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Crystal structures and phase transformations in Ca(BH4)2

✍ Scribed by Yaroslav Filinchuk; Ewa Rönnebro; Dhanesh Chandra

Publisher
Elsevier Science
Year
2009
Tongue
English
Weight
522 KB
Volume
57
Category
Article
ISSN
1359-6454

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✦ Synopsis

Crystal structures of three polymorphs of Ca(BH 4 ) 2 , and related phase transitions, have been identified. Removal of solvent from Ca(BH 4 ) 2 Á2THF results in various mixtures of a-and b-polymorphs of Ca(BH 4 ) 2 . These mixtures were studied by in situ synchrotron powder diffraction in argon atmosphere. The a-Ca(BH 4 ) 2 structure crystallizes in the noncentrosymmetric space group F2dd, and contains an ordered BH À 4 anion. Upon increasing the temperature, the cell parameters a and c of the a-phase approach each other, and at $495 K, a second order a ? a 0 transition takes place resulting in a tetragonal a 0 -phase of space group I-42d, a supergroup of F2dd. The structure of b-Ca(BH 4 ) 2 , which is 3.7-5.6% denser depending on temperature, was described in space group P-4. Crystal structures, variation of the cell parameters, and weight fraction are reported for the three Ca(BH 4 ) 2 phases as a function of temperature.

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