I did not understand your question about determining the quality of ferroelectric samples. The question should be how to determine whether a sample is ferroelectric or not from dielectric studies. This can be checked by doing the temperature dependent dielectric studies. At high temperature (Curie temperature) the dielectric vs Temp plot gives a peak which shows a transition from ferroekectric to paraelectric phase. This peak can give us a clue regarding our material to be ferroelectric or not and simultaneosly determining the curie temperature.

By using the frequency dependent study an increase in dielectric constant response is obtained after saturation of the dielectric constant at high frequency. This response is a typical character for the ferroelectric materials. see the article below.

I have this information. If any one have some better knowledge he can guide you. Best of Luck.

Article Thermally activated variations in conductivity and activatio...

Temperature dependent dielectric studies will only tell you about the phase transition, and if vay the frequency, then it can provide information whether it is a pure ferroelectric phase transition (frenquency independent peak), alternately if the peak positions are varying, and decreasing in height, they may indicate a ferroelectric relaxor effect. There are lot of papers.  The sharpness of the transition indicates whether you have a first order, second order, or a diffused ferroelectric phase transition.

However, you are referring to quality of the ferroelectric from the frequency dependent dielectric studies..

Initially you should obtain a good x-ray diffraction patter of your synthesized powder, or ceramic pellet.

In case you are making ferroelectric ceramics:

A good dielectric (including ferroelectric) should exhibit a low  (tan delta) value. Try to to take a frequecny sweep (10 Hz to at least 1 MHz). and see that your measured tan delta is low. Ceramics which have a good high density, and are well electroded, and non porous, and compositionally homogeneous, would give you a low tan delta.

Any dielectric dispersion in the low frequency data at room temperature can indicate extrinsic effect contribution such as bad electroding. 

Yes simple room temperature measurements of frequency dependent dielectric constant over a large frequency range indicate a lot about the quality of the dielectric sample you have prepared. When you do temperature variation, it will tell you about the ferroelectric nature of the sample.

K. Sreenivas 

Thanks, Dr. K. Sreenivas..