Electronic transport in CrN and related alloys

McGahay, Mary
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Gall, Daniel
Dutta, Partha S.
Shi, Jian
Ullal, Chaitanya
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Materials engineering
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Further exploration of the effects of O in bulk CrN was achieved through substitutional replacement of N with O in epitaxial CrN(001) layers by growing samples in a mixed N2 and Ar+O2 atmosphere. O incorporation facilitates Cr vacancies, yielding a rocksalt-structure solid solution Cr1 x/2N1 xOx with a single compositional parameter x and a measured lattice constant that decreases from a = 0.4175 to 0.4116 nm for x = 0 to 0.59. First-principles calculations predict da/dx = +0.0200, -0.0018, and -0.0087 nm for CrN1-xOx, Cr1-x/3N1-xOx, and Cr1-x/2N1-xOx, respectively. Thus, they confirm, in combination with ion beam compositional analyses and x-ray diffraction results, a vacancy concentration of x/2 per cation site. The room temperature resistivity decreases by over two orders of magnitudes from ρ = 1.5×10-3 to 7.7×10-6 Ω m for x = 0-0.26. This is accompanied by a transition from a negative to a positive temperature coefficient of resistivity, an increase in the Hall mobility from μH = 0.37 to 2.4 cm2/Vs, and an increase in the carrier concentration n = 1.1×1020 to 4.9×1021 cm-3. However, ρ increases again to 6.9×10-5 Ω m for x = 0.34 and to > 10 Ω m for x ≥ 0.59 with a corresponding drop in μH. These results indicate insulator-to-metal and subsequent metal-to-insulator transitions at x = 0.04 ± 0.03 and 0.30 ± 0.03, respectively. The transition to metallic conduction and the measured n for x = 0.01-0.26 are due to substitutional O on anion sites acting as donors and cation vacancies as compensating acceptors. The insulating properties at large x are attributed to increased electron correlation effects.
December 2020
School of Engineering
Dept. of Materials Science and Engineering
Rensselaer Polytechnic Institute, Troy, NY
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