Font Size: a A A

Crystal Growth And Properties Of Magnesium Tantalates

Posted on:2017-04-25Degree:MasterType:Thesis
Country:ChinaCandidate:W Q LiuFull Text:PDF
GTID:2271330482495067Subject:Condensed matter physics
Abstract/Summary:PDF Full Text Request
Because of the long-range order structure of the crystals, more and important position crystals have taken not only in science but also in technology. Therefore, there are very few single crystals exist as natural jewels in nature. They can not satisfy the needs of research and production. To make up for this deficiency and broaden the path to the physical reality and the development of technology, many searchers put their hope in artificial crystals.Among the plenty of variety of ways to grow crystal, the floating zone method is the first choice to grow high melting point oxide or which its process of the growth has a strong response or which has a high demands for impurity distribution, because of its advantages, which are crucible-less, without pollution of simple, without residual stress, high speed of growth, clean and efficient. Within decades since the FZ method been invented, many crystals have been grown by this method, such as the magnetoelectricity crystal MnTiO3, the piezoelectric crystal BaTiO3-GaTiO3, single crystal silicon and so on.With the fast development of satellite communication, modern cell phone and GPS, microwave frequencies dielectric ceramics have been paid increasing attention by not only researchers but also companies, thanks to its important role played in the system of communication. It’s been a research hotpoint for a while to obtain highly effective and high-quality microwave frequencies dielectric materials. And the MgTa2O6 has fantastic dielectric properties (Q X F=59600, ε=30.3, t f=30ppm/℃),making it a potential. Besides due to its band gap structure, and tunnels between layers, MgTa2O6 has a promised application on semiconductor-based potocatalytic water splitting. But in most works, they used polycrystalline simples with the effect of crystal boundary and impurity energy level witch buried its intrinsic properties.In this work, we use FZ-10000-H-VI-VP type Optical Floating Zone Furnace to grow millimeter-sized MgTa2O6 single crystal. Further more we obtain and analyze its Raman spectra and UV-VIS absorbance spectra for the first time.We find out that MgTa2O6 is an indirect bandgap semiconductor with an energy gap Eg=3.86eV. And the band gap used in potocatalytic water splitting is the direct energy gap at r point, Er=4.29eV.Polarized Raman spectra show that all the Raman modes conform the Raman selection rules, but 329cm-1 witch show up at the VV mode and vanish at VH mode witch is opposite according on the Raman selection rules.Temperature dependence Raman spectra show that there is no phase transition in the whole temperature range (-184℃-505 ℃). During the range, all Raman modes show blue shift, broad and intensity decay. The temperature-dependent Raman shift and FWHM broad are considered characterized by phonon-phonon anharmonic interactions. We also obtain the temperature-dependent Raman spectra of the as-grown Mg4Ta2O9. At 84 K, a total of 16 Raman peaks were identified. As the temperature increased, all Raman modes showed blue shift with decreasing intensity, continuously broadening line width, and overlapping. When the temperature reached 834 K, only 12 Raman peaks were left due to overlapping. No new Raman modes were observable after the process began. Theories regarding temperature-dependent Raman wavenumber and FWHM were discussed previously by Wallace. In our experiment, we identified only phonon-phonon anharmonic interactions without any anomalous changes. Therefore, the optical phonon behavior of corundum Mg4Ta2O9 is demonstrably stable in the entire temperature range.Through the research above, we learned about the technique of crystal growth by optical Floating Zone method, laid the root for other crystal growth in the future, learn the basic property of MgTa2O6, and Mg4Ta2O9 and provide a reliably data for the improvement in application.
Keywords/Search Tags:Crystal growth, optical Floating Zone method, MgTa2O6, Raman spectra, band gap structure
PDF Full Text Request
Related items