Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
IEEE Trans Ultrason Ferroelectr Freq Control. 2009 Sep;56(9):1843-9. doi: 10.1109/TUFFC.2009.1259.
Phonons in both ceramic samples KNbO(3) (KN) and K(0.5)Na(0.5)NbO(3) (KNN-50) were investigated from 10 to 900 K by means of Raman, infrared, and THz spectroscopy. First-order transitions from cubic to tetragonal phases were detected at about 755 K (in KN) and 710 K (in KNN-50), where the first component of the polarization appears. Transitions from the tetragonal to the orthorhombic phases take place around 510 and 475 K, respectively. The last transitions from orthorhombic to rhombohedral phases are strongly first-order type. T(C) is shifted from 200 K in KN to about 90 K in KNN-50. All Raman active modes below 200 cm(-1). disappear in KN but not in KNN-50. The overdamped soft mode present at high temperatures in the THz range changes its dielectric strength at each phase transition (when the corresponding component jumps to higher frequencies) and abruptly disappears from THz spectra in the rhombohedral phase, because it stiffens up to 200 cm(-1). This mode has lower frequency and higher dielectric strength in KNN-50.
采用拉曼光谱、红外光谱和太赫兹光谱技术研究了陶瓷样品 KNbO(3) (KN) 和 K(0.5)Na(0.5)NbO(3) (KNN-50) 中的声子。在大约 755 K（在 KN 中）和 710 K（在 KNN-50 中）检测到从立方相到四方相的一级相变，其中出现了极化的第一个分量。四方相到正交相的转变分别发生在大约 510 和 475 K。最后从正交相到菱面体相的转变是强烈的一级类型。T(C)从 KN 中的 200 K 移到 KNN-50 中的约 90 K。所有低于 200 cm(-1)的拉曼活性模式都在 KN 中消失，但在 KNN-50 中没有消失。在太赫兹范围内高温存在的过阻尼软模在每个相变时都会改变其介电强度（当相应的分量跃迁到更高的频率时），并在菱面体相中突然从太赫兹光谱中消失，因为它变硬到 200 cm(-1)。该模式在 KNN-50 中具有更低的频率和更高的介电强度。
