2007 Fiscal Year Final Research Report Summary
Growth of bulk langasite crystal via manipulating the solid-liquid equilibrium phase relationship under an external electric field
| Project/Area Number |
17360002
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Applied materials science/Crystal engineering
|
|---|
| Research Institution | Tohoku University |
|---|
Principal Investigator |
UDA Satoshi Tohoku University, Tohoku University, Institute for Materials Research, Professor (90361170)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
HUANG Xinming Institute for Materials Research, 金属材料研究所, Associate Professor (80375104)
KOH Sinji Institute for Materials Research, 金属材料研究所, Research Associate (50323663)
SIMURA Rayko Institute for Materials Research, 金属材料研究所, Assistant Professor (90420009)
FUJIWARA Kozo Institute for Materials Research, 金属材料研究所, Assistant Professor (70332517)
|
|---|
| Project Period (FY) |
2005 – 2007
|
| Keywords | Crystal Growth / Crystal technology / Phase equilibria / Electric field imposition / Langasite / Chemical potential / Electric double layer / Floating zone method |
|---|
| Research Abstract |
[Purpose of the research] Develop a mechanism and technology to grow a bulk langasite (La_3Ga_5SiO_<14>:LGS) crystal via converting its incongruent-melting state to congruent by applying an externally electric field.
[Achievements]
1. An external electric field modifies the chemical potentials of both solid and liquid phase by adding electrostatic energy that leads to a new equilibrium state in terms of temperature and composition. Based on this mechanism, the incongruent LGS was converted into congruent. The compositional dependence of the electrical permittivity of the phases around LGS composition determines whether or not such a conversion is possible. In the case of LGS conversion, the permittivity should increase toward the La-rich composition.
2. The conversion was successful experimentally when an electric field of 600 V/cm was applied. However, the analytical consideration shows as much larger electric field as 10^4-10^5 V/cm that may be sustained in an electric double layer (~nm) forming at the boundary of melt and platinum crucible wall or at the solid-liquid interface.
3. A floating zone furnace attached with an electric field imposition system was developed. LGS crystal of about 10 mm diameter was successfully grown in congruent manner under an externally applied field of 600 V/cm.
4. The effect of an electric field on the growth process of YBCO crystal via a peritectic reaction, i.e., 211 (Y_2BaCuO_5) + liquid->YBCO (123) was studied. The external electric field enhanced dissolution of the 211 gains, but had almost no effective electric field operating on the transportation process of the solute, and little effect was observed on the attachment kinetics. On the other hand, the external electric field increased the critical energy for the nucleation of the YBCO grains, which retarded the nucleation of the YBCO grains.
|
