Enhancement in thermoelectric power of Ce(Ni_1−xCu_x)₂Al₃: An implication of two‐band conduction

Abstract

The thermoelectric power (TEP), resistivity, and heat capacity of the polycrystalline Ce(Ni 1Àx Cu x ) 2 Al 3 system, for x ¼ 0.0-0.4, are reported. A clear enhancement of TEP at low temperatures is seen upon substitution of Cu and is expected to be useful for low-temperature thermoelectric applications. To understand such an enhanced TEP we have employed a twoband model based on the Ce-4f and conduction bands proposed by Gottwick et al. A clear evolution of a 4f band moving toward the Fermi level that is becoming sharpened is seen and is predicted to be close to resonance. The fit parameters of the TEP (S) are physically reasonable. The resistivity data shows an evolution from a simple compensated metal to a paramagnetic one via the Kondo route. This is in line with TEP parameters. In addition, a clear enhancement seen in the electronic part of the heat capacity upon Cu substitution and the evolution of magnetoresistance behavior corroborates the results. Possible bipolar effects are also taken into consideration along with an electron-phonon interaction term to explain the almost temperature-independent part of the resistivity, still yielding a considerable component of disorder.

Thermoelectric properties of CeNi2Al3 compound: an experimental and theoretical study

“…191). After X-ray diffraction and EDAX analysis it can be determined that the content of the impurity CeAl 2 phase is about 2%, as in previous studies [8] (Fig. 1).…”

“…As was generically observed in many IV compounds [6], CeNi 2 Al 3 exhibits large thermopower (~ 40 μV/K) over a wide temperature range [7]. Upon Cu doping at Ni site, it shows simultaneous optimization of thermoelectric parameters [7,8].…”

Magneto-heat capacity study on Kondo lattice system Ce(Ni 1−x Cu x )2Al3

“…Around 2.9 K another peak was observed for x = 0.0 and 0.1, in the present case (inset of figure 2) where as a sharp rise in C p /T is observed around this temperaure and is attributed to the impurity spins [13]. The low-T rise of C p /T for x = 0.3 and 0.4 is considered to be an intrinsic feature of phase pure samples [5,14,16]. Low-T electronic specific heat coefficient γ 0 estimated by extrapolating the data to 0 K gives a value of 141 and 269 mJ mol −1 K −2 for x = 0.3 and 0.4, respectively.…”

“…This implies that instead of simple local moment a scenario is evolved wherein local magnetic clusters might have been formed due to disorder induced carriers when Cu is doped. It is to be noted that we have already shown disorder induced effects in TEP in our earlier report [16]. Upon application of magnetic fields, J value decreases and reaches to a value lower than that of free ion moment like 1.5 and 2 at 12 T for x = 0.3 and 0.4, respectively.…”

“…These solid solutions also exhibit a proportionality between the initial slope of thermopower S(T ) and the electronic specific heat coefficient as T → 0 K limit [15]. An evolution from a simple compensated metal (x = 0.0) to a paramagnetic one (x = 0.4) was observed in Ce(Ni 1−x Cu x ) 2 Al 3 through the parameters obtained from the two band model fit to the thermoelectric power [16]. In recent times it has * Author for correspondence (vganesan@csr.res.in) also been speculated from the resistivity under magnetic fields that the formation of a Fermi liquid-like behaviour is quite probable and is in line with the expectations of specific heat studies [17].…”