Discharge of ions and space charge formation in CdF₂ crystals with different kinds of electrodes

Abstract

Abstract. -CdF 2 samples provided with different kinds of electrodes and insulations are investigated. It is found that, due to an electron injection which cannot be avoided, metal particles are formed below the surface which act as a kind of « reversible dendritic electrode »; that the cations are discharged by segregation there and/or at the external cathode; that the two known space-charge formation TSC-peaks are related to the blocking of the external electrode and to an electron injection resp. It is finally shown that there are indications of a similar situation in alkali halides.

Charge transport and polarization in effectively insulated and in contacted NaCl crystals below 500 K

“…The results of Sections 6,7 then give, consistently for the TSC, ac and potential distribution data, evidence that in crystals provided with "inert" (graphite, solid metal) electrodes there exists besides the PD-SCH polarization yet a further SCH component. It is caused by the charge transfer between crystal and electrodes realized by electrons and connected with the discharge mechanism of the ionic charge carriers below the surface inside the crystal, in similar lines as in CdF, [14].…”

“…Whereas ideally insulated crystals show besides the well known complex peaks at LT solely one HT-TSC peak, the PD-SP peak, assumedly inert electrodes of colloidal graphite or noble metal even if they match well with the contact surfaces of the crystals like in the case of sputtered gold electrodes [14], give rise, as TSD measurements of KCl [8,291,of CdF,[30,31,141 and of NaCl [32,331 show, to several HT peaks. These findings point unanimously to a polarization caused by several different TS processes.…”

“…On the other hand, Q/SV proves not to be independent of c. But this is, finally, not expected because with increasing c also an increasing electron injection must take place to sustain the current through the crystal. This requires, if the ideas developed in the course of the investigation of CdF, [14,151 are correct an increased field strength at the crystal surface, i.e. an increased Q/SV.…”

“…It is tried to obtain from the data the bulk conductivity at LT, to quantify the effect of the polarization, and to verify these results by comparisons with the bulk conductivity obtained from published loss data and with potential distribution data (Sections 3 to 5). Finally, the available TSC, dielectric loss, and other data of contacted crystals are analyzed with the aim to see how far the electrode processes in NaCl are similar to that suggested some time ago for CdFz [14,151 and how far they can explain, semi-quantitatively at least, various known polarization effects (Sections 6,7). Besides a better idea of the way the charge transfer is realized should be helpful wherever polar crystals are investigated or used for practical purposes.…”

Conductivity and Polarization of NH4Cl between 150 and 500 K

“…The reason of this phenomenon is explained in Section 3.2.3 of [ll]. It is caused by a minute leakage of current orland a charge transfer between the cornponcnts of the measured sandwich, too low to be directly detected, the effect of which however is evident (see [18,191). to 0.73 eV for NH,Cl:NH,.…”