title: Positive holes in magnesium oxide.  Correlation between magnetic, electric, and dielectric anomalies.
abstract: 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.
authors.affiliation: Department of Physics, San Jose State University, California 95192, USA.
authors.forename: F
authors.initials: F
authors.lastname: Batllo
authors.forename: R C
authors.initials: RC
authors.lastname: LeRoy
authors.forename: K
authors.initials: K
authors.lastname: Parvin
authors.forename: F
authors.initials: F
authors.lastname: Freund
authors.forename: M M
authors.initials: MM
authors.lastname: Freund
mesh_terms: 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
chemical_list: D008277:Magnesium Oxide; D008274:Magnesium; D010100:Oxygen