Hall coefficient and resistivity measurements have been made on 29 single crystals (mostly synthetic) of PbS, PbSe, and PbTe between room temperature and 4.2°K. Almost all of the samples had extrinsic carrier concentrations of the order of

10^{18}

per

{cm}^{3}

, as deduced from the Hall coefficients which were essentially constant over the entire temperature range investigated. Hall mobilities were calculated from the Hall and resistivity data, and were found to increase rapidly with decreasing temperature. Between room temperature and about 50°K the mobility behavior was essentially intrinsic and varied approximately as

T^{- 2.2}

. Below 50°K the mobility curves turned gradually toward the horizontal in a manner resembling the residual resistance phenomenon observed in metals. Values as high as 800 000

{cm}^{2}

/v-sec were attained at 4.2°K despite the large carrier concentrations present in all the samples. A simple experiment was performed which suggests that dislocations are the principal scattering mechanism below 50°K, rather than the charged point defects associated with the extrinsic carriers. The possibility that a high static dielectric constant could explain the large mobilities at low temperatures is discussed.

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