Influence On The Thermoelectric Properties For Nb Doped SrTiO₃ By Ion Implatation

Environmental pollution and energy crisis appear all over the world at the end of the 20th century.The reasons of people following their inclinations of mining limited mineral,and a lot of using of all kinds of energy,they lead the rapid depletion of fossil fuels that have accumulated over billions of years.The energy that humans are able to exploit is drying up.Scientists are working on new energy sources,and how to improve energy efficiency.Thermoelectric materials began to attract people's attention.Because these materials can convert waste heat from industrial production into high quality electrical energy through the seebeck effect.In addition,thermoelectric materials can be used not only to generate electricity,but also to use the reverse effect of seebeck-the parafel effect-for thermoelectric refrigeration.In these two processes,it does not produce environmental pollution,and it is green clean energy material.Thermoelectric materials also have the charateristics of small volume,high temperature resistance and long life.Thermoelectric materials make up for the short board of traditional power generation technology,which is widely used in transportation,aerospace,medical equipment and daily life.Thermoelectric materials with practical application value are mostly alloy materials,such as Bi₂Te₃ and Si Ge have been applied in the fields of generator and electric refrigeration.In practice,ZT is required to be greater than 1,so far only a few alloy compounds,such as Bi₂Te₃ and AgPb₁₈SbTe₂₀,meet this requirement.But these two kinds of materials contain harmful heavy metals and other problems,it has limited its large-scale application.Oxide materials have high temperature stable performance,simple preparation process,non-toxic,the advantages of low cost under the attention of people.In recent years,NaCoO p type oxides thermoelectric materials show better performance.Compared with the traditional thermoelectric material,the oxide thermoelectric material has a higher carrier effective mass.The study finds that,the thermal properties of the materials improve a lot after doping some materials.However,the existing doping process has many steps,and the process is complex,especially for thermoelectric thin film materials,which is not suitable for mass production in factories.The production of doped thermoelectric thin film materials can be optimized by ion implantation technique.This paper mainly carries on the following research work:1.Using pulsed laser deposition?PLD?in LaAlO₃?001?single crystal substrate are prepared by high quality Ruddlesden-Popper?RP?homologous phase Sr_n+1Ti_nNb_3n+1?n=1,2,3,??series of thin film.A series of RP phase Sr_n+1Ti_nNb_3n+1n+1 epitaxial thin film samples are obtained by annealing treatment in high temperature reduction atmosphere.The conductivity and seebeck coefficient of these epitaxial films are measured using physical performance test system?PPMS?.Atomic force microscope?AFM?image shows that annealing temperature affects surface morphology.SrTiO₃?STO?and Sr₄Ti₃O₁₀?STO4310?show a metal insulator transition.The freezing effect of carrier is the main effect between 0 and 100 K,and as the temperature rises,the conductivity increases.The phonon freezing effect is the main effect between 100 and 200 K,and the conductivity decreases with the increase of temperature.Sr₃Ti₂O₇?STO327?is a semiconductor conducting behavior.The difference is mainly caused by the change of the n-value of RP phase Sr_n+1Ti_nNb_3n+1,resulting in the change of crystal structure and electron density.At low temperature,the test results of sample conductivity show that the conductivity is determined by the interaction between electrons and electrons.The results of conductivity and seebeck coefficient show that the transport mechanism of carrier is in accordance with the small polaron model.Under the 300 K,STO,STO4310 and STO327 power factor respectively is 0.016,0.017 and 0.006 m W/m×K².The power factor of RP phase Sr_n+1Ti_nNb_3n+1n+1 epitaxial film is smaller.2.Ion implantation is used to carry out the doping of Nb elements in SrTiO₃,which resultes in lattice damage and a large number of lattice defects due to ion implantation.First in different dynamic annealing temperature is 473 K,523 K,573 K,injected a dose of100x10¹⁴/cm²,200x10¹⁴/cm²,300x10¹⁴/cm²,400x10¹⁴/cm²Nb ion,and then at room temperature,the power factor of the tested samples,found in the best dynamic annealing temperature is 573 K,the sample performance is best.Select the temperature as the dynamic annealing temperature of the series.3.SrTi_1-x-x Nb_xO₃?x=0.05,0.10,0.15,0.20?of different Nb contents are prepared by ion implantation,and the dynamic annealing temperature is 573 K,and then annealed treatment are conducted in the high temperature reduction atmosphere.The XRD atlas shows that all of these Nb ion implantation SrTiO₃ films are high quality epitaxial films.The thermoelectric properties of this series of samples are tested at a temperature range of 100 K to 380 K.Injection dose is 300x10¹⁴/cm² samples with the highest power factor,2.5 mW/m×K².Compared to the power factor of 0.44 m W/m·K²in the membrane samples of the research group at 380 K,we have increased five times.