[en] The thermionic emission properties of polycrystalline NdB₆ have been determined as a function of surface composition throughout its single-phase region. the equation log I = 1.673-15637/T+2 log T-0.0042 T/]exp[0.07X/(X-6)]+1] describes the relationship between emitted current flux I (A/cm²), temperature T (K), and surface composition X (B/Nd) between 1200 and 1600 K. The effective work function at 1500 K is 3.22 eV for NdB/sub 6.0/ and 4.04 eV for NdB/sub 8.0/. Previous measurements of the LaB₆ phase were fit by the equation log I = 2.533-15330/T+2 log T-0.5T exp[-0.11X/(X-6)]. This information was used to determine the density of states for the two hexaborides and make predictions about the behavior of various ternary systems