New Synthesis Route for Complex Borides; Rapid Synthesis of Thermoelectric Yttrium Aluminoboride via Liquid-Phase Assisted Reactive Spark Plasma Sintering
Résumé
ceramics are of high interest as high temperature thermoelectric materials with excellent p, n control. In this study, direct synthesis of dense polycrystalline Y x Al y B 14 (x ~0.64, 0.52 ≤ y ≤ 0.67) ceramics was successfully carried out by spark plasma sintering using commercially available precursors. YB 4 , AlB 2 and B powders were reactively sintered with an additive Alf 3 at 1773 K for 5-60 min in reduced Ar atmosphere. The sinterability was remarkably enhanced by liquid phase sintering comparing to conventional synthesis techniques. Phase composition analysis by X-ray diffraction showed that main peaks belong to Y x Al y B 14 with the MgAlB 14 structure type and no peaks of Alf 3 were detected. The thermoelectric behavior was changed from p-type to n-type with increasing Al occupancy. Power factor and ZT values measured in this study were found to be in the same range as the best values previously reported. This original synthesis process is found to be less precursor-consuming as compared to previous synthesis processes, and strikingly, less time-consuming, as the synthesis time, is shortened from 8 h to 5 min for p-type and to 1 h for n-type. The total process time is shortened from ≥3 days to ~4-5 h. This discovery opens the door for more accessible synthesis of complex borides. Thermoelectric materials utilize the solid state Seebeck effect and thereby can directly convert heat to electricity. This energy harvesting technique has some advantages such as reliability, simplicity, environmental-friendliness, and so on. Thermoelectric performance is determined by the dimensionless figure of merit, ZT S T/ 2 σ κ = , where S is Seebeck coefficient, σ is electrical conductivity, T is absolute temperature, and κ is thermal conductivity. However, since S, σ and κ are basically in trade-off relationships, new approaches are required for breakthroughs 1-5. Recently, an important topic is to develop energy harvesting technologies to power IoT (Internet of Things) sensors and devices 6,7. For such a goal, organic, organic-inorganic hybrid, and inorganic materials are being developed to use near room temperature as flexible or micro-sized thermoelectric power generation modules 8,9. On the other hand, at the other extreme of very high temperatures above 1000 K, there are various attractive high temperature thermoelectric applications. Namely, topping cycle for power plants, steelworks, industrial furnaces, etc
Domaines
Chimie
Origine : Publication financée par une institution
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