The Raman spectra of the hexagonal and cubic (spinel) forms of Ge 3 N 4 : an experimental and theoretical study

The Raman spectra of the hexagonal (β) and cubic spinel (γ) forms of Ge3N4, newly obtained by high-pressure synthesis, have been measured and are compared with zone-center phonon frequencies calculated using first principles methods in a plane wave pseudopotential local density approximation. The observed and calculated phonon frequencies are in excellent agreement and we use the calculated values to perform mode assignment for both the phases. Both phases show all the expected Raman active modes.