In recent years, research on strongly correlated conductive and non-conductive materials has become a central topic in materials science. These systems are characterized by strong Coulomb interactions between neighboring cations, leading to the emergence of unique properties that are difficult to harness for practical applications, such as gas sensing. In this article, we review how to enhance the NO2 gas sensing capability in NiWO4, which is considered electrically insulating, by introducing iron as a substituent in nickel sites. We will explore the effects of this substitution, including changes in electronic structure and magnetic properties, which indicate the potential for this material to be used in gas sensing applications. We will also discuss theoretical and experimental results that illustrate how precise manipulation of Coulomb interactions can lead to significant improvements in gas sensor performance.
Properties of Strongly Correlated Electronic Systems
Strongly correlated electronic systems (SCES) exhibit unique properties attributed to the strong Coulomb interaction between neighboring cations within their crystal structure. These systems display excellent behavior in materials such as NiO, where the repulsion between cations results in a pseudo-gap known as the Mott gap. This gap, along with associated properties such as magnetic ordering, depends on the Hopfield parameters related to each cation. These materials offer a new research opportunity as their behavioral patterns may lead to multiple applications, such as gas sensor devices.
NiWO4 represents an interesting case, displaying insulating-like behavior due to the Coulomb repulsion between nickel cations, complicating its use in solid-state applications. It is noteworthy that theoretical and experimental methods show that the conductive properties of these materials are precisely affected by the distribution of cations and their Coulomb effects. The new formula Fe0.5Ni0.5WO4 and the results of this modification enhance the potential for utilizing these systems in advanced applications.
The Effect of Iron Insertion on NiWO4 Properties
Upon inserting iron into nickel sites in NiWO4, significant changes in the physical properties of the metal were observed. Iron reshapes the Coulomb interaction, leading to a substantial improvement in gas sensing. The high efficiency in NO2 response at 200 degrees Celsius is a focal point in the research, where a response was measured resulting in an Rg/Ra value of 11. This performance enhancement was not observed in conventional NiWO4.
Studies indicate that iron plays a crucial role in modulating Coulomb levels in NiWO4. Upon the introduction of iron, an increase in magnetic levels and a shift in the [NiO6] phonon modes were noted. Additionally, theoretical calculations show the preservation of a wide band gap, reinforcing the idea that iron insertion affects the electronic properties in SCES. These results enhance the capability of NiWO4 for use in new technologies, materials processing, and other fields.
Methods and Tools Used in the Research
The research in this study was conducted through multiple methods, including the solid-state reaction method to prepare the NiWO4 and Fe0.5Ni0.5WO4 pastes. High-purity chemicals such as Fe2O3, NiO, and WO3 were used to achieve this mixture. After mixing these materials, thermal treatment was carried out to ensure the formation of the correct crystal structure.
In performance evaluation, a dual-electrode configuration was used, where the pastes were attached to gold electrodes mounted on an alumina base. This method allowed for precise measurement of the system’s response to target gases. Sensor performance was assessed under varying temperature and gas pressure conditions, highlighting the importance of careful experimental design to understand the full impact of the gas sensing mechanism in these systems.
Results
Research on the Sensing Performance of NO2 Gas
The research revealed the outstanding performance of the Fe0.5Ni0.5WO4 model in sensing NO2 gas, highlighting the limitations of the previous performance of NiWO4. The cells recorded a very high response, revealing the positive impact of the studied use of iron in modifying the robustness of the key components. These results not only disclose the nature of the response to gas molecules but also represent an advancement in understanding how to improve the performance of SCES materials.
Additionally, experiments show that the addition of iron enhances interactions with gas molecules and directly affects the material’s resistance. This mechanism relies on the interaction of gas circuits with the surface of the materials, resulting in the development of new features in this field. Furthermore, the results indicate that the interactions occurring at the surface of the material return to initial values after a certain period, providing hope for the possibility of developing practical sensing devices based on these theories and models.
Future Prospects for SCES Systems Applications
Current research conducted on NiWO4 and Fe0.5Ni0.5WO4 opens multiple prospects for new and innovative applications in various fields. These areas include materials used in sensors and energy storage materials. The increased effectiveness of gas sensing makes these systems reliable in environmental and industrial applications.
By continuing to explore the relationship between crystal structure and electronic properties, new materials as SCES systems can provide effective solutions to multiple problems in science and engineering. Techniques like gas sensing represent a small part of the potential, making research into producing new materials or modifying existing ones a continually relevant research opportunity.
Structural Analysis of NiWO4 and Fe0.5Ni0.5WO4 Compounds
Studies have shown that NiWO4 and Fe0.5Ni0.5WO4 compounds retain a single-phase crystalline structure. These results are based on spectroscopic data (Raman) that reveal the presence of 36 unique vibrational modes in the crystalline structure. Among these modes, there are several active modes such as 8 Ag and 10 Bg. The Fe0.5Ni0.5WO4 sample exhibits a slight shift in peak positions due to atomic substitution, where a change in frequency is observed in the NI-O vibrational mode, indicating weakened Ni-O bonds. This shift is an indicator of the interaction between iron and nickel and its effect on oxygen binding with the metals.
Furthermore, the results confirmed peak shifts in vibrational frequencies at 698 cm−1 and 890 cm−1, indicating a different response in the magnetic behavior of the compounds due to the use of iron. Data obtained from the magnetization of the compounds at various temperatures indicate a Néel temperature TN of 63 Kelvin for studying the electrical bond behavior and charge interactions. Through these modifications, Fe0.5Ni0.5WO4 exhibits a higher response in magnetic signaling, reducing attractive coulombic forces and demonstrating more efficient interactions.
Electronic Structure and Hubbard Calculations for NiWO4 and Fe0.5Ni0.5WO4 Compounds
To understand the effect of iron substitution on the electronic structure of the compounds, structural calculations were performed using the Hubbard model. The results show that using repulsive energy at the atomic site in two different ways may enhance accuracy and reduce gaps in energy relationships. These important values are critical for understanding the electrical properties of the structure. Through density functional perturbation theory (DFPT) calculations, high-accuracy Hubbard values were obtained, indicating the presence of complex interactions between atoms.
Density of states (DOS) calculations and the electronic band structure for Fe0.5Ni0.5WO4 compounds showed a range of significant changes due to the presence of transition metals, highlighting profound differences in the charge transfer pattern. The results indicate that the exchange effects have been modified as a result of the site structure differences between iron and nickel. These changes, with electrons in different bonding states, suggest a notable modification in electrical conductivity efficiency and general electronic interaction characteristics.
Performance
Compound Fe0.5Ni0.5WO4 in Gas Detection
A gas detection test was conducted using a system with electrodes to determine the effectiveness of both NiWO4 and Fe0.5Ni0.5WO4. The results revealed an impressive response in the Fe0.5Ni0.5WO4 compound towards NO2 with a response value of Rg/Ra reaching 10.4. This showcases a significant increase in responsiveness compared to the performance of NiWO4, which shows a stable response nearing 2. This difference in performance is highlighted by the structural effects resulting from the addition of iron, enhancing surface reactivity and increasing the compound’s ability to absorb molecules.
The response of Fe0.5Ni0.5WO4 was studied at different temperatures, and the results proved that increasing the temperature significantly enhances gas detection performance. However, the actual compound exhibited difficulty in responding to gases at lower temperatures such as RT (room temperature) and 100 degrees Celsius. The critical operating point was at 200 degrees Celsius, resulting in a substantial improvement in performance and efficiency of increased response rate. Subsequent analyses showed a different response for the Fe0.5Ni0.5WO4 compound compared to other compounds.
Potential Applications of Fe0.5Ni0.5WO4 in Modern Technology
The Fe0.5Ni0.5WO4 compound could open new horizons in sensor technology, as it shows significantly improved gas-sensing properties. These results are promising for the potential use of this compound in developing high-efficiency sensors for detecting gases at low concentrations like NO2. The compound’s strong ability to efficiently detect the presence of these gases makes it suitable for use in industrial and urban environments, where environmental safety and air quality assessment are vital priorities.
Moreover, the improvement of performance metrics under various operating conditions suggests potential applications for Fe0.5Ni0.5WO4 in rapid and continuous gas interaction applications. Its capabilities in environmental safety systems, including early warning systems for monitoring air pollution, could be very beneficial if developed appropriately. Additionally, introducing a new compound like Fe0.5Ni0.5WO4 offers opportunities for future studies to exploit transition metals in modern technological applications.
Improving Gas Sensitivity Performance Using Fe0.5Ni0.5WO4
This research addresses the importance of improving the performance of materials used in gas sensitivity, especially at low concentrations. It was indicated that adding metal elements like iron (Fe) in combination with nickel oxide compounds (NiWO4) significantly contributed to enhancing gas sensitivity performance. According to the results, materials containing Fe showed better response for monitoring nitrogen dioxide (NO2) at 200 degrees Celsius. This is attributed to the role of Fe ions in modifying the gas sensitivity properties, where data showed a clear difference in the response between the original compound NiWO4 and the compound with added Fe.
The modification done by iron has shown to act as an activator that enhances gas adsorption sites, leading to increased charge transport efficiency. This opens the door for using such materials in various chemical applications, including selective gas sensors. This advancement in using Fe0.5Ni0.5WO4 represents a significant achievement in the field of sensing materials, as they can be effectively utilized in monitoring various gases.
The Role of Iron Addition Levels in Expanding the Energy Gap
It has been clarified how the level of iron additions can play a crucial role in expanding the energy gap of the NiWO4 compound. Studies indicate that the electromagnetic interaction between metal ions in NiWO4 opens an energy gap of about 3.0 electron volts, allowing for the modification of energy levels for the added ions. By positioning themselves at specific points within the lattice, these additions influence the conductivity properties and charge transport scheme of the material, making these modifications very suitable for increasing gas sensitivity of the NiWO4 compound when exposed to gases like NO2.
Energy gap
Low energy increases the effectiveness of sensor compounds, facilitating the molecular-level gas sensing process. This contrasts with what was observed in the original compound NiWO4, where the decrease in gas sensitivity at high temperatures was verified. This research represents an important step towards developing more efficient gas sensors capable of operating under varying conditions, highlighting the importance of selecting suitable metal layers for the chemical industry.
Statistical Analysis of Data and Its Future Applications
Scientific research requires a systematic and structured analysis of data to reach accurate conclusions. In this research, a range of statistical methods, such as formal analysis and evaluation techniques, were employed to monitor gas sensitivity performance. The performance of the sensor is measured by various parameters, such as response under different concentrations of gas, as well as the detection limit for gases. These criteria are essential for identifying the strengths and weaknesses of the developed system, allowing for a deeper understanding of the capabilities of new materials.
Additionally, data related to different levels of iron additives are presented as a foundation for developing advanced gas sensors, indicating that these materials are not limited to traditional uses but can also be applied in high-value applications such as environmental monitoring, public health, and industrial information technology. Success in developing precise gas sensors and new discoveries in these systems will significantly contribute to advancements in multiple fields of science and technology.
The Impact of Additives on the Development of Chemical Sensors
The research links levels of additives to changes in the chemical properties of the materials used in sensors. The use of additives like iron is considered an ideal technique for developing new sensors capable of rapidly and accurately responding to target gases. It has been shown that managing the electrostatic force between metal ions effectively improves sensory properties, enhancing the efficiency of sensors and their ability to operate in different environments. Therefore, modern material technologies with the potential use of additives will play a crucial role in innovating highly reliable sensors.
Targeted applications in quality monitoring, toxic gas sensors, and process control technology serve as clear examples of how these materials can be integrated into everyday life. Future research in this area will enhance knowledge and understanding of the chemical processes occurring in sensors, thereby improving their overall performance. Consequently, research into improving gas sensing through modified materials is a strong step towards technological advancement in chemical sensors.
The Practical Importance of Research on Gas Sensitivity
Research related to gas sensitivity is gaining increasing importance in the modern world, reflecting contemporary environmental and industrial challenges. Sensing materials primarily serve to maintain public health and safety by monitoring and identifying pollutants and poisoning resulting from harmful gases. Gas sensing technology is essential in the chemical and environmental industries, contributing to informed decision-making that affects the work environment.
For example, sensors based on Fe0.5Ni0.5WO4 can be used in air monitoring stations to mitigate the risks posed by air pollution and can be applied in safety systems in industrial sites where rapid and direct interaction with toxic gases is necessary. Moreover, this research contributes to enhancing technological innovations and developing effective solutions to daily challenges, such as improving air quality and reducing environmental pollutants.
Electronic Systems Based on Coulombic Links
Coulombic link-based electronic systems (SCES) are considered one of the most intriguing fields in modern physics. These systems refer to the behavior of electrons in materials that interact strongly with each other, leading to the emergence of unique physical properties. One of the most notable features that characterize SCES is the presence of a partial gap, known as the “Mott gap,” which arises from strong electrostatic repulsion between ions. This gap depends on the Hubbard parameter (U) and is typically characterized by a specific magnetic system, where the magnetic arrangement is often in the form of anti-aligned spins. For instance, in nickel oxide (NiO), this gap is clearly evident, making it an intriguing subject for study.
Consider
The complex interplay between the booklets and magnetism in SCES poses a challenge for practical applications, as the complex behavior of these systems makes them difficult to use in traditional electrical devices. However, recent studies have shown the potential to modify these properties through new strategies, opening up new horizons for innovative applications. For instance, the introduction of impurities can improve electrical properties or increase the catalytic activity of the materials. Future applications of SCES systems may include materials for sensing and materials for advanced electronic devices.
Nickel Oxide – Interaction and Properties
Nichrome oxide (NiO) is a common example of Columbic systems, exhibiting interesting electronic properties, including a partial gap caused by repulsion between ions. Research shows that these properties depend significantly on the U parameter of nickel, as increasing this parameter leads to an increase in the energy gap. By employing techniques such as neutron scattering, magnetic ordering in NiO has been confirmed, highlighting how electrical conductivity is influenced by magnetic ordering.
Furthermore, new research indicates significant potential for developing nickel oxide in catalytic applications, with one of the strategies involving substituting some nickel ions with other elements like vanadium (V). This substitution can reduce the strength of the Coulombic binding, enhancing the catalytic sites of the materials. These developments not only bolster the scientific understanding of SCES materials but also promise to expand the range of their future applications in chemical sensing and nanotechnology.
Gas Sensing Systems Based on SCES Materials
Chemoresistive technologies are exciting applications for systems that rely on Coulombic bonds. The idea of these systems lies in their ability to detect and regulate toxic gas molecules by exploiting changes in the electrical resistance of the materials when exposed to gases. To achieve adequate performance, materials must ensure high and consistent absorption of gas molecules on their surface, as this interaction leads to the formation of depleted surface layers, changing resistance.
When gas molecules are absorbed, there is an exchange of electron charges between the gas and the surface, resulting in a change in resistance. The resistance response depends on the type of gas being detected and its relationship with the type of conductivity of the materials. The use of the newly developed NiWO4, improved by introducing iron (Fe) into its structure, shows significant improvement in the performance of NO2 gas sensing, providing these systems with vast potential for diverse applications beyond gas coverage, including environmental and industrial applications. Future strategies should be based on stimulating the chemical and physical properties of the materials to enhance sensing performance.
Manufacturing and Characterization Methods for SCES Materials
The manufacturing process of materials used in SCES involves specific techniques to achieve precise composition and desired properties. In the case of NiWO4 and Fe0.5Ni0.5WO4, the solid-state reaction method was used, which relies on mixing pure materials under certain conditions, followed by a heat treatment process. Using high-quality material standards before starting manufacturing provides a high level of purity, assisting in obtaining consistent properties.
Characterization methods also involve using techniques such as X-ray diffraction and Raman spectroscopy, which allow for studying the crystalline structure and state of the materials. Computational models like Density Functional Theory (DFT) are powerful tools for closely understanding the electronic properties of materials. These methods can provide vital information on how to modify Coulombic bonds, leading to improved electrical performance of the material.
Good practices in material processing and characterization contribute to advancing research related to SCES and pave the way for developing new gas sensing and detection systems. Ongoing research into the design and structural methods of these materials ensures the expansion of their diverse applications and enhances their utility in multiple fields.
Structure
NiWO4 and the Effect of Iron Substitution (Fe)
NiWO4 is a solid compound that possesses advanced electronic properties and is part of systems with strongly correlated electrons (SCES). It is characterized by a wolframite-type crystal structure (P2/c) consisting of angularly interconnected octahedral [NiO6] and [WO6] layers, indicating significant Coulomb repulsion among nickel atoms. To modify this repulsion, iron ions (Fe) were substituted at nickel sites through a solid-state synthesis method. It has been demonstrated that iron cations with oxidation states ranging from +2 to +3 have a similar atomic radius to that of nickel, facilitating the substitution process. Studies have shown that this type of substitution leads to an improvement in magnetic properties and reduces the Coulomb repulsion among nickel atoms.
Using Raman spectroscopy, the results revealed the presence of 36 different vibrational modes, with a shift in the nickel-oxygen vibrational peak observed in Fe0.5Ni0.5WO4, indicating weakened bonding between nickel and oxygen. These results, in conjunction with magnetization measurements, demonstrate that the substitution of iron enhances magnetic properties compared to the original compound, with Fe0.5Ni0.5WO4 exhibiting higher magnetism at a Néel temperature of 63 Kelvin, leading to an overall improvement in the material’s performance.
Theoretical Study and Electronic Structure of Fe0.5Ni0.5WO4
Theoretical calculations were conducted to understand the effects generated by iron substitution. Density Functional Theory (DFT) was used to calculate the Hubbard parameters necessary for greater accuracy in estimating the energy gap of the materials. The results showed that the parameters converge between the new structure Fe0.5Ni0.5WO4 and its counterpart NiWO4, demonstrating the extent of the new structure’s impact on the electronic properties of the material. Regarding the energy state, the results indicated that the levels primarily composed of Fe-3d and O-2p are close to the Fermi energy, suggesting profound changes in the conduction mechanism and the material’s intrinsic properties.
The density accumulation was calculated using modified parameters, and the analysis results indicated that weak conductivity might affect the electron transfer mechanics. The presence of iron states close to the Fermi level enhances charge transport capabilities and boosts the electronic performance of the material. This aligns with experimental results showing a significant improvement in magnetic and electronic properties due to iron substitution. It can be concluded that this change in structure enhances the use of these materials in electrical and magnetic applications.
Gas Sensing Performance of Fe0.5Ni0.5WO4
The materials made from Fe0.5Ni0.5WO4 demonstrated leading performance in gas sensing. Gas sensing tests were conducted using a two-electrode system. The samples were prepared by pressing the synthesized powder onto a gold-coated substrate, with a small amount of ethanol added to stabilize the material. The results showed that the Fe0.5Ni0.5WO4 sample achieved a significantly better response when exposed to certain gases such as NO2, with a response of 10.4, indicating higher effectiveness compared to other samples, including NiWO4, which showed a steady response close to 2.0.
The data shows that temperature plays a crucial role in gas sensing, with the best performance observed at 200 degrees Celsius. The graphical analysis of selectivity demonstrated that Fe0.5Ni0.5WO4 clearly outperforms in sensing NO2 compared to other gases, reflecting the structural modifications that contributed to improved effectiveness and responsiveness of the material. These results indicate the significant potential for using Fe0.5Ni0.5WO4 in practical applications within materials science and gas sensing, resulting from the enhancement of electron transfer capabilities due to iron substitution.
Gas Sensor Response to Different NO2 Concentrations
The gas sensor response to varying levels of NO2 gas was discussed, ranging from a concentration of 20 parts per million (ppm) down to 1 ppm. It is evident that the sensor’s response decreases with diminishing NO2 concentration, with noticeable declines particularly between the concentrations of 10 ppm and 1 ppm. This indicates a nonlinear relationship between the sensor response and gas concentration. However, the sensor’s performance reached a saturation state at concentrations of 10 and 20 ppm, indicating that the sensor does not become more sensitive beyond this level. These results suggest that the sensor has certain limitations in performance when it comes to higher concentrations of NO2, underscoring the need for developing alternative methods to enhance sensor response at lower concentration levels.
Identification
Detection Limits of Sensors in NO2 Applications
The limit of detection (LOD) for the sensor was calculated based on its response to different concentrations of NO2. Analyzing the sensor response at concentrations of 10 ppm, 4 ppm, 2 ppm, and 1 ppm, the limit of detection was determined to be 46.4 parts per billion (ppb). This value indicates the sensor’s ability to detect very small amounts of NO2 with high accuracy. Achieving this low detection level reflects the effectiveness of the materials used in constructing the sensor, which enhances the potential for using this type of sensor in environmental and industrial applications for monitoring pollutant gases.
Materials Used in Sensor Design and Their Impact on Performance
The performance of sensors made from materials such as Fe0.5Ni0.5WO4 and Fe0.25Ni0.75WO4 was studied. The results showed that the level of iron (Fe) doping plays a significant role in improving gas sensing properties. For example, clear differences in sensor response were observed when exposed to different concentrations of NO2 at temperatures up to 200 degrees Celsius, indicating the role of iron as an activating agent for gas adsorption sites. This contributes to enhancing the charge transfer necessary to improve the sensor’s efficiency.
The Effect of Iron Doping on Enhancing Selective Gas Performance
Adding iron to the NiWO4 structure plays a crucial role in enhancing gas sensing performance at high temperatures. This reflects the importance of the chemical composition of sensors in modifying electrical properties. Iron doping reduces the energy required for gas adsorption, thereby improving the sensor’s response to lower concentrations of NO2. By conducting a comprehensive comparison between NiWO4 and Fe0.5Ni0.5WO4, it is evident that iron increases sensing effectiveness, encouraging the use of new materials in the development of gas sensors.
Future Applications of Composite Material-Based Sensors
The results derived from previous studies are an encouraging sign for the development of effective gas sensors based on composite materials. Research is shifting toward the use of more basic chemical elements and increasing doping to achieve improved performance. These innovations open new horizons in various fields such as industrial, environmental, and health applications where these sensors are used to detect toxic gases and maintain air quality.
Financial and Ethical Support in Sensor Development
Emphasizing the importance of financial and research support that has aided in the development of these sensors. Partnerships between national institutions and research centers form a primary catalyst for developing new technologies. Organizations like the National Research Foundation in Korea (NRF) play a significant role in providing funding for research projects focused on improving sensor quality. This collaboration enhances opportunities for innovation and helps reduce production costs, facilitating the marketing of these products in the future.
Challenges Facing Gas Sensor Development
Despite remarkable advancements in gas sensor performance, challenges persist, such as the thermal and chemical stability of sensors when exposed to harsh environmental conditions. Additionally, there is a need for continuous improvement in the sensors’ ability to distinguish the target gas from other gases that may be present in the surrounding environment. These challenges serve as a strong incentive for researchers to continue working on improving materials and sensor designs to achieve higher response levels and enhanced sensing characteristics.
Source link: https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2024.1480356/full
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