Impedance spectroscopy of grain boundaries in nanophase ZnO

Sintered compacts of nanophase ZnO ({similar_to}60 nm average grain size, presintered at 600 {degree}C) were made from powders ({similar_to}13 nm) prepared by the gas-condensation technique. Impedance spectra were taken as a function of temperature over the range 450--600 {degree}C and as a function of oxygen partial pressure over the range 10{sup {minus}3}--1 atm (550 and 600 {degree}C only). The activation energy was determined to be 55 kJ/mole (0.57 eV) and was independent of oxygen partial pressure. The oxygen partial pressure exponent was {minus}1/6. Impedance spectra exhibited nonlinear {ital I}-{ital V} behavior, with a threshold of approximately 6 V. These results indicate that grain boundaries are governing the electrical properties of the compact. Ramifications for oxygen sensing and for grain boundary defect characterization are discussed.

[1]  V. Stubican.  Diffusion of isotopes in surface layers of some oxides , 1993 .

[2]  R. Averback,et al.  Sintering characteristics of nanocrystalline TiO_2 , 1990 .

[3]  S. R. Kurtz,et al.  Electroluminescence in ZnO varistors: Evidence for hole contributions to the breakdown mechanism , 1985 .

[4]  R. Birringer,et al.  Nanocrystalline materials an approach to a novel solid structure with gas-like disorder? , 1984 .

[5]  R. Buhrman,et al.  Ultrafine metal particles , 1976 .

[6]  A. Heinrich,et al.  Electrical properties and non‐stoichiometry in ZnO single crystals , 1981 .

[7]  R. W. Siegel.  Synthesis and properties of nanophase materials , 1993 .

[8]  C. Grovenor.  Grain boundaries in semiconductors , 1985 .

[9]  R. Uyeda,et al.  An Electron Microscope Study on Fine Metal Particles Prepared by Evaporation in Argon Gas at Low Pressure , 1963 .

[10]  Blatter,et al.  Carrier transport through grain boundaries in semiconductors. , 1986, Physical review. B, Condensed matter.

[11]  A. Thölén.  On the formation and interaction of small metal particles , 1979 .

[12]  E. C. Subbarao,et al.  Advances in Ceramics , 1981 .

[13]  M. Mayo,et al.  Nanoindentation of nanocrystalline ZnO , 1992 .

[14]  W. Kenan,et al.  Impedance Spectroscopy: Emphasizing Solid Materials and Systems , 1987 .

[15]  G. Mahan.  Intrinsic defects in ZnO varistors , 1983 .

[16]  K. Hagemark.  Defect structure of Zn-doped ZnO , 1976 .

[17]  B. Kear,et al.  Multicomponent ultrafine microstructures , 1989 .

[18]  J. Bernholc.  Clusters and cluster-assembled materials , 1991 .

[19]  C. Masquelier,et al.  Thickness of Cubic Surface Phase on Barium Titanate Single‐Crystalline Grains , 1994 .

[20]  T. Gupta.  Application of Zinc Oxide Varistors , 1990 .

[21]  Richard W. Siegel,et al.  Synthesis, characterization, and properties of nanophase TiO_2 , 1988 .

[22]  M. Rȩkas,et al.  Surface and bulk electrical properties of the hematite phase Fe2O3 , 1991 .

[23]  F. D. Boer,et al.  Electrical resistivity of nanocrystalline copper , 1993 .