Sample probe to measure resistivity and thermopower in the temperature range of 300–1000K

Abstract

We have fabricated and tested a sample probe that can measure resistivity (ρ) and thermopower (α) on either bar or rod shaped samples over a temperature span of 300–1000K. The design allows us to perform measurements both in vacuum as well as in inert atmosphere and hence suitable for any oxygen sensitive bulk samples. The main feature is the spring assisted pressure contacts between the sample and the two silver blocks, on which the electrical leads as well as thermocouples are mounted. This enables us to establish good thermal contacts over the entire temperature range of measurements between the sample and the thermocouples. To measure the thermopower, a slowly varying temperature difference (ΔT) is generated across the sample by using a small heater. The resulting slope of thermo-emf (ΔV) vs temperature difference (ΔT) plot is used to obtain the thermopower at any temperature. Resistivity is measured in sequence by a linear four-probe method at the same temperature. Hence in a single experiment, both resistivity and thermopower can be measured. Test measurements carried out on Ni and W standards yielded an accuracy of about few percent for both ρ and α.

A high temperature apparatus for measurement of the Seebeck coefficient

“…The corresponding V values are measured and plotted which allows any offset voltage to be eliminated. 6 In our setup, the temperatures of the top heater and the bottom heater are controlled so that T h and T c values oscillate around one value of the temperature, which we use for the average temperature of the sample. In this oscillation mode, the maximum peak-to-peak T of usually about 10-20 • C are applied.…”

“…5 High temperature Seebeck measurements are often subject to irreproducibility and inconsistency in results due to a lack of standardized guidelines for the measurement procedure. 5,6 For example, errors in temperature measurement occur in the high temperature range due to poor thermal contact between the thermocouple and the sample surface, 6 leading to considerable variation of results between laboratories. In this paper, we describe the most commonly used Seebeck coefficient measurement techniques and the associated potential drawbacks between methods.…”

Measuring thermoelectric transport properties of materials

“…The reason for the high scatter is mainly errors in determining the geometric factor, [56][57][58] indicating that this is indeed important in obtaining accurate resistivities. In the PPMS several options exist for measuring the electrical resistivity.…”

Electrical conductivity measurements on disk-shaped samples

“…The benefits of simultaneous measurements of the thermoelectric properties have long been recognized and therefore many custom-built and commercial measurement systems measure two [1][2][3][4][5][6] or three quantities simultaneously. [7][8][9] Simultaneous measurements reduce measurement time, can decrease measurement errors, and facilitate easy interpretation of the measurement results.…”

“…Identification and optimization of thermoelectric materials requires the determination of the thermoelectric figure of merit ZT = σ S 2 κ T , where σ is the electrical conductivity, S the Seebeck coefficient, κ the thermal conductivity, and T the absolute temperature. The benefits of simultaneous measurements of the thermoelectric properties have long been recognized and therefore many custom-built and commercial measurement systems measure two [1][2][3][4][5][6] or three quantities simultaneously.…”