Torben Lapp

Ionic conductivity of pure and doped Li3N

Abstract The ionic conductivity of Li 3 N crystals doped with various metal ions (magnesium, copper and aluminum) or hydrogen has been investigated. The metal ions have a negative effect on the conductivity whereas hydrogen increases it. The intrinsic Li + ionic conductivity of pure Li 3 N is (2·-4)×10 -4 Ω -1 cm -1 at room temperature with an activation energy of 0.26−0.27 eV. Doping with hydrogen to a maximum level of 0.5−1.0 atom% results in a conductivity of 6×10 -3 Ω -1 cm -1 and an activation energy which has been lowered to 0.20 eV. A model is proposed for the action of hydrogen whereby the Li-N bonds next to an NH 2- group are weakened thereby facilatating the creation of Li + Frenkel defects and the vacancy migration. Hydrogen-doped Li 3 N is termed an enhanced intrinsic conductor.

Studies of hydrogen doped lithium nitride

Abstract Single crystals of hydrogen-doped lithium nitride have been grown and relative estimates of dopant concentrations obtained from infra-red transmission studies. This technique together with nuclear reaction analyses has also been used to characterize surface layers of lithium hydroxide/lithium carbonate which form readily on the crystals when exposed to the atmosphere. Complex plane analysis of a.c. conductivity data in the temperature range 25–200°C has enabled the separation of bulk crystal and surface layer properties. A value of 2.8 10 −3 Ω −1 cm −1 at 25°C, with an activation energy of 0.23 ev, for ionic transport perpendicular to the c-axis, within the bulk of the crystal, has been achieved.

Charge recombination processes in minerals studied using optically stimulated luminescence and time-resolved exo-electrons

A time-resolved optically stimulated exo-electron (TR-OSE) measurement system has been developed using a Photon Timer attached to a gas-flow semi-proportional pancake electron detector within a Riso TL/OSL reader. The decay rate of the exo-electron emission after the stimulation pulse depends on the probability of (1) escape of electrons into the detector gas from the conduction band by overcoming the work function of the material and (2) thermalization of electrons in the conduction band, and subsequent re-trapping/recombination. Thus, we expect the exo-electron signal to reflect the instantaneous electron concentration in the conduction band. In this study, TR-OSE and time-resolved optically stimulated luminescence (TR-OSL) were measured for the first time using quartz, K-feldspar and NaCl by stimulating the samples using pulsed blue LEDs at different temperatures between 50 and 250 °C after beta irradiation and preheating to 280 °C. The majority of TR-OSE signals from all the samples decayed much faster than TR-OSL signals irrespective of the stimulation temperatures. This suggests that the lifetime of OSL in these dosimeters arises mainly from the relaxation of an excited state of the recombination centre, rather than from residence time of an electron in the conduction band.