A Theoretical Study On Strain Engineering Of Rare-earth Nickel Oxides Produced By The Pulsed LASER Deposition

Pulsed LASER Deposition(PLD)technology has laid a solid foundation for multi-functional perovskite materials.The structural changes caused by the preparation of the growth substrate by the PLD method may result in a variety of electronic arrangements,such as charge ordering,orbital ordering,and so on.This structural change is caused by the mismatch strain between the intrinsic lattice constant of the perovskite material and the lattice constant of the substrate.Therefore,the structure and performance of the perovskite can be changed by adjusting this strain,which could lead to a variety of applications of the material in related fields.In addition,perovskite rare-earth transition metal oxides have been widely stud-ied as important functional materials.The electronic system has highly correlated spin,charge,orbital and lattice degrees of freedom.This means that there are various inter-actions(such as electron-electron interactions).As a result,the competition among the various symmetries in the crystal has attracted interest.This thesis focuses on the lattice mismatch strain caused by the preparation of the growing substrate by the PLD method.It also explores the charge in the regulated per-ovskite nickel oxide through first-principles calculations based on density functional theory.1.We took HoNiO3 in the rare-earth nickel oxide family of perovskite as the re-search object and carried out theoretical simulation calculations.We studied the order state of charge generated by the mismatch of the lattice caused by the preparation of the growth substrate by the PLD method.The relationship between the Jahn-Teller distor-tion,orbital ordering and charge ordering was explored.The charge arrangement of this type of crystal was explored.The calculation results show that,in the HoNiO3 crystal prepared by the PLD method,the tensile strain of the substrate will cause the HoNiO3 to change from charge ordering to orbit ordering.The lattice structure will transform from breathing mode to the Jahn-Teller distortion.2.We also explored the DyNiO3 crystals in the rare-earth nickel oxide family of perovskite rare-earth transition metals.Due to the strain caused by the substrate,the Ni 3d orbital and O 2p orbital hybridized in the material,causing disproportionation to occur.The charge of the Ni was alternately arranged in three-dimensional space,which generated charge ordering.3.We have extended the research system to explore the more complex double perovskite rare-earth oxide crystal La2MnNiO6.We used first-principles calculations and found that La2MnNiO6 was arranged in B-site charge ordering.In addition,due to the strain caused by the substrate prepared by the PLD method,the crystal exhibits both a monoclinic phase and a rhombohedral phase.