Negative Thermal Expansion Coefficient

Physical nature of negative thermal expansion coefficient (α) in polar-sensitive dielectrics and semiconductors is explained. Physical features of inter-atomic bonds in crystals are manifested in their thermal expansion; in the polar dielectrics it is a peculiar polar-sensitive structure, arisen due to compensation of atoms electronegativity. Negative value of α(T) corresponds to a particular case, when the entropy increases with increasing pressure that is possible only in case of configurational entropy: negative expansion refion on α(T) dependence corresponds to the processes of spontaneous structural ordering. The results obtained for polar crystals can be applied to semiconductors.