Design And Properties Study Of “Phase Transition–Optical Switching” Rare Earth Tantalate For Laser Protection Application

In order to design a new anti-laser radiation ceramic material which has the “phase transition– optical switching” property, i.e. this material process a low reflectivity at room temperature and a relatively high reflectivity at high temperature. The crystal structural property, electronic property and optical property, expecially reflectivity of serial RETaO4(RE = Sc, Y, La, Sm, Eu, Dy, Er) and Ba2RETaO6(RE = Y, La, Pr, Sm, Gd) have been studied by first principle calculation and experimental methods. The molecular dynamics method is applied to evaluate the thermophysicalproperties of the potential materials.The results of the first principle calculation show that, the lattice constant and bond length of RE-O reduce withatomicnumber influenced by lanthanide contraction. While the bond length of Ta-O appearsincreasingtrend.Thesplitting peaks of the4 f states appeared in forbiddenbandare attributed to the combined effects of the spin–orbit interaction and the crystal field. The result reveals that replacing RE lowers theenergy level of RE 4f bands continuously with increasing thenumber of 4f electrons, while the band gap of O2p-Ta5 d increasesfirstlythendecreases. As the 4f states at the Fermi level, the reflectivity reaches the maximum, the reflectivity of the M-type SmTaO4, EuTaO4 and Ba2SmTaO6 at 1.06 ?m is71.97%, 93.47% and 68.91%respectively.The phase transion has a significantimpacton optical properties of SmTaO4. The Fermi level moves from the minimum of 4f states to the maxmum with the low temperature phase transform to high temperature phase. The increase of the reflectivity reaches 60%.The XRD and reflectivity at 1.06?m obtained by experiment have a good agreement with the calculation results. The O2p-Ta5 d band gap reduces obviously with atomicnumber and the reflectivity increases. The highest reflectivity of high temperature phaseat 1.06?mreaches 83.39% and 91.46% within Sr and La doping, which is higher80% and 70%than the low temperature phaserespectively. The calculated thermalconductivity and thermal expansioncoefficient of Ba2-xSrx SmTaO are distributed at 6~6.5 Wm-1K-1and7~7.11×10-6 K-1.