Comparative aspects of the high-pressure behaviour of lanthanide and actinide compounds

All lanthanide and actinide metals which are available as solids in sufficient quantity have undergone structural investigation at elevated pressure and can be systematically compared. Systematics is much less complete for the pressure behaviour of the compounds. We shall see that sufficient information is only available for some of the 1:1 compounds with elements from the fifth and sixth main groups of the periodic table, the monopnictides and the monochalcogenides. This is in part due to radioactivity and scarcity of some of the elements concerned, but also to lack of pressure studies on compounds of some of the more easily accessible lanthanides. The available information on high-pressure structures, transition pressures and compressibilities is presented in the form of graphs and tables. The paper centres on a comparison of the CeX compounds with ThX, on one hand, and with PuX, on the other, where the largest amount of data has been obtained.