Determination of the structure of boron subphosphide by P K
X-ray fluorescence spectra

High-resolution P Kbeta X-ray fluorescence (XRF) spectra of boron subphosphide have been measured and three peaks are distinguished in the broad feature around 2135 eV. The P Kbeta fluorescence spectra of four kinds of model clusters P2, PB3, P2B6, and P2B7 are calculated, and it is found that only the spectra of P2B6 cluster with appropriate parameters best represents the experimental one. Therefore the composition of boron subphosphide is determined to be B12P2 (which corresponds to the P2B6 cluster), not B13P2. The two phosphorus atoms lie along the interstice among boron icosahedra, and each is bonded to the other phosphorus atom and the three boron atoms, forms a distorted tetrahedron.