The investigation of the ionic component of conductivity in TlBr

The dark conductivity has been studied on pure and doped TlBr crystals obtained by Bridgement method with different compositions and pressures of the residual vapors over the melt. The specific resistance of the pure crystals at room temperature was (0.7-2) · 10¹⁰ Ω·cm and that of doped crystals depended on the amount of the incorporated Pb impurity and was equal to 1.8·10¹¹ Ω·cm. The conductivity activation energy near room temperature was equal to 0.8-0.85 eV and 0.6-1.2 eV for the pure and doped crystals, respectively. The conductivity activation energy of the studied crystals is in agreements with the known values of the energies of formation and dislocation of Schottky defects in TlBr at high temperatures. The expression for the dependence of the crystal specific resistance on their content of Pb bivalent cations has been found. The equilibrium concentration of Schottky point defects in the studied TlBr pure crystals has been calculated and it was equal to 6.4·10¹⁴ cm^-3. The displacement mobilities of anionic and cationic vacancies were μ_a = 9.8 ×10^-7 cm² V^-1 c^-1 and μ_c =3.4×10^-10 cm² V^-1 c^-1, respectively. The studies have been carried out within the frame of the ISTC project # 2728.