Simulation study of negative thermal expansion in yttrium tungstate Y₂W₃O₁₂

A simulation study of negative thermal expansion in Y₂W₃O₁₂ was carried out using calculations of phonon dispersion curves through the application of density functional perturbation theory. The mode eigenvectors were mapped onto flexibility models and results compared with calculations of the mode Grüneisen parameters. It was found that many lower-frequency phonons contribute to negative thermal expansion in Y₂W₃O₁₂, all of which can be described in terms of rotations of effectively rigid WO₄ tetrahedra and Y–O rods. The results are strikingly different from previous phonon studies of higher-symmetry materials that show negative thermal expansion. (paper)