The present invention relates to novel alkylhalosilylaminoboranes, in particular alkylchlorosilylaminoboranes, which make it possible to adjust the viscosity of polyborosilazane compounds by varying the number of reactive centers, to novel borosilazane compounds, to novel oligoborosilazane or polyborosilazane compounds which have the structural feature R.sup.1--Si--NH--B--R.sup.2, where R.sup.1 or R.sup.2 or both is/are a hydrocarbon radical having from 1 to 20 carbon atoms, in particular an alkyl, phenyl or vinyl group, to silicon borocarbonitride ceramic powder, to ceramic material based on SiC, SiN and BN and to processes for producing each of these and to the use of the polyborosilazanes and the ceramic materials.