Ultra-low thermal conductivity in scheelite ceramics
AIT LAASRI H. 1, BSAIBESS E. 1, BRAULT D. 1, NATAF G. 1, DELORME F. 1, GIOVANNELLI F. 1
1 GREMAN UMR7347, Blois, France
Materials exhibiting a low thermal conductivity (k) are key components in several devices, e.g. gas engines where they act as thermal barrier coatings and thermoelectric [GN1] coolers. Recently, Liu et al. , predicted ultra-low thermal conductivity in scheelites (ABO4). For instance, BaMoO4 and BaWO4 thermal conductivity are predicted to reach values below 1 Wm−1K−1. In this work[GN2] , we have synthesized BaMoO4 and BaWO4 ceramics and measured their thermal conductivity, which we find to be of 0.8 and 1.2 Wm-1K-1 at 400 K, respectively. This work confirms thus the low thermal conductivity of scheelite structure .
To reach even lower thermal conductivity, we took inspiration from[GN3] perovskites (ABO3) where it has been shown that A-site deficiency leads to significantly lowered thermal conductivity values . Therefore, we have synthesized A-deficient scheelite La2Mo3O12, Ce2W3O12 and La2W3O12 ceramics and measured ultra-low thermal conductivity values (≈ 0.7 Wm−1K−1, 0.4-0.2 Wm−1K−1 and 0.2[GN4] Wm−1K−1, respectively in the range of 400–900 K) .
The impact of vacancies on the reduction in thermal conductivity has been then evaluated in BiVO4 -Bi2/3MoO4 solid solution. Indeed, this solid solution allows to control the amount of vacancies in the structure through the value of x in ?i1-(?/3)?x/3????1-??4 (? denotes vacancies). We find that the thermal conductivity decreases with increasing vacancies content from 1.8 Wm-1K-1 for x=0 down to 1.5, 1.3 and 1.2 Wm-1K-1 for x=0.05, 0.2 and 0.4, respectively at 300 K.
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