I am attempting to charge CCTO samples with DC or very low frequency (.01-.001 Hz) with 5V or less at approximately 150C which should have a capacitance in the Farad range. So far, I've seen no indication that they are building any charge even in the uF range when attempting to charge or discharge them and measure any stored charge even momentarily through an oscilloscope. At temperatures and frequencies needed to reach goal (150C), R/impedance is 100 ohms, and tan delta is greater than 20 (limit of the LCR). I realize CCTO is very leaky and will self-discharge extremely quickly- I just need the samples to charge for extremely short periods or only as long as power is applied.

Permittivity measured with Hioki 3522-50 LCR (and several others) and obtained very similar results even into the millions and billions like many other researchers including for example:

https://www.ijsr.net/archive/v3i11/T0NUMTQxMjIz.pdf which is one of the few that have done work at elevated temperatures.

Sputtered Pt electrodes were previously used, and now using Cu electrochemically deposited electrodes; these are better showing no resistance across the surface and approx. 500k ohms at RT through the CCTO dielectric of 15mm diameter and .3mm thickness.

Samples will pass the expected leakage current, but I expected them to charge if given adequate amperage.

Possible reasons no charge:

1) Matching network required to get them to take a charge? I've attempted this, but possibly not done properly. A network of resistors with DC and AC made no difference. Network using inductors for AC at low frequency would be massive and incredibly expensive, plus I don't think it's possible to place a network capacitor in series with the sample since that would severely limit the charge the sample can hold.

The resistivity drops quickly with increasing temperature, so I had thought about heating the sample until it's resistance is 50 ohm making it match the AC power supply?

2) Wrong capacitance setting on LCR? Other researchers seem to be using Cs setting (high capacitance & low impedance, so Cs seems correct) even though it is never stated in their papers. Capacitance difference between Cs and Cp readings is huge: approx. 10e6 at these elevated temperatures. Even if Cp is required, there should still be stored charge at least in the uF range.

3) Are there any physical limits to stored charge on a capacitor? Obviously can't be infinite, but I've been unable to locate any theoretical limits or equations on a search.

Thanks for any input.