Negative Thermal Expansion of Cyanides. Thermal expansion. Thermal Expansion is the change in volume of a material when heated. Generally, materials increase in volume when heated.
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Thermal Expansion is the change in volume of a material when heated.
Generally, materials increase in volume when heated.
A material’s “coefficient of thermal expansion” tells you how much its volume changes with temperature over time.
A select group of materials actually decrease in size when heated. This is called Negative Thermal Expansion (NTE).
Displacement same direction as axis
Displacement different directions to axis
single-atom and (b) diatomic linkages *
Black circle= heavy atoms
White circle=bridging atoms e.g cyanide
* For polymetric crystalline materials such as Zn
As temperature increases, so does bond energy. The greater the bond energy, the more vibrations so more displacement in either of the modes, the shorter the bond length.