A3: Synthesis from Solid Phase and Solution

Synthesis from solutions is the basis for obtaining single crystals and nanocrystalline materials, providing control over size, shape, and composition of crystals, precipitates, as well as defects. The most widely used synthesis methods from solution are (i) (co)precipitation, (ii) sol-gel, and (iii) solvothermal (especially, hydrothermal) synthesis. These methods all involve starting materials (precursors) that are dissolved in liquid, and some type of chemical process that leads to the conversion of dissolved chemicals into small solid particles that subsequently precipitate and are collected as product. In such procedures, many aspects need to be documented, such as precursor compositions, precursor concentrations, solvent type, treatment temperature, heating rate, and pressure.

Synthesis from solid phases is one of the most used methods for obtaining powders and single crystals. In these methods, starting materials are solid powders. The traditional ceramic method of solid-state synthesis involves pressing desired amounts of starting materials into pellets, then heating the pressed pellet in a controlled atmosphere for several days to several weeks, at temperatures often exceeding 1,000°C, and in some cases, at pressures 10,000 times higher than atmospheric pressure. Given this wide range of possible conditions, many kinds of specialized equipment are employed. In these procedures, many parameters must be documented to ensure reproducibility, including particle size and concentrations of starting materials, heating temperatures, and rates as well as pressure.

In both methods, the goal is to find correlations between parameters for controlling the huge parameter space to finally guide future synthesis procedures. However, discovering – possibly unexpected – trends, requires a large collection of well-documented observations. Obviously, formal metadata definitions and ontologies are key for unraveling the desired trends.