Optical Floating Zone Growth And Characterization Of Several Dielectric Single Crystals

In this thesis, several dielectric single crystals considered as the promisingcandidate to SiO2dielectrics were successfully grown by applying the optical floatingzone technique to improve the dielectric properties and analyzing the factors on thecrystal growth.Firstly, the factors such as the melt zone shape, crystal diameter, rotation rate,temperature distribution, growth rate and growth streak on the crystal quality wereanalyzed. After the growth parameters were optimized, the Ta2O5single crystal with7-9mm in diameter and40-90mm in length was successfully grown. The crystalsymmetry of the grown crystal that has been obtained by optical floating zone methodwas found to be tetragonal. The dielectric permittivity along [100] direction is81.2,which is2.2times of ordinary Ta2O5ceramic. Both the relative permittivity and losstangent show obvious dielectric anisotropy in Ta2O5single crystal. The mechanism ofthe high dielectric permittivity was discussed. So far, none of the previous articlesreported the growth of Ta2O5high-temperature phase (Htet-Ta2O5) single crystal. Thestudy of physical properties along different crystal direction shows great significanceto the development of high-performance Ta2O5-based devices.Secondly, the (Ta2O5)1－x(TiO2)x(x=0.03,0.05,0.08and0.10) single crystal with7-9mm in diameter and50-90mm in length were grown after the segregation effecton the crystal growth was analyzed. The dielectric properties of (Ta2O5)1－x(TiO2)xsingle crystal were significantly improved and the dielectric anisotropy was obviouslyenhanced. In (Ta2O5)0.95(TiO2)0.05single crystal, the dielectric permittivity along [100]direction is711.3, which is9times of Ta2O5single crystal. The enhancement ofdielectric permittivity mainly results from the stability of high temperature phaseowing to the high temperature gradient and rapid growth speed by optical floatingzone method, the geometric distortion, the new vibration modes by Ti-doped, and thesubstitution of different valent ions. The novel (Ta2O5)1－x(TiO2)xsingle crystal withenhanced dielectric permittivity shows great potential for application in high κmaterial and high density capacitive components, and will be applied to meet therequirements of the microelectronics industry.Thirdly, the Nb2O5single crystal was grown by optical floating zone method. Thegrown crystal that has been obtained was typically about8mm in diameter and80mm in length. Nb2O5single crystal has high dielectric permittivity and low losstangent, which shows the potential for application in high density capacitivecomponents and the microelectronics industry.In addition, the Fe:Ti:Al2O3single crystals were grown in air, O2and Arconditions by optical floating zone method. The obtained single crystals presented the best crystal quality when grown in argon. Through Raman spectroscopy measurementat room temperature, the new sharp peak at646cm-1is identified as an importantevidence which makes it similar to the natural blue sapphire. Fe:Ti:Al2O3singlecrystal has high dielectric permittivity and stability of temperature and frequency,which also shows the potential application as dielectric.