Li colloids created by electron-irradiation of LiF: A great wealth of properties

Like in lithium oxide, it is easy to nucleate very pure metallic lithium precipitates by electron-irradiation of lithium fluoride crystals. Irradiations performed near room temperature give metallic colloids which are characterized by electron spin resonance (ESR). The metallic character of the precipitates is demonstrated by the temperature behaviour of the ESR line intensity, which follows the temperature-independent Pauli law. A typical value for the metal concentration is about a few percent. Varying the irradiation parameters, i.e. the total fluence and/or the instantaneous flux, affects considerably the ESR properties of the colloids: first, the ESR line width changes by almost two orders of magnitude, indicating that the sizes of the precipitates strongly depend on these irradiation conditions. Second, when measuring the variation of the ESR intensity, proportional to the metal content, two very different behaviours are observed during recovery (dynamic or isochronal). When the flux is high, an intense and narrow metallic line is obtained, which disappears rapidly with annealing (300 degreesC). For lower flux, the colloids have a broader ESR signal, i.e. a much smaller size, and are not destroyed by annealing until the LiF crystal melts (870 degreesC). Li-7 NMR measurements extending earlier NMR experiments on neutron-irradiated LiF indicate that the Knight-shifted signal is split into two components with different widths. The position of the narrower component seems to correspond to big lithium particles having the features of bulk metallic lithium. The second component is likely to regroup particles of different sizes and geometry with different hyperfine interaction strength. (C) 2002 Published by Elsevier Science B.V.