In situ study of the high pressure high-temperature stability field of TaN and of the compressibilities of ϑ-TaN and TaON

Abstract

The high pressure high-temperature stability of tantalum mononitrides was investigated at 8–23.5 GPa and 1400–3500 K by in situ powder synchrotron X-ray diffraction using the laser-heated diamond anvil cell and ϵ-TaN as starting material. The transformation from ϵ-TaN to ϑ-TaN was observed and ϑ-TaN was confirmed as the stable high-(p, T) tantalum mononitride. At temperatures above 3000 K at 16–23.5 GPa, the formation of a novel quenchable high pressure high-temperature phase was observed. Under nitrogen excess ϵ-TaN reacted with nitrogen to the high-(p, T) phase η-Ta₂N₃ as the main stable phase at 8–13 GPa and about 2000 K. This behaviour is similar to the reaction of pure Ta with nitrogen at high-(p, T) conditions. In addition, we have determined the bulk moduli of ϑ-TaN (B=360(15) GPa), which is less compressible than ϵ-TaN and η-Ta₂N₃, and of TaON (B=267(8) GPa).

Keywords:

• high pressure
• tantalum nitride
• tantalum oxynitride
• X-ray diffraction
• laser-heated diamond anvil cell
• phase stability

Acknowledgements

Financial support from the DFG, Germany, within SPP1236 (Projects FR-2491/2-1, WI-1232/26-1), the BMBF, Germany (Projects 05KS7RF1 and 05K10RFA), and HASYLAB, DESY, Germany is gratefully acknowledged. Portions of this research were carried out at the light source PETRA III at DESY, a member of the Helmholtz Association (HGF). The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Science, of the US Department of Energy under contract DE-AC02-05CH11231. This research was partially supported by COMPRES under NSF Cooperative Agreement EAR 06-49658. We would like to thank S.M. Clark, J. Yan and V. Raju (ALS) as well as H.-P. Liermann (PETRA III) for assistance in using beamlines 12.2.2 (ALS) and P02.2 (PETRA III), and F. Schröder, N. Rademacher, J. Biehler and J.D. Bauer for their help during experiments.

Notes

This contribution is part of the final report summarizing the results of the DFG-priority project SPP1236, which was funded by the Deutsche Forschungsgemeinschaft from 2006–2013.