Differential ac method of thermopower measurement

Abstract

A new differential ac technique is described for rapid and continuous measurement of thermoelectric power of thin metallic ribbons over a wide temperature range. Sinusoidal heating of one thermocouple junction by means of a small resistive heater results in a measuring principle which eliminates spurious thermoelectric voltages in the lead wires and favorably benefits from ac signal processing. The resultant equilibrium temperature of the heated junction contains a constant term depending on thermal parameters of the system, and an oscillating term with a frequency-dependent amplitude. By choosing a suitable sample configuration no corrections are required for the thermal response of the system. By careful shielding of the measuring circuits and using modern lock-in amplifiers noise voltages can be reduced to less than 1 nV for measuring frequencies below 10 Hz. Measurements accurate to 1% are possible, using temperature differences smaller than 10 mK. The effectiveness of this technique is demonstrated by comparing our measurement of the thermoelectric power of an amorphous Fe80B20 alloy with measurements using conventional techniques and by studying the thermopower of an amorphous Fe90Zr10 alloy in the vicinity of its second-order magnetic phase transition.

Temperature Dependence of the Electrical Resistivity of a-FeZr Alloys

“…This kind of reentrant behavior has been observed in a-FeZr alloys containing 8 to 10 at% Zr [6]. Other experiments such as electrical resistivity [7,8], magnetoresistivity [9 to 11] and thermoelectric power [12] were also carried out on a-Fe 90 Zr 10 . This alloy exhibits a resistivity minimum [8,11] similar to that observed in many other amorphous magnetic systems.…”

Computer-controlled thermoelectric power measurement for bulk high T c superconductors

“…2. The upper and lower holder blocks, (6) and (3), are made of OFHC copper. The upper block (6) and the support (2) are glued in place in the sample holder rod.…”

“…The upper and lower holder blocks, (6) and (3), are made of OFHC copper. The upper block (6) and the support (2) are glued in place in the sample holder rod. A screw is used to move the lower block (3) back and forth inside the sample rod along the axis so we are able to measure samples with lengths varying in range from 3 to 15 mm.…”

“…This technique also ensures a good connection between the sample and the holder blocks. The heater coil is made from varnish coated heating wire and wound directly on the upper holder block (6). To reduce the magnetic noise caused by the current flowing in the heater coil, we use an equal number of turns in the clockwise and counterclockwise directions.…”

Simple design for Seebeck measurement of bulk sample by 2-probe method concurrently with electrical resistivity by 4-probe method in the temperature range 300–1000 K

“…Seebeck coefficient metrology includes two well-known methods: the integral method [2][3][4][5][6][7] and differential methods [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. The integral method requires a longer sample so that a large T can be applied across the sample by changing its hot end temperature with no change in temperature of its cold end.…”