I am interested to have a "container" with water mixed with this negative thermal expansion liquid (in right proportions) to obtain a mix that has 0 thermal expansion coefficient. I would like to have it in "room temperature / conditions".
So for a limited range (+/- a few C?) near RT you want zero CTE?
And you are making the container out of something with zero CTE also? (caution, Invar rusts)
You are discovering why people do this with expansion tanks, check valves and back pressure regulators.
There is no safe, simple, stable, water based ZCTE solution.