Thermal disorder in ionic crystals

• Main Author: Jackson, Brian John Hayden
• Published: Imperial College London 1968
• Subjects: 530.4
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.623055

The conductance and space-charge polarization capacity of single crystals of thallous chloride have been measured as a function of frequency between 350°K. and temperatures approaching the melting point. Correlation with available diffusion data indicates that Schottky disorder is present with the chlorine ion vacancy as the predominant charge carrier. Analysis of the capacitance results using a modified space-charge theory gives new values of the enthalpies of formation and motion of the vacancies present. Thus ∆Hs = 1.36 eV. ; ∆Hm(cv) = 0.40 eV. ; ∆Hm(av) = 0.09 eV. The defect concentration at the melting point is ~0.08 atomic %. Similar measurements on thallous bromide show that Schottky defects probably exist in this material with the bromine ion vacancy the more mobile species. The characteristic defect parameters for the bromide closely resemble those for the chloride.