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Superionic compound Li3Sc2(PO4)3: NMR spectra and nuclear magnetic relaxation

1992; Elsevier BV; Volume: 58; Issue: 3-4 Linguagem: Inglês

10.1016/0167-2738(92)90120-e

1872-7689

A. A. Vashman, I. S. Pronin, Sergei E. Sigaryov,

Solid-state spectroscopy and crystallography

The 6,7Li and 31P NMR spectra and the 7LI, 31P spin-lattice relaxation, as well as electrical conductivity and thermal properties have been studied for powder samples of the Li3Sc2(PO4)3 superionic conductor over a wide temperature range. The quadrupole splitting parameters of the 7Li NMR spectra and the 7Li spin-lattice relaxation rate, T1−1, are changed abruptly in the vicinity of phase transition at ⋍530 K. In the high-temperature range the 31P spin-lattice relaxation rate is controlled by a translation motion of lithium ions, while in the low-temperature range it is controlled by a spin diffusion to paramagnetic impurities. A “frozen” EFG model is suggested, which allows to explain a quadrupole structure observed for the 7Li NMR spectra under fast motion of lithium ions over structurally equivalent sites. The 7Li7Li dipolar relaxation mechanism at a distance close to the sum of the radii of two lithium ions is used to explain T1−1 values of 7Li. Three types of lithium ion motion are defined and the corresponding activation energy values have been determined. Anomalous temperature behavior of the 7Li NMR spectra intensity that does not follow the Curie law have been found. Lack of a qualitative agreement between the X-ray data and the parameters of the 7Li NMR spectra observed is discussed.