Capacitance Decrease w/ Applied DC

[ColliLJ]

I would like to understand why my 100uF 6.3V X5R dielectric ceramic capacitor decreases to ~60uF under a 5V applied DC bias. Can anyone explain the physical phenomenon?

 

[ElectroPhysics]

So, you applied 5V to 100uF cap and when you measured its capacitance by some equipment after removing supply it was 60uF. Am I right? Did you measured the capacitance at other voltages too?

 

[ElectroPhysics]

Remember that capacitance is a constant and can't be changed normally if the capacitor is being used under the working voltage mentioned for that component.

 

[ColliLJ]

The decrease in capacitance is while the 5V DC is applied. I can measure the capacitance at 60uF with an applied DC voltage. When I remove the 5V supply (DC Bias = 0V), the measured capacitance goes up to 80uF, which is just barely above the lower limit for the 100uF cap (+/-20%).

The capacitance is not constant! It's a well known phenomenon that some dielectrics decrease in permitivity as a function of an applied DC voltage, or an increase/decrease in temperature, etc. I just wanted to understand the phenomenon.