Positron annihilation in lanthanum hydrides

The measurements of the Angular Correlation of Positron Annihilation Radiation have been performed for pure lanthanum and for 12 samples of lanthanum hydrides LaHx with hydrogen concentrations ranging from x = 2 to x = 3. The evaluation of the data has shown that the values of some annihilation parameters vary strongly with the hydrogen concentration for x > or approx. 2.7. The results can be explained in terms of the electronic structure of the system with an anionic character of the dihydride and defect band formation in hydrides close to the LaH3 composition. (orig.)