During the reporting period, the project concentrated on working packages 1 and 2, namely:
(1) establishing synthesis routes to ternary high-pressure nitride materials, and
(2) uncovering mechanisms of nitride formation via ultrafast X-ray diffraction experiments.
A broad experimental campaign was conducted across ~15 different ternary and quatenary nitrogen-rich systems to test various synthetic strategies including:
a) Azide-mediated high-pressure oxidation,
b) Two-stage high-pressure synthesis with variation of reagents between stages,
c) Single-source precursor decomposition.
Within this working package we have produced more than 20 novel compounds and identified the most efficient routes to ternary nitride perovskites through a two-stage high-pressure synthesis. In parallel, several unexpected high-pressure reaction pathways were uncovered.
For example, reactions involving trace oxides or carbon originating from diamond anvils led to a new class of high-pressure oxides, nitridocarbonates or carbides, demonstrating that careful analysis of impurities can expand chemical discovery in extreme environments.
The goal of WP2 is to investigate the kinetics and mechanisms of high-pressure chemical reactions using time-resolved X-ray diffraction at the European X-ray Free Electron Laser (EuXFEL) facility.
We studied nitride formation in three regimes: direct metal–nitrogen reactions, decomposition of single-source precursors, and reactions of metals with solid nitrogen sources.
The Fe–N system was selected as the initial test case because both pure iron and its nitrides have been extensively studied under extreme conditions, with a wealth of experimental and theoretical data available. However, the mechanisms governing their formation remain poorly understood.
Our studies revealed, for the first time, real-time phase evolution during nitrogen uptake in Fe, via a distinct transformation pathway: Fe / N2 → Fe3N → Fe2N → B8-FeN → cubic FeN. These insights provides a foundation for future rational synthesis of nitrogen-rich nitrides under extreme conditions.
