Search

Ba (Fe 1 / 2 Nb 1 / 2) O 3 ceramics are considered to be promising for technological applications owing to their high dielectric constant over a wide range of temperatures. However, there exists considerable discrepancy over the structural details. We address this discrepancy through a combined x-ray diffraction at room temperature and neutron powder diffraction measurements in the range from 5 K up to room temperature, supplemented by a comparative analysis of the earlier reported structures. Our study reveals a cubic structure with space group P m 3 ¯ m at all measured temperatures. Further, the x-ray near edge structure and extended x-ray absorption fine structure studies on the local environment of the Fe ions is consistent with the cubic symmetry. An appropriate value of U for DFT+ U calculations is obtained by comparison with x-ray absorption spectroscopy, which agrees well with the earlier reported electronic properties. [ABSTRACT FROM AUTHOR]

Topological insulators (TIs) are semiconductors with protected electronic surface states that allow dissipation‐free transport. TIs are envisioned as ideal materials for spintronics and quantum computing. In Bi14Rh3I9, the first weak 3D TI, topology presumably arises from stacking of the intermetallic [(Bi4Rh)3I]2+ layers, which are predicted to be 2D TIs and to possess protected edge‐states, separated by topologically trivial [Bi2I8]2− octahedra chains. In the new layered salt Bi12Rh3Cu2I5, the same intermetallic layers are separated by planar, i.e., only one atom thick, [Cu2I4]2− anions. Density functional theory (DFT)‐based calculations show that the compound is a weak 3D TI, characterized by Z2=(0;0001), and that the topological gap is generated by strong spin–orbit coupling (Eg,calc. ∼ 10 meV). According to a bonding analysis, the copper cations prevent strong coupling between the TI layers. The calculated surface spectral function for a finite‐slab geometry shows distinct characteristics for the two terminations of the main crystal faces ⟨001⟩, viz., [(Bi4Rh)3I]2+ and [Cu2I4]2−. Photoelectron spectroscopy data confirm the calculated band structure. In situ four‐point probe measurements indicate a highly anisotropic bulk semiconductor (Eg,exp. = 28 meV) with path‐independent metallic conductivity restricted to the surface as well as temperature‐independent conductivity below 60 K. [ABSTRACT FROM AUTHOR]

Pure powders of Na(LiZn)S2 can be obtained through a solid-state reaction, and A(LiZn)S2 (A = K, Rb, Cs) result from metathesis reactions between alkali-metal chlorides and the same constituents used to prepare the Na(LiZn)S2 powder. Hence, the metathesis reaction enables extended sulphide chemistry without the use of either H2S gas or very reactive starting materials. By the metathesis reaction it was possible to obtain relatively pure Cs(LiZn)S2. Trigonal Na(LiZn)S2 and tetragonal A(LiZn)S2 (A = K, Rb, Cs) exhibit significant structural similarities, having (LiZn)S2 layers that are separated by alkali-metals (Na–Cs). Against expectations, Cs(LiZn)S2 is orange red in colour, Rb(LiZn)S2 is strongly yellow, K(LiZn)S2 is pale yellow, and Na(LiZn)S2 is colourless. Ultraviolet-visible spectroscopy data on Cs(LiZn)S2 and Na(LiZn)S2 contain several shoulders apart from apparent band-edges close to 3.3 eV. In the former, it seems as if the optical excitations range all the way into green (∼600 nm), which concurs with the observed red colour. Nuclear magnetic resonance investigations on cores 133Cs, 23Na, and 7Li suggest that these ions are firmly held in the atomic lattice, as judged by the resonance frequency widths and relatively long nuclear spin relaxation times (T1), ranging from 10 to 200 seconds for 23Na and 7Li. So there should be only electronic excitations in these compounds. Band-structure calculations of Li–Zn ordered versions of the lattices suggest a direct band-gap in both compounds, corresponding to an excitation from sulphur to zinc. The theoretical band-gaps amount to 2.54 eV for CsLiZnS2 and 1.85 eV for NaLiZnS2, and the steep edges in the density of states are found at 3.3 eV for both cases. As no Li–Zn ordering is observed by X-ray diffraction, there must be an inherent atomic disorder. By theoretical simulations, local Li–Zn anti-site orderings were introduced and the resulting electronic structure was evaluated. However, the simulated optical behaviour could only tentatively explain the spectroscopic data of Na(LiZn)S2; the orange red colour of Cs(LiZn)S2 must be an even more complex phenomenon, as the Li–Zn simulations were insufficient to explain the relatively strong optical activity in the range between 400 and 600 nm. [ABSTRACT FROM AUTHOR]

Single crystal specimens of previously unknown garnet Eu2PbSb2Zn3O12 were grown in a reactive PbO:PbF2 flux medium. The crystals were characterized by a combination of X‐ray crystallography, magnetization measurements, and the optical techniques of Raman, photoluminescence, and UV/Vis spectroscopy. The material exhibits Van Vleck paramagnetism associated with the J = 0 state of Eu3+, which was possible to accurately fit to a theoretical model. Band structure calculations were performed and compared to the experimental band gap of 1.98 eV. The crystals demonstrate photoluminescence associated with the 4f6 configuration of the Eu3+ ions sitting at the distorted 8‐coordinate garnet A site. The title compound represents a unique quinary contribution to a relatively unexplored area of rare earth bearing garnet crystal chemistry. [ABSTRACT FROM AUTHOR]

We uncover four spin-charge ordered ground states in the strong coupling limit of the Kondo lattice model on triangular geometry. The results are obtained using Monte Carlo simulations, with a classical treatment of localized moments. Two of the states at one-third electronic filling (n = 1/3) consist of decorated ferromagnetic chains coupled antiferromagnetically with the neighboring chains. The third magnetic ground state is noncollinear, consisting of antiferromagnetic chains separated by a pair of canted ferromagnetic chains. An even more unusual magnetic ground state, a variant of the 120° Yafet-Kittel phase, is discovered at n = 2/3. These magnetic orders are stabilized by opening a gap in the electronic spectrum: a "band effect." All the phases support modulations in the electronic charge density due to the presence of magnetically inequivalent sites. In particular, the charge ordering pattern found at n = 2/3 is observed in various triangular lattice systems, such as 2H-AgNiO2, 3R-AgNiO2, and NaxCoO2. [ABSTRACT FROM AUTHOR]

Li-doped NKLN ceramic (Na0.5 K0.5)0.935Li0.065NbO3 (NKLN935) in pure and MnO2 doped compositions have been revisited to carry out a detailed analysis of the structural and optical properties. Rietveld analysis of the X-ray diffraction (XRD) pattern reveals the system to be tetragonal (space group P4mm). UV–Visible (UV–Vis) spectroscopy and an equivalent Kubelka–Munk function is used to obtain the optical band gap values. It is reported that with increasing Mn doping, the band gap values decreases, which has been analyzed and understood in terms of the tetragonal structure and is found to be consistent with dielectric properties. [ABSTRACT FROM AUTHOR]

Polyaniline (PANI) film prepared from using water-soluble support polymer polyvinyl alcohol (PVA) has been irradiated with 95 MeV oxygen (O6+) ions at the fluences from 1011to 1012 ions/cm2. The thermal, dielectric, structural and microstructural properties of the samples are investigated by differential scanning calorimeter and thermogravimetric analysis, LCR meter, X-ray diffraction and scanning electron microscope. The structural studies reveal that amorphization on irradiation which may be due to the scission of polymer bonds as there is a signature of columnar tracts and the appearance of voids in the sample increases with increasing O6+ions irradiation-dose. Frequency-dependent spectra of the imaginary electric modulus suggest that long-range conduction in pristine sample changes to short-range,i.e.localized conduction in 95 MeV O6+ion-irradiation PANI–PVA. The behaviour of the ac conductivity reveals that the conduction mechanism in both pristine and irradiated sample is correlated to the barrier hopping model. [ABSTRACT FROM PUBLISHER]

Very recently a quantum liquid was reported to form in H3LiIr2O6, an iridate proposed to be a close realization of the Kitaev honeycomb model. To test this assertion we perform detailed quantum chemistry calculations to determine the magnetic interactions between Ir moments. We find that weakly bond dependent ferromagnetic Kitaev exchange dominates over other couplings, but still is substantially lower than in Na2IrO3. This reduction is caused by the peculiar position of the interlayer species: removing hydrogen cations next to a Ir2O2 plaquette increases the Kitaev exchange by more than a factor of 3 on the corresponding Ir-Ir link. Consequently, any lack of hydrogen order will have a drastic effect on the magnetic interactions and strongly promote spin disordering. [ABSTRACT FROM AUTHOR]

Single crystal specimens of previously unknown garnet Eu2PbSb2Zn3O12 were grown in a reactive PbO:PbF2 flux medium. The crystals were characterized by a combination of X‐ray crystallography, magnetization measurements, and the optical techniques of Raman, photoluminescence, and UV/Vis spectroscopy. The material exhibits Van Vleck paramagnetism associated with the J = 0 state of Eu3+, which was possible to accurately fit to a theoretical model. Band structure calculations were performed and compared to the experimental band gap of 1.98 eV. The crystals demonstrate photoluminescence associated with the 4f6 configuration of the Eu3+ ions sitting at the distorted 8‐coordinate garnet A site. The title compound represents a unique quinary contribution to a relatively unexplored area of rare earth bearing garnet crystal chemistry. [ABSTRACT FROM AUTHOR]

We show that introducing electrons in magnetic clusters and molecular magnets lead to rich phase diagrams with a variety of low-spin and high-spin states allowing for multiple switchability. The analysis is carried out for a quantum spin-fermion model using the exact diagonalization, and the cluster mean-field approach. The model is relevant for a number of molecular magnets with triangular motifs consisting of transition metal ions such as Cr, Cu and V. Re-entrant spin-state behavior and chirality on-off transitions exist over a wide parameter regime. A subtle competition among geometrical frustration effects, electron itinerancy, and Kondo coupling at the molecular level is highlighted. Our results demonstrate that electron doping provides a viable mean to tame the magnetic properties of molecular magnets towards potential technological applications. [ABSTRACT FROM AUTHOR]

With electron filling n  = 1 in theSr2VO4compound, the octahedrally coordinatedt2gorbitals are strongly active when the tetragonal distortion induced crystal field is tuned by external agent such as pressure. Considering the full range of crystal field induced tetragonal splitting in a realistic three-orbital model, collective spin-orbital excitations are investigated using the generalized self-consistent plus fluctuation approach. At ambient pressure, an entangled orbital + antiferromagnetic order is found to be stabilized beyond a critical value (∼30 meV) of spin-orbit coupling which is in the realistic range for 3d ions. The behavior of the calculated energy scales of collective excitations with crystal field is consistent with that of the transition temperatures with pressure as obtained from susceptibility and resistivity anomalies in high-pressure studies., (© 2022 IOP Publishing Ltd.)

Novel functionalities may be achieved in oxide electronics by appropriate stacking of planar oxide layers of different metallic species, MO p and M'O q . The simplest mechanism allowing the tailoring of the electronic states and physical properties of such heterostructures is of electrostatic nature-charge imbalance between the M and M' cations. Here we clarify the effect of interlayer electrostatics on the anisotropic Kitaev exchange in H 3 LiIr 2 O 6 , a recently proposed realization of the Kitaev spin liquid. By quantum chemical calculations, we show that the precise position of H + cations between magnetically active [LiIr 2 O 6 ] 3- honeycomb-like layers has a strong impact on the magnitude of Kitaev interactions. In particular, it is found that stacking with straight interlayer O-H-O links is detrimental to in-plane Kitaev exchange since coordination by a single H-ion of the O ligand implies an axial Coulomb potential at the O site and unfavorable polarization of the O 2p orbitals mediating the Ir-Ir interactions. Our results therefore provide valuable guidelines for the rational design of Kitaev quantum magnets, indicating unprecedented Kitaev interactions of ≈40 meV if the linear interlayer linkage is removed.