Cu, Mg Codoped Bismuth Tantalate Pyrochlores: Crystal Structure, XPS Spectra, Thermal Expansion, and Electrical Properties.
Cu, Mg Codoped Bismuth Tantalate Pyrochlores: Crystal Structure, XPS Spectra, Thermal Expansion, and Electrical Properties.
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DOI：
10.1021/acs.inorgchem.1c03053
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发表时间：
2022-03
影响因子：
4.6
通讯作者：
N. Zhuk;M. Krzhizhanovskaya;A. Koroleva;N. Sekushin;S. Nekipelov;V. Kharton;B. Makeev;V. Lutoev
中科院分区：
文献类型：
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作者：
N. Zhuk;M. Krzhizhanovskaya;A. Koroleva;N. Sekushin;S. Nekipelov;V. Kharton;B. Makeev;V. Lutoev
首次合成了Bi_（1.6）Mg_（0.8-x）Cu_xTa_（1.6）O_（7.2-Δ）体系，在x ≤ 0.56时观察到了焦绿石型固溶体的形成。高温X射线衍射表明，烧绿石相存在于空气中高达1080 °C，在那里它的热分解导致（Mg，Cu）Ta 2 O 6的偏析。端元Bi_（1.6）Mg_（0.24）Cu_（0.56）Ta_（1.6）O_（7.2-Δ）的热膨胀系数从室温的3.3 × 10 ~（-6）° C ~（-1）增加到930 °C时的8.7 × 10 ~（-6）° C ~（-1）。Rietveld精修证实了烧绿石晶体结构是无序的，空间群为Fd 3 <$m：2（Z = 8，编号227）。用铜掺杂导致立方晶胞的适度膨胀，促进陶瓷材料的烧结，并诱导它们的红棕色。X射线光电子能谱表明，Bi（III）和Mg（II）的状态不受掺杂的影响，钽阳离子的有效电荷低于+5，而Cu（II）状态与Cu（I）共存。电子自旋共振谱显示g = 2.2的单线，归因于偶极加宽的Cu 2+信号。Bi1.6Mg0.8-xCuxTa1.6O7.2-Δ陶瓷的介电常数可以达到105，介电损耗角正切在0.2到12的范围内变化。在室温及以上温度下，所有样品都出现了多重介电弛豫。
The pyrochlore-type solid-solution formation in a Bi1.6Mg0.8-xCuxTa1.6O7.2-Δ system, synthesized for the first time, is observed at x ≤ 0.56. High-temperature X-ray diffraction showed that the pyrochlore phase exists in air up to 1080 °C, where its thermal decomposition leads to the segregation of (Mg,Cu)Ta2O6. The thermal expansion coefficients of the end member, Bi1.6Mg0.24Cu0.56Ta1.6O7.2-Δ, increase from 3.3 × 10-6 °C-1 at room temperature up to 8.7 × 10-6 °C-1 at 930 °C. Rietveld refinement confirmed that the pyrochlore crystal structure is disordered with space group Fd3̅m:2 (Z = 8, no. 227). Doping with copper results in a modest expansion of the cubic unit cell, promotes sintering of the ceramic materials, and induces their red-brown color. X-ray photoelectron spectroscopy demonstrated that the states of Bi(III) and Mg(II) are not affected by doping, and the effective charge of tantalum cations is lower than +5, while the Cu(II) states coexist with Cu(I). The electron spin resonance spectra display a single line with g = 2.2, ascribed to the dipole-broadened Cu2+ signal. The dielectric permittivity of Bi1.6Mg0.8-xCuxTa1.6O7.2-Δ ceramics may achieve up to ∼105, with the dielectric loss tangent varying in the range from 0.2 up to 12. Multiple dielectric relaxations are found at room temperature and above for all samples.