Thermal　depoling　phenomena　determine　the　upper　temperature　limit　of　the　piezoelectric　ceramics　in　application.　In　this　paper,　high-densified　KNbO3　ceramics　derived　from　single-crystalline　nanostructures　exhibited　favorable　piezoelectric　constants　d(33),　which　varied　from　105　to　80　pC/N　over　a　broad　temperature　range　from　25　to　225　degrees　C.　In　situ　x-ray　diffraction　combined　with　Raman　spectra　demonstrate　clearly　the　transition　sequence　of　crystallographic　orientations　during　thermal　depoling　process.　The　interaction　between　defect　dipoles　D　and　spontaneous　polarization　inside　domains　P-s　favored　to　preserve　piezoelectric　activity,　while　the　spontaneous　rotation　of　P-s　induced　by　the　phase　transition　resulted　in　the　deliquesce　of　d(33).　(C)　2011　American　Institute　of　Physics.　[doi:10.1063/1.3614541]