Fabrication And Properties Of Wide-bandgap Semiconductor CuAlO₂ Tablets And Films

Energy crisis and environmental pollution pose a great threat to human development.At the same time,a large amount of energy as waste heat will be lost in the process of energy use.How to effectively utilize waste heat is a subject worth studying.Thermoelectric materials can directly convert heat energy into electric energy,but the low energy conversion currently limits their practical application.This is because thermoelectric materials with good performance need to meet three conditions at the same time:good conductivity,high Seebeck coefficient and low thermal conductivity.It must be explained is that these three parameters are interrelated and it's difficult to regulate them independently,which seriously limits the improvement of thermoelectric materials.CuAlO₂ is a kind of promising thermoelectric materials with unique two-dimensional structure,high theoretical thermoelectric properties,high stability and environmental friendliness.CuAlO₂ tablets doped with carbon nanotubes(CNTs)and CuAlO₂ films doped with Ni were prepared by solid-phase reaction and sol-gel method,respectively,which effectively improved their thermoelectric properties.In this paper,we obtained some valuable results.The main research results of this paper are as follows:(1)CuAlO₂ powders were prepared by solid-phase reaction:Al(OH)₃ and Cu₂O powders as raw materials were mixed evenly by high-speed ball milling,and then the high-purity CuAlO₂ powders were successfully synthesized by sintering at 1100?in a muffle furnace.CuAlO₂ tablets were prepared with polyvinyl alcohol(PVA)and solid paraffin as adhesive respectively.It was found that the electrical conductivity and Seebeck coefficient of CuAlO₂ tablets with solid paraffin as adhesives were significantly higher than those of CuAlO₂ tablets with PVA as adhesives.The maximum power factor was 2.72×10^-8 Wm^-1K^-2.Carbon nanotubes/CuAlO₂ composite tablets mixed with different proportions of carbon nanotubes were prepared by using a press.It was found that both the amount of carbon nanotubes and the pressure could significantly change the conductivity of the carbon nanotubes/CuAlO₂ tablets.The maximum power factor of the tablets at room temperature reached 1.31×10^-6 Wm^-1K^-2under the condition of 7 MPa and 1 wt.%carbon nanotubes.As the measured temperature gradually increases,the electrical conductivity of the tablets first decreases and then increases.This is mainly because the carbon nanotubes in the tablets are the main factor at low temperature,while the CuAlO₂ phase is the main factor at high temperature.In addition,the adhesive can effectively stabilize the Seebeck coefficient of the tabets,and the maximum power factor of the tablets is 1.5×10^-6 Wm^-1K^-2 at 350K.(2)The undoped and 3 at.%Ni-doped CuAlO₂ films were prepared by the sol-gel method at different temperatures and annealing atmospheres,and were irradiated with different-doses 86Kr³⁰⁺heavy ions with 300 Me V/u.By swift heavy ions irradiation(SHI)irradiation,the defect concentration of the film is increased and the film density is reduced,thereby improving its electrical conductivity.It is found that the crystallinity of CuAlO₂ films annealed at 900?for 75 min in Ar atmosphere is the best.After swift heavy ions irradiation,the surface roughness of the film can be significantly reduced and the conductivity can be greatly improved.The lowest resistivity of film is11.5?cm.Ni doping can effectively avoid crystallinity loss of CuAlO₂ films and decrease the transmittance of the films.After irradiation,the light transmittance of the film at 550 nm is still as high as 74%.