Malti, I think you should calculate diffusivity , gamma(g), if it is more than 1, then go for VF fitting. lot of materials in literature available for this.( you can see one of paper from our group ,  Materials Research Bulletin 48 (2013) 101–105) 

Following can help you to get your answer( a part from above paper).

A modified Curie–Weiss law  has been proposed to describe the diffuseness of a phase transition The parameter g is regarded as a measure of the diffuseness of the phase transition: g = 1 corresponds to the normal ferroelectric behavior, while

1 < g < 2 corresponds to the diffuse phase transition and g = 2 refer to a relaxor ferroelectric behavior. 

Malti, This paper may help you.

In case you aworking on ceramics, and trying to understand relaxor behavior, our latest paper may help you to some extent. 

I am new comer in the field of Relaxor ferroelectrics, slowly trying understand the proper way, and methods of analysis for true relaxor behavior.

Please do see our latest paper on La doped BaBi4Ti3O12 ceramics, published in the Journal of materials and chemistry of Physics, reference given below, where we have cited many important research papers, that should be read and understood by any new researcher in the field of ferroelectric relaxor behavior.

Materials chemistry and physics, 152 (2015) 13-25

I hope the above paper will be useful to you.

prof. K. Sreenivas