Progress in Physics

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12 October 2020, Volume 38 Issue 6 Next Issue

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Thermal metamaterial: Geometric structure, working mechanism, and novel function

Huang Ji-Ping

2018, 38 (6): 220-238.

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How to freely control heat transfer at macroscopic scale is always a dream of human beings due to important applications in thermal protection, detection, and control/management. Within the past decade (2008-2018), thermal metamaterials have been shown as a promising candidate for this purpose. Here, I review the up-to-date research progress in the field, which mainly includes the following novel phenomena and functional devices together with initial applications: thermal cloak, concentrator, dual function, thermal rotator, macroscopic thermal diode, thermal camouflage, thermal transparency, thermal crystal, energy-free thermostat, abnormal conduction in networks, convection cloak/concentrator/camouflage, and thermal radiation cooling. The underlying mechanisms are presented according to six categories of theory: transformation thermotics, direct solution of Laplace equation, energy band theory, phase transition theory, transformation thermal convection, and thermal radiation theory. I also introduce and comment their prospects from fundamental research to industrial applications. This review has relevance to novel controls of heat transfer (conduction, convection, and radiation) by using artificial structures or devices.

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The orbital-ordering and itinerancy effects on the physical properties in AV2O4 (A = Mn, Fe, Co)

Ma Jie, Lin Gao-Ting, Luo Xuan, Sun Yu-Ping

2018, 38 (6): 239-252.

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Due to the complicated interplays of spin-frustration, orbital-ordering, and electron-itinerancy, the spinel vanadate, AV2O4, exhibits the interesting physical phenomena and attracts a lot of attention in both scientific and industrial areas. With the method of adjusting the A-site ions, we studied the mechanisms of those specific physical properties, such as the magnetic-structural phase transition, the effects of the local and itinerant electrons. Applying the techniques of magnetic susceptibility, specific heat, variable temperature X-ray diffraction and neutron scattering, and first-principles calculations, we studied the systems of Mn1??xCoxV2O4 and Fe1??xCoxV2O4, and found that: (i) For the low Co-doping compounds, the system was subject to local V3+ and A-site Fe2+. The geometrical frustration from the V-tetrahedra was weak, and the orbital sequence action tended to accompany the structural phase transitions with the magnetic ordering. Hence, the spin-lattice coupling was strong. (ii) For the high Co-doping compounds, the strong electronic itinerance decreased the orbital effects of the V-ion, and the exchange energy, JAB, enhanced, which induced the system isotropic. Therefore, the magnetic phase transition temperature increased, while the structural phase transition temperature shifted to a lower temperature or even finally disappears.