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We present a comprehensive study of the inhomogeneous mixed-valence compound, EuPd3S4, by electrical transport, X-ray diffraction, time-domain 151Eu synchrotron Mössbauer spectroscopy, and X-ray absorption spectroscopy measurements under high pressure. Electrical transport measurements show that the antiferromagnetic ordering temperature, TN, increases rapidly from 2.8 K at ambient pressure to 23.5 K at ~19 GPa and plateaus between ~19 and ~29 GPa after which no anomaly associated with TN is detected. A pressure-induced first-order structural transition from cubic to tetragonal is observed, with a rather broad coexistence region (~20 GPa to ~30 GPa) that corresponds to the TN plateau. Mössbauer spectroscopy measurements show a clear valence transition from approximately 50:50 Eu2+:Eu3+ to fully Eu3+ at ~28 GPa, consistent with the vanishing of the magnetic order at the same pressure. X-ray absorption data show a transition to a fully trivalent state at a similar pressure. Our results show that pressure first greatly enhances TN, most likely via enhanced hybridization between the Eu 4f states and the conduction band, and then, second, causes a structural phase transition that coincides with the conversion of the europium to a fully trivalent state. [ABSTRACT FROM AUTHOR]

The structural characterization and electrical transport measurements at ambient and applied pressures of the compounds of the LaAg 1 − x Au x Sb 2 family are presented. Up to two charge density wave (CDW) transitions could be detected upon cooling from room temperature and an equivalence of the effects of chemical and physical pressure on the CDW ordering temperatures was observed with the unit cell volume being a salient structural parameter. As such LaAg 1 − x Au x Sb 2 is a rare example of a non-cubic system that exhibits good agreement between the effects of applied, physical, pressure and changes in unit cell volume from steric changes induced by isovalent substitution. Additionally, for LaAg 0.54 Au 0.46 Sb 2 anomalies in low temperature electrical transport were observed in the pressure range where the lower charge density wave is completely suppressed. [ABSTRACT FROM AUTHOR]

Crystals of a new potassium cobalt(II) iron(II) triorthophosphate salt, K[Co.sub.3]Fe[(P[O.sub.4]).sub.3], as well as amorphous nanoparticles of the same material have been produced by hydrothermal reactions, under supercritical water (SCW) conditions, of equivalent quantities of aq. Co[Cl.sub.2] x 6[H.sub.2]O (2 mol/L) and [K.sub.4][P.sub.2][O.sub.7] (1 mol/L) in concd. HCl in a stainless steel batch reactor at 400-450°C and 25-32 MPa. The dark-violet crystals of the new salt have been characterized by single-crystal X-ray diffraction and IR, Raman, and Mossbauer spectroscopy. The Fe(II) in the new orthophosphate salt must derive from leaching of iron from the stainless steel walls of the reactor by concd. HCl under the SCW conditions. The salt crystallizes in the orthorhombic space group Pnnm, Z = 4, with unit cell parameters as follows: a = 9.672(1) Å, b = 16.457(2) Å, c = 6.2004(8) Å, V = 986.97 [Å.sup.3]. Microporous K[Co.sub.3]Fe[(P[O.sub.4]).sub.3] exhibits infinite chains of corner-sharing [[PO.sub.4.sup.3-]], [Fe[O.sub.6]], and [Co[O.sub.5]] units, which form two large rhombus tunnels, occupied by [K.sup.+] ions, running parallel to [100] in the unit cell. The vibrational spectra have been interpreted partly on the basis of factor group effects and are in accord with the centrosymmetric structure of the material. The particle sizes of this new nanomaterial and their distribution have been determined by scanning electron micrography and laser scattering particle size distribution analysis, while the amorphous nanomaterial has also been characterized by X-ray powder diffraction and Raman spectroscopy. Key words: crystal structure, vibrational and Mossbauer spectra, orthophosphate, nanomaterial. Les cristaux du nouveau sel tri-orthophosphate de potassium, cobalt(II) et fer(II), K[Co.sub.3]Fe[(P[O.sub.4]).sub.3], ainsi que des nano particules amorphe du meme materiel, ont ete produites par reactions hydrothermal dans des conditions supercritique de l'eau. Ils sont obtenus a partir d'un melange equimolaire des solutions aqueuses CO[Cl.sub.2] x 6[H.sub.2]O (2 mol/L), et [K.sub.4][P.sub.2][O.sub.7] (1 mol/L), en milieu acide HCl concentre dans un tube en acier inoxydable a temperatures 400-450°C, et a pression 25-32 MPa. Les cristaux violets fonces du nouveau sel ont ete caracterises par diffraction des rayons-X sur monocristal, et par spectroscopie IR, Raman et Mossbauer. Le Fe(II) du nouveau sel d'orthophosphate provient d'une infiltration a partir de la parois interne du reacteur en acier inoxydable, sous l'effet de l'acide HCl concentre dans les conditions supercritique de l'eau. Le sel cristallise dans le systeme orthorhombique de groupe d'espace Pnnm, avec Z = 4. Les parametres cristallographiques de la maille sont : a = 9.672(1) Å, b = 16.457(2) Å, c = 6.2004(8) Å, V = 986.97 [Å.sup.3]. La structure microporeuse de K[Co.sub.3]Fe(P[O.sub.4])3 se presente sous forme de chaines formees des groupements [P[O.sub.4.sup.3-]], [Co[O.sub.5]] et [Fe[O.sub.6]]. Ils partageant des atomes en commun, creant ainsi deux larges tunnels par maille elementaire. Ils sont alignes le long de l'axe [100], en forme rhomboedre, loges par des cations [K.sup.+]. Les spectres de vibration ont ete interpretes en utilisant l'analyse du groupe facteur des groupements P[[O.sub.4.sup.3-]. L'absence de coincidence entre la plupart des frequences de vibrations IR et Raman est en accord avec la structure centro-symetrique du materiau. La taille et la repartition des nouvelles nanoparticules amorphes ont ete determinees par la micrographic SEM, et l'analyseur de distribution de taille des particules par diffusion laser. Ce materiau est caracterise par diffraction des rayons-X sur poudre et par spectroscopie Raman. Mots cles : structure cristalline, spectres de vibration et Mossbauer, orthophosphate, nanomateriau., Introduction Hydrothermal synthesis has been carried out since the end of the 19th century, mainly in the production of synthetic minerals to imitate natural geothermal processes (1, 2). More recently, [...]

Aqueous solutions of iron salts can be applied to a wood surface to modify its color. When applied on wood, iron ions are chelated by the wood's natural phenolic compounds. The resulting color of the wood surface is due to the type of reaction products formed, such as mono-, bis- and tris- complexes of polyphenols with iron cations. In order to identify the different complexes formed on Quercus alba L. wood's surface and the oxidation state of iron after application of different iron salts on the same wood species which influence the resulting color of wood's surface, Mössbauer spectroscopy was performed directly on iron-stained wood samples. Colors of the stained wood samples, measured by a spectrophotometer, were analyzed in relation to the differences between the reaction products. The results showed that for a given wood species, the oxidation and reduction behavior of the iron depended on both the type of counterion and the oxidation state of the chosen iron salt. [ABSTRACT FROM AUTHOR]

The evolution of the electron delocalization in the ferrous subspectra in a sample of mixed valence ferrous‐ferric freudenbergite has been followed by Mössbauer spectroscopy from 6 K to 650 K. The spectral changes do not involve the ferric component, leading to the conclusion that it is due to a thermally driven delocalization of the sixth d‐electron on the ferrous ions. The phenomenon does not occur in samples of pure ferrous freudenbergite. [ABSTRACT FROM AUTHOR]

An experiment was carried out to pinpoint the temperature of formation of the solid solution on heating LiFeP[O.sub.4]/FeP[O.sub.4] above 500 K to show that small polaron transport is responsible for electron transport. The onset of rapid small polaron hopping on the time scale is precisely correlated with the temperature that the lithium ions begins to disorder in the lattice, showing that the two events are correlated.

Intrinsicmagnetic properties (saturationmagnetization, anisotropy fields, andCurie temperatures) of Ce2Fe14B doped with Al, Ni, and Si are presented. Substitution for Fe by these elements leads to the formation of solid solutions that crystallize in the tetragonal Nd2Fe14B structure. Substituting Al, Ni, or Si for Fe leads to a decrease in both the saturation magnetization and the anisotropy field of Ce2Fe14B. Ni and Si increase the Curie temperature of Ce2Fe14B while Al reduces it.While, for the Ce2(Fe14-xTx)B containingNi, amaximumCurie temperature of 210 °Cwas observed at 9 atom%Ni (x = 1.45), the highest value of 252 °C was found for the Ce2Fe14B containing 14 atom % Si (x = 2.26). [ABSTRACT FROM AUTHOR]

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Transition metal phosphates such as LiFePO4 have been recognized as very promising electrodes for lithium-ion batteries because of their energy storage capacity combined with electrochemical and thermal stability. A key issue in these materials is to unravel the factors governing electron and ion transport within the lattice. Lithium extraction from LiFePO4 results in a two-phase mixture with FePO4 that limits the power characteristics owing to the low mobility of the phase boundary. This boundary is a consequence of low solubility of the parent phases, and its mobility is impeded by slow migration of the charge carriers. In principle, these limitations could be diminished in a solid solution, LixFePO4. Here, we show that electron delocalization in the solid solution phases formed at elevated temperature is due to rapid small polaron hopping and is unrelated to consideration of the band gap. We give the first experimental evidence for a strong correlation between electron and lithium delocalization events that suggests they are coupled. Furthermore, the exquisite frequency sensitivity of Mössbauer measurements provides direct insight into the electron hopping rate. [ABSTRACT FROM AUTHOR]

Crystals of a new potassium cobalt(II) iron(II) triorthophosphate salt, KCo3Fe(PO4)3, as well as amorphous nanoparticles of the same material have been produced by hydrothermal reactions, under supercritical water (SCW) conditions, of equivalent quantities of aq. CoCl2·6H2O (2 mol/L) and K4P2O7 (1 mol/L) in concd. HCl in a stainless steel batch reactor at 400–450 °C and 25–32 MPa. The dark-violet crystals of the new salt have been characterized by single-crystal X-ray diffraction and IR, Raman, and Mössbauer spectroscopy. The Fe(II) in the new orthophosphate salt must derive from leaching of iron from the stainless steel walls of the reactor by concd. HCl under the SCW conditions. The salt crystallizes in the orthorhombic space group Pnnm, Z = 4, with unit cell parameters as follows: a = 9.672(1) Å, b = 16.457(2) Å, c = 6.2004(8) Å, V = 986.97 Å3. Microporous KCo3Fe(PO4)3 exhibits infinite chains of corner-sharing [PO43–], [FeO6], and [CoO5] units, which form two large rhombus tunnels, occupied by K+ ions, running parallel to [100] in the unit cell. The vibrational spectra have been interpreted partly on the basis of factor group effects and are in accord with the centrosymmetric structure of the material. The particle sizes of this new nanomaterial and their distribution have been determined by scanning electron micrography and laser scattering particle size distribution analysis, while the amorphous nanomaterial has also been characterized by X-ray powder diffraction and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

We present a comprehensive study of the inhomogeneous mixed-valence compound, EuPd 3 S 4 , by electrical transport, X-ray diffraction, time-domain 151 Eu synchrotron Mössbauer spectroscopy, and X-ray absorption spectroscopy measurements under high pressure. Electrical transport measurements show that the antiferromagnetic ordering temperature, T N , increases rapidly from 2.8 K at ambient pressure to 23.5 K at ~19 GPa and plateaus between ~19 and ~29 GPa after which no anomaly associated with T N is detected. A pressure-induced first-order structural transition from cubic to tetragonal is observed, with a rather broad coexistence region (~20 GPa to ~30 GPa) that corresponds to the T N plateau. Mössbauer spectroscopy measurements show a clear valence transition from approximately 50:50 Eu 2+ :Eu 3+ to fully Eu 3+ at ~28 GPa, consistent with the vanishing of the magnetic order at the same pressure. X-ray absorption data show a transition to a fully trivalent state at a similar pressure. Our results show that pressure first greatly enhances T N , most likely via enhanced hybridization between the Eu 4 f states and the conduction band, and then, second, causes a structural phase transition that coincides with the conversion of the europium to a fully trivalent state., Competing Interests: Competing interests statement:The authors declare no competing interest.

Electrons in solids often adopt complex patterns of chemical bonding driven by the competition between energy gains from covalency and delocalization, and energy costs of double occupation to satisfy Pauli exclusion, with multiple intermediate states in the transition between highly localized, and magnetic, and delocalized, and nonmagnetic limits. Herein, we report a chemical pressure-driven transition from a proper Mn magnetic ordering phase transition to a Mn magnetic phase crossover in EuMn 2 P 2 the limiting end member of the EuMn 2 X 2 (X = Sb, As, P) family of layered materials. This loss of a magnetic ordering occurs despite EuMn 2 P 2 remaining an insulator at all temperatures, and with a phase transition to long-range Eu antiferromagnetic order at T N ≈ 17 K. The absence of a Mn magnetic phase transition contrasts with the formation of long-range Mn order at T ≈ 130 K in isoelectronic EuMn 2 Sb 2 and EuMn 2 As 2 . Temperature-dependent specific heat and 31 P NMR measurements provide evidence for the development of short-range Mn magnetic correlations from T ≈ 250-100 K, interpreted as a precursor to covalent bond formation. Density functional theory calculations demonstrate an unusual sensitivity of the band structure to the details of the imposed Mn and Eu magnetic order, with an antiferromagnetic Mn arrangement required to recapitulate an insulating state. Our results imply a picture in which long-range Mn magnetic order is suppressed by chemical pressure, but that antiferromagnetic correlations persist, narrowing bands and producing an insulating state.

The series BaIn 1- x Fe x O 2.5+δ , x = 0.25, 0.50, and 0.75, has been prepared under air-fired and argon-fired conditions and studied using X-ray diffraction, d.c. and a.c. susceptibility, Mössbauer spectroscopy, neutron diffraction, X-ray near edge absorption spectroscopy (XANES), and X-ray pair distribution (PDF) methods. While Ba 2 In 2 O 5 (BaInO 2.5 ) crystallizes in an ordered brownmillerite structure, Ibm 2, and Ba 2 Fe 2 O 5 (BaFeO 2.5 ) crystallizes in a complex monoclinic structure, P 2 1 / c , showing seven Fe 3+ sites with tetrahedral, square planar, and octahedral environments, all phases studied here crystallize in the cubic perovskite structure, Pm 3̅ m , with long-range disorder on the small cation and oxygen sites. 57 Fe Mössbauer studies indicate a mixed valency, Fe 4+ /Fe 3+ , for both the air-fired and argon-fired samples. The increased Fe 3+ content for the argon-fired samples is reflected in increased cubic cell constants and in the increased Mössbauer fraction. It appears that the Pm 3̅ m phases are only metastable when fired in argon. From a slightly modified percolation theory for a primitive cubic lattice (taking into account the presence of random O atom vacancies), long-range spin order is permitted for the x = 0.50 and 0.75 phases. Instead, the d.c. susceptibility shows only zero-field-cooled (ZFC) and field-cooled (FC) divergences at ∼6 K [5 K] for x = 0.50 and at ∼22 K [21 K] for x = 0.75, with values for the argon-fired samples in [ ]. Neutron diffraction data for the air-fired samples confirm the absence of long-range magnetic order at any studied temperature. For the air-fired x = 0.50, a.c. susceptibility data show a frequency-dependent χ'(max) and spin glass behavior, while for x = 0.75, χ'(max) is invariant with frequency, ruling out either a spin glass or a superparamagnetic ground state. These behaviors are discussed in terms of competing Fe 3+ -Fe 3+ antiferromagnetic exchange and ferromagnetic Fe 3+ -Fe 4+ exchange. The PDF and 57 Fe Mössbauer data indicate a local structure at short interatomic distances, which deviates strongly from the average Pm 3̅ m model. Fe Mössbauer, PDF, and XANES data show a systematic dependence on x and indicate that the Fe 3+ sites are largely fourfold-coordinated and Fe 4+ sites are fivefold- or sixfold-coordinated., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Sr(2)FeMnO(5+y) was synthesized under two different conditions, in air and in argon, both of which resulted in a cubic, Pm ̅3m, structure with no long-range ordering of oxygen vacancies. The unit cell constants were found to be a(0) = 3.89328(1) Å for argon (y = 0.0) and a(0) = 3.83075(3) Å for air (y = 0.5). In contrast, Ca(2)FeMnO(5) retains long-range brownmillerite oxygen vacancy ordering for either air or argon synthesis. Remarkably, Sr(2)FeMnO(5.0) oxidizes spontaneously in air at room temperature. A neutron pair distribution function (NPDF) study of Sr(2)FeMnO(5.0)(Ar) showed evidence for local, brownmillerite-like ordering of oxygen vacancies for short distances up to 5 Å. Mössbauer spectroscopy results indicate more than one Fe site for Sr(2)FeMnO(5+y)(Ar and air), consistent with the noncubic local structure found by NPDF analysis. The isomer shifts and quadrupole splittings in both air- and argon-synthesized materials are consistent with the 3+ oxidation state for Fe in sites with coordination number four or five. This is confirmed by an L-edge XANES study. Mn is almost entirely in the 3+ state for Sr(2)FeMnO(5.0)(Ar), whereas Mn(4+) is predominantly present for Sr(2)FeMnO(5.5)(air). Magnetic susceptibility data show zero-field-cooled/field-cooled (ZFC/FC) divergences near 50 K for the Ar sample and 25 K for the air sample, whereas Ca(2)FeMnO(5) is long-range G-type antiferromagnetically ordered at 407(2) K. Hyperfine magnetic splitting, observed in temperature-dependent Mössbauer measurements, indicates short-range magnetic correlations that persist up to 150 K for Sr(2)FeMnO(5.0)(Ar) and 100 K for Sr(2)FeMnO(5.5)(air), well above the ZFC/FC divergence temperatures. Neutron diffraction data confirm the absence of long-range magnetic ordering at room temperature and 4 K for Sr(2)FeMnO(5.0)(Ar) but indicate the presence of domains with short-range G-type order at 4 K with an average dimension of ∼50 Å (y = 0); thus, this material is actually a superparamagnet rather than a true spin glass. In sharp contrast, corresponding data for Sr(2)FeMnO(5.5)(air) show mainly a very weak magnetic Bragg peak, indicating that ∼4% of the sample has G-type antiferromagnetic ordering at 4 K., (© 2011 American Chemical Society)