The family of nitrides of group IV is mostly known due to the prediction [1] (followed by numerous experimental studies) of the shortest covalent bond in C₃N₄. The members of this family crystallise with several structures at ambient pressure and the spinel and olivine type phases at high pressures, and amorphous phase at the highest pressures. In this study the pressure behaviour of two polymorphs of a representative of this family, α- and β-Ge₃N₄ is studied.

Ge₃N₄ is a prospective material for application in photodiodes, amplifiers, optic fibres, protective coatings, it has been considered for applications as metal-insulator-semiconductor field effect transistors (MIS FET), as a possible negative electrode material for Li-ion batteries, and photocatalysts. The structure of basic polymorphs is understood since the work of Ruddlesden and Popper [2] who have confirmed that the hexagonal (P6₃/m) β phase is of reduced phenacite type and the (also hexagonal, P3₁c) α phase is structurally a closely related one.

The studied sample (ALDRICH) was a mixture of α and β polymorphs of Ge₃N₄ and contained minor amounts of germanium and germanium oxide. The high-pressure study was performed at the MAX80 diffraction press, F2.1 beamline (Hasylab, DESY). NaCl was used as a pressure standard. The experiments were performed using the energy-dispersive method at diffraction angle of 4.521º. For determination of lattice parameters of the component phases the Le Bail method was chosen. The calculations were performed using the Fullprof 2k (v. 2.70) program. The obtained bulk moduli will be discussed and compared to those reported for all Ge₃N₄ phases.

[1] A.Y. Liu and M.L. Cohen, Prediction of new low compressibility solids.Science 245 (1989), p. 841.

[2] S.N. Ruddlesden, P. Popper, “On the crystal structures of the nitrides of silicon and germanium,” Acta Cryst.11 (1958) 465-468.