Analysis of space charge relaxation by equivalent electric circuit for yttrium doped CaF 2

Abstract

Characteristic behaviours of high temperature ionic thermocurrent (HT ITC) in CaF 2:Y were studied by a usual ITC method with Teflon insulated electrodes in the nominal yttrium concentration range from n=0.002 to 30 mol%. An equivalent electric circuit was used to analyze HT ITC by assuming a space charge flow model with a specific resistivity in the form of ρ( T)= ρ syso T exp( E a / kT). The analysis revealed that a relaxation of the space charges occurred in the specific resistivity from insulating to semi-insulating change-over of CaF 2:Y crystal. In addition, dependences of the peak temperature shift and total charge of HT ITC on the crystal thickness could be explained by taking into account the capacitance of the crystal. And the yttrium concentration dependence of the activation energy for the space charge flow could be well approximated by E a ( n)= E ao − γn 1/3.