Nice, but some suggestions:

1) Turns into THDR when melted? The only practical use I can see from this element would be using pressure to break it, other than that it is just like a more volatile form of QRTZ (same with its broken variant).  Breaking it and reforming it via rapid pressure fluctuations would be the only real power generation method available, but if it exploded everything around it by doing so it ruins the purpose.

2) Could be good for bombs, especially with the fact that BPIZ turns back into its solid variant when reaching its melting point.  Mildly unrealistic, but could make for some hella powerful explosives, especially with ones that release vast amounts of pressure and heat on exploding.

3) Maybe if you apply pressure just under its breaking point (but not quite there), it releases energy?  Of course, if you decide to take this route, its breaking point would need to be raised, as ambient pressure fluctuations (in larger / more complex saves; especially reactors) might set it off.

Other than that though, it seems interesting.  Interested to see where this goes!

EDIT: Just saw that it only releases THDR when melting.  Raises practicality as an element slightly, could use some tweaking though.

suggestions:

1. Should produce spark while under pressure.

2. Tell us a bit more of how the elements look.

3. Elements should only have 4 letter names (except for the stkm2 element).

4. Shouldn't BPIEZ melt at around 750C? It is just the broken form of PIEZ.