| Ferroelectrics have been one of the most attractive research interests in physics since its discovery due to the abundant physical phenomena and effect including piezoelectricity, pyroelectricity, electro-optic effect, acoustic-optic effect and nonlinear optical effect. Since the last few decades, ferroelectric materials have been used in a variety of field like FeRAMs, micro piezoelectric motor, high permittivity thin film capacitor, infrared pyroelectric detectors, optical waveguide, ultrafast switching, phased-array radar, three-dimensional trenched capacitors and laser display (PPLN). It is predictable that the ferroelectrics will have great value in all kinds of field in the near future. Perovskite ferroelectrics have been most studied because of the simple structure and the vast number of the isomorphism. And BaTiO3and PbTiO3are the most superior among them. But BaTiO3has a phase transition near278K which will break the crystal and its high melting temperature is impossible for directly growth from the Czochralski method. And the Pb element in PbTiO3will damage the environment. Recently, Ba1-xCaxTiO3(BCTO) has been suggest to be good ferroelectric materials because it is environment-friendly, can keep ferroelectric-tetragonal phase for a rather large temperature range, also with a good dielectric and ferroelectric properties. Up to now, the research of BCTO is mainly focused on ceramics because the crystal growth is difficult. In this thesis, we systematically studied the growth, properties and the tunable second harmonic generation of the Bao.77Cao.23TiO3(BCTO-23)single crystal. The main contents are as follows:I. Growth of BCTO-23crystalBCTO-23crystals were grown by Czochralski and optical floating zone method, respectively. The factor that affect the crystal quality was discussed including the sintering of poly crystalline materials, the selection of crystal seed, atmosphere and the parameter of crystal growth. Large-sized single crystal of BCTO-23with dimensions up to Φ15x35mm3has been successfully obtained.Ⅱ. Characterization of the properties of BCTO-23crystal Detailed physical characterization was conducted for the BCTO-23crystal:1. The effective segregation coefficients keff of Ba, Ca and Ti are measured by EDS to be1.04,1.02and0.96, respectively. Unit cell parameters of both tetragonal and cubic phase have been calculated from in-situ x-ray powder diffractions. And the shirking of c axis during the phase transition was established.2. Complete set of anisotropic thermal properties have been measured with the increase of temperature:the crystal exhibits a large negative thermal expansion along the c-axis at cubic phase, while thermal expansion along the a-axis is almost negligible. Excess enthalpy curve was calculated and the total energy of the4mm (?) m3m phase transition asymptotes to E=1.175J/g. Thermal conductivity tensor is calculated to be ki=2.520W/m·K and k3=1.442W/m-K at300K.3. From the dielectric constant measurement, it has been found Curie temperature Tc=371.85K, Curie weiss temperature To=365K and Curie constant C=1.2×105K indicating the first-order and displacive transition features of the crystal. P-E hysteresis loops show a saturation polarization of22μc/cm2and a coercive field of12.5kV/cm.Ⅲ. Ferroelectric domain and Noncollinear quasi phase matchingThe180°and90°domain structure of the crystal was observed using a microscope with polarizers. Then the180°domain distribution was calculated. And by using these ferroelectric domains, noncollinear quasi phase matching second harmonic generation was obtained from the415nm to680nm, and the external angle is calculated both in theory and experiment. |
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