Research Content- Method
Material Synthesis
Not to mention that all materials exist in the world are made of combinations of elements. There are little more than 100 elements on the periodic table. The possibility of their combinations seems endless. However, if you study little bit about inorganic chemistry, you know that there are rules to combine elements that you cannot combine them blindly. For inorganic chemists, the periodic table is like a big stage that you can create your own world with your choice of elements. It is like choosing colors for painting on canvas. When you choose colors, you realize that you are tied up with rules of choosing colors and feel that a bit more than 100 of elements are not enough. If there were three times more, or at least twice more elements, I would be able to create better materials.
Unfortunately, it is difficult to create the exact material as you wish it to be. There are various levels in material synthesis. Creators are in different levels including beginner synthetic chemists, technicians who work to create practical materials with the knowledge and extensive experiences of material synthesis, researchers who create original materials with their outstanding insights and sophisticated expertise, and skilled chemists with the enormous knowledge of materials. From a professional’s point of view, it is easy to tell their skills and ability levels by looking at the materials they created. At the same time, their knowledge and skills have nothing to do with whether the materials they created would be useful in society or not (The word, “useful” may not be appropriate. To be used as a practical material means useful for sure, but materials that have interesting shapes, structures, and properties are also useful for some people to satisfy their intellectual curiosities. ).
The words, “chemical materials” unfortunately have a negative connotation. It is true that there are some negative legacies in the development of chemical materials. It is chemists’ responsibility to solve those problems. Chemists instinctively think about synthesizing materials to create their original materials. Today, it is also their mission to consider how these materials contribute in society.
Let’s discuss little more about the skills for material synthesis.
Level I (Beginners)
When a material has one excellent property, everybody desires to improve it. If this material has a system AB, chemists test to see any changes by switching element A to C or element B to D. If you have studied chemistry, you know which elements to choose to place in C and D. If you randomly switch elements, not only you do not know the result of it, but also there is a possibility that you get an amazing result unexpectedly. It depends on your ability (or your luck) not to miss this unexpected result.
Level II (Professionals of inorganic chemistry)
Nature is a treasure house of materials. Since we talk about inorganic chemistry here, the targets are only inorganic materials. For example, the earth is a huge reactor vessel and materials (minerals) that are made in the vessel are the teachers for inorganic chemists. We live in the environment with the temperature around 20 °C and the atmosphere pressure of 1 atm. However, the inside the earth has very high atmosphere pressure and temperature. Therefore, by referring the forming condition of materials on the earth, we believe it is possible to create new materials at our laboratory. It is the first step to success in synthesis to humbly learn from nature.
Level III (Skilled scientists)
Next is the “expert” level. You use the periodic table as a big stage to freely pick and use elements to create materials by believing your knowledge and experiences (and instinct as well) of elements, just as to paint on a blank canvas. It takes time to create distinctive and creative materials. It has been said that it takes ten years for one project. That means there are only a few materials that one skilled inorganic chemist can create in the entire life. Comparing to the rapidly changing world, the flow of this kind of work goes against it. However, that is why it is an academic discipline.
Let’s talk about inorganic synthesis in particular.
The parameters that inorganic chemists always keep in mind include the following: the reaction temperature (from room temperature to 2000 °C); the reaction pressure (from vacuum state to ultra high pressure); solvents (water, organic solvents); forms of raw materials (solid, liquid, and gas). The first step of inorganic synthesis is to arrange the best combination from these parameters.
In the history of inorganic material synthesis, you can see how these parameters have been developed for people to get involved in. Syntheses are done under ordinary temperature and pressure, high temperature and pressure, and even under vacuum condition. Recently, the method that atomic layers are placed at a time under vacuum condition is utilized. However, tools are just tools. It depends definitely on chemists’ characters what kinds of paintings are created.
To create an extraordinary painting that people have never seen, colors to be used and the composition of the painting (target materials, methods, and conditions) have to be thought out deeply. However, even in the sophisticated situation, whether the material will be created ideally is beyond humanity.
Thus, the process of creating materials is similar to the process of creating art. It is an extremely intellectual game and creation.
It is handy if you have various synthetic techniques to create inorganic materials. In addition to regular baking method, we can change the parameters by using high-pressure method and thin film synthesis method. After all, you need to have a strong will and good knowledge, and above all, the enthusiasm to do the experiments.
Thin Film Synthesis
Recently, our laboratory team has been into thin film synthesis. Here, let’s talk about why making thin films is fascinating.
In the beginning part of inorganic chemistry textbooks, there is a chapter of crystal structure. Not just in inorganic chemistry, but also in any textbooks regarding solid chemistry, crystal structure should be mentioned in the beginning part. In its history, it is said that crystals are made up with the smallest repeated units that are endlessly repeated three-dimensionally (they are not actually endless). As it should be mentioned in the textbooks, although the basis of crystal structure is described with unit lattice, ion (or atom) closest packing can also be the basis of crystal structure. There are cubic and hexagonal closest packings. Crystal structures are made with ions that are arrayed in the gaps formed in the tetrahedron and the octahedron.
When you create a material ABX, you either mix A, B, and X and raise the temperature, or mix them in a solvent such as water and deposit the material. In other words, the starting materials should be mixed up to provoke a reaction between them. However, it is difficult to anticipate the result. To create a material as the way you expect it to be, you have to accumulate all of your knowledge and experiences regarding synthesis and crystal structure. But even if you do that, you would never anticipate the exact result. It seems like somebody else is there to decide the result. Let’s talk about the academic discipline to approach to the truth of it some other time.
It is natural that inorganic chemists hope to assemble materials as the way they like. In the study of the structure of cubic closest packing, you learn that B should be stacked on A, then C should be stacked on top of it. However, since this occurs spontaneously, humans cannot do this on our own. It is our dream.
With the technique of gas phase synthesis, it is technically possible to create a material on a board by stacking a layer of atom A, B, and C.
Although it is still very difficult to create materials as you like, the thin film synthesis method makes a little bit easier to synthesize, comparing to the normal synthesis in solid state reaction.
Nowadays, by the development of epitaxial, we work on to synthesize epitaxial thin films for batteries to create a model electrochemical interface. Thin film synthesis is pretty fascinating, as it is so for researchers who work on the bulk synthesis.
Structural Analysis
In addition to the X-ray structural analysis, our lab team researches on material structures with the neutron scattering method. Neutron scattering methods are done at the neutron scattering facility of High Energy Accelerator Research Organization (KEK). Crystal structures and their structural changes in middle and long distance scattering are investigated with the powder diffractometer VEGA, Sirius, and the small angle scattering device SWAN. The analyses are also done in Japan Atomic Energy Agency (JAEA), Argonne National Laboratory in the United Sates, Rutherford Appleton Laboratory in UK, and the Institut Laue-Langevin (ILL) in France.
