Temperature-dependent Synchrotron X-ray Diffraction Research Articles

Magnetoelastic Coupling Evidence by Anisotropic Crossed Thermal Expansion in Magnetocaloric RSrCoFeO6 (R = Sm, Eu) Double Perovskites.

Double perovskite oxides, characterized by their tunable magnetic properties and robust interconnection between the lattice and magnetic degrees of freedom, present an enticing foundation for advanced magnetic refrigeration materials. Herein, we delve into the influence of rare-earth elements on RSrCoFeO6 (R = Sm, Eu) disordered double perovskites by examining their structural, electronic, magnetic, and magnetocaloric properties. Temperature-dependent synchrotron X-ray diffraction analysis confirmed the stability of the orthorhombic phase (Pnma) across a wide temperature range. X-ray photoemission spectroscopy revealed that both Sm and Eu are in the 3+ state, whereas multiple states for Co2+/3+ and Fe3+/4+ are identified. The magnetic investigation and magnetocaloric effect (MCE) analysis brought to light the presence of a long-range antiferromagnetic (AFM) order with a second-order phase transition (SOPT) in both samples. The maximum magnetic entropy change ΔSMmax was approximately 0.9 J/kg K for both samples at applied field 0-7 T, manifesting prominently above Neel temperatures TN ≈ 93 K (Sm) and 84 K (Eu). Nevertheless, different relative cooling powers (RCP) of 112.6 J/kg (Sm) and 95.5 J/kg (Eu) were observed. A detailed analysis of the temperature-dependent lattice parameters shed light on a distinct magnetocaloric effect across the magnetic transition temperature, unveiling an anisotropic thermal expansion [αV = 1.41 × 10-5 K-1 (Sm) and αV = 1.54 × 10-5 K-1 (Eu)] wherein the thermal expansion axial ratio αbSm/αbEu = 0.61 became lower with increasing temperature, which suggests that the Eu sample experiences a greater thermal expansion in the b-axis direction. At the atomic bonding level, the evidence for magnetoelastic coupling around the magnetic transition temperatures TN was found through the anomalies along the average Co/Fe-O bond distance, formal valence, octahedral distortion, as well as an anisotropic lattice expansion.

Intertwined crystal structure, magnetic, and charge transport properties in mixed valent A-site ordered manganite NdBaMn2O6

In the present work, we report a correlation between crystal structure, magnetic, and electrical properties in an exotic magnetic compound, NdBaMn2O6 having ∼92% ordering between Nd and Ba, investigated using temperature-dependent synchrotron x-ray diffraction (XRD), dc magnetization and transport measurements. Temperature-dependent XRD data reveals that the compound undergoes various complex crystallographic phase transitions from high-temperature (T > 320 K) P4/mmm phase to intermediate (320 K – 280 K) Cmmm phase to a mixed (Cmmm and P21am) phase (280 K – 220 K) and to low-temperature P21am phase (T < 220 K). It is found that these crystallographic phase compositions play a crucial role in controlling its magnetic and transport properties. Temperature-dependent dc magnetization data show a sharp drop at the onset of mixed phase (Cmmm + P21am) at 280 K followed by a broad hump at ∼ 220 K where mixed phase to P21am transition occurs, thus indicating a correlation between the structural and magnetic properties. The dc magnetization in the mixed phase region is calculated by considering a superposition of the magnetic moments of Cmmm and P21am phases weighted by the fraction of each phase, which exactly follows the experimental magnetization data. Temperature variation of resistivity data shows a jump at ∼260 K, a temperature corresponding to 50–50% phase composition of Cmmm and P21am phases. The compound shows insulating behavior over a whole temperature range as confirmed from the resistivity data. Further, application of magnetic field causes a shift of magnetic and transport transition temperatures which may be due to the magnetic field induced structural transition in the system.

Origin of linear magnetoresistance in Bi2Te3 topological insulator: Role of surface state and defects

Connection between topological surface states (TSS) and large linear magnetoresistance (LMR) is established in tetradymite Bi2Te3 through tuning of native defects. Thorough analysis of temperature dependent synchrotron X-ray diffraction data quantifies 0-D, 1-D and 2-D defect concentrations. Plausible variation of antisite defects is explained via carrier concentration data. Resistivity data divulge contribution of mixed bulk and surface states in the synthesized samples. High Fermi velocity (∼106 ms−1) and low Fermi energy (∼14 meV) of carriers are obtained. Lower defect concentration sample emerges with high magnetoresistance (MR) and higher mobility. Weak antilocalization (WAL) effect, signature of TSS, is revealed from MR. Large (80%), non-saturating LMR along with ultrahigh mobility (∼1 m2V−1s−1) in Bi2Te3 supports the presence of TSS. Magnetoconductance data are fitted with Hikami-Larkin-Nagaoka equation, obtaining further insight on WAL effect. In addition, extracted parameters like disorder correlation length and coherence length explicate the role of defect density on LMR.

Absence of magnetostriction and transition from rapid positive thermal expansion to negative thermal expansion at high temperatures in Sm0.5Y0.5Fe0.58Mn0.42O3 – A synchrotron X-ray diffraction study

X-ray photoemission spectroscopic (XPS) studies and temperature dependent synchrotron X-ray diffraction (SXRD) investigation have been conducted on polycrystalline samples of Sm0.5Y0.5Fe0.58Mn0.42O3 [SYFM (58-42)]. Room temperature XPS measurements revealed the mixed valance of the Fe and Mn ions along with the traces of oxygen vacancies in the material. The room temperature synchrotron X-ray diffraction (SXRD) of specimen shows the monophasic nature of the prepared composition, without the presence of any magnetic or non-magnetic impurity phases. SXRD measurements at variable temperatures between 298 and 873 K, indicates the absence of magnetostriction in the specimen at the magnetic transition temperatures TSR1 ≈ 348 K, TSR2 ≈ 300 K and TN ≈ 361 K. At much higher temperatures above TN, an anisotropic rapid positive thermal expansion (RPTE) to negative thermal expansion (NTE) of the a lattice parameter of the unit cell is further revealed for T > 573 K. The anomalous variation of phonons, are suggested to give rise to anomalous thermal variation in a lattice parameter of the specimen.

Magnetoelastic Coupling and Cryogenic Magnetocaloric Effect in Two-Site Disordered GdSrCoFeO6 Double Perovskite

The development of new magnetic refrigerants demands an effective investigation of materials with a large magnetocaloric effect in a wide temperature range. Herein, we report on the structural, magnetic, and magnetocaloric properties of the two-site disordered double perovskite GdSrCoFeO6 prepared by the modified solid-state synthesis method. Temperature-dependent synchrotron X-ray diffraction analysis revealed that GdSrCoFeO6 crystallizes in the orthorhombic phase (Pnma), with Gd3+/Sr2+ and Co2+/3+/Fe3+/4+ ions randomly distributed on the A- and B-sites, respectively. An observed lattice parameter anomaly around 60 K indicates the occurrence of the magnetoelastic coupling, which coincides with the presence of ferro/ferrimagnetic (FM/FiM) ordering below TC ≈ 65 K from the magnetic measurements. These results match well with our first-principles calculation prediction of low-temperature magnetic (FM/FiM) and electronic (insulating/metal) transitions related to a combined effect of Co and Fe short- and long-range competitions, crossings of spin state at Co ions, and the hybridization degree between Gd-4f and Co-3d states. Additionally, a modified Arrott plot and Kouvel–Fisher analysis were used to establish the nature of the magnetic phase transition in GdSrCoFeO6, yielding the critical exponent β = 1.46(6)/1.45(6), γ = 1.48(5)/1.17(2), and δ = 2.01(3)/1.80(5), respectively. The specific heat analysis reveals two well-defined broad peaks (∼10 and ∼70 K), which match well with a Schottky anomaly (Gd-4f) and the magnetic transition of FM/FiM to paramagnetic order, respectively. The magnetocaloric effect (MCE) analysis reveals a maximum magnetic entropy change ΔSMmax ≈ 13 J kg–1 K–1 (at ∼8 K) under a field of 0–7 T. These results evidence that the Schottky anomaly and the magnetoelastic coupling seem to be key factors for driving further enhancements to the MCE in GdSrCoFeO6, making it a possible candidate for cryogenic applications.

Rational design of thermally stable polymorphic layered cathode materials for next generation lithium rechargeable batteries

Classical layered transition metal oxides have remained the preferred cathode materials for commercial lithium-ion batteries. Variation in the transition metal composition and local ordering can greatly affect the structure stability. In classical layered cathodes, high concentrations of electrochemically inert Mn elements usually act as a pillar to stabilize the structure. When excess amount of Li and Mn are present in the layered structure, the capacity of the Li-rich layered oxide (molar ratio of lithium over transition metal is larger than one by design) can exceed that expected from transition metal redox. However, the over lithiation in the classical layered structure results in safety issues, which remains challenging for the commercialization of Li-rich layered oxides. To characterize the safety performance of a series of Li-rich layered cathodes, we utilize differential scanning calorimeter and thermal gravimetric analysis; this is coupled with local structural changes using in situ temperature dependent synchrotron X-ray diffraction and X-ray adsorption spectroscopy. These methods demonstrate that the gradual decrease of the Mn–M (M = Ni, Co, Mn and Li) coordination number directly reduces structural stability and accelerates oxygen release. For safety characterization tests in practice, we evaluate the thermal runaway process through accelerating rate calorimeter in 1.0 Ah pouch cells to confirm this trend. Using the insights obtained in this work, we design a polymorphic composition to improve the thermal stability of Li-rich layered cathode material, which outperforms Ni-rich layered oxides in terms of both electrochemical and safety performances.

Coexisting Multiple Martensites in Ni57−xMn21+xGa22 Ferromagnetic Shape Memory Alloys: Crystal Structure and Phase Transition

A comprehensive study of the crystal structure and phase transition as a function of temperature and composition in Ni57−xMn21+xGa22 (x = 0, 2, 4, 5.5, 7, 8) (at. %) magnetic shape memory alloys was performed by a temperature-dependent synchrotron X-ray diffraction technique and transmission electron microscopy. A phase diagram of this Ni57−xMn21+xGa22 alloy system was constructed. The transition between coexisting multiple martensites with monoclinic and tetragonal structures during cooling was observed in the Ni51.5Mn26.5Ga22 (x = 5.5) alloy, and it was found that 5M + 7M multiple martensites coexist from 300 K to 160 K and that 5M + 7M + NM multiple martensites coexist between 150 K and 100 K. The magnetic-field-induced transformation from 7M martensite to NM martensite at 140 K where 5M + 7M + NM multiple martensites coexist before applying the magnetic field was observed by in situ neutron diffraction experiments. The present study is instructive for understanding the phase transition between coexisting multiple martensites under external fields and may shed light on the design of novel functional properties based on such phase transitions.

Spin–phonon interaction and magnetoelastic coupling associated with unusual cluster-glass states in YFe0.9Cr0.1O3

The magnetic, optical phonon behavior of the polycrystalline YFe0.9Cr0.1O3 (YFC-10), prepared by solid-state reaction route, had been studied via static and ac magnetization measurements and Raman spectroscopic techniques respectively. The results indicated that YFe0.9Cr0.1O3 undergoes unusual cluster-glass transitions at low temperatures viz. Tf1 (SG1) = 108 K (Freez.1) and Tf2 (SG2) = 30 K (Freez.2) coexisting with the long-range weak ferromagnetic (WFM) state. Raman spectroscopic (RS) measurements revealed 12 distinct modes of vibrations at all temperatures with 83–433 K. Interestingly, the freezing transition at Tf1 is found to be accompanied by significant phonon renormalization. From the detailed analysis of the line-shape function of the Raman modes, the anomalous T-variation of the peak position and the linewidths suggests the existence of spin-phonon interaction in the present solid solution. Moreover the temperature dependent synchrotron X-ray diffraction studies between 10 and 300 K revealed the anomalous thermal variation of the lattice parameters and microscopic structural parameters such as super-exchange angles and (Fe/Cr)O6 octahedral bond lengths and bond angles at both the freezing transitions. Overall, the system exhibits the strong magnetoelastic and spin phonon coupling over a broad thermal regime viz. from Liquid. N2 to temperatures above room temperature (RT = 300 K) which makes YFe0.9Cr0.1O3 reliable for application purpose.

The mechanism for the enhanced piezoelectricity in multi-elements doped (K,Na)NbO3 ceramics

(K,Na)NbO3 based ceramics are considered to be one of the most promising lead-free ferroelectrics replacing Pb(Zr,Ti)O3. Despite extensive studies over the last two decades, the mechanism for the enhanced piezoelectricity in multi-elements doped (K,Na)NbO3 ceramics has not been fully understood. Here, we combine temperature-dependent synchrotron x-ray diffraction and property measurements, atomic-scale scanning transmission electron microscopy, and first-principle and phase-field calculations to establish the dopant–structure–property relationship for multi-elements doped (K,Na)NbO3 ceramics. Our results indicate that the dopants induced tetragonal phase and the accompanying high-density nanoscale heterostructures with low-angle polar vectors are responsible for the high dielectric and piezoelectric properties. This work explains the mechanism of the high piezoelectricity recently achieved in (K,Na)NbO3 ceramics and provides guidance for the design of high-performance ferroelectric ceramics, which is expected to benefit numerous functional materials.

Structural correlations in the enhancement of ferroelectric property of Sr doped BaTiO3

The effect of Sr doping in BaTiO3 (BTO) with nominal compositions Ba0.80Sr0.20TiO3 (BSTO) have been explored on its structural, lattice vibration, dielectric, ferroelectric and electrocaloric properties. The temperature dependent dielectric results elucidate the enhancement in dielectric constant and exhibit three frequency independent transitions around 335, 250 and 185 K, which are related to different structural transitions. All these transitions occur at lower temperature as compared with pristine BTO, however; remnant electric polarization (Pr) of BSTO is much higher than in BTO. The value of Pr is ∼5 μC cm−2 at room temperature and the maximum Pr ∼ 8 μC cm−2 is observed at tetragonal to orthorhombic and orthorhombic to rhombohedral transitions. The electro-caloric effect shows the maximum adiabatic change in temperature ΔT ∼ 0.24 K at cubic to tetragonal transition. The temperature dependent synchrotron x-ray diffraction and Raman results show correlations between Pr, crystal structure and lattice vibrations. Our results demonstrate the enhancement in ferroelectric properties of BTO with Sr doping. The origin of the enhancement in ferroelectric property is also discussed in correlations with the appearance of superlattice peak around room temperature due to TiO6 octahedral distortion. These enhanced properties would be useful to design lead free high quality ferroelectric and piezoelectric materials.

Structural phase control and thermochromic modulation of VO2 thin films by post thermal annealing

Monoclinic M1 to rutile structural phase transition (SPT) in thermochromic VO2 is accompanied by the insulator to metal transition and transition from an infrared (IR) transparent to IR opaque phase. Fine control over the phase stabilization and the functional properties without additional doping can offer the ability to tailor VO2 thin films for their respective applications. In this work, post deposition thermal annealing was used to control the phase stabilization and the modulation in thermochromic performance of polycrystalline VO2 thin films. Monoclinic M1 to rutile SPT in VO2 thin films was tracked by in-situ temperature dependent synchrotron X-ray diffraction measurements and an increase in the SPT temperature was observed with increasing annealing temperature. Intermediate monoclinic M2 phase emerges near the SPT temperature at higher annealing temperature. Temperature dependent X-ray absorption spectroscopy (XAS) measurements revealed the higher electron correlation effect among the V 3d|| states across the phase transition in VO2 thin film having the intermediate phase. Spectral weight of V 3d|| states was found to increase with the annealing temperature. Lower annealing temperature drives the IR switching temperature towards room temperature while the higher annealing temperature improves the IR switching performance of VO2 thin films.

Mn-Induced Thermal Stability of L10 Phase in Fept Magnetic Nanoscale Ribbons.

Magnetic nanoscale materials exhibiting the L10 tetragonal phase such as FePt or ternary alloys derived from FePt show most promising magnetic properties as a novel class of rare earth free permanent magnets with high operating temperature. A granular alloy derived from binary FePt with low Pt content and the addition of Mn with the nominal composition Fe57Mn8Pt35 has been synthesized in the shape of melt-spun ribbons and subsequently annealed at 600 °C and 700 °C for promoting the formation of single phase, L10 tetragonal, hard magnetic phase. Proton-induced X-ray emission spectroscopy PIXE has been utilized for checking the compositional effect of Mn addition. Structural properties were analyzed using X-ray diffraction and diffractograms were analyzed using full profile Rietveld-type analysis with MAUD (Materials Analysis Using Diffraction) software. By using temperature-dependent synchrotron X-ray diffraction, the disorder–order phase transformation and the stability of the hard magnetic L10 phase were monitored over a large temperature range (50–800 °C). A large interval of structural stability of the L10 phase was observed and this stability was interpreted in terms of higher ordering of the L10 phase promoted by the Mn addition. It was moreover found that both crystal growth and unit cell expansion are inhibited, up to the highest temperature investigated (800 °C), proving thus that the Mn addition stabilizes the formed L10 structure further. Magnetic hysteresis loops confirmed structural data, revealing a strong coercive field for a sample wherein single phase, hard, magnetic tetragonal L10 exists. These findings open good perspectives for use as nanocomposite, rare earth free magnets, working in extreme operation conditions.

Crystal Structure and Thermoelectric Transport Properties of As-Doped Layered Pnictogen Oxyselenides NdO0.8F0.2Sb1-xAsxSe2.

We report the synthesis and thermoelectric transport properties of As-doped layered pnictogen oxyselenides NdO0.8F0.2Sb1−xAsxSe2 (x ≤ 0.6), which are predicted to show high-performance thermoelectric properties based on first-principles calculation. The crystal structure of these compounds belongs to the tetragonal P4/nmm space group (No. 129) at room temperature. The lattice parameter c decreases with increasing x, while a remains almost unchanged among the samples. Despite isovalent substitution of As for Sb, electrical resistivity significantly rises with increasing x. Very low thermal conductivity of less than 0.8 Wm−1K−1 is observed at temperatures between 300 and 673 K for all the examined samples. For As-doped samples, the thermal conductivity further decreases above 600 K. Temperature-dependent synchrotron X-ray diffraction indicates that an anomaly also occurs in the c-axis length at around 600 K, which may relate to the thermal transport properties.

Tunable structural phase transition and superconductivity in the Weyl semimetal Mo1−xWxTe2

The relationship among structural transition, superconductivity, and doping in the Weyl semimetal ${\mathrm{Mo}}_{1\ensuremath{-}x}{\mathrm{W}}_{x}{\mathrm{Te}}_{2}$ has been established through a systematic study of the doping and pressure effects. Doping-dependent resistivity measurements at ambient pressure revealed that the structural transition temperature increases linearly with increasing W content in ${\mathrm{Mo}}_{1\ensuremath{-}x}{\mathrm{W}}_{x}{\mathrm{Te}}_{2}$. The observed structural transition temperature $({T}_{s})$ of ${\mathrm{MoTe}}_{2}$ at ambient pressure is 249 K and that of ${\mathrm{WTe}}_{2}$ is 613 K. Temperature-dependent synchrotron x-ray diffraction measurements further confirmed the structural transition in ${\mathrm{WTe}}_{2}$ at ambient pressure. Pressure was found to continuously suppress the ${T}_{s}$ in ${\mathrm{Mo}}_{0.90}{\mathrm{W}}_{0.10}{\mathrm{Te}}_{2},{\mathrm{Mo}}_{0.60}{\mathrm{W}}_{0.40}{\mathrm{Te}}_{2}$, and ${\mathrm{Mo}}_{0.25}{\mathrm{W}}_{0.75}{\mathrm{Te}}_{2}$, and superconductivity emerges in ${\mathrm{Mo}}_{0.90}{\mathrm{W}}_{0.10}{\mathrm{Te}}_{2}$ and ${\mathrm{Mo}}_{0.60}{\mathrm{W}}_{0.40}{\mathrm{Te}}_{2}$ above 1.25 K when ${T}_{s}$ is suppressed to a lower temperature.

Structural coupling and magnetic tuning in Mn2−xCoxP magnetocalorics for thermomagnetic power generation

Promising materials for magnetic refrigeration and thermomagnetic power generation often display strong coupling between magnetism and structure. It has been previously proposed that MnCoP exhibits this strong coupling, contributing to its substantial magnetocaloric effect near TC = 578K. Here, we show from temperature-dependent synchrotron x-ray diffraction that MnCoP displays a discontinuity in the thermal expansion at TC, with spontaneous magnetostriction that is positive in the a direction and negative in the b direction, highlighting the anisotropic nature of the magnetostructural coupling. Varying the Mn:Co ratio of Mn2−xCoxP within the range of 0.6 ≤ x ≤ 1.4 allows the magnetic properties to be tuned. TC decreases as the composition deviates from stoichiometric MnCoP, as does the saturation magnetization. The magnitude of the magnetocaloric effect, |ΔSM|, decreases as well, due to broadening of the magnetic transition. The large reversible change in magnetization ΔM accessible over a small temperature range under moderate magnetic fields makes these materials promising for thermomagnetic power generation from waste heat.

Antiferroelectric antiferromagnetic type-I multiferroic Cu9O2(SeO3)4Cl6

We report that $\mathrm{C}{\mathrm{u}}_{9}{\mathrm{O}}_{2}{(\mathrm{Se}{\mathrm{O}}_{3})}_{4}\mathrm{C}{\mathrm{l}}_{6}$ is a new multiferroic compound. Comprehensive studies of this compound have been carried out on single crystals as well as polycrystalline samples. Magnetic susceptibility $\ensuremath{\chi}$ and specific heat $C$ with $H\ensuremath{\parallel}c$ axis both reveal an anomaly at ${T}_{N}=37\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ associated with the long-range antiferromagnetic order. However, no signature of this phase transition is seen with the $H\ensuremath{\parallel}b$ axis, providing evidence of the anisotropic nature of its magnetic properties. The results of $\ensuremath{\chi}$ measurements are consistent with the temperature evolution of the intensity of magnetic reflections from the neutron diffraction experiments. The magnetic structure derived from neutron scattering measurements shows that half of the Cu(5) ions carry no moments. Furthermore, an anomaly in the dielectric constant near ${T}_{N}$ and observable magnetoelectric coupling below ${T}_{N}$ are found. At high temperatures, a dielectric peak at ${T}_{E}=267\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is identified with no measurable spontaneous polarization below ${T}_{E}$, thereby suggesting an antiferroelectric order. A steplike anomaly seen in $\ensuremath{\chi}(T)$ at ${T}_{E}$ hints the weak spin-lattice coupling. Concomitantly, high-resolution temperature-dependent synchrotron x-ray diffraction experiments elucidate a local structural distortion at ${T}_{E}$.

Perovskites with a Twist: Strong In1+ Off-Centering in the Mixed-Valent CsInX3 (X = Cl, Br)

The search for new halide perovskites has recently expanded to the double perovskites A2M+M3+X6, which form in the 3D elpasolite structure with alternating M+ and M3+ octahedra. Here, we report the ternary mixed-valent indium compounds CsInX3 (X = Br, Cl). They adopt a tetragonal (space group I4/m) structure, which is a derivative of the charge-ordered double perovskite but with a twisted chain of octahedra along the c-axis. This twist is a result of the off-centering at the In+ site to accommodate its stereochemically active 5s2 lone pair, which induces a 45° rotation of all In3+ octahedra in the chain. This is a non-cooperative rotation that creates pentagonal pyramids in the structure and induces significant disorder, with extensive twinning, which results in partial occupation of different rotations of the same In3+ site. Temperature-dependent synchrotron X-ray diffraction reveals that both compounds form the cubic double perovskite structure at high temperature (Fm3̅m), thus demonstrating that the twist occurs on cooling from the melt. UV–vis spectroscopy reveals band gaps near 2.3–2.4 eV for the bromide and 3.0 eV for CsInCl3. High-pressure electrical transport measurements show significant enhancement in conductivity as pressure increases, indicating a narrowing of the band gap at high pressures. Temperature-dependent transport measurements at high pressure show uniformly semiconducting behavior, with no superconducting transition observed down to 2.4 K. The CsInX3 are unique inorganic halide double perovskites because they are based on a single metal, with CsInBr3 just the third bromide after the mixed metal compounds Cs2AgBiBr6 and Cs2AgTlBr6.

Role of local structural distortion in driving ferroelectricity in GdCrO3

Temperature dependent synchrotron x-ray diffraction and extended x-ray absorption fine structure (EXAFS) studies were performed to understand the role of structural characteristics in driving the magnetoelectric mul- tiferoic properties of GdCrO3. The results suggest that the distortion in the structure appears to be associated with the off-center displacement of Gd-atoms together with octahedral rotations via displacement of the oxygen ions in GdCrO3. In addition, the magnetic coupling below magnetic transition temperature leads to additional distortion in the system via magnetostriction effect, playing a complementary role in the enhancement of ferro- electric polarization. Further, a comparative EXAFS study of GdCrO3 with a similar system YCrO3 suggests that oxygen environment of Gd in GdCrO3 is different from Y in YCrO3, which resulting in an orthorhombic P na21 structure in GdCrO3 in contrast to the monoclinic P 21 structure in YCrO3 .

Temperature-dependent synchrotron X-ray diffraction, pair distribution function and susceptibility study on the layered compound CrTe3

Abstract Results of combined synchrotron X-ray diffraction and pair distribution function experiments performed on the layered compound CrTe3 provide evidence for a short range structural distortion of one of the two crystallographically independent CrTe6 octahedra. The distortion is caused by higher mobility of one crystallographically distinct Te ion, leading to an unusual large Debye Waller factor. In situ high temperature X-ray diffraction investigations show an initial crystallization of a minor amount of elemental Te followed by decomposition of CrTe3 into Cr5Te8 and Te. Additional experiments provide evidence that the Te impurity (&lt;1%) cannot be avoided. Analyses of structural changes in the temperature range 100–754 K show a pronounced anisotropic expansion of the lattice parameters. The differing behavior of the crystal axes is explained on the basis of structural distortions of the Cr4Te16 structural building units. An abrupt distortion of the structure occurs at T≈250 K, which then remains nearly constant down to 100 K. The structural distortion affects the spin exchange interactions between Cr3+ cations. A significant splitting between field-cooled (fc) and zero-field-cooled (zfc) magnetic susceptibility is observed below about 200 K. Applying a small external magnetic field results in a substantial spontaneous magnetization, reminiscent of ferro- or ferrimagnet exchange interactions below ~240 K. A Debye temperature of ~150 K was extracted from heat capacity measurements.

Anisotropic Thermal Expansion of p-Terphenyl: a Self-Assembled Supramolecular Array of Poly-p-phenyl Nanoribbons

The recent discovery of superconductivity in a metallic aromatic hydrocarbon, alkali-doped p-terphenyl, has attracted considerable interest. The critical temperature T c ranges from few to 123 K, the record for organic superconductors, due to uncontrolled competition of multiple phases and dopants concentrations. In the proposed mechanism of Fano resonance in a superlattice of quantum wires with coexisting polarons and Fermi particles, the lattice properties play a key role. Here, we report a study of the temperature evolution of the parent compound p-terphenyl crystal structure proposed to be made of a self-assembled supramolecular network of nanoscale nanoribbons. Using temperature-dependent synchrotron X-ray diffraction, we report the anisotropic thermal expansion in the ab plane, which supports the presence of a nanoscale network of one-dimensional nanoribbons running in the b-axis direction in the P21/a structure. Below the enantiotropic phase transition at 193 K, the order parameter of the C-1 structure follows a power law behavior with the critical exponent α = 0.34 ± 0.02 and the thermal expansion of the a-axis and b-axis show major changes supporting the formation of a two-dimensional bonds network. The large temperature range of the orientation fluctuations in a double well potential of the central phenyl has been determined.