Revealing by secondary electronic emission of internal electric fields in the yttriated zirconia, irradiated by electrons of 1 MeV

The defects due to irradiation in a dielectric material present an activity which can generate macroscopic internal electric fields. A method of investigation of these fields, based on the measure of the Secondary Electronic Emission coefficient, has been developed on a scanning electric microscope. This ones contains two low noise detectors which respectively measure the influence current IIC produced by the charges trapping in the material and the current ISB due to secondary and backscattered electrons which come from the sample. The Secondary Emission coefficient is given by σ=ISB/(ISB+IIC). The charges trapping during an electrons injection leads to a variation of σ for its intrinsic value σ0 relative to the uncharged material, until the stationary value σst=1 corresponding to the auto-regulated condition. This variation is due to the development of an internal electric field produced by the accumulation of the charges trapped during injection. In comparing the evolutions of σ of a fresh yttriated zirconia and of an yttriated zirconia irradiated by electrons of 1 MeV with a dose rate of 1018 e/cm2, it has been revealed that an internal field (due to irradiation) of about 0.5*106 V/m exists at a depth of the micron order. This field, directed towards the outside of the material surface, is attributed to the F+ defects and to the T centers produced by the impact of the electrons of 1 MeV. In carrying out annealings until 1000 K, a progressive disappearance of this field is observed in the temperature range of 400-600 K, directly due to the F+ defects and T centers recovery, as it has been observed by ESR. An internal field three times weaker than the preceding ones has been revealed at a few nm under the surface. Its disappearance from a temperature of 1000 K suggests that it is due to the redistribution of the chemical species into the surface, during the irradiation with electrons of 1 MeV. (O.M.)