How to fit Vogel-Fulcher Tamanna (VFT) equation for analysing ionic conductivity data at different temperatures?

The VFT equation used to analyse ionic conductivity is ??????????????????????????????????????

??? σ = σ? * exp (-Ea / (T - T?))

Rewriting this in logarithmic form:

??????????????????????????????????????? logσ = log(σ?) + log (exp (-Ea / (T - T?)))

?????????????????????????????????????????? ? logσ = log(σ?) + (-Ea / (T - T?)) * log(e).

Let y = logσ, x = 1000 / T, logσ? = A, and Ea * log(e) = B,

then the equation becomes:

y = A - B ((1000 / x) - T?).

Steps to Fit the Data Curve/Plot in Origin

1)??? Prepare the Plot: Plot log(conductivity) versus vs 1000/T

2) Access Nonlinear Curve Fitting: Select the graph, then navigate to: Analysis → Fitting → Nonlinear Curve Fit → Open Dialog.

3) Create a New Fitting Function: Under Category, select User Defined. Click Create New Fitting Function.

4) Define the Fitting Function: Set Function Name to "VFT". For Function Type, choose Expression, then click Next

5) Define the independent and dependant variable as x, y and parameters as A, B, and T?.

6) Provide Parameter Details:

A is the ideal ionic conductivity.

B is the pseudo activation energy and

To is the ideal glass transition temperature.

Enter the units and meaning of these variables. Enter the code in the function body. The code is the VFT equation

?? ????????????A - B / ((1000/x) - To)

7) Click Next and finish to save the function

8) To Fit the Data: ·??????

·?????? Select the plot, go analysis -> Fitting -> Non-linear curve fit -> open dialog

·?????? Select the Function “VFT”, which you built

·?????? Click “Parameter” and

Enter approximate values under A, B and To and click Fit.

·?????? Repeat the Fitting procedure until COD(R^2) = 0.995 or above

Then click done to obtain the Fit.