Physics

This chapter provides an overview of the in vivo biomedical applications of aerogels and the prerequisite studies that were performed prior to conducting in vivo studies and those that were conducted in parallel. The goal of this chapter is to draw the reader's attention to the potential of aerogels as a biomedical material and recent advances in this endeavor. It is not the intent of the author to suggest that aerogels will replace other biomaterials, but rather that a new material is available to the industry and can be manipulated to fill the void other biomaterials have not been able to deliver. Important fundamental studies such as biocompatibility, sterilization, and cell-substrate interactions have been included and can provide the reader with a succinct summary of advances in this field. The majority of the studies referenced here were conducted on silica-based aerogels but can serve as a platform for further studies and expansion of the field to other types of aerogels. This chapter starts with a brief introduction to the design considerations given to materials intended for biomedical applications. A timeline of aerogel-based in vivo and in vitro studies published since 2011 has also been provided. The following sections provide a detailed account of ultrasound and X-ray imaging methods for in vivo tracking of aerogel implants. Next, methods to sterilize aerogels have been discussed followed by a detailed discussion of biocompatibility and biostability of aerogels both in vivo and in vitro. Finally, the potential of aerogels as a neuronal scaffold has been discussed, and response of such cells to the aerogel has been summarized.

Polyurea-crosslinked calcium alginate (X-Ca-Alg) aerogels were investigated under physiological relevant conditions and showed signs of degradation. Geometric and spectral measurements were made to quantify this degradation in vitro and ex vivo. The time dependence in vitro degradation of these aerogels was accelerated in the presence of shear force. Diagnostic ultrasound techniques have been shown to reliably identify X-Ca-Alg aerogels both in vitro and ex vivo as well as detect degradation of these aerogels in these different environments. Geometric measurements of aerogel implants taken from the US images closely match the measurements taken from optical imaging showing the reliability of US imaging and degradation tracking of implants in clinical settings. Acoustic attenuation was also calculated and was shown to indicate and identify aerogel degradation.

The complex and highly tortuous microstructure of aerogels has led to the superior insulating capabilities that aerogels are known for. This open cell microstructure has also created a unique acoustic fingerprint that can be manipulated to achieve maximum acoustic insulation/absorption. The goal of this work was to create a computational approach for predicting sound propagation behavior in monolithic aerogels using the wave solving tool k-wave. The model presented here explores attenuation and loss values as a function of density, angle of incidence of wave, and medium (aqueous and non-aqueous) for frequencies in the range of 0.5--1 MHz. High numerical accuracy without a significant computational demand was achieved. Results indicate that loss increases as a function of frequency and the medium that the incoming wave is travelling through dominates the attenuation, loss, and other characteristics more than angle of incidence, and pore structure.

Long-distance transportation of biological and pharmaceutical materials is currently accomplished with short-duration shipping options as most containers have a limited time that their interior may be held at a steady and low temperature. Aerogels are currently known as the best insulating material and have demonstrated superior thermal insulating capability compared to materials commonly used in shipping and storage industry such as extruded polystyrene and polyurethane foam. Aerogels are lightweight and biologically friendly, which makes this class of materials an excellent choice for biologistic packaging solutions. Previous experiment data and modeling have demonstrated the feasibility of using aerogel as a component material in a wide variety of low-temperature (77--273 K) applications. Modeling was used to further optimize the aerogel packaging in an effort to maximize the thermal insulation capability with respect to conventional packaging dimensions. Simulations of a full-scale aerogel-based packaging solution will be conducted for the transportation of vials under the realistic thermal loads a typical package would experience from packaging to delivery. The results obtained using a full-scale fluid thermal simulation for the aerogel packaging solution will be compared to results obtained using other conventional packaging materials to demonstrate the feasibility of aerogel implementation. Preliminary results show promise for the use of aerogel-based packaging solutions for cold-chain biologistics. With this preliminary research, future researchers may be able to investigate more aerogel-based packaging solutions.

Plasma assisted low-pressure chemical vapor deposition has previously been shown to allow for large area growth of a variety of 2D materials, such as graphene and boron nitride. However, it also presented with degradation of electronic properties owing to decreases in grain sizes and increased inclusion of defects. In this work, we report on the influence of an Ar plasma during the growth of MoS₂. We produce hexagonal and triangular single crystal 2D MoS₂ with sizes up to 10 µm, similar to that achieved without plasma present. Raman analysis also exhibits no significant changes with plasma. However, the plasma does induce changes to the morphology of the MoS₂ crystals, leading to non-uniform edge structures with the degree of non-uniformity scaling with plasma power. Comparing the overall morphology at different temperatures and amounts of precursor material suggests that plasma increases the availability of Mo for growth, which is further evidenced by increased growth zones. Therefore, the use of an Ar plasma may provide a means to reduce required precursor quantities without significantly compromising the overall structure of the resulting MoS₂ crystals.

Selenium is a key chemical element used in photovoltaics and energy storage. It has been classified as an energy-critical element by the American Physical Society and the Materials Research Society. As selenium is crucial to develop energetic applications, various techniques have been used to synthesize selenium nanostructures such as wet chemistry, vapor-phase growth, and pulsed laser ablation. Here, for the first time, the nanoneedle morphology is synthesized by a technique different from e-beam lithography. To achieve this, pulsed laser ablation of a bulk selenium target was performed in various organic solvents and irradiated by a nanosecond Nd: YAG laser in the kHz regime for 5 min. The repetition rate of the pulsed laser allows one to tune the aspect ratio, sharpness, and diameter of the nanoneedle. This morphology is suitable for solar cells and photocells in optoelectronics.

Single vesicle molecular profiling has the potential to transform cancer detection and monitoring by precisely probing cancer-associated extracellular vesicles (EVs) in the presence of normal EVs in body fluids, but it is challenging due to the small EV size, low abundance of antigens on individual vesicles, and a complex biological matrix. Here, we report a facile dual imaging single vesicle technology (DISVT) for surface protein profiling of individual EVs and quantification of target-specific EV subtypes based on direct molecular capture of EVs from diluted biofluids, dual EV-protein fluorescence-light scattering imaging, and fast image analysis using Bash scripts, Python, and ImageJ. Plasmonic gold nanoparticles (AuNPs) were used to label and detect targeted surface protein markers on individual EVs with dark-field light scattering imaging at the single particle level. Monte Carlo calculations estimated that the AuNPs could detect EVs down to 40 nm in diameter. Using the DISVT, we profiled surface protein markers of interest across individual EVs derived from several breast cancer cell lines, which reflected the parental cells. Studies with plasma EVs from healthy donors and breast cancer patients revealed that the DISVT, but not the traditional bulk enzyme-linked immunosorbent assay, detected human epidermal growth factor receptor 2 (HER2)-positive breast cancer at an early stage. The DISVT also precisely differentiated HER2-positive breast cancer from HER2-negative breast cancer. We additionally showed that the amount of tumor-associated EVs was tripled in locally advanced patients compared to that in early-stage patients. These studies suggest that single EV surface protein profiling with DISVT can provide a facile and high-sensitivity method for early cancer detection and quantitative monitoring.

Single-phase Gd₂O₃ nanostructures with different morphologies, such as nanoparticles, nanorods, nanospheres, and nanoplates, were synthesised. Gd2O3 1D nanorods and 2D nanoplate architectures were prepared via the hydrothermal method, while 3D hollow nanospheres were synthesised via homogeneous precipitation. The magnetic and magnetocaloric properties of Gd₂O₃ nanostructured particles were studied as functions of temperature and field. The material demonstrated typical paramagnetic behaviour in the measured temperature range of 3–300 K. The magnetic entropy change (−ΔS_M ) was determined from the magnetic isotherms measured in the 3–38 K temperature range in the field up to 5 T. The maximum change in magnetic entropy (ΔS_M^max) value 11.2 J kg⁻¹ K⁻¹ for the nanoplate, 9.4 J kg⁻¹ K⁻¹ for the nanorod, 9.2 J kg⁻¹ K⁻¹ for the nanosphere, and 10.7 J kg⁻¹ K⁻¹ for the nanoparticle sample was observed at temperature 5 K for the magnetic field of 5 T. Owing to large these Gd2O3 nanostructured particles would be considered promising materials for magnetic refrigeration at cryogenic temperatures.

The study reports the influence of rare-earth ion doping on the structural, magnetic, and magnetocaloric properties of ferrimagnetic Gd_3−xRE_xFe₅O₁₂ (RE = Y, Nd, Sm, and Dy, x = 0.0, 0.25, 0.50, and 0.75) garnet compound prepared via facile autocombustion method followed by annealing in air. X-Ray diffraction (XRD) data analysis confirmed the presence of a single-phase garnet. The compound’s lattice parameters and cell volume varied according to differences in ionic radii of the doped rare-earth ions. The RE³⁺ substitution changed the site-to-site bond lengths and bond angles, affecting the magnetic interaction between site ions. Magnetization measurements for all RE3+-doped samples demonstrated paramagnetic behavior at room temperature and soft-ferrimagnetic behavior at 5 K. The isothermal magnetic entropy changes (−ΔSM) were derived from the magnetic isotherm curves, M vs. T, in a field up to 3 T in the Gd_3−xRE_xFe₅O₁₂ sample. The maximum magnetic entropy change (−ΔS_M^max) increased with Dy³⁺ and Sm³⁺ substitution and decreased for Nd³⁺ and Y³⁺ substitution with x content. The Dy³⁺-doped Gd_2.25Dy_0.75Fe₅O₁₂ sample showed −ΔS_M^max   2.03 Jkg⁻¹K⁻¹, which is  7% higher than that of Gd₃Fe₅O₁₂ (1.91 J · kg⁻¹K⁻¹). A first-principal density function theory (DFT) technique was used to shed light on observed properties. The study shows that the magnetic moments of the doped rare-earths ions play a vital role in tuning the magnetocaloric properties of the garnet compound.

Dopant profiles near the semiconductor–oxide interface are critical for microelectronic device performance. As the incorporation of Si_1−xGe_x into transistors continues to increase, it is necessary to understand the behavior of dopants in Si_1−xGe_x. In this paper, the diffusion and electrical activation of phosphorus within a strained, single-crystal Si_0.7Ge_0.3 layer on Si during oxidation are reported. Both layers were uniformly doped, in situ, with an average phosphorus concentration of 4×10¹⁹ atoms/cm³. After high-temperature oxidation, secondary ion mass spectrometry measurements revealed that the bulk of the phosphorus diffuses out of only the SiGe layer and segregates at the oxidizing SiGe–SiO₂ interface. Hall effect measurements corroborate the observed phosphorus loss and show that the phosphorus diffusing to the oxidizing interface is electrically inactive. Through density functional theory (DFT) calculations, it is shown that phosphorus interstitials prefer sites near the SiGe–SiO² interface. Finally, based on a combination of experimental data and DFT calculations, we propose that the phosphorus atoms are displaced from their lattice sites by Ge interstitials that are generated during SiGe oxidation. The phosphorus atoms then migrate toward the SiGe–SiO₂ interface through a novel mechanism of hopping between Ge sites as P–Ge split interstitials. Once they reach the interface, they are electrically inactive, potentially in the form of interstitial clusters or as part of the reconstructed interface or oxide.

We present multiwavelength high-spatial resolution (∼0.″1, 70 pc) observations of UGC 4211 at z = 0.03474, a late-stage major galaxy merger at the closest nuclear separation yet found in near-IR imaging (0.″32, ∼230 pc projected separation). Using Hubble Space Telescope/Space Telescope Imaging Spectrograph, Very Large Telescope/MUSE+AO, Keck/OSIRIS+AO spectroscopy, and the Atacama Large Millimeter/submillimeter Array (ALMA) observations, we show that the spatial distribution, optical and near-infrared emission lines, and millimeter continuum emission are all consistent with both nuclei being powered by accreting supermassive black holes (SMBHs). Our data, combined with common black hole mass prescriptions, suggest that both SMBHs have similar masses, ∼ 8.1 (south) and ∼ 8.3 (north), respectively. The projected separation of 230 pc (∼6× the black hole sphere of influence) represents the closest-separation dual active galactic nuclei (AGN) studied to date with multiwavelength resolved spectroscopy and shows the potential of nuclear (<50 pc) continuum observations with ALMA to discover hidden growing SMBH pairs. While the exact occurrence rate of close-separation dual AGN is not yet known, it may be surprisingly high, given that UGC 4211 was found within a small, volume-limited sample of nearby hard X-ray detected AGN. Observations of dual SMBH binaries in the subkiloparsec regime at the final stages of dynamical friction provide important constraints for future gravitational wave observatories.

We present James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) integral field spectroscopy of the nearby luminous infrared galaxy NGC 7469. We take advantage of the high spatial/spectral resolution and wavelength coverage of JWST/NIRSpec to study the 3.3 μm neutral polycyclic aromatic hydrocarbon (PAH) grain emission on ∼200 pc scales. A clear change in the average grain properties between the star-forming ring and the central AGN is found. Regions in the vicinity of the AGN, with [Ne iii]/[Ne ii] > 0.25, tend to have larger grain sizes and lower aliphatic-to-aromatic (3.4/3.3) ratios, indicating that smaller grains are preferentially removed by photodestruction in the vicinity of the AGN. PAH emission at the nucleus is weak and shows a low 11.3/3.3 PAH ratio. We find an overall suppression of the total PAH emission relative to the ionized gas in the central 1 kpc region of the AGN in NGC 7469 compared to what has been observed with Spitzer on 3 kpc scales. However, the fractional 3.3 μm–to–total PAH power is enhanced in the starburst ring, possibly due to a variety of physical effects on subkiloparsec scales, including recurrent fluorescence of small grains or multiple photon absorption by large grains. Finally, the IFU data show that while the 3.3 μm PAH-derived star formation rate (SFR) in the ring is 27% higher than that inferred from the [Ne ii] and [Ne iii] emission lines, the integrated SFR derived from the 3.3 μm feature would be underestimated by a factor of 2 due to the deficit of PAHs around the AGN, as might occur if a composite system like NGC 7469 were to be observed at high redshift.

Despite the importance of active galactic nuclei (AGNs) in galaxy evolution, accurate AGN identification is often challenging, as common AGN diagnostics can be confused by contributions from star formation and other effects (e.g., Baldwin–Phillips–Terlevich diagrams). However, one promising avenue for identifying AGNs is “coronal emission lines” (“CLs”), which are highly ionized species of gas with ionization potentials ≥100 eV. These CLs may serve as excellent signatures for the strong ionizing continuum of AGNs. To determine if CLs are in fact strong AGN tracers, we assemble and analyze the largest catalog of optical CL galaxies using the Sloan Digital Sky Survey's Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) catalog. We detect CL emission in 71 MaNGA galaxies, out of the 10,010 unique galaxies from the final MaNGA catalog, with ≥5σ confidence. In our sample, we measure [Ne v]λ3347, λ3427, [Fe vii]λ3586, λ3760, λ6086, and [Fe x]λ6374 emission and crossmatch the CL galaxies with a catalog of AGNs that were confirmed with broad-line, X-ray, IR, and radio observations. We find that [Ne v] emission, compared to [Fe vii] and [Fe x] emission, is best at identifying high-luminosity AGNs. Moreover, we find that the CL galaxies with the least dust extinction yield the most iron CL detections. We posit that the bulk of the iron CLs are destroyed by dust grains in the galaxies with the highest [O iii] luminosities in our sample, and that AGNs in the galaxies with low [O iii] luminosities are possibly too weak to be detected using traditional techniques.

Tuning the electronic properties of transition metals using pyrophosphate (P₂O₇) ligand moieties can be a promising approach to improving the electrochemical performance of water electrolyzers and supercapacitors, although such a material's configuration is rarely exposed. Herein, we grow NiP2O7, CoP2O7, and FeP2O7 nanoparticles on conductive Ni-foam using a hydrothermal procedure. The results indicated that, among all the prepared samples, FeP2O7 exhibited outstanding oxygen evolution reaction and hydrogen evolution reaction with the least overpotential of 220 and 241 mV to draw a current density of 10 mA/cm2. Theoretical studies indicate that the optimal electronic coupling of the Fe site with pyrophosphate enhances the overall electronic properties of FeP2O7, thereby enhancing its electrochemical performance in water splitting. Further investigation of these materials found that NiP2O7 had the highest specific capacitance and remarkable cycle stability due to its high crystallinity as compared to FeP2O7, having a higher percentage composition of Ni on the Ni-foam, which allows more Ni to convert into its oxidation states and come back to its original oxidation state during supercapacitor testing. This work shows how to use pyrophosphate moieties to fabricate non-noble metal-based electrode materials to achieve good performance in electrocatalytic splitting water and supercapacitors.

Although Fe-based materials have undergone morphological changes to alter their electrochemical activity in energy conversion and storage, an optimal strategy to achieve their ideal performance has yet to be discovered. Herein, a novel planar nanoflower and nanotubes-like morphology were established by the phosphorylation and sulfurization of iron hydroxide to obtain iron phosphide (FeP) and iron sulfide (FeS). Due to the presence of P-coordination with Fe-atoms, FeP material possessed improved electrical conductivity, catalytic property, and significantly specific capacitance among all synthesized samples. The potentiodynamic study was conducted in a 1 M basic solution where 216 and 218 mV of overpotentials were required to drag a current density of 10 mA/cm2 for OER and HER. In addition, the high turnover frequency, electrochemical surface area, and greater roughness factor contribute to making FeP the best candidate for H2 production; hence, it was employed for electrolyzer testing, which showed a lower potential of 1.68 V. Furthermore, FeP demonstrated improved electrochemical storage ability in supercapacitor module forms. The FeP clearly illustrated an outstanding specific capacitance of 2100 mF/cm2 and delivered 98 % stability, which is highly significant as it is not yet achieved by others. This work allows morphological tuning to improve electrocatalysis and charge storage in transition metal-based materials.

Keywords: Fe-based nanoparticles, Tuned morphology, Electronic structure optimization, Water-splitting, Supercapacitor

This paper presents the tunable magnetic and magnetocaloric properties of Scandium-doped gadolinium iron garnets, Gd₃ Fe_5-xSc_xO₁₂ (x = 0.0 to 0.25) compounds prepared by a facile auto-combustion method. The sample analyzed has a dominant cubic crystal structure (space group: Ia 3¯ d)) with a small fraction of an orthorhombic secondary phase, as determined by Rietveld analysis of X-ray diffraction patterns. The structural, magnetic, Mössbauer spectroscopy and first-principles density functional theory (DFT) studies show a preferential substitution of Sc3+ at the octahedral site of Fe3+ions. The ferrimagnetic (FIM) transition is present in all samples, with the transition temperature decreasing from 560 K for ×  = 0.0 to 521 K for ×  = 0.25. The Sc3+dopedGd3Fe4.75Sc0.25O12exhibits an improved magnetocaloric effect (MCE) with a maximum magnetic entropy change (-ΔSMmax)3.82 J kg-1K−1, and a higher relative cooling power (RCP) value of 408 J kg−1, which is ∼ 7 % higher than the Gd3Fe5O12(380 J kg−1) sample. These findings suggest that by incorporating Sc3+, the magnetic and magnetocaloric properties of Gd3Fe5-xScxO12 can be tailored for potential applications in low-temperature magnetic refrigeration.

Keywords: Magnetocaloric effect, Magnetic entropy, Magnetic Refrigeration, Autocombustion, Gadolinium Iron Garnet, X-ray Diffraction, Mossbauer spectroscopy

Due to their redox-rich chemistry and distinctive electrical properties, Co-based electrocatalysts for H2 and O2 evolution reactions (HER and OER) have garnered attention; however, in addition to their limited activity, the chemical processes used to prepare them are time-consuming, costly, and potentially hazardous. Herein, we report a facile, rapid, and repeatable approach to preparing CoSx and CoP materials by using a nanoflower-like Co(OH)2 precursor, which was grown in the liquid phase over Ni-foam under microwave impact. Further, the sulfurization of Co(OH)2 nano-flowers produced rod-like CoSx structures. Whereas, phosphorization of Co(OH)2 resulted in mesoporous nanosheet-like CoP architecture, which substantially exposed surface sites and fastened the charge as well as mass transfer, benefitting its electrocatalytic activity, as CoP catalysts displayed a lower HER and OER overpotential of 184 mV and 260 mV to carry 10 mA/cm2 current density than CoSx sample (233 mV and 284 mV), respectively. Moreover, CoP material is possessed to have a high specific capacitance of 4.87 F/cm2. Our cost-effective and scalable synthesis strategy solves the issues related to fabricating inexpensive, efficient, and high-quality transition metal-based materials for energy applications.

Keywords: Microwave, Synthesis, Transition metal oxides, Phosphides, OER, HER, Energy

M-type hexaferrite substituted with cobalt and lanthanum [SrCo_1.5zLa_0.5zFe_{12 - 2z}O₁9 (SCLF; 0.0 < z < 0.5)] was synthesized by auto-combustion Sol--gel methodology. XRD study indicated that prepared specimens exhibit a hexagonal magnetoplumbite phase without any secondary peak. The crystallite size decreases from 48.94 to 28.82 nm as the level of substitution increases in SrM hexaferrite. The micrographs showed an enhancement in the inter-grain connectivity of grains with substitution. Mössbauer spectra revealed the variation observed in hyperfine interactions, isomer shift, quadrupole splitting, and relative area of five sextets of Fe3+ ions. Analysis of Mössbauer depicted that the substituents tend to occupy spin-up 12k-2a sites of crystal lattice from z=0.0 to z=0.3, which elucidated the diminution observed in magnetization. The coercivity gradually decreased from z=0.0 (5026.54 Oe) to z=0.5 (862.47 Oe). The saturation magnetization initially decreased with substitution from z=0.0 to 0.3 and then increased for z=0.4 and 0.5 samples. The magnetic susceptibility (dM/dH) of samples derived from magnetic parameters is high for z=0.0, 0.2, 0.3, and 0.4. Both Ms with tunable Hc and magnetic susceptibility results make them considerable materials for recording applications.

The major center of attraction in renewable energy technology is the designing of an efficient material for both electrocatalytic and supercapacitor (SC) applications. Herein, we report the simple hydrothermal method to synthesize cobalt-iron-based nanocomposites followed by sulfurization and phosphorization. The crystallinity of nanocomposites has been confirmed using X-ray diffraction, where crystalline nature improves from as-prepared to sulfurized to phosphorized. The as-synthesized CoFe-nanocomposite requires 263 mV overpotential for oxygen evolution reaction (OER) to reach a current density of 10 mA/cm2 whereas the phosphorized requires 240 mV to reach 10 mA/cm2. The hydrogen evolution reaction (HER) for CoFe-nanocomposite exhibits 208 mV overpotential at 10 mA/cm2. Moreover, the results improved after phosphorization showing 186 mV to reach 10 mA/cm2. The specific capacitance (Csp) of as-synthesized nanocomposite is 120 F/g at 1 A/g, along with a power density of 3752 W/kg and a maximum energy density of 4.3 Wh/kg. Furthermore, the phosphorized nanocomposite shows the best performance by exhibiting 252 F/g at 1 A/g and the highest power and energy density of 4.2 kW/kg and 10.1 Wh/kg. This shows that the results get improved more than twice. The 97% capacitance retention after 5000 cycles shows cyclic stability of phosphorized CoFe. Our research thus offers cost-effective and highly efficient material for energy production and storage applications.

Metal-organic frameworks (MOFs) have been the subject of intensive structural tuning via methods like pyrolysis for superior performance in electrocatalytic oxygen and hydrogen evolution processes (OER and HER) and supercapacitors. Here, a Co-MOF based on 2-methylimidazole was synthesized using a precipitation approach, and its electrochemical characteristics were tuned via pyrolysis at different temperatures, including 600, 700, and 800 °C. Characterization findings corroborated the formation of Co–N–C moieties from Co-MOF, and XPS analyses indicated that 700 °C was the optimal temperature for achieving a high density of Co–N–C moieties. The optimized Co-MOF-700 sample displayed remarkable HER and OER performance in terms of lower overpotentials of 75 mV and 370 mV as well as small Tafel slopes of 118 mV/dec and 79 mV/dec, respectively. Furthermore, at a current density of 1 A/g, the Co-MOF-700 sample had a specific capacitance of 210 F/g. The enhanced electrochemical properties of Co-MOF-700C as compared to other samples can be attributed to the availability of a high density of Co–N–C sites for catalytic reaction and its porous architecture. This study will expand the knowledge of how compositional and morphological changes in MOFs affect their utility in energy conversion and storage applications.

Keywords: Cobalt, MOF, Temperature effect, Water splitting, Supercapacitor

The detailed structural, magnetic, and cryogenic magneto-caloric properties of chromium-substituted gadolinium iron garnet (Gd₃Fe_5-xCr_xO₁₂) nanocrystalline powders were studied using the facile autocombustion method and a calcination temperature of 1100 °C. The X-ray diffraction pattern showed that all samples were single-phase with cubic Ia3d symmetry. The temperature and field-dependent magnetization data of Gd₃Fe_5-xCr_xO₁₂ samples revealed a ferrimagnetic ordering at low temperatures. Upon Cr³⁺ substitution, the Curie temperature reduced by 7% at x = 0.25 from 560 K for x = 0.00 sample. In a field up to 5 T, the maximum magnetic entropy change was observed as ΔS_M ∼ 3.8 J K⁻¹ kg⁻¹ for x = 0.00 and -ΔS_M ∼ 3.9 J K⁻¹ kg⁻¹ for x = 0.25 sample, while the maximum relative cooling power, RCP, value of 420 J kg⁻¹ was measured for x = 0.25 sample, which is 10% larger than the x = 0.00 (RCP ∼ 380 J kg^\E2\88\921). Therefore, Cr³⁺ substituted Gd₃Fe_5-xCr_xO₁₂ samples exhibit promising magneto-caloric performance and have potential low-temperature magnetic refrigeration applications.