Phase behaviour in the LiBH4-LiBr system and structure of the anion-stabilised fast ionic, high temperature phase

Irene Cascallana-Matias; David A. Keen; Edmund J. Cussen; Duncan H. Gregory

doi:10.1021/acs.chemmater.5b03642

Phase behaviour in the LiBH4-LiBr system and structure of the anion-stabilised fast ionic, high temperature phase

Irene Cascallana-Matias, David A. Keen, Edmund J. Cussen, Duncan H. Gregory

Pure And Applied Chemistry

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Abstract

The fast ionic, high temperature (HT) phase of LiBH4 can be stabilised by Br¯ substitution. Lithium borohydride bromide compounds, Li(BH4)1-xBrx have been synthesized mechanochemically, with and without thermal treatment and the resulting phase behaviour determined as a function of composition. Single phase materials exist for 0.29 ≤ x ≤ 0.50 with conductivity two orders of magnitude higher than LiBH4 at 313 K. Powder neutron diffraction has been used to resolve the details of the crystal structure of one such compound. These demonstrate that 7Li(11BD4)2/3Br1/3 retains the HT structure (hexagonal space group P63mc, a ≈ 4.2 Å, c ≈ 6.7 Å) from 293-573 K. The borohydride bromide exhibits considerable static and dynamic disorder, the latter invoking complex rotational motion of the (BH4)¯ anions.

Original language	English
Pages (from-to)	7780-7787
Number of pages	8
Journal	Chemistry of Materials
Volume	27
Issue number	22
Early online date	26 Oct 2015
DOIs	https://doi.org/10.1021/acs.chemmater.5b03642
Publication status	E-pub ahead of print - 26 Oct 2015

Keywords

phase behavior
composition
crystal structure

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http://pubs.acs.org/doi/10.1021/acs.chemmater.5b03642

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title = "Phase behaviour in the LiBH4-LiBr system and structure of the anion-stabilised fast ionic, high temperature phase",

abstract = "The fast ionic, high temperature (HT) phase of LiBH4 can be stabilised by Br¯ substitution. Lithium borohydride bromide compounds, Li(BH4)1-xBrx have been synthesized mechanochemically, with and without thermal treatment and the resulting phase behaviour determined as a function of composition. Single phase materials exist for 0.29 ≤ x ≤ 0.50 with conductivity two orders of magnitude higher than LiBH4 at 313 K. Powder neutron diffraction has been used to resolve the details of the crystal structure of one such compound. These demonstrate that 7Li(11BD4)2/3Br1/3 retains the HT structure (hexagonal space group P63mc, a ≈ 4.2 {\AA}, c ≈ 6.7 {\AA}) from 293-573 K. The borohydride bromide exhibits considerable static and dynamic disorder, the latter invoking complex rotational motion of the (BH4)¯ anions.",

keywords = "phase behavior, composition, crystal structure",

author = "Irene Cascallana-Matias and Keen, {David A.} and Cussen, {Edmund J.} and Gregory, {Duncan H.}",

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T1 - Phase behaviour in the LiBH4-LiBr system and structure of the anion-stabilised fast ionic, high temperature phase

AU - Cascallana-Matias, Irene

AU - Keen, David A.

AU - Cussen, Edmund J.

AU - Gregory, Duncan H.

PY - 2015/10/26

Y1 - 2015/10/26

N2 - The fast ionic, high temperature (HT) phase of LiBH4 can be stabilised by Br¯ substitution. Lithium borohydride bromide compounds, Li(BH4)1-xBrx have been synthesized mechanochemically, with and without thermal treatment and the resulting phase behaviour determined as a function of composition. Single phase materials exist for 0.29 ≤ x ≤ 0.50 with conductivity two orders of magnitude higher than LiBH4 at 313 K. Powder neutron diffraction has been used to resolve the details of the crystal structure of one such compound. These demonstrate that 7Li(11BD4)2/3Br1/3 retains the HT structure (hexagonal space group P63mc, a ≈ 4.2 Å, c ≈ 6.7 Å) from 293-573 K. The borohydride bromide exhibits considerable static and dynamic disorder, the latter invoking complex rotational motion of the (BH4)¯ anions.

AB - The fast ionic, high temperature (HT) phase of LiBH4 can be stabilised by Br¯ substitution. Lithium borohydride bromide compounds, Li(BH4)1-xBrx have been synthesized mechanochemically, with and without thermal treatment and the resulting phase behaviour determined as a function of composition. Single phase materials exist for 0.29 ≤ x ≤ 0.50 with conductivity two orders of magnitude higher than LiBH4 at 313 K. Powder neutron diffraction has been used to resolve the details of the crystal structure of one such compound. These demonstrate that 7Li(11BD4)2/3Br1/3 retains the HT structure (hexagonal space group P63mc, a ≈ 4.2 Å, c ≈ 6.7 Å) from 293-573 K. The borohydride bromide exhibits considerable static and dynamic disorder, the latter invoking complex rotational motion of the (BH4)¯ anions.

KW - phase behavior

KW - composition

KW - crystal structure

UR - http://pubs.acs.org/doi/10.1021/acs.chemmater.5b03642

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DO - 10.1021/acs.chemmater.5b03642

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JO - Chemistry of Materials

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