拉曼光谱
声子
铁电性
电场
凝聚态物理
相变
波数
分析化学(期刊)
微晶
材料科学
格子(音乐)
矿物学
化学
电介质
结晶学
物理
光学
量子力学
光电子学
色谱法
声学
作者
Javier Alanis,M. C. Rodríguez‐Aranda,Ángel Gutiérrez Rodríguez,Hiram Joazet Ojeda‐Galván,M.E. Mendoza,H. Navarro‐Contreras
摘要
Abstract We report on the preparation and structural characterization of powder samples of the perovskite‐slab layered polycrystalline Sr 2 Nb 2 O 7 (hereafter named SNO) ferroelectric compound. Comparison is performed on samples grown without (SNO) and with an applied electric field of 3.34 kV/cm (SNOE). The Raman effect produced by these samples as a function of temperature, from 27°C (room temperature) to 400°C is presented and discussed. Significant differences are observed and discussed among SNO and SNOE. The electric field promotes the growth of platelets, preferentially oriented along the (0b0) planes. The temperature coefficients of 35 phonon wavenumbers were determined for both samples. A majority of the phonons exhibit monotonic wavenumber softening's with increasing temperatures, but a significant number of them show discontinuities on the wavenumber temperature slopes at two temperatures 215°C and 307 ± 5°C. The first temperature corresponds to the well‐known incommensurate phase to the ferroelectric phase transition (Phases III to II). The second temperature is indicative of an unreported phase transition for both the SNO and SNOE samples. For the sample SNOE, a phonon f7 (at 121 cm −1 at room temperature) displays a behavior that may be indicative of the existence of another ordering parameter that vanishes at 488 ± 5°C in the SNOE sample, induced by the electric field applied during the growth. The phonon broadenings with temperature are explained in terms of the Klemens model, which considers that the broadenings are due to the thermal expansion of the lattice, with a substantial contribution in magnitude from anharmonic phonon–phonon interactions.
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