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| - Nuclear Magnetic Resonance Study of the Rotational Motion and the Phase Transition in LiBH4
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| Abstract
| - To study the rotational motion of BH4 tetrahedra in LiBH4, we have measured the 1H and 11B nuclear magnetic resonance spectra and spin−lattice relaxation rates in this compound over wide ranges of temperature (92−424 K) and resonance frequency (14−90 MHz for 1H and 14−28 MHz for 11B). In the low-temperature (orthorhombic) phase of LiBH4, our spin−lattice relaxation results are consistent with a coexistence of two types of the rotational motion of BH4 tetrahedra with the activation energies of 0.182 ± 0.003 eV and 0.251 ± 0.004 eV. For both types of motions, the jump rates of the reorientations reach the values of the order of 1011 s−1 near the upper limit of the temperature range of the orthorhombic phase stability (T0 ≈ 381 K). In the high-temperature (hexagonal) phase, both the 1H and 11B spin−lattice relaxation rates are governed by an additional low-frequency fluctuation process (with the characteristic rate of the order of 107 s−1 just above T0) due to the translational diffusion of Li ions.
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| - Rotational Motion and Phase Transition in LiBH4
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