Changes In Unit Cell Parameters Research Articles

Investigating Cathode Dynamics in Realistic Desalination Reactors Using Operando High-Energy Synchrotron X-Ray Microscopy

Four billion people suffer from lack of clean water at least one month of the year.[1] This critical water shortage applies not only to the supply of potable water, but also to water for use in industrial, agricultural, and energy applications. While water resources like seawater are abundant, hardly any water resource is clean enough for direct use. Desalination provides a methodology to render unusable waters from such water resources fit for use. An innovative and particularly energy-efficient electrochemistry-based approach is the Desalination Battery (DB), which stores the energy input during desalination in chemical bonds between ions and faradaic electrode, allowing for its recovery during the salination process. DBs are at the forefront of the water-energy nexus[2]. While they are promising for seawater desalination (e.g., for seawater to brackish water conversion), practical implementation and their full potential still need to be unlocked. To this end, foundational understanding of the atomic- to electrode-scale physics/chemistry underlying functionality and degradation must be unraveled.Towards this end, we utilized our unique flow-by reactor setup to combine electrochemistry, conductivity, and temperature measurements with high-energy (75 keV) operando synchrotron X-ray diffraction (HEXRD) microscopy. Our investigation encompasses both the atomic and electrode levels, using a 3-electrodes setup with LiMn2O4 and Na0.44MnO2 as electrode active materials. As such, we were able to simulate a realistic electrode environment for operando measurements, as well as observe spatially resolved structural changes by scanning the beam across the electrodes surface. These phenomena are manifested through changes in unit cell parameters and the emergence of new phases during desalination cycles. Specifically, we tracked the changes in XRD patterns over the course of several desalination cycles in LiCl and NaCl solutions, as well as synthetic seawater and mixed solutions of LiCl/MgCl2. We were able to observe high selectivity of LiMn2O4 towards Li+, even in the highly concentrated synthetic seawater solutions, and could not observe the emergence of a new Mg+ rich phase down to potentials of 0 V vs. AgCl. Na0.44MnO2 exhibited good cycling behavior in synthetic seawater akin to pure NaCl solutions, and apart from the Na+ rich phase showed no signs of additional new phases, suggesting a highly selective nature towards Na+. Furthermore, we compared constant current and constant potential protocols and observed distinct differences in peak shift behavior. Ongoing analysis of the unit cell parameters and atomic positions allows us to allocate specific intercalation sites to specific potentials, providing foundational insight into the chemistry and physics underlying the selectivity of these materials.Literature:[1] M. M. Mekonnen, et al., Sci Adv 2016, 2, e1500323.[2] Q. Li, et al., Adv Sci (Weinh) 2020, 7, 2002213.

High Capacity and Fast Kinetics Enabled by Metal-Doping in Prussian Blue Analogue Cathodes for Sodium-Ion Batteries.

Prussian blue analogues (PBAs) have gained tremendous attention as promising low-cost electrochemically-tunable electrode materials, which can accommodate large Na+ ions with attractive specific capacity and charge-discharge kinetics. However, poor cycling stability caused by lattice strain and volume change remains to be improved. Herein, metal-doping strategy has been demonstrated in FeNiHCF, Na1.40Fe0.90Ni0.10[Fe(CN)6]0.85 ⋅ 1.3H2O, delivering a capacity as high as 148 mAh g-1 at 10 mA g-1. At an exceptionally high rate of 25.6 A g-1, a reversible capacity of ~55 mAh g-1 still can be obtained with a very small capacity decay rate of 0.02 % per cycle for 1000 cycles, considered one of the best among all metal-doped PBAs. This exhibits the stabilizing effect of Ni doping which enhances structural stability and long-term cyclability. In situ synchrotron X-ray diffraction reveals an extremely small (~1 %) change in unit cell parameters. The Ni substitution is found to increase the electronic conductivity and redox activity, especially at the low-spin (LS) Fe center due to inductive effect. This larger capacity contribution from LS Fe2+C6/Fe3+C6 redox couple is responsible for stable high-rate capability of FeNiHCF. The insight gained in this work may pave the way for the design of other high-performance electrode materials for sustainable sodium-ion batteries.

Attractive and repulsive forces in a crystal of [Rb(18-crown-6)][SbCl6] under high pressure.

The compression behavior of [Rb(18-crown-6)][SbCl6] crystal under pressure up to 2.16 (3) GPa was investigated in a diamond anvil cell (DAC) using a mixture of pentane-isopentane (1:4) as the pressure-transmitting fluid. The compound crystallizes in trigonal space group R3 and no phase transition was observed in the indicated pressure range. The low value of pressure bulk modulus [9.1 (5) GPa] found in this crystal is a characteristic of soft materials with predominant dispersive and electrostatic interaction forces. The nonlinear relationship between unit-cell parameters under high pressure is attributed to the influence of reduced intermolecular H...Cl contacts under pressure over 0.73 GPa. It also explains the high compression efficiency of [Rb(18-crown-6)][SbCl6] crystals at relatively low pressures, resulting in a significant shift of the Rb atom to the center of the crown ether cavity. At pressures above 0.9 GPa, steric repulsion forces begin to play a remarkable role, since an increasing number of interatomic H...Cl and H...H contacts become shorter than the sum of their van der Waals (vdW) radii. Below 0.9 GPa, both unit-cell parameter dependences (P-a and P-c) exhibit hysteresis upon pressure release, demonstrating their influence on the disordered model of Rb atoms. The void reduction under pressure also demonstrates two linear sections with the inflection point at 0.9 GPa. Compression of the crystal is accompanied by a significant decrease in the volume of the voids, leading to the rapid approach of Rb atoms to the center of the crown ether cavity. For the Rb atom to penetrate into the center of the crown ether cavity in [Rb(18-crown-6)][SbCl6], it is necessary to apply a pressure of about 2.5 GPa to disrupt the balance of atomic forces in the crystal. This sample serves as a compression model demonstrating the influence of both attractive and repulsive forces on the change in unit-cell parameters under pressure.

The Influence of Polyvinyl Alcohol Porogen Addition on the Nanostructural Characteristics of Hydroxyapatite.

Hydroxyapatite (HA) is a porous material widely developed in various research fields because of its high biodegradability, biocompatibility, and low toxicity. In this research, HA was synthesized using a hydrothermal method with chicken eggshells as a calcium source and various concentrations of polyvinyl alcohol as a porogen (2.5%, 5.0%, and 7.5% by wt). The structure and morphology of HA were determined by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. HA was obtained with varying concentrations of polyvinyl alcohol (PVA) porogen according to Inorganic Crystal Structure Database (ICSD) standard. Based on analysis using a refinement method, changes in unit cell parameters (cell volume and lattice strain) of HA synthesized using PVA porogen compared to the standard, the chi square (χ2) and index of R values were relatively low, validating the acceptable of the data. In addition, HA [Ca10(PO4)6(OH)2] with hexagonal structure and the P63/m space group was successfully obtained. Morphological analysis of HA by SEM found that HA has a spherical shape, and the porosity of HA increases with increasing concentrations of polyvinyl alcohol. The highest porosity was obtained with an addition of 5.0 wt% of PVA porogen (HAP3), reaching 69.53%.

Synthesis, structural and spectroscopic investigations of dolomite-type MSn(BO3)2 with M = Mn, Fe, Co and Ni

Abstract Dolomite-type MSn(BO3)2 phases for M = Mn, Fe, Co and Ni have been synthesized using solid-state synthesis carried out in sealed quartz tubes. X-ray powder diffraction data Rietveld refinements confirm the rhombohedral space group R 3 ‾ $R\overline{3}$ for all compositions. The change in unit-cell parameters follows the increasing nature of the radius of the M-cations. Both the MO6 and SnO6 octahedra are found to be quite regular. 119Sn Mössbauer spectroscopy investigations complement the almost undistorted nature of the SnO6 octahedra and the tetra-valent charge of the tin-atoms. Detailed vibrational features are described from the Raman and the FTIR spectral data collected at ambient conditions. The frequency shifts of some selective Raman and IR bands are explained in terms of the change of cationic sizes and the respective M–O bond distances. The UV/Vis diffuse reflectance data are analyzed using the RATD method, leading to direct bandgaps for all the investigated samples. The wide bandgap semiconductors (3 – 4 eV) show increasing transition energies with increasing cation sizes of the high-spin M-cations in the dolomite types.

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.

Competitive incorporation of Mn and Mg in vivianite at varying salinity and effects on crystal structure and morphology

Vivianite, a ferrous phosphate mineral, can be an important phosphorus (P) sink in non-sulfidic, reducing coastal sediments. The Fe in the crystal structure of vivianite can be substituted by other divalent metal cations such as Mn2+ or Mg2+. Since Mg is much more abundant in coastal porewaters than Mn, the more frequent reports of Mn substitution in vivianites of coastal sediments has been suggested to indicate a preferential incorporation of Mn over Mg into the crystal structure of vivianite. However, although both Mn and Mg substitution in vivianite are environmentally relevant, it is yet unknown whether Mn or Mg is preferentially incorporated and how these isomorphic substitutions alter the crystal structure and morphology of vivianite, parameters which may influence vivianite reactivity. Here, we studied the incorporation of Mn and/or Mg in vivianites formed by co-precipitation at pH 7 in the presence of varying dissolved Mn and/or Mg concentrations and solution salinities resembling an estuarine gradient from 0 to 9 psu. In total, 19 different vivianites were synthesized, with up to 50% of Fe substituted by Mn and Mg. Thermodynamic equilibrium calculations showed that aqueous Mg speciation was altered with increasing salinity, while Mn speciation was less affected, likely explaining the preferential incorporation of Mn in the vivianite structure at higher salinities. 57Fe-Mössbauer spectroscopy revealed that both Mn and Mg were preferentially incorporated in the double-octahedral Fe position, at which intervalence charge transfer is possible during the oxidation of vivianite. In contrast to Mg, which is redox inactive, incorporated Mn can participate in heteronuclear intervalence charge transfer with Fe. Thus, incorporation of either cation may impact the reactivity of vivianite under oxidizing conditions in element specific ways. Results of complementary analyses including X-ray diffraction, electron microscopy and Fe K-edge X-ray absorption spectroscopy further showed that incorporation of Mn and/or Mg led to smaller particle size, increased crystal roughness and thinner crystals, as well as systematic changes in unit cell parameters. These observed changes in crystal morphology might impact the reactivity of vivianite in natural environments and thus the effect of cation incorporation in vivianite should be considered when studying Fe and P cycling in coastal sediments.

Structural features of Li0.55Ag0.45InSe2 and Li0.37Ag0.63InSe2 crystals

Li0.55Ag0.45InSe2 crystals with orthorhombic structure were grown by the Bridgman-Stockbarger method with Li0.37Ag0.63InSe2 microcrystals of tetragonal modification found on their surface.The effect of substitution of silver and lithium ions on the evolution of structural properties in Li0.55Ag0.45InSe2 and Li0.37Ag0.63InSe2 phases was investigated. A fundamental difference in the change of unit cell parameters in the temperature range of 100–300 K has been revealed. A negative temperature expansion coefficient along the c axis was detected in the tetragonal modification Li0.37Ag0.63InSe2.

The investigation of highly stable low strain orthorhombic Na2TiSiO5 as anode material for lithium ion batteries and the migration behavior of Na-Li ions

As a member of silicate anode materials, orthorhombic Na2TiSiO5, synthesized by solid state method, has excellent electrochemical properties and is a promising Lithium-ion battery anode material with long cycle stability and low strain. At a current density of 100 mA g−1, Na2TiSiO5 has a reversible capacity of 395.2 mA h g−1 after 200 cycles with Coulombic efficiencies more than 97%. A reversible capacity of 251.3 mA h g−1 after 1000 cycles is retained with Coulombic efficiencies more than 98%. ex-situ experiments show the high structural stability and a less than 0.67% change of unit cell parameters in the charge/discharge process. The bond valence energy landscape (BVEL) calculation reveals 12 voids, namely, 4c-1, 4c-2, 2b and 2a, in a unit cell. That corresponds to a nominal composition Na2Li(4c-1)Li(4c-2)Li0.5(2b)Li0.5(2a)TiSiO5 and a theoretical capacity of 398.1 mAh g−1. The ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) calculations show that for both primitive orthorhombic Na2TiSiO5 and Li+ inserted Na2TiSiO5, Na+/Li+ are not active. However, with the insertion of 4C Li+, the occurrence of the synergic diffusion of Na+ and Ti4+ (4c Na+ -> 4c Ti4+ and 4c Ti4+ -> 2b vacancy) reliefs the extra strain, improves the structural stability during charge/discharge. The formation energy convex hull reveals 3 intermediate phases, that is Na2LiTiSiO5, Na2Li2TiSiO5 and Na2Li2.75TiSiO5, in the charge/discharge process.

Thermal expansion of the nanocrystalline titanium diboride

The research of thermal expansion of nano- and microcrystalline TiB2 in the temperature range of 298–1473 K was carried out by the high-temperature X-ray diffraction method. The grain size effect on the temperature dependence of a and c parameters of TiB2 hexagonal unit cell was established. For nanocrystalline TiB2 with the 5–7 nm coherent scattering region, we found the linear dependence of the metric of the cell on temperature. The thermal expansion coefficient (TEC) of nanocrystalline TiB2 does not depend on temperature and equals 3.58‧10−6 K−1 and 9.92‧10−6 K−1 for the a and c axis respectively. For the microcrystalline TiB2, we detected the nonlinear temperature dependence of unit cell parameter a, which points to the effect of temperature on the coefficient of thermal expansion along a basal plane. The TECa rises from 6.02·10−6 to 9.94·10−6 К−1 in the range of 300–1473 K, while the TECc weakly depends on temperature and remains constant ∼8.38·10−6 К−1, leading to isotropic thermal expansion of microcrystalline TiB2 at 1273–1473 K. The equations which describe the changes of unit cell parameters and coefficients of thermal expansion of nano- and microcrystalline TiB2 as temperature functions are determined.

Second‐Order Photonic Topological Corner States in Square Lattices with Low Symmetry

AbstractIn most cases, higher‐order topological insulating phases are observed in crystalline materials and photonic/phononic crystals with high crystalline symmetries. Few exceptions include amorphous and quasi‐crystalline matters, which have recently been demonstrated to exhibit such topological phases as well. This report reveals analytically and numerically that the photonic crystals with asymmetric sublattices can also exhibit second‐order topological insulating phases. The appearance of band inversion for the change of unit cell parameters, the quantized 2D polarizations and topological corner charges, and the generation of corner states explicitly reveal the existence of such second‐order photonic topological insulating phases. Quite interestingly, for arbitrarily shaped asymmetric unit cells, second‐order topological corner states are also observed, provided that the intercell coupling dominates over the intracell one.

Density-Functional Tight-Binding Parameters for Bulk Zirconium: A Case Study for Repulsive Potentials

Density-functional tight-binding (DFTB) parameters are presented for the simulation of the bulk phases of zirconium. Electronic parameters were obtained using a band structure fitting strategy, while two-center repulsive potentials were created by particle swarm optimization. As objective functions for the repulsive potential fitting, we employed the Birch-Murnaghan equations of state for hexagonal close-packed (HCP), body-centered cubic (BCC) and ω phases of Zr from density-functional theory (DFT). When fractional atomic coordinates are not allowed to change in the generation of the equation-of-state curves, long-range repulsive DFTB potentials are able to almost perfectly reproduce equilibrium structures, relative DFT energies of the bulk phases, and bulk moduli. However, the same potentials lead to artifacts in the DFTB potential energy surfaces when atom positions in the unit cell are allowed to fully relax during the change of unit cell parameters. Conventional short-range repulsive DFTB potentials, while inferior in their ability to reproduce DFT bulk energetics, are able to correctly reproduce the qualitative shape of the DFT potential energy surfaces, including the location of global minima, and can therefore be considered more transferable.

Structural Assessment of Fluorine, Chlorine, Bromine, Iodine, and Hydroxide Substitutions in Lead Arsenate Apatites (Mimetites)–Pb5(AsO4)3X

Five lead-arsenate apatites (mimetites)-Pb5(AsO4)3X—where X denotes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and hydroxide (OH)—were synthesized via precipitation from aqueous solutions. The crystal structures were determined through Rietveld refinement of powder synchrotron X-ray data. All the compounds crystallized in the hexagonal class symmetry (space group P63/m). The Rietveld refinement indicated that mimetite-Cl, -Br, -I, and -OH had an anion deficiency at position X. Substitution of halogens in a mimetite structure brought about systematic changes in unit-cell parameters, interatomic distances, and metaprism twist angles φ, proportional to the substituted halogen’s ionic radius. Mimetite-OH did not follow the linear correlations determined within the series. Twist angle φ, a useful device for monitoring changes in apatite topology, ranged from 20.34° for mimetite-F to 11.42° for mimetite-I. The geometric method has been proposed for determining the diameter of hexagonal channels hosting halogens in apatites. A comparison of the results with halogenated pyromorphites showed similar systematic trends: the substitutions in mimetites have comparable effect on the interatomic distances as in their phosphorous analogues.

Microstructure and Properties of Lead-Free Perovskite Ceramics on the Base of KNN Perovskite

The influence of LiSbO3 on the structure, microstructure, dielectric, ferroelectric and local piezoelectric properties of (K0.5Na0.5)NbO3 ceramics has been studied. Changes in unit cell parameters correlated with ionic radii changes and high effective local d33 piezoelectric coefficient values were observed depending on solid solutions compositions.

Structure and Behavior of the Ni End-Member Schreibersite Ni3P under Compression to 50 GPa

To better understand the potential presence of light element alloys of Fe and Ni in the Earth’s interior, the crystal structure and compressional behavior of the Ni-P binary compound, schreibersite (Ni3P), have been investigated using synchrotron X-ray diffraction experiments. Both powder and two single-crystal samples of synthetic Ni3P (in different orientations with respect to the loading axis of the diamond anvil cell) were compressed up to approximately 50 GPa at ambient temperature. The compressional data obtained for Ni3P were fitted with a 3rd order Birch–Murnaghan equation of state. All data indicated that the c/a ratio of unit cell parameters remained approximately constant up to about 30 GPa but then increased progressively with pressure, exhibiting a second slight discontinuity at approximately 40 GPa. The changes in unit cell parameters at ~30 GPa and ~40 GPa suggested discontinuous changes in magnetic ordering. Moreover, the threshold of these subtle discontinuities is sensitive to the stress state and orientation of the crystal in the diamond anvil cell. This study is the first report on the compressional behavior of both powder and single-crystal schreibersite at high-pressure (up to 50 GPa). It offers insights into the effects of Ni3P components on the compressional behavior of the Earth’s core.

Complex Salts Containing [Pd(NH3)4]2+ Cations and $$\text{WO}_4^{2-}$$ and $$\text{W}_7\text{O}_{24}^{6-}$$ Anions: The Precursors of Pd–W Metal Alloys

Two crystal structures containing [Pd(NH3)4]2+ cations and $$\text{WO}_4^{2-}$$ and $$\text{W}_7\text{O}_{24}^{6-}$$ anions are studied. For the [Pd(NH3)4]WO4 structure at 150 K the following crystallographic data are obtained: a = 7.4626(3) A, c = 15.5718(8) A, space group I41/amd, V = 867.20 A3, Z = 4. With increasing temperature to 400 K, the unit cell parameters change in different directions: a increases by 0.032 A, c decreases by 0.036 A. The total increase in the unit cell volume is 5 A3. In a range of 150 K to 400 K, the observed W-O distances decrease by 0.019 A from 1.778(18) A to 1.759(3) A. For the [Pd(NH3)4]3W7O24·4.4H2O structure at 298 K the crystallographic data are as follows: a = 8.3409(2) A, b = 22.2654(6) A, c = 10.5450(3) A, β = 104.449(1)°, space group P21/m, V = 1896.41 A3, Z = 2. In the heptatungstate anion the shortest are the W—O distances with the terminal O atoms (1.731–1.745 A). The distances to the bridging O atoms connecting two W atoms are 1.930–2.406 A; those connecting three W atoms are 1.882–2.234 A, and those connecting four W atoms are 2.192–2.220 A. It is shown that the [Pd(NH3)4]3W7O24·4.4H2O structure has a pseudohexagonal motif in the a direction. The thermal decomposition of the salts is performed in the presence of LiH in the He atmosphere at 1273 K. The ex situ powder X-ray diffraction study reveals the formation of Pd–W alloys.

The TbNiIn1-xMx (M = Al, Ge, Sb) systems

Interaction of the components in TbNiIn 1- x Al x , TbNiIn 1- x Ge x and TbNiIn 1- x Sb x systems at 873 K was investigated by means of X-ray phase and partially local analysis in full concentration range. The samples for the investigation were synthesized by arc-melting purity metals with subsequent annealing at 873 K for a month. Phase analysis was carried out by X-ray powder diffraction (DRON-2.0M, Fe K α-radiation, PANalytical X’Pert Pro, Cu K a- radiation, Guinier FR552, Cu K a-radiation). The EDX analysis of the samples and single crystal was carried out by REMMA-102-02 and Zeiss EVO MA10. The influence of Indium substitution by other p -element on the nature of interaction and solubility type was determined. Solubility ranges for solid solutions were found and changes of unit cell parameters were calculated: TbNiIn 1-0 Al 0-1 (ZrNiAl-type structure, space group P - 62 m , a = 0.7449–0.6997(2), c = 0.378–0.3889(1) nm); TbNiIn 1-0 . 6 Ge 0-0 . 4 (ZrNiAl-type structure, space group P - 62 m , а = 0.7449–0.74348(6), с = 0.378–0.38063(4) nm); TbNiGe 1-0 . 5 In 0-0 . 5 (TiNiSi-type structure, space group Pnma , а = 0.69499–0.69598(7), b = 0.42306–0.42475(4), с = 0.72813–0.72996(7) nm); TbNiSb 1 . 0-0 . 6 In 0-0 . 4 (MgAgAs-type structure, space group F -43 m , a = 0.62662(2)–0.62011(5) nm). The crystal structures of the TbNiIn 0 . 28 Al 0 . 72 compound were investigated by single crystal X-ray analysis (Stoe IPDS II diffractometer, Mo K α-radiation). The refined compositions are confirmed by the results of the EDX analysis (Zeiss EVO MA10 scanning electron microscope). The structures were solved and refined using JANA2006 package: ZrNiAl-type structure, space group P - 62 m, Pearson symbol hP 9, a = 0.71452(6), c = 0.38394(3) nm, R 1 = 0.0152, 307 F 2 values, 15 variables). The formation of solid solutions and the character of the unit cell parameters variation in the studied and related systems briefly discussed. Keywords: indium, solid solution, powder data, single crystal, crystal structure.

Deviations from Vegard's Law and Intense Raman Scattering in Low‐Doped Bi2Mo1−xWxO6 (x = 0–10%) Ceramics

Hume‐Rothery rules along with Vegard's law form the basis of systematic doping variation resulting into similar changes in unit cell parameters and volume. Many recent reports have highlighted positive–negative departure from Vegard's law in binary semiconducting systems and a few oxide alloys as well. The current work targets investigations on the missing response of bismuth molybdate on low tungsten doping onto molybdenum sites (Bi2Mo1−xWxO6). Bismuth molybdate and bismuth tungstate have been widely reported for lattice oxygen migration‐driven photocatalytic response and pressure‐sensitive Raman scattering. Octahedral tilting in low‐tungsten‐doped Bi2Mo0.94W0.06O6 carries an interesting lattice oxygen folding toward a–c plane. As a result, unit cell polarity increases drastically and becomes a source for intense Raman scattering phase that is normally observable at pressures around 8.3 GPa. An interesting departure from Vegard's law behavior at around 5–6% tungsten doping confirms nearly identical unit cell structure rather than mix unit cell‐based alloy formation.

Photoluminescence of complete solid solutions α-Y1-xEuxB5O9 by sol-gel synthesis and thermal decomposition from Y1-xEux[B6O9(OH)3

Completed solid solutions of Y1-xEux[B6O9(OH)3] were prepared by boric acid flux method and the structure of Eu[B6O9(OH)3] was determined by single crystal X-ray diffraction (XRD). The successful cationic doping was supported by the linear change of unit cell parameters obtained by Le Bail fitting on powder XRD. Thermal treatments on Y1-xEux[B6O9(OH)3] will lead to the dehydration, re-crystallization into TD-α-Y1-xEuxB5O9, and decomposition to α-Y1-xEuxB3O6 eventually. For comparison, the sol-gel method was also applied to prepare SG-α-Y1-xEuxB5O9. Rietveld refinements on powder XRD was applied to obtain the crystallographic data for α-YB5O9. PL investigation indicated that the existence of hydroxyl groups weakened the Eu3+ charge transfer (CT) in Y1-xEux[B6O9(OH)3]. In α-Y1-xEuxB5O9, an intense CT absorption was detected and a bright right emission was observed. Moreover, both series of phosphors exhibited a right shift of CT maximum wavelength due to the expansion of unit cell and the delayed concentration at x = 0.6.

Structural Changes in Ytterbium Ferrite YbFe2O4 in the Temperature Range From–150 °C TO 300 °C

Structural changes and thermal expansion of the iron ferrite sample YbFe2O4 of a rhombohedral modification are studied by high-temperature X-ray diffraction and differential thermal analysis. It is demonstrated that no phase transitions are observed in the temperature range from–150 °C to 300 °С. There are only anisotropic changes in unit cell parameters due to changes in Yb–O and Fe–O bond lengths.