THE STRUCTURE OF β-LaNi5· H6 AND THE HYDROGEN OCCUPATION

There were three different versions on the space group of β-LaNi5·Hx(x6) based on the neutron diffrection measurements: P31 m, P321 and P6/mmm. The arguments were investigated by a synthetical study which combinated the proton NMR second moment and the confi-gurational entropy analyses. The statement involved: to make clear a concept of the rigid repel-lence correlation radius rc; to deduce the corelation coefficient taples for P31 m, P321 and P6/ mmm at different rc's; to propose possible statistical assumptions based on the occupation numbers provided by the neutron diffrections; to modify the formula for calculating the configura-tional entropy and to contrast the calculated values with the experimental value of configuration-al entropy; to contrast the NMR second moment calculated under the same statistical assumption with the value of the NMR experiment; to select out a appropriate version which is capable to fit all the experimental facts. Having conducted such a synthetical study, the conclusion is that the space group of β-LaNi5·H6 should be P6/mmm.