One of several compounds that have been reported, including the following: NbB₂; melting point, 3,050 degrees C; sp gr, 7.0; thermal expansion, 5.9 X 10_-6parallel to a and 8.4 X 10_-6parallel to c; NbB, melting point, 2,300 degrees C; sp gr, 7.6; Nb₃B₄melts incongruently at 2,700 degrees C; sp gr, 7.3.