Phase transition hysteresis at the antiferroelectric-ferroelectric boundary in PbZr1−xTixO3

$\mathrm{Pb}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ exhibits an antiferroelectric-ferroelectric phase boundary at the composition $x\ensuremath{\sim}0.06$. Around this boundary, several questions need to be answered, such as the stabilizations of different phases with a small amount of compositional difference, the sequence of phase transitions, the coexistence of crystal structures, and potential applications. In this work, we have carried out systematic structural investigations of single crystals and ceramics with several compositions across the phase boundary. The phase diagram for $x\ensuremath{\le}0.07$ has been established. A complex phase coexistence is found near the phase boundary, which leads to an unusual transition sequence. It is confirmed that $Pbam$ and $R3c$ structures maintain a subtle balance at the phase boundary, which may be perturbed by a slight change in the concentration or external stimuli. These findings provide unique insights into understanding the antiferroelectric-ferroelectric competition and, hence, into designing alternative materials for energy storage and conversion.