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The negative phonon confinement effect in nanoscopic sodium nitrite

机译：纳米亚硝酸钠中的负声子约束效应

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A nanocomposite of porous glass and a NaNO2 ferroelectric (channels of similar to 7 nm diameter) was studied using infrared reflectivity, THz transmission and Raman spectroscopy as a function of temperature in the range of 300-500 K, including the ferroelectric transition. From the infrared and THz response the effective dielectric function was calculated and compared with the dielectric functions calculated from the Bruggeman and Lichtenecker models of the effective medium, using the known data on the polar phonon modes of the NaNO2 single crystals. The results show good qualitative agreement, indicating that the stiffening of the effective modes is due to local depolarization fields on the glass-ferroelectric interfaces. The nonpolar Raman modes show no substantial modification compared to those of the bulk NaNO2. Some signatures of the ferroelectric transition were even seen. The results indicate that the intrinsic size effect (phonon confinement) is negligible in this nanocomposite.
机译：使用红外反射率，太赫兹透射率和拉曼光谱，研究了多孔玻璃和NaNO2铁电体（直径约7 nm的纳米复合材料）随温度的函数，包括铁电跃迁，范围为300-500K。根据红外和太赫兹响应，使用NaNO2单晶的极性声子模式的已知数据，计算有效介电函数，并将其与根据有效介质的Bruggeman和Lichtenecker模型计算出的介电函数进行比较。结果显示出良好的定性一致性，表明有效模式的硬化归因于玻璃-铁电界面上的局部去极化场。与块状NaNO2相比，非极性拉曼模式没有实质性改变。甚至可以看到铁电转变的一些特征。结果表明，在这种纳米复合材料中，内在尺寸效应（声子限制）可忽略不计。

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