Electrical Transport And Thermal Expansion Properties Of Lead Titanate Nanowires

As a typical perovskite material,lead titanate(PbTiO3)and its modified materials are widely used in ferroelectric nonvolatile memory(FeRAM),pressure sensors,high frequency piezoelectric filters,etc.due to their good piezoelectricity,ferroelectricity,etc.In recent years,with the rapid development of micro-electromechanical systems(MEMS),more urgent requirements are put forward for miniaturization of ferroelectric materials,especially one-dimensional perovskite ferroelectric materials.Firstly,this paper introduces the research status,structural characteristics and preparation methods of perovskite phase oxides.Secondly,one-dimensional mesoporous lead titanate nanowires prepared by hydrothermal method and their structural characterization are introduced.On this basis,the reasons for the formation of mesopores and the regulation of their size and quantity were studied.The influence of mesopores on the electrical transport and thermal expansion properties of lead titanate nanowires due to the introduction of interfaces in the mesopores was investigated.The microstructure and properties of the prepared nanowires were characterized by high resolution transmission electron microscope(HRTEM),spherical aberration corrected scanning transmission electron microscope(Aberration-corrected STEM),electron energy loss spectroscopy(EELS),in-situ electrical sample holder,in-situ frozen sample holder(Gatan 671),in-situ X-ray diffraction(XRD)and other equipment and testing methods.The main research results are as follows:(1)Single crystal mesoporous PbTiO3 nanowires were synthesized by hydrothermal method,and the nanowires grew along the C axis.The nanowire has a diameter of 50-300nm and a length of 3-15.m u.m,and exhibits good ferroelectricity.Mesoporous PbTiO3 nanowires with different pore size distribution can be obtained with different heat treatment time,and it is found that PbTiO3 nanowires with dispersed pores can obtain more polarized charges.This is because the existence of the interface introduces a large number of defects,such as oxygen vacancies and oxygen ions,which release free electrons under the electric field.Therefore,the electrical properties of PbTiO3 nanowires can be controlled by adjusting the size and number of mesopores,which means that one-dimensional single crystal ferroelectric nano devices with any strength will be expected to be realized.(2)An in-situ experiment of a single mesoporous PbTiO3 nanowire is designed.It is found by fitting that oxygen vacancies and oxygen ions do not participate in conduction under low electric field,and the voltage-current relationship follows Ohm’s law.Under higher bias voltage,it shows Schottky emission,and ln(J)-E1/2 data meet better linear rule.At higher bias voltage,the hybrid emission mechanism is shown.In addition,the appearance and disappearance of domain walls are also observed,which indicates that multiple domains can be realized inside a single PbTiO3 nanowire,thus providing theoretical basis for the realization of multi-bit memory.(3)Through in-situ temperature change experiments,it is found that single crystal mesoporous PbTiO3 nanowires exhibit zero thermal expansion in the temperature range of 93 to 623K.Through EELS characterization,it is found that the positive polarization surface of mesopores is enriched with a large amount of oxygen ions,and the negative polarization surface is enriched with oxygen vacancies,so that the mesopores and the nearby areas are polarized and shielded,and show a positive expansion phenomenon.Therefore,the zero thermal expansion performance of single crystal mesoporous PbTiO3 nanowires is attributed to the combination of negative thermal expansion of the matrix and positive thermal expansion of mesopores and nearby areas caused by ferroelectricity.Compared with room temperature,the ferroelectricity of PbTiO3 matrix is enhanced at low temperature,which shows that the interface enriched ions of mesopores are increased.Different from the method of zero expansion through doping,this provides a feasible idea for single crystal materials to achieve zero expansion through interface regulation.