Fundamental study to grow single crystals with high performances operated up to high temperatures in donor-doped materials for energy harvesting

An energy-harvesting material with high energy-conversion constant (d 33 × g 33 ) and Curie temperature (T C ) is required to effectively harvest the mechanical energy which has not been recycled into electrical energy. Here, we present an eco-friendly single-crystals, the 3rd generation material, for energy harvesting with the excellent d 33 × g 33 of 118 10 -12 m 2 N -1 (d 33 =1030 pCN -1 ) and high T C of 390°C, prepared by simple heat-treatment. A donor (not an acceptor) has been doped to (K,Na)NbO 3 (KNN)-based materials to obtain single-crystals through exceptionally abnormal grain growth (AGG). The severe AGG in a donor-doped KNN is explained by the donor effect to locally accelerate the volatilization of metals earlier. In particular, a donor-doped PbTiO 3 (PT + Bi 3+ ) material as well as a donor-doped KNN material allows for the synthesis of a single-crystal seed through the simple molten salt method. These findings advance understanding of sintering mechanisms in metal-volatile oxides and offer significant progress in energy-harvesting materials.