Formula used:
The diffusion coefficient of point 1 is given by,
D0ZnO1=D0ZnO0exp(−ΔH D 0ZnO kT1) ....... (I)
Here, D0Zn01 is the diffusion coefficient of point 1, D0ZnO is the pre-exponential constant for oxygen diffusion into ZnO, k is the Boltzmann’s constant, T1 is the temperature at point 1 and ΔHD0ZnO is the activation enthalpy for oxygen into ZnO.
The diffusion coefficient of point 2 is given by,
D0ZnO2=D0ZnO0exp(−ΔH D 0ZnO kT2) ....... (II)
Here, D0Zn02 is the diffusion coefficient of point 1 and T2 is the temperature at point 2.
The ratio of diffusion coefficient of points 1 and 2 is given by,
D 0 ZnO 1 D 0 ZnO 2 =D 0 ZnO 0 exp( − Δ H D 0ZnO k T 1 )D 0 ZnO 0 exp( − Δ H D 0ZnO k T 2 )=exp( − Δ H D 0ZnO k T 1 )exp( − Δ H D 0ZnO k T 2 )=exp[−( Δ H D 0ZnO k)( 1 T 1 − 1 T 2 )] ....... (III)
Calculation:
The activation enthalpy is calculated as,
Substitute 1×10−12 cm2/s for D0ZnO1, 1×10−18 cm2/s for D0ZnO2, 8.62×10−5 eV/atom⋅K for k, 1587 K for T1 and 1075 K for T2 in equation (III).
1× 10 −12 cm 2/s1× 10 −18 cm 2/s=exp[−( Δ H D 0ZnO 8.62× 10 −5 eV/ atom ⋅K)( 1 1587 K− 1 1075 K)]106=exp[−ΔH D 0ZnO(−3.48 atom/ eV)]ln( 106)=ΔHD 0ZnO(3.48 atom/eV)ΔHD 0ZnO=ln( 10 6 )3.48 atom/eV
Solve further,
ΔHD 0ZnO=13.823.48 atom/eV=(3.97 eV/atom× 96.521× 10 3 J/ mole of O atoms 1 eV/ atom )=3.83×105 J/mole of O atoms
The diffusion coefficient is calculated as,
Substitute 1×10−12 cm2/s for D0ZnO1, 8.62 ×10−5 eV/atom⋅K for k, 1587 K for T1 and 3.97 eV/atom for ΔHD0ZnO in equation (I).
1×10−12 cm2/s=D0 ZnO0exp(− 3.97 eV/ atom ( 8.62× 10 −5 eV/ atom ⋅K )( 1587 K ))D0 ZnO0=( 1× 10 −12 cm 2 /s × 10 −4 m 2 1 cm 2 )exp( −29.02)=1× 10 −16 m 2/s2.32 × 10 −13=0.40×10−3 m2/s
Conclusion:
Therefore, the activation enthalpy is 3.83×105 J/mole of O atoms and the pre exponential constant is 0.40×10−3 m2/s.