Elastic constants of NaBH₄ and LiBH₄: Instability of β-LiBH₄

¹  Institute of Modern Physics, Northwest University - Xian 710069, PRC
²  Department of Physics, Fudan University - Shanghai 200433, PRC
³  Department of Electronic Science, Northwest University - Xian 710069, PRC

Corresponding author: jiangzy@nwu.edu.cn

Received: 16 September 2009
Accepted: 19 October 2009

Abstract

The structural properties and mechanical stabilities of α-NaBH₄ and -LiBH₄ have been investigated using first-principles calculations. Elastic constants of α-NaBH₄ and -LiBH₄ are calculated from the second derivative of total energy as a function of strain. The calculated structural parameters and elastic constants of α-NaBH₄ are in good agreement with the available experimental data. Our calculations show that -LiBH₄ with space group is unstable under the distortions (0, 0, 0, , , 0) and (0, 0, 0, 0, 0, ) and these distortions lead to a Martensitic transformation into Cc and structures, respectively. Thermodynamically, -LiBH₄ with space group is more likely changed into a structure, which is consistent with experimental results.