Theoretical study of the sodium nitrite piezoelectricity and elasticity

The five piezoelectric stress coefficients eik of orthorhombic Im 2m NaNO2 were calculated by ab initio quantum mechanical methods, employing the Berry phase theory, with an all-electron basis set of localized Gaussian-like functions and either a DFT-GGA or a Hartree-Fock Hamiltonian. DFT results are larger by about 30% than HF ones. The purely ionic and electronic contributions to piezoelectricity were evaluated by computing the internal and external (clamped-ion), respectively, components of each coefficient. In the e34 case the clamped-ion component is dominant, indicating that the electronic contribution prevails over the ionic one of opposite sign. In all other cases the overall piezoelectric effect is ruled by the ionic contribution. The full set of elastic constants was also computed, by means of which the piezoelectric strain coefficients dik could be derived. These are discussed and compared to experimental data from the literature. © 2005 IOP Publishing Ltd.