Thermocurrent measurement

Thermocurrent measurements were performed on crystals of RbsNbjOFig and K5Nb3OFi8 along the c direction [440, 443]. Fig. 112 shows the temperature dependences of the pyroelectric coefficients close to room temperature. 

A variety of techniques has been employed to investigate aliovalent impurity-cation vacancy pairs and other point defects in ionic solids. Dielectric relaxation, optical absorption and emission spectroscopy, and ionic thermocurrent measurements have been most valuable ESR studies of Mn " in NaCl have shown the presence of impurity-vacancy pairs of at least five different symmetries. The techniques that have provided a wealth of information on the energies of migration, formation and other defect energies in ionic solids are diffusion and electrical conductivity measurements. Electrical conductivity in ionic solids occurs by the motion of ions through vacancies or of interstitial ions. In the case of motion through vacancies, the conductivity, a, is given by... 

Using data obtained from thermocurrent, piezoelectric and dilatometric measurements, the first and second pyroelectric coefficients were calculated for the Rb5Nb3OFi8 crystal. Fig. 114 presents the results. 

A modification is the thermocurrent dosimeter. In this case the detector may be a thin crystal of synthetic sapphire 10 mm, thickness 1 mm) between thin metal electrodes. When the crystal is heated after having received a certain dose, the trapped electrons are released and cause a current to pass between the electrodes. The peak of the integrated current is a measure of absorbed dose. The effect is referred to as RITAC (radiation induced thermally activated current) and the technique is named TC (thermocurrent) dosimetry. Because it is instrumentally easier to measure an electric current than light, the TC dosimeter may replace the TLD in time. 

---