Russian Journal of Physical Chemistry B

, Volume 1, Issue 6, pp 653–660 | Cite as

Hindered rotation and phase transition in sodium gallohydride according to the NMR data

Thermodynamics and Phase Transitions


Polycrystalline sodium gallohydrides with different hydrogen isotope compositions, NaGaH4, NaGaH2.56D1.44, and NaGaD4, were studied over the temperature range 100–375 K by the 2H, 23Na, and 69,71Ga NMR methods in magnetic fields of 1.4, 1.88, and 7.04 T. The data on spin-lattice deuteron relaxation T 1(2H) were used to determine the activation energy (∼35 kJ/mol) of anion rotational motions and quadrupole coupling constant (QCC) χ Q 0 (2H) = 90 kHz for the rigid lattice. To within measurement errors, the activation energy and 2H QCC were independent of the isotope composition. The low-temperature 2H NMR line was a doublet with 2H QCC χ(2H) = 70 kHz. The difference between χ 0 and χ(T) was interpreted in terms of the librational averaging of the electric field gradient (EFG) according to the Bayer equation. The frequency of librations at 113 K was estimated (31 cm−1). The shape of the 69,71Ga NMR line was indicative of second-order quadrupole interaction with a nonzero asymmetry parameter η of the EFG tensor. Temperature variations in the QCC and η parameter at gallium were considered using the distorted tetrahedron model. The η value changed from 0.65 to zero (axial EFG tensor symmetry characteristic of tetragonal lattices) over the temperature range 140–295 K and again increased to 0.3 at 300–365 K, which was evidence of a change in the orientation of the distorted tetrahedral anion in the lattice. Changes in the asymmetry parameter were in agreement with the phase transition in sodium gallohydride recorded as a heat capacity jump.


Electric Field Gradient Asymmetry Parameter Quadrupole Coupling Constant Hydrogen Isotope Composition Electric Field Gradient Tensor 
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Copyright information

© Pleiades Publishing, Ltd. 2007

Authors and Affiliations

  • V. P. Tarasov
    • 1
  • G. A. Kirakosyan
    • 1
  • S. I. Bakum
    • 1
  1. 1.Kurnakov Institute of General and Inorganic ChemistryRussian Academy of SciencesMoscowRussia

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