Crafting perovskite SrTaO2N nanotubes at mild nitridation conditions: Balancing nanostructure control and phase conversion

Abstract

Obtaining phase pure and highly crystalline SrTaO2N from its oxide precursors solid–solid mixture requires very high nitridation temperatures (above 1000 °C), which promotes structural defects and sintering. To obtain free-standing SrTaO2N nanotubes (NTs) while preserving their tubular morphology, here we developed a methodology using an intermediate hydrothermal process before nitridation using Ta2O5 or Ta3N5 nanotubes as precursors. The key to obtain SrTaO2N NTs lies in the formation of hydrated Sr-Ta oxide phase obtained through intermediate hydrothermal process, thereby, phase pure SrTaO2N NTs were formed at 850 °C for 10 h for both Ta precursors. Amorphous nature of Ta2O5 NTs presented better reaction selectivity for the formation of SrTaO2N NTs compared to Ta3N5. To preserve the nanotubular morphology, prolonged nitridation is favorable, in contrast to increasing temperature that promotes sintering. This work emphasizes on the importance of an intermediate hydrothermal process before nitridation for Sr-Ta interdiffusion and a balanced trade-off between nitridation time and temperature to control phase and morphology of SrTaO2N NTs.