Study Of Magnetic And Electrical Transport Properties Induced By Oxygen Vacancies In ABO₃ Perovskites

Transition metal oxides have abundant physical properties due to the existence of multivariant interactions of lattice,charge,orbit,and spin.Oxygen defect engineering is one of the important methods to study the novel properties of transition metal oxides.Oxygen defects include oxygen vacancy and oxygen doping.This work focuses on the magnetic and electrical transport properties induced by oxygen vacancies in perovskite.Three typical perovskite oxide materials of Fe-SrTiO_3-δ,BaTiO_3-δ,and Sr-NdNiO₃ were used as prototypes to study the effect of oxygen vacancies on magnetic properties and electrical transport properties.The main contents are as follows:1.Fe-SrTiO_3-δwas prepared by ultra-high vacuum annealing.Oxygen vacancies cause 0.05%crystal lattice expansion and high conductivity.The type of carriers are electrons,the carrier concentration and the maximum mobility is 1.084×10¹⁹/cm³ and8493 cm²/V·s,respectively.Oxygen vacancies induce ferromagnetism,and the coercive field reaches 7700 Oe at 2 K.A new magnetic phase transition was discovered in Fe-SrTiO_3-δat 18 K,which originated from the coeffect of oxygen vacancies and metal cations,and forms two magnetic phases Fe³⁺-O^2--Ti³⁺and Ti³⁺-O^2-in the crystal.2.BaTiO_3-δwas prepared by ultrahigh vacuum annealing and hydrogen high-temperature annealing.BaTiO_3-δsamples were multiferroic semiconductors.BaTiO_3-δis ferromagnetic which is derived from oxygen vacancies.BaTiO_3-δprepared by hydrogen annealing has obvious room temperature ferromagnetism with a coercive field of 400 Oe at 2 K.Annealed BaTiO_3-δis a semiconductor.The ferroelectricity of BaTiO_3-δdecreased after annealing,and the SHG signal intensity decreased by 59%.3.Sr-NdNiO₃ thin films were grown by the off-axis magnetron sputtering method under different conditions of temperature and oxygen pressure.The growing temperature of 550℃and oxygen pressure of 0.02 Torr is the best way to grow the film.The thickness of the film grown in 5 hours is about 20 nm and the metal-insulation transition of the film appears at 75 K.The XRD diffraction peak of Sr-NdNiO₃ thin-film disappeared after calcium hydride annealing,and the thin film became an insulator.