B-cation effect on relaxor behavior and electric properties in Sr₂NaNb_5−xSb_xO₁₅ tungsten bronze ceramics

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• 作者：Jianyong Fan^c ; Bian Yang^b ; ^{yangbian90@snnu.edu.cn" class="auth_mail" title="E-mail the corresponding author} ; Lingling Wei^a ; ¹ ; ^{weill@snnu.edu.cn" class="auth_mail" title="E-mail the corresponding author} ; Zhongming Wang^b
• 关键词：Structural modulation ; Phase transition ; Tungsten bronze niobates ; Dielectric anomaly ; Relaxor ferroelectric
• 刊名：Ceramics International
• 出版年：2016
• 出版时间：15 February 2016
• 年：2016
• 卷：42
• 期：3
• 页码：4054-4062
• 全文大小：2576 K

文摘

Sr₂NaNb_5−xSb_xO₁₅ ceramics (SNNS, x=0.0, 0.3, 0.5, 1.0) with ‘filled’ tungsten bronze structure were prepared by the conventional solid-state reaction method. Effects of introducing Sb concentration in B-sites on the microstructure, dielectric and ferroelectric properties were investigated in detail. With increasing of Sb concentration, the crystal structure of SNNS ceramics distorted slightly from the TB orthorhombic Ccm2 phase to tetragonal P4bm phase, and then to paraelectric P4/mbm phase at room temperature. The smaller ionic radius of Sb⁵⁺ (0.60 Å) compared with that of Nb⁵⁺ (0.64 Å) contributed to the shrinkage of crystal structure. It was found that accompanying with the introduction of Sb, some unique dielectric and ferroelectric behavior emerged for SNNS ceramics. Only the samples with x<0.5 showed additional dielectric anomaly in low-temperature range, which was attributed to the incommensurate superstructure ICS-associated dielectric dispersion process caused by local structural fluctuation. With increasing of Sb concentration, T_c shifted to lower temperatures, and the diffuse phase transition and relaxor behavior appeared to be exceptionally induced around T_c at higher Sb concentration. The underlying mechanisms of relaxor behavior induced by different Sb concentration in B-sites for SNNS ceramics were clarified in detail. Moreover, the ferroelectric properties deteriorated and even disappeared at higher Sb concentration, because the ceramics showed P4/mbm phase structure as a result of decreasing of T_c to lower than room temperature.