Negative Thermal Expansion in Polar Crystals

The physical nature of quite unusual physical phenomenon - negative thermal expansion - is considered. This effect in solids is conditioned by the self-ordering in internal structure, that usually seen in the polar and magnetic crystals. The negative expansion is associated with nature of non-centrosymmetric crystals which is caused by the difference in electroneutrality of atoms forming polar crystal. The negative expansion is specified by the configurational entropy due to the structural ordering in the pyroelectrics and ferroelectrics. In electronics, the negative thermal expansion can be applied in thermal compensators as well as in the technology for control thin films with certain characteristics.