Ion Sublattice Research Articles

Magnetic ordering in double perovskites with 4d and 5d elements

B-site ordered double perovskites of the type AA′BB′O6 have attracted attention recently due to unusual and unpredictable modes of magnetic order. Of particular interest are materials where AA′ = Ba, Sr or La and B′ = Mo,Ru,Os and Re and B is a diamagnetic ion such as Li+,Na+,Ca2+, Mg2+, Zn2+ or Cd2+.Crystal symmetries encountered are Fm-3m, I4/m and P21/n as a function of the Goldschmidt tolerance factor which in turn impose local symmetries at the magnetic B′ site of m-3m, 4/m and -1, respectively. The magnetic ions have electronic configurations 4d1, 4d3,5d1, 5d2 and 5d3 with nominal spins, S = 1/2,1 and 3/2. Spin orbit coupling is very large, reaching ~ 0.5eV for the 5d ions, and plays a more important role than in the more familiar 3d-based magnetic materials. Geometric frustration, the B′ ion sublattice is f.c.c., based on edge sharing tetrahedra, also is of critical importance. Observed magnetic ground states range from spin glasses (without apparent disorder), collective spin singlets, ferromagnets and antiferromagnets. Often, ordered moments are a small fraction of a Bohr magneton. Systematic behavior is elusive. For example Ba2YReO6 and Ba2CaOsO6 (both Fm-3m) have the same unit cell constant to within .01 % and both are based on 5d2 ions but the former is a highly unconventional spin glass and the latter orders antiferromagnetically below 50K. Recent results on this class of magnetic materials will be described in the context of existing theories.

Theoretical Insights into Li Ion Diffusion in β—Li3PS4 solid Electrolyte

The attractive safety and long-term stability of all solid-state batteries has added a new impetus to the discovery and development of solid electrolytes for lithium batteries. Sulfide-based compounds are promising in terms of conductivity and cyclability, and in the chemical systems Li2S—P2S5/GeS2/SnS2, crystalline compounds like Li3PS4,[1] Li10GeP2S12 (LGPS)[2] and Li10SnP2S12[3] have garnered attention because the achievable Li ion conductivity is comparable to liquid electrolytes.Li3PS4 is one of the stable compositions in the Li2S—P2S5 system. It exists in two phases: the room temperature phase, γ—Li3PS4 and the high temperature phase, β—Li3PS4. Liu et al reported ionic conductivity on the order of 1.6*10-4 S/cm in nanosized Li3PS4, whereas a very low ionic conductivity on the order of 10-7 S/cm was reported in the bulk phases of Li3PS4. [1, 4] The increase in conductivity was rationalized by the formation of nanoscale crystallites and the stabilization of the disordered high conductivity β phase at the nanoscale. The distinct features of β phase (Pmna, SG:62) are the higher symmetry and partially occupied Li-ion sites compared to γ phase (Pmn21, SG:31). We focus on β—Li3PS4with emphasis on the role of Li-ion site disorder and the local chemical environment responsible for the observed high ionic conductivity.We used a series of ab initio molecular dynamics simulations to understand the Li-ion diffusivity in β—Li3PS4. We determined the Li-ion diffusivity, the temperature dependence diffusivity, and analyzed the trajectories to determine the mechanisms and structural origins of the high Li diffusivity. We find that Lithium ion diffusion is facilitated by the vibrational modes related to P—S bond stretch, and the diffusion is facile with an activation barrier on the order of 0.35 eV. Lithium ions exhibit pseudo-liquid like behavior at elevated temperatures (~600 K) while the PS4 3- anions vibrate about their lattice positions. Our results provide further insights into the arrangement of Li ion sub-lattice in the crystal structure of β—Li3PS4, role of lithium-ion disorder on ionic conductivity and the local chemical environment responsible for Li-ion sub-lattice melting and consequent improvement in ionic conductivity.This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Computing resources provided by the National Energy Research Scientific Computing Center, supported by US-DOE Office of Science under Contract DE-AC02-05CH11231, were used and gratefully acknowledged.1. Liu, Z., Fu, W., Payzant, E. A., Yu, X., Wu, Z., Dudney, N. J., Kiggans, J., Hong, K., Rondinone, A. J., and Liang, C., Anomalous High Ionic Conductivity of Nanoporous β-Li3PS4. Journal of the American Chemical Society, 2013. 135(3): p. 975-978.2. Kamaya, N., Homma, K., Yamakawa, Y., Hirayama, M., Kanno, R., Yonemura, M., Kamiyama, T., Kato, Y., Hama, S., Kawamoto, K., and Mitsui, A., A lithium superionic conductor. Nat Mater, 2011. 10(9): p. 682-686.3. Bron, P., Johansson, S., Zick, K., Schmedt auf der Günne, J., Dehnen, S., and Roling, B., Li10SnP2S12: An Affordable Lithium Superionic Conductor. Journal of the American Chemical Society, 2013. 135(42): p. 15694-15697.4. Tachez, M., Malugani, J.-P., Mercier, R., and Robert, G., Ionic conductivity of and phase transition in lithium thiophosphate Li3PS4. Solid State Ionics, 1984. 14(3): p. 181-185.

Evidence of Weak Ferromagnetism in Pb(Fe2/3W1/3)O3 Powders by Means of Non-resonant Microwave Absorption

We report on the effects of temperature and dc magnetic field on non-resonant microwave absorption measurements at X-band (8.8–9.8 GHz) in Pb(Fe2/3W1/3)O3 powders, for the 294–425 K temperature range. Two techniques are used: the magnetically modulated microwave absorption spectroscopy (MAMMAS) and the low-field microwave absorption (LFMA). MAMMAS response showed distinctive features associated with para-antiferromagnetic transition at T N =334.3 K, and below T N a weak ferromagnetism is also observed, and it is attributed to canting of Fe+3 ion sublattices in the antiferromagnetic matrix. The low-field microwave absorption (LFMA) is used to give further knowledge on this material, where this technique also gives evidence of the magnetic transition, suggesting a weak ferromagnetism at room temperature.

Detection of para–antiferromagnetic transition in Bi2Fe4O9 powders by means of microwave absorption measurements

An electron paramagnetic resonance (EPR) study of Bi2Fe4O9 powders is carried out in X-band (8.8–9.8GHz) and the 200–350K temperature range. For all the temperatures, the EPR spectra show a single broad line attributable to Fe3+ (S=5/2) ions. The onset of the para–antiferromagnetic transition has been determined from the temperature dependence of the parameters deduced from EPR spectra: the peak-to-peak linewidth (ΔHpp) and the resonant field (Hres); a weak ferromagnetism is also observed at low temperature and it is attributed to canting of Fe3+ ion sublattices in the antiferromagnetic matrix. The magnetically modulated microwave absorption spectroscopy (MAMMAS) and the low-field microwave absorption (LFMA) are used to give further information on this material. These techniques give evidence of the magnetic transition, suggesting a weak ferromagnetism at low temperature.

Thermal Variation of Structure and Electrical Conductivity in Bi4YbO7.5

The thermal behavior of the oxide ion-conducting solid electrolyte Bi4YbO7.5 was investigated using a combination of variable temperature X-ray and neutron powder diffraction, thermal analysis (DTA and TGA), and ac impedance spectroscopy. The title compound shows a fluorite-type structure throughout the measured temperature range (20-850 degrees C), with a phase separation at ca. 600 degrees C into a cubic delta-type phase and an orthorhombic phase of assumed stoichiometry Bi17Yb7O36. This type of transition is a relatively common feature in bismuth oxide-based systems and can limit their practical application. Here, the transition was carefully studied using isothermal measurements, which showed that it is accompanied by changes in oxide-ion stoichiometry, as well as significant disorder in the oxide ion sublattice in the delta-type phase. These results correlate with the observed electrical behavior. Analysis of the total neutron scattering through reverse Monte Carlo (RMC) modeling reveals details of the coordination environments for both cations. The oxide-ion vacancy distribution seems to be consistent with a favoring of vacancy pairs, although vacancy pairs exhibit the highest frequency as they have the maximum likelihood. A vacancy ordering model based on three vacancies per cell is presented.

Quantum theory of magnetoelectricity in rare-earth multiferroics: Nd, Sm, and Eu ferroborates

The quantum theory of magnetoelectricity in rare-earth ferroborates is developed. It is shown that the electric polarization in the materials is induced by means of two single-ion mechanisms: effective magnetic and crystal fields produce the electric dipole moment directly in the electronic $4f$ shells of rare-earth ions (the electronic contribution) and also through displacement of oppositely charged ion sublattices (the ionic one). The magnetoelectrical properties are described in detail for the neodymium, samarium, and europium ferroborates. In particular, the field and temperature dependencies of polarization are obtained.

Chessboard/Diamond Nanostructures and the A-site Deficient, Li1/2–3x Nd1/2+xTiO3, Defect Perovskite Solid Solution

The crystal chemical origin of nanoscale chessboard/diamond ordering in perovskite-related solid solutions of composition Li0.5–3xNd0.5+xTiO3 (LNT, x ∼ 0.02–0.12) is investigated. Experimental and simulated scanning transmission electron microscopy (STEM) images are found to be consistent with the compositional modulation model proposed by previous authors. However, these earlier models do not satisfactorily explain other features observed in high-resolution STEM and TEM images, such as the two-dimensional {100} lattice fringes with the same periodicity, √2ap × √2ap, as the local LNT unit cell viewed along the [001] direction (where ap is the parent perovskite unit cell parameter). Based on bond valence sum calculations, we propose a new set of crystal structures for LNT in which Li ions are primarily bonded to only two O ions, and order one-dimensionally with √2ap periodicity. Bright-field STEM image simulations performed for this new model reproduced the experimentally observed √2ap lattice fringes, thus strongly suggesting that the finer features of the high-resolution (S)TEM images are the result of Li ion ordering and associated local structural relaxation. In this new model, the LNT chessboard supercell then results from the ordered combinations of two sublattices: the Li ion sublattice and its translational variants on the one hand, and the Nd0.5TiO3 sublattice and its oxygen octahedral tilt twin variants on the other. Dielectric measurements indicate the presence of long-lived polar clusters that are easily activated under an applied electric field. This suggests that these clusters consist of spatially correlated Li ions.

Temperature-dependent IR and Raman scattering studies of phase transitions in K2MgWO2(PO4)2

Temperature-dependent Raman scattering and IR experiments were performed on K2MgWO2(PO4)2, which is derived from KTP by the replacement of two Ti4+ ions with Mg2+ and W6+ cations. These studies revealed significant changes in phonon properties of these materials with increasing temperature due to the onset of phase transitions at 436, 537 and 637 K. Analysis of the obtained data showed that disordering processes in the sublattice of potassium ions play a significant role in the mechanism of these phase transitions. However, these transitions are also accompanied by weak tilts of the nearly rigid PO4, WO6 and MgO6 groups. Present results also provide strong arguments that the phase transition at 637 K can be classified as occurring from the normal high-temperature phase with D4 point symmetry into a modulated or incommensurate phase with the same D4 point symmetry. Our results also show that the order–disorder (displacive) contribution to the phase transition mechanism is significantly stronger (weaker) in K2MgWO2(PO4)2 when compared to KTP.

Synthesis, Crystal Structure, and Magnetic Properties of Li3Mg2OsO6, a Geometrically Frustrated Osmium(V) Oxide with an Ordered Rock Salt Structure: Comparison with Isostructural Li3Mg2RuO6

The novel osmium-based oxide Li(3)Mg(2)OsO(6) was synthesized in polycrystalline form by reducing Li(5)OsO(6) by osmium metal and osmium(IV) oxide in the presence of stoichiometric amounts of magnesium oxide. The crystal structure was refined using powder X-ray diffraction data in the orthorhombic Fddd space group with a = 5.88982(5) Å, b = 8.46873(6) Å, and c = 17.6825(2) Å. This compound is isostructural and isoelectronic with the ruthenium-based system Li(3)Mg(2)RuO(6). The magnetic ion sublattice Os(5+) (S = 3/2) consists of chains of interconnected corner- and edge-shared triangles, which brings about the potential for geometric magnetic frustration. The Curie-Weiss law holds over the range 80-300 K with C = 1.42(3) emu·K/mol [μ(eff) = 3.37(2) μ(B)] and θ(C) = -105.8(2) K. Below 80 K, there are three anomalies at 75, 30, and 8 K. Those at 75 and 30 K are suggestive of short-range antiferromagnetic correlations, while that at 8 K is a somewhat sharper maximum showing a zero-field-cooled/field-cooled divergence suggestive of perhaps spin freezing. The absence of magnetic Bragg peaks at 3.9 K in the neutron diffraction pattern supports this characterization, as does the absence of a sharp peak in the heat capacity, which instead shows only a very broad maximum at ∼12 K. A frustration index of f = 106/8 = 13 indicates a high degree of frustration. The magnetic properties of the osmium phase differ markedly from those of the isostructural ruthenium material, which shows long-range antiferromagnetic order below 17 K, f = 6, and no unusual features at higher temperatures. Estimates of the magnetic exchange interactions at the level of spin-dimer analysis for both the ruthenium and osmium materials support a more frustrated picture for the latter. Errors in the calculation and assignment of the exchange pathways in the previous report on Li(3)Mg(2)RuO(6) are identified and corrected.

Characterization of atomic step structures on CaF2(111) by their electric potential

The structure and polarity of step edges on cleaved CaF2(111) are investigated by non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy. Ledges produced by cleaving the crystal appear with two distinctly different polarities denoted as type I and type II arising from the sectioning of ledges with steps having different polarities. With respect to the stoichiometric terrace, the surface potential is slightly reduced at ledges predominately composed of type I steps, while the potential of ledges predominantly composed of type II steps is significantly higher (typically 100 mV). We propose that the positive potential of type II steps stems from low coordinated Ca2+ ions inducing a dipole at step edges and confirm this by atomically resolved NC-AFM images revealing the Ca2+ ion sub-lattice with repulsive-mode imaging contrast.

Study of magnetic inhomogeneity in β-Cu3Fe4V6O24

The temperature dependence of dc magnetization and electron paramagnetic resonance (EPR) spectra of the β-Cu3Fe4V6O24 multicomponent vanadate were investigated. Dc magnetic measurements showed the presence of strong antiferromagnetic interactions (Curie-Weiss temperature, Θ ∼ 80 K) at high temperatures, while zero-field-cooled (ZFC) magnetization revealed a cusp-like maximum in low fields at T f1 = 4.4 K, which coincides with the splitting of the ZFC and FC curves. Another maximum was registered at T f2 = 3.0 K. These two temperatures (T f1 and T f2) could be regarded as freezing temperatures in the spin glass state of two magnetic sublattices of Fe1 and Fe2 ions. The EPR spectrum of β-Cu3Fe4V6O24 is dominated by a nearly symmetrical, very intense and broad resonance line centered at g eff ∼ 2.0 that could be attributed to iron ions. Below 10 K, an additional EPR spectrum with g 1 = 2.018(1) and g 2 = 2.175(1) appears, as well as a very weak line at geff = 1.99(1). The former spectrum is probably is due to divalent copper ions, and the latter line due to vanadium V4+ complexes. The temperature dependence of EPR parameters (g-factor, linewidth, integrated intensity) was determined in the range of 3–300 K. Two low-temperature maxima in the temperature dependence of the integrated intensity (at 40 and 6 K) were fitted with a function suitable for pairs of exchange-coupled Fe3+ ions. A comparison of dc magnetic susceptibility and EPR integrated intensity indicates the presence of spin clusters, which play an important role in determining the low-temperature magnetic response of β-Cu3Fe4V6O24.

Defect structure and its nomenclature for mixed conducting lanthanum tungstates La28–xW4+xO54+3x/2

Based on results from experimental and theoretical studies of the crystal structure of lanthanum tungstate (La28−xW4+xO54+32xv2−32x), we present a defect model comprising an inherently disordered and partially occupied oxide ion sublattice, which rationalizes hydration and ionic conduction of the materials in the undoped state. Applying the model to experimental conductivity data enables extraction of defect thermodynamics and transport parameters of protons, oxide ions and electronic defects. The standard enthalpy and entropy changes of the hydration of inherent oxygen vacancies are estimated to be −83 kJ/mol and −125 J/mol K (per mole of H2O), respectively.

Theoretical investigation of NMR spectra in rare-earth manganites

The work is aimed to theoretical investigation of orbital and magnetic structure of manganites. The orbitally-dependent exchange interaction model was used in order to describe the superexchange interaction in all range of RMnO3 (R = La, Pr, Nd, Tb, Dy, Ho) orfhorhombic compounds. The model of nearest-neighbour and next-nearest neighbour exchange was used to describe the magnetic structures of manganites with small rare-earth ion sublattice (R = Dy, Tb, Ho). We investigate different types −A, E, non-collinear - of magnetic structures. The models of NMR spectra calculation of Mn3+ ion in RMnO3 compounds are proposed. The theoretical study of the magnetic structure could distinguish The NMR-spectra of antiferromagnetic (A or E) or strongly non-collinear ordering type.

A discussion on the magnetization calculation in polycrystalline antiferromagnetic system: Application to EuTiO3

In this work a numerical methodology is theoretically proposed to calculate the magnetization of a polycrystalline system, considering a microscopic Hamiltonian model, which describes a magnetic system consisting of two sublattices of different magnetic ions coupled by exchange interactions and with parallel and perpendicular direction of the magnetic field. The influence of changing the applied magnetic field direction on an antiferromagnetic system was systematically analyzed. The proposed numerical method was applied to the cubic perovskite EuTiO3 and a good agreement with the experimental data was obtained.

KAgF 3: Quasi-one-dimensional magnetism in three-dimensional magnetic ion sublattice

The electronic structure and magnetic properties of the Jahn–Teller-distorted perovskite KAgF 3 have been investigated using the full-potential linearized augmented plane-wave method. It is found that KAgF 3 exhibits significant quasi-one-dimensional antiferromagnetism with the ratio of exchange constant | J ⊥ | (perpendicular to the z-axis) and J (along the z-axis) about 0.04, although the sublattice of magnetic ion is three-dimensional. The strong quasi-one-dimensional antiferromagnetism originates from the C-antiferro-distortive orbital ordering of the Ag 2 + 4 d 9 ions. The orbital ordered antiferromagnetic insulating state in KAgF 3 is determined by on-site Coulomb repulsion to a large extent.

Commentary on the superconducting and magnetic properties of the ruthenocuprates

Presented in this commentary is a short discussion of the superconducting and magnetic properties of selected compounds of ruthenocuprates, with an emphasis given to the RuSr2GdCu2O8 compound. The ruthenocuprates, which form derivative class in the cuprate family, continue raising interest for there evidenced presence of magnetic ordering in the sublattice of Ru ions, which in polycrystalline samples of RuSr2GdCu2O8 sets at Tm ≈ 132 K, and at low temperatures may become simultaneous with the superconducting phase (Tc,max ≈ 50 K)-all that in the crystal structure derived from well known REBa2Cu3O7 cuprate superconductor. While several here invoked recent results advocate for an intrinsically inhomogeneous nucleation of superconductivity within this structure, the formed superconducting phase carries potential of maintaining substantial anisotropy with then interesting consequence for probing the cuprate characteristic superconductivity in these compounds.

Weak ferromagnetism in the magnetoelectric [formula omitted] detected by microwave power absorption measurements

An electron paramagnetic resonance (EPR) study in polycrystalline magnetoelectric Y CrO 3 is carried out at the X-band (8.8–9.8 GHz) in the 85–300 K temperature range. For all the temperatures, the EPR spectra show a single broad line attributable to Cr 3+ ( S = 3 / 2 ) ions. The onset of the antiferro–paramagnetic transition has been determined from the temperature dependence of parameters deduced from the EPR spectra: the integrated intensity ( I E P R ), the g-factor and the peak-to-peak linewidth ( Δ H p p ). Below 140 K, a weak ferromagnetism is observed and it is attributed to canting of Cr 3+ ion sublattices in the antiferromagnetic matrix. Low-field microwave absorption (LFMA) is used to give further knowledge on this material; where this technique also gives evidence of the magnetic order, suggesting a weak ferromagnetism at low temperature.

Luminescence of Mn 2+ ions in Tb 3Al 5O 12 garnet

The paper is dedicated to investigation of the Mn 2+ luminescence in Tb 3Al 5O 12 (TbAG) garnet, as well as the processes of excitation energy transfer between host cations (Tb 3+ ions) and activators (Mn 2+ and Mn 2+–Ce 3+ pair ions) in single crystalline films of TbAG:Mn and TbAG:Mn,Ce garnets which can be considered as promising luminescent materials for conversion of LED's radiation. Due to the effective energy transfer between TbAG host and activator, Mn 2+ ions in TbAG possess the bright orange luminescence in the bands peaked at 595 nm with a lifetime of 0.64 ms which are caused by the 4T 1→ 6A 1 radiative transitions. The simultaneous process of energy transfer is realized in TbAG:Mn,Ce: (i) from Tb 3+ to Mn 2+ ions; (ii) from Tb 3+ cations to Ce 3+ ions and then partly to Mn 2+ ions through Tb 3+ ion sublattice and Ce–Mn dipole–dipole interaction.

Theory of dynamic spin susceptibility in terms of the t-J-V model: Comparison with neutron scattering data for Pr0.88LaCe0.12CuO4 − x and La2 − x Sr x CuO4

A formula for the dynamic spin susceptibility is derived in terms of the t-J-V model. This formula makes it possible to explain the main features of recent experiments on neutron scattering in the electron-doped superconductor Pr0.88LaCe0.12CuO4 − x . In particular, the proposed theory reproduces well a V-shaped relief in the frequency behavior of the imaginary part χ″(Q, ω) of the susceptibility of the Pr0.88LaCe0.12CuO4 − x compound in the vicinity of the wave vector Q = (π,π) and the scaling behavior of the position of the maxima in the dependence of the function χ″(Q, ω) T on the quantity ω/T. The magnetism of the high-temperature superconductors is dual. These materials contain charge carriers, on the one hand, and localized spins in the copper ion sublattice, on the other hand. Both these systems are strongly coupled to each other. The mode of collective oscillations is common. The magnetism of localized spins “freezes” with the appearance of the superconducting gap. The recently revealed double-peak structure of the imaginary part χ″(Q, ω) of the susceptibility in superconductors of the La1.84Sr0.16CuO4 type is explained. The low-frequency absorption peak is located within the superconducting gap and interpreted as a manifestation of the branch of spin excitons, and the high-frequency absorption peak predominantly corresponds to renormalized collective oscillations of localized spins.

Structure of Ga2O3(ZnO)6: a member of the homologous series Ga2O3(ZnO) m

The structure of Ga(2)O(3)(ZnO)(6) was determined using single-crystal X-ray diffraction techniques in the space group Cmcm. The metal ion sublattice resembles some of the Zn ions in the wurtzite ZnO structure. The oxygen ion sublattice in Ga(2)O(3)(ZnO)(6) also resembles some of the O ions in ZnO. Structural relationships between Ga(2)O(3)(ZnO)(6) and ZnO are discussed, illustrating the process for obtaining the centrosymmetric Ga(2)O(3)(ZnO)(6) structure from the noncentrosymmetric ZnO. Structures of phases in the homologous series Ga(2)O(3)(ZnO)(m) are predicted on the basis of the structural data for Ga(2)O(3)(ZnO)(6). The structures of even m are constructed by simply extending the structure units seen in Ga(2)O(3)(ZnO)(6), while those of odd m consist of structure units which are of different types from those used for even m.