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The size of the component ions (cation and anion) is critical in determining the crystal structure because it influences the way the ions can pack together in the crystal lattice. The larger the anion, the greater the space that the cation needs to occupy. This difference in size can lead to the formation of different structures. Ceramic compounds follow the radius ratio rule, which is the ratio of the cation to anion radii that determines the coordination number and the resulting crystal structure.

The charge of the ions also influences the crystal structure because it affects the electrostatic interaction between the ions in the compound. The higher the charge, the stronger the ionic interaction, which can result in a more compact and energetically stable structure. Charge stoichiometry plays an important role, as the overall charge of the crystal lattice must be neutral. This can affect the ratio of cations to anions and determine how they arrange themselves to form a crystal structure. In conclusion, the two main characteristics of the component ions that determine the crystal structure are the size of the ions (ionic radii) and the charge of the ions (ionic charge). These factors help determine the preferred crystal structure based on the electrostatic and geometric properties of the ions involved.