I recently researched about Superionic Ice which basically is Water under so much pressure and heat that it turns into a black hot ice. I read this article about it too. I found out Superionic ice exists inside Earth but I cant make sense of how it got into the core, considering that any water in the ocean basically is sealed off from at least below the mantle because it would immediately evaporate causing bubbles of the vapor to rise until it cools again.
Probably not. While the interior of Earth easily exceeds the 40 GPa pressure required to make superionic ice and we know now that tectonic processes can cycle water deep into the mantle, the temperature profile is likely hot enough to keep the water in a supercritical fluid state. The water may be hot enough in the deep mantle to undergo significant ion formation whether solid or fluid.
The supercritical water may be included into diamonds, which retain sufficient internal pressure to condense the water as Ice VII when they come to the surface and cool off.