Phase equilibria and dielectric properties of Bi_3+(5/2)xMg_{2鈭?span style='font-style: italic'>x}Nb_3-(3/2)xO_{14鈭?span style='font-style: italic'>x} cubic pyrochlores

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• 作者：P.Y. Tan ; K.B. Tan ; C.C. Khaw ; Z. Zainal ; S.K. Chen ; M.P. Chon
• 关键词：A. Powder ; solid-state reaction ; C. Impedance ; D. Niobates ; E. Capacitors ; Pyrochlore
• 刊名：Ceramics International
• 出版年：April, 2014
• 年：2014
• 卷：40
• 期：3
• 页码：4237-4246
• 全文大小：1384 K

文摘

Subsolidus pyrochlores with the proposed formula, Bi_3+(5/2)xMg_2鈭?em>xNb_3鈭?3/2)xO_14鈭?em>x (0.14鈮?em>x鈮?.22) were successfully synthesised at the firing temperature of 1025 掳C using conventional solid-state reaction. The excess Bi³⁺ charge was offset by removal of relative proportion of Mg²⁺ and Nb⁵⁺ together with creation of oxygen non-stoichiometry in order to preserve electroneutrality of the system. These samples were crystallised in cubic structure with space group of Fd3m, No. 227 and their refined lattice parameters were in the range of 10.5706 (3)-10.5797 (7) 脜. The surface morphologies of the samples as confirmed by scanning electron microscopy analysis were of irregular shaped grains while their crystallite sizes of ~30-85 nm were calculated using the Scherrer equation and the Williamson-Hall method. No thermal event was discernable indicating these pyrochlores were thermally stable within a studied temperature range of ~30-1000 掳C. The recorded dielectric constants of Bi_3+(5/2)xMg_2鈭?em>xNb_3鈭?3/2)xO_14鈭?em>x (0.14鈮?em>x鈮?.22) subsolidus pyrochlores were generally above ~160 and their dielectric losses were in the order of 10^鈭?-10^鈭? at the frequency of 1 MHz and temperature of ~30 掳C. Meanwhile, these ceramic samples also exhibited negative temperature coefficient of relative permittivity between 鈭?28 and 鈭?42 ppm/掳C in the temperature range of ~30-300 掳C.