Study On The Thermal Stability And Kinetics Of Thermal Decomposition Of KBe₂BO₃F₂

With the development of 193 nm lithography and the processing of micro and nano precision laser, specially some instruments such as high-resolution photoelectron spectroscope and PEEM, and the fundamental research of chemical reaction dynamic the demands for deep ultraviolet（DUV） laser sources are becoming more and more important. The exploring of solid-state DUV laser source has been in a hot research in the international laser science. Using the nonlinear optical, frequency conversion on laser can be achieved and DUV coherent light sources can be obtained. So exploring a frequency doubling crystal that can realizes the DUV light output is one of hotspots in the field of laser and material science. Until now, KBe₂BO₃F₂（KBBF） is one of the most excellent nonlinear optical（NLO） crystals that can generate DUV below 200 nm by direct second harmonic. It is expected to produce 6th harmonic generation of lasers.KBBF is a kind of incongruent melting compounds, and the growth methods for KBBF crystals mainly contains the flu method and hydrothermalmethodat present. However there are obvious shortcomings: the serious impact of agent concentration, temperature gradient, etc. and the long growth period. The crystal growth habit may be changed with different growth method. The study of the oriented reduced-pressure melts growth method can overcome the shortages of the two methods mentioned above. Andthe process and kinetics of thermal decomposition of KBBF should really be the basis of the oriented reduced-pressure melts growth method.Therefore, the study will become a key which can promote KBBF crystals application as a laser frequency doubling device.In this paper, the high purity raw material powders for growth of KBBF has been synthesized and the thermal stability of KBBF in some vacuum was studied by thermal analysis. The process and kinetics of thermal decomposition of KBBF were also studied by thermal analysis at different heating rates, combined with Malek method and the SEM images.The results showed that a direct and efficient method of KBBF raw material preparation was introduced in step-wiseheating by compared experiments; The melting point of KBBF was decreased to 800℃ below the TG temperature 880℃ in some vacuum; The study on the thermal decomposition of KBBF showed that the process was an irreversible one-way reaction, and with the increasing of heating rate TG curves and DSC curves were gradually tended to high temperature, i.e., the temperature of the same conversion rate would be higher, as is the maximum reaction rate; The activation energy E and pre-exponential factor A were calculated by Doyle and Kissinger Methods, and the values were 440.988kJ/mol and 1.414×1019s-1 respectively; Based on the analysis and calculation, the thermal decomposition process of KBBF belonged to spherical symmetric three-dimensional phase interface reaction（R3）, and the differential equation was deduced as well.