Phase Transitions in Ferroelectric KNb O 3

摘要: It is shown that ferroelectric KNb${\mathrm{O}}_{3}$ undergoes another phase transition at -10\ifmmode^\circ\else\textdegree\fi{}C in addition to two transitions previously reported 225\ifmmode^\circ\else\textdegree\fi{} and 435\ifmmode^\circ\else\textdegree\fi{}C. At this lowest KNb${\mathrm{O}}_{3}$, on cooling, changes its orthorhombic structure a rhombohedral one, change accompanied by sharp of the dielectric constant. The specific heat anomalies three were measured, results are compared with case BaTi${\mathrm{O}}_{3}$.