Cation exchange route to a Eu(II)-Containing tantalum oxide
Cation exchange route to a Eu(II)-Containing tantalum oxide
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DOI：
10.1016/j.jssc.2023.124338
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发表时间：
2023-09
影响因子：
3.3
通讯作者：
Shaun O’Donnell;Eric A. Gabilondo;Subhendu Jana;A. Koldemir;T. Block;M. Whangbo;Reinhard K. Kremer;Rainer Pöttgen;Paul A. Maggard
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文献类型：
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作者：
Shaun O’Donnell;Eric A. Gabilondo;Subhendu Jana;A. Koldemir;T. Block;M. Whangbo;Reinhard K. Kremer;Rainer Pöttgen;Paul A. Maggard
制备含Eu（II）氧化物的传统合成努力主要涉及从EuO或受控的高还原气氛开始的高温反应。相反，更适合于靶向合成新的、潜在亚稳的Eu(II)-氧化物的化学合成方法尚未被探索。本文发现了一种新的含Eu（II）氧化物的阳离子交换途径，例如EuTa4-xO11(x= 0.04)，并通过粉末x射线衍射确定了其结构(Space groupP6322 (#182),a= 6.2539(2) Å；C = 12.3417(2) Å)。该化合物来源于Na2Ta4O11的阳离子交换，通过与EuBr2at 1173 K的反应，并被一半的二价Eu阳离子取代。Rietveld精化显示出Eu阳离子在两个可能的阳离子位点之一上的优先顺序，即Wyckoff位点2d（~ 94%; Eu1）和2b（~ 6%; Eu2）。总能量计算证实了2点Eu阳离子的能量偏好。在Eu阳离子和ta6八面体层内出现了~ 1%的钽空位，从电荷平衡的角度考虑，Eu（II）部分氧化为Eu（III）阳离子的比例为~ 20%。151Eu Mössbauer光谱在78 K下测得Eu(II):Eu（III）比值为69:31，前者信号线宽ofΓ= 7.6(2) mm s-1。温度相关磁化率符合居里魏斯表达式（μeff= 6.2 μBand θCW=−10 K），确定为Eu(II)/Eu（III）阳离子的混合物。发现euta4 - xo11的光学带隙为~ 1.5 eV（间接），与Na2Ta4O11的光学带隙为~ 4.1 eV相比显着红移。自旋极化电子结构计算表明，这种红移源于eu4f7态作为高能价带的加入。因此，这些结果证明了一种新的阳离子交换方法，它代表了一种有用的合成途径，可以合成具有可调磁性和光学性质的新型含Eu（II）氧化物。
Traditional synthetic efforts to prepare Eu(II)-containing oxides have principally involved the use of high temperature reactions starting from EuO or a controlled, highly-reducing, atmosphere. Conversely,chimie douceapproaches that are more amenable to the targeted syntheses of new, and potentially metastable, Eu(II)-oxides have yet to be explored. Herein, a cation-exchange route to new Eu(II)-containing oxides, e.g., EuTa4-xO11(x= 0.04), has been discovered and its structure determined by powder X-ray diffraction (Space groupP6322 (#182),a= 6.2539(2) Å; c = 12.3417(2) Å). The compound derives from the cation exchange of Na2Ta4O11, via a reaction with EuBr2at 1173 K, and replacement by half the number of divalent Eu cations. Rietveld refinements show preferential ordering of the Eu cations over one of the two possible cation sites, i.e., Wyckoff site2d(∼94%; Eu1) versus 2b(∼6%; Eu2). Total energy calculations confirm an energetic preference of the Eu cation in the 2dsite. Tantalum vacancies of ∼1% occur within the layer of Eu cations and TaO6octahedra, and ∼20% partial oxidation of Eu(II) to Eu(III) cations from charge balance considerations.151Eu Mössbauer spectroscopy measured at 78 K found a Eu(II):Eu(III) ratio of 69:31, with a relatively broad line width of the former signal ofΓ= 7.6(2) mm s–1. Also, the temperature-dependent magnetic susceptibility could be fitted to a Curie Weiss expression, giving a μeff= 6.2 μBand θCW= −10 K and confirming a mixture of Eu(II)/Eu(III) cations. The optical bandgap of EuTa4-xO11was found to be ∼1.5 eV (indirect), significantly redshifted as compared to ∼4.1 eV for Na2Ta4O11. Spin-polarized electronic structure calculations show that this redshift stems from the addition of Eu4f7states as a higher-energy valence band. Thus, these results demonstrate a new cation-exchange approach that represents a useful synthetic pathway to new Eu(II)-containing oxides for tunable magnetic and optical properties.