Anhydrous copper tellurite sulfate, Cu
TeO
(SO
)
, has been synthesized
vapor transport reactions in sealed silica glass ampoules. In measurements of magnetization
, magnetic susceptibility
, ...specific heat
and X-band electron spin resonance, a long-range antiferromagnetic order at
= 13 K and an
-
magnetic phase diagram have been established. One-third of Cu
ions were found to form magnetically silent dimers. A peak in dielectric permittivity
, which accompanies the Néel order, allows considering Cu
TeO
(SO
)
as a magnetoelectric multiferroic material of the second type. Density functional theory calculations provided estimations of leading exchange interaction parameters.
Anhydrous copper tellurite sulfate, Cu3TeO3(SO4)2, has been synthesized via vapor transport reactions in sealed silica glass ampoules. In measurements of magnetization M, magnetic susceptibility χ, ...specific heat Cp and X-band electron spin resonance, a long-range antiferromagnetic order at TN = 13 K and an H–T magnetic phase diagram have been established. One-third of Cu2+ ions were found to form magnetically silent dimers. A peak in dielectric permittivity ϵ, which accompanies the Néel order, allows considering Cu3TeO3(SO4)2 as a magnetoelectric multiferroic material of the second type. Density functional theory calculations provided estimations of leading exchange interaction parameters.
Three tetraphenylborates of mononuclear Mn(III) cation complexes with hexadentate ligands, the products of the reaction between a N,N'-bis(3-aminopropyl)ethylenediamine and salicylaldehydes with the ...different haloid substitutions at the 5 or 3,5 positions, have been synthesized: Mn(5-F-sal-N-1,5,8,12)BPh
(1), Mn(3,5-diCl-sal-N-1,5,8,12)BPh
(2) and Mn(3,5-Br,Cl-sal-N-1,5,8,12)BPh
(3). Their crystal structure, dielectric constant (ϵ) and magnetic properties have been studied. Ligand substituents have a dramatic effect on the structure and magnetic properties of the complexes. With decreasing temperature, the complex (1) shows a gradual spin crossover from the high-spin state (HS) to the HS:LS intermediate phase, followed by an abrupt transition to the low-spin state (LS) without changing the crystal symmetry. The complexes 2 and 3 are isostructural, but have fundamentally different properties. Complex 2 demonstrates two structural phase transitions related to sharp spin crossovers from the HS to the HS:LS intermediate phase at 137 K and from the intermediate phase to the LS at 87 K, while complex 3 exhibits only one spin transition from the HS to the HS:LS intermediate phase at 83 K.
The iron(
iii
) anionic complex based on a pyruvic acid thiosemicarbazone ligand with the lithium cation LiFe
III
(thpy)
2
·3H
2
O (
1
) has been synthesized and characterized by FTIR spectroscopy, ...powder and single crystal X-ray diffraction, direct current magnetic susceptibility measurements, and
57
Fe Mössbauer spectroscopy. Moreover, the molecular structure of the Fe(thpy)
2
−
anion has been determined for the first time. The Fe(thpy)
2
−
units in the triclinic
P
1&cmb.macr; lattice of
1
are assembled into layers parallel to the
bc
plane. The Li
+
cations and water molecules are located between the layers and the structure is stabilized by hydrogen bonding. The Fe(thpy)
2
−
anions form interconnected dimer pairs through hydrogen bonds and short contacts with Fe Fe separation of 6.7861(4) Å. According to dc magnetic measurements, compound
1
demonstrates an incipient spin-crossover transition from the LS (
S
= 1/2) to the HS (
S
= 5/2) state above 250 K. The Bleaney-Bowers equation for a model of an isolated LS dimer with a mean-field correction was applied to fit the experimental data of magnetic susceptibility dependence on temperature in the temperature range of 2-250 K. The intra-dimer
J
1
= −1.79(1) K and inter-dimer
J
2
= −0.24(3) K antiferromagnetic coupling constants were defined. The analysis of the
57
Fe Mössbauer spectra at 80 K and 296 K confirms the presence of the shortened distances between the iron nuclei. Moreover, the influence of the lithium cation on the stabilization of the LS state was shown for the Fe(thpy)
2
−
anion. BS-DFT calculations for the optimized structure of two isolated Fe(thpy)
2
−
anions also correctly predict a weak exchange
J
1
(calc) = −0.92 K. DFT calculations revealed the OPBE (GGA-type) functional that correctly predicts the spin-crossover transition for the iron(
iii
) thpy compounds. Besides, the effect of the N
2
O
4
, N
2
S
2
O
2
, and N
2
Se
2
O
2
coordination environments on the energy stabilization of the LS state of iron(
iii
) anionic thpy complexes was noted as well.
The X-ray structure of the anionic complex based on a pyruvic acid thiosemicarbazone ligand LiFe
III
(thpy)
2
·3H
2
O has been determined for the first time.
Display omitted
•Basic thermodynamic properties of Nd-francisites are reported.•Rare-earth spectroscopy revealed the spin-reorientation.•Magnetic phase diagrams of Cu3Nd(SeO3)2O2X (X = Cl, Br) are ...established.
The kagome lattice of copper ions in francisite-type compounds is quite sensitive to external stimuli, being easily affected by temperature and magnetic field. The rare-earth ions inserted between buckled layers of transition metal add new dimension to magnetism in these systems. Neodymium francisites, Cu3Nd(SeO3)2O2X (X = Cl, Br), experience long range magnetic order at TN = 34 K (Cl) or 35.2 K (Br) and spin reorientation transition at TR = 4 K (Cl) or 4.6 K (Br) marked by sharp anomalies in magnetization M, specific heat Cp, and optical spectra. The spin reorientation of Cu2+ ions is due to d-f interaction of transition and rare-earth magnetic subsystems. Under action of modest external field B < 2 T both compounds exhibit metamagnetic phase transition, largely hysteretic in case of Cl compound at T < TR.
The superconducting transition temperature (Tc) of tetragonal Fe1+δSe was enhanced from 8.5 K to 44 K by chemical structure modification. While insertion of large alkaline cations like K or solvated ...lithium and iron cations in the interlayer space, the Fe2Se2 interlayer separation increases significantly from 5.5 Å in native Fe1+δSe to >7 Å in KxFe1-ySe and to >9 Å in Li1-xFex(OH)Fe1-ySe, we report on an electrochemical route to modify the superconducting properties of Fe1+δSe. In contrast to conventional chemical (solution) techniques, the electrochemical approach allows to insert non-solvated Li(+) into the Fe1+δSe structure which preserves the native arrangement of Fe2Se2 layers and their small separation. The amount of intercalated lithium is extremely small (about 0.07 Li(+) per f.u.), however, its incorporation results in the enhancement of Tc up to ∼44 K. The quantum-mechanical calculations show that Li occupies the octahedrally coordinated position, while the Fe2Se2 layers remain basically unmodified. The obtained enhancement of the electronic density of states at the Fermi level clearly exceeds the effect expected on basis of rigid band behavior.
The evolution of the Boson heat capacity peak in a typical metallic glass upon structural relaxation and partial crystallization is studied. It is found that heat treatment changes the peak height in ...both fully amorphous and partially crystalline states in line with the prediction of the Interstitialcy theory.
The height of the Boson heat capacity peak in a typical metallic glass subjected to structural relaxation and partial crystallization is a linear function of the defect concentration calculated within the framework of the Interstitialcy theory. The slope of this dependence agrees with the theory.
The n = 3–6 members of a new perovskite-based homologous series Bi3n+1Ti7Fe3n–3O9n+11 are reported. The crystal structure of the n = 3 Bi10Ti7Fe6O38 member is refined using a combination of X-ray ...and neutron powder diffraction data (a = 11.8511(2) Å, b = 3.85076(4) Å, c = 33.0722(6) Å, S.G. Immm), unveiling the partially ordered distribution of Ti4+ and Fe3+ cations and indicating the presence of static random displacements of the Bi and O atoms. All Bi3n+1Ti7Fe3n–3O9n+11 structures are composed of perovskite blocks separated by translational interfaces parallel to the (001)p perovskite planes. The thickness of the perovskite blocks increases with n, while the atomic arrangement at the interfaces remains the same. The interfaces comprise chains of double edge-sharing (Fe,Ti)O6 octahedra connected to the octahedra of the perovskite blocks by sharing edges and corners. This configuration shifts the adjacent perovskite blocks relative to each other over a vector 1/2110p and creates S-shaped tunnels along the 010 direction. The tunnels accommodate double columns of the Bi3+ cations, which stabilize the interfaces owing to the stereochemical activity of their lone electron pairs. The Bi3n+1Ti7Fe3n–3O9n+11 structures can be formally considered either as intergrowths of perovskite modules and polysynthetically twinned modules of the Bi2Ti4O11 structure or as intergrowths of the 2D perovskite and 1D anatase fragments. Transmission electron microscopy (TEM) on Bi10Ti7Fe6O38 reveals that static atomic displacements of Bi and O inside the perovskite blocks are not completely random; they are cooperative, yet only short-range ordered. According to TEM, the interfaces can be laterally shifted with respect to each other over ±1/3a, introducing an additional degree of disorder. Bi10Ti7Fe6O38 is paramagnetic in the 1.5–1000 K temperature range due to dilution of the magnetic Fe3+ cations with nonmagnetic Ti4+. The n = 3, 4 compounds demonstrate a high dielectric constant of 70–165 at room temperature.
The authors measure the low temperature heat capacity of a Pd‐based metallic glass and derive the Boson peak height in relation with the enthalpy changes occurring upon structural relaxation and ...crystallization. The Boson peak height was also calculated within the framework of the Interstitialcy theory as a function of the excess enthalpy of glass with respect to the maternal crystal. A good agreement between experiment and calculation is found.
The height of the Boson heat capacity peak in a typical metallic glass depends on the excess enthalpy of the non‐crystalline state with respect to the maternal crystal. The calculation of the peak height within the framework of the Interstitialcy theory provides a good agreement with the experimental data.
The Bi3n+1Ti7Fe3n–3O9n+11 materials are built of (001)p plane-parallel perovskite blocks with a thickness of n (Ti,Fe)O6 octahedra, separated by periodic translational interfaces. The interfaces are ...based on anatase-like chains of edge-sharing (Ti,Fe)O6 octahedra. Together with the octahedra of the perovskite blocks, they create S-shaped tunnels stabilized by lone pair Bi3+ cations. In this work, the structure of the n = 4–6 Bi3n+1Ti7Fe3n–3O9n+11 homologues is analyzed in detail using advanced transmission electron microscopy, powder X-ray diffraction, and Mössbauer spectroscopy. The connectivity of the anatase-like chains to the perovskite blocks results in a 3a p periodicity along the interfaces, so that they can be located either on top of each other or with shifts of ±a p along 100p. The ordered arrangement of the interfaces gives rise to orthorhombic Immm and monoclinic A2/m polymorphs with the unit cell parameters a = 3a p, b = b p, c = 2(n + 1)c p and a = 3a p, b = b p, c = 2(n + 1)c p – a p, respectively. While the n = 3 compound is orthorhombic, the monoclinic modification is more favorable in higher homologues. The Bi3n+1Ti7Fe3n–3O9n+11 structures demonstrate intricate patterns of atomic displacements in the perovskite blocks, which are supported by the stereochemical activity of the Bi3+ cations. These patterns are coupled to the cationic coordination of the oxygen atoms in the (Ti,Fe)O2 layers at the border of the perovskite blocks. The coupling is strong in the n = 3, 4 homologues, but gradually reduces with the increasing thickness of the perovskite blocks, so that, in the n = 6 compound, the dominant mode of atomic displacements is aligned along the interface planes. The displacements in the adjacent perovskite blocks tend to order antiparallel, resulting in an overall antipolar structure. The Bi3n+1Ti7Fe3n–3O9n+11 materials demonstrate an unusual diversity of structure defects. The n = 4–6 homologues are robust antiferromagnets below T N = 135, 220, and 295 K, respectively. They show a high dielectric constant that weakly increases with temperature and is relatively insensitive to the Ti/Fe ratio.
PDF
