Lattice Parameter Expansion Research Articles

Structural evolution of zirconium diboride under gamma irradiation and thermal annealing

Understanding the thermal properties and enhancing the performance of zirconium diboride (ZrB2) under extreme conditions is crucial, especially given its role as a burnable absorber in nuclear fuel pellets and its potential applications in accident-tolerant fuels. This study explores the structural alterations of ZrB2 crystals induced by gamma irradiation and subsequent thermal annealing. ZrB2 crystals were exposed to absorption doses of 300 kGy, 1000 kGy, 1500 kGy, and 3000 kGy using a 60Co gamma source, followed by thermal treatment at 1173 K under vacuum conditions. Also, Monte Carlo simulations were utilized to analyze the energy deposition and distribution of gamma quanta within the material during irradiation, highlighting Compton effects up to 0.23 MeV. X-ray diffraction analysis elucidated the impact of gamma radiation on ZrB2 crystal lattice parameters, space group, and volume expansion coefficient. Post-irradiation analysis revealed a maximum degree of amorphization and investigated mechanisms governing lattice parameter expansion. Thermal annealing at 1173 K significantly enhanced crystallinity, reducing amorphization to 0.2 % at an absorption dose of 3000 kGy and facilitating the restoration of the crystal's columnar structure. This comprehensive investigation provides insights into the intricate interplay between gamma irradiation, thermal processing, and resulting structural changes in ZrB2 nanocrystals, essential for applications in radiation-exposed environments.

Deciphering ore-forming fluid evolution processes of the Yuerya gold deposit, eastern Hebei, China: Insights from pyrite texture, trace element and sulfur isotope compositions

The Yuerya gold deposit, a representative gold deposit associated with Mesozoic granites in the eastern Hebei region, is located in the eastern Hebei-western Liaoning gold ore-concentrated area, the northern margin of the North China Plate. The orebody is mainly preserved in the Yanshanian granite and its contact zone with the carbonate rocks of the Gaoyuzhuang Formation, and the main ore mineral is pyrite. Based on the pyrite texture, geochemical characteristics of the in-situ trace element analysis, and sulfur isotope, the pyrite in the mining area is classified into five generations (Py1, Py2, Py3, Py4a, and Py4b). Five generations of pyrite all have an average Te/Se ratio > 1, and their average Co/Ni ratios are 1087.27, 43.97, 4.17, 12.62, and 4.99, respectively, indicating that the ore-forming fluid predominantly originates from magmatic-hydrothermal. In-situ sulfur isotopic analysis using LA–MC–ICP–MS shows that the δ34S values of the five generations of pyrites ranged from 0.3 ‰ to 9.6 ‰; the mean values are 3.8 ‰ (Py1, n = 4), 4.2 ‰ (Py2, n = 10), 2.6 ‰ (Py3, n = 18), 4.0 ‰ (Py4a, n = 20) and 4.6 ‰ (Py4b, n = 29), respectively. Approximately 32 % of the results exceed 5.0 ‰, surpassing the values indicative of a magmatic-hydrothermal source. Thermodynamic simulations reveal that the fluctuations in the oxidation state of the ore-forming fluid is not the predominant cause of δ34S enrichment in the pyrite. Our studies suggest that sulfur is primarily derived from mantle-crust mixtures, with some contributions from the wallrock of the Gaoyuzhuang Formation. The results from LA–ICP–MS trace element analysis of pyrites reveal a significant enrichment of As-Bi-Te-Tl alongside Au in the ore-forming fluid. Additionally, the results of ore-forming elements in three typical cross sections of different wallrocks in the mining area also show that Au, Ag, As, and Pb are closely related. Therefore, it is considered that the over-enrichment of As could be an important factor leading to the precipitation of Au. Pyrite undergoes expansion of the mineral lattice parameters or lattice dislocation due to the substitution of S with As, creating space for the growth of solid-solution Au. Subsequently, some of the solid-solution Au within pyrite is liberated through internal oscillations, forming the visible gold particles.

Synthesis and Structure of Barium Hexaferrite BaFe12–xInxO19 (x = 0–1)

This study presents the results of the synthesis and examination of indium-substituted barium hexaferrite samples with the formula BaFe12–xInxO19. The ferrites were obtained via a solid state synthesis method. The substitution level of indium, represented by x(In), was varied from 0 to 1 in 0.25 increments. The stoichiometric formulas of the compounds were calculated using the EDS data. The powder X-ray diffraction analysis indicated that all samples form a single crystalline phase with the M-type hexaferrite structure. Parameters of the crystal unit cell were calculated from powder diffraction data. An expansion of the crystal lattice parameters was observed as iron was substituted with indium, from x = 0 to x = 0.84. The Curie temperatures of the synthesized ferrites were determined using differential scanning calorimetry (DSC) method. It is established that the Curie temperature decreases from 452 to 292°C with In content growth from x = 0 to x = 0.84 in the BaFe12–xInxO19.

“Study of structural, optical, morphology and magnetic properties of samarium doped magnesium nanoferrites (MgSmxFe2-xO4) using sol-gel auto-combustion method”

The study presents a comprehensive report on Sm3+-doped magnesium ferrite (MgSmxFe2-xO4) and its properties across various x values (0.025, 0.075, 0.1, 0.125, and 0.150). The study utilized multiple characterization techniques, such as X-ray diffraction (XRD), Fourier transmission infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), UV–visible spectroscopy (UV–vis), Thermogravimetry Differential Thermal Analysis (TG-DTA), High-resolution transmission electron microscopy (HR-TEM), and scanning electron microscopy (SEM) to investigate the structural, magnetic, thermal, optical, and morphological properties of the material. The study determined various parameters, such as x-ray density, lattice constant, crystallite size, and radii on octahedral and tetrahedral sites. An increase in Sm3+ content resulted in an expansion of lattice parameters and a reduction in crystallite size, observed at 13.342 nm in single-phased samples. FT-IR spectroscopy confirmed Sm3+ ion substitution in octahedral sites, while transmission electron microscopy revealed spherical nanoparticles. The UV–vis spectroscopy observed an increase in Sm3+ leads to a corresponding rise in the energy band gap values transitioning from 2.0864, 2.1090, 2.1410, 2.1517, and 2.1850 eV of x = 0.025 to 0.150 respectively. Magnetic measurements indicated decreased magnetization with doping, attributed to particle size dependence. Overall, this study provides valuable insights into the magnetic properties and structural characteristics of Sm3+-doped magnesium ferrite nanomaterials, potentially advancing the development of advanced materials for diverse applications.

The Superconductivity in Bi-Doped BaFe2As2 Single Crystals.

We have successfully synthesized a series of Bi-doped BaFe2As2 high-quality single crystals for the first time. X-ray diffraction (XRD) patterns show an expansion of lattice parameter c with Bi doping, indicating a negative pressure effect. By investigating the resistivity, a Fermi liquid (FL) to non-Fermi liquid (NFL) crossover is observed from normal state to antiferromagnetic order state, accompanied by three superconducting transitions labeled as SC I, SC II and SC III, which are supposed to be induced by three superconducting realms with various Bi concentrations. Thus, we propose that the NFL behavior is closely related to the presence of superconductivity. The magnetic susceptibility measurements further speculate that the SC I and SC III phases should exhibit filamentary superconductivity while the SC II exhibits a possible bulk superconductivity of TC~7 K.

Assessing the impact of triaxial strain on carrier mobility and dielectric properties in cubic CsBCl3 (B = Pb, Sn, or Ge) perovskites: A first principles study

Investigating the strain and pressure dependence of perovskite materials can provide valuable insights into their structural and electronic responses, enabling the fine-tuning of their properties for various technological applications. This study investigates the influence of controlled lattice compression and expansion on the acoustic phonon-limited carrier mobility in CsBCl3 (B = Pb, Sn, Ge) perovskites, revealing tunable electronic bandgaps ranging from 0.3 to 1.2 eV by varying the B cation type and applied triaxial strain. The research demonstrates significant and monotonic carrier mobility modulation under pressure, with changes of up to 124% even at modest strain levels of −2%, along with linearly increasing exciton binding energy with lattice parameter expansion.

Effect of High Al Content AlGaN Buffer Layer on the Properties of GaN‐on‐Silicon Materials

The lattice parameter and thermal expansion coefficient mismatch between the silicon substrate and GaN lead to high tensile stress, which makes the GaN epitaxial layer prone to cracking. Effective compensation of tensile stress on GaN to prevent cracking is an important issue in GaN epitaxial growth. In this work, GaN‐on‐silicon materials with different AlGaN buffer layer structures are prepared by metal‐organic chemical vapor deposition (MOCVD). The GaN epitaxial material with a smooth and crack‐free surface is fabricated by inserting 7 AlGaN buffer layers. The crystal quality of GaN is characterized using high resolution X‐ray diffraction (HRXRD). The full‐width half maximum (FWHM) value of GaN(002) and GaN(102) crystal plane is 398 and 780 arcsec, respectively. The surface root mean square (RMS) roughness of GaN material is 0.31 nm, and the vertical breakdown voltage (BV) of the epitaxial wafer reaches 918 V. The results show that high Al content of the AlGaN buffer layer can effectively reduce the tensile stress and dislocation density of the GaN layer when the entire AlGaN layer thickness remains constant. Suppressing the generation of surface cracks and improving the crystal quality can improve the vertical breakdown voltage and two‐dimensional electron gas (2‐DEG) characteristics of GaN epitaxial wafers.

Impact of Nd Doping on Electronic, Optical, and Magnetic Properties of ZnO: A GGA + U Study

The electronic, optical, and magnetic properties of Nd-doped ZnO systems were calculated using the DFT/GGA + U method. According to the results, the Nd dopant causes lattice parameter expansion, negative formation energy, and bandgap narrowing, resulting in the formation of an N-type degenerate semiconductor. Overlapping of the generated impurity and Fermi levels results in a significant trap effect that prevents electron-hole recombination. The absorption spectrum demonstrates a redshift in the visible region, and the intensity increased, leading to enhanced photocatalytic performance. The Nd-doped ZnO system displays ferromagnetic, with FM coupling due to strong spd-f hybridization through magnetic exchange interaction between the Nd-4f state and O-2p, Zn-4s, and Zn-3p states. These findings imply that Nd-doped ZnO may be a promising material for DMS spintronic devices.

Design and Synthesis of Cubic K3-2 x Bax SbSe4 Solid Electrolytes for K-O2 Batteries.

Developing K-ion conducting solid-state electrolytes (SSEs) plays a critical role in the safe implementation of potassium batteries. In this work, a chalcogenide-based potassium ion SSE is reported, K3 SbSe4 , which adopts a trigonal structure at room temperature. Single-crystal structural analysis reveals a trigonal-to-cubic phase transition at the low temperature of 50 °C, which is the lowest among similar compounds and thus provides easy access to the cubic phase. The substitution of barium for potassium in K3 SbSe4 leads to the creation of potassium vacancies, expansion of lattice parameters, and a transformation from a trigonal phase to a cubic phase. As a result, the maximum conductivity of K3-2 x Bax SbSe4 reaches around 0.1 mS cm-1 at 40 °C for K2.2 Ba0.4 SbSe4 , which is over two orders of magnitude higher than that of undoped K3 SbSe4 . This novel SSE is successfully employed in a K-O2 battery operating at room temperature where a polymer-laminated K2.2 Ba0.4 SbSe4 pellet serves as a separator between the oxygen cathode and the potassium metal anode. Effective protection of the K metal anode against corrosion caused by O2 is demonstrated.

Subtle variation in lattice parameter and thermal expansion due to heating and cooling of a high-entropy fluorite oxide (Zr0.2Ce0.2Hf0.2Y0.2Al0.2)O2-δ between 1200 and 1500 °C in air

High-entropy fluorite oxides (HEFOs) must be evaluated under various test conditions to be used as advanced thermal barrier coating (TBC) materials. This study investigated the chemical valence, lattice parameters, and thermal expansion coefficient (TEC) of an HEFO (Zr0.2Ce0.2Hf0.2Y0.2Al0.2)O2-δ heated and cooled between 1200 °C and 1500 °C in air. Thermogravimetry-differential scanning calorimetry (TG-DSC) was used to probe the temperature ranges of the reduction and oxidation reactions, and X-ray photoelectron spectroscopy was used to determine the valence states of the chemical elements. In-situ high-temperature X-ray diffraction was used for examining the crystal phase and calculating the TECs. The results show that chemical valences related to Zr, Hf, Y, and Al oxidation states were maintained during the entire thermal cycle, whereas these for Ce underwent partial valence transitions. In other words, Ce4+ was partially reduced to Ce3+ when heated from (1200–1300) °C, and Ce3+ was partially re-oxidized to Ce4+ as the temperature increased from 1400 °C to 1500 °C. Such chemical reactions correlate well with the TG-DSC results. The TEC values ranged from (9.58–9.28) × 10−6 K−1 and exhibited a weak, nonlinear dependency on temperature, decreasing with an increase in temperature, except when heated from 1200 °C to 1240 °C. The reduction and oxidation reactions had a minor effect on the TEC and the differences due to heating and cooling were appreciable yet subtle when compared to that at the same temperature, with the maximum difference being less than 0.2 × 10−6 K−1.

Mobile oxygen in layered nickelates of perovskite-type

The influence of the different types of oxygen on the structure and electrical conductivity of the perovskite-type nickelates were investigated. The nickelates La2NiO4+δ, La0,6Sr1,4NiO4–δ, Sr3Al0,75Ni1,25O7–δ were synthesised using the solidstate reaction route. Phase composition was determined by X-ray powder diffraction analysis. The iodometric titration technique was used to specify the oxygen content of the powders. Oxygen desorption and absorption, including oxygen index variation, were investigated by oxygen solid electrolyte coulometry (OSEC). Electroconductive properties of samples were studied by a standard DC four-point method. Utilizing OSEC technique, three mobile and one regular type of oxygen were observed in the perovskite layered nickelates with P/RS and 2P/RS structure. These four types of mobile oxygen differ in the binding energy to the crystal lattice and crystallographic positions. The desorption-sorption processes of various types of mobile oxygen have different effects on the thermal expansion of crystal lattice parameters. The regular oxygen, occupying the apex of octahedron, affects the lattice parameters most prominently. This type of oxygen changes the character of the temperature dependence of specific resistivity sufficiently. Interstitial oxygen does not yield such anomalies.

Ligand field luminescence in the honeycomb Mott insulator α-RuCl3

Novel electronic structure is central to Kitaev-like quantum spin liquid ground state in the van der Waals antiferromagnet α-RuCl3. In this octahedral low-spin system, the rich bandstructure includes Mott–Hubbard insulating bandgap of ∼1.1 eV and ligand field induced gap of ∼2 eV. Though the bandgap is extensively reported in previous optical and photoemission studies, the latter gap is less understood. In this regard, we probed the ligand field-induced electronic structure of bulk α-RuCl3 single crystals via unpolarized photoluminescence (PL) spectroscopy under linearly polarized excitation in the visible region. We observed the broad principal PL peak at E PL 1.87 eV, close to the energy required for the optical transition across the ligand field splitting gap (∼2 eV). This gap (E PL) monotonically increases with temperature, described by the thermal expansion of lattice parameters dominating the electron–phonon interaction in this Honeycomb Mott insulator. Moreover, we observed the multiplet structure of the PL spectra, which can be explained by parity-forbidden d–d transitions in the light of single ion ligand-field theory. We attribute the broad PL linewidths to strong vibronic coupling modeled by the Huang–Rhys parameter. Further we observed the signature of structural transitions, indicated by thermal hysteresis in normalized integrated PL intensity.

Structural Size Effect in Capped Metallic Nanoparticles

The surfactant used during a colloidal synthesis is known to control the size and shape of metallic nanoparticles. However, its influence on the nanoparticle (NP) structure is still not well understood. In this study, we show that the surfactant can significantly modify the lattice parameter of a crystalline particle. First, our electron diffraction measurements reveals that NiPt nanoparticles around 4 nm in diameter covered by a mixture of oleylamine and oleic acid (50:50) display a lattice parameter expansion around 2% when compared to the same particles without surfactant. Using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDX) techniques, we show that this expansion can not be explained by crystal defects, twinning, oxidation, or atoms insertion. Then, using covered NPs in the 4-22 nm size range, we show that the lattice parameter evolves linearly with the inverse of the NP size, as it is expected when a surface stress is present. Finally, the study is extended to pure nickel and pure platinum NPs, with different sizes, coated by different surfactants (oleylamine, trioctylphosphine, polyvinylpyrrolidone). The surfactants induce lattice parameter variations, whose magnitude could be related to the charge transfer between the surfactant and the particle surface.

Anion/cation substitution in lead-free double-perovskite films: for band-gap optimization

During the past few years, halide double perovskites have been extensively explored for designing eco-friendly and stable perovskite-family absorber materials. In this work, thin films of Cs2AgBiBr6 double perovskites were successfully fabricated with the aim of obtaining a lead-free system. Optical studies confirmed the large band gap of 2.33 eV of Cs2AgBiBr6 films. Post-synthetic vapor treatment of Cs2AgBiBr6 thin films, with tin (IV) iodide (SnI4; SI), was performed to engineer their optical response. Structural and optical studies confirmed the phase purity of the various SI-treated films. X-ray diffraction studies further showed a systematic shift toward lower 2θ values, which signified the expansion of lattice parameters on SI substitution in the Cs2AgBiBr6 structure. The as-prepared pristine and SI-treated films showed good coverage with a reasonably large grain size. Furthermore, the optical studies revealed a 0.47 eV reduction in the band gap of SI-treated films, as opposed to a small band-gap change of approximately 0.22 eV when the pristine Cs2AgBiBr6 film was treated with cesium iodide (CsI). This showed the role of the combined effects of charge-balancing defects and compositional substitution in band-gap lowering in Cs2AgBiBr6. The controlled doping in lead-free double perovskites for improved optical properties might help in strengthening their use for future optoelectronic applications.

Combining experimental and modelling approaches to understand the expansion of lattice parameter of epitaxial SrTi1-xTaxO3 (x = 0–0.1) films

Cubic SrTiO3 is widely used as a model perovskite oxide due to its exotic optical, electronic, magnetic, superconducting, and ferroelectric properties, which are dominantly influenced by its lattice parameter. This paper reports on the experimental observation of Ta5+ dopant-induced expansion of the perpendicular lattice parameter (a⊥) of (001) heteroepitaxial SrTixTa1-xO3 (x = 0–0.1) films grown at substrate temperature (Tg) of 750 °C under 5 × 10-5 mbar oxygen partial pressure (pO2). The experimental results demonstrate the synthesis of very high-quality epitaxial thin films in which almost all the Ta5+ dopants are substituted. However, not all the carriers are activated due to compensating defects. All these films have smooth surfaces and are stoichiometric in compositions. The value of a⊥ increases linearly with increasing Ta or free carrier concentrations. This expansion is modelled via density functional theory (DFT). The influences of three effects are considered in the present modelling: (i) ionic radius of Ta dopant (ii) deformation potential due to hydrostatic strain energy (iii) concentration of free carrier. Further calculations of a⊥ are also performed by considering the influence of substrate and the results overestimate the experimental values by ∼ 1 %. Further experiments on other perovskite systems are required to establish the efficacy of these modelling approaches.

Interrelation of micro-strain, energy band gap and PL intensity in Ce doped ZnS quantum structures

Three-dimensional (3-D) quantum structures (QSs) of ZnS and Cerium (Ce) doped ZnS were synthesized via chemically affordable sol-gel process. Influence of Ce doping and thus induced micro-strain on the structural, morphological, and optical characteristics was explored. XRD confirmed the formation of single-phase zinc blende ZnS. Estimated average crystal size corresponding to highest intensity XRD peak (111) varied within 1.65–4.65 nm which are comparable with Bohr radius of ZnS. Due to the size mismatch between Ce and Zn, micro-strain and vacancies were found to be developed in host matrix of ZnS. Thermodynamic calculations validated an expansion and contraction in lattice parameter due to Ce doping. FTIR spectra confirmed the presence of different functional groups related to Zn and S. Photoluminescence (PL) emissions observed at 420, 461, 509 and 560 nm are related to the defect states such as interstitial sulfur, zinc interstitial, sulfur vacancies and zinc vacancies respectively. Rise of another emission peak in doped ZnS at 600 nm was due to 5d → 4f energy level transitions in Ce3+ ions. Evolved micro-strain profile, PL intensity and energy band gap variation were analogous to each other with respect to doping concentration. Microscopic images confirmed the structural transformation to cuboidal shaped ZnS QSs with increase in doping concentration. EDX and XPS supported the elemental analysis along with oxidation states of the available elements such as Zn, S and Ce.

Defect mediated structural, optical, electrical and mechanical properties of mechano-synthesized PbTe nanostructure as a superior thermoelectric material: Correlation among electrical, mechanical and optical properties

This work reports on the formation of anti-site defects in mechanically alloyed PbTe samples and their anomalous effects on the optical and electrical properties of the sample. PbTe nanoparticles have been synthesised by mechanical alloying of the elemental Pb and Te powders mixed in stoichiometric ratio under an inert (Ar) atmosphere for different time durations. The structural and microstructural characterisations have been carried out by analysing X-ray diffraction (XRD) patterns, field-emission scanning electron microscope (FESEM), and high-resolution transmission electron microscope (HRTEM) images. The elemental composition has been revealed from the energy-dispersive X-Ray (EDX) spectrum. The phase pure cubic PbTe is formed within just 30 min of milling. The Rietveld analysis of XRD patterns, FESEM, and HRTEM images revealed the crystallite size reduction and the increase in r.m.s. lattice strain with the increase in milling durations. Inclusions of more and more anti-site defects of type [PbTe] with increasing milling time are reflected in the expansion of the cubic lattice parameter with milling durations. Fourier-transform infrared (FTIR) spectrum reveals that PbTe is a narrow bandgap semiconductor, and the bandgap shows a redshift with increased milling time and reduced crystallite size. This anomalous behaviour of the optical bandgap with reduced particle size is well explained by Urbach tailing due to increased defects in the more extended milled sample. The positions of the conduction and valence bands in the milled PbTe samples are determined for different milling times. The DC conductivity study also shows anomalous behaviour; electrical conductivity increases with particle size reduction in more extended milling time samples. It is resolved by considering that the carrier concentration increases with a longer milling time due to induced anti-site defects while milling. It results in bandgap reduction with milling durations and shows the predominant effect of electronic conductivity over ionic conductivity. The conduction mechanism is explained as per the Pertritz model, and the dependence of activation energies on particle size and temperature has been explained in detail. The Vickers hardness of the milled samples is determined, and its variation with grain size is explained with the Hall-Petch relation. The improved electrical conductivity with increased milling is also manifested in the measured hardness values.

Shedding Synchrotron Light on Catalyst Strain Dynamics in Electrochemical Environment

In the case of heterogeneous catalysis (where the reactions occur onto the catalyst surface), the most promising approach in material design follows the Sabatier principle: the ability of the surface to bind adsorbates and the strength of the bonds define the reaction thermodynamics and kinetics. In this respect, the catalyst surface chemistry and structure (crystallographic orientation of the facets and/or strain) are used as levers to optimize its performance. However, it is largely accepted that the structure of PEMWE anode and PEMFC cathode catalysts does not remain unaltered over the long term operation due to harsh (electro)chemical conditions and it is of a high interest to understand the structural changes during the electrocatalysis. In this contribution we use X-ray diffraction techniques to qualitatively and quantitatively describe those changes and shed light on the strain evolution in nanostructured catalysts during operation in the electrochemical environment.Using the newly upgraded 4th generation EBS source at European Synchrotron Radiation Facility, we study Pt and Pd catalysts in liquid half cells at various potentials. In the Pd case we focus on the phase and structural dynamics during H insertion, allowing to unveil the electrochemically-driven Pd hydrides phase transition, which was until now mostly investigated in the gas phase. The fine XRD patterns measured operando provided the first detection of theoretically predicted supersaturated and undersaturated metastable states, involved in a core-shell mechanism of the phase transition (Figure 1) [1].In the case of Pt nanocatalyst, monitoring the structural features of the catalyst during cyclic voltammetry permits studying adsorption and oxidation processes. Deconvoluting both effects (adsorption and oxidation) is possible by following different parameters of the analyzed XRD patterns with high temporal resolution. Such experiments reveal important dynamic trends linked to the surface oxidation and degradation, directly impacting the output of accelerated stress tests (AST) [2]. Carefully determining the charge passed through the circuit during the CV also allows to establish a near-linear correlation between the expansion of the bulk lattice parameter of Pt nanoparticles and their oxide surface coverage. Since the latter is known to be a descriptor of catalysts activity toward numerous reactions (oxygen reduction and fuel oxidation), the measurement of the lattice parameter according to this simple diffraction approach allows experimental access to this descriptor during operando measurements in device-relevant sample environments [2]. This constitutes a main advantage compared to spectroscopic techniques and is foreseen to find a wide range of applications, as demonstrated by measuring the structural behavior of the state-of-the-art PtNiIr octahedra catalyst in operating PEMFC. In this case, the results allow correlating the degradation of the catalysts cycled to different lower potentials with the oxidation and strain dynamics. Based on this data, the operating conditions for this catalyst can be determined, further defining the application of this material.[1] Chattot, R. et al., J. Am. Chem. Soc. 143(41), 17068–17078 (2021).[2] Martens, I. et al., ACS Appl. Energy Mater. 2 (11), 7772-7780 (2019). Figure 1

Local structural evolution in the anionic solid solution ZnSexS1−x

The century-old Vegard`s law has been remarkably accurate in describing the evolution of the lattice parameters of almost all solid solutions. Contractions or expansions of lattice parameters of such systems depend on the size of the guest atom being smaller or larger than the host atom it replaces to form the solid solution. This has given rise to the concept of ``chemical pressure'' in analogy to the physical pressure. We have investigated using EXAFS the evolution of the local structure in terms of atom-pair distances extending up to the third-nearest neighbors in the family of compounds, $\mathrm{Zn}{\mathrm{Se}}_{x}{\mathrm{S}}_{1\ensuremath{-}x}$ as an example of an anionic solid solution, in contrast to all previous studies focusing on cationic solid solutions. Our results establish several common features between these two types of solid solutions, while strongly suggesting that the concept of a chemical pressure is inaccurate and misleading. Most interestingly, we also find a qualitative difference between the cationic solid solutions, reported earlier, and the anionic solid solution.

Structural and optical properties along with magnetization reversal and bipolar switching in CeCr1−xFexO3 (x = 0 and 0.05) nanoparticles

Nano-crystalline, CeCr1−xFexO3 (x = 0 and 0.05) compounds synthesized by a facile nitrate-solution combustion method are crystallized in orthorhombic, Pnma structure. Reitveld refinement of diffraction patterns reveal an expansion of lattice parameter and lattice volume after the substitution of Fe. Structural analysis evidences an increase in distortion in orthorhombic structure due to bending of Cr-O6 octahedra which is a sheer consequence of the lattice expansion. The optical band gap decreases from 2.9 to 2.6 eV due to the increase in particle size and decrease in strain after Fe substitution estimated from Williamson-Hall analysis. Besides the decrease in Neel temperature from 260 to 253 K after Fe incorporation, temperature-dependent magnetization exhibits some peculiar features such as compensation temperature, Tcomp, and spin reorientation temperature, TSR. While TSR enhances from 15 to 30 K, we observe two Tcomp at 13 and 110 K for x = 0.05 in contrast to only one Tcomp at 61 K for the pristine phase. Moreover, we for the first time demonstrate a stable switching behavior of magnetization by varying the external field in the same direction. The increase in Tcomp and TSR along with a decrease in band gap from 2.9 eV to 2.6 eV makes this material suitable for bipolar magnetic switching and photocatalytic applications.