Structural Effects Behind the Low Temperature Nonconventional Relaxor Behavior of the Sr2NaNb5O15 Bronze

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• 作者：Almudena Torres-Pardo ; Ricardo Jim茅nez ; Jos茅 M. Gonz谩lez-Calbet ; Ester Garcı ; ́ ; a-Gonz谩lez
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：December 5, 2011
• 年：2011
• 卷：50
• 期：23
• 页码：12091-12098
• 全文大小：462K
• 年卷期：v.50,no.23(December 5, 2011)
• ISSN：1520-510X

文摘

An exhaustive temperature dependent structural and dielectric study of the tetragonal tungsten bronze-type Sr₂NaNb₅O₁₅ (SNN) compound has been performed in the 300鈥?00 K temperature range, by combining X-ray, neutron diffraction, and transmission electron microscopy with dielectric measurements, in order to clarify the structural effects responsible for the observed low temperature dielectric properties. Interestingly, a relevant second anomaly in the dielectric constant, in addition to the ferroelectric (FE) to paraelectric (PE) transition at T_C = 518 K is found at T 鈮?240 K, revealing a relaxor-like behavior of the material at low temperature. This phenomenon has been previously observed in FE perovskite-type phases and referred to as the re-entrant phenomenon. However, FE polarization tends to vanish below this low temperature dielectric anomaly and this fact is not expected for a classical relaxor-ferroelectric phase. Although there is no structural transition from RT to 100 K, there is a change in the elastic properties of the material in the considered temperature range and the intense anomaly at 240 K could be associated to a smeared-out phase transition to a frustrated FE/ferroelastic (FEL) low temperature state in correlation with subtle structural effects.