When we talk about a material to be used as a dielectric.

a few things should be clarified.

1) Stability of the material - (frequency range)

2) Stability of the material versus temperature (Temperature range).

3) Stability is regarding (dielectric constant and dielectric loss) versus frequency and temperature. 

4) Break down voltage of a capacitor

In most ferroelectric materials all the above mentioned properties, or stability characteristics vary widely with temperature and frequency.

Unfortunately the high dielectric constant of a ferroelectric is never able to satisfy many a time the requirement for real capacitor applications in electronics.

For example Ta2O5 capacitors are widely used in electronics and are well known for their good stability characteristics.  So different aplications will necessitate different materials. 

So one should be very careful in trying to select a ferroelectric material for a dielectric application.

K. Sreenivas

 Plz. find attachment containing dielectric constant values of four ferroelectrics ; zoom200%; page:174- SEE AT THE BOTTOM OF TABLE

 Of the paper

The International Journal of Microcircuits and Electronic Packaging, Volume 23, Number2, Second Quarter 2000( pp:172-80) (ISSN 1063-1674)

In the family of ferroelectrics, barium titanate (BaTiO3)  is the

most frequently utilized ferroelectric material with a high dielectric constant. For making of the composite materials it is best option.

You may use PZT or BSZT.

Dear Manohar

Thank you very much, the paper you introduced to me was very good.

Dear Dr Kooti

Sol. gel. prepared lead zirconate titanate can be one of the best choice as it gives dielectric constant in the range of 80000 at room temperature.

You can use PZT-PZN-PMnN material for your application

It depends very much on the loss tangent. A material may have a huge dielectric constant at low frequency, only to roll off at just a few MHz. PZT is a good example. The first problem is the non-stoichiometric grain boundary, so in thin films, an under annealed amorphous phase, can let you keep a good dielectric constant to 10 Ghz (eg. BST). So, without knowing your application, I will assume thin films. For at least 2 GHz, for Mobile phones, you can use amorphous BST doped with Fe (about 2-3 at%. The amorphous phase does not give you great Dielectric constant, only about 200-400, but it will not roll off with frequency. (Look at epsilon prime and epsilon double prime. Their ratio is the tan delta, which is the ac leakage), Things like iron dope KTN can give you great dielectric constant, but watch the roll off. Also, lots of roll off give you dielectric heating and eventually failure. (BST=Barium Strontium Titanate, KTN PotassiumTantalum Niobate). Great Barium titanate solid solutions with iron  and Niobium gives you also large values.Also some relaxor ferroelectric like PMnN etc. - but they roll off with frequency.

You may use Ca and Zr modified BaTiO3.....

Many thanks to all of you dears for your help and valuable comments.

When we talk about a material to be used as a dielectric.

a few things should be clarified.

1) Stability of the material - (frequency range)

2) Stability of the material versus temperature (Temperature range).

3) Stability is regarding (dielectric constant and dielectric loss) versus frequency and temperature. 

4) Break down voltage of a capacitor

In most ferroelectric materials all the above mentioned properties, or stability characteristics vary widely with temperature and frequency.

Unfortunately the high dielectric constant of a ferroelectric is never able to satisfy many a time the requirement for real capacitor applications in electronics.

For example Ta2O5 capacitors are widely used in electronics and are well known for their good stability characteristics.  So different aplications will necessitate different materials. 

So one should be very careful in trying to select a ferroelectric material for a dielectric application.

K. Sreenivas

You can use triglycine sulphate TGS, very promising ferroelectric material 

Regards 

Seham 

Invention of Barium titanate made a significant advance toward the making small high dielectric parts for the electrical industry.

Normally perovskite materials, specially barium titanate and barium strontium titanate are good candidate for delectric applications. Recent researches are focusing the processing of this materials to upgrade their functionalities.

With best regards,

Rouholah Ashiri

Thank you all dears for your help interesting comments.