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Title: Tracking the Progression of Anion Reorientational Behavior between α-Phase and β-Phase Alkali-Metal Silanides, MSiH3, by Quasielastic Neutron Scattering

Abstract

Quasielastic neutron scattering (QENS) measurements over a wide range of energy resolutions were used to probe the reorientational behavior of the pyramidal SiH3- anions in the monoalkali silanides (MSiH3, where M = K, Rb, and Cs) within the low-temperature ordered β-phases, and for CsSiH3, the high-temperature disordered α-phase and intervening hysteretic transition region. Maximum jump frequencies of the β-phase anions near the β-α transitions range from around 109 s-1 for β-KSiH3 to 1010 s-1 and higher for β-RbSiH3 and β-CsSiH3. The β-phase anions undergo uniaxial 3-fold rotational jumps around the anion quasi-C3 symmetry axis. CsSiH3 was the focus of further studies to map out the evolving anion dynamical behavior at temperatures above the β-phase region. As in α-KSiH3 and α-RbSiH3, the highly mobile anions (with reorientational jump frequencies approaching and exceeding 1012 s-1) in the disordered α-CsSiH3 are all adequately modeled by H jumps between 24 different locations distributed radially around the anion center of gravity, although even higher anion reorientational disorder cannot be ruled out. QENS data for CsSiH3 in the transition region between the α- and β-phases corroborated the presence of dynamically distinct intermediate (i-) phase. The SiH3- anions within i-phase appear to undergo uniaxial small-angular-jump reorientations thatmore » are more akin to the lower-dimensional β-phase anion motions rather than to the multidimensional α-phase anion motions. Moreover, they possess orientational mobilities that are an order-of-magnitude lower than those for α-phase anions but also an order-of-magnitude higher than those for β-phase anions. Combined QENS and neutron powder diffraction results strongly suggest that this i-phase is associated chiefly with the more short-range-ordered, nanocrystalline portions (invisible to diffraction) that appear to dominate the CsSiH3.« less

Authors:
 [1];  [2];  [2];  [3];  [4];  [5];  [3]
  1. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Univ. of Picardie Jules Verne (France)
  3. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  4. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Univ. of Maryland, College Park, MD (United States); Carnegie Inst. of Washington, Washington, DC (United States)
  5. Russian Academy of Sciences (RAS), Ekaterinburg (Russian Federation). Ural Branch
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1482794
Report Number(s):
NREL/JA-5900-72808
Journal ID: ISSN 1932-7447
Grant/Contract Number:  
AC36-08GO28308
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 122; Journal Issue: 42; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; diffraction; nanocrystals; negative ions; neutron scattering; temperature

Citation Formats

Dimitrievska, Mirjana, Chotard, Jean-Noël, Janot, Raphaël, Faraone, Antonio, Tang, Wan Si, Skripov, Alexander V., and Udovic, Terrence J. Tracking the Progression of Anion Reorientational Behavior between α-Phase and β-Phase Alkali-Metal Silanides, MSiH3, by Quasielastic Neutron Scattering. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.8b08257.
Dimitrievska, Mirjana, Chotard, Jean-Noël, Janot, Raphaël, Faraone, Antonio, Tang, Wan Si, Skripov, Alexander V., & Udovic, Terrence J. Tracking the Progression of Anion Reorientational Behavior between α-Phase and β-Phase Alkali-Metal Silanides, MSiH3, by Quasielastic Neutron Scattering. United States. doi:https://doi.org/10.1021/acs.jpcc.8b08257
Dimitrievska, Mirjana, Chotard, Jean-Noël, Janot, Raphaël, Faraone, Antonio, Tang, Wan Si, Skripov, Alexander V., and Udovic, Terrence J. Mon . "Tracking the Progression of Anion Reorientational Behavior between α-Phase and β-Phase Alkali-Metal Silanides, MSiH3, by Quasielastic Neutron Scattering". United States. doi:https://doi.org/10.1021/acs.jpcc.8b08257. https://www.osti.gov/servlets/purl/1482794.
@article{osti_1482794,
title = {Tracking the Progression of Anion Reorientational Behavior between α-Phase and β-Phase Alkali-Metal Silanides, MSiH3, by Quasielastic Neutron Scattering},
author = {Dimitrievska, Mirjana and Chotard, Jean-Noël and Janot, Raphaël and Faraone, Antonio and Tang, Wan Si and Skripov, Alexander V. and Udovic, Terrence J.},
abstractNote = {Quasielastic neutron scattering (QENS) measurements over a wide range of energy resolutions were used to probe the reorientational behavior of the pyramidal SiH3- anions in the monoalkali silanides (MSiH3, where M = K, Rb, and Cs) within the low-temperature ordered β-phases, and for CsSiH3, the high-temperature disordered α-phase and intervening hysteretic transition region. Maximum jump frequencies of the β-phase anions near the β-α transitions range from around 109 s-1 for β-KSiH3 to 1010 s-1 and higher for β-RbSiH3 and β-CsSiH3. The β-phase anions undergo uniaxial 3-fold rotational jumps around the anion quasi-C3 symmetry axis. CsSiH3 was the focus of further studies to map out the evolving anion dynamical behavior at temperatures above the β-phase region. As in α-KSiH3 and α-RbSiH3, the highly mobile anions (with reorientational jump frequencies approaching and exceeding 1012 s-1) in the disordered α-CsSiH3 are all adequately modeled by H jumps between 24 different locations distributed radially around the anion center of gravity, although even higher anion reorientational disorder cannot be ruled out. QENS data for CsSiH3 in the transition region between the α- and β-phases corroborated the presence of dynamically distinct intermediate (i-) phase. The SiH3- anions within i-phase appear to undergo uniaxial small-angular-jump reorientations that are more akin to the lower-dimensional β-phase anion motions rather than to the multidimensional α-phase anion motions. Moreover, they possess orientational mobilities that are an order-of-magnitude lower than those for α-phase anions but also an order-of-magnitude higher than those for β-phase anions. Combined QENS and neutron powder diffraction results strongly suggest that this i-phase is associated chiefly with the more short-range-ordered, nanocrystalline portions (invisible to diffraction) that appear to dominate the CsSiH3.},
doi = {10.1021/acs.jpcc.8b08257},
journal = {Journal of Physical Chemistry. C},
number = 42,
volume = 122,
place = {United States},
year = {2018},
month = {10}
}

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Figures / Tables:

Figure 1 Figure 1: Structural differences between the ordered $β$-MSiH3 and disordered $α$-MSiH3 (M = K, Rb, Cs) phases showing the respective near-neighbor cation environments (7-coordination for the former and 6-coordination for the latter). M+ alkali metal cations are denoted by green spheres, whereas the pyramidal SiH3- anions are denoted by bluemore » Si spheres and white H spheres. N.B., although one specific anion orientation is highlighted in α-MSiH3, the multiple H atoms distributed radially around the Si atom represent all of the possible H positions associated with the orientationally disordered SiH3- anions in this structure. N.B., $i$-MSiH3 is meant to be a general term to denote the possible formation of ‘intermediate” phases in the transition regions with intermediate SiH3- anion orientational mobilities between those for the $β$-MSiH3 and α-MSiH3 phases.« less

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