Nanomechanical properties of lead iodide (PbI2) layered crystals

Lead iodide is a layered crystal whose layers are binding by van der Waals weak forces. Layered crystals have slip systems at the basal or layer plane. The slip system of lead iodide is composed by the (0001) plane and 〈112̄0〉 direction. Single crystals of lead iodide, produced by ionic exchange reaction, were deposited on glass substrate. The mechanical properties were analyzed by nanoindentation technique. The indentations were made in same direction of the c axis of the crystal, with a Berkovich indenter. Pop-in excursions of the indenter in the loading curve were observed. The origin of these excursions is discussed considering the breakage of layers and their intercalation into the existing ones. The pile-up around indentation impression was observed through scanning electron microscopy. Hardness anisotropy was found and the hardness variation with tip orientation can be explained by the effective resolved shear stress model (ERSS).