Prediction of Novel Tin Nitride Sn<i>_x</i>N<i>_y</i> Phases Under Pressure

Abstract

In this publication, ab initio evolutionary simulations are employed to predict stable and metastable structures and compositions in the binary Sn–N diagram under pressure. We predict the emergence of several (meta)stable SnxNy phases for 11 different compositions upon compression ranging from Sn:N = 2:1, 3:2, 1:1, 3:4, 1:2, 1:3, 1:4, 1:5, 1:6, 1:8, and 1:20. Eleven stable phases and 14 metastable phases are characterized, and their atomic and electronic structures are discussed on the basis of advanced orbital and electron density analyses, as well as by simple models (such as Zintl–Klemm, VSEPR, etc.). These models are noteworthily applied to account for the pressure-induced gap increase in Sn3N4 under pressure. Beyond the theoretical prediction, experimental viability of these phases is also evaluated through a careful analysis of their dynamic and thermal stabilities. This leads to the identification of three possible quenchable nitrogen-rich phases, Pa3̅ SnN2, Imm2 SnN3, and P1̅ SnN4, whose potential as a high energy-density material (HEDM) is finally estimated. Our crystal structure prediction searches also lead to the identification of the tin tetrapentazolate Sn(N5)4 compound, which is thermodynamically stable in the 42–62 GPa pressure range (I4̅ phase), and metastable but thermally stable up to 600 K at ambient pressure (P1̅ phase). Sn(N5)4 is the richest polynitrogen-tin-predicted HEDM in the studied binary phase Sn–N diagrams at 0–200 GPa.