The effect of Al/Si ratio on the transport properties of the layered intermetallic compound CaAl₂Si₂

Abstract

We report the results of the electrical resistivity and Seebeck coefficient as well as thermal conductivity measurements on the stoichiometric CaAl(2)Si(2) and non-stoichiometric CaAl(1.75)Si(2.25), CaAl(1.9)Si(2.1), CaAl(2.1)Si(1.9), and CaAl(2.25)Si(1.75) compounds in the temperature range 10-300 K. It has been found that the magnitude of electrical resistivity decreases for the non-stoichiometric samples, attributed to the shift of Fermi energy from the dip of the density of states as a consequence of the changed Si/Al content. In addition, a systematic change in the magnitude of Seebeck coefficient as a function of Al/Si concentration has been observed. The results have been associated with the effect of hole/electron doping on the Fermi level density of states. A detailed analysis of the electrical resistivity and Seebeck coefficient suggests the presence of two types of charge carrier and the temperature dependent changes in their mobility. From the thermal conductivity results, we correlated the extent of disorder and Al/Si ratio with various thermal scattering mechanisms in the investigated temperature range.

Electronic structure and transport properties of SrAl2Si2: Effect of yttrium substitution

“…Within the two-band model, it allows us to consider a contribution from a semiconducting like holes in addition to a metallic term as a possible explanation for the observed exotic thermoelectric transport behavior in SrAl 2 Si 2 . It should be pointed out that these interpretations are consistent with the observations in the isostructural compound CaAl 2 Si 2 [14] and the high-temperature result obtained from a single crystal of Sr 2 Al 2 Si 2 [10].…”

“…The T-dependent S in SrAl 2 Si 2 exhibits a broad minimum with an absolute value of about 100 mV/K near 130 K, and then attains a positive slope at high temperatures. The upturn of S in SrAl 2 Si 2 at high temperatures is attributed to the contribution of thermally excited positive carriers across the pseudogap [11,14]. The change in the slope for S at around 130 K suggests the existence of lighter electron and heavier hole pockets in the band structure of SrAl 2 Si 2 .…”

On the ferromagnetism of AlFe2B2

“…On the other hand, a fraction of the Fe at 4j sites might have been substituted by B or Al atoms (even though the measured lattice parameters are very close to those reported for single crystal AlFe 2 B 2 ) [2]. Analogous atomic intermixing was reported to occur in Ca(Al 0.5 Si 0.5 ) 2 [17], and CaAl 2-x Si 2 þ x (jxj o0:25) [18]. Mossbauer Spectra collected at various temperatures.…”

NMR probe of pseudogap characteristics inCaAl2−xSi2+x

“…It is worthwhile mentioning that a recent Seebeck coefficient ͑S͒ measurement on CaAl 2−x Si 2+x also exhibits a similar tendency. 23 As compared to the magnitude of S in CaAl 2 Si 2 , an enlargement of the electron pocket along with a reduction of the hole ones due to an upward shift of E F is responsible for the increase of S value in CaAl 1.9 Si 2.1 . On the other hand, the decrease of S value in CaAl 2.1 Si 1.9 could be associated with a downward shift of E F as a partial replacement of Si by Al in CaAl 2 Si 2 .…”