The Electrical Properties Study Of La₂Ti₂O₇ Under High Pressure

La₂Ti₂O₇ belongs to A₂B₂O₇ perovskite structure materials,which is a new type of synthetic functional ceramic powder with good piezoelectric and ferroelectric properties.It has been applied in the bottom electrode of ferroelectric film,electro-optical equipment and information memory.As is known to all,pressure is a"clean"tool that can change the electrical and structural properties of a material without introducing other factors when acting on it.It is hoped that perovskite-like materials with new structure and properties can be obtained by studying the electrical properties of materials under high pressure.Therefore,the electrical properties and material structure of La₂Ti₂O₇under high pressure are studied in this paper,and the changes of resistivity,energy band structure and other properties of La₂Ti₂O₇under extreme environment are discussed in depth.Using the diamond anvil cell technology,we studied the high-pressure in-situ electrical transport,Raman spectrum and ultraviolet absorption spectrum of La₂Ti₂O₇and finally obtained the following results:(1)Through in situ high pressure Raman spectroscopy test,it was found that the Ti-O vibration Raman peak(589 cm^-1)appeared an inflection point near 2.0 GPa under pressure,and it first shifted to low wavenumber and then high wavenumber with the pressure increasing.Before 7.0 GPa,the 445 cm^-1Raman peak was almost stationary at the beginning,and then suddenly increased with the pressure increasing.We believe that the sudden change of these Raman vibration peaks is caused by the electronic phase transition of La₂Ti₂O₇under pressure.When the pressure reaches16.5 GPa,the Raman vibration peaks gradually widen and disappear,which is believed to be caused by the gradual amorphosis of La₂Ti₂O₇under high pressure.(2)Through the in-situ AC impedance spectrum of high pressure,it was found that when the pressure was lower than 3.0 GPa,the electrical parameters of La₂Ti₂O₇had discontinuous changes at 3.0 GPa and 7.9 GPa with the increase of the pressure.Between 0 and 3.0 GPa,the resistance decreases with the increase of pressure.At the same time,there is always an inductance arc in the low frequency region of Nyquist impedance spectrum.However,when the pressure increases to 3.0 GPa,the inductance arc disappears.In the range of 7.9 to 16.5 GPa,the resistance value decreases with the increase of pressure.In the range of 16.5-30.0 GPa,the resistance value gradually tends to be stable.We believe that these two resistance changes are related to the electronic phase transition of La₂Ti₂O₇under high pressure,and the amorphous La₂Ti₂O₇under pressure leads to the gradual stabilization of the resistance.