Twin formation and morphology of vapour grown silver halide crystals

Crystals of pure AgX (X= Cl, Br) were grown from the vapour phase on copper and quartz substrates. For both AgBr and AgCl the same morphologies appear namely, cubic, {100} tabular, {100} tabular with {411} twinning, cubo-octa hedral, {111} tabular and needle shaped. These morphologies are the same as obtained for pure silver bromide from precipitation. So, the role of the s olvent in the growth process could be examined. The vapour growth morpholog y turns out to depend strongly on the temperature difference between the fu rnace and the substrate. At low temperature difference the {100} faces were observed, whereas at higher driving force the {111} faces became more visi ble. At a critical temperature difference twin planes parallel to the {111} faces were formed resulting in tabular crystals (multi-parallel twinning) and needle shaped crystals (also non-parallel twinning). Due to the occurre nce of {111} tabular crystals for both AgBr and AgCl and the constant drivi ng force during the experiments, conclusions can be drawn about the twinnin g event and the growth mechanism.