I set an half slab on an slime block with a sticky piston underneath to push both blocks up. i first tried with netherbrick slabs, the game just crashed. to investigate, i tried different slab types. i've encountered crashs with netherbrick and quarz slabs. after the crash with the quarz slab, my world file became corrupted and can't be opened again.
1. build 2blocks high with sandstone
2. remove the bottom block
3. put a sticky piston ontop of the upper sandstoneblock facing upwards
4. put a slimeblock ontop of the sticky piston
5. put a half slab (netherbrick/quarz) ontop of the slimeblock
6. place a redstone torch under the sandstoneblock to power the piston
please let me know if my world could be restored, the files are still in the "save" folder.