Synthesis of the perovskite-type oxyfluoride AgTiO2F: an approach adopting the HSAB principle
Synthesis of the perovskite-type oxyfluoride AgTiO2F: an approach adopting the HSAB principle
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钙钛矿型氟氧化物AgTiO2F的合成：采用HSAB原理的方法
DOI：
10.1039/d0dt01518k
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发表时间：
2020
影响因子：
4
通讯作者：
Ueda Koichiro
中科院分区：
文献类型：
--
作者：
Inaguma Yoshiyuki;Sugimoto Ken;Ueda Koichiro
研究了一种硬软酸碱(HSAB)原理合成氟氧化合物的方法。以Ag+离子为软酸，F-−为硬碱，合成了一种以O2-−离子为软碱，以Ti4+离子为强酸的氟氧化物AgTiO2F，它比F-−离子更软碱，比Ag+更硬。因此，在常压和高压下通过固相反应合成了钙钛矿型氟氧化物AgTiO2F，并在4 GPa1000℃下热处理30min，得到了杂质相较少的PV型相。光学二次谐波(SHG)响应的缺失和Rietveld修正的结果表明，该化合物是中心对称的，并且在空间群I4/mcm的基础上，显示出Ti(O，F)6八面体沿c轴的反相倾斜。阴离子位置上的O/F有序性尚未得到澄清。通过比较KTiO2F和NaTiO2F，从HSAB原理和PV型相形成的热力学角度讨论了PV型AgTiO2F的相稳定性。AgTiO2F为淡黄色，在可见光区的带隙能为2.8eV，这源于软阳离子Ag+与O2−之间的共价键，它是一个比F−更软的阴离子。我们认为HSAB原理可用于选择合成含氧氟化物的阳离子。
A synthetic approach for oxyfluorides involving the hard and soft acids and bases (HSAB) principle was examined. Using AgF composed of the Ag+ ion as a soft acid and F− as a hard base, we attempted to synthesize an oxyfluoride, AgTiO2F, that included the O2− ion as a softer base than the F− ion and the Ti4+ ion as a harder acid than the Ag+ ion. Consequently, a perovskite (Pv)-type oxyfluoride AgTiO2F was synthesized by a solid-state reaction under ambient pressure and under high pressure, and a heat treatment at 1000 °C for 30 min under a pressure of 4 GPa produced the Pv-type phase with minimal impurity phases. The lack of an optical second harmonic generation (SHG) response and the result of Rietveld refinement indicated that the compound is centro-symmetric and shows the anti-phase tilt of Ti(O, F)6 octahedra along the c-axis on the basis of the space group I4/mcm. O/F ordering on the anion site was not clarified. The phase stability of a Pv-type AgTiO2F is discussed in terms of the HSAB principle and the thermodynamics in the formation of the Pv-type phase by comparing KTiO2F and NaTiO2F. AgTiO2F has a light yellow color and a band gap energy of 2.8 eV in the visible region, which originates from the covalent bonding between the soft cation Ag+ and O2− as a softer anion than F−. We propose that the HSAB principle is useful for selecting a cation for the synthesis of oxyfluorides.