On the negative Poisson ratio in monocrystalline zinc

For common single hexagonal crystals, the values of the compliance coefficients are such that the Poisson ratios vmn and v1n are positive for all θ. However, for single crystals of Zn: s11 = 8.22, s33 = 27.7, s44 = 25.3, s12 = 0.60 and s13 = -7.0, so that the coefficients s11 and s12 are of the same sign. Consequently, for θ = 0, v12 = -s12/s11≈-0.073<0. Thus, the Poisson ratio of monocrystalline Zn in its basal plane is negative. The negative values of the Poisson ratio for transversely isotropic material are precluded by stability requirements.