Compressibility measurements and phonon spectra of hexagonal transition-metal nitrides at high pressure: {epsilon}-TaN, {delta}-MoN, and Cr{sub 2}N

Journal Article · Mon Jan 01 00:00:00 EST 2007 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.75.014104· OSTI ID:20976631

Soignard, Emmanuel ^[1]; Shebanova, Olga; McMillan, Paul F ^[2]

---

1. Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604 (United States)
2. Christopher Ingold Laboratory and Materials Chemistry Centre, Department of Chemistry, University College London, London WC1H 0AJ, United Kingdom and Davy-Faraday Research Laboratory, Royal Institution of Great Britain, London W1S 4BS (United Kingdom)

We report compressibility measurements for three transition metal nitrides ({epsilon}-TaN, {delta}-MoN, Cr{sub 2}N) that have structures based on hexagonal arrangements of the metal atoms. The studies were performed using monochromatic synchrotron x-ray diffraction at high pressure in a diamond anvil cell. The three nitride compounds are well-known high hardness materials, and they are found to be highly incompressible. The bulk modulus values measured for {epsilon}-TaN, Cr{sub 2}N, and {delta}-MoN are K{sub 0}=288(6) GPa, 275(23) GPa, and 345(9) GPa, respectively. The data were analyzed using a linearized plot of reduced pressure (F) vs the Eulerian finite strain variable f within a third-order Birch-Murnaghan equation of state formulation. The K{sub 0}{sup '} values for {epsilon}-TaN and {delta}-MoN were 4.7(0.5) and 3.5(0.3), respectively, close to the value of K{sub 0}{sup '}=4 that is typically assumed in fitting compressibility data in equation of state studies using a Birch-Murnaghan equation. However, Cr{sub 2}N was determined to have a much smaller value, K{sub 0}{sup '}=2.0(2.0), indicating a significantly smaller degree of structural stiffening with increased pressure. We also present Raman data for {epsilon}-TaN and {delta}-MoN at high pressure in order to characterize the phonon behavior in these materials. All of the Raman active modes for {epsilon}-TaN were identified using polarized spectroscopy. Peaks at low frequency are due to Ta motions, whereas modes at higher wave number contain a large component of N motion. The high frequency modes associated with Ta-N stretching vibrations are more sensitive to compression than the metal displacements occurring at lower wave number. The mode assignments can be generally extended to {delta}-MoN, that has a much more complex Raman spectrum. The x-ray and Raman data for {epsilon}-TaN show evidence for structural disordering occurring above 20 GPa, whereas no such change is observed for {delta}-MoN.

• OSTI ID: 20976631
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 75, Issue 1; Other Information: DOI: 10.1103/PhysRevB.75.014104; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CHROMIUM NITRIDES
COMPRESSIBILITY
DIAMONDS
EQUATIONS OF STATE
HARDNESS
MOLYBDENUM NITRIDES
MONOCHROMATIC RADIATION
PHONONS
PRESSURE RANGE GIGA PA
PRESSURE RANGE MEGA PA 10-100
RAMAN SPECTRA
TANTALUM NITRIDES
TRANSITION ELEMENTS
X RADIATION
X-RAY DIFFRACTION