Research On Preparation And Electrical Properties Of C12A7:e~-

[Ca₂₄Al₂₈O₆₄]⁴⁺:4e^–?C12A7:e^-?is an inorganic electride formed by a three-dimensional cage structure and electrons randomly distributed in the cages.C12A7:e^-as an electride that can stably exist at room temperature,it is considered to have the opportunity to be used as a new type of cathode material in many display devices and electron source devices because of its lower work function and excellent conductivity.At present,the main synthesis methods of C12A7:e^-include melt-solidification method,metal vapor reduction method and thermionic implantation method.These methods all indirectly obtain C12A7:e^-from the insulating oxide C12A7:O^2-,with long synthesis cycle and complex preparation process.In order to solve these problems,this paper adopts aluminothermic method to synthesize polycrystalline C12A7:e^-powder without heterogeneous phase in one step.This method is fast and simple.The main research contents and results of the paper include:1.The band structure and density of states of C12A7:O^2-and C12A7:e^-were calculated using the CASTEP module in Materials Studio software,and the reasons for the good electrical conductivity and low work function exhibited by C12A7:e^-were analyzed.The calculation results show that,compared with the insulating oxide C12A7:O^2-,the reason why C12A7:e^-has metal-like conductivity is that it has a unique semi-filled cage conduction band structure near its Fermi level.The calculation results of the state density of C12A7:e^-indicate that the electrons in the cage conduction band are mainly s-state electrons of Ca.2.C12A7:e^-was synthesized in one step by the aluminothermic method.XRD,SEM and other characterization methods were used to analyze the product's phase composition,micro-morphology et al.The experimental results showed that the incorporation of aluminum powder played a key role in the solid-phase synthesis of the C12A7:e^-.When the sintering temperature is 1250?and the concentration of aluminum powder is 5%²5%,C12A7:e^-can be synthesized effectively,and no obvious heterogeneous phase is detected in the product.Among all the prepared samples,the samples with a sintering temperature of 1250°C and an aluminum powder concentration of 10%have good micro-morphology.The particle size is about 1⁸?m.The particle surface is clean and the edges are clear.It is absorbed by diffuse reflection.The electron density of the sample was 1.45×10²¹ cm^-3.3.The thermionic emission test was performed on the powdered C12A7:e^-sample prepared by the aluminothermic method.The test results showed that the sample with a concentration of 10%aluminum powder and a sintering temperature of 1250°C had the largest emission current density.When the anode voltage is 900 V and the test temperature is 1250°C,the emission current density is 0.22 A·cm^-2,the average effective work function is 2.79 eV,the Richardson work function is 2.40 eV,and the Richardson constant is 5.16.4.The resistance of the block C12A7:e^-sample was tested with a DC resistance tester and its corresponding conductivity was calculated.The experimental results show that when the sintering temperature is 1250°C,the electrical conductivity of the sample gradually increases with the increase of the concentration of aluminum powder,and the conductivity of the sample with the concentration of aluminum powder at 10%has the largest change.The sample with a concentration of 25%has the largest conductivity(1.11S·cm^-1).