Modulated phases in NaNbO3: Raman scattering, synchrotron x-ray diffraction, and dielectric investigations
Modulated phases in NaNbO3: Raman scattering, synchrotron x-ray diffraction, and dielectric investigations
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DOI：
10.1088/0953-8984/17/33/003
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发表时间：
2005-08
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影响因子：
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通讯作者：
Y. Yuzyuk;P. Simon;E. Gagarina;L. Hennet;D. Thiaudiére;V. Torgashev;S. I. Raevskaya;I. Raevskiĭ;L. A. Reznitchenko;J. Sauvajol
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文献类型：
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作者：
Y. Yuzyuk;P. Simon;E. Gagarina;L. Hennet;D. Thiaudiére;V. Torgashev;S. I. Raevskaya;I. Raevskiĭ;L. A. Reznitchenko;J. Sauvajol
测量了NbO3NaNbO_3各相的拉曼光谱，发现高温U、T2和T1相存在明显的无序现象，布里渊区在转变为调制的S、R、P和N相的过程中发生了复杂的折叠，并伴随着沿M-T-R线的竞争性区边界软模(同相和异相八面体倾斜)。广泛的拉曼光谱研究结合X射线衍射和介电测量证实了在NbO4中存在无公度(InC)相。X射线衍射实验表明，在410-460K的温度范围内存在因瓦效应，对应于沿b方向调制的NbO6八面体的转动所对应的InC相。实验表明，P相由三个相组成：单斜晶系(Pm)在250-410K之间，InC相在410-460K之间，正交相(Po)在460-633K之间。在向铁电三方相N相的低温转变过程中，起源于布里渊区M点和T点的所有折叠模突然消失，N相拉曼光谱变得简单得多，所有的峰都被指认出来。
Raman spectra of sodium niobate (NaNbO3) were obtained in all phases and revealed a significant disorder in the high-temperature U, T2 and T1 phases and a complicated folding of the Brillouin zone at the transitions into modulated S, R, P and N phases associated with the competitive zone-boundary soft modes (in-phase and out-of phase octahedral tilts) along the M–T–R line. An extensive Raman study combined with x-ray diffraction (XRD) and dielectric measurements confirmed the presence of the incommensurate (INC) phase in sodium niobate. XRD experiments revealed the invar effect in the temperature interval 410–460 K corresponding to the INC phase associated with rotations of the NbO6 octahedra modulated along the b-direction. Our experiments suggest that the phase P consists of three phases: monoclinic (Pm) between 250 and 410 K, INC between 410 and 460 K, and orthorhombic (Po) between 460 and 633 K. At the low-temperature transition to the ferroelectric rhombohedral N phase all folded modes originating from the M- and T-points of the Brillouin zone abruptly disappear, Raman spectra in the N phase become much simpler and all peaks were assigned.