Journal Article PZT crystal symmetry density functional theory (DFT) discrete microscopic Landau-Ginzburg-Devonshire (dmLGD) approach domain structures electrocaloric effect electromechanical responses energy conversion entropy ferroelastic domains ferroelectric domain walls, ferroelectric perovskites, order parameters ferroelectric materials ferroelectricity ferroelectrics ionic conduction machine learning octahedral rotation perovskite oxides pyroelectric effect scanning-probe microscopy strain thin-film epitaxy three-state ferroelastic switching