The Second-Harmonic Generation Effect Of YLaAlO₃ Perovskite Oxide Thin Film

In recent years, perovskite oxide materials gained extensive attention by people as functional materials. The broken inversion symmetry caused by the J-T distortion effect, strain and oxygen octahedral rotation mechanism can make materials arise spontaneous polarization. Those materials with broken inversion symmetry have properties such as ferroelectricity, piezoelectricity etc., which make them become one of the important materials studied by people. However, the J-T distortion effect and strain mechanism have restrictions on certain conditions, thus the ubiquitous mechanism, oxygen octahedral rotation, draws people’s attention to study and attempt to improve it. In reality, many perovskite oxide single crystals such as LaAlO3 and YA103 are inversion symmetry structure, belonging to the non-polar point group. This greatly reduces the species of perovskite oxide materials with ferroelectricity and other applications as functional materials.In this paper, we mainly study on the polarization properties of YLAO thin film, which makes YAO and LAO as the source materials while they are non-polar structures. We use second harmonic generation which is sensitive to the change of structure symmetry as our testing method with temperature variation since the polarization properties of YLAO thin film are closed related to the symmetry of the crystal lattice structure. We found that with the increase of temperature, the lattice structure of YLAO thin film existed a polarization phase transition during 150K to 200K temperature region. After we detected such experimental phenomenon, we explain our results through consulting a large number of literature. The structure is rhombohedral which is made up of oxygen octahedrons in the form of a-a-c- out-phase rotation mechanism in low temperature environment. With the increase of temperature, oxygen octahedral rotation transformation for a-a-c+ in-phase rotation mechanism and the lattice structure becomes the orthorhombic system. This phenomenon shows that the change of temperature can result in the changes of oxygen octahedral rotation mechanism in perovskite oxide materials.Through our experiment, we found that two non-polarizable materials grown in together would appear lattice mismatch and polarization due to the effect of oxygen octahedral rotation. This result plays an important role to widen the species of perovskite materials with inversion symmetry broken. People can put two or more kinds of non-polar perovskite oxides growing together to create new kind of polar perovskite oxide, which meets various application requirements.