Study On Preparation And Properties Of (Al_1-xGa_x)₂O₄ Transparent Ceramics

Spinel-type transparent ceramics exhibit high transmittance in the visible to mid-infrared wavelength range,as well as have good thermo-mechanical properties,which make them have wide application areas in both national defense and civil fields.Since the advent of Mg Al₂O₄transparent ceramics,spinel-type transparent ceramic materials such as Al ON,Mg Al ON,and Mg O·n Al₂O₃have been successively developed.For a long time,the composition design,optical and mechanical properties control of spinel-type transparent ceramics have been the focus of research in the field of transparent ceramics.In this study,the composition design,material preparation,structural analysis,and properties of Mg(Al_1-xGa_x)₂O₄spinel-type transparent ceramics were carried out.For this study,Mg(Al_1-xGa_x)₂O₄powders with different compositions were designed and prepared.The results of crystal structure analysis indicate that the crystal structure was significantly affected by the composition change.The lattice constants and anion parameters increase and decrease linearly with the increase of the x value,respectively.Mg²⁺,Al³⁺ions gradually occupy the octahedron preferentially,and Ga³⁺ions gradually occupy the tetrahedron preferentially.The cations occupying sites influence each other.Al³⁺ions for 0≤x≤0.5 were dominated by the Mg²⁺ions no matter in the tetrahedral or octahedral sites;The occupancy of Ga³⁺ions for 0.15≤x≤1 is dominated by Mg²⁺ions in the octahedral sites.Mg(Al_1-xGa_x)₂O₄ceramics with different compositions show different sintering behaviors.In pressureless sintering,as the value of x increases,the sintering activity of the green body increases gradually.In HIP sintering,the sintering behavior of x=0,0.75,and 1 samples are similar.A relatively high temperature is required to effectively eliminate the residual pores of the pre-sintered body and obtain a high transmittance.The samples of other compositions can obtain higher optical transmittance at a relatively lower temperatures.The samples with other compositions could obtain high transmittance by HIP near the pre-sintering temperature.When x≤0.1,it was found that a small amount of Ga³⁺ions substituted for Al³⁺ions could promote the densification of ceramics during sintering and inhibit the growth of grains during HIP sintering to a certain extent.The results indicate that the change of composition could significantly affect the optical,mechanical,thermal,and dielectric properties of Mg(Al_1-xGa_x)₂O₄transparent ceramics.The in-line transmittance of all samples is over 67%at 1064 nm.UV and IR cut-off wavelengths of Mg(Al_1-xGa_x)₂O₄ceramics red-shift with increasing x.The Vickers hardness of full compositions is between 11.65～13.58 GPa,the bulk modulus is between 192.94～201.37 GPa,Young’s modulus is between 257.35～282.08 GPa.the thermal conductivity is between 11.46～21.32 W·（m·K）^-1,the thermal expansion coefficient is between 6.54～7.75×10^-6K^-1and the dielectric constant is between8.54～9.93.In addition,the theoretical model of bond valence could be well applied to predict the thermal and mechanical properties of the Mg(Al_1-xGa_x)₂O₄transparent ceramic system,and the maximum deviation between the predicted value and the experimental value is less than 3%.In this study,a series of Mg(Al_1-xGa_x)₂O₄transparent ceramics were designed and prepared.Through the crystal structure analysis and material property characterization of the system.The relationship among the composition,structure,and properties of Mg(Al_1-xGa_x)₂O₄transparent ceramics were preliminarily established by resolving crystal structure and characterizing material properties.This work provides an important research basis for the development of new Mg(Al_1-xGa_x)₂O₄spinel-type transparent ceramics.