The influence of the lanthanide cation type and calcination temperature on the crystal, local, and electronic structures of both individual and high-entropy (HE) Ln chromates/chromites (Ln = La - Yb, and Y) prepared by a coprecipitation is studied by using synchrotron X-ray diffraction, X-ray absorption fine structure spectroscopy, Raman and Fourier transform infrared spectroscopies, scanning electron microscopy with energy-dispersive Xray spectroscopy, simultaneous thermal analysis, and inductively coupled plasma atomic emission spectroscopy. Calcination of X-ray amorphous precursors at 550 degrees C resulted in the formation of individual LnCrO4 chromates with monoclinic (sp. gr. P21/n for Ln = La) or tetragonal (sp. gr. I41/amd for Ln = Sm - Yb, Y) structure. The PrCrO4 and NdCrO4 samples were a mixture of monoclinic and tetragonal phases. The HE LnCrO4 chromates were characterized by tetragonal structure regardless of the Ln3+ cation type involved. A further increase in temperature >= 650 degrees C led to the formation of Ln chromites having the orthorhombic symmetry (sp. gr. Pnma for LaCrO3, sp. gr. Pbnm for individual Ln = Pr - Yb, Y, and HE chromites). For all synthesized LnCrO3 samples, the lattice parameters, unit cell volumes, Cr-O-Cr bond angles, average Ln-O distances diminish with decreasing the Ln3+ cation radius. On the contrary, the octahedral distortions within CrO6 units increase with decreasing the Ln3+ cation radius. An analysis of the electronic structure showed the presence of an oxidation state (3+) for both Ln and Cr cations in all synthesized precursors and Ln chromites, and Cr5+ for Ln chromates. The local environment of the Ln3+ and Cr3+ cations in HE Ln chromites is close to that of similar ions in individual compounds. The local environment of the La3+ cation in La-containing compounds differs significantly from that of Ln3+ cations in other Ln chromites (Ln = Nd, Sm, Eu, Gd, Dy, Ho, Yb, Y).

Low-temperature superconductivity has been known since 1957 to be described by BCS theory for effective single-band metals controlled by the density of states at the Fermi level, very far from band edges, the electron–phonon coupling constant l, and the energy of the boson in the pairing interaction w0, but BCS has failed to predict high-temperature superconductivity in different materials above about 23 K. High-temperature superconductivity above 35 K, since 1986, has been a matter of materials science, where manipulating the lattice complexity of high-temperature superconducting ceramic oxides (HTSCs) has driven materials scientists to grow new HTSC quantum materials up to 138 K in HgBa2Ca2Cu3O8 (Hg1223) at ambient pressure and near room temperature in pressurized hydrides. This perspective covers the major results of materials scientists over the last 39 years in terms of investigating the role of lattice inhomogeneity detected in these new quantum complex materials. We highlight the nanoscale heterogeneity in these complex materials and elucidate their special role played in the physics of HTSCs. Especially, it is highlighted that the geometry of lattice and charge complex heterogeneity at the nanoscale is essential and intrinsic in the mechanism of rising quantum coherence at high temperatures.

The synthesis and detailed study of six series of high-entropy complex oxides containing lanthanides (Ln) and transition metals with the general formula Ln(2)M(2)O(7) (Ln = La-Yb, and Y; M = Ti, Zr, and Ce) with the number of different Ln cations not less than six in each case are reported. The influence of synthesis conditions (types of the Ln(3+) and M4+ cations, calcination temperature) used in the synthesis via either coprecipitation or sol-gel method on the crystal and local structures of target materials is comprehensively surveyed. The studies were carried out using a combination of long- (s-XRD), medium- (Raman, FT-IR, SEM-EDS) and short-range (XAFS) sensitive techniques, as well as AES-ICP and STA. It was established that the ratio of the cation radii gamma = (r) over bar (3+)(Ln)/(r) over bar (4+)(M) is the main factor that determines the type of initially formed crystal structure. In the boundary region (gamma similar to 1.42-1.47), the average radius of lanthanide cation ((r) over bar (3+)(Ln)), along with the (r) over bar (3+)(Ln)/(r) over bar (4+)(M) ratio, also plays a significant role in the type of the resulting crystal structure of the high-entropy lanthanide complex oxides. The presence of inhomogeneity in the distribution of elements in precursors significantly affects the phase composition of the resulting high-entropy oxides. An increase in the calcination temperature promotes not only the occurrence of subsequent phase transitions, but also an increase in the single-phase nature of the resulting high-entropy complex rare-earth oxides. At the same time, the cations included in the composition retain some independence, despite the fact that they occupy one crystallographic position in the resulting crystal structure.

The influence of Yb3+ cations substitution for Pr3+ on the structure and catalytic activity of (Pr1−xYbx)2Zr2O7 powders synthesized via coprecipitation followed by calcination is studied using a combination of long- (s-XRD), medium- (Raman, FT-IR, and SEM-EDS) and short-range (XAFS) sensitive methods, as well as adsorption and catalytic techniques. It is established that chemical composition and calcination temperature are the two major factors that govern the phase composition, crystallographic, and local-structure parameters of these polycrystalline materials. The crystallographic and local-structure parameters of (Pr1−xYbx)2Zr2O7 samples prepared at 1400 °C/3 h demonstrate a tight correlation with their catalytic activity towards propane cracking. The progressive replacement of Pr3+ with Yb3+ cations gives rise to an increase in the catalytic activity. A mechanism of the catalytic cracking of propane is proposed, which considers the geometrical match between the metal–oxygen (Pr–O, Yb–O, and Zr–O) bond lengths within the active sites and the size of adsorbed propane molecule to be the decisive factor governing the reaction route.

The synthesis and detailed study of six series of high-entropy complex oxides containing lanthanides (Ln) and transition metals with the general formula Ln2M2O7 (Ln = La-Yb, and Y; M = Ti, Zr, and Ce) with the number of different Ln cations not less than six in each case are reported. The influence of synthesis conditions (types of the Ln3+ and M4+ cations, calcination temperature) used in the synthesis via either coprecipitation or sol–gel method on the crystal and local structures of target materials is comprehensively surveyed. The studies were carried out using a combination of long- (s-XRD), medium- (Raman, FT-IR, SEM-EDS) and short-range (XAFS) sensitive techniques, as well as AES-ICP and STA. It was established that the ratio of the cation radii γ = r̄Ln3+/r̄M4+ is the main factor that determines the type of initially formed crystal structure. In the boundary region (γ∼ 1.42–1.47), the average radius of lanthanide cation (r̄Ln3+), along with the r̄Ln3+/r̄M4+ ratio, also plays a significant role in the type of the resulting crystal structure of the high-entropy lanthanide complex oxides. The presence of inhomogeneity in the distribution of elements in precursors significantly affects the phase composition of the resulting high-entropy oxides. An increase in the calcination temperature promotes not only the occurrence of subsequent phase transitions, but also an increase in the single-phase nature of the resulting high-entropy complex rare-earth oxides. At the same time, the cations included in the composition retain some independence, despite the fact that they occupy one crystallographic position in the resulting crystal structure.

BaPb1−xBixO3 (BPBO) bismuthate, showing high TC superconductivity for 0.05 < x < 0.35, is an archetypal system for studying the complex inhomogeneity of perovskite lattice favoring the emergence of quantum coherence, called the superstripes phase. Local lattice fluctuations, detected by EXAFS; nanoscale stripes, detected by electron microscopy; and two competing crystalline structures, detected by diffraction, are known to characterize the superconducting phase. At nanoscale [BaBiO3] centered nanoscale units (BBO) coexist with BaPbO3 centered (BPO) units in the BPBO perovskite; therefore, we expect a tensile microstrain in BPO units due the misfit strain between the two different lattices. Here, we report the measurement of the spatial micro-fluctuations of the local tensile microstrain ε in the BaPO units in superconducting Ba(Pb1−xBix)O3 crystals with x1 = 0.19 an x2 = 0.28. We show here the feasibility of applying the scanning dispersive micro-X-ray absorption near edge structure (SdμXANES) technique, using focused synchrotron radiation, to probe the microscale spatial fluctuations of the microstrain in BPO units. This unconventional real-space SdμXANES microscopy at the Pb L3 edge has been collected in the dispersive mode. Our experimental method allows us to measure either the local Bi chemical concentration x and the local lattice microstrain of local BBO and BPO units. The 5 × 5 micron-size spots from the focused X-ray beam allowed us to obtain maps of 1600 points covering an area of 200 × 200 microns. The mapping shows a substantial difference between the spatial fluctuations of the microstrain ε and the chemical inhomogeneity x. Moreover, we show the different relations ε(x) in samples with lower (x1 = 0.19) and higher (x2 = 0.28) doping respect to the optimum doping (x = 0.25).

— The regularities of completely reversible valence transition Eu 3+ → Eu 2+ → Eu 3+ in complex europium oxides have been investigated using a combination of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XANES + EXAFS) synchrotron methods. The influence of the type of M 4+ cations on the reduction and oxidation, as well as the formation and evolution of the crystalline and local structure of the Eu_1-x^2 + Eu_x^3 + MO_3 + x/2 ( M = Ti, Zr, Hf) compounds is established. It is shown that oxidation of initially reduced Eu 2+ M O 3 samples leads to the formation of mixed-valence (MV) state Eu 2+ /Eu 3+ with inhomogeneous charge distribution, causing a phase transition with formation of partially amophized intermediate metastable phases Eu 3+ M O 3.5 having a monoclinic structure (sp. gr. Р 12 1 1). An increase in the oxidative annealing temperature to 1000°С facilitates further phase transition with the formation of stable cubic phases Eu _2^3 + M 2 O 7.

The influence exerted by specific synthesis protocol conditions on the crystal, local atomic and electronic struc-tures of various types of Ce chromates/chromites prepared by the coprecipitation is studied using synchrotron X-ray diffraction, X-ray absorption fine structure (XAFS), Raman and Fourier transform infrared (FT-IR) spec-troscopies, and simultaneous thermal analysis. Cerium chromate heptahydrate [Ce+(3) (2) (Cr+O-6(4))3(H2O)(5)]center dot 2H(2)O with the monoclinic structure (sp. gr. P-21/c) has been synthesized and characterized structurally for the first time. It has been established that calcination of all types of precursors in air at a temperature >= 450 degrees C leads to the formation of a mixture of CeO2 and Cr2O3 phases. The calcination in vacuum at 1200 degrees C affords CeCrO3 (with the orthorhombic structure, sp. gr. Pnma(62)), which upon repeated heating to above 650-700 degrees C in air tends to decompose into CeO2 and Cr2O3 phases. Long-range XRD data correlate well with the results of techniques sensitive to the local structure parameters, such as XAFS, Raman and FT-IR. XANES spectra measured at the Cr K-and Ce L3- edges strongly imply that the synthesis procedures are accompanied by concerted redox transformations Cr6+ -> Cr3+ and Ce3+ <-> Ce4+.

Fast and local probes, such as X-ray spectroscopy, X-ray diffraction (XRD), and X-ray microscopy, have provided direct evidence for nanoscale phase separation in high temperature perovskite superconductors composed of (i) free particles coexisting with (ii) Jahn Teller polarons (i.e., charges associated with local lattice distortions) not detected by slow experimental methods probing only delocalized states. Moreover, these experimental probes have shown the formation of a superstripes phase in the pseudogap regime below T* in cuprates. Here, we focus on the anomalous temperature dependence of short range X-ray diffraction CDW reflection satellites with high momentum transfer, probing both charge and lattice fluctuations in superconducting HgBa2CuO4+y (Hg1201) in the pseudogap regime below T* and above Tc. We report compelling evidence of the anomalous anticorrelation of the coherence volume with the peak maximum amplitude of the CDW XRD satellite by cooling below T*. This anomalous temperature trend of the short-range striped Jahn Teller polaronic CDW puddles is in agreement with predictions of the Q-ball theory of the quark gluon plasma extended to cuprates, providing compelling evidence for non topological soliton puddles of striped condensate of pairs in the pseudogap phase.

The features of the electronic and local atomic structure of erbium metalloporphyrins Er(acac)TPPBr8 and Er(acac)TPP and precursor tetraphenylporphyrins TPP and TPPBr8 are studied by X‑ray photoelectron spectroscopy and X-ray absorption spectroscopy. Using photoelectron spectroscopy, the structural parameters of the Er4 d, N1s, C1s, O1s, and Br3d core levels and the valence band are determined. The change in the electronic structure of tetraphenylporphyrins with the introduction of the central erbium atom is established, which consists in a uniform redistribution of the electron density between nitrogen atoms of the pyrrole and aza groups. The effect of the addition of bromine in the meso-position of the macrocycle on the parameters of the local atomic structure of the erbium-porphyrin complex is determined from analysis of the X-ray absorption spectra, and the integer trivalent state of the metal (Er3+) in rare-earth metalloporphyrins is confirmed.

We studied the effect of artificial pinning centers in the form of nanoinclusions of stannate BaSnO 3 (BSO) and zirconate BaZrO 3 (BZO) barium on the critical current of high-temperature superconducting tapes of the second generation (2G) based on YBa 2 Cu 3 O 7 − δ films (YBCO). It has been found that the introduction of BaZrO 3 nanoinclusions increases the critical current at 77 K for the magnetic field direction parallel and normal to the tape surface, while the introduction of BaSnO 3 nanoinclusions decreases the critical current in both cases. To elucidate the origin of a different impact of nanoinclusions we examined the local structure of the YBCO-matrix using x-ray absorption spectroscopy (EXAFS and XANES). The spectra were collected at K -edges of Cu, Sn, and Zr at the European Synchrotron (ESRF). It was revealed that the introduction of BaZrO 3 nanoinclusions increases the stiffness of copper–oxygen bonds in superconducting CuO 2 plane and minimizes their static disorder in the YBCO matrix, while the introduction of BaSnO 3 nanoinclusions leads to a significant increase in static disorder with a relatively weak effect on the stiffness of Cu–O bonds. These changes in the local structure become decisive for changing the macroscopic properties of high-temperature superconductor-tapes.

The effect of synthesis conditions on the features of the long- and short-range order of Ln2(WO4)3 (Ln = Gd, Dy, Ho, Yb) powders synthesized via coprecipitation of salts has been studied by a complex of physico-chemical techniques including synchrotron X-ray powder diffraction, X-ray absorption spectroscopy, Raman and infrared spectroscopy, and simultaneous thermal analysis. It was found that crystallization of amorphous precursors begins at 600 °C/3 h and leads to the formation of the monoclinic structure with sp. gr. C12/c1(15) for Ln2(WO4)3 (Ln = Gd, Dy) and with sp. gr. P121/a1(14) for Ln = Yb, whereas crystallization of Ho precursor requires even higher temperature. After annealing at 1000 °C, the P121/a1(14) phase becomes the dominant phase component for all heavy lanthanoid types except for Ln = Gd. It was shown that the Ln (Ln = Dy, Ho, and Yb) tungstates with the P121/a1(14) monoclinic structure correspond to trihydrates Ln2(WO4)3·3H2O formed due to a rapid spontaneous hydration under ambient conditions. It was concluded that the proneness to hydration is due to a specific structure of the P121/a1(14) phase with large voids available to water molecules. Modifications in the local structure of Ln-O coordination shell accompanying the structure type change and hydration are monitored using EXAFS spectroscopy.

The influence exerted by the specific type of the lanthanide cation and calcination temperature on the crystal and local structures of Ln2(WO4)3 tungstates (Ln = La-Dy) prepared by a coprecipitation is studied using synchrotron X-ray diffraction, X-ray absorption fine structure (XAFS) spectroscopy, Fourier transform infrared (FT-IR) and Raman spectroscopies, photoluminescence, simultaneous thermal analysis, and inductively coupled plasma atomic emission spectroscopy. The combination of these experimental techniques enabled a structural insight into Ln tungstates at multiple characteristic scales, i.e. short-range of metal atom coordination (XAFS), medium-range of the network of chemical bonds (FT-IR and Raman spectroscopies), and long-range or 3D periodicity within crystallites (XRD). It is found that the onset of amorphous precursor crystallization is observed at 575-600 circle C/3 h and leads to the formation of Ln2(WO4)3 nanocrystalline powders with a monoclinic (sp. gr. C12/c1 (15)) structure. An increase in the calcination temperature leads to the growth of crystallite size and a decrease in microstrains. In the case of Dy2(WO4)3 an additional orthorhombic phase emerges (sp. gr. Pbcn(60)) at 1000 circle C. It is shown that the local structure of all well-crystallized compounds being studied contains lanthanide ions in the form of Ln3+ and tungsten ions in the form of WO42 tetrahedra. The local structure in the monoclinic phase can be represented as a superposition of two non-equivalent tungstate tetrahedra: W(1)O4 (C2 site symmetry) and W(2)O4 (C1 site symmetry). The LnO8 polyhedra are strongly irregular, and the Ln3+ cations occupy low-symmetry sites. (c) 2022 Elsevier B.V. All rights reserved.

Second-order intensity interferometry was employed to study the spatial and temporal properties of the European X-ray Free-Electron Laser (EuXFEL). Measurements were performed at the soft x-ray Self-Amplified Spontaneous Emission (SASE3) undulator beamline at a photon energy of 1.2 keV in the Self-Amplified Spontaneous Emission (SASE) mode. Two high-power regimes of the SASE3 undulator settings, i.e., linear and quadratic undulator tapering at saturation, were studied in detail and compared with the linear gain regime. The statistical analysis showed an exceptionally high degree of spatial coherence up to 90% for the linear undulator tapering. Analysis of the measured data in spectral and spatial domains provided an average pulse duration of about 10 fs in our measurements. The obtained results will be valuable for the experiments requiring and exploiting short pulse duration and utilizing high coherence properties of the EuXFEL.

The effect of the Ln3+ cation type on the composition and structure of a wide range of hydrated lanthanide chromates (Ln = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Yb, Y) has been studied. It was found that hydrated Ln chromates can be divided into several groups in terms of their composition and structure. The synthesized chromates of light lanthanides crystallize into heptahydrates [Ln2(CrO4)3(H2O)s] 2H2O (Ln = La, Pr, Nd, Sm) and tetrahydrate Eu2(CrO4)3.4H2O with a monoclinic structure (sp. gr. P21/c). The chromates of heavy lanthanides (Ln = Gd, Dy, Ho, Yb, Y) remain X-ray amorphous.

The crystal/local structure and morphology of hydrated molybdenum oxides particles obtained by acidic precipitation of molybdates solutions were studied using X-ray diffraction, X-ray absorption spectroscopy, scanning electron microscopy, Raman and IR spectroscopy. The precipitation of ammonium heptamolybdate solutions (pH = 1.00) at room temperature result in the formation of poorly crystallized hydrated molybdenum oxides. At the same time, acidification of the sodium molybdate solutions does not lead to the appearance of precipitates for several days. Heating to 90 degrees C and aging the reaction suspension prepared from both ammonium heptamolybdate and sodium molybdate results in the formation of prismatic h-MoO3 particles with the hexagonal crystal structure. It was shown that distorted octahedra MoO6 are the basic structural units in the formed hydrated molybdenum oxides. Along with the presence of Mo=O and Mo-O bonds, the presence of water molecules, hydroxyl ions, and NH4+ (or Na+) ions was detected in the structure of hydrated MoO3. The type of Mo salt and acid significantly affects the morphology of h-MoO3 particles. Large h-MoO3 particles are formed by aggregation of small ones and Ostwald ripening due to the "dissolution - precipitation" process.

The discovery of superconductivity above 250 K at high pressure in LaH10 and the prediction of overcoming the room temperature threshold for superconductivity in YH10 urge for a better understanding of hydrogen interaction mechanisms with the heavy atom sublattice in metal hydrides under high pressure at the atomic scale. Here we use locally sensitive X-ray absorption fine structure spectroscopy (XAFS) to get insight into the nature of phase transitions and the rearrangements of local electronic and crystal structure in archetypal metal hydride YH3 under pressure up to 180 GPa. The combination of the experimental methods allowed us to implement a multiscale length study of YH3: XAFS (short-range), Raman scattering (medium-range) and XRD (long-range). XANES data evidence a strong effect of hydrogen on the density of 4d yttrium states that increases with pressure and EXAFS data evidence a strong anharmonicity, manifested as yttrium atom vibrations in a double-well potential.