Growth Of Ba_1-xSr_xTiO₃Crystals By The Optical Floating Zone Method And Properties

With the rapid development of science and technology and industry on a globalscale, as one of three backbones of modern civilization, material science has graduallyoccupied the material foundation of new society. The single crystal as one of the mostimportant function material, have a wide range of applications in electronic devices,solid state laser, optical instruments and other fields. Ba1-xSrxTiO3（BST）with thestructure of the perovskite structure is a common function material. Because of itshigh permittivity, excellent dielectric, ferroelectric, lightning and physical properties,it has been broadly used in capacitors and other electronic devices, large scaledynamic random access memory, microwave devices and other fields. Single crystalsof Ba1-xSrxTiO3were grown by the optical floating zone method. The grown crystalsof Ba1-xSrxTiO3（x=0、0.01、0.016、0.02）up to6-10mm in diameter and up to60-100mm in length was obtained. The properties of Ba1-xSrxTiO3were tested todescribe the quality of crystal. The work filled the blanks of using the optical floatingzone method to grow large Ba1-xSrxTiO3. This paper mainly includes the followingfour aspects:1. BST crystal growthUniform, pure phase and dense raw BST polycrystalline rods with threecomponents were prepared using the conventional solid-phase synthesis method.Growing the BST (x=0、0.01、0.016、0.02) crystals by optical floating zone method,which need the proper temperature and rate of feeding and growth, and rotation, usedthe polycrystalline rods. The main factors affecting the quality of grown crystals inthe growth procedure were investigated. As a result of the tension of BST moltenzone surface is weak, the BST polycrystalline rod with high quality is theprecondition of crystal growth. The halogen lamp power must match the other growthparameters to keep the stabilization of the melting zone in growth process. The key ofgrowing out high-quality crystal without cracks and inclusions is cooling with cold airand using the technique of necking and expanding shoulder.2. BST crystal structure analysisThe power XRD patterns of the grown BST (x=0、0.01、0.016、0.02) crystalswere measured. The result shows that the BST crystals which were grown by theoptical floating zone method were pure phase of cubic perovskite structure. At the same time the crystal cell parameters were got. The crystals density which weremeasured by the method of buoyancy were compared with the crystals density whichwere calculated by using the data of the crystal cell parameters.3. Quality characterization of BST crystalsThe BST crystals surface with metallic luster and visible growth striation aresmooth, and there are no visible defects. Three components of BST crystal has carriedon the X ray double crystal rocking curve test on direction (110) after grinding andpolishing. The rocking curves shows complete symmetry. There is no second peak.4. Spectrum of BST crystalsThe transmittance spectra of BST crystals were measured by usingspectrophotometer with the wavelength range of250～2000nm. The transmissionspectrum shows the transmittance of BST crystals is above80%with the wavelengthrange of800～2000nm. The obvious absorption appears at around800nm. And it canbe seen that with the increment of the incorporation of Sr2+, infrared transmittanceincreases. The Raman spectrum of direction (100) and (110) were measured. Thepreliminary research and analysis has been carried on.