultra-find convergence of the total energy
  and the energy cutoff were chose.
• Spin polarization was taken into account in this
  study.

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4. 4 Examples

• Example 1 migration energy of oxygen ion in the
  BaCo0.875B0.125O3(B Sc, Mn, Ni, Fe, Co, Y, Nb,
  In, Sn)

Figure 4.2 Migration energy of oxygen ion in the
BaCo0.875B0.125O3 system
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4. 4 Examples

• Example 2migration energy of oxygen ion in the
  Ba0.875A0.125CoO3(A La, Sr, Ba, Ca)

Figure 4.3 Migration energy of oxygen ion in the
Ba0.875A0.125CoO3 system
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4. 4 Examples

• Example 3 Calculation for oxygen ion migration
  in SrBO3
• The aim of calculation was to choose a better
  element as a B-site dopant in SrTiO3 to lower the
  oxygen ion migration energy and thus increase the
  oxygen ion conductivity. The ion migration energy
  was referred to as the activation energy for
  oxygen ion conduction. The ion migration energies
  in SrBO3 (BSc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn,
  Ga, Ge, As, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Cd, In,
  Sn and Sb)

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Figure 4.4 Migration energy of oxygen ion in the
SrBO3 system
X. Li et al. / Electrochemistry Communications 10
(2008) 15671570
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4.5 Testing Methods

• Electron-blocking method
• Thermogravimetric testing
• Concentration cell
• Chemical titration