Uncontrollable expansion of PbZn1/3Nb2/3O3-PbTiO3 perovskite⇒pyrochlore transition during spark plasma sintering: Mechanism proposal using infinite periodic minimal surfaces

The PbZn_1/3Nb_2/3O₃-PbTiO₃ phase (PZN-PT) prepared by mechanosynthesis exhibits interesting relaxor properties when transformed into nanostructured ceramic by spark plasma sintering. When trying to obtain denser ceramic to enhance physical properties, the PZN-PT phase transformation from perovskite to pyrochlore structure induces the graphite die explosion. An explanation of this phenomenon is based on the reorganization of the lone pairs corresponding to Pb²⁺ cations into the large cavities of pyrochlore network, inducing an important cell volume increase, together with the speed of transformation depicted in the light of infinite periodic minimal surfaces describing the perovskite (P-surface) and the pyrochlore (F-surface) networks, respectively.