I'm looking for a dielectric material that can be used in a capacitor subject to AC, which should have the following characteristics: 1. Should be able to be used in high power and high frequency situations 2. Should have as high a permittivity as possible 3. Exhibits the highest possible polarising velocity of its ions when subject to AC electric fields. #3 is the unusual one. It refers to the small displacements that occur in a dielectric when polarised. I want the charges on the polarised molecules to move as fast as possible for a given applied voltage. Maximum velocity will correspond, for sinusoidal AC, to the zero-volts crossing point, since maximum acceleration occurs at peak volts - and velocity and acceleration are phased 90 degrees apart for a sinewave. I am wondering whether a liquid dielectric would be the best bet in respect of #3. How does one calculate the value of the polarising velocity in any case, for the kind of dielectrics commonly used in HV capacitors?