First-principles study on the elastic properties of Sr–Ti–O ceramics

Layered perovskite SrO(SrTiO3)n (n=1,2) and SrTiO3 were analyzed using the density functional theory within a generalized gradient approximation. The elastic properties of SrTiO3, Sr2TiO4, and Sr3Ti2O7, including the bulk modulus, shear modulus, Youngʹs modulus, Poissonʹs ratio, and elastic anisotropy ratios, were investigated. Results show that hardness decreases with decreasing SrTiO3/SrO ratio. Except for C66, all elastic constants tend to decrease with decreasing volume. When the Sr2TiO4 and Sr3Ti2O7 volumes are higher than 15.8 and 16.9 إ3/atom (or lower than 10.4 and 10.1 إ3/atom), respectively, C33 (or C66) decreases to zero and the structure becomes unstable. Phase transition and shear generation along the YZ direction occur under high-positive pressure (low volume) and high-negative pressure (high volume) conditions, respectively.