LI-7 NMR AND IONIC-CONDUCTIVITY STUDIES OF LANTHANUM LITHIUM TITANATEELECTROLYTES

Lanthanum Lithium titanate compounds belonging to the solid solution ( La(2/3-x)Li(3x)square(1/3-2x))TiO3 have been investigated by powder X- ray diffraction analysis, electrical conductivity and Li-7 nuclear mag netic resonance (NMR) spectroscopy. These materials are purely ionic c onductors with a maximum ionic conductivity of 3.9 x 10(-4) S cm(-1) a t room temperature found for x = 0.08. Li-7 NMR and room temperature c onductivity measurements indicate that there are two kinds of lithium ions with different environments and different mobilities present in t hese materials, This result is in agreement with the crystal structure established by powder X-ray diffraction analysis. Different values of the activation energy have been obtained from spin-lattice relaxation time T-1 measurements at low temperatures and from conductivity measu rements (0.12 eV and 0.37 eV respectively). Moreover, the characterist ic vibration frequency for the ionic hopping motion obtained from T-1 measurements (nu(0) approximate to 10(11) Hz) is an order of magnitude lower than that of typical phonon frequency, namely, 10(12)-10(13) Hz . These results may suggest that the motion of the mobile lithium ions is highly correlated and/or that the dimensionality of the motion has a 2D character.