Achieved highest performance in material that shrinks without expanding when heated

A research team at the Tokyo Institute of Technology and others has developed a new material that shrinks in volume when heated. A volume change of 9.3%, which is the highest shrinkage rate due to heat, was confirmed for oxides containing strontium. If it is applied to semiconductor equipment and precision machined parts, it may be possible to eliminate the problem of thermal expansion during operation. The company aims to commercialize the technology by promoting improvements such as cost reduction.

When the material is heated, the atomic arrangement changes from rectangular (left) to square (right).

The research team had previously synthesized a material that mixed bismuth with oxides of lead and vanadium and demonstrated a record volume change of 7.9%. Now, when strontium is added to the material, it undergoes a volume change of 9.3% when heated from 177 degrees Celsius to 427 degrees Celsius.

The performance achieved was the highest ever in terms of shrinkage rate with increasing heat, and was obtained using materials containing manganese and nitrogen (1.4%), which are commercially available for research, and oxides of bismuth and nickel mixed with iron (2.4%). greatly surpass.

Using the large-scale synchrotron radiation facility "Spring 8" in Hyogo Prefecture, the crystal structure was analyzed, and the mechanism of shrinkage when heated was investigated in detail.

When the material was heated, the rectangular bonded structure gradually replaced the square bonded structure, and the volume decreased. It was also found that two different structures coexist in the material. Masaki Higashi, a professor at Tokyo Institute of Technology, hopes that the new model will serve as a guideline for improvements.

Bismuth, which has been used in the past, has the effect of promoting structural changes due to temperature, but has the problem of reducing the size of the rectangle before it shrinks. The addition of strontium made the rectangle larger, making it easier for the volume change to occur when it changed to a square.

Synthesizing the new material requires pressures similar to those used to synthesize synthetic diamonds, so the costs will be higher. There is also the problem that it contains lead, a toxic substance, and that the temperature at which it shrinks when heated does not match the temperature at which it expands when cooled. Aiming for improvement by changing the type and composition of elements.