ABSTRACT
This chapter shows that Y. I. Frenkel defects in silver bromide (AgBr) are responsible for the whole of both black and white and colour photography. Photography is one of the most widely used of all information storage methods. Perhaps surprisingly, both black and white and colour photography are possible only because of the presence of point defects in the crystals used. Whilst in most crystals with the sodium chloride (NaCl) structure W. Schottky defects are the major structural point defect type present, it is found that the silver halides, including AgBr, favour Frenkel defects. The defects arising from balanced populations of cation and anion vacancies in any crystal, not just NaCl, are known as Schottky defects. Hence, NaCI refers to the rock salt structure type while NaCl means the compound sodium chloride. The unit cell of the rock salt structure type is cubic, with a lattice parameter of about 0.5 nm.
