Search

A new oxofluoride Co15F2(TeO3)14 has been prepared by optimized hydrothermal synthesis involving a complex mineralization process. The crystal structure consists of a three-dimensional network of CoO5(O,F) octahedra, distorted CoO5 square pyramids, TeO3 trigonal pyramids and grossly distorted TeO3+3 octahedra, which are linked by sharing corners and edges. The Te(IV) lone pairs are accommodated within novel pyritohedron-shaped [(TeO3)14]28− units. This special framework provides a much larger free space that allows Te atoms to vibrate with a large amplitude, which leads to extremely low lattice thermal conductivity. Magnetic susceptibility data for Co15F2(TeO3)14 show antiferromagnetic ordering below 9.6 K with a substantial orbital component to the effective magnetic moment. An S = 3/2 honeycomb-like spin network was carefully analyzed by experimental techniques and first principles calculations. [ABSTRACT FROM AUTHOR]

The cubic BaCoO∼2.2 was announced in the early 50's as the final product of high temperature self-reduction within the BaCoO3−δ series. However, apart from this report no clear characterization has been provided to date. Here, we confirm after the preparation of single crystal and powder samples that in this compound the ratio of oxygen vacancies is close to 27% in absence of any long range ordering. It follows that BaCoO2.22 appears as the most oxygen deficient cubic perovskite stabilized at room temperature, its tolerance factor being displaced close to 1 by the combination of large Ba2+ and Co2/3+ ions in the A and B sites. The tolerance factor plays a limiting role for re-oxidation and fluorination using topochemical routes, despite the high concentration of available vacancies. Single crystal XRD data and DFT structural relaxation show that the Co sites are off-centered inside pseudo-tetrahedra leading to reinforced magnetic exchanges. Robust antiferromagnetic ordering is suggested to occur above 400 K while this compound shows a semi-conducting behavior. It was also possible to prepare an even more reduced mixed metallic phase of formula BaCo0.5Fe0.5O2.16. [ABSTRACT FROM AUTHOR]

The crystal structure of the new phase BaCoII2(AsIII3O6)2·2(H2O) is built from the stacking of infinite [BaCO2(As3O6)2·H2O] sheets containing ∞[CoIIO4]6- chains interconnected by perpendicular ∞[AsIIIO2]- chains. It shows a metamagnetic transition below ~9 K at a critical field of ~0.11 T, leading to a moment value of 70% of the expected saturation, related to the spin flip between individual robust canted ferromagnetic chains. We propose a field-dependent scenario with magnetic moments lying in the CoIIO6 octahedral basal planes, fully compatible with our experimental results. Magnetic measurements under ac-field show slow spin dynamics with an intrinsic single-chain magnet (SCM)-like component slightly modified in the field-aligned regime. The characteristic relaxation time and energy barrier are about τo = 5.1 × 10-10 s and δτ = 35.3 K at Hdc = 0, respectively, which falls close to values found for other (but organometallic) SCM CoII chains. This magnetic behavior is unique in the field of pure-inorganic compounds. [ABSTRACT FROM AUTHOR]

The combination of oxo-bismuthite slabs with counter oxo-anions main often leads to a series of layered Sillen-related compounds. For electroneutrality, it is convenient that the structure incorporates aliovalent cations such as Bi3+/M2+ ions that could be confined either in the Bi/O slabs or in the interleave. In the case of SO42- oxo-anions, only two compounds have been reported for M = Co, Cu, while interesting magnetic topologies emerge in absence of any prior characterization. Our reinvestigation of these systems using crystal growth in Bi2O3 flux led to the full structural characterization of [Bi2CoO3](SO4) (I) and [Bi6.2367Cu1.6O8](SO4)3 (II), which both exhibit pleated [Bi/M/O] slabs running in doubled cells comparatively to previous reports. (I) shows an interesting weak ferromagnetism (~0.2 µB/Co) below 17 K arising from Dzyaloshinskii-Moriya interactions in Co2+ zigzag chains, while (II) is essentially a paramagnet despite the presence of Cu2O6 dimers. Finally in the novel [Bi6O6](CoO2)(SO4)2 (III), the Co2+ ions are ordered with sulfate in the interleaves, leading to a noncentrosymmetric crystal structure. [ABSTRACT FROM AUTHOR]

A new oxofluoride Co15F2(TeO3)14 has been prepared by optimized hydrothermal synthesis involving a complex mineralization process. The crystal structure consists of a three-dimensional network of CoO5(O,F) octahedra, distorted CoO5 square pyramids, TeO3 trigonal pyramids and grossly distorted TeO3+3 octahedra, which are linked by sharing corners and edges. The Te(IV) lone pairs are accommodated within novel pyritohedron-shaped [(TeO3)14]28− units. This special framework provides a much larger free space that allows Te atoms to vibrate with a large amplitude, which leads to extremely low lattice thermal conductivity. Magnetic susceptibility data for Co15F2(TeO3)14 show antiferromagnetic ordering below 9.6 K with a substantial orbital component to the effective magnetic moment. An S = 3/2 honeycomb-like spin network was carefully analyzed by experimental techniques and first principles calculations. [ABSTRACT FROM AUTHOR]

In this work, we use first principles methods, to predict a mechanically and dynamically stable crystal structure of ThCrAsN which is iso-structural to ThXAsN (X = Mn,Fe,Co,Ni). We have investigated its mechanical, thermal, magnetic and electronic properties. Our calculation reveals that the magnetic ground state of ThCrAsN is G-AFM. Bader charge analysis reveals a significant inter-layer charge transfer between ThN and CrAs layers. Electronic structure of ThCrAsN is thoroughly investigated by evaluation of density of states, band structure and FSs for NM as well as G-AFM phases. Our calculation predicts a metallic behaviour for both the phases. Existence of FS pockets, consisting of multiple Cr-d orbitals at different parts of the Brillouin zone is observed. The influence of electron correlation effects on the electronic structure of ThCrAsN has been investigated using the Hubbard model. We also evaluate Lindhard response function to study the FS nesting which indicate a stronger FS nesting along Γ-X direction as compared to the Γ-M direction. Furthermore, we have examined the alterations in the density of states resulting from the partial substitution of Cr atom with Mn atom in ThCrAsN. Our findings suggest the occurrence of a metal-insulator transition in ThCrAsN upon Mn doping. [Display omitted] • Mechanical and dynamical stability of ThCrAsN. • Magnetic ground state of ThCrAsN is G-AFM. • Electronic structure of ThCrAsN in terms of density of states, band structure and Fermi surface. • Metal-insulator transition in ThCrAsN upon Mn doping. [ABSTRACT FROM AUTHOR]

Polycrystalline KLa5O5(VO4)2 is prepared by firing stoichiometric amounts of La(OH)3, V2O5, and K2CO3 in air (Al2O3 crucible, 1. [ABSTRACT FROM AUTHOR]