High-resolution Neutron Diffraction Research Articles

Origin of Polarization in Bismuth Sodium Titanate-Based Ceramics.

The classical view of the structural changes that occur at the ferroelectric transition in perovskite-structured systems, such as BaTiO3, is that polarization occurs due to the off-center displacement of the B-site cations. Here, we show that in the bismuth sodium titanate (BNT)-based composition 0.2(Ba0.4Sr0.6TiO3)-0.8(Bi0.5Na0.5TiO3), this model does not accurately describe the structural situation. Such BNT-based systems are of interest as lead-free alternatives to currently used materials in a variety of piezo-/ferroelectric applications. A combination of high-resolution powder neutron diffraction, impedance spectroscopy, and ab initio calculations reveals that Ti4+ contributes less than a third in magnitude to the overall polarization and that the displacements of the O2- ions and the A-site cations, particularly Bi3+, are very significant. The detailed examination of the ferroelectric transition in this system offers insights applicable to the understanding of such transitions in other ferroelectric perovskites, particularly those containing lone pair elements.

Solid-state and sol-gel synthesis of neodymium molybdate Nd5Mo3O16+δ and study of their crystal structure in the temperature range of 300–700 K by the neutron diffraction

The solid-state and sol-gel synthesis of Nd5Mo3O16+δ neodymium molybdate has been investigated. The sequence of chemical transformations was studied using differential thermal analysis, X-ray diffraction analysis, and infrared spectroscopy. It has been demonstrated that the solid-state synthesis occurs stepwise through the formation of Nd2(MoO4)3 and phases with monoclinic structures. The using of the sol-gel method allows obtaining a single-phase neodymium molybdate directly after decomposition of the organic precursor and decreasing of the synthesis temperature by 200 K. The investigation of the crystal structure was carried out by high resolution neutron diffraction, which revealed non-uniform changes in the neodymium-oxygen interatomic distances with increasing temperature.

The impact of A-site cations on the crystal structure and magnetism of the new double perovskites ALaCoTeO6 (A = Na and K).

In this work, we report the structural and magnetic characterization of two new B-site rock-salt ordered double perovskites ALaCoTeO6 (A = K+ and Na+) with mixed A-site cations. KLaCoTeO6 crystallizes in the space group P4/nmm with a long-range ordering degree of 84.8% for the A-site K+/La3+ cations, whereas NaLaCoTeO6 adopts an unexpected triclinically distorted I1̄-structure with Na/La3+ disordering, validated by combined Rietveld refinements against high-resolution neutron diffraction data and Cu Kα1 X-ray powder diffraction data. Magnetic susceptibility at low temperatures shows clear antiferromagnetic (AFM) transitions for both compounds. KLaCoTeO6 exhibits the highest AFM transition temperature of 20 K amongst all the Co/Te-ordered 3C-type A2CoTeO6 (A = Pb2+, Sr2+, and Ca2+) and ALaCoTeO6 double perovskites due to its larger Co2+-O-Te6+ bond angle and A-site cationic ordering-induced larger distortion of the Co2+-based face-centered cubic sublattice. Moreover, we found that the average radius of the A-site cations plays a decisive role in the AFM transition temperatures of all these ordered double perovskites, that is, a larger A-site cation always results in a higher AFM transition temperature. This provides a strategy to subtly manipulate the magnetic properties of ordered double perovskites.

Magnetization process of cubic Fe3O4 submicron particles: First-order reversal curves and neutron diffraction studies

We have studied magnetization process of 260 nm sized cubic Fe3O4 particles below and above the Verwey transition temperature Tv∼ 110 K, by measurements of magnetic first-order reversal curves (FORCs) and high-resolution power neutron diffraction. The FORC diagram exhibits two distinct FORC distribution peaks below Tv, which shift towards the origin, merge into a single peak on heating, whereas only a single FORC peak appears above Tv. Neutron diffraction measurements under magnetic fields revealed a minimum of the magnetic intensity at a magnetic field of ∼−300 Oe, being close to the reversal field where the FORC peak is located. These results were interpreted as due to a reorientation and reversal of a spin vortex core, which accompany a large magnetic irreversibility.

Solid state synthesis and investigation of double oxides in х/6Pr6O11 – MoO3 (2 ≤ х ≤ 6) series

The polycrystalline samples of the x/6Pr6O11 – MoO3 (2 ≤ x ≤ 6) series were prepared by conventional solid-state route. The phase formation was studied by XRD analysis in the temperature range of 1000 – 1200 °C. After calcination at 1100 °С, the formation of praseodymium molybdate with Pr4MoO9+δ composition is observed, which decomposes into a mixture of Pr2MoO6 and Pr6MoO12+δ phases at 1200 °С. It was first established that Pr4MoO9+δ praseodymium molybdate has a monoclinic lattice with parameters a = 16.7211(9) Å, b = 11.9894(7) Å, c = 9.5588(5) Å, β = 109.6149(7) °, sp. gr. C 2/m. Crystal structure was refined by high resolution neutron diffraction data. The homogeneity regions of Pr4MoO9+δ and Pr6MoO12+δ were determined to be 4 < x < 4.2 and 4.57 < x < 6, respectively. It was shown that the conductivity of this molybdates increases with praseodymium oxide content in the Pr5Mo3O16+δ – Pr4MoO9+δ – Pr6MoO12+δ series.

Phase transition of AgTaO3 using high-resolution neutron diffraction

Phase transition of AgTaO₃ using high-resolution neutron diffraction

Unusually large magnetic moment and tricritical behavior of the CMR compound NaCr2O4 revealed with high resolution neutron diffraction and SR

The mixed valence Cr3+/Cr4+ compound NaCr2O4, hosts a plethora of unconventional electronic properties. In the present study, muon spin rotation/relaxation (SR) and high-resolution time-of-flight neutron powder diffraction measurements were carried out on high-quality samples to clarify the complex magnetic ground state of this unique material. We identified a commensurate canted antiferromagnetic order (C-AFM) with a canting angle of the Cr spin axial vector equal to , and an estimated Cr moment . Such an unusually large value of is compatible with the existence of high-spin Cr sites created by the presence of an unconventional negative charge transfer state in NaCr2O4. In addition to the C-AFM structure, a novel magnetic supercell was also revealed. Such supercell display an incommensurate (IC)-AFM propagation vector (0 0 ), having a Cr moment . It is suggested that the C-AFM and IC-AFM modulations have two different electronic origins, being due to itinerant and localized contributions to the magnetic moment respectively. Finally, the direct measurement of the magnetic order parameter for the C-AFM structure provided a value of the critical exponent , suggesting a non conventional critical behavior for the magnetic phase transition in NaCr2O4.

Li3–xZrx(Ho/Lu)1–xCl6 Solid Electrolytes Enable Ultrahigh-Loading Solid-State Batteries with a Prelithiated Si Anode

We report two new families of lithium metal chloride solid electrolytes Li3–xZrx(M)1–xCl6 (0 ≤ x ≤ 0.8; M = Ho or Lu) with ionic conductivities of up to 1.8 mS cm–1 and a low activation energy of 0.34 eV. Structural elucidation via high-resolution neutron diffraction determines the Li ion distribution in trigonal Li3HoCl6, orthorhombic-I Li3LuCl6, and orthorhombic-II Li2.4Zr0.6(Ho/Lu)0.4Cl6. The last compound exhibits well-connected Li-ion pathways and abundant Li-ion carriers/vacancies to promote diffusion. All-solid-state batteries with Li2.6Zr0.4(Ho/Lu)0.6Cl6 solid electrolytes and NCM85 cathodes exhibit stable cycling up to 4.6 V vs Li+/Li, which is even preserved up to 4.8 V. Stable cathode interphases are formed for both electrolytes upon cycling to 4.3, 4.6, and 4.8 V cutoff potentials, as identified by a ToF-SIMS analysis. Solid-state cells with a prelithiated Li0.7Si anode exhibit a significantly increased initial coulombic efficiency of 94.5% compared to Si and a high areal capacity of up to 16.3 mAh·cm–2.

Structural and Photoluminescence Characterization of Oxyfluorides for Phosphor Applications

ConspectusRare-earth-containing phosphors were crucial to the advances made to compact fluorescent lamps (CFLs), which assisted in protecting a widely used halophosphate phosphor from degrading after exposure to a high ultraviolet flux. The CFL phosphors are often coated twice by depositing a light coat of rare-earth-containing phosphors over the inexpensive halophosphate phosphor, which generates white light with high efficacy and a good color rendering index and possesses a balance between phosphor cost and performance. Costs of phosphors can be mitigated by requiring lower rare-earth ion concentrations or by completely eliminating rare-earth ions, which was one of the main goals of investigating the oxyfluorides Sr3AlO4F and Ba2SrGaO4F as potential phosphors. Changes in the Sr3AlO4F and Ba2SrGaO4F structures were studied using high-resolution neutron diffraction annealing these materials in 5%H2/95%Ar and 4%H2/96% Ar, respectively. Annealing in these atmospheres causes self-activated photoluminescence (PL) to occur under 254 nm light, which makes them ideal materials for rare-earth-free CFL phosphors. Additionally, these hosts possess two distinct sites for isovalent or aliovalent substitution of Sr denoted as the A(1) and A(2) sites. Ga3+ can be substituted for Al3+ at the M site, which is known to have an impact on the self-activated PL emission color. The structural distortions noted included closer packing in the FSr6 octahedrons and AlO4 tetrahedrons in the Sr3AlO4F structure as compared to in air-annealed samples, which show no PL emission. Temperature-dependent studies reveal that both the air- and reductively annealed samples have identical thermal expansion within this temperature range (3-350 K). High-resolution neutron diffraction at room temperature confirmed the tetragonal structure (I4/mcm) for Ba2SrGaO4F, a novel material in the Sr3AlO4F family of materials, has been synthesized via a solid-state method. Analysis of the refined Ba2SrGaO4F structure at room temperature revealed expansion in the lattice parameters and its polyhedral subunits between the reductively annealed and air-annealed samples, which are correlated with the PL emission. Previous studies related to the application of these host structure types revealed that they have potential as commercial solid-state lighting phosphors due to their ability to resist thermal quenching as well as accommodate various levels of substitutions that will assist with color tunability.

Sawtooth lattice multiferroic BeCr2O4 : Noncollinear magnetic structure and multiple magnetic transitions

Noncollinear magnetic structures and multiple magnetic phase transitions in a sawtooth lattice antiferromagnet consisting of ${\mathrm{Cr}}^{3+}$ are experimentally identified in this work, thereby proposing the scenario of magnetism-driven ferroelectricity in a sawtooth lattice. The title compound, ${\mathrm{BeCr}}_{2}{\mathrm{O}}_{4}$, displays three magnetic phase transitions at low temperatures---at ${T}_{N1}\ensuremath{\approx}7.5$ K, at ${T}_{N2}\ensuremath{\approx}25$ K, and at ${T}_{N3}\ensuremath{\approx}26$ K---revealed through magnetic susceptibility, specific heat, and neutron diffraction in this work. These magnetic phase transitions are found to be influenced by externally applied magnetic fields. Isothermal magnetization curves at low temperatures below the magnetic transitions indicate the antiferromagnetic nature of ${\mathrm{BeCr}}_{2}{\mathrm{O}}_{4}$ with two spin-flop-like transitions occurring at ${H}_{c1}\ensuremath{\approx}29$ kOe and ${H}_{c2}\ensuremath{\approx}47$ kOe. Our high-resolution x-ray and neutron diffraction studies, performed on single crystal and powder samples, unambiguously determined the crystal structure as orthorhombic $Pbnm$. By performing the magnetic superspace group analysis of the neutron diffraction data at low temperatures, the magnetic structure in the temperature range ${T}_{N3,N2}&lt;T&lt;{T}_{N1}$ is determined to be the polar magnetic space group $P21nm.{1}^{\ensuremath{'}}(00g)0s0s$ with a cycloidal magnetic propagation vector ${\mathbf{k}}_{1}=(0,0,0.090(1))$. The magnetic structure in the newly identified phase below ${T}_{N1}$ is determined as $P21/b.{1}^{\ensuremath{'}}[b](00g)00s$ with the magnetic propagation vector ${\mathbf{k}}_{2}=(0,0,0.908(1))$. The cycloidal spin structure determined in our work is usually associated with electric polarization, thereby making ${\mathrm{BeCr}}_{2}{\mathrm{O}}_{4}$ a promising multiferroic belonging to the sparsely populated family of sawtooth lattice antiferromagnets.

What Determines the Critical Electric Field of AFE-to-FE in Pb(Zr,Sn,Ti)O3-Based Perovskites?

Electric-field-induced antiferroelectric-ferroelectric (AFE-FE) phase transition is a prominent feature of antiferroelectric (AFE) materials. The critical electric field of this phase transition is crucial for the device performance of AEFs in many applications, but the determining factor of the critical electric field is still unclear. Here, we have established the correlation between the underlying structure and the critical electric field by using in situ synchrotron X-ray diffraction and high-resolution neutron diffraction in Pb(Zr,Sn,Ti)O3-based antiferroelectrics. It is found that the critical electric field is determined by the angle between the average polarization vector in the incommensurate AFE state and the [111]P polarization direction in the rhombohedral FE state. A large polarization rotation angle gives rise to a large critical electric field. Further, density functional theory (DFT) calculations corroborate that the lower energy is required for driving a smaller angle polarization rotation. Our discovery will offer guidance to optimize the performance of AFE materials.

Unusual Changes of C−H Bond Lengths in Chiral Zinc Complexes Induced by Noncovalent Interactions

AbstractIn order to better understand the effect of non‐covalent weak interactions on molecules, we have explored a variety of weak interactions, such as improper H‐bonding (HB), tetrel bonds (TBs) and halogen bonds, in fluorinated chiral zinc complexes. High resolution neutron diffraction studies revealed a methylene carbon‐hydrogen bond elongation and shortening due to TB and improper HB interactions, respectively. To show the accumulative effects of multiple weak interactions on the C−H bond, three types of tetrel bonds have been carefully examined. We have also shown how C−H bond elongation can be easily offset by forming an improper HB with the H atom from this C−H bond. Non‐covalent interaction and electrostatic potential analysis investigations have been used to affirm the nature of the interactions based on density functional theory (DFT) and other related calculations.

Unusual Changes of C−H Bond Lengths in Chiral Zinc Complexes Induced by Noncovalent Interactions

AbstractIn order to better understand the effect of non‐covalent weak interactions on molecules, we have explored a variety of weak interactions, such as improper H‐bonding (HB), tetrel bonds (TBs) and halogen bonds, in fluorinated chiral zinc complexes. High resolution neutron diffraction studies revealed a methylene carbon‐hydrogen bond elongation and shortening due to TB and improper HB interactions, respectively. To show the accumulative effects of multiple weak interactions on the C−H bond, three types of tetrel bonds have been carefully examined. We have also shown how C−H bond elongation can be easily offset by forming an improper HB with the H atom from this C−H bond. Non‐covalent interaction and electrostatic potential analysis investigations have been used to affirm the nature of the interactions based on density functional theory (DFT) and other related calculations.

Investigating the Li+ substructure and ionic transport in Li10GeP2-xSbxS12 (0 ≤ x ≤ 0.25).

Understanding the correlation between ionic motion and crystal structure is crucial for improving solid electrolyte conductivities. Several substitution series in the Li10GeP2S12 structure have shown a favorable impact on the ionic conductivity, e.g. the replacement of P(+V) by Sb(+V) in Li10GeP2S12. However, here the interplay between the structure and ionic motion remains elusive. X-Ray diffraction, high-resolution neutron diffraction, Raman spectroscopy and potentionstatic impedance spectroscopy are employed to explore the impact of Sb(+V) on the Li10GeP2S12 structure. The introduction of antimony elongates the unit cell in the c-direction and increases the M(1)/P(1) and Li(2) polyhedral volume. Over the solid solution range, the Li+ distribution remains similar, an inductive effect seems to be absent and the ionic conductivity is comparable for all compositions. The effect of introducing Sb(+V) in Li10GeP2S12 cannot be corroborated.

New Insights into the Volume Isotope Effect of Ice Ih from Polarizable Many-Body Potentials.

The anomalous volume isotope effect (VIE) of ice Ih is calculated and analyzed based on the quasi-harmonic approximation to account for nuclear quantum effects in the Helmholtz free energy. While a lot of recently developed polarizable many-body potential functions give a normal VIE contrary to experimental results, we find that one of them, MB-pol, yields the anomalous VIE in good agreement with the most recent high-resolution neutron diffraction measurements─better than DFT calculations. The short-range three-body terms in the MB-pol function, which are fitted to CCSD(T) calculations, are found to have a surprisingly large influence. A vibrational mode group decomposition of the zero-point pressure together with a hitherto unconsidered benchmark value for the intramolecular stretching modes of H2O ice Ih obtained from Raman spectroscopy data unveils the reason for the VIE: a delicate competition between the latter and the librations.

Design of High-Performance Solid Electrolytes Guided By Crystal Structure Characterization and Understanding

Solid electrolyte is the key component in all-solid-state-batteries that is currently limiting the commercialization of this technology. An ideal solid electrolyte should have high room temperature ionic conductivity, low electronic conductivity, good compatibility with both cathode and anode, good mechanical properties, high air and moisture stability and low manufacture cost. Among these requirements, the improvement of ionic conductivity is prioritized as the conductivity of most existing solid electrolyte is still much lower than that of conventional liquid electrolyte.The improvement of ionic conductivity and design and development of solid electrolyte materials are closely related to our understanding on the ionic diffusion mechanism in solids and the structure-property relationship. We believe that rational design of high-performance solid electrolyte should start from careful characterization and good understanding of the crystal structure. Here we report the crystal structure characterization on sulfides and halide solid electrolytes and the design and development of novel solid electrolytes based on our findings in structural characterizations. Ex situ high resolution synchrotron X-ray and neutron diffraction and pair distribution function analysis are used to understand the crystal structures in great details. In situ X-ray diffraction for different synthesis methods is coupled with variable temperature electrochemical impedance spectroscopy to understand the structure-property relationship in the solid electrolytes. The design, synthesis and electrochemical evaluation of several solid electrolytes will be presented and discussed.

Bulk vs. surface structural phases in Fe-27Ga alloy

The crystal structure of the bulk quenched Fe-27Ga alloy has been studied using high-resolution neutron and X-ray diffraction to determine the phase distribution over the volume of the material. Neutron diffraction results have shown that the bulk sample consists of completely ordered D03 phase. X-ray diffraction (XRD) with a long acquisition time has allowed investigating precisely the surface layer with a thickness of ∼ 4–16 µm after surface preparation by different methods. The obtained results have confirmed the presence of the ordered D03 phase. Additionally, the required mechanical and/or chemical treatments of the sample for the XRD experiments led to the formation of extra phases with less ordered structures, B2 and A2, in the surface layer. It has been found that the ratio and volume fraction of the additional phases depend on contact duration of the alloy with the air atmosphere. Existence of significant amounts of m-D03 phase, which is considered by several authors to be responsible for the giant magnetostriction of Fe-Ga alloy, is excluded by both neutron and XRD data.

Energy landscape for Li-ion diffusion in the garnet-type solid electrolyte Li6.5La3Zr1.5Nb0.5O12 (LLZO-Nb)

Abstract A comprehensive understanding of the nexus of diffusion mechanisms on the atomic scale as well as structural influences on the ionic motion in solid electrolytes is key for further development of high-performing all-solid-state batteries. Therefore, current research not only focuses on the search for innovative materials, but also on the study of diffusion pathways and ion dynamics in ionic conductors. In this context, we report on the extended characterization of the ionic electrolyte Li6.5La3Zr1.5Nb0.5O12 (LLZO-Nb). The commercially available material is analyzed by a combination of powder X-ray (either lab- or synchrotron-based) and neutron diffraction. Details of lithium disorder were obtained from high-resolution neutron diffraction data, from which the ionic transport of Li ions was determined by applying the maximum entropy method in combination with the one-particle potential formalism.

Structural phase transition in cobalt oxyfluoride Co3Sb4O6F6 observed by high-resolution synchrotron and neutron diffraction

A structural transition was observed in non-centrosymmetric oxyfluoride Co3Sb4O6F6 at TS ∼180 K from a cubic phase (I4‾3m) to a c > a tetragonal phase (I4‾), through high-resolution neutron and synchrotron powder diffraction. In addition, specific heat, magnetization, and dielectric measurements were performed to investigate this phase transition. Although the specific heat and dielectric constant showed anomalies at TS, no transition to a ferroelectric phase was observed in the polarization hysteresis loop down to 30 K. Moreover, a magnetic structure analysis using neutron powder diffraction data revealed a transition from a paramagnetic phase to a G-type antiferromagnetic phase at TN ∼67 K, at which a peak was also observed in the specific heat measurements. The magnetic moments of Co2+ were aligned along the tetragonal c-axis with a Co2+ moment of 2.80(1) μB at 13 K. The rotation and deformation of the CoO2F4 octahedron due to the large displacement of F atoms were observed at TS from the structural analysis, which play an important role in the structural phase transition in Co3Sb4O6F6.

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.