by Dr. Lewis Downie
At the most general level, solid state chemistry is concerned with the physical properties and reactions of chemicals and materials which are in the solid-state; i.e. are neither gases nor liquids. This is of course a rather broad church and over time this branch of chemistry has become more colloquially known to deal with non-molecular solids. Within this there are many potential avenues of research from semiconductors to photovoltaic cells, catalysis to metallurgy.
A significant number of the materials at the centre of study in solid-state chemistry are synthesised by solid-state reaction. This is a reaction technique that often requires high energies in order to encourage the movement of ions through a solid. This is usually achieved by mixing two (or more!) powdered starting solids together, and then heating the resultant powder mixture to high temperatures (typically 500 – 1600°C) for hours to days. Unlike liquid or gas phase reactions, however, there are occasions when more time will not lead to the completion of the reaction. In these cases the product has built up between our reactants and is preventing the further diffusion of ions. This is easily solved as we can then remix the resultant powder and heat again.