Growth And Magneto-optical Properties Of Several Rare Earth Titanate Pyrochlore Single Crystals

This thesis reports the systemic investigations of materials synthesis, crystal growth, elementary physics parameters and magneto-optical properties about Gd2Ti2O7、Dy2Ti2O7、Ho2TiO7 and (Tb1-xDyx) 2Ti2O7 (x=0,0.08,0.13,0.20) crystals.The polycrystalline materials were synthesized by the state-phase reaction method or the liquid-phase reaction method. The sintering method of the polycrystalline materials were studied. XRD and infrared spectrum were used to analyze the compositions of polycrystalline materials. The measured susceptibility of polycrystalline materials provided the reference for choosing the target crystals.These crystals had been successfully grown by Czochralski method. The growth techniques of the rare earth titanate pyrochlores (RE2Ti2O7) were investigated by regulating the gradient of temperature field、rotation rate、pulling speed、annealing period and furnace atmosphere. Gd2Ti2O7、Dy2Ti2O7、Ho2Ti2O7 and (Tb1-xDyx)2Ti2O7 (x=0,0.08,0.13,0.20) crystals with large size and high optical quality were obtained. Dy2Ti2O7 crystal with 19-20 mm in diameter and 21 mm in length and Ho2Ti2O7 crystal with approximately 22-23 mm in diameter and up to 10 mm in length were successfully obtained.Powder XRD、Rietveld refinement、thermal expansion coefficient、Vickers hardness and magnetic susceptibility were measured for detecting the structure and the physics properties of as-grown crystals.The transmission spectra at 400-2000 nm wavelength range were measured at room temperature, and the absorption spectra were calculated. Faraday rotations of several crystals were measured using laser sources at 532、633 and 1064 nm wavelengths. The Verdet constants were obtained by fitting and calculating the data of Faraday rotations in different intensities of magnetic field. Dy2Ti2O7、Ho2Ti2O7 and (Tb1-xDyx)2Ti2O7 (x=0,0.08,0.13,0.20) crystals have larger Verdet constants than that of TGG at 532、633 and 1064 nm wavelengths.The effect of different annealing atmospheres and oxygen vacancy concentrations on the absorption spectra and magneto-optical property of Dy2Ti2O7 crystal was investigated by first-principles calculation based on the density functional theory.The results show that (Tb1-xDyx) 2Ti2O7 (x=0,0.08,0.13,0.20) crystals in 500-1500nm wavelength range, Dy2Ti207 crystal in 600-760nm and Ho2Ti2O7 crystal in 700-1080nm can be potential magneto-optical candidate materials.