Sulfides of U$sub 3$S$sub 5$ type formed by U and the rare earths Ln$sub 2$/ sup III/US$sub 5$ (Ln/sup III/ = La to Gd) and Ln/sup II/U$sub 2$S$sub 5$ (Ln/sup II/ = Sm/sup II and Eu/sup II/) and their solid solutions