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著者：X.G. Zheng題名：Giant negative thermal expansion in magnetic nanocrystals発表情報：International conference of Smart Structures/NDE 2009キーワード：概要：抄録：Most solids expand when they are heated but a property known as negative thermal expansion (NTE) has been observed in a number of materials, including the oxide ZrW2O8 (1) and the framework material ZnxCd1-x(CN)2 (2, 3). This unusual behaviour can be understood in terms of low-energy phonons, while the colossal values of both positive and negative thermal expansion recently observed in another framework material, Ag3[Co(CN)6], has been explained in terms of the geometric flexibility of its metal-cyanide-metal linkages (4). Thermal expansion can also be stopped in some magnetic transition metal alloys below their magnetic ordering temperature, a phenomenon known as the Invar effect (5,6), and the possibility of exploiting materials with tunable positive or negative thermal expansion in industrial applications has led to intense interest in both the Invar effect and NTE.
Here we report the finding of giant negative thermal expansion in magnetic nanocrystals of CuO and MnF2. The lattice constants of the nanocrystals at various temperatures were investigated by synchrotron X-ray diffraction. We found a large NTE effect (β=--1.06 10-4K-1) for 5nm nano crystals of CuO below its magnetic ordering temperature (Fig. 1). By comparison the renowned NTE compound ZrW2O8 has β=--2.6 10-5K-1 (1-3). Similar result was observed for nano particles of MnF2 but not for NiO. Larger particles of CuO and MnF2 also show prominent Invar effect below their magnetic ordering temperature constant, whereas this behaviour is not observed in NiO. We propose that the NTE effect in CuO (which is four times larger than that observed in ZrW2O8) and MnF2 is a general property of nanoparticles in which there is strong coupling between magnetism and the crystal lattice.英語フィールド
Author：X.G. ZhengTitle：Giant negative thermal expansion in magnetic nanocrystalsAnnouncement information:International conference of Smart Structures/NDE 2009An abstract：Most solids expand when they are heated but a property known as negative thermal expansion (NTE) has been observed in a number of materials, including the oxide ZrW2O8 (1) and the framework material ZnxCd1-x(CN)2 (2, 3). This unusual behaviour can be understood in terms of low-energy phonons, while the colossal values of both positive and negative thermal expansion recently observed in another framework material, Ag3[Co(CN)6], has been explained in terms of the geometric flexibility of its metal-cyanide-metal linkages (4). Thermal expansion can also be stopped in some magnetic transition metal alloys below their magnetic ordering temperature, a phenomenon known as the Invar effect (5,6), and the possibility of exploiting materials with tunable positive or negative thermal expansion in industrial applications has led to intense interest in both the Invar effect and NTE.
Here we report the finding of giant negative thermal expansion in magnetic nanocrystals of CuO and MnF2. The lattice constants of the nanocrystals at various temperatures were investigated by synchrotron X-ray diffraction. We found a large NTE effect (β=--1.06 10-4K-1) for 5nm nano crystals of CuO below its magnetic ordering temperature (Fig. 1). By comparison the renowned NTE compound ZrW2O8 has β=--2.6 10-5K-1 (1-3). Similar result was observed for nano particles of MnF2 but not for NiO. Larger particles of CuO and MnF2 also show prominent Invar effect below their magnetic ordering temperature constant, whereas this behaviour is not observed in NiO. We propose that the NTE effect in CuO (which is four times larger than that observed in ZrW2O8) and MnF2 is a general property of nanoparticles in which there is strong coupling between magnetism and the crystal lattice.