The solid-state reaction route is the most widely used method for the preparation of polycrystalline solids from a mixture of solid starting materials (a). Materials do not usually react at room temperature and it is therefore necessary to heat at high temperatures (often to 1000 to 1500 °C). The reaction depends on environment conditions, structural properties of the reactants, surface area of the solids, their reactivity and the thermodynamic free energy change associated with the reaction. In order to synthesize complex materials, reactants are weighed out in the required amounts (c) and usually mixed by means of agate mortar and pestle (b). Some volatile organic liquid – preferably acetone or alcohol – can be added to the mixture to aid homogenization. If a specific shape is required (e.g. pellets for PLD-targets), evacuable pellet dies can be used (b). However, pelleting of samples is also preferred prior to heating, since it increases the area of contact between the grains.
For the subsequent reaction at high temperatures, it is necessary to choose a suitable container material which is chemically inert to the reactants under the heating conditions used (d,e). Depending on the synthesis temperature crucibles or boats made by noble metals (e.g. platinum, gold) or ceramics (e.g. alumina) are usually suitable. The heating process as well as the control of the background atmosphere depend very much on the form and reactivity of the reactants.