Are there attempts to investigate phase states at negative pressure? Phase diagrams of various compounds and systems usually include only positive pressure. But I wonder whether it is possible to somehow investigate them under negative pressure?

Are there materials that change phase if mechanically stretched? For instance given that metallic form is sometimes achieved at high pressure, can a negative pressure applied to a metal produce a non-metalic form?

Or maybe the effect of negative pressure may be achieved by electrically uniformly charging the material?
I think there is a little misconception here.
There are no negative absolute pressures. When someone talks about negative pressures, they are referring to values under atmospherical pressure, this is,between 0 and 1 atm.
There are many ways of creating this vacuum, and of course, that matter has been studied under these conditions, for example, this kind of negative pressures are applied to get the boiling point of substances reduced, so thermolabile compounds can be vaporized (or the solvent which contains them) under its decomposition temperature.