Crystal liquid composition control

Ndj Ba2-xCusO crystals grown by modified TSSG method with liquid composition control... 

Since nanoscale metal nanoparticles are applicable to a number of areas of technological importance, the nano-structured materials chemistry will occupy much attention of scientists. It is certain that controlling the primary structures of metal nanoparticles, that is, size, shape, crystal structure, composition, and phase-segregation manner is still most important, because these structures dominate the physical and chemical properties of metal nanoparticles. Now the liquid phase synthesis facilitates the precise control of the primary structures. 

In the case of Y123, variation of the initial flux composition is advantageous in the preparation of thick crystals by the self-flux method (sect. 5.1) or in the control of crystalline film orientation in the LPE method (sect. 5.4). However, for LRl 23 crystals the control of liquid composition is crucial even for their superconductivity enhancement. 

Nucleation is necessary for the new phase to form, and is often the most difficult step. Because the new phase and old phase have the same composition, mass transport is not necessary. However, for very rapid interface reaction rate, heat transport may play a role. The growth rate may be controlled either by interface reaction or heat transport. Because diffusivity of heat is much greater than chemical diffusivity, crystal growth controlled by heat transport is expected to be much more rapid than crystal growth controlled by mass transport. For vaporization of liquid (e.g., water vapor) in air, because the gas phase is already present (air), nucleation is not necessary except for vaporization (bubbling) beginning in the interior. Similarly, for ice melting (ice water) in nature, nucleation does not seem to be difficult. 

Inspired by these Surface Science studies at the gas-solid interface, the field of electrochemical Surface Science ( Surface Electrochemistry ) has developed similar conceptual and experimental approaches to characterize electrochemical surface processes on the molecular level. Single-crystal electrode surfaces inside liquid electrolytes provide electrochemical interfaces of well-controlled structure and composition [2-9]. In addition, novel in situ surface characterization techniques, such as optical spectroscopies, X-ray scattering, and local probe imaging techniques, have become available and helped to understand electrochemical interfaces at the atomic or molecular level [10-18]. Today, Surface electrochemistry represents an important field of research that has recognized the study of chemical bonding at electrochemical interfaces as the basis for an understanding of structure-reactivity relationships and mechanistic reaction pathways. 

The second point is that the composition of the crystal is controlled mainly by the composition of the liquid phase equilibrated with the solid phase. A crystal grown at the interface of the solid and liquid is cooled under the same Pasj but the composition of the grown crystal does not change during this process except at the surface of the crystal. This may be due to the difference of reaction rate between the gas-liquid and gas-solid phases, i.e. the reaction rate between gas and liquid is faster than that between gas and solid. 

---