The behaviour of Gd impurity in Bridgeman grown lead telluride crystals and the effect of Gd on the electrical properties and magnetic susceptibility of Gd doped crystals are studied. Gd is shown to behave like a donor impurity, although not in the usual sense of the word, and can cause PbTe crystals to become paramagnetic. Electronic conduction of Gd doped crystals is explained as resulting from a change in the relation between point defect concentration in the metal subsystem and that in the Te subsystem in favour of the latter. The Gd distribution along ingots can be accounted for only by assuming that the Gd segregation coefficient increases as the melt becomes Gd depleted.

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The effective magnetic momentum peff of Gd-impurities in the Pb1-xSnxTe(Gd) crystals as a function of crystal composition x with 0 < x < 0.25 is studied. It is shown that with the increase in tin content in the crystals from 0 to 0.15, p(Gd) increases slowly from 37 to 43.Then p2eff(Gd) increases abruptly to 63 value when x = 0.16 ± 0.01. For subsequent increase x > 0 . 1 7 p 2 e f f ( G d ) r e ma i n s c o n s t a n t a t 6 3 . P o s s i b l e r e a s o n s of observed changes of peff (Gd) and possible mechanisms of in fluence of the Pb 1 -x Snx Te crystal field on the effective magnetic momentum value of Gd -impurities in the crystals under study are analysed.

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