Low temperature synthesis and characterization of single phase multi-component fluorite oxide nanoparticle sols

We report for the first time a simple, scalable approach for the synthesis of single-phase multi-component fluorite oxide nanoparticle sols: Gd0.2La0.2Y0.2Hf0.2Zr0.2O2 (GLYHZ) and Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2 (GLCHZ) using chemical co-precipitation followed by peptization in acidic medium under mild conditions (≤80 °C). High resolution transmission electron microscopy (HRTEM) along with selected area electron diffraction (SAED) studies confirm fully crystalline single-phase cubic fluorite nanoparticles having a particle size of about 2–3 nm with a narrow size distribution was obtained. The powder X-ray diffraction (XRD) and Rietveld refinement studies of samples calcined at 500 °C for 4 hours confirm a single phase solid solution and a lack of secondary phases

Structural and luminescent properties of Eu3+ doped multi-principal component Ce0.2Gd0.2Hf0.2La0.2Zr0.2O2 nanoparticles

We report the luminescent properties and local structural studies of multi-principal component Ce0.2Gd0.2Hf0.2La0.2Zr0.2O2 oxide nanoparticles using Eu3+ as a luminescent dopant. A simple chemical co-precipitation of metal salts accompanied by peptization in an acidic medium was carried out to obtain various compositions of Eu3+-doped Ce0.2Gd0.2Hf0.2La0.2Zr0.2O2 nanoparticle sols. The sols were dried in an oven at 110 °C for 24 h, and the resultant powder was calcined in static air for 2 h at 500 °C, 750 °C, and 1000 °C. The calcined nanoparticles were characterized by using x-ray diffraction (XRD), UV–Visible spectroscopy (UV–Vis), and Photoluminescence spectroscopy (PL). All the calcined Eu3+-doped samples revealed a single-phase cubic fluorite solid solution without any phase separation. PL studies on various concentrations of Eu3+ doping and calcination temperatures have been evaluated. The Eu3+ emission features are excitation wavelength-dependent. In addition, PL emission intensity increased with increasing Eu3+ concentration and calcination temperatures. The luminescent properties of these multi-principal component oxides were associated with its local environment based on the location of Eu3+ inside the host lattice. The asymmetric ratios calculated from the emission spectrum provided an insight into the local environment around the Eu3+ ion and confirmed that the system contains disordered defects even when heat treated at higher temperatures showing a stable defect fluorite structure. The reported Eu3+ doped Ce0.2Gd0.2Hf0.2La0.2Zr0.2O2 nanoparticles will be a suitable candidate for imaging as well as in lighting applications

Single-phase Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2 and Gd0.2La0.2Y0.2Hf0.2Zr0.2O2 nanoparticles as efficient photocatalysts for the reduction of Cr(VI) and degradation of methylene blue dye

We report for the first time the use of noble metal-free multi-component equiatomic oxide as photocatalysts with excellent performance for natural sunlight driven degradation of Cr(VI) and methylene blue dye. The multi-component oxide nanoparticles with a composition Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2 and Gd0.2La0.2Y0.2Hf0.2Zr0.2O2 were synthesized by simple co-precipitation followed by peptization in acid to obtain nanoparticle sol and calcined at 500 °C. The nanopowders were characterized by x-ray diffraction (XRD), UV–Visible spectroscopy (UV–Vis), and high-resolution transmission electron microscopy (HRTEM). The complete (∼100%) reduction of Cr(VI) to Cr(III) was observed after 90 and 100 min for the calcined Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2 and Gd0.2La0.2Y0.2Hf0.2Zr0.2O2 respectively, under exposure to natural sunlight. In addition, 70% degradation of methylene blue is observed in 180 min. The effective photocatalytic activity of multi-component oxides can be attributed to their unique composition containing five components in equimolar amounts. The role of oxygen vacancies in photocatalytic reduction of Cr(VI) and the degradation of methylene blue is also discussed

Humidity-Independent Methane Gas Detection in Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2-based Sensor Using Polynomial Regression Analysis

Chemiresistive gas sensors (CGS) are continuously being developed over other methods for detecting gas/vapor concentrations because of their simplicity of fabrication, compatibility with conventional DC circuits and high accuracy measurement convenience. However, humidity strongly influences sensing response, while the trade-off between humidity independence and gas response is one of the major barriers to limiting CGS for practical applications. In this regard, highly selective methane (CH4) gas sensor is fabricated using Gd0.2La0.2Ce0.2Hf0.2Zr0.2O2 (Ce-HEC) as a sensing material and the relative humidity (RH) effect on sensing response has been investigated. Indeed, the RH effect on the sensor response is high and can be seen in all gas concentrations at various RH levels. Therefore, humidity compensation model (HCM) is developed by fitting multivariate polynomial regression techniques to reduce the anti-interference humidity effect. HCM estimates the gas concentrations with a mean absolute percentage error of 5.81%, and a mean absolute error is 3.43 ppm. This study offers a simple and novel strategy for humidity-independent detection of gas/vapors in CGS and estimates gas concentrations with minimum error. IEE

Enhancing the mechanical properties of high-entropy alloys through severe plastic deformation: A review

High-entropy alloys (HEAs) are one of the breakthroughs in the past decade in alloy development that have the potential to exhibit outstanding physical, mechanical, and chemical properties. This allows HEAs to be highly versatile materials for use in a variety of applications. Through reasonable composition design and post-manufacturing processes, HEAs can show superior properties compared to traditional alloys, which are highly demanded for novel emerging technologies. Severe plastic deformation (SPD) has been known as one of the most popular post-manufacturing processes for enhancing the mechanical properties of HEAs. However, there is still a lack of knowledge about the microstructure, physical, and mechanical properties of HEAs subjected to SPD processes. This review is concerned with the production of nano/ultrafine-grained HEAs using SPD techniques such as severe cold rolling (SCR), high-pressure torsion (HPT), and equal channel angular pressing (ECAP). Also, the characteristics of HEAs with respect to SPD are demonstrated, such as reduced grain growth and phase decomposition. These characteristics increase the possibility of producing nanostructured high-entropy alloys (NsHEAs) with multiple principal elements by SPD processes or by post-annealing and enable extremely high superplasticity at high strain rates. Finally, these findings introduce SPD as not only a processing tool to improve the physical and mechanical properties of HEAs, but also as a synthesis tool to fabricate novel HEAs with superior properties compared to conventional engineering materials, especially for high-tech applications