This research provides a deeper understanding, prediction, and manipulation of the surface reconstructions of rutile TiO 2 (110), holding implications for a diverse range of applications and technological advancements involving rutile-based materials. The emergence and disappearance of these asymmetric structures can be controlled by adjusting the oxygen partial pressure. Our findings highlight the pivotal role played by repulsive electrostatic interaction among the small polarons −formed by excess electrons following the removal of neutral oxygen atoms− and the subsequent surface relaxations induced by these polarons.
Density functional theory calculations were employed to complement the experimental observations. Here, we directly observe the asymmetric surface reconstruction of rutile TiO 2 (110)-(1×2) with atomic-resolution using in situ spherical aberration-corrected scanning transmission electron microscopy. The insights revealed here not only deepen our understanding of the electronic properties and structural and magnetic ordering transition under high pressure of square lattice antiferromagnets AMoOPO4Cl (A = K, Rb), but also push the boundaries of knowledge by recognizing the role of nonmagnetic ions P 3s in magnetic exchange coupling.The reconstruction of rutile TiO 2 (110) holds significant importance as it profoundly influences the surface chemistry and catalytic properties of this widely used material in various applications, from photocatalysis to solar energy conversion. The loss of mirror plane symmetry in P4/n phase, makes the P 3s orbitals activate to participate the magnetic interaction, giving rise to competitive ferromagnetic superexchange interaction, in addition to antiferromagnetic direct one, and consequently initiating the magnetic ordering transition. Furthermore, the mechanism underlined responsible for the magnetic ordering transition at high pressure has been disclosed in terms of density of states and spin density isosurface analysis across the transition.
More importantly, the P4/n phase, involving the mutually twisting of MoO5Cl and PO4 polyhedra, satisfactorily reproduces the experimentally observed structural transition and the subsequent magnetic ordering transition from columnar antiferromagnetic ordering to Néel antiferromagnetic one, identified to be the appropriate high pressure structure. Our results indicated that the columnar antiferromagnetic ordering, experimentally determined, is the magnetic ground state of the ambient P4/nmm phase, stabilized by the predominant antiferromagnetic next nearest neighbor interaction J2 in the diagonal directions of square lattice, regardless of the effective Hubbard amendment values. By means of ab initio density functional theory calculations with taking electronic correlation and van der Waals force into account, we conduct a comprehensive studies of electronic and magnetic properties, as well as structural and magnetic ordering evolution under pressure of the square lattice antiferromagnets AMoOPO4Cl (A = K, Rb) containing Mo5+ ions with, the potential candidates for achieving quantum phases theoretically predicted, existing in the boundary regimes for spin-J1 -J2 square lattice magnets.