New Tungsten Bronze-type Crystal Csbn Growth And Properties Of Research

In recent years there has been tremendous surge of interests in the development and demonstration of crystals with the structure of tetragonal tungsten bronze (TTB). The materials family of the tetragonal tungsten bronzes (TTBs) is very attractive due to its outstanding ferroelectric, pyro- and piezoelectric and photorefractive properties, such as SrxBa1-xNb2O6(SBN), (KxNa1-x)2(SryBa1-y)n-zNb2O6(KNSBN), K2Li2-xNb5+xO15+2x(KLN), Pb1-xBaxNb2O6(PBN) and Ba2NaNb5O15 (BNN).The niobates crystals with the TTB structure have many voids in the structure, so we can improve the quality and change their various properties by materials designing and doping. The researches in the field are reported frequently by the researchers in recent years.In 2001 the CBN28 crystal with the dimensions of lcm in the diameter and 5.3cm in the length was grown by a research team of Kolon University Germany. They found that the curie temperature of CBN is 280℃, which is 200℃ high that the widely used SBN. It indicates that CBN has more potential applications.In the thesis we mainly studies the crystal growth, structure analysis, thermal, dielectric and optical properties, moreover, we studies the properties of waveguides, which is fabricated by ion implanting technique.1. Crystal growthWe adopted solid-phase synthesis method to purity the polycrystalline materials and the solid impurities can be effectively removed. With moderate growth techniques, such as the proper calefaction and cooling speed, crawling and rotation rate, high-optical-quality and large dimension single crystal can be successfully grown. The experiment phenomena during crystal growth have been discussed. The effective segregation coefficients of Ca, Sr, Ba and Nb ions in the growth process of CaxSryBa1-x-yNb2O6 crystal have been investigated in order to control the settled proportion of the elements in the melt.2. Structure analysisThe structure of CSBN crystal was studied by X-ray method. X-ray analysis can be confirmed that CSBN crystals are tetragonal and of the SBN type. The parameters of CSBN crystals were calculated according to their X-ray diffraction data. The diffraction peaks in the X-ray powder diffraction pattern were also indexed. The average density of CBN-28 was determined to be 5.372g/cm3 by a Buoyancy method, and the hardness is Moh's 7. In the end we also observed the ferroelectric domains by the TEM and SEM and only found the 180° dommains.3. Thermal, dielectric and optical propertiesThe thermal properties, such as thermal expansion and specific heat of CSBN crystals were discussed. Thermal problems are important in the growth and applications of crystals. If a crystal possesses a large anisotropic thermal expansion coefficient, the crystal may be easy cracked in crystal growth.We analyzed the room-temperature transmission and found that it is transparent in the measured range of 360-3200nm. The curie temperatures of CSBN crystals were obtained by the curves of capacity changes with the temperatures. We found that CSBN's Curie temperatures changed linearly with the composition of the crystals, which are important data to the materials designing.4. He+ ion implanted CBN waveguidePlanar optical waveguides has first been formed by He+ implantation at doses of 1 x 1016 ions/cm2 in the CBN crystal. We have used the prism-coupling method to measure the dark modes and their effective refractive indices. The refractive index profile of the waveguide has been reconstructed by RCM.