High-resolution Synchrotron X-ray Diffraction Research Articles

Quantifying magnetic anisotropy using X-ray and neutron diffraction

In this work, the magnetic anisotropy in two iso-structural distorted tetrahedral Co(II) complexes, CoX 2tmtu2 [X = Cl(1) and Br(2), tmtu = tetra-methyl-thio-urea] is investigated, using a combination of polarized neutron diffraction (PND), very low-temperature high-resolution synchrotron X-ray diffraction and CASSCF/NEVPT2 ab initio calculations. Here, it was found consistently among all methods that the compounds have an easy axis of magnetization pointing nearly along the bis-ector of the compression angle, with minute deviations between PND and theory. Importantly, this work represents the first derivation of the atomic susceptibility tensor based on powder PND for a single-molecule magnet and the comparison thereof with ab initio calculations and high-resolution X-ray diffraction. Theoretical ab initio ligand field theory (AILFT) analysis finds the d xy orbital to be stabilized relative to the d xz and d yz orbitals, thus providing the intuitive explanation for the presence of a negative zero-field splitting parameter, D, from coupling and thus mixing of d xy and . Experimental d-orbital populations support this interpretation, showing in addition that the metal-ligand covalency is larger for Br-ligated 2 than for Cl-ligated 1.

Phase Analysis of Australian Uranium Ore Concentrates Determined by Variable Temperature Synchrotron Powder X-ray Diffraction.

The chemical speciation of uranium oxides is sensitive to the provenance of the samples and their storage conditions. Here, we use diffraction methods to characterize the phases found in three aged (>10 years) uranium ore concentrates of different origins as well as in situ analysis of the thermally induced structural transitions of these materials. The structures of the crystalline phases found in the three samples have been refined, using high-resolution synchrotron X-ray diffraction data. Rietveld analysis of the samples from the Olympic Dam and Ranger uranium mines has revealed the presence of crystalline α-UO2(OH)2, together with metaschoepite (UO2)4O(OH)6·5H2O, in the aged U3O8 samples, and it is speculated that this forms as a consequence of the corrosion of U3O8 in the presence of metaschoepite. The third sample, from the Beverley uranium mine, contains the peroxide [UO2(η2-O2)(H2O)2] (metastudtite) together with α-UO2(OH)2 and metaschoepite. A core-shell model is proposed to account for the broadening of the diffraction peaks of the U3O8 evident in the samples.

Magnetic and transport properties of the mixed 3d–5d–4f double perovskite Sm2CoIrO6

Iridium-based double perovskites having mixed 3d–5d–4f magnetic sub-lattices are expected to exhibit exotic magnetic phenomenon. In this paper, we report a study of structural, magnetic and transport properties of the mixed 3d–5d–4f double perovskite Sm2CoIrO6 (SMCO), which crystallizes in monoclinic structure with space group P21/n and the crystal symmetry remains same throughout the measured temperature down to 15 K. High resolution synchrotron x-ray diffraction reveals an isostructural phase transition around 104 K. Magnetization measurements on polycrystalline samples indicate that SMCO orders ferrimagnetically at T FiM = 104 K; while, a second transition is observed below 10 K due to the rare-earth (Sm3+) ordering. The ferrimagnetic transition is well-understood by Néel's two-sublattice model, which is primarily ascribed to antiferromagnetic coupling between Co2+ and Ir4+ sub-lattices. Electronic transport measurement shows the insulting behaviour of SMCO, which follows Mott variable-range hopping conduction mechanism. However, dielectric measurements as a function of temperature rules out the presence of magneto dielectric coupling in this compound.

X-ray Crystal Structure Analysis of Magnetoelectric Metal UNi4B

The crystal structure of the magnetoelectric metal UNi4B was determined from high-resolution synchrotron X-ray diffraction experiments using single-crystalline samples. The direct method and the least-square refinement indicate a structural model with the space group Cmcm (no. 63, \(D_{2h}^{17}\)), where U atoms form a pseudo-triangular lattice in the U–Ni–B layers stacking along the a-axis alternately with the Ni layers. The refined values of the structural parameters including anisotropic atomic displacement parameters are provided for all atoms in the unit cell. The obtained structural model is discussed in terms of the magnetoelectric effect reported for this compound.

High magnetic coercive field in Ca‐Al‐Cr substituted strontium hexaferrite

The structural and magnetic properties of Sr0.67Ca0.33Fe9Al3−xCrxO19 submicrometric powders with substitution levels ranging from x = 0 up to x = 3, prepared by sol-gel synthesis method, have been investigated. The powders were characterized by high resolution synchrotron X-ray diffraction, scanning electron microscopy, powder neutron diffraction and MPMS-SQUID magnetometer. The structural analysis shows that upon Ca-substitution of SrFe12O19 at the Sr site and Al–Cr at the Fe sites, the magnetoplumbite structure is preserved, even for large levels of substitutions. The X-ray powder diffraction peak broadening and Williamson-Hall plots analyses indicate an increase of crystallites size and relaxation of the microstrain with increasing amounts of Chromium. The magnetic hysteresis loops reveal high coercivity fields at room temperature, with the highest value of HC = 1125 kA/m (1.41 T) obtained for Sr0.67Ca0.33Fe9Al2.5Cr0.5O19 powder interesting to develop free-Rare Earth high coercivity magnets. The saturation magnetization and remanence values increase monotonically with increasing Cr content while the switching field decreases. The structural Rietveld refinement of combined X-ray/neutron diffraction data shows the affinity of Al3+ and Cr3+ cations to migrate mainly towards (2a) Fe-Oh2 and (12k) Fe-Oh3 sites and only minor amounts is found on the (4f1) Fe-Oh1 octahedral sites. The structural observations corroborate the magnetic properties, demonstrating a correlation between the structure and magnetic properties in Ca–Al–Cr substituted strontium hexaferrite. The role of the particle size to maximize the coercivity properties is discussed.

Xuite, Ca3Fe2[(Al,Fe)O3(OH)]3, a new mineral of the garnet group: Implications for the wide occurrence of nanominerals

Abstract Xuite, Ca3Fe2[(Al,Fe)O3(OH)]3, is a new member of the garnet supergroup discovered in basaltic scoria from Menan Volcanic Complex, Idaho, U.S.A. Oxidation of Fe-bearing pyroclasts at high temperatures led to the formation of xuite, together with luogufengite, valleyite, and hematite. The measured crystal size of xuite ranges from ~200 to 800 nm. The empirical chemical formula of xuite is (Ca0.92Mg0.08)3(Fe0.96Ti0.04)2[(AlO4H)0.44(FeO4H)0.33 (SiO4)0.05(☐O4H4)0.18]3. Xuite has a space group of Ia3d; its unit-cell parameter refined from high-resolution synchrotron X-ray diffraction (XRD) data is a = 12.5056(5) Å, with Z = 8 (calculated density = 3.53 g/cm3). Fourier-transform infrared spectroscopy spectrum of xuite shows absorption bands at 3682 and 3579 cm−1, indicating the presence of OH– in the hydrogarnet structure. In situ high-temperature synchrotron XRD combined with thermogravimetry and differential scanning calorimetry reveals that xuite undergoes dehydroxylation to form brownmillerite (Ca2FeAlO5) from ~236 to ~396 °C. Xuite occurs in the form of nanocrystals with a soft magnetic property, which provides important insights into the origin of basaltic scoria and associated paleomagnetism. Xuite was also found in Wyoming paralava, suggesting the possibility of its wide occurrence in various geological environments. The mineral was named after Huifang Xu and Hongwu Xu in honor of their sustained contributions to mineral sciences.

P2-Na2/3Mn0.8M0.1M′0.1O2 (M = Zn, Fe and M′ = Cu, Al, Ti): A Detailed Crystal Structure Evolution Investigation

Incorporation of various transition metals has been shown to improve the electrochemical performance of Mn-rich Na-ion cathode materials. A greater comprehension of the role of dopant ions, particularly with regard to Mn-rich layered oxides as materials for the positive electrode of Na-ion batteries, is required for their continual development. Here two similar series of Mn-rich P2 cathode materials P2-Na2/3Mn0.8M0.1M′0.1O2 (M = Fe, Zn and M′ = Cu, Al, Ti) are explored, focusing on structural analysis using high-resolution operando synchrotron X-ray diffraction. Notably, under the cycling conditions employed, no P2 to O2 phase transitions toward the charged state were identified for any of the materials investigated. Particularly stable solid solution evolution was observed for P2-Na2/3Mn0.8Zn0.1Cu0.1O2 and P2-Na2/3Mn0.8Zn0.1Al0.1O2 when cycled at 40 mA.g–1 which reflects the electrochemical properties of the materials investigated herein and illustrates that Zn is an excellent choice of dopant for Mn-rich cathode materials. Moreover, the better cyclability of P2-Na2/3Mn0.8Zn0.1Al0.1O2 compared with P2-Na2/3Mn0.8Zn0.1Cu0.1O2 is in keeping with the minimal structural changes observed. This demonstrates that although oxidation state predictions to optimize the initial Mn oxidation state are a good way of initially selecting materials, to truly exploit Mn-rich P2-type materials it is necessary to build up an in-depth understanding of both oxidation states and the associated Jahn–Teller distortion as well as the subtle interplay of synergistic and antagonistic interactions between dopants. Overall, this study illustrates the value of structural investigations to assist in the rational design and validation of novel high-performance materials; the results highlight that the interplay between dopants in addition to the average Mn oxidation state are both crucial considerations when designing high-performance Mn-rich layered oxide materials.

R3(Fe,T)29 intermetallic compounds - Magnetoelastic coupling in Sm3(CoxFe1-x)29-yCry

The thermal expansion of the rare earth intermetallic compounds Sm3(CoxFe1-x)29-yCry (x = 0.9, y = 7; x = 0.8, y = 6.5; x = 0.7, y = 6) have been systematically investigated by high resolution synchrotron x-ray diffraction measurements (~120–480 K; ~ 300–823 K). The magnetic and thermal properties of Sm3(Fe0.9Co0.1)24Cr4 have been studied as a typical example of the Sm3(CoxFe1-x)29-yCry system by magnetic measurements (ac susceptibility, ~ 5–300 K; DC magnetisation, ~ 77–650 K) and specific heat measurements (~2–300 K). The Debye temperature of Sm3(Co0.9Fe0.1)22Cr7 was found to be θD = 410 ± 10 K from analyses of the specific heat data while the density of states at the Fermi level was N(EF) = 5.08 ± 0. 04 ev−1 atom−1. A pronounced contribution of the nuclear specific heat of Sm3(Co0.9Fe0.1)22Cr7 is evident below 5 K with the nuclear specific heat coefficient found to be A = 758 ± 30 mJ mol−1 K−1. Rietveld analyses of the x-ray diffraction data demonstrate the remarkable magneto-volume anomalies of Sm3(CoxFe1-x)29-yCry around their Curie temperatures TC with negative values of the volume magnetostriction detected below the Curie temperatures and values in the range ωs = − 1.1 × 10−3 to ωs = − 4.3 × 10−3 at 300 K.

Cyan-Light-Emitting Chalcogenometallate Phosphor, KGaS2:Eu2+, for Phosphor-Converted White Light-Emitting Diodes.

A novel KGaS2 phosphor host that emits a cyan light was discovered to fill the cyan gap in the visible spectrum of phosphor-converted white light-emitting diodes (pc-wLEDs). KGaS2, belonging to the chalcogenometallates of the type ABQ2, was synthesized via a solid-state route with compositions optimized to achieve a phosphor host that would achieve the best photoluminescence (PL) properties. The activation with Eu2+ gave rise to PL in the cyan region of the spectrum with a PL maximum at ∼498 nm, as measured under the near-UV (420 nm) and blue (450 nm) excitations. The PL properties at the near-UV excitation are found to be much better, as compared to those obtained at the blue excitation. The Rietveld analysis, using high resolution synchrotron X-ray diffraction calibrated at a wavelength of 1.522 Å and selected area electron diffraction (SAED) pattern analysis of the composition optimized with the highest PL intensity, revealed a centrosymmetric monoclinic structure in the C2/c space group. The stoichiometry of the optimized composition, as estimated using Rietveld refinement, was revealed as KGa0.921S1.882:Eu2+. The decay curve measurement, using time-resolved spectroscopy, yielded a 10% decay time of 0.41 μs, which is much smaller compared with the decay time of the commercially available β-SIALON phosphor that has a 10% decay time of 1.71 μs. The white pc-LED, fabricated with a cyan phosphor, had a higher value on the color rendering index and a lower value for color correlated temperatures, as compared with the version fabricated without a cyan phosphor, which makes this novel phosphor suitable for applications as a pc-wLED.

Towards cubic symmetry for Ir4+ : Structure and magnetism of the antifluorite K2IrBr6

Crystal structure, electronic state of Ir$^{4+}$, and magnetic properties of the antifluorite compound K$_2$IrBr$_6$ are studied using high-resolution synchrotron x-ray diffraction, resonant inelastic x-ray scattering (RIXS), thermodynamic and transport measurements, and ab initio calculations. The crystal symmetry is reduced from cubic at room temperature to tetragonal below 170 K and eventually to monoclinic below 122 K. These changes are tracked by the evolution of the non-cubic crystal-field splitting $\Delta$ measured by RIXS. Non-monotonic changes in $\Delta$ are ascribed to the competing effects of the tilt, rotation, and deformation of the IrBr$_6$ octahedra as well as tetragonal strain on the electronic levels of Ir$^{4+}$. The N\'eel temperature of $T_N=11.9$ K exceeds that of the isostructural K$_2$IrCl$_6$, and the magnitude of frustration on the fcc spin lattice decreases. We argue that the replacement of Cl by Br weakens electronic correlations and enhances magnetic couplings.

Crystal Structure of Moganite and Its Anisotropic Atomic Displacement Parameters Determined by Synchrotron X-ray Diffraction and X-ray/Neutron Pair Distribution Function Analyses

The crystal structure of moganite from the Mogán formation on Gran Canaria has been re-investigated using high-resolution synchrotron X-ray diffraction (XRD) and X-ray/neutron pair distribution function (PDF) analyses. Our study for the first time reports the anisotropic atomic displacement parameters (ADPs) of a natural moganite. Rietveld analysis of synchrotron XRD data determined the crystal structure of moganite with the space group I2/a. The refined unit-cell parameters are a = 8.7363(8), b = 4.8688(5), c = 10.7203(9) Å, and β = 90.212(4)°. The ADPs of Si and O in moganite were obtained from X-ray and neutron PDF analyses. The shapes and orientations of the anisotropic ellipsoids determined from X-ray and neutron measurements are similar. The anisotropic ellipsoids for O extend along planes perpendicular to the Si-Si axis of corner-sharing SiO4 tetrahedra, suggesting precession-like movement. Neutron PDF result confirms the occurrence of OH over some of the tetrahedral sites. We postulate that moganite nanomineral is stable with respect to quartz in hypersaline water. The ADPs of moganite show a similar trend as those of quartz determined by single-crystal XRD. In short, the combined methods can provide high-quality structural parameters of moganite nanomineral, including its ADPs and extra OH position at the surface. This approach can be used as an alternative means for solving the structures of crystals that are not large enough for single-crystal XRD measurements, such as fine-grained and nanocrystalline minerals formed in various geological environments.

Bayesian analysis reveals the impact of load partitioning on microstructural evolution in Ti-6Al-4V during in-situ tensile loading

An in-situ high-resolution synchrotron X-ray diffraction (XRD) experiment is used to measure microstructural damage accumulation (DA) during loading of an extruded sample of the α−β titanium alloy Ti-6Al-4V. A Bayesian analysis is utilised to quantify the DA by extracting microstructure distributions and their evolution from XRD line-profile data as the sample undergoes monotonic tensile loading. The Bayesian results are evaluated independently against extensive transmission electron microscopy (TEM) measurements of the starting and deformed material.An understanding of the evolution of microstructural DA prior to crack formation is critical to aero-engine critical rotating parts. This information can be incorporated in fatigue lifing models to reduce uncertainty and improve prediction.

Zero Thermal Expansion in Ta2Mo2O11 by Compensation Effects.

Although zero thermal expansion (ZTE) materials have broad application prospects for high precision engineering, they are rare. Here, a new ZTE material, Ta2Mo2O11 (αl = 0.37 × 10-6 K-1, 200-600 K), is reported. A joint study of high-resolution synchrotron X-ray diffraction, temperature- and pressure-dependent Raman spectroscopy, and first-principles calculations was performed to investigate the structure and dynamics of Ta2Mo2O11 with the aim of understanding its ZTE mechanism. Ta2Mo2O11 displays a layered structure, stacking along the [001] direction. Analysis of the phonon modes indicates that positive and negative contributions to thermal expansion are balanced, and a shrinkage occurs along the layers, while the interlayer distance expands with increasing temperature, thus giving rise to the ZTE behavior of Ta2Mo2O11. The present study provides a promising ZTE material and new insights into the mechanisms of thermal expansion.

A Promising Positive Electrode Material for Na+/Li+ Hybrid-Ionbatteries: Monoclinic-Orthorhombic Na1.1Li2.0V2(PO4)3/C Composite

In this paper, we report a new single death-to-fire Na1.1Li2.0V2 (PO4) 3 / C (NLVP / C) compound cathode synthesized from a mono-clinical LVP through a soft ion exchange reaction for use in Na+/Li+ hybrid ion batteries. Thermal studies, High Resolution Synchrotron X-ray diffraction (XRD), and electrochemical data check the room temperature stabilization of the monoclinic-orthorhombic NLVP / C composite phase. In particular, we report application of monoclinic orthorhombic NLVP / C composite as positive materials in Na half-cell. This monoclinic-orthorhombic NLVP/C composite cathode delivered a discharge capacity of 115 mAh g−1 with an average discharge potential of 3.47 V. Corresponding in situ synchrotron XRD patterns recorded during initial electrochemical cycling clearly indicate a series of two-phase transitions and confirm the structural stability of the NLVP/C composite cathode during insertion and extraction of the hybrid ions. In addition, the estimated average working potential and energy density at the initial cycle for the monoclinic orthorhombic NLVP/C composite cathode (3.47 V vs Na/Na+ and 102.5 Wh kg−1, respectively) are higher compared with those of the pyro-synthesized rhombohedral Na3V2(PO4)3 (3.36 V vs Na/Na+ and 88.5 Wh kg−1) cathode. Thus, this study shows the feasibility of using a soft ion-exchange reaction at 150 °C to facilitate the formation of composite phases suitable for rechargeable hybrid-ion battery applications.

Structure, thermal stability, optoelectronic and electrophysical properties of Mg- and Na-codoped bismuth niobate pyrochlores: Experimental and theoretical study

Novel bismuth niobates Bi1.5Mg1–xNaxNb1.5O7–δ and Bi1.5Mg0.9–xNaxNb1.5O7–δ (0 ≤ x ≤ 0.50) with the pyrochlore structure have been investigated experimentally and theoretically. The compounds were synthesized by an organic-inorganic precursors combustion method. The pyrochlore structure was formed at x = 0.10; 0.25 for cation completed and 0.25; 0.40 for cation deficient compositions, respectively. From differential scanning calorimetry (DSC) and thermogravimetry (TG), the thermal stability of the compounds up to their melting points (1250–1270 °C) was concluded. The single-crystal forms of the pyrochlores can be easily obtained from the melts. Structural characterization was performed using a Rietveld refinement against X-ray diffraction (XRD) as well as the simultaneous refinement using high resolution neutron powder diffraction (NPD) and synchrotron X-ray diffraction (SXRD) data. According to the results, the displacements of A (from 16c to 96g) and O′ (from 8a to 32e or 96g) atoms from ideal pyrochlore sites as well as the Na atoms distribution in the bismuth sub-structure, and the Mg atoms in the niobium sub-structure were determined. The same distribution of dopants in the structure was proven by DFT-PBE simulations of crystal structure and thermodynamic properties. The most preferable (Bi1.5Mg0.5)(Nb1.5Mg0.5)O7 and (Bi1.5Na0.5)(Nb1.5Mg0.5)O7 models were predicted. Both calculated/experimental direct band gap values were found to decrease from Mg-doping (3.20/3.21 eV) to Mg, Na-codoping (3.16/3.15 eV). The electrical properties were investigated by impedance spectroscopy method in air, in oxygen, and humid atmospheres in the temperature range of 25–750 °C. The typical dielectric behavior of the compounds up to 200 °C was detected. With the Na content rising the increasing of ε′ values from 86 (x = 0) to 145 (x = 0.4) was revealed at the same tanδ ≈ 0.0025 (1 MHz, 25 °C). Calculated temperature coefficients of capacitance (TCC) values varied from −594 to −724 ppm/°C (25–280 °C). Besides, contribution from electronic conductivity (T < 360 °C), proton transport below 360–400 °C as well as the ionic (oxygen) conductivity at T > 400 °C were observed.

Synchrotron high-resolution XRD and thermal expansion of synthetic Mg calcites

The structural parameters and the thermal behavior of a complete series of Ca–Mg carbonates synthesized at high pressure and temperature (1–1.5 GPa, 1273–1373 K) in the range 0–50 mol% MgCO3 have been investigated by in situ powder synchrotron high-resolution X-ray diffraction at ambient and up to 1073 K under self-controlled CO2 partial pressure. The crystal structures are disordered Mg calcite in the range 1–41 mol% MgCO3, and Ca dolomite at 49 mol% MgCO3. New calibration curves of the cell parameters for the Mg content and thermal expansion from ambient to 1073 K are given. Short-range structural effects of cation substitution and ordering and their thermal behavior as a function of Mg content were identified from three sets of data: the peak broadening, the cell parameter strains and the Raman band enlargements. Both intra- and inter-crystalline levels of compositional heterogeneity are identified and allow splitting the Mg calcites into two groups: low- and high-Mg calcites. The low-Mg calcites (up to 22 mol% MgCO3) are homogeneous in Mg content with short-range ordering. High-Mg calcite (up to 41 mol% MgCO3) displays domains with different local ordering configurations and similar or slightly different Mg contents, and to which is added a compositional variation between crystals, as determined by EMP, of the order of ± 0.8 mol% MgCO3. The cation ordering in Ca-rich dolomites similarly occurs in high-Mg synthetic calcites. The role of (CO3)2− group ordering is shown to be an important factor in the formation of Ca–Mg carbonates.

Impact of Li Doping on the Structure and Phase Stability in AgNbO3.

The impact of Li doping on the temperature-induced phase transitions in silver niobates Ag1-xLixNbO3 has been investigated using a combination of high-resolution powder neutron diffraction and synchrotron X-ray diffraction. Considering both the cell metric and distortions of the NbO6 octahedra, estimated by Rietveld refinements, it is shown that the sequence of temperature-induced phases in AgNbO3 is P21am → Pcam → Cmcm → P4/mbm → Pm3̅m. This sequence is simpler than that proposed in earlier studies. Evidence is presented for a second-order Jahn-Teller distortion in the Pcam phase. At x > 0.05, Li doping favors the formation of a rhombohedral phase in space group R3c, and such samples display the temperature-induced sequence R3c → Pbnm → Cmcm → P4/mbm → Pm3̅m. Unusual volume changes associated with the phase transitions point to the potential importance of lattice matching in optimizing the properties of thin films of doped AgNbO3.

Magnetoelastic coupling in DyFe11.4Nb0.6

The structural and magnetic properties of the rare-earth transition metal compound DyFe11.4Nb0.6 have been investigated over its magnetically order state by variable temperature high resolution synchrotron x-ray diffraction (85 K - 650 K) together with ac magnetic susceptibility (10 K - 300 K), DC magnetization (300 K - 600 K) and heat capacity (2 K - 300 K) measurements. The magnetic ordering temperature has been determined to be TC = 538(5) K while with decreasing temperature, two spin reorientations have been detected around Tsr1 = 265(±5 K) and Tsr2 = 140(±5) K. The Debye temperature θD = 412(±10) K derived from the specific heat measurements of DyFe11.4Nb0.6 agrees well with the values reported for related compounds, while the density of states at the Fermi level was found to be N(EF) = 3.8 ev−1 atom−1. Refinements of the synchrotron x-ray diffraction patterns indicate the occurrence of magnetoelastic couplings at all three magnetic transitions, the Curie temperature TC and spin reorientation temperatures Tsr1 and Tsr2. The linear thermal expansion has been determined over the temperature range 85 K - 650 K and substantial magneto-volume effects shown to persist at temperatures up to 596 K, significantly above the Curie temperature. Similarly, the spontaneous volume magnetostriction ωs of DyFe11.4Nb0.6 extends to 1.17 TC, well above the Curie temperature TC = 538(5) K. The spontaneous volume magnetostriction has the value ωs = 1.08 × 10−2 at 85 K. The properties of such materials offer potential for applications in functional structures.

Grain size and structure distortion characterization of α-MgAgSb thermoelectric material by powder diffraction**Project supported by the National Natural Science Foundation of China (Grant No. 11675255) and the National Key R&D Program of China (Grant No. 2016YFA0401503).

Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99.

Magnetocaloric effect in the vicinity of the magnetic phase transition in NdCo2−xFex compounds

In the present paper, the magnetocaloric effect (MCE) of ${\mathrm{NdCo}}_{2\ensuremath{-}x}{\mathrm{Fe}}_{x}$ ($x\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}0$, 0.2, 0.4, 0.6) compounds was investigated by magnetization measurements. The temperature-dependent high-resolution synchrotron x-ray diffraction study shows a magnetostructural transition from the paramagnetic cubic phase to the ferromagnetic tetragonal phase below their Curie temperatures. Differential scanning calorimetry analysis shows the absence of thermal hysteresis, indicating the second-order nature of the magnetostructural phase transition in these compounds. The maximum values of magnetic entropy change ($\mathrm{\ensuremath{\Delta}}{S}_{M}$) and wide operating temperature (OT) are obtained under a field change of 5 T, which are 7.33 ${\mathrm{Jkg}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$, 6.45 ${\mathrm{Jkg}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$, 5.71 ${\mathrm{Jkg}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$, 4.70 ${\mathrm{Jkg}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$ and 78 K, 82 K, 85 K, 92 K for $x$ = 0, 0.2, 0.4, and 0.6, respectively. The corresponding values of relative cooling power (RCP) are 529.96 ${\mathrm{Jkg}}^{\ensuremath{-}1}$, 497.25 ${\mathrm{Jkg}}^{\ensuremath{-}1}$, 470.55 ${\mathrm{Jkg}}^{\ensuremath{-}1}$, and 428.31 ${\mathrm{Jkg}}^{\ensuremath{-}1}$. The observed wide OT range and large RCP values are comparable with Gd, ${\mathrm{Gd}}_{5}{\mathrm{Ge}}_{2}{\mathrm{Si}}_{2}$, and some rare-earth-based giant magnetocaloric materials, making this series of compounds suitable for magnetic refrigeration.