Study On Preparation And Properties Of CaF₂and Y³⁺, Nd³⁺:SrF₂Transparent Ceramics By Hot-forged Method

CaF2and SrF2are an important direction for the study of solid laser mediumbecause of its advantages such as broad range of transmittance and lower phonon.Transparent ceramic posses a series of advantages such as better mechanicalproperty,thermostability and allowing the preparation of large size sample. However,the CW laser operation for the fluoride transparent ceramic manufactured by powdersintering technology has not been obtained because of the problems of fluoridepowders chemistry and relevant technology processes. The deformation of fluoridesingle crystal can be achieved by hot-forged technology, which introduce low-andhigh-angle grain boundaries and become polycrystal during press-forged process.The presence of these grain boundaries are beneficial to the improvement of thematerial mechanical properties. Thus in this paper CaF2and Y3+, Nd3+-codoped SrF2transparent ceramic based on single crystal was fabricated by hot-forged technologyThe CaF2polycrystals with similar structure of transparent ceramic werefabricated by hot-forged technology. The influence of relative deformation onmicrostructure of crystal was investigated by XRD and optical microscope.Theresults show that as the deformation increases, the obvious grain structure willappeared in the CaF2crystal and the XRD diffraction pattern is identical with theCaF2polycrystal diffractogram.The mechanical properties such as microhardness, compressive strength andbending strength for the CaF2single crystal and CaF2crystal with different relativedeformation at750℃and850℃were measured. The results show these mechanicalproperties of the crystals after hot-forged were improved. The transmittance of theCaF2single crysta and crystal with different relative deformation at850℃wastested.The results show that the transmittance of the single crystal and the crystalafter hot-forged is similar and higher than92%Y3+,Nd3+-codoped SrF2laser ceramic was fabricated by hot-forgedtechnology.The influence of relative deformation on microstructure of crystal wasinvestigated by optical microscope and SEM. The results show that the obvious grainand a regular layered parallel lamellae structure will appear with increase of deformation. moreover the deformation the lager is, the more obvious the structure is.The gain structure similar to polycrystalline ceramic has been formed in theY3+,Nd3+:SrF2sample with75%relative deformation at1150℃.The gain size is notuniform.The size of the finest grains does not exceed1um, and the largest grainsreach a size of10um. The gain structure consists of a layered parallel lamellae,which is as same as the fluoride laser ceramics based on crystal by hot-forgedtechnology in the wordThe mechanical properties such as microhardness,compressive strength,bendingstrength and fracture toughness for the single crystal and Y3+, Nd3+-codoped SrF2crystal with different deformation at1050℃and1150℃were measured. The resultsshow that the microhardness and fracture toughness of the crystals after hot-forgedwere improved,but the compressive strength and bending strength were notimproved.The fracture toughness of the crystal with75%deformation at1150℃is ashigh as0.98MPa.m1/2, nearly two times high than the single crystal (0.491MPa.m1/2).The transmittance and absorption spectra of single crystal and crystal after hot-forgedwere measured at room-temperature.The results show that the absorption intensityand transmittance of the crystal after hot-forged are decreased. The luminescent andlaser properties for the Y3+, Nd3+: SrF2laser ceramic with75%relative deformation at1150℃and single crystal were measured. The results show that the fluorescenceintensity is decreased and fluorescence lifetime is shortened. The CW laser operationwith slope efficiency30.7%was obtained in the Y3+, Nd3+: SrF2laser ceramic. Theslope efficiency30.7%for the ceramic is just inferior to the slope efficiency31.9%for the single crystal.