Environmental evaluation of oxynitride synthesis pathways using Life Cycle Assessment

(Thermal) ammonolysis (A) and urea-based nitridation (U) remain the most established oxynitride synthesis routes, with U increasingly promoted as a more sustainable alternative. However, there is no quantitative environmental evaluation to verify this yet. A recently proposed lower-partial-pressure-ammonia route (AN) might also have lower environmental impact, and microwave-induced-plasma assisted ammonolysis (P) has emerged as a promising approach that enables the measurement of transport properties in dense oxynitrides, while lowering overall resource consumption. In this study, a comparative Life Cycle Assessment (LCA) of these four synthesis routes was performed using LaTiO 2 N as a model system. X-ray diffraction and hot gas extraction analysis show that route A achieves the highest phase purity, whereas all other routes show traces of unreacted precursor oxide. The AN and U routes additionally show evidence of TiN and La 2 O 3 formation. Route P results currently in the lowest phase purity, showing the need for future process condition adjustments. Nevertheless, electrical conductivity (210.7 S/m) and Seebeck coefficient (−128.8 μV/K) at T = 343 K could be measured for the P-derived sample, demonstrating its potential for transport property characterisation of oxynitride pellets. The LCA focused on six impact categories: climate change, non-renewable energy use, acidification, freshwater eutrophication, carcinogenic human toxicity, and material/mineral resource depletion. Synthesis A consistently exhibited the highest environmental impact, followed by AN, U, and P. These findings provide the first quantitative comparison of environmental impacts across major oxynitride synthesis routes and highlight the potential of route P as the lowest-impact alternative once phase purity challenges are addressed. • First quantitative Life Cycle Assessment comparing four oxynitride synthesis routes • Classical ammonolysis shows highest phase purity but highest environmental impact • Plasma route has lowest environmental impact but needs further process optimisation • Plasma-assisted synthesis directs towards bulk LaTiO 2 N for transport measurements