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 o f 1300-1500 K). The lattice constant of gamma -Ge3N4 is measured to be 0.82 0 63 +/-0.000 19 nm, and the crystal density 6.581 g/cm3, by the powder x-r ay diffraction. The stability of gamma -Ge3N4 also has been investigated un der shock wave compression. It is found that the spinel structure is very s table, and up to at least 63 GPa (temperature of similar to 1700 K) there i s no indication of the formation of a postspinel phase. (C) 2001 American I nstitute of Physics.