Thermoelectric properties of Mg₂Si_1−xC_x crystals grown by the vertical Bridgman method

Abstract

Multicrystalline Mg 2 Si crystals were grown using a Brigdman method combined with a die-casting growth technique. Although molten and/or vapor-phase Mg at elevated growth temperatures exhibit high chemical reactivity with the surrounding crucible materials, the use of an alumina crucible with a BN coating allowed single phase crystal growth and Mg 2 Si of good crystalline quality. Incorporation of carbon into the Mg 2 Si was observed to form Mg 2 Si 1-x C x . For x=0.01 and 0.03, a lower thermal conductivity and higher figure of merit than those of Mg 2 Si were observed in the temperature range from room temperature to 773 K. The maximum figure of merit was 0.62 at 773 K for a Mg 2 Si 0.99 C 0.01 sample.

Vacancies in magnesium silicide – stoichiometric vacancies preferred?

“…Nevertheless, it may play an important role in upcoming new matarials for photo voltaics. It is indeed a semiconductor with a bandgap of 0.77 eV [2]. Additionally, it is consisting of non-poisonous elements and possesses a reasonably low melting temperature of 1102 °C.…”

Non-wetting crystal growth of Mg2Si by vertical Bridgman method and thermoelectric characteristics

“…The BN-based anti-adhesion coating on the alumina crucible can provide a non-stick condition in a very reproducible manner. As has been reported previously, the growth of Mg 2 Si could also be achieved using BN crucibles, such as hexagonal or pyrolytic BN, and dense graphite and alumina crucibles with BN encapsulation [15,16]. In view of crucible fabrication costs, graphite or alumina with BN encapsulation seem to be realistic.…”

“…Seebeck coefficient and electrical conductivity of the grown ingot over the range from 345 to 840 K. Data for the non-encapsulated sample were obtained from Ref. [16]. highly temperature-dependent Seebeck coefficient, a lower electrical conductivity and phonon-oriented thermal conductivity, compared to the sample with no anti-adhesion encapsulation.…”

“…From following results of thermoelectric measurements, samples with and without using BN encapsulation are shown in figures to understand the effect of encapsulation [16]. Fig.…”