Nuclear Magnetic Resonance Investigation of the Metal-to-Semiconductor Transition in Crystalline CdO

R. P. Benedict and D. C. Look
Phys. Rev. B 2, 4949 – Published 15 December 1970
PDFExport Citation

Abstract

Measurements of the Cd113 nuclear-spin-lattice relaxation time (T1) and resonance frequency shift (K) were carried out in several samples of polycrystalline n-type CdO over the temperature (T) range 1.4-300°K, frequency (ν) range 2-10 MHz, and carrier concentration (Ne) range 3.3-44×1018 cm3. For Ne>1019 cm3, we find that T1Ne23T1 and KNe13, showing that the nuclei are interacting with degenerate conduction electrons. Furthermore, the Korringa relationship holds and the calculated electron density at a nucleus is almost the same as that in a free atom, indicating that the electrons are in the host-lattice conduction band. The Hall constant is independent of temperature, also suggesting that there is no separate impurity band. Conversely, for Ne<1019 cm3 none of the above-mentioned relationships holds and we must invoke a model in which the electrons are concentrated near impurity centers, forming an impurity band, with nuclei near the centers experiencing strong contact interactions while nuclei far from the centers experience only indirect interactions through nuclear-spin diffusion. These two groups of nuclei do not maintain a common spin temperature and thus the recovery of the magnetization is nonexponential. Finally, the concentration (N) at which the impurity wave functions no longer form a band is estimated from the Mott criterion to be about 2×1018 cm3, slightly below our lowest-concentration sample. Thus, assuming that NeN, we find that for N<2×1018 cm3 the impurity wave functions are localized, for 2×1018<N<1019 cm3 the electrons are free to move in an impurity band, and for N>1019 cm3 the Fermi level crosses into the host-lattice conduction band.

  • Received 25 May 1970

DOI:https://doi.org/10.1103/PhysRevB.2.4949

©1970 American Physical Society

Authors & Affiliations

R. P. Benedict

  • Air Force Institute of Technology, Wright-Patterson Air Force Base, Dayton, Ohio 45433

D. C. Look

  • Department of Physics, University of Dayton, Dayton, Ohio 45433

References (Subscription Required)

Click to Expand
Issue

Vol. 2, Iss. 12 — 15 December 1970

Reuse & Permissions
Access Options
Author publication services for translation and copyediting assistance advertisement

Authorization Required


×
×

Images

×

Sign up to receive regular email alerts from Physical Review B

Log In

Cancel
×

Search


Article Lookup

Paste a citation or DOI

Enter a citation
×