High-temperature Neutron Diffraction Research Articles

Charge Transport in the A6B2O17 (A = Zr, Hf; B = Nb, Ta) Superstructure Series

The electrical properties of the entropy stabilized oxides: Zr6Nb2O17, Zr6Ta2O17, Hf6Nb2O17 and Hf6Ta2O17 were characterized. The results and the electrical properties of the products (i.e. ZrO2, HfO2, Nb2O5 and Ta2O5) led us to hypothesize the A6B2O17 family is a series of mixed ionic-electronic conductors. Conductivity measurements in varying oxygen partial pressure were performed on A6Nb2O17 and A6Ta2O17. The results indicate that electrons are involved in conduction in A6Nb2O17 while holes play a role in conduction of A6Ta2O17. Between 900 °C–950 °C, the charge transport in the A6B2O17 system increases in Ar atmosphere. A combination of DTA/DSC and in situ high temperature X-ray diffraction was performed to identify a potential mechanism for this increase. In-situ high temperature X-ray diffraction in Ar does not show any phase transformation. Based on this, it is hypothesized that a change in the oxygen sub-lattice is the cause for the shift in high temperature conduction above 900 °C–950 °C. This could be: (i) Nb(Ta)4+- oxygen vacancy associate formation/dissociation, (ii) formation of oxygen/oxygen vacancy complexes (iii) ordering/disordering of oxygen vacancies and/or (iv) oxygen-based superstructure commensurate or incommensurate transitions. In-situ high temperature neutron diffraction up to 1050 °C is required to help elucidate the origins of this large increase in conductivity.

Using neutron diffraction to explore lithium displacement within cubic phase stabilised Ga-doped Li6.75La3Zr1.75Ta0.25O12 lithium garnet oxides

Typical Li6.75La3Zr1.75Ta0.25O12 exists as a mixture of tetragonal and cubic arrangements, but adding small amounts of Ga3+ (Li6.75–3xGaxLa3Zr1.75Ta0.25O12 x ≥ 0.1) resulted in a single cubic (I a-3d) phase lithium garnet oxide. Following the stabilisation of the cubic phase, the effects on lithium distributions were explored with neutron powder diffraction concerning Ga3+ content and temperature. Increasing the amount of Ga3+ reduced the amount of lithium within the structure, directly decreasing the Li 96h site occupancy and showing a minimal effect on the Li 24d site occupancy. High-temperature neutron diffraction studies revealed the migration of lithium from the Li 24d site to the Li 96h with increasing temperature. The inclusion of Ga3+ improved the total ionic conductivity over the gallium-free system. However, with increasing gallium content (x > 0.1), a negative correlation between the garnet's gallium content and total lithium ionic conductivity is observed, showing how the total amount of free lithium ions impact the system's total ionic conductivity. Though the electrolytes explored here show some limitations, the lithium-ion displacement trends with doping and temperature give us further insight into how these lithium garnet systems respond to chemical and physical change.

Machine learning based prediction of space group for Ba(Ce0.8-xZrx)Y0.2O3 perovskite-type protonic conductors

Space groups of Ba(Ce0.8-xZrx)Y0.2O3 (0 ≤ x ≤ 0.8) perovskite-type protonic conductors of wide temperature range from 25 to 900 °C in dry and wet atmospheres are predicted using various machine learning (ML) models. For the prediction, the data including the chemical formulas of the crystal materials as well as space group obtained via high-temperature X-ray diffraction (HT-XRD) and high-temperature neutron diffraction (HT-ND) between 25 and 1000 °C were inputted. 4 different ML models have been constructed using a Random Forest (RF), a Multi-Layer Perceptron (MLP) and a XGBoost, with different data set using experimental data (907 sets of 41 compositions), Magpie descriptor, and additional Inorganic Crystal Structure Database (ICSD) literature data (110 sets of 18 compositions). In the classification problem of space group prediction and phase diagram mapping, accuracy = 0.940 and F1 score = 0.785 is achieved by RF model with coordination number (C.N.) = 9 of oxygen of A-site cation.

Tuning the melting point and phase stability of rare-earth oxides to facilitate their crystal growth from the melt

The challenge of growing rare-earth (RE) sesquioxide crystals can be overcome by tailoring their structural stability and melting point via composition engineering. This work contributes to the advancement of the field of crystal growth of high-entropy oxides. A compound with only small REs (Lu,Y,Ho,Yb,Er)2O3 maintains a cubic C-type structure upon cooling from the melt, as observed via in-situ high-temperature neutron diffraction on aerodynamically levitated samples. On the other hand, a compound with a mixture of small and large REs (Lu,Y,Ho,Nd,La)2O3 crystallizes as a mixture of a primary C-type phase with an unstable secondary phase. Crystals of compositions (Lu,Y,Ho,Nd,La)2O3 and (Lu,Y,Gd,Nd,La)2O3 were grown by the micro-pulling-down (mPD) method with a single monoclinic B-type phase, while a powder of (Lu,Y,Ho,Yb,Er)2O3 did not melt at the maximum operating temperature of an iridium-rhenium crucible. The minimization of the melting point of the two grown crystals is attributed to the mismatch in cation sizes. The electron probe microanalysis reveals that the general element segregation behavior in the crystals depends on the composition.

Oxygen nonstoichiometry effects in spin Seebeck insulating Y3−xPrxFe5O12+ δ materials

Yttrium iron garnet (Y3Fe5O12) and its derivatives are ferrimagnetic spin Seebeck insulating materials crucial for the spin transport based phenomena such as the spin Seebeck effect (SSE) and spin Hall magnetoresistance. Structure–property correlation studies of such materials under different conditions are useful for optimizing the relevant constraint in the existed phenomena. The usage of Y3Fe5O12 type materials over the broad range of temperature conditions (27–450 °C) in SSE is under study. We report here the structure–property correlation in spin Seebeck insulating Y3−xPrxFe5O12+δ oxides as a representative material and introduce the additional degrees of freedom in the crystal system relevant to the spin transport based phenomena under high temperature conditions. The natural tendency of having oxygen nonstoichiometry in an iron garnet family of materials strengthens the Fe–O–Fe superexchange interaction, which, in turn, tends to increase the spin voltage correlated magnetic parameters. The analysis of experimental high temperature neutron diffraction data (over 27–450 °C) reveals the oxide ion nonstoichiometry and excess oxide ion transport pathways at moderate temperature 150 °C in the crystal lattices of studied garnet materials. Oxide ion nonstoichiometry, ionic transport, and electron hopping in crystal lattices cause a tremendous variation of electrical conductivity (10−11–10−2 S cm−1) over a moderate change of temperature (27–450 °C). The occurrence of electrical transport in the required thermal gradient over the garnet material in SSE can evoke the additional degrees of freedom in the usage of such materials at high temperatures. The present work provides a new outlook in terms of structure–property correlation for spin transport based materials.

Neutron diffraction investigation of copper tellurite glasses with high real-space resolution

High real-space resolution neutron diffraction measurements up to 34 Å−1 were performed on a series of xCuO–(100 − x)TeO2 (x = 30, 40 and 50 mol%) glasses that were synthesized by the melt-quenching technique. The Fourier transformation of neutron diffraction structure factors was used to generate the pair distribution functions, with the first peak at 1.90 Å due to the overlapping Te–O and Cu–O atomic pairs. Reverse Monte Carlo (RMC) simulations were performed on the structure factors and the six partial atomic pair distributions of Cu–Cu, Cu–Te, Cu–O, Te–Te, Te–O and O–O were calculated. The Te–O and Cu–O distributions are very similar and asymmetrical, which revealed that there is a significant short-range disorder in the tellurite network due to the existence of a wide range of Te—O and Cu—O bond lengths. A high-Q (magnitude of momentum transfer function) neutron diffraction study revealed that the average Te–O coordination number decreases steadily from 3.45 to 3.18 with an increase in CuO concentration from 30 to 50 mol% in the glass network. Similar coordination number modifications were earlier found by the RMC analysis of neutron diffraction data sets of copper tellurite glasses that were performed up to lower Q maximum values of 9.5 Å−1. The comparison of high-Q and low-Q neutron diffraction studies reveals that RMC is a powerful and possibly the only technique that is available to elucidate the glass short-range and medium-range structural properties when diffraction data are available up to low Q values of, say, 9.5 Å−1, and when cation–oxygen bond lengths are strongly overlapping and cannot be resolved by Fourier transformation. In situ high-temperature (473 K) neutron diffraction studies of 50CuO–50TeO2 glass revealed that significant distortion of the tellurite network occurs with heating.

Property Improvement of Additively Manufactured Ti64 by Heat Treatment Characterized by In Situ High Temperature EBSD and Neutron Diffraction

Among various off-equilibrium microstructures of additively manufactured Ti-6Al-4V alloy, electron beam powder bed fusion, in which three dimensional metallic objects are fabricated by melting the ingredient powder materials layer by layer on a pre-heated bed, results in a specimen that is nearly free of the preferred orientation of the α-Ti phase as well as a low beta phase fraction of ∼1 wt%. However, when further heat treatment of up to 1050 ∘C was applied to the material in our previous study, a strong texture aligning the hexagonal basal plane of α phase with the build direction and about 6% β phase appeared at room temperature. In this study, to understand the mechanism of this heat treatment, the grain level microstructure of the additively manufactured Ti-6Al-4V was investigated using in situ high temperature EBSD up to 1000 ∘C, which allows the tracking of individual grains during a heat cycle. As a result, we found a random texture originating from the fine grains in the initial material and observed a significant suppression of α phase nucleation in the slow cooling after heating to 950 ∘C within the α and β dual phase regime but close to the the β-transus temperature at ∼980 ∘C, which led to a coarse microstructure. Furthermore, the texture resulting from phase transformation of the additively manufactured Ti-6Al-4V assuming nucleation at the grain boundaries was modeled, using the double Burgers orientation relationship for the first time. The model successfully reproduced the measured texture, suggesting that the texture enhancement of the α phase by the additional heat treatment derives also from the variant selection during the phase transformation and nucleation on grain boundaries.

Recent Advances in Cobalt-Free Nickel-rich Li-ion Battery Cathode Materials for Next Generation Electric Vehicles

Recently, battery research community has been grappling with the burgeoning question of ensuring sustainability in battery technologies that would enable next generation electric vehicles. In the past decade, extreme cobalt price fluctuations have severely constrained the supply chains of battery manufacturing industries as most mainstream lithium ion batteries still largely employ cobalt containing cathode materials. To keep battery costs low to ~80$/kWh, and to ensure a sustainable future for electric vehicles, a multitude of research efforts have been directed towards exploring nickel rich cathode chemistries boasting high capacities >200 mAh/g. Though the question of sustainability is not completely addressed through the use of nickel rich compositions, these systems still remain the most promising alternatives when considering the performance requirements of modern electric vehicles. In this context, our team has been exploring the development of novel classes of layered lithium ion battery cathode materials with '0' cobalt in their compositions. Our team has systematically investigated new classes of cobalt-free nickel-rich battery cathodes, having the general formula, LiNixM1yM2zO2 (where, M1 and M2 are other metal ions, x + y + z = 1)[1,2] and evaluated their performance in the quest of identifying the best nickel rich variant. These layered nickel-rich cobalt-free cathodes have similar crystal structure and properties to conventional cobalt containing cathodes such as NCMs and NCAs while delivering comparable and in some cases better electrochemical performance. Here, I will present our research efforts in the development of these novel cathode formulations starting from compositional landscape investigations, advanced characterizations followed by electrochemical performance assessments. Specifically, in-situ high temperature X-Ray and Neutron diffraction techniques were employed to investigate the calcination and phase formation behavior while operando investigations using X-Ray diffraction and Mössbauer spectroscopy were employed to obtain a mechanistic understanding of the redox behavior exhibited by these systems. Best performing compositions were upscaled in continuous stirred tank reactors to kilogram levels, following which, slot-die coating process was employed to fabricate electrodes that were later assembled in pouch format full cells for electrochemical performance assessments[3]. The work presented here summarizes recent results of this early stage research and development endeavor to highlight the immense potential that these nickel-rich class of cathodes can offer towards development of next generation cost effective lithium ion batteries for electric vehicle applications in the coming decades.

Crystal Structure Evolution of UCl3 from Room Temperature to Melting

Uranium trichloride (UCl3) is actively researched to develop and improve applications ranging from molten salt reactors to actinide processing, including spent fuel reprocessing. Here, we report for the first time the crystal structure evolution between room temperature and melting point from in situ high-temperature neutron diffraction to quantify, for example, the thermal expansion of the hexagonal a and c lattice parameters. The results are compared with density functional theory calculations. The melting point of UCl3 is determined by differential scanning calorimetry to be 1108.2 ± 0.2 K.

(Invited) Cobalt Free Li-Ion Battery Cathode Materials for Next Generation Electric Vehicles

The battery manufacturing industry has a cobalt problem! Over the recent years, rapid fluctuations in cobalt prices have created a drastic supply chain constraint that threatens to derail the burgeoning projections for electric vehicles over the next few decades. To reduce the cost of modern batteries to ~80$/kWh (to sustain the growing electric vehicle demands), it has become paramount that the amount of cobalt, the most expensive present-day battery cathode raw material, should be reduced to less than 50 mg at the cell level. Moreover, it is also important that any alternative cathode material developed, should facilitate a seamless integration into existing global battery manufacturing infrastructures to avoid a complete overhaul. The search for viable alternatives that address these challenges simultaneously is a continuing quest in today's battery research and development sectors. In this context, our team through a paradigm shifting approach has developed a new class of layered lithium ion battery cathode material with '0' cobalt in its composition. This new class of battery cathodes, termed the NFA class, has the general formula, LiNixFeyAlzO2 (where, x + y + z = 1)[1,2]. These layered cobalt-free cathodes are analogous in crystal structure and material properties to mainstream cobalt containing cathodes such as NCMs and NCAs while delivering comparable and in some cases better electrochemical performance. Here, I will present our efforts in the systematic development of these novel cathodes starting from compositional landscape investigations and advanced characterizations employing NFA material synthesized using the lab-scale sol-gel process. Through our approach, in-situ high temperature X-Ray and Neutron diffraction techniques were used to investigate the calcination and phase formation behavior while operando investigations using X-Ray diffraction and Mössbauer spectroscopy were employed to obtain a mechanistic understanding of the charge/discharge process of this new cobalt-free cathode material. Following these, the most promising compositional variants were upscaled using the co-precipitation process in continuous stirred tank reactors for obtaining kg levels of cathode material. Systematic optimization of reaction process variables ensured good particle morphologies, homogeneities and composition control. Electrochemical performance assessments performed in both half-cell and full-cell configurations tested in different voltage windows with upper cut-off voltages ranging from 4.1V to 4.5V demonstrated that the optimized NFA compositional variants deliver high capacities >200 mAh/g at 0.1C with good capacity retention >80% when cycled at C/3. Full pouch-cells (>1.5Ah) were then assembled using NFA electrodes fabricated using the slot-die coating technique with the upscaled cathode material demonstrating reasonable capacity retentions[3]. While the work presented here is still in an early stage of research, the immense potential that these NFA class of cathodes could have as viable candidates towards development of next generation cost effective lithium ion batteries is highlighted here. Overall, our research efforts in the development of this new class of cobalt-free cathodes aims to mitigate the battery industry's cobalt problem paving a promising pathway towards the wide adoption of electric vehicles in the coming decades.

Reversible Phase Transformations in Novel Ce‐Substituted Perovskite Oxide Composites for Solar Thermochemical Redox Splitting of CO2

AbstractThermochemical splitting of CO2 and H2O via two‐step metal oxide redox cycles offers a promising approach to produce solar fuels. Perovskite‐type oxides with the general formula ABO3 have recently gained attention as an attractive redox material alternative to the state‐of‐the‐art ceria, due to their high structural and thermodynamic tunability. A novel Ce‐substituted lanthanum strontium manganite perovskite‐oxide composite, La3+0.48Sr2+0.52(Ce4+0.06Mn3+0.79)O2.55 (LSC25M75) is introduced, aiming to bridge the gap between ceria and perovskite oxide‐based materials by overcoming their individual thermodynamic constraints. Thermochemical CO2 splitting redox cyclability of LSC25M75 evaluated with a thermogravimetric analyzer and an infrared furnace reactor over 100 consecutive redox cycles demonstrates a twofold higher conversion extent to CO than one of the best Mn‐based perovskite oxides, La0.60Sr0.40MnO3. Based on complementary in situ high temperature neutron, synchrotron X‐ray, and electron diffraction experiments, unprecedented structural and mechanistic insight is obtained into thermochemical perovskite oxide materials. A novel CO2 splitting reaction mechanism is presented, involving reversible temperature induced phase transitions from the n = 1 Ruddlesden–Popper phase (Sr1.10La0.64Ce0.26)MnO3.88 (I4/mmm, K2NiF4‐type) at reduction temperature (1350 °C) to the n = 2 Ruddlesden–Popper phase (Sr2.60La0.22Ce0.18)Mn2O6.6 (I4/mmm, Sr3Ti2O7‐type) at re‐oxidation temperature (1000 °C) after the CO2 splitting step.

Phase stability of U5Si4, USi, and U2Si3 in the uranium–silicon system

The intermetallic compound U3Si2 has received interest in recent years for use as accident tolerant fuels in light water reactors due to its combination of high thermal conductivity, reasonably high melting point, and high uranium density compared to UO2. Although U3Si2 is well characterized there are ucertainties about the remaining phases in the U–Si system which could be potential fission products of the silicide fuel. In an effort to better detail the U–Si binary phase diagram, the 44–60 at.% Si region of the U–Si phase diagram was investigated experimentally by analyzing samples with nominal compositions U/Si = 5/4, U/Si = 1/1 and U/Si = 2/3 using SEM-EDS, XRD, and high temperature time-of-flight neutron diffraction, supported by DFT calculations. Both the U/Si = 5/4 and the U/Si = 2/3 samples were composed of two phases, U3Si2 + USi and USi + U3Si5 for U/Si = 5/4 and U/Si = 2/3, respectively. Both U5Si4 and U2Si3 were found from DFT calculations to have imaginary phonon frequencies and an enthalpy of formation above the U–Si convex hull, and thus likely to be thermodynamically unstable compared to the other phases, consistent with the experimental results.In the literature there are three different structures that are proposed for the USi phase, and for the first time, high temperature neutron diffraction measurements were collected on the compound synthesized with the U/Si = 1/1 composition to verify the correct structure. The structure of the USi phase was confirmed to be tetragonal with the I4/mmm space group from room temperature to 1100 °C. The USin crystal structure has 6 U atom sites and 8 Si atoms sites of which two are partially occupied.

A novel insight into the primary creep regeneration behaviour of a polycrystalline material at high-temperature using in-situ neutron diffraction

Primary creep regeneration (PCR) is observed during cyclic creep deformation in many engineering alloys. PCR is a phenomenon in which reverse inelastic strain fully, or partially, resets the early creep strain hardening memory of the material. The current understanding regarding the origin of the PCR behaviour in engineering alloys is limited to the phenomenological observations from the changes in dislocation structures whereas a good mechanistic understanding of the PCR behaviour is crucial for developing robust plasticity-creep predictive models. In this study, we investigated the micromechanical origin of PCR behaviour in type 316H stainless steel at 650 °C using high-temperature mechanical testing and neutron diffraction. A cyclic creep experiment was conducted in-situ at a neutron diffraction beamline, during which various degrees of unloading and reverse loading were applied to the specimen, followed by creep deformation under a load above the material's yield strength. Partial PCR was observed after reverse plastic loading for all the creep dwells, which is contrary to current high-temperature lifetime assessment's procedures advice which is to account for full recovery of primary creep after any reverse plastic loading. The extent of PCR is observed to be proportional to the magnitude of reverse plastic strain up to a level of 0.5% reverse plastic strain. From the measured neutron diffraction data, a strong correlation was observed between the changes in magnitude of the accumulated intergranular residual lattice strains and the macroscopic primary creep strain. Moreover, the increases of lattice strain to saturation and transition from primary creep to secondary regime occur at the same time. Based on these correlations it can be postulated that the PCR behaviour observed due to cyclic loading in type 316H stainless steel at elevated temperature originates from the accumulation of intergranular residual lattice strains during the reverse plastic loading and those time-dependent changes during the creep dwells.

High temperature neutron diffraction investigation of U3Si2

The U-Si system is actively undergoing studies due to its promise as a component of an accident tolerant nuclear fuel. The crystal structure of the U3Si2 compound in the U-Si system was investigated as a function of temperature from room temperature to 1298 K for a sample of approximately 42.02 at.% Si composition and 1373 K for a sample with approximately 42.10 at.% Si using high temperature time-of-flight neutron diffraction on the High-Pressure Preferred Orientation (HIPPO) diffractometer at Los Alamos Neutron Science Center (LANSCE). The simultaneous Rietveld refinement of five histograms from the five HIPPO detector backs (40°, 60°, 90°, 120°, and 145°) provided datasets for the lattice parameters, anisotropic atomic displacement parameters, and atomic positions as a function of temperature.To explore the possibility of a homogeneity range, two sample compositions were analyzed, a 40.02 at.% Si (near stoichiometric) and a potentially hyperstoichiometric (40.10 at.% Si) sample. While minor differences in the anisotropic atomic displacement parameters between the two samples were observed, over the entire investigated temperature range no additional phases were found indicative of a single phase sample and the ability of the U3Si2 compound to accommodate nonstoichiometry, suggesting that the U3Si2 compound is not a line compound confirming previous determinations. However, the differences observed in the average coefficient of linear thermal expansion identified between the two compositions warrant future investigation.SynopsisHigh temperature time-of-flight neutron diffraction measurements were carried out on 2 different compositions of U3Si2 and detailed analyses of the U3Si2 crystal structure as a function of temperature to 1298 K (for a 42.02 at.% Si sample) and 1373 K (for a 42.10 at.% Si sample) were performed. Anisotropic atomic displacement parameters, bond lengths, thermal expansion, coefficient of thermal expansion, and related properties were assessed as a function of temperature as well as the location of excess Si atoms and compared with simulation predictions.

Difference in Oxide Ion Conduction Properties of Oxide Ion Excess and Cation Deficient PbWO4s and Oxide Ion Deficient CaWO4

Introduction When lanthanum ions are partly substituted for lead in PbWO4 with sheelite-type structure, high oxide ion conduction appeared at elevated temperature [1]. From the density measurement, it has been reported that oxide ion interstitials are formed for the substitution as Pb1-xLaxWO4+x/2, while Pb1-xLa2/3WO4 shows the defect structure of cation deficiency. While the former system exhibits a little higher oxide ion conduction, both systems show approximately unity of the oxide ion transport number. In recent years, it is also found that CaWO4 with the mineral name of scheelite also exhibit the oxide ion conduction by partly substituting potassium ions for calcium site as Ca1-xKxWO4-x/2. In addition to the electrochemical measurements, we have investigated the high-temperature neutron diffraction on these experiments to clarify the oxide ion conduction paths at high-temperatures. We have reported these results separately and have not compared with concerning defect structure. In the present study, we compare the conduction paths between three types of scheelite-type structured oxide ion conductors from the results of high-temperature neutron diffraction. Experimental Pb1-xLaxWO4+x/2 (x = 0.2), while Pb1-xLa2/3WO4 (x = 0.1) and Ca1-xKxWO4-x/2 (x = 0.2) were prepared by conventional solid-state reaction method started from PbO, La2O3, H2WO4, CaCO3 and K2CO3. The sintering temperatures were selected as 900ºC for PbWO4-based materials and 1000ºC for CaWO4s. The crystalline phase of the obtained samples was confirmed by X-ray diffraction. The sintered samples with the amount of c.a. 10 g are set into a vanadium holder with a thin quartz tube to prevent the reaction of sample with holder, which was mounted to the neutron diffractometer SHRPD in J-PARC. Diffracted neutrons were collected at various temperatures up to 800ºC. Structure analyses were performed by using Z-Rietveld, and the trace of nuclear density was calculated by Z-MEM. BVS calculations were also carried out based on the refined structure data. Results and Discussions Fig. 1 exhibits the nuclear density map of (a) Pb1-xLaxWO4+x/2, (b) Pb1-xLa2/3WO4 and (c) Ca1-xKxWO4-x/2 deduced by maximum entropy method based on the neutron diffraction data collected at 800ºC. For Pb1-xLaxWO4+x/2 with the oxide ion interstitials, nuclear density seems to be distributed to the interstitial site, while the latter two systems without oxide ion interstitials, much less amount of nuclear density is observed at the interstitial sites. Therefore, Pb1-xLaxWO4+x/2 system possess the three-dimensional conduction path allowing higher oxide ion conductivity at elevated temperatures. We will also discuss the conduction path in terms of the bond valence sum.

Hole doping and antiferromagnetic correlations above the Néel temperature of the topological semimetal (Sr1−xKx)MnSb2

Neutron diffraction and magnetic susceptibility studies of orthorhombic single crystal {\Ksub} confirm the three dimensional (3D) C-type antiferromagnetic (AFM) ordering of the Mn$^{2+}$ moments at $T_{\rm N}=305 \pm 3$ K which is slightly higher than that of the parent SrMnSb$_2$ with $T_{\rm N}=297 \pm 3$ K. Susceptibility measurements of the K-doped and parent crystals above $T_{\rm N}$ are characteristic of 2D AFM systems. This is consistent with high temperature neutron diffraction of the parent compound that display persisting 2D AFM correlations well above $T_{\rm N}$ to at least $\sim 560$ K with no evidence of a ferromagnetic phase. Analysis of the de Haas van Alphen magnetic oscillations of the K-doped crystal is consistent with hole doping.

Mapping the structural transitions controlled by the trilinear coupling in Ca3-xSrxTi2O7

We present the results of the high-temperature neutron and x-ray diffraction experiments on the Ca3–xSrxTi2O7 (x = 0.5, 0.8, 0.85, 0.9) compounds. The ferro- to paraelectric transition in these hybrid improper ferroelectric materials arises from the so-called trilinear coupling. Depending on the strontium content, various structures and phase transitions, different from theoretical predictions, emerge. The in situ x-ray powder diffraction indicates a direct ferro- to paraelectric transition between the orthorhombic A21am and the tetragonal undistorted I4/mmm phase for x ≤ 0.6. We identified a reduction in the trilinear coupling robustness by increasing the Sr-doping level to lead to the emergence of the intermediate tetragonal P42/mnm phase and the gradual suppression of the orthorhombic phase. The observed character of the structure transitions and the Ca3–xSrxTi2O7 phase diagram are discussed in the framework of theoretical models of other related hybrid improper ferroelectric systems.

Synthesis and Structural Determination of the Disordered Bixbyite Cu3-x Sb1+x O5.5+3x/2 with Spin-Glass Behaviour.

The ternary copper antimony oxide Cu3-x Sb1+x O5.5+3x/2 (x=0.23) has been synthesized under 0.8-1.3 MPa pO2 at 1022-1082 °C. Rietveld refinements of X-ray and neutron powder diffraction patterns concluded that the oxide adopts a bixbyite type structure, crystallising in the cubic space group Ia-3 with the unit cell parameter a=9.61164(4) Å at room temperature from powder neutron diffraction data. The cationic 8b and 24d sites were found to be occupationally disordered where both Cu and Sb could be found on both sites. This is supported by X-ray absorption spectroscopy experiments showing more than one possible Cu environment. There was a significant net deficiency of oxygen in the compound which was first inferred from observations of a thermochromic-like phenomena and also seen from in situ high temperature neutron diffraction experiments. Magnetic susceptibility and magnetization measurements show paramagnetic behaviour with spin-glass like transition below 6 K.

High-pressure neutron diffraction study of Pd3Fe

High-pressure neutron diffraction data from powder and single-crystal samples of atomically disordered (Fm3¯m) and ordered (Pm3¯m) Pd3Fe were collected up to pressures of 15 GPa, and high-pressure SQUID magnetometry data were collected up to 6 GPa. The data show a subtle decrease in the magnetic moment with applied pressure, resulting in a transition to a paramagnetic state by approximately 8 GPa at 300 K. Diffraction results have been used to determine the equation of state, resulting in a bulk modulus of 176.78(9) GPa for the disordered powder and 187.96(7) GPa for the ordered single-crystal samples, approximately 20% more compressible than previously reported from X-ray measurements. High-temperature superconducting quantum interference device magnetometry was used to confirm the ambient pressure Curie temperature of the sample (545 K), which was further investigated using high-temperature single-crystal neutron diffraction at ambient pressure.

Structural complexities and sodium-ion diffusion in the intercalates Na x TiS2: move it, change it, re-diffract it.

After momentary attention as potential battery materials during the 1980s, sodium titanium disulphides, like the whole Na–Ti–S system, have only been investigated in a slapdash fashion. While they pop up in current reviews on the very subject time and again, little is known about their actual crystal-structural features and sodium-ion diffusion within them. Herein, we present a short summary of literature on the Na–Ti–S system, a new synthesis route to Na0.5TiS2-3R1, and results of high-temperature X-ray and neutron diffractometry on this polytype, which is stable for medium sodium content. Based thereon, we propose a revision of the crystal structure reported in earlier literature (missed inversion symmetry). Analyses of framework topology, probability-density functions, and maps of the scattering-length density reconstructed using maximum-entropy methods (all derived from neutron diffraction) reveal a honeycomb-like conduction pattern with linear pathways between adjacent sodium positions; one-particle potentials indicate associated activation barriers of ca. 0.1 eV or less. These findings are complemented by elemental analyses and comments on the high-temperature polytype Na0.9TiS2-2H. Our study helps to get a grip on structural complexity in the intercalates NaxTiS2, caused by the interplay of layer stacking and Na–Ti–vacancy ordering, and provides first experimental results on pathways and barriers of sodium-ion migration.