ITC study of Ga+-, Ge2+-, and Sn2+-doped alkali halides

The search of the off-centre displacement of an impurity ion from the cryst al lattice site in the ground electronic state has been performed by the io nic thermocurrent (ITC) method for Ga+, Ge(2+)v(c)(-) and Sn(2+)v(c)(-) cen tres in some alkali halides. No ITC peak has been found at T > 5K for Ga+ i ons. One ITC peak at the temperatures 187-214 K has been observed for Ge(2)v(c)(-) and Sn(2+)v(c)(-) centres. It has been concluded that due to the p resence of a cation vacancy v(c)(-) near a Ge2+ ion, the latter is shifted towards v(c)(-). As a result, only one off-cenrre position of the Ge2+ ion with a deep potential minimum is possible. The reorientations of the off-ce ntre Ge2+ ion can occur only due to v(c)(-), jumps around Ge2+ at the tempe ratures near 200 K where reorientations of Ge(2+)v(c)(-), dipoles become po ssible. The same may also be true for Sn(2+)v(c)(-), centres. The position of v(c)(-) with respect to Ge2+ and Sn2+ ions in potassium halides is discu ssed.