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An Exploration In Ti1-xFexO2 Crystal Growth Using Optical Floating Zone Method

Posted on:2008-02-23Degree:MasterType:Thesis
Country:ChinaCandidate:Z Y GongFull Text:PDF
GTID:2121360212496847Subject:Condensed matter physics
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The significance of Crystal growth, is for the developments of high and new technology, the crystal is an important material basis of the information age. It is the group carrier of laser produce, frequency conversion and the transformation of sound, light, heat, electricity, magnetism and force, which has extensive and important applications in sustainable development of the national economy and national defense construction. The other significance is many of the basic character can be carried out and develop only from the nature of the crystal state in basic researches. In 2006 the National 863 plans projects listed in Low-symmetry characteristics, Growth discipline Study and Application explore of the functional crystal as an special item, "Its scientific objective is that through the Low-symmetry characteristics, Growth discipline study and application explore the functional crystals, a number of important functions in crystal preparation researches is going to be carried out. Two major research directions for the future are the importance functions of crystal growth and applications, several major breakthroughs with important applications, however, access to quality meet practical requirements of the single crystal materials. Addressed their specific application, it is launched the key scientific and technological problems, its practical uses is to provide scientific basis and key technologies." Therefore, crystal growth, involved many of the key scientific and technological problems, increasingly attracts more and more people. We choose iron-doped TiO2 to study, using the latest technology developed in Four ellipsoidal mirror infrared furnace (FZ-T-10000-H-VI-VP) and the optical floating zone method to make crystal growth happen. Meanwhile, this paper discusses the impact of the excessive Co in the LaCoO3 powders, using solid-phase synthesis method.Experiments:1. Fe is doped with different ratios by two methods: ball-milling and manual grinding. The equipment used in Crystal growth is Four Ellipsoidal Mirrors Infrared Furnace (FZ-T-10000-H-VI-VP) which is imported from Japan. The structure, morphology and micro-components of the sample analyzed using XRD, and micro-Raman spectroscopy.2. The experiments have chosen La2O3 and Co3O4 Powder as initial raw materials to prepare LaCoO3 perovskite oxides using a solid-phase sintering method. The structure, morphology and micro-components of the sample analyzed using XRD, XPS and micro-Raman spectroscopy.Results and Analyses:1. Fe is manually grinded into the doping of pure TiO2. The ratios are Ti : Fe = 1 : 0.005,1 : 0.01,1 : 0.03. Ball millings are carried out using an iron can by 20h in low energy mode. The above four different ratios doped TiO2 powder are made into a length of about 60 mm rod, then sintering 1550℃, which is prepared for crystal growth. Meanwhile a growth program using pure TiO2 is carried out as an contrast. XRD analyses indicate that Fe exists as Fe2TiO5 in TiO2 when doped more than 0.01 using manual grinding method. However the existence of Fe can not be observed by ball-milling method. It is because that the milling process can make Fe enter the lattice of TiO2. Therefore no XRD spectra of the Fe peaks are detected. 2. In the process of crystal growth, the melting zone is stable when using pure TiO2 till the end of the process. With the gradually increasing of the amount of Fe-doped, the time that the stability of the melting zone keeps becomes shorter. the samples of the growth process change a lot compared with the pure ones. A metallic sheen can be seen on the surface.3. Floating zone growth samples The XRD and Raman analyses show that pure TiO2's melting zone is stable and can get larger size of the crystal. In Ti : Fe = 1 : 0.005 and 1 : 0.01 ratios cases, the melting zone can be stabilized for shorter periods of time, but the products still have a certain degree of crystalline orientation, the more Fe contents, the smaller size can get. Fe is still not found in XRD spectra. It is indicated that the growth process can make a small amount of doping materials into the lattice. In Ti : Fe = 1 : 0.03 ratios cases, the melting zone is stable in shortest time, and the basic orientation is no crystallization and Fe can be observed. It is indicated that the growth process can not make more doping materials enter the lattice. Fe is dissociated around the TiO2 lattice. However, using ball-milling method , although the melting zone is the least stable, the samples still have a certain degree of crystalline orientation because of the Fe has entered the lattice.These results above show that the doping level directly affects the melting zone's stability in the growth process. Incorporation of Fe lattice will not affect the direction of the crystalline of TiO2. no incorporation of Fe has an adverse impact of crystal orientation.4. In the preparation process, we used the excessive ratio of Co3O4 to make sure of completely response of La2O3 due to the volatilization of Co. The Experiment inspects a different ratios (0%~15% excessive atomic ratio of Co) and the reaction time on the impact of the final product. Results of XRD, XPS and high temperature conductivity showed that with the reduction of excessive Co., the contents of miscellaneous phases decreased. With the increase of sintering time, the contents of miscellaneous phases is gradually reduced, however, during a long time sintering, a Few LaCoO3 powders decomposed. pure phase of LaCoO3 powders can be acquired under the condition of Co in excess of 0% through 70h sintering, However, as raw materials under these conditions are prepared for a long cycle (about 210h), and it always contains always contain La(OH)3 in La2O3 powders even taken an advance burning. So in the ratios of 0% (stoichiometry), Co is still excessive. Crystal growth also need the original powder to be made to rods, and through high-temperature sintering. Whether LaCoO3 powder will decompound or not, it is necessary to be considered in next steps.Conclusions:1. The amounts of Fe-doped directly impact on the extent of the melting zone's stability in crystal growth process. Incorporation of Fe in lattice will not affect the direction of the crystalline. No incorporation of Fe in lattice will make a larger adverse impact of crystal orientation.2. Initial raw materials of LaCoO3 have a significant impact of the growth process of floating zone method. The purity of Co3O4 and La2O3 and the conditions of sintering will make LaCoO3 decomposition. It must be considered over all to find a best way to make pure LaCoO3 powders.3. Crystal growth is a difficult technical work because some practical technique and experience that can not be theoretically explained nor be denoted through measuring characterization, but they are very important. A lot of experience was accumulated about the growth using doped materials, and these works is beneficial for the crystal growth of oxides with a high melting point using optical floating zone method.
Keywords/Search Tags:Ti1-xFexO2
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