ABSTRACT
Often light will provide the energy needed to allow the electrons to migrate and the material is said to show photoconductivity. When thermal energy alone is sufficient to free the electrons, the electronic conductivity will rise with increasing temperature. The materials just described have been discussed in terms of an ionic model. It would be useful to set up a theory for electronic conductivity that retained the simple picture. The electronic conductivity is due to additional electrons or holes created by the defect chemistry of the system. These are also localized or trapped at ions or other defects within crystal, but not too strongly. They contribute to electronic conductivity by jumping or hopping from one site to another under the influence of an electric field. In particular, non-stoichiometry must be accompanied by compensating defects which maintain overall electrical neutrality in the material. The importance of electrical properties makes it worthwhile searching for simpler ways of introducing electronic defects into crystals.
