Value Of Seebeck Coefficient Research Articles

Tellurium-nanowire-doped thermoelectric hydrogel with high stretchability and seebeck coefficient for low-grade heat energy harvesting

To harvest low-grade heat energy from human body, flexible thermoelectric generators (TEGs) are highly necessitated and have attracted significant interests. However, developing novel thermoelectric materials with high stretchability and seebeck coefficient is still challenging. Here we report a tellurium-nanowire-doped (Te-NW-doped) PEDOT:PSS/polyvinyl alcohol (TPP) hydrogel with excellent mechanical and thermoelectric characteristics. The effect of Te-NWs doping on the thermoelectric characteristics has been systematically investigated and the optimized TPP hydrogel exhibits a large seebeck coefficient value of 787 μV K−1, a low thermal conductivity of 0.468 W m−1 K−1, and a high tensile strain value of ⁓ 400%. Furthermore, a wearable thermoelectric module with a staggered Z-shaped structure is developed to achieve a voltage output of 138 mV when it is applied on the human arm. After being integrated with a power management unit, the TPP TEG module enables the operation of electronic devices like a commercial calculator and a white LED, which exhibits great potential for applications in human heat energy harvesting and wearable electronics.

Complex microstructure induced high thermoelectric performances of p-type Bi–Sb–Te alloys

In this research, we have fabricated the complex microstructure features along with the high density of twin boundaries using the combination of magnetic pulse compaction (MPC) and spark plasma sintering (SPS), which are exclusively improved the thermoelectric transport properties of p-type Bi0.5Sb1.5Te3 alloys via effective scattering of carriers and phonons at the grain boundary interfaces. The texture analysis confirmed the formation of bimodal (mixed grains) microstructural features in MPC + SPS specimens sintered at 350 °C, and 400 °C respectively due to the adhesion of fine grains (grain growth) and initiation of recrystallization at high temperatures. In addition to high density of twin structure, high-angle grain boundaries have also been identified. The power factor of 3.53 mW/m.K2 was obtained for the MPC + SPS at 400 °C due to increased Seebeck coefficient and larger electrical conductivity values. The maximum reduced thermal conductivity of 1.14W/mK was recorded due to a significant reduction in lattice thermal conductivity, which is mainly owing to strong scattering of phonons at the formation of mixed grain microstructures with high-density dislocations. As a result, maximum figure of merit, ZT = 1.17was achieved for MPC + SPS at 400 °C temperature.

Microstructure and thermoelectric properties of nanoparticled copper selenide alloys synthesized using a microwave-assisted hydrothermal method

With the fabrication of high-performance thermoelectric (TE) materials, developments are being made in enhancing the figure of merit, zT , of TE materials. Liquid-like binary copper selenide (Cu 2 Se) chalcogenides recently gained significant recognition because of their anomalous but fascinating electrical and thermal transport performances. In this study, a facile synthesis technique was adopted in fabricating Cu 2 Se nanoparticles using a rapid microwave-assisted hydrothermal route at different reaction times. The results were compared with those of the Cu 2 Se solid-state (SS) sample synthesized using the traditional melting and annealing technique. X-ray diffraction patterns revealed successful synthesis of nanoparticles and a phase transition from orthorhombic α -phase and cubic β -phase to a single orthorhombic structure after hot-pressing. Scanning electron microscopic images revealed that although the grain sizes of the nanoparticle (NP) bulk samples increased with the reaction time of the microwave hydrothermal process, the grain sizes were significantly smaller than that of the SS sample. Additionally, NP bulk samples exhibited plenty of nano-grains and pores that are absent in the SS sample. The size and distribution of the grains and pores were measured to study their effects on the transport of carriers and phonons. The NP30 sample exhibited the highest power factor of 983.3 μW K − 2 m at 673 K among the NP samples, exhibiting intermediate values of resistivity and Seebeck coefficient that are close to those of the SS sample. Moreover, the NP samples exhibited appreciably lower thermal conductivity than the SS sample that is attributed to strengthened phonon scattering. The minimum thermal conductivity of the NP05 sample, 0.78 WK −1 m − 1 at 348 K, is 1.7 times lower than that of the SS sample. Finally, a maximum zT of 0.56 at 673 K, being approximately 1.3 times higher than that of the SS sample owing to the optimized thermal conductivity, was achieved for the NP30 sample. This value is comparable to or higher than that reported for Cu 2 Se synthesized using the traditional SS method. Investigations revealed that the proposed microwave hydrothermal synthesis technique is a facile, rapid, and reliable method that results in Cu 2 Se alloys with excellent TE performance.

Magnetic Properties of CuCr1−xLaxS2 Thermoelectric Materials

The magnetic properties (magnetic susceptibility, magnetic moment) and Weiss constant for lanthanum-doped CuCr1−xLaxS2 (x = 0; 0.005; 0.01; 0.015; 0.03) solid solutions were studied using static magnetochemistry at 80–750 K. The samples were characterized by both powder X-ray diffraction and energy-dispersive X-ray spectroscopy. It was shown that synthesized samples are single-phased up to x ≤ 0.01. The presence of the additional phase in the solid solutions with x > 0.015 caused deviation from the simple isovalent Cr3+→Ln3+ cationic substitution principle. It was found that magnetic susceptibility and the Weiss constant are significantly affected by both magnetic properties and lanthanum concentration for the solid solutions doped up to x = 0.01. The largest magnetic moment value of 3.88 µB was measured for the initial CuCrS2-matrix. The lowest value of 3.77 µB was measured for the CuCr0.99La0.01S2 solid solution. The lowest Weiss constant value of −147 K was observed for the initial matrix; the highest one was observed for CuCr0.99La0.01S2 (−139 K). The largest Seebeck coefficient value of 373 µV/K was measured for CuCr0.985La0.015S2 at 500 K; the obtained value was 3.3 times greater compared to the initial CuCrS2-matrix. The field dependence of the magnetic susceptibility allowed one to conclude the absence of ferromagnetic contributions in the total magnetic susceptibility of CuCr1−xLaxS2. The data on magnetic properties can be successfully utilized to investigate the limits of doping atom suitability and order–disorder phase transition temperature in CuCrS2-based solid solutions.

Thermoelectric properties of Ru2TiGe Heusler phase

We report a study of structural, magnetic, heat capacity and thermoelectric properties of a Ru-based Heusler alloy, Ru2TiGe. The magnetic measurements reveal that at higher temperatures, diamagnetic and Pauli paramagnetic contributions dominate the magnetic behaviour whereas, at lower temperatures (T ≤ 20 K), superparamagnetic interaction among clusters is observed. The development of such magnetism, however, does not exhibit any noticeable influence in thermoelectric properties. Though the temperature dependence of electrical resistivity exhibits a metal-like nature, the large value of Seebeck coefficient leads to an appreciable power factor of the order of 0.54 mW/mK2 at 300 K. Large power factor as well as low thermal conductivity results in a value of zT = 0.025 at 390 K for Ru2TiGe that is orders of magnitude higher than that of the other pure Heusler alloys and point towards its high potential for practical thermoelectric applications.

High thermoelectric power factor of n-type Bi2(Se,S)3 via synergetic influence on the charge carrier concentration and energy filtering effect

Excellent thermoelectric performance is sought to address essential energy concerns, including the impact of energy consumption on the environment. In this work, we have synthesized the Bi2Se3 thin film using a simple thermal evaporation route and post‑sulfurized it for different durations at (773 K). The crystal structure change from rhombohedral to orthorhombic with different post‑sulfurization times has been confirmed via x-ray diffraction. The atomic vibrational modes of Bi2(Se,S)3 thin films have been examined by Raman spectroscopy. The surface morphology of Bi2(Se,S)3 thin films have been observed using a scanning electron microscope. The Seebeck coefficient values enhanced from 155.1 to 203.5 μV/K with post‑sulfurization time due to increased charge carrier concentration and energy filtering effect. The electrical conductivity improved from 90.2 to 118.7 S/m of the as-deposited sample to the highest post‑sulfurized sample due to improving charge carrier concentration and changing the crystal structure from rhombohedral to orthorhombic structure. We have achieved the maximum power factor of Bi2(Se,S)3 thin film of the 4.86 μWcm−1 K−2 at room temperature. Obtaining the highest power factor has a straightforward approach to fabricating commercial thermoelectric material.

Enhanced thermoelectric properties of SWCNT by new nitrogen chains doping

Single walled carbon nanotubes (SWCNT) are attractive materials for thermoelectric (TE) devices because of their unique one-dimensional structure and provide us for developing a flexible TE devices due to their mechanical properties. In this paper, the TE properties of pristine small SWCNT (3,3) and three new nitrogen (N) doping models namely CN, C2N2 (doping by two N-chains) and C4N2 (doping by three N-chains) are calculated using the density functional theory (DFT) combined with Boltzmann's semi-classical transport theory. Dynamical and energetic stability of the compounds are confirmed from the phonon density of states curve and formation energy calculations. The values of Seebeck coefficient (S), electrical conductivity (σ), thermal conductivity (κ), power factor (PF) and figure of merit (ZT) are reported at different temperature and discussed in detail. The results show that N-doping significantly improves the TE properties of the pristine nanotube and show a reasonable agreement with previous experiments and ab-initio calculations. It was found that the C2N2 configuration presents the largest Seebeck coefficient of 70.53 μV/K and the figure of merit ZT of 0.25 compared to other doping models. N-chains doping is therefore a new suitable way to improve the TE properties of small SWCNT in order to making them a good candidate for flexible TE devices.

Effective decoupling of grain boundaries and secondary phase interfaces for enhanced thermoelectric performance of Cu1.8S/WS2 nanocomposites

Copper Sulfide (Cu1.8S) has influentially concerned the increasing attention in mid-temperature thermoelectric materials. The inherent low Seebeck coefficient and high thermal conductivity of Cu1.8S hinders the thermoelectric performance. The superionic conductivity exhibited by Cu1.8S phase possess characteristic phonon-liquid electron-crystal property eliminate transverse phonon vibrations. In this study, improved thermoelectric performance for the Cu1.8S material was obtained through the efficient strategy of compositing with WS2 nanoparticles. A minimum thermal conductivity of 1.4 W/mK at 753 K for the Cu1.8S/5 wt. % WS2 nanocomposite. Along with the increased Seebeck coefficient values, the thermal conductivity is suppressed by WS2 composite due to the formation of Cu2WS4 secondary phase which strengthens the phonon scattering. The evident reduction in the thermal conductivity, coupled with less affected Seebeck coefficient, led to increased figure of merit (zT) of 0.46 at 753 K, which is 95 % higher than that of pure Cu1.8S. This work provides a distinguished improvement in the performance of Cu1.8S thermoelectric material thereby enabling its employment in the application of waste heat harvesting.

The role of hetero-interface structures in enhancing the power factor of Cu2Se/x% Y2O3 composite thermoelectric materials

In this study, we have investigated the structural, thermal, electrical, and mechanical properties of the composite system Cu2Se/x% Y2O3 (0 ≤ x ≤ 1.00) as a function of varying Y2O3 concentration, x. The successful incorporation of Y2O3 in the Cu2Se matrix is carried out using the solid-state reaction method, and the same is confirmed by X-ray diffraction analysis. Due to the low concentration of Y2O3, all the prepared composites exhibit monoclinic crystal structure with P2/m space group within the X-ray detection limit at room temperature. The oxidation state of the studied composites is investigated using X-ray photoelectron spectroscopy (XPS). The composites exhibit an increase in mechanical hardness as a function of Y2O3 concentration, whereas the electrical resistivity shows no systematic variation with Y2O3 concentration. The highest resistivity is observed for the sample with x = 1%. The measured Seebeck coefficient (S) value increases with increasing temperature. The positive values of S indicate that the positive charge carriers (holes) dominate the thermoelectric transport. The thermal conductivity of the composites increases as compared to the Cu2Se pristine sample. The overall power factor and ZT of studied composites were found to decrease with the addition of Y2O3 to the Cu2Se system.

Theoretical investigations of optoelectronic and transport properties of halide based K2YAuX6 (X = Cl, Br) double perovskites

Intriguing optoelectronic and transport properties with huge compositional range and structural stability make double perovskites interesting for energy harvesting technologies. Here we theoretically investigate the structural, optical, mechanical, and transport properties of K2YAuX6 (X = Cl, Br) double perovskites using the WIEN2K code. Based on the calculated values of the tolerance factor and enthalpy of production, the thermodynamic and structural stability is affirmed. The ductile nature of these compositions is revealed in the computation of Poisson’s ratio (>0.26) and Pugh’s (1.75) ratio. The involvement of s-states of K, p-states of Cl/Br, and d-states of Y and Au in the formation of valence and conduction band edges is exhibited from the density of state plots. Using the Tran-Blaha mBJ potential and spin-orbital coupling, the energy bandgap value for K2YAuCl6 and K2YAuBr6 is reported as 3.20, and 2.70 eV, respectively, which is suitable for the fabrication of light-emitting diodes. Optical behavior is further explored regarding complex dielectric constant, refractive index, optical conductivity, optical loss, and absorption factor. The small value of thermal conductivity with large value of electrical conductivity, Seebeck coefficient, power factor, and figure of merit revealed the potential of these materials for the fabrication of light-emitting diodes and thermoelectric generators.

A DFT study of optoelectronic, elastic and thermo-electric properties of the double perovskites Rb2SeX6 (X=Br,Cl)

Thermo-electric (TE) material applications reduce reliance on traditional energy resources by converting heat to electric energy. We have studied, for the first time, the thermo-electric properties of Rb2SeX6 (X=Br,Cl). Using norm-conserving pseudo potentials in a plane wave basis set of Quantum Espresso code, the optoelectronic, elastic and thermo-electric properties of Rb2SeX6 (X=Br,Cl) have been investigated using density functional theory. Generalized Gradient Approximation of Perdew Burke Ernzerhof (GGA-PBE) and Generalized Gradient Approximation of Perdew Burke Ernzerhof adapted for Solid (GGA-PBESol) exchange correlation functionals were employed in all calculations. The band structure plots suggest that the studied double perovskites have indirect band gaps. Rb2SeBr6 band gap values of 1.7574/ 1.569 eV (using GGA-PBE/PBEsol) are remarkably similar to that of two effective inorganic/organic perovskites FAPbI3 and MAPbI3 . Maximum peaks generated from refractive index results indicate possible solar cell uses of the materials because they are in the visible and ultraviolet ranges. The results of other optical properties such as absorption coefficients, electron energy loss, conductivity, and reflectivity concludes that Rb2SeX6 (X=Br,Cl) have good values for electron generation, high potential for applications in the optoelectronic industry and are semiconductor in nature. The calculated shear anisotropy values of Rb2SeBr6/Cl6 are 3.09/1.71, suggesting that they are isotropic materials. With calculated Poisson’s ratio of 0.32 and 0.26, the materials are predicted to be ductile in nature. The two materials are appropriate for thermo-electric applications since their thermal to electrical conductivity ratio are small (the order of 10-5). The calculated minimum values of Seebeck coefficient values of 0.198×103 / 0.166 ×103 (mV/K) at 750 K, for Rb2SeBr6/Cl6 are positive, indicating that they have p-type conduction. Figure of merit values at all temperature range considered are greater than one (ZT > 1) for both Rb2SeBr6 and Rb2SeCl6, suggesting that they are good thermo-electric materials. The results of the calculations provide the basis for the industrial application of Rb2SeBr6/Cl6 as solar cells.

Metal Complex Molecular Junctions as Thermoelectric Devices.

Single-molecule junctions and self-assembled monolayer junctions are attractive architectures for thermoelectric devices. However, given the poor thermoelectric performance of organic molecules investigated so far, molecules characterized by high conductance and Seebeck coefficient values are desired to be explored. Metal complexes are promising possible active components of high-performance thermoelectric devices given that metal-ligand combinations and functions can be made to vary to modulate the transmission functions, thus strongly influencing conductance and Seebeck coefficient. In this concept article are described recent studies wherein thermoelectric measurements were conducted on metal complex junctions. Furthermore, the potential for the use of the junctions in thermoelectric devices is discussed.

Thermoelectric Properties of Porous SiC/SiO2/C Composite from Carbonized Cryptomeria japonica Wood

Electric power generation by thermoelectric material utilizing radiated heat of from roof’s house, engine and others is potential clean energy in tropical areas such as Indonesia. In this study, thermoelectric materials such as silicon carbide (SiC/SiO2/C) composites were developed from carbonized Cryptomeria japonica wood infiltrated ethyl silicate-40 by sintering at 1400, 1600 and 1800 ºC for 30 min under N2 atmosphere. This study aimed to examine the morphology, microstructure and thermoelectric properties of porous SiC/SiO2/C composites. SiC/SiO2/C composites sintered at 1600 ºC with low value of thermal conductivity was potential for the development of thermoelectric material. The oxidation of SiC/SiO2/C composite sintered at 1600 °C which removed parts of residual silica and carbon, transformed the composite exhibiting p-type semiconductor with low values of Seebeck coefficient of to that exhibiting n-type semiconductor with high values Seebeck coefficient. A maximum of figure of merit of 6.25 x 10--5 K-1 was obtained at 140 ºC in the oxidized SiC/SiO2/C composite sintered at 1600 °C. The comparatively high figure of merit indicates the potentiality the material for thermoelectric purpose.

The Charge Distribution, Seebeck Coefficient, and Carrier Concentration of CuCr0.99Ln0.01S2 (Ln = Dy-Lu).

The atom oxidation states were determined using the binding energies of the core S2p-, Cu2p-, Cr2p-, and Ln3d-levels in CuCr0.99Ln0.01S2 (Ln = Dy-Lu) solid solutions. The charge distribution on the matrix elements (Cu, Cr, and S) remained unaffected after cationic substitution. The sulfur atoms were found to be in the S2- oxidation state, the copper-Cu+, and the chromium-Cr3+. The cationic substitution of the initial CuCrS2-matrix occurred via the isovalent mechanism. The obtained results were compared with the electrophysical properties for CuCr0.99Ln0.01S2. The measured carrier concentration was from 1017 to 1018 cm-3. The largest Seebeck coefficient value of 157 µV/K was measured for CuCr0.99Yb0.01S2 at 500 K. The cationic substitution with lanthanides allowed one to enhance the Seebeck coefficient of the initial CuCrS2-matrix.

Facile fabrication of Cu2O nanowire networks with large Seebeck coefficient for application in flexible thermoelectrics

The development of thermoelectrical nanowires and nanowire networks is crucial for application in self-powered electronics and flexible heat-to-power conversion devices. While Cu2O is a perspective p-type thermoelectric material, its research is mostly focused on the investigation of the properties of thin films or rigid cement composites with Cu2O powder fillers. In this work, Cu2O nanowire networks were fabricated by a simple technique and their thermoelectrical properties were investigated for the first time. Cu2O nanowire networks were obtained by annealing prefabricated CuO nanowire networks in an inert atmosphere at low pressure of 0.2 Torr. After annealing, nanowire networks showed a complete transition of CuO phase to Cu2O. Seebeck coefficient of Cu2O nanowire networks reached 2000 μV K−1. The estimated power factor of the Cu2O networks was found to be comparable with the Seebeck coefficient values of the state-of-the-art Cu2O thin films. The demonstrated in this work simple low-cost method for the fabrication of Cu2O nanowire networks illustrates the potential of this material for further applications in flexible thermoelectric devices.

First principles study on structural, mechanical, and thermoelectric properties of half-Heusler alloy (KLiTe)

In this study, the structural, optoelectronics, elastic, and transport properties of KLiTe were estimated from first principles computations using the FP-LAPW technique and semi-classical Boltzmann transport theory The exchange–correlation is addressed employing the generalized gradient approximation with Perdew-Burke-Ernzerhof scheme (GGA-PBE). In order to distinguish between the brittle and ductile properties, the Poisson and Pugh's ratio was calculated. The semiconductor KLiTe is demonstrated to have a direct band gap. The compound under investigation exhibits significant Seebeck coefficient and power factor values. The high-power factor of 8.3 × 1011 W/K2ms. that KLiTe exhibits at 1200 K makes it a potentially viable material for thermoelectric applications. Due to their high figure of merit values, the results obtained indicate that KLiTe could be a strong contender for thermoelectric generator applications at low and moderate temperature.

Investigation of structural, morphological, thermal, and thermoelectric properties of Zn1−xCuxAl2O4 (0.0 ≤ x ≤ 0.1)

Most promising oxide thermoelectric (TE) materials such as perovskites, layered oxide materials, Al-doped ZnO, etc, have been reported. In the present work, Zn1−x Cu x Al2O4 (0.0 ≤ x ≤ 0.1) samples were synthesized by a simple hydrothermal method. The structural, optical, morphological, and TE properties of Zn1−x Cu x Al2O4 (0.0 ≤ x ≤ 0.1) have been investigated. XRD analysis reveals that ZnAl2O4 has a single-phase cubic structure and Cu is completely dissolved in the ZnAl2O4 lattice. Thermal analysis shows that ZnAl2O4 has high thermal stability up to 1000 °C. From the UV–vis DRS analysis, the energy band gap of ZnAl2O4 decreased from 3.30 eV to 2.82 eV with increasing the content of Cu. Carrier concentration and mobility of the samples were measured by the Hall effect. The values of a carrier concentration of undoped ZnAl2O4 and Zn0.9Cu0.1Al2O4 are obtained to be 3.836 × 1013 cm−3 and 3.3 × 1016 cm−3 at 313 K and 9.6 × 1013 cm−3 for pure and 5.5 × 1016 cm−3 for Zn0.9Cu0.1Al2O4 at 673 K. TE properties of the synthesized samples have been analyzed as a function of temperature. With the optimum values of Seebeck coefficient and electrical conductivity, Zn0.9Cu0.1Al2O4 shows the highest power factor of 0.50 μW/mK2 while the pure ZnAl2O4 shows a maximum power factor of 0.19 μW/mK2 at 673 K. The Zn0.9Cu0.1Al2O4 exhibits a relatively high zT of 2.4 × 10−4 at 673 K, while pure ZnAl2O4 has a zT value of 0.4 × 10−4 at 673 K. The obtained values reveal the improvement of TE properties by increasing the Cu content in the sample.

Synthesis, crystal structure, optical, thermoelectric, and electrochemical studies of Ba2Cu2.1(1)Ag1.9(1)Se5

We present the synthesis and characterization of single crystals and polycrystalline samples of Ba2Cu2.1(1)Ag1.9(1)Se5. A single-crystal X-ray diffraction study confirms its monoclinic structure (space group: C2/m) with lattice parameters of a = 16.0342(15) Å, b = 4.4162(4) Å, c = 9.1279(9) Å, β = 124.005(2)°, V = 535.82(9) Å3, and Z = 2. The structure of Ba2Cu2.1(1)Ag1.9(1)Se5 consists of polyanionic [∞2Cu2.1(1)Ag1.9(1)Se5]4− layers. The negative charges on these layers are counterbalanced by the filling of Ba2+ cations in the structure. The Ag and Cu atoms are statistically disordered at the same sites. The Ag/Cu atoms are bonded with four Se atoms in a distorted tetrahedral fashion. The structure also contains linear Se34− units with intermediate Se⋯Se interaction of 2.7734(14) Å. The Ba2Cu2.1(1)Ag1.9(1)Se5 can be charge-balanced as (Ba2+)2(Cu+)2.1(Ag+)1.9(Se2−)2(Se34−)1. The optical absorption study performed on a polycrystalline sample with a loaded composition of Ba2Cu2.1Ag1.9Se5 reveals a direct bandgap of 1.0(2) eV, and the indirect bandgap was found to be below 0.5 eV. The resistivity study also confirmed the semiconducting nature of the sample. The thermoelectric properties, including thermal conductivity and Seebeck coefficient, have been studied as a function of temperature. The polycrystalline Ba2Cu2.1Ag1.9Se5 has a very low thermal conductivity value of 0.46 W/mK at 673 K. The positive sign of the Seebeck coefficient values indicates the polycrystalline Ba2Cu2.1Ag1.9Se5 is a p-type semiconductor with holes as the majority of charge carriers. Further, the charge storage behavior of the material was investigated for supercapacitor application. The material delivers 76 F g−1 at 0.5 A g−1 current density in 1 M KOH electrolyte and is stable for 10,000 cycles retaining 85% capacitance.

Enhancement in the electrical transport properties of CaMnO3via La/Dy co-doping for improved thermoelectric performance.

The untiring endeavour towards green energy is a trending research among the research community. Thermoelectric materials are of vital importance here owing to their emission-free operation. As a righteous candidate, calcium manganate materials are being explored to increase its figure of merit. In this study, the structural, microstructural, electrical transport, and high-temperature thermoelectric measurements of LaxDyxCa1-2xMnO3 {x = 0.025 (L25D25), 0.05 (L50D50), 0.075 (L75D75), and 0.1 (L100D100)} were systematically performed. The structural confirmation of the synthesised sample was validated using X-ray diffraction, which also revealed the orthorhombic (space group: Pnma) crystallisation of co-doped samples with no traces of secondary peaks. A significant increase in the unit cell volume was observed with rare earth substitutions. The morphological studies revealed that the prepared samples were highly dense and the grain size was reduced with rare earth concentration. The substitution of La and Dy enhanced the conductivity values of pristine CMO by two orders of magnitude due to the high concentration of charge carriers and the presence of Mn3+ ions due to rare earth doping. The conductivity increased with rare earth concentrations but diminished for x = 0.1 due to the localization of charges. The Seebeck coefficient values were negative for all the prepared samples, indicating electrons as the predominant carriers over the entire operating range. A minimum κ of 1.8 W m-1 K-1 was achieved for La0.1Dy0.1Ca0.8MnO3 and the maximum value zT obtained was 0.122 at 1070 K for La0.075Dy0.075Ca0.85MnO3.

Application of lamellar nickel hydroxide membrane as a tunable platform for ionic thermoelectric studies.

The recent trend in thermoelectric literature suggests that ionic thermoelectric (i-TE) materials are ideal for directly converting low-grade waste heat into electricity. Here, we developed a unique platform for i-TE studies by stacking two-dimensional sheets of β-Ni(OH)2 prepared by a bottom-up method. The lamellar membrane of β-Ni(OH)2 (Ni-M) itself does not display significant thermovoltages, but when doped with mobile anion-generating species (like aminopropyl functionalized magnesium phyllosilicate or organic halide salts), it exhibits significant negative Seebeck coefficient (up to -13.7 ± 0.2 mV K-1). Similarly, upon doping with cation-generating species like poly(4-styrene sulfonic acid) (PSS), it displays positive Seebeck coefficient values (up to +12 ± 1.9 mV K-1). The positive and negative i-TE materials prepared by doping Ni-M are assembled into ionic thermopiles capable of generating thermovoltages up to 1 V, at ΔT = 12 K. The Ni-M-based nanofluidic systems demonstrated an additional path of electricity harvesting by connecting colder zones of the positive and negative i-TE materials with other ion conducting membranes. In contrast to organic polymer-based i-TE systems, the Ni-M based system exhibited consistent performance despite being exposed to high temperatures (∼200 °C, 5 minutes).