Conductivity Of ZnO Research Articles

Thermal conductivity suppression in ZnO with AlZn2O4and ZnP2for thermoelectric applications.

In this study, intrinsic ZnO powder was sintered and intercalated with particles. The resulting powder, along with a commercial p-type product, was consolidated into bulk materials, and their thermal conductivity was measured across a temperature range of 350 K to 700 K. The thermal conductivity of the commercial p-type ZnO was found to be lower than that of intrinsic ZnO, attributed to controlled doping. Notably, our demonstration illustrated that the thermal conductivity can be reduced by a factor of 5-10 in the presence of AlZn2O4 and ZnP2 precipitates. This methodology presents a feasible approach for the future design of ZnO-based thermoelectric materials, particularly for thermal heat scavenging applications.&#xD.

Facet dependent ultralow thermal conductivity of zinc oxide coated silver fabric for thermoelectric devices

The conversion efficiency of a thermoelectric power generator depends on the dimensionless figure-of-merit (ZT) of the constituent thermoelectric materials, which is mainly determined by their Seebeck coefficient as well as the electrical and thermal conductivity. ZnO holds promise for thermoelectric applications, yet its use is currently limited by low electrical conductivity and high thermal conductivity. Herein, we demonstrate how thermal conductivity of ZnO can be significantly reduced by intelligently combining it with a cellulose-based Ag fabric using a one-step hydrothermal method, and how different ratios of zinc nitrate hexahydrate (ZNH) to hexamethylenetetramine (HMT) can be used to fine-tune the thermoelectric performance of the resulting composite. We show that as-prepared samples have a composite structure of Ag, Zn and O without any other impurity phases. We propose that the facet dependent crystal growth orientation, from the c-axis in (101) planes to the a-axis in (100) plane, amplify phonon scattering within the material, impeding effective heat transfer and thereby lowering overall thermal conductivity to 0.046 W/mK at room temperature for composites with a 1:1 ZNH to HMT ratio.

Investigation of physicochemical characteristics of Dy3+ modified ZnO nanoparticles

In this report, pristine and Dy3+ modified ZnO nanoparticles [Zn(1-x)DyxO NPs, where x = 0, 0.05, and 0.10] were synthesized using the sol–gel route, and their physicochemical characteristics were investigated. x-ray diffractograms of all the compositions possess P63mc space group depicting hexagonal crystallinity with wurtzite-type crystal structure with no signature of impurities as confirmed using the Rietveld refinement technique. The granular microstructure displayed grain growth with Dy3+ incorporation in the ZnO crystal framework and an increment in average grain size was found to be 22.83 nm for x = 0 to 36.34 nm. The optical energy band gap also increased from 3.35 eV to 3.88 eV with Dy3+ doping in the host ZnO. Dy3+ substitution inhibits the conduction in ZnO and improves the resistivity (36 Ωcm–79 Ωcm) as carrier concentration diminishes from 7.36 × 1016 cm−3 to 4.23 × 1016 cm−3. Similarly, the mean free path length for ZnO and Dy3+ doped ZnO NPs declines from 0.0301 nm to 0.0198 nm. Dielectric properties of all the compositions were investigated using an LCR impedance analyzer and it was observed that Dy3+ substitution enhances the value of the dielectric constant from 32 to 91 with a low tangent loss at 50 Hz.

Investigations on electrical conductivity and dielectric properties of p-type ZnO by doping N synthesized from sol–gel method

Investigations on electrical conductivity and dielectric properties of p-type ZnO by doping N synthesized from sol–gel method

An Efficient and Stable Inverted Structure Organic Solar Cell Using ZnO Modified by 2D ZrSe2 as a Composite Electron Transport Layer

AbstractAs an electron transport layer (ETL) widely used in organic solar cells (OSCs), ZnO has problems with energy level mismatch with the active layer and excessive defects on the ZnO surface, which can reduce the efficiency of OSCs. Here, ZnO/ZrSe2 composite is fabricated by modifying ZnO with 2D ZrSe2. The XPS and first‐principles calculation (FPC) show that ZnO obtains electrons from ZrSe2 and forms interfacial dipoles toward the active layer, which decreases the work function of ZnO, thus reducing the interface barrier and favoring the collection of electrons in OSCs. At the same time, after ZrSe2 modification, the oxygen vacancy density on the ZnO surface decreases, thus improving the conductivity of ZnO. More importantly, the femtosecond transient absorption (Fs‐TA) shows that ZrSe2 selectively traps holes from the active layer, which prevents the holes from entering the ZnO, thereby reducing the probability of electron recombination. Finally, ZnO/ZrSe2 composite is used as a novel ETL in OSCs with PBDB‐T: ITIC, PM6:Y6 and PM6: L8‐BO as active layers, and obtaining 12.09%, 16.34%, and 18.24% efficiency, respectively. This study provides a method for the interface modification of ZnO, and further investigates the role of 2D nanosheets in the interface modification.

Synthesis, Characterization, Dielectric, and Electrical Conductivity Studies of Zinc Oxide Nanoparticles

A co-precipitation technique is used to synthesize of ZnO nanoparticles. The synthesized ZnO nanoparticles were characterized by UV-visible spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), photoluminescence, Fourier-Transform Infrared Spectroscopy (FTIR), and X-ray diffraction (XRD). The size of the nanoparticles was wide-ranging from 1 nm to 100 nm, corresponding to the HR-TEM analysis. The photoluminescence study of ZnO nanoparticle shows emission in the UV region. The particle dimension of ZnO nanoparticle has also been studied through XRD. Dielectric spectroscopy of synthesized ZnO NPs pellet has been studied at a wide frequency range 10−1 to 105 Hz. The capacitance and dielectric permittivity of ZnO nanoparticles drop continuously with frequency as dipoles have less time to align in the field. Dielectric permittivity of ZnO pellets increase up to 5 mm thickness and subsequently drop, perhaps due to raise in resistivity. The dielectric loss of ZnO pellet has been examined as a function of frequency. The electrical conductivity of ZnO nanoparticles rise exponentially with frequency. Based on the dielectric studies, the dielectric permittivity and electrical conductivity of ZnO are highly depending on thickness and frequency range. The percolation threshold of ZnO pellets has been found between 4-5 mm thicknesses.

The dependence of electrical conductivity of MgxZn1–xO ceramics on phase composition

The structural and electrical characteristics of (Mg,Zn)O ceramics produced using the solid state reaction at 1100 °C for 3 hours were studied applying X-ray diffraction and IR reflection spectroscopy as well as means of direct current measurements versus MgO content in initial charge (varied from 0 to 100 mol.%). It has been shown that electrical conductivity extracted from the IR reflection spectra corresponds to that of hexagonal phase in a solid solution, while plasmon in cubic phase was not observed. The electron concentration in the hexagonal grains of solid solution prepared with MgO content below 30 mol. % in the charge was found to be close to that of ZnO grains. It shows the tendency to decrease with further growth of the MgO content, which was explained by extraction of zinc interstitials, responsible for ZnO conductivity, from ZnO under formation of the MgZnO cubic phase. The direct current measurements have shown the lower conductivity as compared to the value estimated from IR reflection spectra. This fact along with the superlinearity of current-voltage characteristics has been explained by the presence of intergranular barriers, which does not allow obtaining information on the concentration of free electrons in the grain by this method. The possible nature of intergranular barriers as well as the role of grain boundaries in the DC conductivity of samples has been discussed.

Lattice thermal conductivity of ZnO: experimental and theoretical studies.

ZnO has been explored using different approaches such as doping, nanostructuring, 2D confinement, and introduction of interface effects for improving thermoelectric performance and lowering thermal conductivity. Herein, the lattice thermal conductivity (κL) of ZnO determined from Raman thermometry, the 3ω-method and simulation using three-phonon scattering is presented. The average Debye temperature (θD) of A1(TO) and E2(high) modes estimated utilizing bond-order-length-strength correlation with local bond averaging effects is ∼422 K. The average κL of ZnO calculated using the theoretical coefficient of Slack's equation, θD, and Grüneisen parameter (γ) in Slack's equation is 2.75 W m-1 K-1, which is significantly lower than the κL ∼ 50.9 W m-1 K-1 simulated by considering the Perdew-Burke-Ernzerhof functional with Hubbard and non-analytical corrections. The coefficient of Slack's equation is determined from the κL ∼ 31 W m-1 K-1 of ZnO measured using the 3ω-method for the accurate estimation of the κL. The experimental coefficient of Slack's equation with Raman thermometry data yields κL ∼ 50.6 W m-1 K-1, which is higher than the value obtained using the 3ω-method but consistent with the theoretical value. Thus, three-phonon anharmonicity describes the κL of ZnO associated with Raman scattering. The method adopted to calculate κL will help for the in-depth analysis of phonon dynamics and the design of wurtzite-ZnO-related power electronics.

Surface functionalization of ZnO nanoparticles with sulfonate molecules as the electron transport layer in quantum dot light-emitting diodes

Phenylated sulfonate ligands were used to modify the surface of ZnO NPs for fabricating bright and efficient QLEDs.

Sintering mechanism and electrical conductivity of ZnO added BaCe0.8Zr0.1Y0.1O3-δ proton conducting perovskites

The sintering mechanism and electrical conductivity of ZnO added BaCe0.8Zr0.1Y0.1O3-δ (BCZY) proton conducting perovskites were investigated. The additions of 0.1 to 3 wt% ZnO to BCZY promoted the sintering of the BCZY pellet samples, and the samples with ZnO showed impermeable bodies with relative densities ≥90% after firing at 1400 °C for 6 h. First-principles calculations suggest that Ba in BaZnO2 is more stable than in perovskites, and Zn is hardly soluble in BCZY. These theoretical results indicate that ZnO reacts with Ba in the BCZY perovskites. The melting points of the BaO and ZnO mixtures were approximately 1100 °C. Because their liquid phase should react with excess Y component in the perovskite, the liquid phase containing Y component enhances the densification of the doped perovskite by the liquid phase sintering. The electrical conductivities of BCZY perovskites with ZnO content ranging between 0.1 wt% and 3 wt% varied from 1.3 × 10−2 to 1.5 × 10−2 S/cm at 600 °C in an atmosphere of 3.0% H2O, 19.4% H2 and 77.6% N2. The electrical conductivities of BCZY perovskites with ZnO were comparable to those of the dense BCZY perovskite without ZnO. The present result suggests that addition of a small amount of ZnO is appropriate for enhancing the sintering and retaining the high electrical conductivity of BCZY.

Improving CO2 sensing and p-n conductivity transition under UV light by chemo-resistive sensor based on ZnO nanoparticles

Chemo-resistive gas sensors for CO2 detection were fabricated using ZnO nanoparticles synthesized by the hydrothermal method. The CO2 sensors were activated by thermal and/or UV light exposure. While the resistance changes of sensors exposed to CO2 at high temperatures (150–300 °C) exhibited noise, those activated by UV light remained stable, indicating that UV light can improve CO2 sensing. Good response, short response time (<10 s), stability, a linear calibration curve, and high sensitivity were obtained under UV light. Therefore, the UV-activated sensor could be applied in practical environments for CO2 monitoring. Furthermore, the measurements for CO2 also showed that the p-n transition was observed with changes in temperature. The CO2 sensor acted as p-type at RT, while it acted as n-type at 80 °C. The p-type conductivity of ZnO at RT, which can be attributed to Zn vacancies acting as acceptors, was confirmed through PL and EDX spectra, as well as Hall Effect measurements. It should be noted that the p-n transition in sensors based on undoped materials under UV irradiation at low temperatures (<100 °C) has been less reported. The n-p transition could offer intriguing opportunities to customize the electronic properties of the nanostructured devices.

High-concentration F-incorporated ZnO thin films doped via femtosecond-laser hyperdoping

ZnO is a transparent conductive oxide that has received great attention over the past few decades, as it is a key component in light-emitting diodes, gas sensors, and solar cells. However, the electrical conductivity of intrinsic ZnO is not ideal, and thus, ZnO is often doped with appropriate elements such as fluorine (F). Unfortunately, the lack of adequate precursors in traditional doping methods may increase the difficulty of ZnO doping with F. In this work, we realized, for the first time, high-concentration F-doped ZnO thin films with a high Hall mobility of 20.7 cm2/V/s via femtosecond-laser hyperdoping. The highest atomic percentage of F was determined to be 8.3 at.%, which was over three times larger than that of previously reported F-doped ZnO films. Compared with pristine ZnO, the highest carrier concentration of the F-doped ZnO could be increased by four orders of magnitude, and the resistivity could be reduced by three orders of magnitude. Our results demonstrated that the femtosecond-laser hyperdoping technology could achieve efficient non-metallic hyperdoping of ZnO with high transparency and Hall mobility, thereby reducing the power dissipation and improving the current carrying capacity of ZnO-based devices.

Study of the Sensor Properties of Ordered ZnO Nanorod Arrays for the Detection of UV Radiation

Zinc oxide is one of the most promising materials used to create devices in the ultraviolet (UV) range. In this article, we study the sensor properties of ordered ZnO nanorod arrays grown by chemical vapor deposition. The possibility of their use as an indicator of UV radiation to control the dose of UV radiation, both from natural and artificial light sources, is assessed. The X-ray diffraction, Raman spectroscopy (RS), and cathodoluminescence (CL) data demonstrate the high quality of nanorods. Based on the ZnO nanorod array, a sensor prototype was fabricated based on the change in ZnO conductivity under the UV irradiation. A compari-son of the response of such a sensor with the readings of a UV radiometer showed a high correlation.

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.

Three-level homogeneous model for the study of heat transfer mechanism in metallic nanofluids

To explain heat conduction mechanism in nanofluids, different existing models have been analysed, but none of these can predict exact variation of thermal conductivity with volume concentration. In present study, it is found that the static and dynamic contributions of nanoparticles in the base fluid are responsible for its conductivity. Unfortunately, these both aspects have not been included in any of the existing model. We have modified the Xuan model including effect of shape and size of nanoparticles (static contribution) and allocation of nanoparticles, temperature, junction layer, congregate pattern, and Brownian diffusion (dynamic contribution) to propose a new model which can predict the exact mechanism of thermal conductivity of nfs. We have tested the proposed model to compute the thermal conductivity of Al2O3, ZnO, Ag, CuO, Co3O4 and Fe2O3 based nanofluids at different volume concentrations. Computed results using our proposed model are in very good agreement with experimental data.

Acoustoelectric Effect of Rayleigh and Sezawa Waves in ZnO/Fused Silica Produced by an Inhomogeneous In-Depth Electrical Conductivity Profile

The acousto-electric (AE) effect associated with the propagation of Rayleigh and Sezawa surface acoustic waves (SAWs) in ZnO/fused silica was theoretically investigated under the hypothesis that the electrical conductivity of the piezoelectric layer has an exponentially decaying profile akin to the photoconductivity effect induced by ultra-violet illumination in wide-band-gap photoconducting ZnO. The calculated waves' velocity and attenuation shift vs. ZnO conductivity curves have the form of a double-relaxation response, as opposed to a single-relaxation response which characterizes the AE effect due to surface conductivity changes. Two configurations were studied which reproduced the effect of UV light illumination from the top or from the bottom side of the ZnO/fused silica substrate: 1. the ZnO conductivity inhomogeneity starts from the free surface of the layer and decreases exponentially in depth; 2. the conductivity inhomogeneity starts from the lower surface of the ZnO layer contacting the fused silica substrate. To the author's knowledge, this is the first time the double-relaxation AE effect has been theoretically studied in bi-layered structures.

Investigation of electrophysical, photo- and gas-sensitive properties of ZnO–SnO2 sol–gel films

Thin nanocomposite films based on tin dioxide with a low content of zinc oxide (0.5–5[Formula: see text]mol.%) were obtained by the sol–gel method. The synthesized films are 300–600[Formula: see text]nm thick and contains pore sizes of 19–29[Formula: see text]nm. The resulting ZnO–SnO2 films were comprehensively studied by atomic force and Kelvin probe force microscopy, X-ray diffraction, scanning electron microscopy, and high-resolution X-ray photoelectron spectroscopy spectra. The photoconductivity parameters on exposure to light with a wavelength of 470[Formula: see text]nm were also studied. The study of the photosensitivity kinetics of ZnO–SnO2 films showed that the film with the Zn:Sn ratio equal to 0.5:99.5 has the minimum value of the charge carrier generation time constant. Measurements of the activation energy of the conductivity, potential barrier, and surface potential of ZnO–SnO2 films showed that these parameters have maxima at ZnO concentrations of 0.5[Formula: see text]mol.% and 1[Formula: see text]mol.%. Films with 1[Formula: see text]mol.% ZnO exhibit high response values when exposed to 5–50[Formula: see text]ppm of nitrogen dioxide at operating temperatures of [Formula: see text]C and [Formula: see text]C.

Performance Enhancement of Cadmium‐Free Quantum‐Dot Light‐Emitting Diodes via Cl‐Passivated Zn1−x−ySnxMgyO Nanoparticles as Electron Transport Layers

AbstractAlthough cadmium (Cd)‐based nanocrystals have enabled high‐performance quantum‐dot light‐emitting diodes (QLEDs), their mass production is likely to be affected by environmental protection policies. Among all the potential Cd‐free candidates, Cu‐In‐Zn‐S (CIZS) nanocrystals (NCs) have attracted particular interests. Still, the performance of the corresponding LED is currently limited by imbalanced charge injection and luminescence quenching, which are both related to the ZnO‐based electron transporting layer (ETL). This work demonstrates that ZnO nanoparticles (NPs) doped with Sn, Mg (Zn1−x−ySnxMgyO), and passivated with Cl are promising to resolve the above issues. All‐solution‐processed QLEDs based on Cd‐free CIZS NCs are fabricated by using Zn0.9Sn0.1O NPs as the ETL, and the peak external quantum efficiency (EQEmax) was nearly twice that of ZnO (EQEmax = 1.74%). The main reason is that the incorporation of Sn can reduce the conductivity of ZnO by an order of magnitude. Combining the advantages of Zn0.9Sn0.1O, Zn0.8Sn0.1Mg0.1O@Cl NPs are designed by the co‐doping of Mg and Cl passivation. The EQEmax and current efficiency based on Zn0.8Sn0.1Mg0.1O and Zn0.8Sn0.1Mg0.1O@Cl as ETLs are further increased to 4.84%, 14.00 cd A−1 and 5.53%, 15.99 cd A−1, respectively. The positive effects of Mg ions can remarkably optimize energy level structure to balance charge injection, while Cl can further passivate defects. The findings offer a new guideline for developing Cd‐free light‐emitting diodes.

Acoustoelectric Effect for Rayleigh Wave in ZnO Produced by an Inhomogeneous In-Depth Electrical Conductivity Profile.

The acousto-electric (AE) effect associated with the propagation of the Rayleigh wave in ZnO half-space was theoretically investigated by studying the changes in wave velocity and propagation loss induced by in-depth inhomogeneous changes in the ZnO electrical conductivity. An exponentially decaying profile for the electrical conductivity was attributed to the ZnO half-space, for some values of the exponential decay constant (from 100 to 500 nm), in order to simulate the photoconductivity effect induced by ultra-violet illumination. The calculated Rayleigh wave velocity and attenuation vs. ZnO conductivity curves have the form of a double-relaxation response as opposed to the single-relaxation response which characterizes the well-known AE effect due to surface conductivity changes onto piezoelectric media. As to the author's knowledge, this is the first time the double-relaxation AE effect has been theoretically predicted.

Evaluation of the effects of the presence of ZnO -TiO2 (50 %–50 %) on the thermal conductivity of Ethylene Glycol base fluid and its estimation using Artificial Neural Network for industrial and commercial applications

In this study, the thermal conductivity (knf) of ZnO -TiO2 (50 %–50 %)/ Ethylene Glycol hybrid nanofluid using Artificial Neural Networks (ANNs) was predicted. The nanofluid was prepared at different volume fractions (φ) of nanoparticles (φ = 0.001 to 0.035) and temperatures (T = 25 to 50 °C). In this study, an algorithm is presented to find the best neuron number in the hidden layer. Also, a surface fitting method has been applied to predict the knf of nanofluid. Finally, the correlation coefficients, performances, and Maximum Absolute Error (MAE) for both methods have been presented and compared. It could be understood that the ANN method had a better ability in predicting the knf of nanofluid compared to the fitting method. This method not only showed better performance but also reached a better MAE and correlation coefficient.