Tetragonal Structure Research Articles

Synthesis, crystal structure of Ca6Sb2O11 from experiments and DFT-electron structure calculation

This article reports a new perovskite compound Ca6Sb2O11. The X-ray powder diffraction technique was used to analyze its crystal structure. The results show that Ca6Sb2O11 has a tetragonal structure with the I4/m space group, and the lattice parameters are a = b = 5.658 (1) Å, c = 7.984 (1) Å, α = β = γ = 90°. It exhibits a typical A4B'2B″2X12-x anoxic multi-perovskite structure with rock-salt ordering of the B-site cations. The compound's chemical composition and valence states were characterized through scanning electron microscopy-energy dispersion spectrum (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies was confirmed by electron paramagnetic resonance (EPR) spectroscopy. A chemical and structure transition temperature and the full melting temperature of Ca6Sb2O11 were measured, with values of 1515 ± 3 K and 1720 ± 3 K, respectively. The density functional theory (DFT)-electron structure calculation results show that Ca6Sb2O11 is an indirect wide-band gap (∼4.47 eV) semiconductor material, which agrees well with the experimental value (∼4.38 eV) obtained through diffuse reflection spectroscopy (DRS). Moreover, the top of the valence band and bottom of the conduction band are mainly contributed to by O-2p and Ca-3d states, respectively.

Photocatalytic water splitting over K6M10.8O30 (M = Ta, Nb) with a partially filled tetragonal tungsten bronze structure

Abstract K6M10.8O30 (M = Ta, Nb) with partially filled C sites in a tetragonal tungsten bronze structure represented as the general formula (A1)4(A2)2C4M10O30 shows photocatalytic activity for water splitting under UV light irradiation upon loading with suitable cocatalysts. An apparent quantum yield of the optimized NiO(0.2 wt%)-loaded K6Ta10.8O30 for water splitting is 13% at 248 nm.

Zinc and [Zinc, Nickel]: Co‑doped SnO2 nanoparticles as prospective electron transport layer materials for efficient lead free-MASnI3 perovskite solar cells

In this study, we explore the potential of both pristine and doped tin oxide (SnO2) as promising materials as the electron transport layer (ETL) for efficient lead free-methylammonium tin iodide (MASnI3) perovskite solar cells (PSCs). The pristine, Zinc (Zn) doped, and Nickel (Ni)-Zn co-doped SnO2 nanoparticles with a constant concentration of Zn while changing the concentration of Ni were synthesized by using the hydrothermal method. The effect of doping and co-doping on optical, structural, and electrical properties of SnO2 nanoparticles was investigated using different microscopic and spectroscopic tools. The X-ray diffractograms showed that pristine, doped, and co-doped SnO2 nanoparticles have better crystallinity and tetragonal rutile crystal structure. The fingerprint functional groups and elemental composition were confirmed by FTIR absorption peaks, EDX, and XPS, respectively. The UV–Vis DRS spectroscopy results revealed that the optical band gap reduced from 2.90 eV for pristine SnO2 to 2.26 eV for co-doped 1 wt (wt) % Ni-Zn-SnO2 nanoparticles and can be tuned with a variation of wt % of Ni. Further, the photoluminescence emissions of all SnO2 nanoparticles in the range of 307 to 494 nm are related to oxygen vacancies or defects. Moreover, BET results confirms larger surface area for 1 wt % Ni-Zn-SnO2, which can help in better electron-hole pair separation. The electrical conductivity studies confirm that the synthesized nanoparticles exhibit excellent ohmic contact behavior and show a notable increase in electrical conductivity for 1 wt% Ni-Zn-SnO2 nanoparticles. Further, the suitability of both pristine and doped SnO2 as ETL material for the MASnI3-based PSCs was simulated using SCAPS-1D software. The best power conversion efficiency of 29.60 % was achieved for FTO/1 wt % Ni-Zn-SnO2/MASnI3/Spiro-OMeTAD/Au. This investigation highlights the potential of co-doped materials as promising candidates for the development of efficient PSCs.

Bio-ultrasonic synthesis of tin oxide quantum dots: effect of bio-carbon and their UV photocatalytic activity

An ecofriendly synthesis is realized to elaborate tin oxide quantum dots (SnO2 -QDs) using the plant aqueous extract of Aloe Barbadensis Miller (Aloe Vera) and SnCl4.5H2O at room temperature as a biological solvent and a precursor respectively. The effect of Aloe Vera extract concentration on the properties of SnO2-QDs has been studied. Morphological and structural properties of the as synthesized nanoparticles have been characterized using field effect-scanning electron microscopy (FE-SEM) and x-ray diffraction (XRD). The chemical composition of the nanoparticles was studied by Raman, energy dispersive x-ray (EDX) and Fourier transformation infra-red (FTIR) spectroscopy. The optical properties were investigated by UV–Vis spectrophotometer. The x-ray diffraction analysis showed that all samples have a tetragonal rutile structure, with an estimated crystal size closed to the exciton Bohr radius, indicating a strong confinement of the carriers in the material. The crystallite size of SnO2-QDs nanoparticles decreases as Aloe Vera plant extract concentration increases. The formation of SnO2-QDs and the presence of graphitic carbon in samples were confirmed by Raman spectroscopy, EDX analysis and Fourier transformation infra-red (FTIR) spectroscopy. The blue shift in absorption is the most likely due to the quantum confinement effect. An Ostwald-repining growth model based on the concept of surface energy has been proposed to explain the kinetic growth of SnO2 QDs. The photocatalytic activities of the as-prepared powders were confirmed by the fast and efficient degradation of methylene blue (MB).

Transition metal ion doped Mg-Zn manganites for optoelectronic device applications

This work aimed at synthesizing Mg0.5Zn0.5Mn1.95(Fe/Co/Ni)0.05O4 nanoparticles using sol–gel auto-combustion method. Structural studies (XRD, Rietveld, Raman) confirmed the tetragonal spinel structure with I41/amd space group and average crystallite size ranged between 18–22.8 nm. The morphologies and compositions of these nanoparticles were studied using SEM and EDX. UV–Vis spectra demonstrated significant enhancement in the absorbance values. The estimated optical band gaps vary between 1.6 to 1.77 eV. Frequency-dependent dielectric and impedance spectroscopic studies (at room temperature) reveal exciting results. Thus, tailoring of dielectric properties and optical band gaps of these transition metals doped Mg-Zn manganite nanoparticles may find potential applications in optoelectronics devices.

First‐principles calculations on LaX3 (X: Sb, Sn) as electrode material for lithium‐ion batteries

AbstractUsing first‐principle calculations, we investigate the rare‐earth intermetallic compound LaX3 (X = Sb and Sn) as a cathode material for rechargeable lithium‐ion batteries (LIBs). The calculations have been performed to look into the stability of the structure and the electronic properties of host LaX3 as well as its lithiated phases, LixLa1−xX3 (0 < x ≤ 1). In this study, we have observed a structural phase transformation of these intermetallic compounds from a cubic to a tetragonal structure upon lithiation to host structure. The ground state energy is calculated using the WIEN2k package to determine the structure stability and volume change due to lithium addition, which is further used to calculate the formation energy, open circuit voltage (OCV), and lithium‐ion storage capacity. The equilibrium structural parameters for all the phases are determined by achieving a total energy convergence of 10−4 Ry. The estimated band structure along high‐symmetry lines in the first Brillouin zone and the total as well as partial density of states demonstrate unequivocally that the addition of lithium does not change the metallic nature of these electrode materials. We have also calculated the theoretical lithium‐ion storage capacity and OCV for all the compounds. Despite a higher value for OCV larger than 5 V, many of the investigated materials could not be found suitable from a synthesis point of view due to positive formation energies. The formation energy calculation shows that LaSb3, with a 50% concentration of Li, is the most stable compound out of those investigated here. The calculated OCV for Li0.5La0.5Sb3 is 4.27 V. This is substantially higher than the value obtained up to this point for LIBs, which ranges from 3.20 to 3.65 V/cell. These improved results related to the most stable alloy (Li0.5La0.5Sb3) investigated in this work indicate that it is necessary to check the experimental feasibility of its synthesis and actual device performance.

Influence of growth temperature on structural, optical, morphological and photoelectrochemical characteristics of vertically aligned hydrothermally synthesized TiO2 nanorods

Herein, vertically oriented TiO2 nanorods were prepared on FTO substrate using hydrothermal synthesis. The influence of growth temperature on structural, optical, morphological and photoelectrochemical characteristics were analyzed. The FESEM and AFM results validated the formation of TiO2 nanorods. XRD spectra revealed the formation TiO2 tetragonal crystal structure with the rutile phase. UV–vis data showed an increase in the visible light absorption and a narrowing of the energy band gap with increasing in reaction temperature. Based on PEC studies, all the samples showed good light response and pronounced photocurrent density under light conditions. The highest possible photocurrent density of 78.8 μA/cm2 at 1.2V vs Ag/AgCl was recorded from TiO2 film with hydrothermal growth temperature of 200°C for 3 h s. This performance is attributed to narrow bandgap (2.89eV) and longer lifetime of carriers (0.3s). This result was validated by data from EIS, whereby the fast separation and transfer of photogenerated charge carriers were demonstrated.

Impact of deposition temperature on persistent photoconductivity of SnO2 thin films deposited using spray pyrolysis technique suitable in optoelectronic synaptic devices

In this study, nanocrystalline tin oxide thin films that exhibited enhanced persistent photoconductivity (PPC) were prepared using spray pyrolysis technique. The effect of deposition temperature on different aspects of photoconductivity of these films were analysed using different characterization techniques. Raman analysis confirmed the tetragonal rutile structure of the films and also indicated their nanocrystalline nature, while XPS analysis verified the presence and oxidation states of tin and oxygen in the films. The films demonstrated UV sensing capability under above-bandgap illumination, generating electron-hole pairs and enhancing electrical conductivity. The deposition temperature of the film influenced their photocurrent characteristics, showcasing varied responses in terms of photosensitivity and photocurrent. Enhancement of photoresponse was observed with the increase in deposition temperatures of the samples. Notably, films deposited at 450 and 500 °C exhibited the more persistent photocurrent at the tested deposition temperatures. The surface defects, oxygen vacancies and grain boundaries played a significant role in sustaining PPC by ionizing vacancies and creating persistent carriers even after light exposure by trapping free carriers and impeding recombination. From the exponential fitting and extrapolation of the decay curves, the sample prepared at 450 °C was observed to be the most suitable film in application point of view for fabricating devices that make use of persistent photoconductivity. Overall, this work highlights the effectiveness of modulation of deposition temperature in influencing photoconductor parameters of spray pyrolyzed tin oxide films, offering potential applications in non-volatile memory, bionic optoelectronics, neuromorphic computing and bioelectronics.

Investigations of structural, photoluminescence, colorimetric, lifetime, and luminous efficiency of Tb3+ and Sm3+ co-doped calcium tungstate for WLEDs

Structure, photoluminescence, colorimetric, and thermoluminescence analysis of Ca1-x-yTb2x/3Sm2y/3WO4; x = 0.01; y = 0.01–0.05 ceramics are reported in this manuscript. The materials are made by the use of the solid-state method. Reitveld refinements of the obtained X-ray diffraction patterns are done by using the Fullprof Suite software. The obtained results denoted that the synthesized materials have a tetragonal structure and I41/a space group. Energy bandgaps are found in the UV–visible absorbance spectra. Photoluminescence investigations of the phosphors are done. The critical quenching concentrations of the phosphor are found to be x = 0.01; and y = 0.04. Moreover, the critical distance of energy shift with the adjacently presented ions is computed. Dexter’s theory is employed to elucidate that the dipole-dipole electronic interactions are the imperative reasons for the transfer of energy in the phosphor. The white color of emission is achieved for x = 0.01, y = 0.04 Tb, and Sm doped CaWO4 material. Moreover, great values in color purity, correlated color temperature, color rendering index as well as luminous efficiency of radiation are obtained from the CIE Chromaticity coordinates. Quantum yield efficiency of x = 0.01, y = 0.04 Tb & Sm codoped CaWO4 is measured. Photoluminescence decay analysis of all the samples is done to study the long-after glow properties and also the average lifetime values are evaluated. This is an indication of the suitable usage of the prepared materials in the white light-emitting diodes. Concentration as well as dose-dependent Thermoluminescence spectroscopy is investigated thoroughly. Kinetic parameters are calculated by deconvoluting the spectra of x = 0.01; y = 0.01 Tb & Sm codoped CaWO4 irradiated with 15 min of UV excitation dose. These results are denoted by high trap depth, second-order kinetics, and low UV dosimetry of the phosphor.

Origin of Temperature Coefficient of Resonance Frequency in Rutile Ti1−xZrxO2 Microwave Ceramics

In this study, we report the effect of Zr4+ doping on the optical energy gap and microwave dielectric properties of rutile TiO2. Rietveld analysis explicitly confirmed that Zr4+ occupies the octahedral site, forming a single-phase tetragonal structure below the solubility limit (x < 0.10). Notably, at x = 0.025, a significant enhancement in Q × fo was observed. This enhancement was attributed to the reduction in dielectric loss, associated with a decrease in oxygen vacancies and a lower concentration of Ti3+ paramagnetic centers. This conclusion was supported by Raman and electron paramagnetic resonance spectroscopy, respectively. The origin of high τf in rutile Ti1−xZrxO2 is explained on the basis of the octahedral distortion/tetragonality ratio, covalency, and bond strength.

Ferroelectric behavior arising from polar topologies in epitaxially strained SrTiO3-δ ultrathin films

In this work, we show that epitaxially strained SrTiO3-δ thin films, grown by ion-beam sputtering onto (001)Nb:SrTiO3 substrates, exhibit a ferroelectric behavior. At the atomic-scale, through high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, it was possible to identify the presence of polar nanoregions with non-trivial polar topological structures in the SrTiO3-δ film, which are induced through oxygen vacancies. To further confirm the presence of strained regions with a polar structure, Raman spectroscopy and high-resolution X-ray diffraction were employed and it was possible to confirm the presence of a tetragonal structure in the SrTiO3-δ film, with a tetragonality ratio (c/a) of 1.005. Scanning probe microscopy and macroscopic polarization-electric field hysteresis loops show ferroelectric behavior with maximum polarization of ∼1.5 μC/cm2, remnant polarization of ∼0.4 μC/cm2 and coercive field of ∼0.3 MV/cm. This work opens a window for exploring novel polar topological effects in sub-10 nm thin film materials for non-volatile memory application.

An investigation of glass, ITO, and quartz transparent substrates on Pd/SnO2 hydrogen sensor structure and sensitivity

Hydrogen energy has great potential as a fuel for the future, but its leakage poses a major threat. Thus, our main concern is to detect it very quickly. In this work, we investigate the effect of transparent glass, ITO, and quartz substrates on hydrogen gas sensing properties of magnetron sputter- deposited Pd-capped SnO2 (Pd/SnO2) thin film sensor material. The XRD study reveals that all Pd-capped SnO2 thin films deposited on different substrates has polycrystalline tetragonal structure. Sensors fabricated on quartz substrates exhibit homogeneous grain distributions at the interface, whereas sensors deposited on ITO and glass substrates have randomly size grains distribution at the interface. Sensors deposited on glass and ITO show lower sensitivity compare to sensors fabricated on quartz substrate at a working temperature of 250°C. The Pd/SnO2 sensor @ quartz shown a maximum response of ∼ 9.3 and better stability toward 500 ppm hydrogen gas, and a fast response/recovery time of 30/26 s for 5 ppm hydrogen gas. The sensor @ quartz substrate shows a small reduction in response and baseline at 60% RH. The sensor fabricated on quartz substrate exhibits better selectivity toward hydrogen gas and significant stability for long duration of three months in high humid conditions. The performance of the Pd/SnO2 thin sensor fabricated on quartz proves that the sensor based on average grains have a wide potential for real hydrogen gas monitoring.

Low temperature fabrication of Ba0.9Cs0.3Cr2.1Ti5.9O16 ceramic waste form for cesium immobilization using Bi2O3 as sintering aid

In this paper, we present a productive low-temperature fabrication of Cs-hollandite ceramics by adding Bi2O3 as a sintering aid to achieve high cesium retention. The effects of Bi2O3 addition on the phase composition, crystal structure and aqueous stability of the stoichiometric Ba0.9Cs0.3Cr2.1Ti5.9O16 ceramic waste form were investigated. It was found that adding Bi2O3 can effectively reduce the sintering temperature and promote densification of Cs-containing hollandite products. The Cs-hollandite ceramic with 2 wt% Bi2O3 sintered at 1000 °C showed a single phase with > 98 % cesium retention, which was ∼ 200 °C lower and ∼ 11 % retention rate higher than those of reported Cs-bearing hollandite. Moreover, the leached sample remained stable tetragonal structure, the LRCs was in the order of 10-3 g·m-2·d-1 after 28 days and the leaching indexes > 8, exhibiting good aqueous stability. This route can be considered as a promising solution to prevent cesium loss for incorporating the cesium waste in ceramic hosts.

Enhancing strength and ductility of extruded Ti-alloy-reinforced Al-Mg-Si composites: Roles of interface nanostructures and chemical bonding

A comprehensive understanding of interface nanostructures and chemical interactions is required for solving the strength-plasticity trade-off dilemma of Al/Ti composites. Continuously Ti-reinforced Al-matrix composites with superior strength and ductility are fabricated via a novel extrusion technique. The unique strain-hardening mechanism of the Al/Ti composite plates at low strains is attributed to the coupling effects of the strong interface constraint potency, the mechanical incompatibility between the soft Al and hard α-Ti, and a large elastic strain of hard α-Ti. Interlocking structures with atomic interdiffusion are observed at the Al/Ti interface. Mechanical and thermal effects induce lattice distortion and atomic superdiffusion, thus resulting in an interfacial intermixing zone with substantial dislocations and misfit strain. These characteristics produce a strong interface constraint effect during tensile, causing superior strain/dislocation hardening and uniform plasticity. Nanoclusters with cubic structures and dispersed dislocations are detected in the three-dimensional (3D) atomic intermixing zone at the Al/TiAl3 interface, accompanied by the aggregation of Mg. The nanostructures with numerous dislocations in the 3D Ti/TiAl3 transition zone feature lattices with partially tetragonal structures and ordered Ti-Al(Si) clusters. Ab initio calculations indicate that the strong chemical interaction between Si and Ti atoms not only improves the interface bonding strength, but also disturbs the lattices and broadens the transition zone. Moreover, the 3D interface transition zones, accompanied by dispersed dislocations, improve the interface constraint potency and hardening capability of the annealed Al/Ti composite plate. This work sheds light on the capability of the extrusion technique to produce fiber-reinforced Al-matrix composites with superior mechanical properties and provides new strategies for improving the chemical bonding strength and interface constraint effect via the interface invasion of specific elements.

Photocatalysis and antimicrobial activity of ZnO@TiO2 core-shell nanoparticles

Wet chemical synthesis was used in this instance to create ZnO@TiO2 core-shell nanoparticles. By examining X-ray diffraction and Selected Area Electron Diffraction patterns, it was determined that the phase formation of prepared nanoparticles was a hexagonal primitive structure of ZnO and Tetragonal bcc structure of anatase phase of TiO2 devoid of impurity peaks. It was discovered that crystallites were 25 nm in size on average. The results of a surface morphology analysis utilizing High-Resolution Scanning Electron Microscopy and High-Resolution Transmission Electron Microscopy show that all of the particles are spherical. The energy dispersive X-ray spectroscopy study provided proof for the existence of core-shell elemental compositions. Fourier-Transform Infrared spectrum revealed the presence of characteristics of metal bonding with oxygen of ZnO and TiO2. UV-visible absorption analysis exhibited absorption peak in the UV region and the band gap energy of ZnO@TiO2 core-shell nanoparticles. The thermal behavior of ZnO@TiO2 core-shell nanoparticles was analyzed by using Thermogravimetric Analysis, Differential scanning calorimetry, and Differential Thermal Analysis techniques. The X-ray photoelectron spectroscopy analysis exhibited the coating of TiO2 (shell) on the surface of ZnO (core) for the formation of a core-shell nanostructure. Due to its extremely small crystallite size, wide surface area, and reduced band gap, the ZnO@TiO2 core-shell sample demonstrated outstanding photocatalytic activity when rhodamine-B dye was photocatalytically degraded in the presence of UV light irradiation. Finally, the antibacterial and antifungal activities of ZnO@TiO2 core-shell nanoparticles were investigated, and it was shown that antifungal activity was superior to antibacterial activity. A suitable material for environmental and biological applications that produced core-shell nanoparticles displayed regulated grain size, outstanding photocatalytic performance, and high antifungal activity.

The quasi-binary phase diagrams of R 2Fe14B–Ce2Fe14B (R = Nd, Pr) systems

Abstract The phase relations of the R 2Fe14B–Ce2Fe14B (R = Nd, Pr) pseudobinary systems have been investigated by using X-ray powder diffraction, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and differential thermal analysis. The X-ray powder diffraction results show that continuous solid solutions were formed in this R 2Fe14B–Ce2Fe14B (R = Nd, Pr) pseudobinary systems, and all (R , Ce)2Fe14B solid solutions belong to the tetragonal structure with space group P42/mnm. With the increase in Ce content, the lattice parameters a, c, the peritectic reaction temperatures of the (R, Ce)2Fe14B (R = Nd, Pr) solid solutions decrease linearly, and the cell volume V varies in the form of the regression line. Based on the X-ray powder diffraction results and differential thermal analysis data, the quasi-binary phase diagrams of the R 2Fe14B–Ce2Fe14B (R = Nd, Pr) systems have been established.

Forecasting optical response in lieu of electronic properties of TlCaF3 via halogen substitution for UV filtration: a DFT perspective

ABSTRACT It is demonstrated that the substitution of Cl, B, and I at different concentrations in TlCaF3 significantly alters the phase, electronic band structure and optical, elastic, mechanical and anisotropic properties of the material. At 2.81% and 5.63% concentrations of all substituted elements, the cubic phase of TlCaF3 transforms into a pseudo-cubic tetragonal phase. With the addition of substitutional atoms, a systematic considerable narrowing of the bandgap is seen, and it can be either direct or indirect depending on the symmetrical positions. The bandgap shrinking can be addressed, in part, via the total/partial/elemental density of states (DOS) in line with structural variations. From the optical response, the refractive index rises with substitution atoms. According to the mechanical stability requirements for each substitution, the determined elastic constants for cubic and tetragonal structures match. Additionally, using elastic parameters, it is possible to estimate the unique mechanical features to evaluate the ductility and brittleness of pure and substituted compounds. Furthernore, Cl, Br and I-atoms’ substitution would make them a suitable choice for improved optimisation in ultraviolet filters (UVF) due to the existence of their absorption spectra in the ultra-violet region and the modification in structural, electrical, optical, elastic and mechanical properties.

Electrical properties and conduction mechanisms of Ba0.75Sr0.25Ti1-xZrxO3 ceramics synthesized by sol-gel route

A series of Ba0.75Sr0.25Ti1-xZrxO3 (x = 0, 0.01, 0.03, 0.05, and 0.1) ceramics were synthesized via a facile sol-gel route. The confirmation of a tetragonal structure was achieved through Rietveld refinement of the powder X-ray diffraction (XRD), and the finding was subsequently corroborated by Raman spectroscopy. The Scanning electron microscopy (SEM) confirmed the roughly cubical-shaped grains and average grain size is 0.31 μm for x = 0 and 0.70 μm for x = 0.05. The electrical properties such as dielectric constant, dielectric loss and ac/dc conductivity were investigated as a function of temperature and frequency. The Jonscher's universal power law (JPL) and Arrhenius equation have been used for the analysis of conductivity. The electrical conductivity variation at intermediate frequencies was explained using JPL. The Super-linear power law (SPL) explains the electrical response at higher frequencies. The temperature-dependent frequency exponents ‘s1’ and ‘s2’ were employed to predict the quantum mechanical tunneling (QMT), non-overlapping small polarons hopping (NSPT), and correlated barrier hopping (CBH) conduction mechanisms.

Production of High-Coercive nanostructured Nd-Fe-B alloy by chemical method

For the first time, a nanostructured alloy powder with high coercive force was obtained by a chemical method without the addition of Dy, which can compete with physical methods of production. The work carried out a study of the influence of stoichiometric composition on the magnetic properties of nanostructured Nd-Fe-B alloys. Alloys with different contents of Nd, Fe, and B were synthesized: Nd12Fe84B6, Nd14Fe80B6, Nd16Fe76B8, and Nd16Fe72B8. With a decrease in the iron content in the first two compositions, a decrease in the iron content in the soft magnetic phase α-Fe was observed, which led to an increase in the coercive force Hc and a decrease in the values of Ms and Mr. Experiments have shown that an increase in the content of Nd and B promotes the formation of the hard magnetic phase Nd2Fe14B and an increase in the coercive force. For example, the nanostructured Nd16Fe76B8 alloy demonstrated a maximum coercive force of Hc = 8439 Oe, while compensating for the values of Ms (109 emu*g−1) and Mr (78 emu*g−1). A comprehensive study of the nanostructured Nd16Fe76B8 alloy was carried out, including structural analysis. XRD using FullProff and Vesta software revealed the tetragonal crystal structure of the Nd2Fe14B phase, providing details of the atomic arrangement. The unit cell contains four layers with Nd and Fe atoms, and boron atoms are embedded in the center of the octahedron of Nd and Fe atoms, playing an important role in the magnetic exchange interaction. The results of Mössbauer spectroscopy confirmed the presence of the Nd2Fe14B phase and revealed details of the state of Fe atoms in the structure of six sextets.

The Butterfly Effect: Multifaceted Consequences of Sensitizer Concentration Change in Phase Transition-based Luminescent Thermometer of LiYO2:Er3+,Yb3.

In response to the ongoing quest for new, highly sensitive upconverting luminescent thermometers, this article introduces, for the first time, upconverting luminescent thermometers based on thermally induced structured phase transitions. As demonstrated, the transition from the low-temperature monoclinic to the high-temperature tetragonal structures of LiYO2:Yb3+,Er3+ induces multifaceted modification in the spectroscopic properties of the examined material, influencing the spectral positions of luminescence bands, energy gap values between thermally coupled energy levels, and the red-to-green emission intensities ratio. Moreover, as illustrated, both the color of the emitted light and the phase transition temperature (from 265 K, for LiYO2:Er3+, 1%Yb3+, to 180 K, for 10%Yb3+), and consequently, the thermometric parameters of the luminescent thermometer can be modulated by the concentration of Yb3+ sensitizer ions. Establishing a correlation between the phase transition temperature and the mismatch of ion radii between the host material and dopant ions allows for smooth adjustment of the thermometric performance of such a thermometer following specific application requirements. Three different thermometric approaches were investigated using thermally coupled levels (SR = 1.8%/K at 180 K for 1%Yb3+), green to red emission intensities ratio (SR = 1.5%/K at 305 K for 2%Yb3+), and single band ratiometric approach (SR = 2.5%/K at 240 K for 10%Yb3+). The thermally induced structural phase transition in LiYO2:Er3+,Yb3+ has enabled the development of multiple upconverting luminescent thermometers. This innovative approach opens avenues for advancing the field of luminescence thermometry, offering enhanced relative thermal sensitivity and adaptability for various applications.