Magnetic and thermoelectric properties of R3Cu3Sb4 (R=La, Ce, Gd, Er)

Abstract

The rare-earth compounds R3Cu3Sb4 (R=La, Ce, Gd, Er) were synthesized in order to evaluate their potential for thermoelectric applications. Melting in closed tantalum tubes was used to get the materials without loss of volatile Sb components. The structure and the thermal expansion coefficients of these compounds were determined by temperature-dependent x-ray diffraction measurements. We also determined the effective magnetic moments of the rare-earth ions and their valence state. The resistivity of the compounds was measured over a large temperature range from 2 to 470 K. Hall-effect measurements were performed in the range from 30 to 470 K. Additionally, the thermopower and the thermal conductivity were determined. On the basis of the measured data, an estimation of the thermoelectric potential of this group of materials will be given.

Ce3Cu3Sb4: a Canted Antiferromagnetic Semimetal

“…With a heating rate of 4°C/min the liquefaction could be easily determined. Tm was found to be 1740f50 K which is much lower than the reported 2295 K [12]. In Ref.…”

“…[11] a maximum is stated at 19 K. In Ref. [12] a maximum is observed at 4 K. These differences are probably related to the quality of the samples. The rising branch of the resistivity with decreasing temperature has been fitted in all preceding publications with an exponential law p α exp(Εg /2kT) and an energy gap of 7 meV [10, 11] and 5.2 meV [12] or 2.3 meV [12], as a result of a confusion in the text and Fig.…”

“…The electrical conductivity is still a product of the carrier concentration and the mobility and as long as it is not proven which of the two parameters is changing, the claim of a semiconductor is not convincing. In fact between 300 and 30 K, covering most of the rise of the resistivity towards lower temperature, the Hall effect has been measured [12] and no change in carrier concentration has been observed. The mobility, however, can also be thermally activated, in which case one speaks of a trapped magnetic polaron [13,14] (and references quoted therein), which becomes liberated below TC of a ferromagnet.…”

“…In Ref. [12] the melting points of various R3Cu 3 Sb4 alloys (with R being a rare earth) have been collected and Ce3Cu 3 Sb4 has been claimed to have the highest Tm . Compared with Gd3Cu3Sb4 this is improbable since a 4f1 material always has a lower Tm than the corresponding, electronically more stable 4f7 compound.…”

“…In Ref. [12] a maximum of the resistivity near 4 K is shown. A flt of the rising branch with decreasing temperature with the above formula yields an activation energy of 5.2 meV, but these authors never claim Ce3Cu3Sb4 to be a ferromagnetic semiconductor.…”