**5.1 Experimental protocol**

564 Sintering of Ceramics – New Emerging Techniques

electric field as well as by a maximum amount of net trapped charge in the sample, Qst,

state and then the practical choice of the injection time tinj is determined by the achievement of this state. The evolution of the net trapped charges Qt during injection, which can be

Fig. 6. Evolution with time, at 473 K, of the net charge, Qt, during the first pulse injection in polycrystalline alumina sample (d = 4.5 µm). The quantity Qt is derived from the currents of Fig. 5 via Eq. 7. The solid line represents the exponential fit of the data, as

<sup>t</sup> Q (t) Q 1 exp = −− <sup>τ</sup>

where τc is the charging time constant (found equal to 2.07x10-3 s), which characterizes the

The method described above gives the opportunity to evaluate the quantity of trapped charges during irradiation. If the probed zone is initially uncharged, Qt(t) characterizes the quantity of charges that accumulates after an irradiation time t. Depending on the insulator conduction properties, the accumulated charges can either remain localized or partially (or even totally) spread out of the irradiated volume (discharge phenomenon). Hence, the measurement of the ability of the material to spread charges is of technological interest. In this paragraph, we give details of the experimental procedure developed for the measurement of this ability and we define a recovery parameter allowing the quantitative

c

(11)

The best fit of data represented in Fig. 6, leads to an exponential time evolution:

t st

charging kinetic of the material in the used experimental conditions.

**5. Measurement of the ability to spread charges** 

evaluation of the extent of discharge.

ind <sup>0</sup> <sup>−</sup> I (t) dt . The steady state is interesting because it will be taken as a reference

equal to inj <sup>t</sup>

given by Eq. 11.

deduced from Eq. 7, is shown in Fig. 6.

**net trapped charges Qt(pC)** 

To characterize the degree of spreading (of discharge), we set up a protocol allowing its evaluation. The procedure consists in analysing the states of charging deduced from two pulse electron injections over the same area, separated by some lapse of time as explained in the three following stages.
