Combine effect of doping and strain on the thermodynamics, ferroelectric, electronic, and magnetic properties of PbTiO3

Abstract

Multiferroic materials become prominent as they utilize both the charge and spin degree of electrons, which have tremendous scope in solid-state electronic-based devices. Herein, the combined effect of transition metals (TM = Fe, Co, and Ni) doping and biaxial ([110]) strain on the thermodynamics, electronic, and multiferroic properties of PbTiO3 (PTO) perovskite oxide is investigated by the inclusion of Hubbard parameter U. Formation energetics computed by utilizing the Convex Hull analysis, confirm the structural stability of the TM-doped motifs, while elastic properties affirm the mechanical regularity. In addition, positive frequencies of the phonon dispersion bands maintained the dynamical cohesion of the systems. Our results revealed that the magnitude of spontaneous polarization (P) decreases from 84.3 μCcm−2 to 70.2/67.8/63 μCcm−2 due to the reduction of the structural distortions when Fe/Co/Ni ions are doped at Ti site, which agrees well with the recent experiment [J. Phys. Chem. C 125, 12342 (2021)]. Strikingly, all the strained systems exhibit a higher P amplitude than that of the unstrained one. The most striking feature of the present study is that the Co-doped motif predicted a metallic behavior for −5% biaxial ([110]) strain. Along with this, the Ni-doped structure demonstrates a reasonable amplitude of spin-polarization with respect to strain. A high to low (2.0–0.5)/low to high (0.5–1.0) spin-state transition is observed at a critical strain of −1%/−2% in Fe/Ni, while Co lies in a low spin state with S = 0.5. Finally, spin-magnetization isosurfaces plots established that magnetism mainly arises from the admixture of 3dz2, 3dx2−y2, 3dyz + xz, and 3dxy orbitals.