High-pressure thermoelectricity measurement using a Paris-Edinburgh press

Figure Caption: (a) Paris-Edinburgh set-up at HPCAT 16-BM-B beamline with the sample cell assembly in place. (b) Schematic design of the sample cell assembly. The top disc (green) represents an MgO and mica disc for insulation, and the gray disc below represents a graphite heater. The two vertical arrows represent the direction of heat flow. Also shown are the spring coils (not to size) that protects the thermocouple/electrode wires inside it. (c) A radiographic image of the sample assembly.
Figure Caption: (a) Paris-Edinburgh set-up at HPCAT 16-BM-B beamline with the sample cell assembly in place. (b) Schematic design of the sample cell assembly. The top disc (green) represents an MgO and mica disc for insulation, and the gray disc below represents a graphite heater. The two vertical arrows represent the direction of heat flow. Also shown are the spring coils (not to size) that protects the thermocouple/electrode wires inside it. (c) A radiographic image of the sample assembly.

Thermoelectric materials have a wide range of applications, such as commercial refrigeration, energy-efficient engines, etc.  Their effectiveness has certain limitations, however, expressed by a dimensionless figure of merit, ZT = (α2σ/κ)T, where α is the Seebeck coefficient, σ the electrical conductivity, κ the thermal conductivity, and T the temperature. To obtain insight into the effects of structure and phase variation on the figure of merit, a technique for in-situ high-pressure thermoelectricity measurement has been developed at the HPCAT by utilizing a Paris-Edinburgh press. The dedicated sample cell design is composed of an asymmetric heat source, directional heat flow guides, thermally transparent but electrically insulating windows, and thermocouple electrode wires of which the Seebeck coefficients are already known. Seebeck coefficient, electrical resistance, and relative thermal conductance of a sample can be measured simultaneously at a given pressure and temperature condition, thereby the relative variations in the figure of merit as the function of pressure can be evaluated. The first demonstration has been successfully made for known Bi I and II phases by showing a dramatic sensitivity of the thermoelectricity across the phase boundary. More details can be found in: Baker et al. J. Synchrotron Rad. 23, 1368-1378, 2016.