Pyroelectricity\nin Ferroelectric PbTiO<sub>3</sub> Enhanced by <i>A</i>‑Site\nCation Contribution and\nNegative Thermal Expansion

The primary and secondary pyroelectric\neffect in ferroelectric\ntetragonal PbTiO<sub>3</sub> perovskite oxide has been studied with\nquantum chemical methods. Hybrid PBEsol0 density functional method\naccurately reproduces the experimental crystal structure of PbTiO<sub>3</sub> and enables systematic studies on the pyroelectricity, lattice\nthermal conductivity, and other physical properties of PbTiO<sub>3</sub>. Phonon anharmonicity and finite-temperature phonon properties necessary\nfor the study of primary pyroelectricity are determined with the use\nof Self-Consistent Phonon Theory. Secondary pyroelectricity and the\nnegative thermal expansion of PbTiO<sub>3</sub> are investigated with\nquasi-harmonic approximation. In comparison to another tetragonal\nferroelectric perovskite oxide BaTiO<sub>3</sub>, the primary pyroelectric\ncoefficient of PbTiO<sub>3</sub> is increased by the contributions\nof the polarized Pb(II) <i>A</i>-site cations, and the secondary\npyroelectric coefficient is increased by the negative thermal expansion.