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Demonstrating the Expansion of an Iron Compound with Decreasing Temperature (Negative Thermal Expansion) (Press Release)

Release Date
27 May, 2011
  • BL02B2 (Powder Diffraction)
- New feature of iron: expected to be applied to precision components

Japan Science and Technology Agency
Ehime University
Japan Synchrotron Radiation Research Institute
RIKEN

　

As part of the Use-Inspired Fundamental Research of Japan Science and Technology Agency (JST), Ikuya Yamada, Assistant Professor at the Graduate School of Science and Engineering, Ehime University, and his colleagues have succeeded in observing the expansion of an iron compound with decreasing temperature.

Ordinary substances expand with increasing temperature and contract with decreasing temperature (positive thermal expansion).1) Thermal expansion causes the destruction of materials such as glass, which breaks when boiled water is poured on it. It is expected that this problem will be solved by the development of materials with a near-zero thermal expansion rate. Hence, efforts are being made to develop substances with negative thermal expansion,2) namely, substances that contract with increasing temperature and expand with decreasing temperature (Fig. 1), and to combine these substances with substances exhibiting positive thermal expansion to obtain materials with a zero thermal expansion rate.3) However, because the number of substances with giant negative thermal expansion is limited, the development of substances with such a property has been desired.

In this study, the research group succeeded in synthesizing a new ferrioxide (SrCu3Fe4O12) with a complex perovskite structure5) by ultrahigh-pressure synthesis4) at a pressure of 15 GPa and a high temperature of 1,000oC. By crystallography using the high-brilliance X-rays at SPring-8, they found that this substance has a significant negative thermal expansion at temperatures below its freezing point. This is the first ferrioxide to exhibit negative thermal expansion. Also, it was found that the negative thermal expansion of this substance is caused by the exchange of electrons between the copper and iron in relation to the state of the strontium sites, which is different from the conventional mechanism of negative thermal expansion.

The breakdown and damage of recently developed high-precision machines and materials due to thermal expansion has become a serious problem. It is expected that the newly discovered mechanism of negative thermal expansion in this study can be applied to the development of future zero-thermal-expansion materials, leading to their application to precision components and machines.

The achievements of this study were published online in the German scientific journal Angewandte Chemie International Edition.

Publication:
"Giant Negative Thermal Expansion in the Iron Perovskite SrCu3Fe4O12"
Ikuya Yamada, Kazuki Tsuchida, Kenya Ohgushi, Naoaki Hayashi, Jungeun Kim, Naruki Tsuji, Ryoji Takahashi, Masafumi Matsushita, Norimasa Nishiyama, Toru Inoue, Tetsuo Irifune, Kenichi Kato, Masaki Takata and Mikio Takano
Angewandte Chemie International Edition (2011), published online 6 June 2011

<<Glossary>>
1)　Thermal expansion (positive thermal expansion)
Ordinary substances expand with increasing temperature and contract with decreasing temperature. This phenomenon is called thermal expansion. The amount of expansion per unit temperature increase (thermal expansion rate) is positive in most substances.

2)　Negative thermal expansion
Some substances contract with increasing temperature and expand with decreasing temperature. Because the thermal expansion rate is negative for these substances, this phenomenon is called negative thermal expansion. This phenomenon is very important for the development of zero-thermal-expansion (see below) materials that do not contract or expand when the temperature changes.

3)　Zero thermal expansion
This is the property of no expansion or contraction with a change in temperature. It is expected that materials with zero thermal expansion can be manufactured by combining substances with positive thermal expansion and those with negative thermal expansion.

4)　Ultrahigh-pressure synthesis
Methods of synthesizing substances at a pressure of several GPa or higher are generally known as high-pressure synthesis or ultrahigh-pressure synthesis. These methods enable the synthesis of substances that cannot be synthesized at atmospheric pressure. In this study, a new substance was successfully synthesized at a pressure of 15 GPa, which is higher than the pressure used in general high-pressure synthesis (up to approximately 10 GPa).

5)　Complex perovskite
A perovskite (general expression: ABO3) is a common crystal structure of metal oxides. A complex perovskite is a perovskite structure in which the A site or B site, which is generally occupied by a single metal, is occupied by several different metals. In SrCu3Fe4O12, the A site is occupied by two metals, Sr and Cu.

<<Figures>>

Fig. 1 Schematic of positive and negative thermal expansion
Fig. 1 Schematic of positive and negative thermal expansion

Fig. 2 Crystal structure of SrCu3Fe4O12
Fig. 2 Crystal structure of SrCu3Fe4O12

Sr, Cu, Fe, and O are indicated by green, red, brown, and blue balls, respectively.

Fig. 3 Change in volume of SrCu3Fe4O12 with temperature
Fig. 3 Change in volume of SrCu3Fe4O12 with temperature

The volume at room temperature is taken as the reference value (=1).


For more information, please contact:
Dr. Ikuya Yamada (Ehime University)
　　E-mail：mail
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