Chapter 3: Defect Equilibria Flashcards
What is the coefficient K called?
Mass action or equilibrium constant
What does the coefficient K tell us?
That a particular ratio of products and reactants is maintained constant at equilibrium (but it does change with temp)
What are the conditions for dG when a reaction goes forward, backwards and reaches equilibrium?
- Forward (spontaneous) reaction: dG < 0
- Backwards: dG > 0
- Equilibrium: dG = 0
What happens to the number of sites N in a material when n vacancies are created?
The amount of sites goes from N to N+n_v
How do we express the configurational entropy of mixing?
S_conf = k ln W
- k is boltzmann’s constant
- W is the thermodynamic probability (also known as Ω)
How is the thermodynamic probability (W or Ω) defined?
W = (N + n_v)!/(N!n_v!)
What is the thermodynamic probability, W?
It represents e.g. the number of distinguishable ways one can distribute n_v vacancies on N + n_v lattice sites
What is Stirlings approximation?
ln x! = x ln x - x
What is the site fraction of vacancies in a crystal?
n_v /(N + n_v)
What is the change in enthalpy upon forming vacancies?
n_v times deltaH
