Precipitate-domain wall topologies in hardened Li-doped NaNbO₃

Ferroelectric hardening is an absolute requirement for potential applications of piezoceramics in high-power devices. A very recent work demonstrates that ferroelectric hardening by pinning domain walls with precipitates introduced during processing is feasible, akin to precipitation hardening in metals. With the precipitation of plate-like LiNbO₃ in Li-doped NaNbO₃ piezoceramics, ferroelectric hardening was achieved, exhibiting an enhanced mechanical quality factor (Q_m). The specific morphology and corresponding orientation of the LiNbO₃ platelets, exhibiting {110}_PC habit planes, were characterized by transmission electron microscopy (TEM). The experimentally revealed crystallographic structures and strain incompatibility were found to correlate well with the thermodynamic simulation of the minimum-energy aspect ratio. In particular, the topology of the precipitate-domain wall assembly was clarified, revealing a full pinning on the domain walls by the incorporated plate-like precipitates. The revealed topology provides a fundamental basis for future optimization strategies for platelet hardening in new lead-free piezoceramics for high-power applications.