Positive holes in magnesium oxide.  Correlation between magnetic, electric, and dielectric anomalies.
Magnetic susceptibility measurements of high purity MgO single crystals (<50-wt. ppm transition metals) by means of a vibrating-sample magnetometer shows an anomaly at 800 K.  At the same temperature the electric conductivity increases anomalously, the static dielectric constant epsilon increases from 9 to approximately 150, a pronounced positive surface charge appears, and Fe2+ in the MgO matrix oxidizes to Fe3+.  The data are consistent with O2(2-) (peroxy) defects, representing self-trapped, spin-paired positive holes at Mg2+ vacancy sites.  Diamagnetic at low temperatures, the holes start to decouple their spins > 600 K, probably forming at first V0 centers (two O- at an Mg2+ vacancy), then V- centers (single O- at an Mg2+ vacancy), and releasing mobile O- states.  These O- represent itinerant charge carriers on acceptor levels near the O 2p-dominated valence band and conduct by O- /O2- valency fluctuations.  The O- concentration is of the order of 8 X 10(19) cm-3.
Batllo
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Department of Physics, San Jose State University, California 95192, USA.
LeRoy
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Parvin
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Freund
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Freund
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D003460:Crystallization; D004553:Electric Conductivity; D004560:Electricity; D004583:Electrons; D008274:Magnesium / Q000032:analysis; D008277:Magnesium Oxide / Q000032:analysis*; D008280:Magnetics; D010100:Oxygen / Q000032:analysis; D013696:Temperature
D008277:Magnesium Oxide; D008274:Magnesium; D010100:Oxygen