Nonstoichiometric is a fancy term for substances that don’t follow the precise, fixed ratios of elements you’d typically expect in a perfect chemical formula. Imagine a substance that’s supposed to have a specific number of atoms of one element for every atom of another, but in reality, it has a bit more or a bit less of certain elements, creating a sort of chemical imbalance. These materials are like rebellious compounds that can’t be pinned down into neat, tidy formulas. Instead, they exist in a state of flux, adapting to environmental conditions like temperature, pressure, or even the presence of other chemicals.
One of the classic examples of nonstoichiometric materials are metal oxides, like titanium dioxide (TiO₂), which may have slightly more or less oxygen than what the formula suggests, creating defects in the crystal structure. These defects can make the material act a bit unpredictably, affecting its electrical conductivity, optical properties, and chemical reactivity. For instance, iron oxide (FeₓOₓ₋₁) can be a nonstoichiometric compound, where the ratio of iron to oxygen is slightly off. This gives rise to interesting properties that are distinct from the ideal stoichiometric form, such as the ability to absorb light in different ways or serve as an efficient catalyst.