Synchrotron X-ray Diffraction Data Research Articles

Synthesis, Crystal Structure Analysis and Electrochemical Properties of MgxNi1-XO2.

INTRODUCTION Currently, the secondary battery having a high energy density as a high performance secondary battery has been developed. Although polyvalent cations secondary batteries such as Mg and Ca batteries are a promising candidate, polyvalent cations secondary battery as alternative to lithium ion batteries has not been reported. In the lithium-ion battery, LiNi0.5Mn1.5O4 was well known to show two-electron reaction from Ni2 + to Ni4+ and high potential of 4.7 V. Interestingly, the electrochemical characteristic of LiNi0.5Mn1.5O4 was due to firing temperature changes. Therefore, the oxides consisted of Mg and Ni can be expected to be high potential and capacity from a viewpoint of the combination with divalent cations and two-electron reaction. However, synthesis of the oxides consisting of Mg and Ni has been only reported in the limited chemical composition, MgNiO2 and Mg0.67Ni1.33O2, and not reported the synthesis of other Mg / Ni ratio1,2). The present study was aimed at examination of difference in the electrochemical properties due to the difference in the firing temperature, controlling the rock-salt type MgxNi1-xO2 to Mg/Ni ratio, and evaluation as a magnesium ion battery cathode material. EXPERIMENTAL MgxNi1-xO2 was synthesized by a reverse coprecipitation synthesis1). MgxNi1-xO2 synthesized by nitrate aqueous solution of Mg and Ni were mixed to Na2CO3 solution while heating to 80° C, and the precursor dried (100 ° C, Air, 24h), and firing (550 - 950° C, Air, 24h). It was examined that the change in Mg/Ni ratio by changing the concentration of Na2CO3 solution. The samples were characterized by powder X-ray diffraction and ICP measurements. We also examined the valence of Ni by XAFS analysis (BL14B2, SPring-8). Before Charge-discharge test, active material and conductive agent in a weight ratio of 10:3 carbon coating (300rpm, 2h) by a planetary ball-mill. The positive electrodes were mixed active material and a conductive carbon and a binder (PTFE) at 5: 5: 1 weight ratio. Negative electrode used Mg metal or AZ31, electrolyte used 0.5 mol/L-Mg(N(CF3SO2)2)2/Acetonitrile (AN) or 1.0 mol/L-Mg(N(CF3SO2)2)2/Triglyme (G3). We attempted the Rietveld analysis (RIETAN-FP) and MEM analysis (Dysnamia) using the measured synchrotron X-ray diffraction data(BL19B2, SPring-8) RESULTS AND DISCUSSION The synthesized samples were identified as Rock-salt structure with space group Fd-3m by powder X-ray diffraction. To refine the crystal structure of the samples, we performed the Rietveld analysis using the synchrotron X-ray diffraction (e.g. R wp=5.60%, R e=2.35%). In addition, the results of ICP analyses for the compounds revealed that Mg/Ni ratio of the samples were ranged from 0.28 to 0.48 by changing Na2CO3 aq. concentration. The XAFS analysis, the valence state of Ni was determined to be divalent (Fig.1). The intensity ratio of d 111/d 200increased with the increasing the Mg/Ni ratio in the X-ray diffraction. We performed a charge-discharge test. Results of the charge-discharge test using AN showed 217mAh/g for the sample fired at 950 °C . The sample being higher Mg/Ni ratio tended to show higher capacity. However, the capacity might increase by a side reaction because of the electrochemical reaction occurred at extremely low voltage. To solve this reaction, electrolyte was changed from AN to G3 and the current collector was changed from Pt to Ni. As a result for such condition, it showed high reversibility and suppressed the side reactions. We examined the elimination of Mg by an oxidizing agent of NO2BF4. Since the lattice constants did not change before and after treatment, it was suggested elimination of Mg by chemical treatment was difficult. Therefore, we partly replaced Mg with Ca for the improvement of electrochemical property.We confirmed that (Mg,Ca)xNi1-xO2 was synthesized from the increase of the lattice parameter. As a result of the charge-discharge test for (Mg,Ca)xNi1-xO2, discharge potential was increased from 0.5V to 0.8V. Therefore, it may be possible to significantly improve the properties of Mg secondary battery of rock-salt type by Ca substitution. It was performed by help of ALCA-SPRING and shows thanks to the members concerned. References 1)S. Yagi et al., Jpn. J. Appl. Phys., 52,025501 (2013). 2)T. Ichitsubo, T. Adachi, S. Yagi, T. Doi, J.Mater.Chem., 21, 11764(2011). Figure 1

Search for Spinel Type Cathode Materials of Magnesium Secondary Battery By First-Principles Calculation and the Battery Properties, Crystal and Electronic Structure of Cathode Material

INTRODUCTION Currently, the cathode materials of the high-capacity lithium ion battery have been developed. However it is difficult to be tremendous capacity improvement. Therefore divalent magnesium ions have been noted. Due to approximately the same ionic radius of Mg2+ as the Li+, the theoretical capacity of magnesium per volume is higher than lithium, so that magnesium secondary batteries are expected as a next-generation battery. The charge-discharge test of the positive electrode material, such as MgCo2O4, was performed. Although the stable crystal structure and diffusion mechanism of Mg ions is not clear. In this study, the electrochemical evaluation and the crystal structure analysis of the MgCo2O4 and Li2-xCo2O4 were performed and the crystal structure determined by Rietveld analysis. Moreover, the first-principles calculation for MgCo2O4 evaluated the electronic structure especially in the M-O bond. The purpose of this study was to resolve the relationship between the phase stability and Mg/Co mixing in the crystal structure. EXPERIMENTAL MgCo2O4(MCO) was synthesized by reverse co-precipitation method2). Li2Co2O4 was synthesized by solid-state reaction which was chemically delithiated by using the Na2S2O8. The resulting materials were identified by XRD and determined by ICP for the composition of the metals. The charge/discharge test (HS cells : 3.5~0 V vs. Mg/Mg2+; three electrode cells : 0.345 - -0.855V vs. Ag/Ag+, the negative electrode metal Mg or Mg alloy (AZ31), reference electrode : Ag, separator : polypropylene or glass fiber filter, electrolyte : 0.5M-Mg(N(SO2CF3)2)2/CH3CN or Triglyme). These samples were performed by synchrotron X-ray diffraction (BL02B2, SPring-8). It was also investigated for the valence state of Co by XAFS (BL01B1, SPring-8). In addition, the first-principles calculations were performed for the three types of structure models that extends the unit cell of the MCO(VASP-code in 2 × 2 × 1 cell) and were evaluated for binding and the structural stability. RESULTS AND DISCUSSION The XRD for MCO and Li2Co2O4 showed that all of the diffraction peaks were attributed to the spinel structure (S.G.Fd-3m). The Rietveld analysis for the synchrotron X-ray diffraction data showed that Mg and Co in MCO were almost disorderly distributed and cation mixing. Chemically delithitated Li2Co2O4 sample, i.e. Li2-xCo2O4, was synthesized. From the results of charge-discharge test of MCO and Li2-xCo2O4 (counter Mg), the overvoltage of Li2-xCo2O4 was lower than that of MCO, since diffusion path of Mg could be secured by the regular arrangement of Mg/Co. As a result of the charge / discharge test of MCO using three-electrodes cell, we found a plateau of about 2.6 V (Mg/Mg2+) at the discharge (Fig.1). We also investigated the phase stability, Mg/Co mixing, and electronic structure of MCO by first-principles calculations. It was found that the model where the Mg occupied at only 8a site and Co occupied 16d site was stable arrangement. The electron densities between Co-O for all models exhibited higher than those of Mg-O and it means high covalency of Co-O. Therefore, the Mg of the 8a site became weak bond to oxygen to deintercalate. By Mg/Co mixing, the diffusion path of Mg would be inhibited by strong covalent bonds of Co-O. Then, MCO showed larger overvoltage than less mixing of Li2-xCo2O4. It was performed by help of ALCA-SPRING and shows thanks to the members concerned. References 1) N. Kamioka, T. Ichitubo, T. Uda, S. Imashuku, Y. Taninuchi and E. Matsubara, Materials Transactions, 49, 4, pp.824-828 (2008). 2) S.Yagi et al., Jpn. J. Appl. Phys., 52, 025501(2013). Figure 1

Cation distribution in CuFe2O4 nanoparticles: Effects of Ni doping on magnetic properties

The Cu1−xNixFe2O4 nanoparticles (with x = 0, 0.3, 0.5, 0.7, and 1) were synthesized by using spray co-precipitation method at annealing temperature Ta = 900 °C in air for 5 h. The crystal structure, microstructure, oxidation state, and magnetic properties of the samples were characterized by using X-ray diffraction, synchrotron X-ray diffraction, scanning electron microscopy, X-ray absorption spectroscopy, and vibrating sample magnetometer. It was shown that all the samples have cubic structure. Lattice constant and grain size decrease, while the Curie temperature TC increases with increasing of Ni2+ content. A small amount of Fe2+ was found in all the samples. Cation distribution was determined by using a combination of magnetization measurements, extended X-ray absorption fine structure analysis, and Rietveld refinement from synchrotron X-ray diffraction data. It was indicated that Ni2+ ions occupy in octahedral site only, while Cu2+ ions distribute in both tetrahedral and octahedral sites. The variation of magnetic parameters is discussed based on Ni2+ concentration, grain size, the cation distribution, surface effect, and the presence of Fe2+ ion in the samples.

Glassy Distribution of Bi3+/Bi5+ in Bi1–xPbxNiO3 and Negative Thermal Expansion Induced by Intermetallic Charge Transfer

The valence distribution and local structure of Bi1–xPbxNiO3 (x ≤ 0.25) were investigated by comprehensive studies of Rietveld analysis of synchrotron X-ray diffraction (SXRD) data, X-ray absorption spectroscopy (XAS), hard X-ray photoemission spectroscopy (HAXPES), and pair distribution function (PDF) analysis of synchrotron X-ray total scattering data. Disproportionation of Bi ions into Bi3+ and Bi5+ was observed for all the samples, but it was a long-ranged one with distinct crystallographic sites in the P1 triclinic structure for x ≤ 0.15, while the ordering was short-ranged for x = 0.20 and 0.25. An intermetallic charge transfer between Bi5+ and Ni2+, leading to large volume shrinkage, was observed for all the samples upon heating at ∼500 K.

Structural studies of Bi2O3-Nb2O5-TeO2 glasses

Bi2O3-Nb2O5-TeO2 glasses show unusual annealing behavior with appearance of spherulites within the matrix glass structure for the Bi0.5Nb0.5Te3O8 composition. The textures resemble those found previously among polyamorphic Al2O3-Y2O3 glasses containing metastably co-existing high- and low-density phases produced during quenching. However the spherulites produced within the Bi2O3-Nb2O5-TeO2 glass are crystalline and can be identified as an “anti-glass” phase related to β-Bi2Te4O11. We used high energy synchrotron X-ray diffraction data to study structures of binary and ternary glasses quenched from liquids within the Bi2O3-Nb2O5-TeO2 system. These reveal a glassy network based on interconnected TeO4 and TeO3 units that is related to TeO2 crystalline materials but with larger Te…Te separations due to the presence of TeO3 groups and non-bridging oxygens linked to modifier (Bi3+, Nb5+) cations. Analysis of the viscosity-temperature relations indicates that the glass-forming liquids are “fragile” and there is no evidence for a LLPT occurring in the supercooled liquid. The glasses obtained by quenching likely correspond to a high-density amorphous (HDA) state. Subsequent annealing above Tg shows mainly evidence for direct crystallization of the “anti-glass” tellurite phase. However, some evidence may exist for simultaneous formation of nanoscale amorphous spherulites that could correspond to the LDA polyamorph. The quenching and annealing behavior of Bi2O3-Nb2O5-TeO2 supercooled liquids and glasses is compared with similar materials in the Al2O3-Y2O3 system.

Compressional behavior of omphacite to 47 GPa

Omphacite is an important mineral component of eclogite. Single-crystal synchrotron X-ray diffraction data on natural (Ca, Na) (Mg, Fe, Al)Si2O6 omphacite have been collected at the Advanced Photon Source beamlines 13-BM-C and 13-ID-D up to 47 GPa at ambient temperature. Unit cell parameter and crystal structure refinements were carried out to constrain the isothermal equation of state and compression mechanism. The third-order Birch–Murnaghan equation of state (BM3) fit of all data gives V 0 = 423.9(3) A3, K T0 = 116(2) GPa and K T0′ = 4.3(2). These elastic parameters are consistent with the general trend of the diopside–jadeite join. The eight-coordinated polyhedra (M2 and M21) are the most compressible and contribute to majority of the unit cell compression, while the SiO4 tetrahedra (Si1 and Si2) behave as rigid structural units and are the most incompressible. Axial compressibilities are determined by fitting linearized BM3 equation of state to pressure dependences of unit cell parameters. Throughout the investigated pressure range, the b-axis is more compressible than the c-axis. The axial compressibility of the a-axis is the largest among the three axes at 0 GPa, yet it quickly drops to the smallest at pressures above 5 GPa, which is explained by the rotation of the stiffest major compression axis toward the a-axis with the increase in pressure.

Investigation on Average and Local Crystal Structures and Electronic Structure Change of Li-Rich Solid Solution Cathode Material 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 during Charge-Discharge Process Using Neutron Beam and Synchrotron X-Ray Sources and First-Principles Calculations

Significant progress continues to be made with regard to on high capacity lithium ion batteries in order to meet the requirement for the electric power and electric vehicles. The solid solution cathode material of Li2MnO3 and LiMO2 (M = Mn, Ni, Co) have attracted attention over the last ten years because they deliver high discharge capacity [1]. On the other hand, it was reported as the one of the problems that discharge voltage of this material decreases by repeating charge and discharge process. But the mechanism of the voltage fade is not clear. To commercialize the solid solution materials, it is necessary to solve the problem. In this study, we focused on the above problem. Our previous report described a transition metal rearrangement that occurs between 4.6 and 3.3 V during the initial discharge process [2]. In this paper, the average and local crystal structures, and the electronic structure of pristine (0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2) and samples after 1st discharge and after 5th discharge were investigated using a combination of a pair distribution function (PDF) analysis and first-principles calculations. 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 was synthesized by coprecipitation method, and its average crystal structure was determined by Rietveld analysis using powder neutron diffraction measurements (BL20, J-PARC) and synchrotron X-ray diffraction measurements (BL02B2, SPring-8). In addition, we carried out first-principle calculation (VASP-code, WIEN2k-code) in order to discuss the electronic state theoretically. Also, we used Pair Distribution Function (PDF) analysis using neutron total scattering (BL21, J-PARC) and synchrotron X-ray total scattering (BL04B2, SPring-8) in order to discuss the detailed local structure. To discuss the structural changes associated with the repeating charge and discharge process, we carried out X-ray absorption spectroscopy in addition to VASP-code and PDF analysis using synchrotron X-ray total scattering. First, the average and local crystal structures, and the electronic structure of 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 were investigated using a combination of a pair distribution function (PDF) analysis and first-principles calculations. The results of a Rietveld analysis using neutron diffraction data showed that 0.4Li2MnO3- 0.6LiMn1/3Ni1/3Co1/3O2 belonged to space group C2/m. Based on the site occupancy results, Mn was localized at 4g sites, and Ni and Co were present at both 4g and 2b sites. Both the maximum entropy method using synchrotron X-ray diffraction data, and calculations using WIEN2k, showed that the covalencies between Mn at 2b sites and O at8j sites in the transition metal layer, and between 2c and 8j sites in the lithium layer, were relatively low. A PDF analysis using both synchrotron X-ray and neutron total scattering data produced good fits to the observed data, and identified local differences in the average structure, such as the precise locations of Li and O. Although some distortion existed, the refined structure contained Mn-O6, Ni-O6, and Co-O6 tetrahedra. The bond lengths corresponded to the ionic radii, so that the valence of Mn, Ni and Co in this material before charging was tetravalent, between divalent and trivalent, and trivalent, respectively. These results were consistent with the valence obtained from the density of states calculated by the WIEN2k code, thus confirming that the local structural model was appropriate. Second, the structural changes associated with the repeating charge and discharge using after 1st discharge and after 5th discharge were investigated. By the comparison of this material before charge, after 1st discharge and after 5th discharge using PDF analysis, it was indicated that Li deviated from the plane of Li layer associated with the repeating charge and discharge. While the bond distance of Mn-O and Co-O was longer, that of Ni-O was shorter. From the results, the both the valences of Mn and Ni approached to trivalent with the repeating charge and discharge,. These local structural changes related to the decrease of discharge voltage by repeating charge and discharge. Acknowledgement This work was supported in part by JSPS KAKENHI Grant Number 25420718. [1] M.M. Thackeray, et al., J. Mater. Chem. 15, 2257 (2005). [2] Y. Idemoto et al, Electrochimica Acta, , 153, 399(2015).

Oxygen substitution effects in Li10GeP2S12 solid electrolyte

For the lithium super-ionic conductor Li10GeP2S12, the partial substitution of sulfur by oxygen is achieved via a solid-state reaction. The solid-solution range of oxygen is found to be 0 ≤ x < 0.9 in Li10GeP2S12−xOx. Structure refinements using synchrotron X-ray diffraction data confirm the preference for oxygen substitution in the PS4 tetrahedra. The local structural change in the P(S/O)4 tetrahedra upon substitution is also indicated by Raman spectroscopy. Ionic conduction properties are maintained even after the oxygen substitution in Li10GeP2S12; the ionic conductivity of Li10GeP2S12−xOx (0.3 ≤ x ≤ 0.6) ranges from 1.03 × 10−2 to 8.43 × 10−3 S cm−1 at 298 K. No redox current is observed by cyclic voltammetry from nearly 0 to 10 V versus Li/Li+ except for that due to the lithium deposition/dissolution reactions. All-solid-state batteries using Li10GeP2S12−xOx (x = 0.3 and 0.6) as solid electrolytes with Li metal anodes show discharge capacities exceeding 100 mAh g−1 and better cycling performance compared to batteries using the original Li10GeP2S12. The partial substitution of oxygen for sulfur in Li10GeP2S12 affords a novel solid electrolyte, Li10GeP2S12−xOx, with high conductive properties and electrochemical stability.

Operando Diffraction During Li Battery Operation Using Neutron and Synchrotron X-Ray Radiations

Performing in situ and operando measurements on electrode materials for Li-ion and Na-ion batteries is of importance for their understanding and improvement. Electrode materials need to be studied in their environment (in situ) and in real time while they function (operando), since they normally operate in non-equilibrium conditions. Real-time experiments upon charge/discharge of the electrodes (i.e. upon lithium or sodium extraction/insertion from/into the electrodes) unveil dynamics that are not accessible by other means and allow a more complete understanding of the electrodes’ functioning. The use of different probes is an important requirement for the study of such reactions. The combined use of X-Ray Powder Diffraction (XRPD), Synchrotron radiation XRPD and Neutrons Powder Diffraction (NPD) allows observing any atomic element in any crystalline electrode. However, custom setups are required to carry out operandodiffraction experiments on batteries. We will address the development of a sample environment suitable for both electrochemistry and neutron powder diffraction using an electrochemical cell featuring a (Ti,Zr) alloy and a deuterated version of the electrolyte [1]. The cell is able to function using massive electrodes (massive on the battery scale, but a small sample for neutrons) with good performances and able to give NPD patterns of high quality for data analysis. Importantly, we showed the possibility to succeed in reliable structural refinements (by the Rietveld method) and thus to observe structural modifications in details, from unit cell parameters to atomic coordinates and even site occupancy factors. We will discuss a few studies done with this setup, namely the observation of lithium extraction from different samples in the family of spinels Li1+xMn2-xO4. We performed NPD in real time on three samples (LiMn2O4, Li1.05Mn1.95O4 and Li1.10Mn1.90O4) and showed how the Li/Mn ratio influences the phase diagram of the material [2]. New insights obtained from high resolution – high flux Synchrotron X-Ray diffraction data will be presented, in particular the existence of a Li+ and Mn3+/Mn4+ ordering within the spinel-delithiated composition Li0.5Mn2O4[3]. Acknowledgements This research is performed in the frame of the French network RS2E (http://www.energie-rs2e.com) and of the European network ALISTORE-ERI (http://www.alistore.eu).

Dynamics of electron density, spin-phonon coupling, and dielectric properties ofSmFeO3nanoparticles at the spin-reorientation temperature: Role of exchange striction

Samarium orthoferrite $(\mathrm{SmFe}{\mathrm{O}}_{3})$ has been the subject of debate on the existence or nonexistence of ferroelectric properties. It has a high spin-reorientation transition temperature ${T}_{\mathrm{SR}}$ (480 K). Detailed synchrotron x-ray diffraction and Raman spectroscopy dielectric investigations in the 300 to 600 K temperature range of $\mathrm{SmFe}{\mathrm{O}}_{3}$ nanoparticles $(\ensuremath{\sim}65\phantom{\rule{0.16em}{0ex}}\mathrm{nm})$ have been performed. Raman spectroscopy established the existence of strong spin-phonon coupling and magnetostriction in the system. Magnetic measurements showed a spin-reorientation transition region from 480 to 450 K similar to that of a single crystal. The dielectric constant confirmed a clear anomaly around ${T}_{\mathrm{SR}}$. The signature of unusual relaxor ferroelectric behavior in $\mathrm{SmFe}{\mathrm{O}}_{3}$ nanoparticles from 380 to 480 K was observed in the dielectric properties. The electron density plots obtained using Rietveld refinement of the synchrotron x-ray diffraction data showed the displacement of the Sm and Fe ions, which can play a key role in the anomalous behavior at ${T}_{\mathrm{SR}}$. The analysis indicated the presence of magnetoelectric coupling due to the exchange interaction between Sm and Fe spins in $\mathrm{SmFe}{\mathrm{O}}_{3}$ nanoparticles.

Comparison of the structural evolution of the O3 and P2 phases of Na2/3Fe2/3Mn1/3O2 during electrochemical cycling

The recent development and the in-depth analysis of O3-phase Na2/3Fe2/3Mn1/3O2 has enriched the understanding of the overall electrochemical performance relating to the phase transitions during cycling of layered oxide cathodes. In order to understand the correlation between the initial polymorphs, their phase transitions during cycling without bias from starting Na concentration, we directly compare the structural evolution of O3- and P2-phase Na2/3Fe2/3Mn1/3O2 utilizing time-resolved in situ synchrotron X-ray diffraction data. The complex phase transitions along with multiple regions of solid solution and biphasic evolution are identified based on time (or voltage) of cycling progress. The focus of this work is at relatively high C-rates of 1C and C/2.5, where a direct comparison of the evolution of the O3 and P2 type Na2/3Fe2/3Mn1/3O2 phases are made, showing striking differences which do have ramifications on the short and long-term electrochemical performance of these electrodes. An example of the mid-term structural evolution of the O3 electrode shows that it can transform to the P2 electrode with electrochemical cycling.

Selenides Based Sodium Superionic Conductors

All-solid-state Na-ion batteries that operate at or close to room temperature are a promising next-generation battery technology with enhanced safety and reduced manufacturing cost. An indispensable component of this technology is the solid state electrolyte that allows rapid shuttling of the mobile cation (i.e., Na+) between the cathode and anode. However, there are very few fast Na-ion conductors with ionic conductivity approaching that of the liquid counterparts (i.e., 1 mS cm-1). Compared to oxides and sulfides, selenides form a huge unexplored chemical space for fast ionic conductor discovery. Based upon ionic size considerations, selenide-based compounds may provide a more suitable structural framework for the rapid diffusion of the much larger Na+ cations compared with Li+. This consideration led us to an extensive search of fast Na-ion conductors in the Se-based chemical space via high-throughput computational screening, and has identified cubic Na3PSe4 as one of the most promising candidates. In this work, we present the synthesis and structural characterization of Na3PSxSe4-x (x = 0, 1, 2, 3, 4). The structures of these phases are determined from high-resolution synchrotron X-ray diffraction data, which allow us to unambiguously identify a tetragonal-to-cubic phase transition with increasing Se concentration in Na3PSxSe4-x. The Na-ion conductivity and activation energy for Na-ion diffusion were further characterized via variable temperature impedance spectroscopy, from which a negative correlation between the activation barrier and Se concentration can be established. Of particular note is that the x = 4 end member (i.e., cubic Na3PSe4) possesses a room-temperature ionic conductivity exceeding 0.1 mS cm-1, and does not require high temperature sintering to minimize grain boundary resistance, making it a promising solid-state electrolyte candidate for all-solid-state Na-ion battery applications. These experimental results were complemented by ab initio computation through which we demonstrate an intriguing interplay between the tetragonal-to-cubic phase transition, defect formation, and Na+ migration. This work has two important implications for future studies in related fields: (1) selenide based compounds represent a promising platform for the discovery of new fast Na-ion conductors; and (2) the current study opens up new opportunities for the exploration of Se and/or S based battery chemistry, such as the construction of all-solid-state Na/Se battery.

High-Pressure Synthesis, Crystal Structure, and Magnetic Properties of Sr2MnO3F: A New Member of Layered Perovskite Oxyfluorides.

We have successfully synthesized Sr2MnO3F, a new layered perovskite oxyfluoride with a n = 1 Ruddlesden-Popper-type structure using a high-pressure, high-temperature method. Structural refinements against synchrotron X-ray diffraction data collected from manganese oxyfluoride demonstrated that it crystallizes in a tetragonal cell with the space group I4/mmm, in which the Mn cation is located at the octahedral center position. This is in stark contrast to the related oxyhalides that have square-pyramidal coordination such as Sr2MO3X (M = Fe, Co, Ni; X = F, Cl) and Sr2MnO3Cl. There was no evidence of O/F site order, but close inspection of the anion environment centered at the Mn cation on the basis of bond-valence-sum calculation suggested preferential occupation of the apical sites by the F ion with one oxide ion in a random manner. Magnetic susceptibility and heat capacity measurements revealed an antiferromagnetic ordering at 133 K (=TN), which is much higher than that of the chloride analogue with corrugated MnO2 planes (TN = 80 K).

Structural and electronic features of binary Li₂S-P₂S₅ glasses.

The atomic and electronic structures of binary Li2S-P2S5 glasses used as solid electrolytes are modeled by a combination of density functional theory (DFT) and reverse Monte Carlo (RMC) simulation using synchrotron X-ray diffraction, neutron diffraction, and Raman spectroscopy data. The ratio of PSx polyhedral anions based on the Raman spectroscopic results is reflected in the glassy structures of the 67Li2S-33P2S5, 70Li2S-30P2S5, and 75Li2S-25P2S5 glasses, and the plausible structures represent the lithium ion distributions around them. It is found that the edge sharing between PSx and LiSy polyhedra increases at a high Li2S content, and the free volume around PSx polyhedra decreases. It is conjectured that Li+ ions around the face of PSx polyhedra are clearly affected by the polarization of anions. The electronic structure of the DFT/RMC model suggests that the electron transfer between the P ion and the bridging sulfur (BS) ion weakens the positive charge of the P ion in the P2S7 anions. The P2S7 anions of the weak electrostatic repulsion would causes it to more strongly attract Li+ ions than the PS4 and P2S6 anions, and suppress the lithium ionic conduction. Thus, the control of the edge sharing between PSx and LiSy polyhedra without the electron transfer between the P ion and the BS ion is expected to facilitate lithium ionic conduction in the above solid electrolytes.

Disorder and defects are not intrinsic to boron carbide.

A unique combination of useful properties in boron-carbide, such as extreme hardness, excellent fracture toughness, a low density, a high melting point, thermoelectricity, semi-conducting behavior, catalytic activity and a remarkably good chemical stability, makes it an ideal material for a wide range of technological applications. Explaining these properties in terms of chemical bonding has remained a major challenge in boron chemistry. Here we report the synthesis of fully ordered, stoichiometric boron-carbide B13C2 by high-pressure–high-temperature techniques. Our experimental electron-density study using high-resolution single-crystal synchrotron X-ray diffraction data conclusively demonstrates that disorder and defects are not intrinsic to boron carbide, contrary to what was hitherto supposed. A detailed analysis of the electron density distribution reveals charge transfer between structural units in B13C2 and a new type of electron-deficient bond with formally unpaired electrons on the C–B–C group in B13C2. Unprecedented bonding features contribute to the fundamental chemistry and materials science of boron compounds that is of great interest for understanding structure-property relationships and development of novel functional materials.

Unravelling the low thermal expansion coefficient of cation-substituted YBaCo4O7+δ

With an aim to understand the origin of the low thermal expansion coefficients (TECs), cation-substituted YBaCo4O7-type oxides have been investigated by in-situ neutron diffraction, bond valence sum (BVS), thermogravimetric analysis, and dilatometry. The compositions YBaCo3ZnO7+δ, Y0.9In0.1BaCo3ZnO7+δ, and Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ were synthesized by solid-state reaction at 1200 °C. Rietveld refinement of the joint synchrotron X-ray and neutron diffraction data shows that the Zn and Fe dopants have different preferences to substitute the Co ions in the 6c and 2a sites. The bulk thermal-expansion coefficients of YBaCo3ZnO7+δ, Y0.9In0.1BaCo3ZnO7+δ, and Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ are, respectively, 9.42, 9.76, and 9.06 × 10−6 °C−1. Neutron diffraction data show that the low anisotropic TEC along the a-axis is the main contributor to the low bulk TECs. With the substitution of In, Zn, and Fe in Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ, the anisotropic and bulk TECs could be reduced to 8.94 and 9.06 × 10−6 °C−1, respectively, mainly due to the suppression of the change in Co–O bond length in CoO4 polyhedra. The observed weight loss during heating is due to the loss of interstitial oxide ions, as revealed by neutron diffraction and BVS map. Y0.9In0.1BaCo3Zn0.6Fe0.4O7+δ has the lowest area-specific cathodic polarization resistance of 0.14 Ω cm2 (Rtotal/2) at 700 °C in air.

Hydrothermal Synthesis, Crystal Structure, and Superconductivity of a Double-Perovskite Bi Oxide

Double-perovskite Bi oxides are a new series of superconducting materials, and their crystal structure and superconducting properties are under investigation. In this paper, we describe the synthesis and characterization of a new double-perovskite material that has an increased superconductive transition temperature of 31.5 K. The structure of the material was examined using powder neutron diffraction (ND), synchrotron X-ray diffraction (SXRD), and transmission electron microscopy (TEM). Rietveld refinement of the sample based on ND and SXRD data confirmed an A-site-ordered (K1.00)(Ba1.00)3(Bi0.89Na0.11)4O12 double-perovskite-type structure with the space group Im3m (No. 229). This structural analysis revealed the incorporation of Na with Bi in the structure and a bent bond between (Na, Bi)–O–(Na, Bi). TEM analyses also confirmed a cubic double-perovskite structure. This hydrothermally synthesized compound exhibited a large shielding volume fraction, exceeding 100%, with onset of superconductivity at ∼31...

The W-WO2oxygen fugacity buffer (WWO) at high pressure and temperature: Implications forfO2buffering and metal-silicate partitioning

Synchrotron X-ray diffraction data were obtained to simultaneously measure unit-cell volumes of W and WO2 at pressures and temperatures up to 70 GPa and 2300 K. Both W and WO2 unit-cell volume data were fit to Mie-Gruneisen equations of state; parameters for W are K T = 307 (±0.4) GPa, K ′T = 4.05 (±0.04), γ = 1.61 (±0.03), and q = 1.54 (±0.13). Three phases were observed in WO2 with structures in the P 21/ c , Pnma , and C 2/ c space groups. The transition pressures are 4 and 32 GPa for the P 21/ c-Pnma and Pnma-C 2/ c phase changes, respectively. The P 21/ c and Pnma phases have previously been described, whereas the C 2/ c phase is newly described here. Equations of state were fitted for these phases over their respective pressure ranges yielding the parameters K T = 238 (±7), 230 (±5), 304 (±3) GPa, K ′T = 4 (fixed), 4 (fixed), 4 (fixed) GPa, γ = 1.45 (±0.18), 1.22 (±0.07), 1.21 (±0.12), and q = 1 (fixed), 2.90 (±1.5), 1 (fixed) for the P 21/ c , Pnma , and C 2/ c phases, respectively. The W-WO2 buffer (WWO) was extended to high pressure using these W and WO2 equations of state. The T - f O2 slope of the WWO buffer along isobars is positive from 1000 to 2500 K with increasing pressure up to at least 60 GPa. The WWO buffer is at a higher f O2 than the iron-wustite (IW) buffer at pressures lower than 40 GPa, and the magnitude of this difference decreases at higher pressures. This implies an increasingly lithophile character for W at higher pressures. The WWO buffer was quantitatively applied to W metal-silicate partitioning by using the WWO-IW buffer difference in combination with literature data on W metal-silicate partitioning to model the exchange coefficient ( K D) for the Fe-W exchange reaction. This approach captures the non-linear pressure dependence of W metal-silicate partitioning using the WWO-IW buffer difference. Calculation of K D along a peridotite liquidus predicts a decrease in W siderophility at higher pressures that supports the qualitative behavior predicted by the WWO-IW buffer difference, and agrees with findings of others. Comparing the competing effects of temperature and pressure the results here indicate that pressure exerts a greater effect on W metal-silicate partitioning.

NIR-to-NIR and NIR-to-blue light upconversion in stoichiometric NaYb(MO4)2(M = Mo, W)

Polycrystalline NaYb(MoO4)2 and NaYb(WO4)2 exhibited NIR-to-NIR and NIR-to-blue light upconversion under 973 nm excitation. The emission spectra were dominated by a strong NIR (∼795 nm) band. Blue (∼475 nm), green (∼525 and 545 nm), and red (∼650 nm) bands were also observed. The origin of these bands was investigated using a combination of steady-state and time-dependent spectrofluorometry, elemental analysis, and Rietveld analysis of synchrotron X-ray diffraction data. The strong NIR emission at ∼795 nm was assigned to two-photon upconversion from Yb3+-sensitized Tm3+, which was found to be present at trace levels (∼1 ppm) in both NaYb(MoO4)2 and NaYb(WO4)2. Due to the high efficiency of the energy-transfer from Yb3+ to Tm3+, the intensity of the NIR emission exhibited a linear dependence on the excitation power. Green and red bands were assigned to two-photon upconversion from Yb3+-sensitized Er3+, which was also found to be present at trace levels in both hosts (∼1 ppm). In the case of the blue emission, power-dependence and time-dependent spectrofluorometric studies favored cooperative luminescence of Yb3+–Yb3+ dimers, rather than three-photon upconversion from Yb3+-sensitized Tm3+. Local clustering of Yb3+ ions yielding Yb3+–Yb3+ dimers that interact cooperatively under NIR excitation was feasible considering (i) the intrinsic disorder of Na+ and Yb3+ over the same crystallographic site, and (ii) the shortest distance between two adjacent Yb3+ ions (∼3.81 A). The significance of probing energy-transfer processes relevant to light absorption and emission in fully concentrated metalate hosts is highlighted.

Recrystallization, Phase Composition, and Local Structure of Amorphous Lactose from the Total Scattering Pair Distribution Function

Total scattering pair distribution function (TSPDF) analysis of synchrotron X-ray diffraction data has been used to study the structural characteristics of amorphous lactose and its subsequent recrystallization on aging. This shows that the recrystallization kinetics vary substantially between spray dried, lyophilized, and melt quenched samples aged at 40 °C/75% relative humidity (RH), although all samples consistently form the stable α monohydrate when crystallization does occur. Using TSPDF it was possible to quantify the amount of amorphous and crystalline phases present, as well as to extract other structural information such as crystallite size, as a function of time during aging from the different starting materials. We also were able to determine a correlation between a higher degree of local molecular ordering in the amorphous phase with decreased stability against recrystallization. This study shows the rich information that may be obtained from a TSPDF analysis of recrystallization from the amorphous state in organic systems.