Thermal expansion is critical problem in devises which is demand for high accuracy, for example, semiconductor industry, optical communications and precision machining. Techniques for controlling thermal expansion is needed in these fields. Materials with negative thermal expansion (NTE) property is recently gathering attention for compensating the thermal expansion of materials. Most material expanse on heating, but NTE is not a special property. Our group reported that coefficient of thermal expansion of perovskite BiNi1-xFexO3 (BNFO) reaches -180 ppm K-1 near room temperature and it is demonstrated that 18 vol. % addition of the present compound compensates for the thermal expansion of epoxy resin. However high pressure and high temperature process is needed for synthesis of BNFO so this material is far from commercial use because of a view point of cost.

This time, I visited in Northwestern University placed on Evanston, northern city from Chicago. Professor Kenneth Poeppelmeier group, our collaborator, found out that perovskite GaScO₃ can be synthesized by heating of hydroxide hydrogel at low temperature. One of the reasons why BNFO cannot be obtained at low pressure is the decomposition of perovskite structure in ambient pressure when it is heated, so the process using hydroxide hydrogel can be a clue to solve the problem.

I discuss with professor and his graduate student, Ryan Paull and succeeded in obtaining hydroxide precursor for BNFO to synthesized in mild process. I am confident that this results will lead to reduction of pressure and scale-up, which is linked to cost problems.

This visit was not only for research but also for build relationships. I am grateful for being able to receive this kind of opportunity.

物質理工学院材料系材料コース
博士後期課程2年　 西久保匠
滞在先: Northwestern University, Chemistry Department