Features of Poisson’s ratio behavior of auxetic materials

The anisotropic and isotropic (for polycrystals) Poisson ’s ratios of halogenides, halogenates, cyanides of alkali metals and halogenides of copper, silver, thallium and ammonium have been defined under standard conditions on the basis of the known experimental data of the stiffness constants, c ij, of cubic ionic singlecrystals with different types of crystal lattice (В1, В2, В3, NaClO 3). At room temperature and atmospheric pressure LiF and copper halogenides have negative value of Poisson ’s ratio in the direction (along 1ī0 ). At the same time, the Poisson ’s ratio in the direction is abnormally positive in cyanides of alkali metals. Temperature (LiF, NaCN) and pressure (CuCl) dependences of Poisson ’s ratios have been researched.