Influence of Charged Defects on Mechanical Properties of Lead Sulfide

摘要

A chemical etch, suitable for revealing dislocation etch pits on cleaved crystals of PbS, has been utilized to reveal rosette patterns formed upon indentation of specimens whose charge‐carrier concentration had been fixed by high‐temperature equilibration in controlled sulfur pressure. Hardness and rosette wing length are nearly independent of concentration of free electrons in the range 2×1017 to 3×1019 cm-3. This is true for n‐type material prepared by introduction of an excess of lead or by addition of a high concentration of bismuth donors to the PbS. Similar measurements on p‐type, sulfur excess crystals, pure or containing silver as an acceptor addition, reveal a marked dependence of hardness and wing length on concentration of holes. For hole concentrations above 8×1017 cm-3, rapid hardening is observed with an attendant decrease in rosette size. It is suggested that this behavior results from an electrostatic interaction between charged dislocations and acceptor point defects.