Preparation And Properties Of Y₂O₃-based Transparent Ceramics

Yttrium oxide（Y₂O₃）based transparent ceramics have excellent performance characteristics such as high optical transmittance,wide range of transparent wavelengths,good stability,high thermal conductivity and good mechanical properties,and are a widely used substrate material for laser and fluorescent applications.At the same time,as a new type of optically transparent material,it has very wide application prospects in many military and civilian applications such as aerospace infrared windows and domes,deep-sea sonar detection and electronic display devices.However,being an oxide with a very high melting point（>2400℃）makes the preparation of high-quality Y₂O₃ transparent ceramics require demanding conditions.Therefore,effective sintering to reduce the temperature and prepare high quality Y₂O₃ transparent ceramics is the focus of researchers’attention.In this paper,Y₂O₃ transparent ceramics with only a single Y metal element using YF₃as a sintering aid in the matrix and Sc₂O₃ forming(Y_1-xSc_x)₂O₃ two-phase solid solution transparent ceramics were prepared by using commercial Y₂O₃ powder as the initial raw material,respectively,to effectively reduce the preparation sintering temperature and obtain high-quality Y₂O₃-based transparent ceramics.The mechanism of the obtained Y₂O₃-based transparent ceramic YF₃ assisted sintering action,optical properties,thermal properties and mechanical properties were investigated.The details of the study are as follows:（1）YF₃ was used as a sintering aid for Y₂O₃ powders initially of nanoscale,and Y₂O₃transparent ceramics were obtained at relatively low temperatures of 1400-1550℃using the vacuum sintering method.After ball milling and dispersion,forming and other ceramic preparation processes YF₃ and voids are uniformly present in Y₂O₃embryos,and YF₃becomes liquid phase during sintering and heat preservation making Y₂O₃ particles creep and rearrange rapidly,so that the grain boundary voids present between the grains are rapidly discharged along the grain boundaries,resulting in rapid densification of Y₂O₃transparent ceramics without abnormal growth of grain size.The optical transmittance of the Y₂O₃transparent ceramic sample with a YF₃ concentration ratio of 0.50 at.%was 57.9%at 1100 nm,and the subsequent secondary hot isostatic sintering increased the transmittance to 82.4%at 1100 nm.However,the liquid-phase sintering effect caused by YF₃ resulted in a slight growth of Y₂O₃ transparent ceramic grain size and therefore a slight decrease in Vickers hardness.The thermal conductivity of Y₂O₃ ceramic samples with a YF₃concentration ratio of 0.75 at.%at room temperature reached 15.56 W/（m·K）,compared to11.25 W/（m·K）for ceramic specimens without the addition of YF₃ sintering aid,and the optimal concentration of YF₃ is about 0.50 at.%based on the combined results of optical transmission and thermal properties.（2）Transparent ceramics of(Y_1-xSc_x)₂O₃ two-phase solid solution were obtained with Y₂O₃and Sc₂O₃ sesquioxides,all with a single cubic yttrium oxide structure.The formation of(Y_1-xSc_x)₂O₃ solid solution reduces the preparation temperature of Y₂O₃ transparent ceramics and effectively promotes the dense ceramics.(Y_0.714Sc_0.286)₂O₃ samples have a wide range of optically transparent wavelengths in the range of 0.35～8 m,and their online transmittance remains above 81%in the range of 0.6～6μm,highlighting their advantages as laser substrates and window material.thermal properties,the thermal conductivity of(Y_1-xSc_x)₂O₃ ceramics decreases to some extent,from 11.12 W/（m·K）for pure Y₂O₃（x=0）to 7.20,5.53,5.55 and 6.24 W/（m·K）for(Y_1-xSc_x)₂O₃ at x=0.167,0.231,0.286 and 0.355at room temperature.In terms of thermal properties,the thermal conductivity of(Y_1-xSc_x)₂O₃ ceramics decreases to some extent,from 11.12 W/（m·K）for pure Y₂O₃（x=0）to7.20,5.53,5.55 and 6.24 W/m·K)for(Y_1-xSc_x)₂O₃ at x=0.167,0.231,0.286 and 0.355 at room temperature;for mechanical properties,(Y_1-xSc_x)₂O₃ solid solution transparent ceramics at x=0.23～0.31 have significantly higher mechanical properties due to solid solution strengthening.Their Vickers hardness（H_v）,fracture toughness(K_IC)and biaxial strength（δ_b）are 30%～50%higher than those of pure Y₂O₃ceramics.（3）A series of Eu-emitting red fluorescent transparent ceramics were successfully prepared by using(Y_1-xSc_x)₂O₃ as the substrate and introducing the red fluorescent rare earth element Eu with the chemical formula((Y_1-xSc_x)_1-yEu_y)₂O₃（x=0～025,y=0.005～0.075）as the equipped target.For the((Y_0.75Sc_0.25)_0.925Eu_0.075)₂O₃ ceramic sample,the transmittance in the visible region was 77%higher,and the highest red fluorescence emission peak around 613 nm under 468 nm wavelength excitation was the Eu³⁺electric dipole leap belonging to ⁵D₀→⁷F₂.The weak emission peak positions of Eu³⁺ions jumping from ⁵D₀ to ⁷F₁,⁷F₃ and ⁷F₄ are around 590,650 and 700 nm,respectively.In the series((Y_1-xSc_x)_0.97Eu_0.03)₂O₃ fluorescent transparent ceramic specimens（x=0～0.25）,the QY gradually increased from 59.88%to 78.34%with the increase of Sc（x）content.As the Sc/Y ratio increases,the highest peak of densification occurs within the(Y_1-xSc_x)₂O₃ system;in addition,the transmittance also changes regularly,the absorption of light is more dense within the matrix,and Eu³⁺enters the cell lattice completely,and the probability of Eu³⁺entering the lattice increases as the Sc/Eu ratio increases;therefore,the(Y_1-xSc_x)₂O₃transparent ceramic matrix is a good matrix material for Eu³⁺red fluorescence emission at613 nm.