In this communication, we prepared composites of Cobalt (Co) and Chromium (Cr) substituted strontium ferrite (Sr(CoCr)xFe12-2xO19) with spinel ferrite (CoFe2O4) at a 4:1 weight ratio, varying the substitution levels from x = 0.0 to 1.0. The X-ray diffraction analysis confirmed the presence of both hard (M-type) and soft (spinel) ferrite phases in the substituted composites, without any impurity phase. Fourier infrared spectroscopy identified two distinct absorption bands at 584 cm-1 cm-1 and 542 cm-1, primarily associated with iron oxide, and a band at 409.6 cm-1 attributed to Co-O bonds. Field emission scanning electron microscopy (FESEM) revealed hexagonal platelet-shaped particles alongside randomly oriented small spherical-shaped grains. Substitution improves the performance of microwave absorbers, such as reflection loss increased from x = 0.0 (-10.54 dB) to x = 1.0 (-29.60 dB, more than 90% absorption);-10 dB bandwidth of 1 GHz was observed in the x = 1.0 sample at thickness 8.1 mm. Composite x = 0.8 displayed a bandwidth-to-thickness ratio and percentage bandwidth of 3.4E-04 and 8.9% with 8.5 mm at 9.157 GHz frequency. Composite x = 0.8 showed the optimal values for Zreal (1.091) and Zimg (-0.054), resulting in the highest reflection loss (-29.92 dB) at 9.15 GHz with 8.5 mm thickness.

In the current work, a sol-gel combustion technique has been adopted to synthesize Co-Cd substituted SrM hexaferrite. The X-ray patterns of incorporated samples showed the magnetoplumbite structure, accompanied by some secondary phases of CoFe2O4. The morphological studies of the z = 0.6, 0.8, and 1.0 revealed the densification of grains, which enhances the inter-particle contact. The energy dispersive spectra exhibited peaks of cadmium, cobalt, strontium, oxygen, and ferrite, signifying the formation of Co-Cd substituted SrM hexaferrite. Mössbauer spectra revealed that the substituent tends to occupy spin-down sites 4f1 and 4f2 of the crystal lattice from z = 0.2 to 0.6, elucidating a significant increase in saturation magnetization. A large value of coercivity 4273.50 Oe, 3612.63 Oe, and 4551.28 Oe was observed for z = 0.4, 0.6, and 1.0 samples, respectively, with a squareness ratio greater than 0.5, indicating the existence of single-domain particles. The high values of saturation and remanent magnetization with tunable coercivity and squareness ratio make the prepared sample suitable for recording applications.

Ferroelectric and antiferroelectric thin and thick films with strong electrocaloric (EC) responses are attractive for solid-state cooling. In this study, 0.75PbMg1/3Nb2/3O3-0.25PbTiO3 (PMN-25PT) relaxor ferroelectric thin films deposited on LSAT substrates by pulsed laser deposition exhibit a giant negative EC effect near 150 °C, with a maximum temperature change of -38.3 K and an entropy change of -29.4 J kg-1 K-1. A large positive EC effect is also observed near 120 °C, yielding ΔT = 33.4 K and ΔS = 27.5 J kg-1 K-1, comparable to the best reported values. The films show nanoscale columnar grains that promote polar nanoregions, leading to high polarization, large dielectric breakdown strength, and a diffuse, frequency-dependent dielectric response. Polarization-electric field loops measured from 30 °C to 190 °C reveal the excellent thermal stability of energy storage, which remains robust after 108 charge-discharge cycles. Moreover, the films demonstrate efficient harvesting of low-grade waste heat, achieving an energy conversion density of ∼18.7 J cm-3 per cycle over 0-2.5 MV cm-1 and a wide temperature range of 30-140 °C, as evaluated using pyroelectric Olsen cycles. These results highlight PMN-25PT thin films as promising candidates for advanced energy storage and electrocaloric cooling applications.

Present work reports comparative study on the structural, micro-structural, magnetic, optical, and electrical properties of Sr2Co2CrxFe12-xO22 (x = 0, 2, and 4) hexaferrites synthesized in the presence of citric acid and lemon juice using the modified citrate-gel auto-combustion technique. These properties were investigated using various instrumental techniques like FTIR, XRD, SEM, EDAX, UV-Vis, Raman spectroscopy, VSM, and low-and high frequency dielectric measurements. XRD analysis shows presence of the Y-type phase as major, with minor phases of M-type and spinel. With the substitution of Cr3+-content, the values of lattice constant a remained almost constant in all samples, but c decreased from 43.76 & Aring; to 43.58 & Aring;, and 43.66 & Aring; to 43.53 & Aring;, whereas unit cell volume (Vcell) also decreased in samples synthesized in the presence of citric acid and lemon juice (heated at 1000 degrees C for 5 h), respectively. Also as Cr-content increased from x = 0.0 to 2.0, the percentage of Y-phases increased, and the M-phase decreased in both samples synthesized in the presence of citric acid and lemon juice. An average crystallite size (Dxrd) is decreased in samples prepared using lemon juice. The surface morphology changes with Cr content, and small and large agglomerated grains are visible, a few samples show a hexagonal platelet structure. The range of the average grain size is found from 471 nm to 814 nm. EDAX analysis confirmed the presence of Cr-ions in all samples in accordance with their stoichiometric ratios. The band gap of the samples was reduced from 2.26 eV to 1.68 eV with Cr3+-substitution. In the Raman spectra, the shifting position of the Raman band was observed after Cr3+-substitution. Saturation magnetization (MS) was found to change from 31.52 to 52.10 emu/g. along with remanence magnetization (Mr): 12.06-27.89 emu/g, and coercivity (HC): 1005.6-1787.8 Oe. The Cr3+ substituted samples had Mr/MS ratios exceeding 0.5, suggesting a single-domain magnetic structure, as well as Mr/MS ratios smaller than 0.5, indicating the presence of a multi-domain structure. Dielectric measurement shows the typical behavior of ferromagnetic materials. A single semicircle arc is present in the pure sample in the Cole-Cole type plot (M-y vs M-y). The complex modulus and impedance plots demonstrate that all samples exhibit a non-Debye type relaxation behavior across the frequency range of 20 Hz to 2 MHz. The obtained high-frequency results of citric derived samples with a loss tangent of less than 0.08 from 5 to 20 GHz enunciate their good scope for antenna substrate application.

SrCoxZnxFe12-2xO19/PANI composites were developed, and an investigation of morphology, dielectric, electrical, and optical properties was performed. X-ray diffraction analysis was conducted to examine the prepared composite's phase and structure, revealing an M-type structure formation. Co and Zn doping lead to a drop in the crystallite size from 32.08 to 23.24 nm. The morphological investigation was conducted using scanning electron microscopy, which revealed the formation of grain clusters. Sample x = 0.0 has the maximum dielectric constant, epsilon' = 770.90, for 100 Hz. A non-monotonic effect had been perceived for the dielectric constant and loss tangent due to the doping. The electric modulus of the composites incurred a non-Debye-type relaxation. Increasing the doping levels of Co2+ and Zn2+ decreased the relaxation time. The electric/dielectric characteristics were affected by grains and grain boundaries, as indicated by Impedance spectroscopy. Tauc plots were used to determine the band gaps of the prepared composites, which range from 1.47 to 2.15 eV.

With the rapid expansion of wireless communication, radar systems, and high-frequency electronics, effective control of electromagnetic emissions has become increasingly important. Three-dimensional (3D) microwave absorbers have emerged as promising materials to mitigate this problem owing to their multiscale, hierarchical porous architectures. These structures enable improved impedance matching and enhanced attenuation compared with conventional planar or bulk absorbers. This review presents an integrated analysis of 3D carbon lattices, ferrite and ceramic micro-architectures, biomimetic porous scaffolds, core–shell heterostructures, and multilayer composites. For complex architectures, the clear understanding of how morphology, interface density, and phase crystallinity govern absorption efficiency remains limited. There are significant challenges associated with structural instability, scalability limitations, uncontrolled conductivity, etc. It causes impedance mismatch as well as difficulties in simultaneously optimizing multiple energy dissipation pathways.Recent advances include lightweight aerogels, nature-inspired structures, and metal/carbon-based heterostructures with enhanced attenuation capability. This review emphasizes how dielectric and magnetic loss mechanisms are affected by multiscale porosity, interfacial engineering, and phase composition influence. Notably, optimized materials have demonstrated reflection loss values below −50 dB and effective absorption bandwidths exceeding 5–10 GHz at thickness around 2–3 mm. This highlights the strong potential of these materials. This manuscript critically evaluates current performance limitations and outlines targeted optimization strategies. It is done to guide the rational development of next-generation, broadband, efficient, and morphologically adaptable three-dimensional microwave-absorbing materials. These advancements are particularly relevant for applications in aerospace, stealth technology, electromagnetic interference (EMI) shielding, and advanced electronic systems.

Microwave absorbers are used to mitigate the unwanted wireless/electromagnetic signals that interfere with the functioning of electrical/electronic devices. In this article, Co2+-Hf4+-doped M-type Ba-Sr hexagonal ferrite samples have been synthesized using a solid-state ceramic method. The phase structure and surface morphology were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The magnetic hysteresis was investigated with a vibrating sample magnetometer (VSM). A two-port vector network analyzer characterized the microwave absorption in terms of frequency, dopants, and geometrical thickness of the samples. XRD confirmed that the produced powders are of M-type hexaferrite structure without any additional phases. SEM revealed inhibition of grain growth with dopants and small grain size, as well as grain cluster formation. This morphological behavior caused a reduction in coercivity and enhanced microwave absorption. As a consequence, the dopants caused a better soft magnetic nature with a room temperature (r.t.) coercivity ( H-c ) varying between 788 Oe ( x=0.0 ) and 489 Oe ( x=1.0 ). The measured dielectric constant/dielectric loss and permeability/magnetic loss parameters were increased with dopants. The dopants caused an increase in the absorption from -20.67 dB at 6.5 mm in the undoped composition ( x=0.0 ) to -40.21 dB at 1.6 mm in the doped composition ( x=1.0 ). Additionally, a -10-dB absorption bandwidth of 3.13 GHz was exhibited in x=1.0 from the 8.47- to 11.60-GHz frequency band, while x=0.4 revealed a -10-dB absorption bandwidth of 1.92 GHz from 10.48 to 12.40 GHz. Microwave absorption has been substantiated by impedance matching/ lambda /4 mechanism, and absorption peaks have been tuned in the desired frequency spectrum by careful selection of thickness/dopants. Significant variations were seen associated with dopant-based tuning of absorption peaks in the frequency spectrum, an increase in microwave absorption, and a decrease in the thickness of the samples. The tunable performance metrics and economical synthesis imply the potential application of prepared compositions for microwave absorbers and passive device applications for wireless communication.

Lead free piezoelectric ceramics 0.94Na(0.5)Bi(0.5-x)Sc(x)TiO(3-0.06)BaTiO(3) (x = 0.0, and 0.05) doped with Scandium (Sc) were prepared by a standard solid state reaction. Structural properties of samples were studied using powdered XRD and Raman spectroscopy. The coexistence of rhombohedral and tetragonal phases in both ceramics is observed from the XRD. Dielectric measurements and analysis were performed from room temperature to 450 degrees C at various frequencies. The relaxor nature of the ceramics was observed with the diffusive phase transition at the dielectric maxima. The substitution of Scandium in NBT-6BT has increased the transition temperatures T-d and T-m.

M-type hexaferrites SrCoyNiyFe12−2yO19 (y = 0.2, 0.4, 0.6) developed using the sol–gel method. The phase purity was investigated using X-ray diffraction (XRD) analysis. The formation of needle-shaped grain structures was observed from scanning electron microscopy (SEM). The various magnetic parameters viz-a-viz saturation magnetization (Ms), coercivity (Hc), remanence (Mr), and anisotropy field (Ha) were determined using hysteresis loops. The coercivity Hc decreased from 3955 to 3007 Oe, while an increment in saturation magnetization M_s from 72.01 to 105.77 emu/g was observed. Reflection loss v/s frequency graphs were used to investigate the absorption characteristics of the prepared compositions. The doping of Ni2+ and Co2+ has enhanced the absorption characteristics. The composition y = 0.4 (SCNF 2) had the highest RL of − 34.49 dB at a small thickness of 3.5 mm with an input impedance (Zin) of 366.07 Ω (Zreal = 365.97 Ω, Zimg = − 8.65 Ω). The composition SCNF 3 had the highest bandwidth of 0.84 GHz among all the compositions. The broad bandwidth, low thickness, and high absorption make the developed samples very suitable in the field of defense and commercial applications as microwave absorbers.

M-type hexaferrites SrCoxZrxFe12-2xO19 had been prepared using the sol-gel method. Zr4+ and Co2+ substitution effects on structural, dielectric, and electrical properties had been performed. The frequency range opted for the analysis of the prepared ferrites was 100 Hz to 2 MHz. X-ray diffraction (XRD) analysis validated the development of the hexagonal phase at the same time obtained patterns indicated no presence of a secondary phase. The inclusion of Co2+ and Zr4+ caused a decrement in the crystallite size from 41.47 to 29.77 nm. To investigate the morphology of prepared ferrites scanning electron microscopy (SEM) had been conducted, which indicated the development of needle-shaped platelet structures. Non-monotonically varied dielectric constant and loss tangent were obtained by the inclusion of Co-Zr. The electric modulus showed a non-Debye-type relaxation for all the prepared compositions. The increase in doping of Co-Zr caused a reduction in relaxation time. The impedance spectroscopy illustrated the impact of grains as well as grain boundaries on the electrical properties. The simulated electrical parameters are in good agreement with the measured ones.

CaMoO4:Pr3+/Yb3+ phosphors were synthesized employing the solid-state reaction, whereas the temperature dependence of up-conversion (UC) luminescence properties under 980 nm excitation and the potential application as an optical temperature sensor were investigated. X-ray diffraction (XRD) analysis demonstrated the absence of secondary phase, confirming the formation of a single phase for the materials investigated and that codoped samples have the same structure as CaMoO4. Phosphors were excited at 980 nm demonstrating blue, green, red emissions correlated to transitions from Pr3+ ions. Moreover, optical temperature-sensing properties were analyzed employing the Fluorescence Intensity Ratio (FIR) technique, whereas relative (SR) and absolute (SA) sensitivities were calculated from Thermally Coupled Levels (TCL) and Non-Thermally Coupled Levels (NTCL) from Pr3+ ions. The highest sensitivity values were obtained for NTCL 600 nm/650 nm, with SA = 14.81 x 10(-3) K-1 and S-R = 1.93 % K-1 demonstrating that the CaMoO4:Pr3+/Yb3+ system could be employed as optical temperature sensors in the high-temperature region.

This study examines the synthesis, characterization, and assessment of the electromagnetic properties of BaCoxAlxFe12-2xO19 (0.0 <= x <= 1.0) nano-hexaferrites produced through the sol-gel auto-combustion technique. This approach was selected due to its capacity to generate uniform, nanoscale particles while maintaining controlled stoichiometry and phase purity. The synthesized hexaferrites were subjected to a thorough analysis of their structural, morphological, magnetic, and electromagnetic properties. This was accomplished through the application of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), vibrating sample magnetometry (VSM), and vector network analyzer (VNA) techniques. The analysis through XRD validated the emergence of a pure hexagonal M-type phase, noting a reduction in lattice parameters corresponding to an increase in Co-Al substitution. The FE-SEM images demonstrated notable variations in grain size and morphological changes due to doping, shifting from large fused grains to smaller, platelet-like structures. Magnetic investigations revealed a non-linear pattern in saturation magnetization (Ms), which first diminished as Fe3+ was replaced by Co2+ and Al3+, subsequently experiencing a minor rise attributed to decreased porosity and improved exchange interactions. The coercivity (Hc) exhibited a declining trend as Co-Al doping increased, which can be linked to the effects of grain size and a reduction in anisotropy. The study of electromagnetic properties emphasized the significance of permittivity (epsilon'), permeability (mu'), and impedance matching in relation to microwave absorption characteristics. The principle of impedance matching and the quarter-wavelength mechanism were essential in enhancing microwave absorption, achieving reflection loss (REL) values of -46.55 dB at 10.05 GHz for W5 (x = 1.0). The examination of eddy current losses, bandwidth-to-thickness ratio, and S-parameters provided additional evidence for the effectiveness of Co-Al-substituted BaM hexaferrites as proficient electromagnetic wave absorbers in radar and EMI shielding applications. This study demonstrates that BaCoxAlxFe12-2xO19 hexaferrites are highly adaptable materials with significant potential for use in microwave absorbers, stealth coatings, and EMI shielding systems. The capacity to adjust their structural, magnetic, and dielectric characteristics via deliberate substitution paves the way for innovative uses in advanced electromagnetic fields.

The dielectric properties of the Ba2TiSi2O8 (BTS) ceramic matrix added with strontium titanate (SrTiO3) at varying concentrations were investigated in this work using Impedance Spectroscopy (IS). The Rietveld refinement method was employed to analyze the presence of a secondary phase, (Ba0.3Sr0.7)TiO3, in the composites, while scanning electron microscopy (SEM) was used to examine the morphologies of the synthesized composites. According to the IS results, it was observed that the relative dielectric permittivity (epsilon(r)') of the composites increases with the addition of SrTiO3, a fact attributed to the formation of the new phase (Ba0.3Sr0.7)TiO3 (epsilon(r)' similar to 623). The Nyquist plot was utilized to study the dielectric behavior, and the grain and grain boundary effects in the ceramic samples were numerically modeled using an equivalent circuit (CPE). The activation energy (E-a) of the ceramic composites was determined to range from 1.76 to 1.92 eV. Additionally, the temperature coefficient of capacitance (TCC) values for the composites doped with 10 % and 15 % strontium titanate (SrTiO3, by mass) showed within the range of +/- 1500 ppm degrees C-1. The BTS-STO system, which has not been explored previously, overcomes the thermal instability of pure STO (typical TCC > +/- 2000 ppm/degrees C) and similar compounds such as (Ba,Sr)TiO3.

The rapid advancement of wireless communication technologies and electronic devices has led to a surge in electromagnetic (EM) pollution, posing risks to human health and the performance of sensitive electronic systems. Addressing this challenge, hexagonal ferrites have emerged as promising candidates for microwave absorption due to their exceptional magnetic properties, high Curie temperature, and efficient dielectric performance. This study focuses on the synthesis, structural characterization, and performance evaluation of BaCoxCdxFe12-2xO19/PANI composites with varying Co2+ and Cd2+ substitutions (x = 0.0 (YP1), 0.6 (YP2), and 1.0(YP3)). Using a sol-gel combustion method, the composites were characterized through X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), electrochemical impedance spectroscopy (EIS), and magnetic analysis to investigate their suitability for electromagnetic interference (EMI) shielding applications. The results demonstrate a systematic reduction in crystallite size, lattice parameters, and unit cell volume with increasing Co2+ and Cd2+ doping. Electrical impedance analysis reveals that the grain boundary resistance (Rgb) and capacitance (Cgb) are critical for enhancing dielectric properties and energy dissipation mechanisms. YP2 shows the lowest grain resistance (Rg = 0.005 M Omega) and the highest grain boundary capacitance (Cgb = 2.39 x 1010 mu F), which translates to superior impedance matching and energy dissipation. Magnetic characterization highlights the influence of doping on reducing coercivity and achieving moderate saturation magnetization. Electromagnetic performance analysis identifies YP2 (3.2 mm thickness) as the best-performing sample, achieving a maximum reflection loss (REL) of-55.54 dB at 10.56 GHz with a bandwidth-to-thickness ratio (BTR) of 2.91E-03 and percentage bandwidth (PBW) of 32.67 %. These findings demonstrate the potential of Co2+ and Cd2+ substituted hexaferrite composites as cost-effective, lightweight, and thermally stable materials for advanced EMI shielding applications.

Synthesis of M-type hexaferrites SrCoxZnxFe12−2xO19 has been performed using the sol-gel method. The phase purity was investigated using X-ray diffraction (XRD) analysis. The formation of needle-shaped grain structures was observed from scanning electron microscopy (SEM). Magnetic hysteresis analysis was carried out to determine the various magnetic parameters. Furthermore, the absorption characteristics were also investigated. The coercivity decreased from 6263 to 4027 Oe, however, the saturation magnetization increased (89.32 to 101.9 emu/g). Zn2+ and Co2+ doping has enhanced the absorption as composition SCZF 2 had the highest RL of -39.74 dB at 6.9 mm with a bandwidth of 1.26 GHz at a matching input impedance (Zin) of 370.72 Ω (Zreal=370.89 Ω and Zimg=4.70 Ω). The highest − 10 dB broad bandwidth of 1.52 GHz was obtained at 6.5 mm in composition SCZF 3. The observed lightweight, wideband characteristics of fabricated samples have good scope for absorber applications in defense and commercial applications.

Co-Zn co-doped M-type hexaferrites SrCoyZnyFe12−2yO19 have been developed employing the sol–gel method. X-ray diffraction (XRD) was carried out to analyze the phase purity, and scanning electron microscopy (SEM) was used to investigate the morphology of the developed ferrite. The magnetic characterization was performed by determining various magnetic parameters including saturation magnetization (Ms), coercivity (Hc), remanence (Mr), and anisotropy field (Ha). The microwave absorption performance was investigated by utilizing reflection loss (RL) versus frequency graphs. The impact of relaxation peaks in complex permittivity/permeability and eddy current loss on absorption performance has also been investigated. The crystallite size reduces with the increase in the doping level of Co-Zn and ranges between 38.77 nm and 26.42 nm. Morphology suggested good inter-grain connectivity with decreased particle size at a higher doping level. A decrease in coercivity (Hc) from 3026 Oe to 948 Oe was observed. On a similar note, saturation magnetization (Ms) decreased from 90.29 emu/g to 76.59 emu/g. Absorption characteristics were enhanced by doping with Zn2+ and Co2+. The highest RL of −41.72 dB at a thickness of 1.9 mm with an input impedance (Zin) of 379.55 Ω (Zreal = 379.50 Ω, Zimg = −5.68 Ω) was obtained for y = 1.0. It also possessed the highest bandwidth of 2.02 GHz among all the compositions. The developed ferrites can be the prime applicant as an absorber in the field of defense and commercial applications due to their broad bandwidth, low thickness, and high absorption.

This investigation employed the sol-gel technique to prepare Co2+-Cu2+ doped M-type barium-strontium hexagonal ferrite. X-ray diffraction (XRD), along with field emission scanning electron microscopy (FESEM), have been utilized to investigate the crystal structure and morphology of the grains, respectively. An impedance analyzer was utilized to evaluate electrical parameters at room temperature. The formation of an M-type hexagonal crystal *-structure was confirmed by the X-ray diffraction profile, along with minor traces of hematite. In SEM analysis, it was seen that as doping levels are increased, the small size of each grain becomes prominent in the grain clusters, giving rise to a prominent rice-grain shape. The dielectric loss tangent is increased, and the dielectric constant is decreased as doping levels rise. The interplay between grain boundaries and grains has a notable impact on relaxation characteristics across various doping concentrations, leading to the presence of both strong and partial relaxations in low and high-frequency domains. This behavior contributes to the development of either depressed or expanded semicircles influenced by the interactions at grain and grain boundary levels. Analysis of the Cole-Cole plots for electric modulus indicated significant conductivity relaxation. Different relaxation periods were observed in correlation with the conductivity relaxation, and spectra of the electric modulus confirmed the material’s non-Debye behavior.

Strontium hexaferrite (SrFe12O19) nanoparticles were prepared by the green sol-gel auto combustion method with mandarin orange peel extract acting as the reducing/chelating agent and combustion fuel. X-ray diffraction analysis confirmed the formation of an M-type magnetoplumbite phase consisting of randomly oriented hexagonal crystallite platelets 38 nm thick and 47 nm wide. The dielectric, conductivity, and impedance metrics were examined in the frequency range of 8 Hz to 5 MHz with temperature variation from 20 to 55 degrees C. The dielectric constant and loss decreased with frequency increment in conjunction with the Maxwell-Wagner model. An increase in temperature caused activation and accumulation of activated charge carriers at grain boundaries enhancing polarization and increasing dielectric parameters in the low-frequency region. Cole-Cole plots for electrical modulus revealed the role of both grain and grain boundaries behind the charge transport phenomenon. Increase in temperature activated the charge carriers and reduced the relaxation time. The variation of electrical parameters of grains/grain boundary aligned with simulated values derived from the equivalent circuit model. The Jonscher power law governed polaron hopping through the correlated barrier hopping model of the conduction. The Kohlrausch, Williams, and Watts function demonstrated non-Debye relaxation for peaks observed in the imaginary part of the electric modulus. Both the real and imaginary parts of complex impedance decreased with the rise in temperature due to thermal agitation of charge carriers and their release, while increasing SrFe12O19 conductivity. The grain and grain boundary resistances reduced from 6.52 MS2 to 3.80 MS2, 55.59 to 7.33 MS2, respectively, while the grain boundary capacitance increased from 74.14 to 130.45 pF in the temperature range 20-55 degrees C.

In this study, Co2+ and Ce3+ substituted BaCoxCexFe12-2xO19 hexaferrites, combined with polyaniline (PANI), were synthesized via the sol-gel combustion method to explore their structural, dielectric, magnetic, and microwave absorption properties. Substitution levels (x = 0.0 (XP1), 0.6 (XP2), and 1.0 (XP3)) were investigated, revealing significant modifications in structural and electromagnetic characteristics with increasing Co-Ce doping. Field Emission Scanning Electron Microscopy (FESEM) confirmed a transition from well-separated grains in XP1 to densely packed and fused grains in XP3. Dielectric analysis showed a frequency-dependent decrease in real part of permittivity and imaginary part of permittivity, aligning with Maxwell-Wagner polarization. XP1 exhibited the highest real part of permittivity (epsilon ') of 12,791.13 at low frequencies, while XP3 demonstrated reduced imaginary part of permittivity, attributed to enhanced grain boundary effects. Magnetic measurements revealed a reduction in saturation magnetization (Ms) from 45.92 emu/g in XP1 to 33.42 emu/g in XP3, reflecting the impact of Co2+ and Ce3+ doping on Fe3+ superexchange interactions. Impedance spectroscopy highlighted significant grain boundary effects, with XP3 exhibiting the highest grain boundary resistance, while XP1 showed superior conductivity. Microwave absorption analysis demonstrated effective reflection loss (REL), with XP3 achieving the highest REL of-33.29 dB at 11.48 GHz at 9.9 mm thickness, attributed to superior impedance matching (|Zin| = 364.37 Omega). XP1 displayed effective broadband absorption, with a maximum REL of-36.34 dB at 10.05 GHz and broader frequency coverage. These results establish Co-Ce substituted BaCoxCexFe12-2xO19/PANI composites as promising materials for electromagnetic interference (EMI) shielding and broadband microwave absorption applications.

Erbium-doped lanthanum niobate single-crystal fibers were successfully grown via the laser-heated pedestal growth technique for high-performance optical temperature-sensing applications. High-purity La2O3, Nb2O5, and Er2O3 precursors were ball-milled, calcined, and extruded into rods, followed by LHPG processing under a CO2 laser to produce crack-free, transparent SCFs with Er-3 (+) concentrations ranging from 2.5 to 10.0 mol%. Structural and optical characterization confirmed high crystallinity and transparency, with absorption bands attributed to Er-3 (+) electronic transitions. Upconversion luminescence under 980 nm excitation revealed green (531 and 551 nm), red (668 nm), and near-infrared (800 nm) emissions from Er-3 (+) transitions, with optimal UC intensity at 7.5 mol% Er-3 (+). Temperature-dependent UC studies (303-483 K) demonstrated thermally coupled levels (TCLs: H-2(11/2) and S-4(3/2)) and non-thermally coupled levels (NTCLs: I-4(9/2)/F-4(9/2) and I-4(9/2)/S-4(3/2)) for luminescence thermometry. The TCL-based sensitivity reached 3.59 x 10(-)(3) K--(1) (absolute) and 1.03 % K--(1) (relative), while NTCLs exhibited superior performance, with maximum relative sensitivity of 3.31 % K--(1) (I-4(9/2)/S-4(3/2)) and repeatability > 98 %. The enhanced sensitivity arises from pronounced thermal quenching of S-4(3/2) and F-4(9/2) emissions and thermally activated population of the I-4(9/2) state. These results highlight LaNbO4:Er-3 (+) SCFs as promising candidates for high-precision optical thermometry, combining robust synthesis, stability, and competitive sensitivity metrics compared to existing UC-based sensors.