Thermal Polymorphism and Decomposition of Y(BH4)3

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• 作者：Dorthe B. Ravnsbæ ; k ; Yaroslav Filinchuk ; Radovan ern ; Morten B. Ley ; Drthe Haase ; Hans J. Jakobsen ; Jrgen Skibsted ; Torben R. Jensen
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：April 19, 2010
• 年：2010
• 卷：49
• 期：8
• 页码：3801-3809
• 全文大小：956K
• 年卷期：v.49,no.8(April 19, 2010)
• ISSN：1520-510X

文摘

The structure and thermal decomposition of Y(BH₄)₃ is studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXD), ¹¹B MAS NMR spectroscopy, and thermal analysis (thermogravimetric analysis/differential scanning calorimetry). The samples were prepared via a metathesis reaction between LiBH₄ and YCl₃ in different molar ratios mediated by ball milling. A new high temperature polymorph of Y(BH₄)₃, denoted β-Y(BH₄)₃, is discovered besides the Y(BH₄)₃ polymorph previously reported, denoted α-Y(BH₄)₃. β-Y(BH₄)₃ has a cubic crystal structure and crystallizes with the space group symmetry Pmm and a bisected a-axis, a = 5.4547(8) Å, as compared to α-Y(BH₄)₃, a = 10.7445(4) Å (Pa). β-Y(BH₄)₃ crystallizes with a regular ReO₃-type structure, hence the Y³⁺ cations form cubes with BH₄⁻ anions located on the edges. This arrangement is a regular variant of the distorted Y³⁺ cube observed in α-Y(BH₄)₃, which is similar to the high pressure phase of ReO₃. The new phase, β-Y(BH₄)₃ is formed in small amounts during ball milling; however, larger amounts are formed under moderate hydrogen pressure via a phase transition from α- to β-Y(BH₄)₃, at 180 °C. Upon further heating, β-Y(BH₄)₃ decomposes at 190 °C to YH₃, which transforms to YH₂ at 270 °C. An unidentified compound is observed in the temperature range 215−280 °C, which may be a new Y−B−H containing decomposition product. The final decomposition product is YB₄. These results show that boron remains in the solid phase when Y(BH₄)₃ decomposes in a hydrogen atmosphere and that Y(BH₄)₃ may store hydrogen reversibly.