Preparation of pure Higher Manganese Silicides through wet ball milling and reactive sintering with enhanced thermoelectric properties

• Fast synthesis of pure HMS via wet ball milling and SPS reactive sintering.
• Powders prepared by dry ball milling and wet ball milling show evident differences.
• Prepared undoped MnSiγ have competing ZT compared to the state of the art HMS.

A simple and effective process is used to synthesize undoped Higher Manganese Silicides (HMS), involving ball milling under soft conditions to obtain homogeneous mixtures of constituting elements, and subsequent spark plasma sintering for a direct solid state reaction. For comparison purpose, the ball milling step is carried out under both dry and wet conditions using n-hexane as the liquid medium, Analysis of the granulometry demonstrates that the wet milling process in n-hexane results in finer particles, thus improving the reaction rate later on. According to X-ray diffraction and scanning microscopy, materials produced via wet milling and spark plasma sintering contain only HMS while dry milled samples contain MnSi impuritties. The Seebeck coefficient of the wet milling sample is 20% higher, while its electrical resistivity is 23% lower than those of the dry milling one over the whole temperature range. Moreover, the thermal conductivity was reduced up to 30% when using n-hexane as milling media. The maximum thermoelectric figure of merit obtained is 0.55 at 850 K, a high value for undoped HMS.