Approaching extremely low thermal conductivity by crystal structure engineering in Mg 2 Al 4 Si 5 O 18
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Jiemin Wang and Jingyang Wanga) High-performance Ceramics Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China (Received 18 September 2015; accepted 20 November 2015)
One of the challenges in developing a low thermal conductivity material addresses on searching lightweight ceramic without heavy or rare-earth (RE) elements. Mg2Al4Si5O18 interests us for its very low density and complex crystal structure. The first-principle calculations were performed to predict mechanical and lattice thermal conductivity of hexagonal and orthorhombic phases of Mg2Al4Si5O18. According to Debye approximation and the Slack model, the lattice thermal conductivity varies with temperature in 804.6/T and 719.7/T, yielding 2.95 and 2.64 W/(mK) at room temperature, respectively. The high temperature limits of thermal conductivities are as low as 1.33 and 1.29 W/(mK). The thermal conductivities of both polymorphs of Mg2Al4Si5O18 are lower than most of RE-containing silicates and zirconates. The present work suggests that Mg2Al4Si5O18 is a promising lightweight ceramic with extremely low thermal conductivity. We also highlight that enhancing complexity of the crystal structure rather than incorporating heavy RE elements may be an alternative wisdom to explore lightweight thermal insulators.
I. INTRODUCTION
Materials with low thermal conductivity have long been investigated for their broad applications, especially as thermal insulation materials. Researchers usually follow a selection guideline proposed by D.R. Clarke1 to search for candidate materials. It says that materials with low thermal conductivity should satisfy four principal conditions: a large molecular weight, a complex crystal structure, nondirectional bonding, and a large number of different atoms per molecule. Accordingly, many studies have been focused on candidates, such as rare-earth silicates,2 zirconates,3,4 and phosphates,5,6 since introducing rare-earth elements is an effective way to increase the atomic mass as well as bonding heterogeneity. However, in view of the sustainable development and cost minimization of thermal insulators, it is imminent to explore a new strategy in which rare-earth elements are no longer crucial to reduce thermal conductivity. As an aluminosilicate free of a rare-earth element, magnesium cordierite (Mg2Al4Si5O18) was taken as the cutting-in point to enrich the scope of material selection. It has been reported to own very low thermal conductivity at
Contributing Editor: Yanchun Zhou a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.367 J. Mater. Res., Vol. 30, No. 24, Dec 28, 2015
room temperature (RT) [;3 W/(mK)]7,8 compared with other candidates (details summarized in Table I7–10). At the same time, the density of Mg2Al4Si5O18 is much lower (;2.51 g/cm3) than most thermal insulation materials. Recently, some lightweight materials with low thermal conductivity like MPO4,5 MP2O7,11,12 and MSiO413 have attra
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