I can only find a silver laden epoxy by Rite Lok (SL65) and something similar by Chemtronics. There seems to be nothing else available - apart from these two formulations. So I would consider any electrically conductive epoxy. It is odd that there appears a lack of this type of adhesive.
An epoxy is prefered because I put the adhesive on by hand, and a single mistake will end up gluing the pzt so it can't move. An epoxy resin can be taken off with white spirit. The PZT is being glued to PZT. There are two failure modes, either the bond isn't strong enough and the two layers of pzt split, or the silver laden epoxy melts when I put the volts up.