Thermoelectric power generation technology is now expected to help overcome global warming and climate change issues by recovering and converting waste heat into electricity, thus improving the total efficiency of energy utilization and suppressing the consumption of fossil fuels that are supposedly the major sources of CO2 emission. Thermoelectric oxides, composed of nontoxic, naturally abundant, light, and cheap elements, are expected to play a vital role in extensive applications for waste heat recovery in an air atmosphere. This review article summarizes our previous and ongoing studies on SrTiO3-based materials and further discusses nanostructuring approaches for both SrTiO3 and CaMnO3 materials. ZnMnGaO4 is taken as a model case for constructing a self-assembled nanostructure. The present status of thermoelectric oxide module development is also introduced and discussed.

Oxide Thermoelectric Materials: A Nanostructuring Approach

We review and critique the recent developments on multifunctional oxide materials, which are gaining a good deal of interest. Recongnizing that this is a vast area, the focus of this treatment is mainly on high-κ dielectric, ferroelectric, magnetic, and multiferroic materials. Also, we consider ferrimagnetic oxides in the context of the new, rapidly developing field of negative-index metamaterials. This review is motivated by the recent resurgence of interest in complex oxides owing to their coupling of electrical, magnetic, thermal, mechanical, and optical properties, which make them suitable for a wide variety of applications, including heat, motion, electric, and magnetic sensors; tunable and compact microwave passive components; surface acoustic wave devices; nonlinear optics; and nonvolatile memory, and pave the way for designing multifunctional devices and unique applications in spintronics and negative refraction-index media. For most of the materials treated here, structural and physical propertie...

Oxides, Oxides, and More Oxides: High-κ Oxides, Ferroelectrics, Ferromagnetics, and Multiferroics

Electrical conductivity and complex impedance analysis of 20% Ti-doped La0.7Sr0.3MnO3 perovskite

The effect of particle size on the transport properties (resistivity and thermopower) of La0.5Pb0.5MnO3 has been investigated both in the presence and in the absence of magnetic field B=0.0–1.5 T (maximum). Grain size, dc conductivity; and the metal–insulator transition temperature Tp of the sample increase with increasing annealing time. Grain size has, however, comparatively little effect on the Seebeck coefficient S. Magnetoresistance is higher for the samples with smaller grain sizes. dc magnetic susceptibility also increases with increasing grain size. High temperature (T>θD/2) resistivity data well fit the small polaron hopping model. Polaron hopping energy WH decreases but polaron radius rp increases with the increase of grain size. In the metallic regime (for T<Tp), resistivity data fit well with ρ=ρ0+ρ2.5 T2.5 and the transport mechanism is attributed mainly to the magnon-carrier scattering (∼T2.5). In all the samples with different grain sizes, S changes sign below Tp. In contrast to magnetoresi...

Particle size and magnetic field dependent resistivity and thermoelectric power of La0.5Pb0.5MnO3 above and below metal–insulator transition

The samples Ni1+x−yZnyTix Fe2−2xO4; y=0.1, 0.0≤x≤0.5 were prepared in a single-phase spinel structure as indicated from X-ray analysis. Electrical conductivity and dielectric measurements at different temperatures from 300 K to 600 K in the frequency range from 42 Hz to 5 MHz have been analyzed. The relation of conductivity with temperature revealed a semiconductor to semimetallic behavior as Ti4+ concentration increases. The conduction mechanism depends mainly on the valence exchange between the different metal ions in the same site or in different sites. The dielectric constant as a function of temperature and frequency showed that there is a strong dependence on the compositional parameter x. The electrical modulus has been employed to study the relaxation dynamics of charge carriers. The result indicates the presence of correlation between motions of mobile ion charges. The activation energies extracted from M′(ω) and M″(ω) peaks are found to follow the Arrhenius law. The electrical conductance of the samples found to be dependent on the temperature and frequency.

Electrical conductivity and complex electric modulus of titanium doped nickel–zinc ferrites

Magnetoresistance and magnetothermoelectric power of La 0.5 Pb 0.5 Mn 1-x Cr x O 3

Non-adiabatic small-polaron hopping conduction in Pr0.65Ca0.35−xSrxMnO3 perovskites above the metal–insulator transition temperature

Development of pulsed magnetic field and study of magnetotransport properties of K-doped La1–xCax–yKyMnO3 CMR materials

Above the semiconductor-to-metallic transition (SMT) temperature (Tp), transport properties of the La1−xPbxMnO3+δ (0 ≤ x ≤ 0.5)-type mixed valence oxides with Tp between 230 and 275 K (depending on x) have been thoroughly examined for a small-polaron hopping conduction mechanism of the carriers. Although the variable range hopping (VRH) model was used earlier to fit the entire conductivity data above SMT, we noticed two distinct regions (above and below θD/2; θD is the Debye temperature) where different types of conduction mechanisms are followed. The high temperature (T > θD/2) conductivity data of all the Pb-doped samples follow the adiabatic hopping conduction mechanism, while those of LaMnO3 (x = 0) showing no SMT follow the non-adiabatic hopping conduction mechanism of Mott or Emin with reasonable values of polaron radius, hopping distance, polaron binding energy, activation energy, etc being different for different systems. The VRH model, however, fits the corresponding low temperature (T < θD/2) data of all the samples. Both resistivity ρ(T) and thermoelectric power S(T) follow a similar microscopic theory above Tp supporting the small-polaron hopping mechanism. Thermoelectric power also showed appreciable magnetic field dependence around SMT.

https://iopscience.iop.org/article/10.1088/0953-8984/13/42/310/pdf

B.K. Chaudhuri

Papers

Magnetoresistance and magnetothermoelectric power of La 0.5 Pb 0.5 Mn 1-x Cr x O 3

Non-adiabatic small-polaron hopping conduction in Pr0.65Ca0.35−xSrxMnO3 perovskites above the metal–insulator transition temperature

Development of pulsed magnetic field and study of magnetotransport properties of K-doped La1–xCax–yKyMnO3 CMR materials

Adiabatic and non-adiabatic small-polaron hopping conduction in La1−xPbxMnO3+δ (0.0 ≤ x ≤ 0.5)-type oxides above the metal–semiconductor transition

Effect of Ni doping in rare-earth manganite La0.7Pb0.3Mn1−xNixO3 (x=0.0–0.5)