Observation of Dislocations in CaWO4 by Transmission Electron Microscopy

Abstract

The distribution of dislocations in deformed calcium tungstate was studied by electron transmission microscopy. The photomicrographs confirmed earlier optical observations that (001) 〈100〉 is the slip system of this material between 500°–900°C. Screw dislocations, long edge-dislocation dipoles, quadrupoles, and tangles of dislocations were observed in foils prepared from specimens deformed at 500°C. Specimens deformed at 700°C showed similar features, except that many of the long dipoles had split into long strings of prismatic loops. At 900°C the loops were more isolated and sometimes grew to a diameter exceeding the thickness of the foil. Many single dislocations could also be seen with nearly pure edge or screw orientation. Two models are proposed for quadrupole formation and their relative stability considered. Strain hardening is thought to be due to the interaction of dislocations with multipoles and prismatic circular loops.