Expansion Of Unit Cell Research Articles

Tungsten Bronze W3Nb2O14 Nanorod: The Low-Strain and Preferred Orientation Enables Long-Life for High-Rate Lithium-Ion Storage.

Tungsten bronze oxides have emerged as attractive materials for energy storage owing to their fast charge-discharge property. However, the internal weakness of low capacity and short cycling performance impedes their development in wide application. In this work, the tungsten bronze W3Nb2O14 nanorods with preferred orientation (001) were prepared by hydrothermal method for the first time. It not only displays high-rate performance but also exhibits high capacity (201 mA h g-1 at 0.2 C) and long cycling property (80% capacity retention at 50 C after 3000 cycles). Notably, in situ XRD revealed the c evolution frustrates the V increase, and the maximum unit-cell volume expansion is only 2.9% during lithiation/delithiation, reflecting the long cycle performance is benefit from the low strain and preferred orientation. The ex-situ 6Li NMR spectra revealed that the lithiation and delithiation present preference based on the size of tunnels in the crystal framework.

Breathing Transition and Effective Iodine Adsorption in a Temperature-Responsive Zn-Based Flexible Metal-Organic Framework.

A porous and flexible Zn-MOF was synthesized under solvothermal conditions by using the ligand 2,5-furandicarboxylic acid (2,5-FDA). This flexible Zn-MOF demonstrates a temperature-triggered breathing effect. At low temperature (100 K), we obtained the high-symmetry MOF denoted as SM-A with a unit cell volume of 1958 Å3, characterized by triangular narrow pore (np) channels. Upon increasing the temperature from 100 K to 298 K, the lower symmetry referred to as SM-B was obtained, featuring rhombic large pore (lp) channels, along with an expanded unit cell volume of 7823 Å3. This temperature-induced phase transition involves distortion of the channels and a change in the dimensionality of the framework from 3D (SM-A) to 2D (SM-B). The flexible behavior and phase transition were thoroughly justified with the help of single-crystal X-ray diffraction and differential scanning calorimetry. Additionally, BET analysis revealed a surface area of 85.504 m2/g, with mesopores of 3.05 nm. Leveraging the large-pore channels, SM-B at room temperature was employed as an adsorbent for the removal of hazardous iodine in both the vapor and the solution phases. The discovery of such dynamic MOFs holds potential and may pave the way for novel strategies in advanced applications.

Physicochemical properties of La0.5Ba0.5Co1-xFexO3-δ (0 ≤ x ≤ 1) as positrode for proton ceramic electrochemical cells

We report on essential properties of materials in the series La0.5Ba0.5Co1-xFexO3-δ as positrodes for proton ceramic electrochemical cells (PCECs). The unit cell and thermochemical expansion coefficient (TCEC) of these cubic perovskites decrease with iron content x, the TCEC of La0.5Ba0.5FeO3-δ going as low as 11·10-6 1/K. The materials behave as LaMO3 perovskites with small band gaps and Ba acting as acceptors compensated by electron holes and oxygen vacancies. The electrical properties are dominated by p-type conduction with high large polaron mobilities for the Co-rich compositions at low temperatures, shifting towards small polaron mobilities with increasing Fe content. X-ray absorption spectroscopy (XAS) shows that Co is in a high spin state and takes on the main part of the cation oxidation state changes, and that hole states are in orbitals overlapping with the O 2p states, confirming the large polaronic behaviour, while holes on Fe are more localised at the cation. Hydration is more pronounced in inert atmospheres, as hydration of oxygen vacancies is easier than hydrogenation and increases with Fe content, in line with the commonly accepted finding that delocalization of holes disfavours protonation. Fe-rich compositions benefit from lower TCEC and higher hydration and hence expected proton permeability, at the cost of lower electronic conductivity. The surfaces are hydrophobic irrespective of Fe content, suggesting weak chemisorption of the underlaying water layer, possibly giving relatively many available surface sites for oxygen adsorption, but limited surface proton conductance – both of importance to positrodes for operando PCECs.

Unveiling Morphology-Structure Interplay on Hydrothermal WO3 Nanoplatelets for Photoelectrochemical Solar Water Splitting.

Photoelectrochemical (PEC) water splitting offers a sustainable route for hydrogen production, leveraging noncritical semiconductor materials. This study introduces a seed layer-free hydrothermal synthesis approach for semiconductor photoanodes based on tungsten trioxide (WO3) nanoplatelets. Aiming to boost the efficiency of photoelectrochemical water splitting through optimization of the synthesis parameters of bare WO3, focusing on temperature, time, and layer thickness, we systematically explored their effects on the morphological, structural, and optical characteristics of WO3 photoanodes. Combining a low-temperature regime (90 °C for 12 h) with a multilayer strategy (up to six-layers) resulted in significant improvements in photocurrent. Particularly, the five-layer sample exhibited a remarkable increase of over 70% compared to the single-layer photoanode. Morphological aspects, particularly the fractal dimension of nanoplatelets and the emergence of the (220) crystalline orientation, usually neglected, were found to play pivotal roles in modulating the PEC response. Rietveld refinement of X-ray diffraction patterns further underscored the importance of crystallographic facets, volume unit cell expansion, and microstrain in influencing photocurrent outcomes. Furthermore, we adapted the Mott-Schottky equation to incorporate the fractal dimension reflecting the nanostructures' nature, usually set to a planar interface. Our findings highlight the interchange between nanoplatelet morphology and structural parameters in determining the PEC efficiency of WO3 photoanodes.

4[formula omitted] Electron Localization–Delocalization studies in CeMg[formula omitted] and PrMg[formula omitted] alloys under Pressure

The pressure dependence of magnetic moment in CeMg3 and PrMg3 has been studied through ab initio electronic structure calculations based on density functional theory (DFT). Positive as well as negative pressure conditions were simulated by different degrees of unit cell compression or expansion and a fit of the total energy to the Birch–Murnaghan equation of state. At ambient and negative pressures, the calculated magnetic moments for both the compounds reveal localized behaviour of 4f electrons. For increasing positive pressures, the magnetic moment of Ce in CeMg3 has been observed to diminish smoothly, becoming zero at a critical pressure of PC∼ 18 GPa indicative of pressure induced moment instability caused by an increase of f-conduction electron hybridization leading to delocalization of the 4f electrons. In contrast, the magnetic moment of Pr in PrMg3 does not show appreciable change with pressure, indicating strongly localized nature of the 4f electrons.

A stable ZnMn2O4 cathode for aqueous Zn-ion batteries via Ni doping to suppress Mn dissolution

ZnMn2O4 (ZMO) emerges as a promising cathode for aqueous Zn-ion batteries due to its high theoretical capacity of 224 mAh g−1 and operating voltage of ∼1.9 V (vs. Zn2+/Zn). However, it suffers from capacity degradation over cycling, attributed to the dissolution of redox-active Mn through Mn3+ disproportionation. In this study, we propose a strategy to stabilize ZMO cathodes by transforming Mn3+ into Mn4+ via Ni doping, aiming for charge balance. The ZnMn2−xNixO4 (x = 0, 0.5, 1.0, and 1.5) with different Ni amounts was prepared by straightforward precipitation and calcination. The mitigation of redox-active Mn dissolution enhanced the specific capacity of all Ni-doped ZMO compared to 201 mAh g−1 of ZMO. ZnMn1.5Ni0.5O4 and ZnMnNiO4 exhibit 277 and 278 mAh g−1, respectively, surpassing ZMO’s theoretical capacity (224 mAh g−1) of ZMO. This additional capacity was attributed to MnOx deposition on the cathode and the charge storage reaction with Zn-ion within the MnOx deposit. Furthermore, Ni doping induces a structural transition of the tetragonal into a cubic spinel, expanding the unit cell volume. This structural modification combined with suppressed Mn dissolution contributes to improved cycling stability. ZnMnNiO4 exhibits 80 % retention of initial capacity after 1000 cycles, outperforming ZMO (57 % retention). The expanded unit cell reduces repulsion between inserted Zn ions, enabling a higher rate performance than pure ZMO. The change in Mn valence states induced by Ni doping enhanced the lifespan and rate capability of ZMO cathodes, underscoring their potential as cathodes for Zn-ion batteries.

Tuning Optical and Electrical Properties of Vanadium Oxide with Topochemical Reduction and Substitutional Tin.

Vanadium oxides are widely tunable materials, with many thermodynamically stable phases suitable for applications spanning catalysis to neuromorphic computing. The stability of vanadium in a range of oxidation states enables mixed-valence polymorphs of kinetically accessible metastable materials. Low-temperature synthetic routes to, and the properties of, these metastable materials are poorly understood and may unlock new optoelectronic and magnetic functionalities for expanded applications. In this work, we demonstrate topochemical reduction of α-V2O5 to produce metastable vanadium oxide phases with tunable oxygen vacancies (>6%) and simultaneous substitutional tin incorporation (>3.5%). The chemistry is carried out at low temperature (65 °C) with solution-phase SnCl2, where Sn2+ is oxidized to Sn4+ as V5+ sites are reduced to V4+ during oxygen vacancy formation. Despite high oxygen vacancy and tin concentrations, the transformations are topochemical in that the symmetry of the parent crystal remains intact, although the unit cell expands. Band structure calculations show that these vacancies contribute electrons to the lattice, whereas substitutional tin contributes holes, yielding a compensation doping effect and control over the electronic properties. The SnCl2 redox chemistry is effective on both solution-processed V2O5 nanoparticle inks and mesoporous films cast from untreated inks, enabling versatile routes toward functional films with tunable optical and electronic properties. The electrical conductance rises concomitantly with the SnCl2 concentration and treatment time, indicating a net increase in density of free electrons in the host lattice. This work provides a valuable demonstration of kinetic tailoring of electronic properties of vanadium-oxygen systems through top-down chemical manipulation from known thermodynamic phases.

Unexpected concentration dependence of Ba2+ dominant substitution in addition to La3+ in cubic Nd3+-doped BaLaLiWO6 perovskites

There is a great need in material science to find and investigate new RE3+ ion-doped inorganic materials suitable for producing sintered ceramics of high transparency.Prospective candidates for transparent ceramics should crystalize in highly symmetric crystal systems, so BaLaLiWO6 characterized by a cubic structure (s.g. Fm3¯m) seems to be a good candidate for accomplishing this highly challenging task.A series of micro-crystalline samples activated by Nd3+ ion (0–20 mol%) was produced via the solid-state reaction. Nd3+ ion was chosen as a laser dopant and structural probe. For the first time, the BaLaLiWO6 crystal structure was solved from the single crystal.The originality of this research results from the unexpected substitution of divalent Ba2+ ions by trivalent Nd3+ ones till up to 7 mol% and above this value the replacement of probably both Ba2+ and La3+ ions. Exchange of Ba2+ by Nd3+ ions leads to the formation of cationic vacancies due to the charge compensation effect: 3Ba2+ → 2Nd3+ + □ (vacancy in La3+ cationic sublattice), well-manifested in unit cell expansion with consequences in the spectroscopic characteristics. XRD and SEM methods in combination with emission and absorption spectroscopic ones used at cryogenic temperature helped to determine the substantial properties of this perovskite which could find application in optics. Slightly different cationic positions substituted by the Nd3+ ion and its non-homogeneous arrangement in the Ba2+/La3+ site, detected by spectroscopy with selective excitation under laser at 77 K, is pointed out. The crystal disorder of the cation environment is revealed in broad absorption and emission bands even at low temperature.

Emergence of Perovskite and Hashemite-type phases in chromium doped (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ oxides: Formation, Rietveld refinement and Raman spectra

Perovskite- and Hashemite-type oxides are relevant due to their applications as oxidizing agent, photocatalyst, nutrient, fuel cells, gas sensors, batteries materials. An attempt has been made here to synthesize (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ(x = 0 – 1.0) and characterized with regards to structure and Raman vibrations. It depicts (a) pure cubic (Ba0.90Sr0.10)FeO3-δ phase, (b) cubic+orthorhombic, and (c) single orthorhombic (Ba0.90Sr0.10)CrO4 phase for x = 0–0.10, 0.20 – 0.80, and 1.0, respectively. It exhibits (i) decrease of cubic lattice parameter (ac)as 4.020 – 3.926 Å, (ii) expansion of orthorhombic unit cell, (iii) complete appearance of chromium in 6+ state for x = 1.0, and (iv) decrease of bond length and angle both with chromium. The bond lengths corresponding to Ba/Sr-O ∼ 2.84 Å, Fe-O ∼2.04 Å and Ba/Sr-O1 ∼ 3.227 Å, Ba/Sr-O2 ∼ 2.893 Å, Ba/Sr-O3 ∼2.859 Å have been derived for cubic (x = 0) as well as orthorhombic structure (x = 1.0), respectively. The bond angles e.g., Cr-O1-Cr ∼ 129°, Cr-O2-Cr ∼ 104.3° and Cr-O3-Cr ∼ 83.3° have been found for x = 1.0. Moreover, the bond Cr-O1 is compressed and Cr-O2 is more stretched than Cr-O3 bond. The morphology has also been changed to bigger size (nm) and shows different nature with chromium content. Raman spectra for Hashemite-type (Ba0.90Sr0.10)CrO4 reveal bands at ∼350, 360, 401, 425, 861, 886 and 904 cm−1 and arise due to symmetric (υ1, υ2) and antisymmetric (υ3, υ4) bending/ stretching mode. The present findings suggest potential applications of (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ oxides.

Computational investigation of the structural, elastic, electronic, and thermodynamic properties of chloroperovskites GaXCl3 (X = Be, Ca, or Sr) using DFT framework

In this study, we employed the pseudopotential plane wave approach to examine the influence of the X atom (X = Be, Ca, or Sr) on the physical properties of isostructural chloroperovskites GaXCl3. The GGA-PBEsol functional was employed to simulate the exchange–correlation interactions. The computed equilibrium lattice parameters exhibit a high level of concordance with the existing theoretical findings. The cohesion energy and enthalpy of formation were computed to verify the energetic stability of the materials under consideration. The determined values of the single-crystal elastic constants (Cij) indicate that GaBeCl3 remains mechanically stable up to a hydrostatic pressure of 18 GPa. Similarly, GaCaCl3 preserves its stability up to 5 GPa, while GaSrCl3 remains mechanically stable up to 1.25 GPa. The projected Cij values were used to estimate several elastic moduli and related properties, including the shear and bulk moduli, sound wave speeds, Young’s modulus, Poisson’s ratio, and Debye temperature. The energy band structures of the studied compounds, as predicted by the HSE06 functional, demonstrate their wide bandgap semiconductor nature. Specifically, GaBeCl3 demonstrates an indirect bandgap of 3.828 eV, while GaCaCl3 reveals an indirect bandgap of 4.612 eV and GaSrCl3 has an indirect bandgap of 4.405 eV. The quasiharmonic Debye approach was employed to examine various thermal parameters, including the temperature dependence of the unit cell volume, bulk modulus, expansion coefficient, Debye temperature, isochoric and isobar heat capacities, Grüneisen parameter, and entropy function. It has been shown that GaBeCl3 demonstrates a lower thermal expansion coefficient and a higher Debye temperature in comparison to GaCaCl3 and GaSrCl3.

Layered rare-earth stabilized Bi2O3: Organic amines intercalation under ambient conditions and their role as a solid adsorbent for iodine

Intercalation chemistry is pivotal in discovering the dimension-dependent properties of 2D materials and expanding their applications. Layered bismuth oxide with composition Bi0.775Ln0.225O1.5 (Ln = La, Pr, Nd, Sm, and Eu) has been demonstrated to intercalate both aliphatic and aromatic amines, resulting in the unit cell expansion along the c-axis. Aliphatic amines were present in a vertical orientation, whereas aromatic amines preferred a horizontal orientation. The intercalated amine concentrations ranged from 0.15 to 0.54 mole per mole of the host. Among the chosen amines, ethylenediamine intercalation enhanced the c-axis of Bi0.775Pr0.225O1.5 by 20 Å, justified by the high amounts of intercalant and intermolecular hydrogen bonding between them, resulting in a bilayer arrangement. The lamellar-plate-like morphology filled with intercalants and twinning collapse was noticed in the FESEM and SAED patterns after the intercalation process. The ethylenediamine intercalated Bi0.775Pr0.225O1.5 was further evaluated for iodine adsorption from non-aqueous solutions through chemisorption following pseudo-second-order kinetics. The X-ray diffraction peaks after adsorption suggested bilayer to monolayer transformation aided by chemical alterations within the host's van der Waals gaps. The N–I vibration mode, observed in the FTIR spectrum of the iodine-adsorbed sample, further augmented the interaction between the two during adsorption.

Structural Study of Nematogenic Compound 5OS5

The S-(4-pentylphenyl) 4-(pentyloxy)benzothioate, forming the nematic phase, is investigated by X-ray diffraction in temperatures between 263 K and 365 K, with the support of differential scanning calorimetry and polarizing optical microscopy. The microscopic observations show changes within the solid state, while X-ray diffraction does not indicate any transitions between the crystal phases. The Rietveld refinement shows that the crystal phase formed from the melt is the same monoclinic crystal phase with the P21/c space group as reported for a single crystal grown from an ethanol solution. The temperature dependence of the unit cell parameters in the 263–335 K range is determined and the coefficients of thermal expansion are obtained. The unit cell expands on heating along the longer ac-diagonal and b-axis while, along the shorter ac-diagonal, a very small shrinkage occurs. The diffraction patterns of the liquid crystalline nematic phase indicate the formation of dimers via hydrogen bonding. Density functional theory calculations (def2TZVPP basis set, B3LYP-D3(BJ) correlation-exchange functional) are applied for geometry optimization of an isolated molecule and selected dimers.

Enhancing low-temperature electrochemical kinetics and high-temperature cycling stability by decreasing ionic packing factor

Present-day Li+ storage materials generally suffer from sluggish low-temperature electrochemical kinetics and poor high-temperature cycling stability. Herein, based on a Ca2+ substituted Mg2Nb34O87 anode material, we demonstrate that decreasing the ionic packing factor is a two-fold strategy to enhance the low-temperature electrochemical kinetics and high-temperature cyclic stability. The resulting Mg1.5Ca0.5Nb34O87 shows the smallest ionic packing factor among Wadsley–Roth niobate materials. Compared with Mg2Nb34O87, Mg1.5Ca0.5Nb34O87 delivers a 1.6 times faster Li​+ ​diffusivity at −20 ​°C, leading to 56% larger reversible capacity and 1.5 times higher rate capability. Furthermore, Mg1.5Ca0.5Nb34O87 exhibits an 11% smaller maximum unit-cell volume expansion upon lithiation at 60 ​°C, resulting in better cyclic stability; at 10C after 500 cycles, it has a 7.1% higher capacity retention, and its reversible capacity at 10C is 57% larger. Therefore, Mg1.5Ca0.5Nb34O87 is an all-climate anode material capable of working at harsh temperatures, even when its particle sizes are in the order of micrometers.

Effect of fullerene C60 on phase transition enthalpy of paraffin wax: Calorimetry and structural analysis

In this paper, the effect of minor fullerene С60 admixtures on the phase transitions enthalpy of phase change material (PCM) is studied experimentally. For this purpose, the stable molecular solutions of the paraffin wax (PW) and fullerene С60 were explored in terms of the effective heat capacity and enthalpy of diffuse phase transitions over the (27…65) °С temperature range and C60 mass fraction up to 0.000746 g∙g−1. The choice of C60 as PW admixture was based on the hypothesis that a small amount of C60 contributes to a modification of the PW internal structure and, as a consequence, to a change in its caloric properties. Some factors that may affect the uncertainty for the obtained experimental data were examined. It was shown that the phase transition enthalpy for the PW/C60 in the (40…60) °C temperature range increase from 154.0 J∙g−1 (for pure PW) to 194.7 J∙g−1 (for PW containing 0.000746 g∙g−1 of C60) during cooling and decrease from 233.2 J∙g−1 (pure PW) to 182.3 J∙g−1 (PW containing 0.000746 g∙g−1 of C60) during heating. The results obtained indicate the defining influence of С60 on the PW structure in the liquid and solid states. It was confirmed by an additional structural analysis, which reported that pure PW has a minimal cell volume compared to PW/С60. The C60 addition into PW contributes to the expansion of the cell, indicating that the molecules lose their tight packing. A clear dependence between the enthalpy of melting and unit cell volume for PW/C60 samples was found. It was observed that unit cell expansion of PW due to the addition of C60 reduces the enthalpy hysteresis in the heating-cooling cycle – a key parameter that affects the efficiency of a thermal energy storage material. This positive effect may be due to structural transformation in PW during the melting-solidification cycles.

Study of Crystal Structure and Magnetics Properties in the Normal State of Electron-Doped Eu<sub>2-</sub><i><sub>x</sub></i>Ce<i><sub>x</sub></i>Cu<sub>0.97</sub>Zn<sub>0.03</sub>O<sub>4+</sub><i><sub>α-δ</sub></i> in Overdoped Regime

The normal state of high-Tc superconducting cuprates is crucial to understanding of the mechanism in superconductivity. There are two main ways to remove superconductivity so that the sample is in a normal state, that is by applying a large magnetic field or adding impurities such as Zn to the sample. To investigate the crystal structure and magnetic properties in the normal state of electron-doped high-Tc cuprates in overdoped regime, Eu2-xCexCu0.97Zn0.03O4+α-δ (ECCZO) with x = 0.16, 0.17, 0.18, and 0.19 has been synthesized by the solid-state reaction method. The crystal structure and magnetic properties of the samples were characterized by XRD and SQUID measurements. The results of XRD measurements shows all samples have T’-structure and the values of lattice parameters a, CuO bond length, and crystallite size increased with increasing x. On other hand, the value of lattice parameters c decreased with increasing x, causing the expansion of the tetragonal unit cell in the horizontal direction. From susceptibility measurements, in the normal state with 3% of Zn impurity all samples have the paramagnetic behaviour. The magnetic parameters of these samples analysed by the Curie law. With increasing of Ce concentration, the C and the are increased. The increase in the magnetic parameters since the increasing in magnetic ordering.

Enhanced Li-Ion Conductivity and Air Stability of Sb-Substituted Li4GeS4 toward All-Solid-State Li-Ion Batteries

Sulfide inorganic materials have the potential to be used as solid electrolytes (SEs) in Li-ion all-solid-state batteries (ASSBs) owing to their high ionic conductivity and mechanical softness. However, H2S gas release in ambient air is a critical issue for realizing scalable production of these materials. In the present study, we designed aliovalent substitutions of Sb5+ for Ge4+ in Li4GeS4 to produce a series of materials with a general nominal composition of Li4–xGe1–xSbxS4. With increasing Sb substitution up to the solubility limit (x = 0.4), the unit cell expands, the ionic conductivity increases, and the activation energy decreases. Among the series, the material with x = 0.4 displays the highest ionic conductivity, ∼10–4 S cm–1 at 303 K, 2 orders of magnitude higher than that of the unsubstituted Li4GeS4, and the main phase of the material is determined to be Li3.68Ge0.69Sb0.31S4 by the X-ray Rietveld refinement. It also shows high air stability: 70% of the initial ionic conductivity is retained without any structural degradation after exposure to air with a relative humidity of 15% for 70 min at 303 K, in contrast to a control sample of Li3PS4 retaining only 10% of the initial conductivity. A press cell composed of a TiS2 composite cathode, an In–Li alloy anode, and a Li3.68Ge0.69Sb0.31S4 electrolyte showed excellent cycle performance, demonstrating the electrolyte as a dry-air-stable SE candidate for ASSBs. These results provide insights into the synthesis design of air-stable SEs with appropriate compositions and improved performance.

Effect of Ce4+→Ce3+ conversion on the structural and luminescence properties of Ce4+ doped Gd2Ti2O7 pyrochlore oxide

Ternary oxides with cerium oxide as dopant are now useful as blue chip for the production of WLED's. In this present work, pyrochlore oxides Gd2Ti2-xCexO7 with doping concentration x = 0, 0.04, 0.08, 0.12, and 0.16, were prepared through standard solid-state reaction route. A pyrochlore structured phase is formed in the synthesized series as confirmed by conventional techniques; i.e., X-ray diffraction and Raman spectroscopy. Both techniques were revealed a systematic unit cell expansion as a function of doping concentration. The SEM micrograph confirms the formation of spherically agglomerated micron sized grains. In the later section of the manuscript, Ce4+→Ce3+ conversion effect on structural and luminescent properties were investigated. A relatively larger amount of cell expansion and accumulation of the strain is observed in the pyrochlore structured reduced samples. X-ray photoelectron spectroscopic (XPS) was used to investigate the oxidation state of the Gd, and Ti cations and oxygen anion. PL excitation spectra showed two broad bands centered around 255 nm and 360 nm due to the 4f→5d transition of Ce3+ ions at λem = 425 nm. Moreover, PL emission spectrum shows a broad peak around 425 nm at λex = 360 nm due to the 5d to 2F7/2 and 2F5/2 transitions. We observed that for the Ce4+→Ce3+ conversion both the PL emission and excitation spectra give far better results as compared to unreduced samples. Concentration quenching effect was observed for the doping concentration of 4% of cerium dopant. For 4% doping of cerium ion, CIE chromaticity results showed that the reduced as well as unreduced samples produce a bright blue colored emission line. The present study provides an insight about the potential use of Ce4+→Ce3+: Gd2Ti2O7 to synthesize blue LED chips for the fabrication of WLED's.

Temperature Dependent Crystal Structure of Nd2CuTiO6: An In Situ Low Temperature Powder Neutron Diffraction Study

Herein we reported the crystal structure and crystal chemistry of orthorhombic perovskite type Nd2CuTiO6 in between 2 K and 290 K as observed from the in situ temperature-dependent powder neutron diffraction (PND) studies. It is observed that the cations in octahedral sites are statistically occupied, and the ambient temperature orthorhombic structure is retained throughout the temperature range of the study. Absence of any long-range magnetic ordering down to 2 K is confirmed by both low-temperature PND and magnetization studies. The lattice shows strong anisotropic thermal expansion with increasing temperature, viz. almost no or feeble negative expansion along the a-axis while appreciably larger expansion along the other two axes (αb = 10.6 × 10−6 K−1 and αc = 9.8 × 10−6 K−1). A systematic change in the rotation of octahedral units with temperature was observed in the studied temperature range, while the expansion of unit cells is predominantly associated with the polyhedral units around the Nd3Ions. The temperature-dependent relative change in unit cell parameters as well as coefficients of axial thermal expansion show anomalous behavior at lower temperatures, and that seems to be related to the electronic contributions to lattice expansion.

Thermal Expansion and Rattling Behavior of Gd-Filled Co4Sb12 Skutterudite Determined by High-Resolution Synchrotron X-ray Diffraction.

In this work, Gd-filled skutterudite GdxCo4Sb12 was prepared using one step method under high pressure in a piston-cylinder-based press at 3.5 GPa and moderate temperature of 800 °C. A detailed structural characterization was performed using synchrotron X-ray diffraction (SXRD), revealing a filling fraction of x = 0.033(2) and an average <Gd-Sb> bond length of 3.3499(3) Å. The lattice thermal expansion accessed via temperature-dependent SXRD led to a precise determination of a Debye temperature of 322(3) K, from the fitting of the unit-cell volume expansion using the second order Grüneisen approximation. This parameter, when evaluated through the mean square displacements of Co and Sb, displayed a value of 265(2) K, meaning that the application of the harmonic Debye theory underestimates the Debye temperature in skutterudites. Regarding the Gd atom, its intrinsic disorder value was ~5× and ~25× higher than those of the Co and Sb, respectively, denoting that Gd has a strong rattling behavior with an Einstein temperature of θE = 67(2) K. As a result, an ultra-low thermal conductivity of 0.89 W/m·K at 773 K was obtained, leading to a thermoelectric efficiency zT of 0.5 at 673 K.

Tunable Enzyme-Assisted Mineralization of Apatitic Calcium Phosphate by Homogeneous Catalysis

While it has long been mimicked by simple precipitation reactions under biologically relevant conditions, calcium phosphate biomineralization is a complex process, which is highly regulated by physicochemical factors and involves a variety of proteins and other biomolecules. Alkaline phosphatase (ALP), in particular, is a conductor of sorts, directly regulating the amount of orthophosphate ions available for mineralization. Herein, we explore enzyme-assisted mineralization in the homogeneous phase as a method for biomimetic mineralization and focus on how relevant ionic substitution types affect the obtained minerals. For this purpose, mineralization is performed over a range of enzyme substrate concentrations and fluoride concentrations at physiologically relevant conditions (pH 7.4, T = 37 °C). Refinement of X-ray diffraction data is used to study the crystallographic unit cell parameters for evidence of ionic substitution in the lattice, and infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) are used for complementary information regarding the chemical composition of the minerals. The results show the formation of substituted hydroxyapatite (HAP) after 48 h mineralization in all conditions. Interestingly, an expansion of the crystalline unit cell with an increasing concentration of the enzyme substrate is observed, with only slight changes in the particle morphology. On the contrary, by increasing the amount of fluoride, while keeping the enzyme substrate concentration unchanged, a contraction of the crystalline unit cell and the formation of elongated, well-crystallized rods are observed. Complementary IR and XPS data indicate that these trends are explained by the incorporation of substituted ions, namely CO32- and F-, in the HAP lattice at different positions.