Electric and Dielectric Properties of Polycrystalline Yttrium Iron Garnet: Space-Charge-Limited Currents in an Inhomogeneous Solid

摘要: The dc conductivity of $n$-type polycrystalline yttrium iron garnet has been measured at temperatures near room temperature as a function the applied voltage. At voltages below critical value an Ohmic behavior is observed, while above this we find $i\ensuremath{\propto}{V}^{\ensuremath{\alpha}}$, with $\ensuremath{\alpha}=1.2\ensuremath{-}5.1$. ac and dielectric permittivity both show large dispersion in ${10}^{\ensuremath{-}3}$-${10}^{5}$-Hz frequency range, e.g., static relative ${\ensuremath{\epsilon}}_{s}\ensuremath{\approx}4000$ high-frequency ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}=18$. results are interpreted terms two-layer model well-conducting grains (e.g., ${\ensuremath{\sigma}}_{300 \mathrm{K}}\ensuremath{\approx}7.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$) measuring 4 \ensuremath{\mu}m separated from each other by poorly conducting boundary layers \mathrm{K}}\ensuremath{\approx}1.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ thickness 0.02 \ensuremath{\mu}m. low voltages, conduction determined layer. higher current space-charge limited. A developed for space-charge-limited currents inhomogeneous solid kind. All experimental can be explained qualitatively model. For one sample measurements have quantitatively analyzed. Good agreement theory found if assume exponential distribution density states trapping centers form ${\mathfrak{N}}_{t}(E)=\frac{{N}_{t}}{k{T}_{t}}{e}^{\frac{(E\ensuremath{-}{E}_{c})}{k{T}_{t}}}$, ${N}_{t}=3.3\ifmmode\times\else\texttimes\fi{}{10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ ${T}_{t}=1110$ K. 300 K, region grain layer ($Vl10$ V), Fermi level situated 0.88 eV band; upon charge injection its position rises, externally voltage 500 V, to about 0.63 band. Annealing experiments different oxygen pressures that regions which reoxidized during cooling sintering 1430 \ifmmode^\circ\else\textdegree\fi{}C temperature.