Ionic conductivity in three crystalline phases of LiBH₄ under pressure

Abstract

The AC electrical conductivity of LiBH₄ was investigated below 2 GPa between 1 Hz and 1.6 MHz. The high-temperature phase has an ionic conductivity of up to 0.01 S cm⁻¹, while the low-temperature phases have conductivities two orders of magnitude lower. All phases show an Arrhenius behaviour with activation energies E _a between 0.5 and 0.7 eV, in good agreement with earlier data except for phase III, which is found to have the highest activation energy of the phases studied. The high-temperature phase has a minimum in E _a near 1 GPa, close to the triple point, correlated with a sudden change in activation volume. These features may indicate an isostructural phase transition. The conductivities of the ambient temperature phases increase temporarily by an order of magnitude after transitions between these phases, probably due to new diffusion channels via structural defects. The phase diagram agrees well with earlier results.

Keywords:

• ionic conductivity
• phase transition
• phase diagram
• dielectric measurements
• complex hydride

Acknowledgements

The work on ionic conduction under high pressure was supported by the National Natural Science Foundation of China (grant No. 11104105). We also acknowledge support from the Swedish Research Council for research cooperation and exchange between Sweden and China through grant No. 348-2008-6081.

Notes

^†This paper was presented at the L^th European High Pressure Research Group (EHPRG 50) Meeting at Thessaloniki (Greece), 16–21 September 2012.