Growth And Properties Of Several B-site Doped Pyrochlore Tb₂Ti₂O₇,Magneto-optical Crystals

Synthesis and crystal growth by Czochralski method were reported systematically of several B-site doped pyrochlore Tb2Ti2O7 as Tb2Ti2-xSixO7,Tb2Ti2-xMnxO7 and Tb2Ti2-xVxTbxO7 magneto-optical crystals in this thesis,and the structures,physical properties and magneto optical properties of these crystals were explored.Polycrystalline materials were prepared by solid-state reaction;XRD and FT-IR were employed to determine the appropriate doping concentrations and sintering processes.The large size single crystals of Tb2Ti2-xSixO7,Tb2Ti2-xMnxO7 and Tb2Ti2-xVxTbxO7 crystal were successfully obtained by utilizing the Czochralski method and adjusting the appropriate process parameters as follow,the(111)direction columnar alike crystals were selected as seeds,the pulling and rotation rates were 0.7?1.0 mm/h and 6-12 r/min,respectively,and the annealing times were about 40 h.The crystals were all with more than 25 mm in diameter and over 11 mm in length.The cracking-free wafers in certain dimensions were acquired by subsequent orientation,cutting,grinding and polishing.ICP and EDS analysis of the crystal powder were employed to determine chemical formula of the crystals.With XRD analysis and Rietved refinement,the unit cell parameters were calculated,showing that the crystals as-grown were all pyrochlore Tb2Ti2O7 phase with the space group Fd3m and the effects of doping elements on the unit cell parameters were also discussed.Variable temperature(2?300 K)magnetic susceptibility study showed that the crystals grown were paramagnetic materials and the Curie temperatures were calculated.In addition,the hardness and density of part crystals were determined by micro vickers and pycnometer,respectively.The crystal transmittance spectra were measured at the 400?1700 nm at room temperature and the probabilities.of part crystals poor transmittance at some bands were analyzed.The Faraday rotation angles were measured at different bands(532 nm,635 nm,1064 nm)by the self-assembly tester,then the Verdet constants of crystals were fitting calculated to be compared with TGG,resulting in the Verdet constants of Tb2Ti2-xSixO7,Tb2Ti2-xMnxO7 and Tb2Ti2-xVxTbxO7 crystals all greater than TGG.Re-annealing of the wafers in various atmospheres were attempted to observe the influences on transmission and explain the mechanism of color changes.The growth habit and morphology of Tb2Tix2O7 crystal were analyzed by BFDH?Growth Morphology and Equilibrium Morphology calculation showing that(111)was the developing facet which matched well with the experimental fact.In summary,Tb2Ti2-xSixO7 crystal are expected to become eminent magneto optical crystals at 500?1500 nm;Tb2Ti2-xMnxO7 may be promising magneto optical crystals at 700?1500 nm;Tb2Ti2-xVxTbxO7 crystals have larger Verdet constants,however,the application band is relatively short,more suitable synthesis methods or re-annealing are required to gain better crystal.