Vibrational Spectroscopic Study of Subtle Phase Transitions in Alkali Borohydrides: Comparison with First-Principles Calculations

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• 作者：Nina Verdal ; Terrence J. Udovic ; Wei Zhou ; John J. Rush ; Daniel J. De Vries ; Michael R. Hartman
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：January 17, 2013
• 年：2013
• 卷：117
• 期：2
• 页码：876-883
• 全文大小：418K
• 年卷期：v.117,no.2(January 17, 2013)
• ISSN：1932-7455

文摘

Neutron vibrational spectra have been measured for the alkali borohydrides KBH₄, RbBH₄, and CsBH₄. The BH₄^{鈥?/sup> torsional band for each compound changes noticeably across the corresponding low-temperature phase transition previously identified using thermodynamic (NaBH₄, KBH₄, RbBH₄, and CsBH₄) and crystallographic (NaBH₄ and KBH₄) techniques. Previous neutron diffraction measurements show that the transitions for both NaBH₄ and KBH₄ are order鈥揹isorder transitions involving the relative orientations of the BH₄鈥?/sup> anions. However, diffraction measurements for both RbBH₄ and CsBH₄ fail to unequivocally identify long-range-ordered phases below the transitions. The present measurements of BH₄鈥?/sup> torsional as well as translational optic bands across the transitions, corroborated by first-principles phonon calculations, suggest that the subtle RbBH₄ and CsBH₄ transitions are indeed analogous to those observed for NaBH₄ and KBH₄ but of shorter range.}