Unusual thermoelectric behavior of packed crystalline granular metals

Abstract

Loosely packed granular materials are intensively studied nowadays. Electrical and thermal transport properties should reflect the granular structure, as well as intrinsic properties. We have compacted crystalline CaAl-based metallic grains and studied the electrical resistivity and the thermoelectric power as a function of temperature ͑T͒ from 15 to 300 K. Both properties show three regimes as a function of temperature. It should be pointed out: (i) The electrical resistivity continuously decreases between 15 and 235 K, (ii) with various dependencies, e.g., ӍT −3/4 at low T, while (iii) the thermoelectric power (TEP) is positive, (iv) shows a bump near 60 K, and (v) presents a rather unusual square root of temperature dependence at low temperature. It is argued that these three regimes indicate a competition between geometric and thermal processes-for which a theory seems to be missing in the case of TEP. The microchemical analysis results are also reported, indicating a complex microstructure inherent to the phase diagram peritectic intricacies of this binary alloy.

Influence of Zeeman splitting and thermally excited polaron states on magnetoelectrical and magnetothermal properties of magnetoresistive polycrystalline manganite La 0.8 Sr 0.2 MnO 3

“…The Curie temperature gradually decreases from T C = 284K (for 100Oe) to T C = 281K (for 500Oe). The electrical resistivity was measured by the standard four-probe method using currents up to 10mA (see [8,9]). The temperature dependence of the measured electrical resistivity (Fig.…”

Granular matter: A wonderful world of clusters in far-from-equilibrium systems

“…The (positive) thermoelectric power (46) shows a bump near 60K, after an unusual square root of temperature dependence at low temperature (Fig. 8).…”

“…CaAl 2 . We have used an original route (46) and have obtained tiny crystals. The chemical analysis has indicated a complex microstructure inherent to the phase diagram intricacies (47).…”

On the origin of unusual transport properties observed in densely packed polycrystalline CaAl2

“…7 from Ref. 7 ) with presumably narrow enough grain distribution and quasi-homogeneous low-energy barriers between the adjacent grains.…”

“…Though no tangible superconducting signals were detected, a rather unusual transport properties have been found in these interesting compounds (see Ref. 7 for more details on sample preparation and actual measurements). In particular, the electrical resistance clearly exhibits a power-like (rather than exponential, expected for conventional low-temperature localization scenarios 8,9 ) temperature behavior with resistivity ρ ∝ T −3/4 for 15K < T < 70K (Fig.…”