Crystal structures and electronic properties of Sn 3 N 4 polymorphs synthesized via high-pressure nitridation of tin

The crystal structures, compression behaviors, and electronic properties of Sn 3 N 4 polymorphs were investigated by means of high-pressure in situ measurements, transmission electron microscopy, and DFT ab initio calculations. The direct nitridation of tin above a pressure of 29.5 GPa by using a laser-heated diamond anvil cell resulted in the synthesis of highly crystalline monoclinic Sn 3 N 4 which so far is consistent with the reported one. On the other hand, it was newly discovered that the monoclinic Sn 3 N 4 undergoes phase transition twice along with decompression at ambient pressure. Advanced synchrotron X-ray powder diffraction measurements and TEM analyses on the recovered sample demonstrate that the newly recovered Sn 3 N 4 crystallizes with orthorhombic symmetry and consists of irregularly shaped SnN 5 and SnN 6 . DFT ab initio calculations reveal that this newly recovered orthorhombic Sn 3 N 4 is an indirect band gap semiconductor having a narrower electronic energy gap than that of cubic spinel-type Sn 3 N 4 . The present results demonstrate that high-pressure nitridation is a powerful method to synthesize highly crystalline Sn 3 N 4 polymorphs and reveal the new crystal chemistry of group IVA nitrides with respect to the variety of crystal structures and electronic properties.