These unusual materials can help to overcome many of the engineering challenges caused by thermal expansion in, for example, fuel cells or optical components. We have identified a new approach for controlling thermal expansion through fluoride doping of niobium oxyfluorides. A small fluoride content increase leads to zero and then negative thermal expansion. To our knowledge this is the first instance of negative thermal expansion in an oxyfluoride.
Although most materials expand when heated, a small minority actually contract or retain the same volume over wide temperature ranges.