Vibrational properties of β-KSiH₃ and β-RbSiH₃: a combined Raman and inelastic neutron scattering study

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• 作者：Janos Mink ; Yuan-Chih Lin ; Maths Karlsson ; Carin Ö ; sterberg ; Terrence J. Udovic ; Henrik Fahlquist and Ulrich Hä ; ussermann
• 刊名：Journal of Raman Spectroscopy
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：48
• 期：2
• 页码：284-291
• 全文大小：1872K
• ISSN：1097-4555

文摘

The hydrogen storage materials ASiH₃ (A = K and Rb) represent complex metal hydrides built from metal cations and pyramidal SiH₃⁻ ions. At room temperature, SiH₃⁻ moieties are randomly oriented because of dynamical disorder (α-modifications). At temperatures below 200 K, ASiH₃ exist as ordered low-temperature (β) modifications. The vibrational properties of β-ASiH₃ were characterized by a combination of Raman spectroscopy and inelastic neutron scattering. Internal modes of SiH₃⁻ are observed in the spectral range 1800–1900 cm⁻¹ (stretching modes) and 890–1000 cm⁻¹ (bending modes). External modes are observed below 500 cm⁻¹. Specifically, SiH₃⁻ librations are between 300–450 cm⁻¹ and 270–400 cm⁻¹ for A = K and Rb, respectively, SiH₃⁻ translations are between 95 and 160 cm⁻¹, K⁺ translations are in the range 60–100 cm⁻¹ and Rb⁺ translations in the range 50–70 cm⁻¹. The red-shift of libration modes for A = Rb is associated with a 15–30% reduction of the libration force constants of SiH₃⁻ ions in β-RbSiH₃. This correlates with a lower temperature for the β–α order–disorder phase transition (278 vs 298 K). Libration modes become significantly anharmonic with increasing temperature but are maintained up to at least 200 K. The vibrational properties of ASiH₃ compare well to those of alkali metal borohydrides ABH₄ (A = Na–Cs). Copyright