Thermoelectric Properties Of ZnO Research Articles

The influence mechanism of high-valence rare earth element doping on the thermoelectric properties of ZnO

The influence mechanism of high-valence rare earth element doping on the thermoelectric properties of ZnO

Enhancement of thermoelectric properties of transition metals, nickel and copper dually doped ZnO

Thermoelectricity is one of the potential sustainable energy sources, that can be treated as a remedy for the present energy scarcity as it is a clean-green technology. ZnO is a promising multifunctional metal oxide and its thermoelectric conversion property is highly exploited in the field of waste heat recovery. Herein, the impact of nickel and copper substitution on the thermoelectric properties of ZnO is investigated. The structural and morphological analysis of the doped materials confirmed the hexagonal wurtzite structure of ZnO. The strain induced in the lattice and the variation of crystallite size established the substitution of the dopants into the host matrix. The optical band gap energy shows a reduction from 3.1 eV to 2.15 eV with a redshift in the absorption edge. The electrical conductivity and Seebeck coefficient of ZnO increased upon doping. The most remarkable result of nickel and copper doping is the enhancement of the Seebeck coefficient to 1318 µV/K. As a result of the lattice distortion created due to the dual substitution of the dopants, the thermal conductivity is considerably reduced to 8.36 W/mK. The power factor enhancement and degradation of thermal conductivity give rise to a six-fold increase in the thermoelectric figure of merit of the material.

Flexible in-plane thermoelectric modules based on nanostructured layers ZnO and ZnO:In

In this study, with the aim of developing flexible in-plane thermoelectric module we deposited via SILAR method 0.3–1.4 thick nanostructured layers of undoped and indium doped zinc oxide on Kapton polyimide (PI) substrates and thus prepared ZnO:In/PI and ZnO/PI samples. We analyzed surface morphology, crystal structure, chemical composition, optical, electrical and thermoelectric properties of ZnO and ZnO:In thin films grown via SILAR on PI substrates. It was shown that ZnO:In/PI samples are consisted of flower-like ZnO:In microstructures with rod petals having pencil-like ends. ZnO/PI samples have lily flower-like ZnO microstructures with rounded petals. Despite the fact that crystal structure and optical properties of the nanostructured ZnO:In and ZnO films were almost the same, their morphology determined the electrical and thermoelectric properties. More compact 1.4 µm thick ZnO layer in sample ZnO/PI provided the best thermoelectric power factor ≈ 8 µW/(m·K2) due to its lower resistivity at near-room ≈ 0.15 Ω cm. Among four samples of the prepared flexible in-plane thermoelectric modules with single legs in the form of PI strips 3 cm long and 0.5 cm wide, covered with the semiconductor film ZnO or ZnO:In and having thin-film Al ohmic contacts at the edges, the TE module based on ZnO/PI showed the best output characteristics. At the temperature difference 50 К, its output power density reaches 10 µW/cm2, which is commensurate with the up-to-date values for solid miniature and flexible TEGs.

Role of intrinsic defects on thermoelectric properties of ZnO:Al films

In this study, we explored the role of the intrinsic defects on the tuning thermoelectric (TE) performance of Al-doped ZnO (ZnO:Al) films. The intrinsic defects of the Zn interstitial (Zni) and the oxygen vacancy (VO) were controlled by varying the Zn content by using the radio frequency atomic source vacuum evaporation method. In the Zn-rich case, the excessive Zn formed Zni to provide most of the carriers. VO became the main origin of the carriers with a decreasing Zn content. When the Zn content was 55.2% and 52.5%, the segregation of Zni decreased the carrier concentration and subsequently, enhanced the resistivity and the Seebeck coefficient. The ZnO:Al film with a Zn content of 52.5% had the highest power factor of 274.03 μW·m−1·K−2 at 819 K. In addition, the higher Zni concentration had a more prominent effect on thermal conductivity. The thermal conductivity increased to 1.756 W·m−1·K−1 from 0.608 W·m−1·K−1 with the Zn content decreasing from 55.2% to 50.6%. The ZT value reached the highest of 0.121 when the film had the optimum Zn concentration of 51.5%. This study concluded that the tuning of the intrinsic defects was an effective method to enhance the TE performance.

Thermoelectric, Electronic, and Optical Response of Nanostructured Al‐doped ZnO @ 2D‐TiC Composite

AbstractZnO is one of the sought‐out materials for thermoelectricity. This study investigates the effect of aluminum doping, and titanium carbide (TiC) modification on the thermoelectric properties of ZnO through the synthesis of undoped ZnO, Al‐doped ZnO (Al‐ZnO), and TiC modified Al‐doped ZnO (TiC@Al‐ZnO) nanocomposite by the hydrothermal method and mechanical alloying. XRD, TEM, and SEM were used for structural and morphological studies. The electrical and thermal conductivity measurements on the nanocomposite were obtain using Van der pauw 4 probe collinear method. A decrease in thermal conductivity of ZnO from 7.62 to 5.75 W/cm K is observed after been modified with Al and TiC. TiC@Al‐ZnO nanocomposite exhibits the lowest thermal conductivity and highest power factor than Al‐doped ZnO. Furthermore, the impact of TiC and Al revealed an enormous effect on the Seebeck coefficient of ZnO reaching 105 μV K−1 AT 960 K, and a figure of merit value of 0.28 at 960 K. The increase in negative Seebeck coefficients suggests that the amount of active charge carrier, with significant energy, was temperature and structure depend. The experimental data obtained in this work showed the effect of both Al concentration and TiC nanosheet reinforcement on the thermoelectric properties of ZnO.

Enhanced optical and thermoelectric properties of ZnO by tin and fluorine codoping: First-principles DFT calculations

Ab initio density functional calculations of the structural, optoelectronic, thermoelectric and thermodynamic properties of ZnO codoped with tin and fluorine with possible application as Transparent Conductive Oxides (TCO’s), are reported in this work. This study shows that incorporation of Sn and F into the ZnO matrix converts it to a degenerate semiconductor. The calculated optical absorption coefficients show that the four compounds ZnO, Sn:ZnO, F:ZnO and Sn:F:ZnO have transparent properties in the visible range. At 900[Formula: see text]K, the Seebeck coefficient of Sn:F:ZnO is greatly improved with respect to the undoped ZnO. A maximum electrical conductivity value of [Formula: see text]S cm[Formula: see text]s[Formula: see text] is predicted for Sn-doped ZnO. ZT increases with temperature to a maximum value of 0.13 at 900[Formula: see text]K for tin and fluorine codoped ZnO.

Thermoelectric Properties of Al Doped ZnO Thin Films Fabricated through Inkjet Printing

The effects of Al doping to the thermoelectric properties of ZnO thin films fabricated through ink-jet printing were studied in this paper. Ink-jet printing was used to deposit the Al doped ZnO thin films. A minimum of 50 print cycles was required to obtain continuous film with approximately 9 μm thick thin films. It was possible to obtain high thermoelectric properties of ZnO by controlling the ratios of dopant added and the temperature of the heat treatments.The XRD traces of Al doped ZnO exhibit a polycrystalline hexagonal structure for the wurtzite phase of ZnO. There were no additional phase detected for Al doped ZnO thin films with increasing amount of Al dopants and heat treatment temperature. The results show Al doping had improved the thermoelectric properties of ZnO with an increased in electrical conductivity. The electrical conductivity of pure ZnO thin film (5 S/cm) was enhanced with increasing the dopant to 4wt% Al doped ZnO (114 S/cm). Negative Seebeck values were observed for all the samples that indicated n-type semiconductor. Pure ZnO samples have a measured Seebeck coefficient-17.63 μV/K decreased to-14.35 μV/K with 4 wt% Al doped.

Enhanced thermoelectric properties of N-doped ZnO and SrTiO3: A first-principles study

This work presents electronic and thermoelectric properties of ZnO and SrTiO3 in the presence of nitrogen impurity have been investigated by means of the theoretical first-principles calculations. It is found that N-doped ZnO has a smaller band gap compared to the pure counterpart. This material also exhibits the enhanced thermoelectric properties of the positive Seebeck coefficient and higher electrical conductivity per relaxation time. Furthermore, SrTiO3 with nitrogen impurity possess the smaller energy gaps. For thermoelectric properties, ZT of undoped SrTiO3 decreases as temperature increases. Nevertheless, ZT of N-doped SrTiO3 increases with temperature. Therefore, the introduction of nitrogen impurity to ZnO and SrTiO3 is an alternative way to improve their thermoelectric efficiencies.

Phonon Scattering and Electron Doping by 2D Structural Defects in In/ZnO.

In/ZnO bulk compounds have been synthesized using a simple solid-state process. In this study, both the structural features and thermoelectric properties of the Zn1-xInxO series with ultralow indium content (0 ≤ x ≤ 0.02) have been studied. High-angle annular dark-field scanning transmission electron microscopy analyses highlight that indium has the ability to create multiple basal plane and pyramidal defects that produce ZnO domains with inverted polarity starting from dopant concentrations as low as 0.25 atom %. Interestingly, the formation of parallel inversion boundaries consisting of InO6 octahedra in the ZnO4 tetrahedra matrix is responsible for phonon scattering while increasing electrical conductivity, thereby enhancing the thermoelectric properties. This effect of multiple extended two-dimensional defects on the thermoelectric properties of ZnO is reported for the first time with such low indium doping. On the chemistry side, the present results point toward a lack of In solubility in the ZnO structure. Moreover, this study is a step forward to the synthesis of other thermoelectric compounds where dopant-induced planar defects in bulk transition metal compounds have the potential to enhance both phonon scattering and electronic conductivity.

Flexible Thermoelectric ZnO–Organic Superlattices on Cotton Textile Substrates by ALD/MLD

The thermoelectric properties of both pristine ZnO and ZnO–organic superlattice thin films deposited on a cotton textile are investigated. The thin films are fabricated by atomic layer deposition/molecular layer deposition, using hydroquinone as the organic precursor for the superlattices. The resulting thin‐film coatings are crystalline, in particular when deposited on a textile substrate with a thin predeposited Al2O3 seed layer. The thermoelectric properties of the ZnO and ZnO–organic superlattice coatings are comparable to those for thin films deposited on conventional inorganic substrates; Al doping can be employed to further improve the thermoelectric properties. The ZnO–organic superlattice thin films moreover show enhanced resistance to mechanical strain. Due to the higher flexibility and lower thermal conductivity in comparison to pristine ZnO thin films, the ZnO–organic superlattice thin films are a possible material platform for flexible thermoelectrics that can be integrated in textiles and applied in wearable electronics.

Thermoelectric properties of Al and Mn double substituted ZnO

The effects of Al and Mn single and double substitution on structure, composition, and thermoelectric properties of ZnO have been investigated in three series of compounds; Zn1−xAlxO, Zn1−xMnxO (x=0,0.02,0.04,0.06,0.08) and Zn1−2xAlxMnxO (x=0,0.01,0.02,0.03,0.04) prepared by thermal decomposition method. While the lattice structure is not affected by the substitutions, properties of the material are. Al and Mn have opposite effects on electrical conductivity and Seebeck coefficient of ZnO. Al substitution leads to an increase in electrical conductivity while Mn substitution increases absolute value of Seebeck coefficient. Double substituted samples seem to exhibit the effects from both ions though the increase in absolute value of Seebeck coefficient is less significant comparing to that observed in Mn single substituted samples. Nevertheless, the change in electrical conductivity is more pronounced and dominant in the power factor calculation. Thus the most conductive sample in this work, Zn0.98Al0.02O, shows the highest power factor of 1.03×10−4WK−2m−1at 800K. The best double substituted sample is Zn0.98Mn0.01Al0.01O which gives a power factor of 4.79×10−5WK−2m−1 at the same temperature.

Hybrid inorganic–organic superlattice structures with atomic layer deposition/molecular layer deposition

A combination of the atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques is successfully employed to fabricate thin films incorporating superlattice structures that consist of single layers of organic molecules between thicker layers of ZnO. Diethyl zinc and water are used as precursors for the deposition of ZnO by ALD, while three different organic precursors are investigated for the MLD part: hydroquinone, 4-aminophenol and 4,4′-oxydianiline. The successful superlattice formation with all the organic precursors is verified through x-ray reflectivity studies. The effects of the interspersed organic layers/superlattice structure on the electrical and thermoelectric properties of ZnO are investigated through resistivity and Seebeck coefficient measurements at room temperature. The results suggest an increase in carrier concentration for small concentrations of organic layers, while higher concentrations seem to lead to rather large reductions in carrier concentration.

Electrical and thermoelectric properties of ZnO under atmospheric and hydrostatic pressure

Temperature (for T = 77–400 K) and pressure (for P ≤ 8 GPa) dependences of conductivity σ(T,P). Hall coefficient R H(T, P), and Seebeck coefficient Q(T) were studied in single-crystal n-ZnO samples with the impurity concentration N i = 1017 − 1018 cm−3 and free-electron concentration n = 1013−1017 cm−3. Single crystals were grown by the hydrothermal method. Dependence of the ionization energy of a shallow donor level on the impurity concentration E d1(N d) is determined, along with the pressure coefficients for the ionization energy ∂E d1/∂P and static dielectric constant ∂x/∂P. A deep defect level with the energy E d2 = 0.3 eV below the bottom of the conduction band is found. The electron effective mass is calculated from the obtained data on the kinetic coefficients R H(T) and Q(T).

Effect of Rare-Earth Cation Doping on Enhancement of The Thermoelectric Power of Zinc Oxide

ABSTRACTWe investigated the effects of doping of rare-earth ions (Ce, Pr, Nd, Sm, and Eu) on the thermoelectric properties of ZnO, especially Seebeck coefficient in the temperature range from 100 to 800 °C. The data were scattered more or less depending on the doping species, but it was commonly found that the rare-earth doped samples showed higher Seebeck coefficients with compared to those for Al-doped samples. The highest values were observed for Nd-doped one ranging from -360 to -400μVK−1 in the temperature range observed, the lowest ones for Pr-doped one ranging from -250 to -310 μVK−1, whereas those for Al-doped one ranging from -80 to -140 μVK−1. It should also be pointed out that the power factor at 100 °C for Pr-doped ZnO was twice or more as much as that for Al-doped one. From the results it seemed that rare earth doping is effective for enhancement of thermoelectric power of ZnO.

出発原料に酸化物超微粒子を用いたZnOおよび(Zn<SUB>0.98</SUB>Al<SUB>0.02</SUB>)O熱電材料の微細構造と熱電特性

Thermoelectric properties of ZnO and (Zn0.98Al0.02)O alloys sintered under different pressures, from ultra fine powder have been investigated. The samples are with a grain size under 10 μm. Electrical conductivity, Seebeck coefficient and thermal conductivity of the samples are measured at temperatures ranging from 337 to 973 K. Electrical conductivity of the samples decreases with increasing temperature. Seebeck coefficient of the samples showed negative and the absolute value increased with increasing temperature. Thermal conductivity of the samples decreased with increasing temperature. The electrical conductivity and Seebeck coefficient appeared relatively insensitive to grain size, while the thermal conductivity did.