Phase transformation of germanium nitride (Ge3N4) under shock wave compression

The phase transformation behavior of hexagonal germanium nitride, including both alpha- and beta -Ge3N4, has been studied under shock wave compression. The shock compressed quenched samples indicate phase transformation from hexagonal into a cubic spinel structure (gamma -Ge3N4). This transformation is completed with increasing shock pressure up to 40-46 GPa (temperature of 1300-1500 K). The lattice constant of gamma -Ge3N4 is measured to be 0.820 63 +/-0.000 19 nm, and the crystal density 6.581 g/cm3, by the powder x-ray diffraction. The stability of gamma -Ge3N4 also has been investigated under shock wave compression. It is found that the spinel structure is very stable, and up to at least 63 GPa (temperature of similar to 1700 K) there is no indication of the formation of a postspinel phase. (C) 2001 American Institute of Physics.