Jahn-Teller Activity Research Articles

Improving cycling performance of the NaNiO2 cathode in sodium-ion batteries by titanium substitution

O3-type layered oxide cathodes, such as NaNi0.5Mn0.5O2, have garnered significant attention due to their high theoretical specific capacity while using abundant and low-cost sodium as intercalation species. Unlike the lithium analog (LiNiO2), NaNiO2 (NNO) exhibits poor electrochemical performance resulting from structural instability and inferior Coulomb efficiency. To enhance its cyclability for practical application, NNO was modified by titanium substitution to yield the O3-type NaNi0.9Ti0.1O2 (NNTO), which was successfully synthesized for the first time via a solid-state reaction. The mechanism behind its superior performance in comparison to that of similar materials is examined in detail using a variety of characterization techniques. NNTO delivers a specific discharge capacity of ∼190 mAh g−1 and exhibits good reversibility, even in the presence of multiple phase transitions during cycling in a potential window of 2.0‒4.2 V vs. Na+/Na. This behavior can be attributed to the substituent, which helps maintain a larger interslab distance in the Na-deficient phases and to mitigate Jahn–Teller activity by reducing the average oxidation state of nickel. However, volume collapse at high potentials and irreversible lattice oxygen loss are still detrimental to the NNTO. Nevertheless, the performance can be further enhanced through coating and doping strategies. This not only positions NNTO as a promising next-generation cathode material, but also serves as inspiration for future research directions in the field of high-energy-density Na-ion batteries.

Spin-orbital Jahn-Teller bipolarons

Polarons and spin-orbit (SO) coupling are distinct quantum effects that play a critical role in charge transport and spin-orbitronics. Polarons originate from strong electron-phonon interaction and are ubiquitous in polarizable materials featuring electron localization, in particular 3d transition metal oxides (TMOs). On the other hand, the relativistic coupling between the spin and orbital angular momentum is notable in lattices with heavy atoms and develops in 5d TMOs, where electrons are spatially delocalized. Here we combine ab initio calculations and magnetic measurements to show that these two seemingly mutually exclusive interactions are entangled in the electron-doped SO-coupled Mott insulator Ba2Na1−xCaxOsO6 (0 < x < 1), unveiling the formation of spin-orbital bipolarons. Polaron charge trapping, favoured by the Jahn-Teller lattice activity, converts the Os 5d1 spin-orbital Jeff = 3/2 levels, characteristic of the parent compound Ba2NaOsO6 (BNOO), into a bipolaron 5d2 Jeff = 2 manifold, leading to the coexistence of different J-effective states in a single-phase material. The gradual increase of bipolarons with increasing doping creates robust in-gap states that prevents the transition to a metal phase even at ultrahigh doping, thus preserving the Mott gap across the entire doping range from d1 BNOO to d2 Ba2CaOsO6 (BCOO).

Possible routes to superconductivity in the surface layers of V-doped Mg1−δTi2O4 through multiple charge transfers and suppression of Jahn-Teller activity

Superconductivity in the family of spinel oxides is very rare owing to their robust Mott-insulating nature. About half a century ago, ${\mathrm{LiTi}}_{2}{\mathrm{O}}_{4}$ became the first reported spinel compound to show superconductivity with a 12 K transition temperature. Since then, several unsuccessful attempts were made to enhance the ${T}_{\mathrm{c}}$ of this family of materials. However, a very recent experiment [A. Rahaman et al., arXiv:2209.02053] has reported superconductivity at a higher temperature (below $\ensuremath{\sim}16$ K) in the V-doped ${\mathrm{Mg}}_{1\ensuremath{-}\ensuremath{\delta}}{\mathrm{Ti}}_{2}{\mathrm{O}}_{4}$ thin surface layer while its bulk counterpart remains Mott insulating. The superconducting ${T}_{\mathrm{c}}$ of this material is significantly higher compared to other engineered ${\mathrm{MgTi}}_{2}{\mathrm{O}}_{4}$ thin films grown on different substrates. From our first-principles analysis, we have identified that Mg depletion significantly reduces Jahn-Teller (JT) activity and antiferromagnetic superexchange at the surface layer of V-doped ${\mathrm{Mg}}_{1\ensuremath{-}\ensuremath{\delta}}{\mathrm{Ti}}_{2}{\mathrm{O}}_{4}$ due to considerable charge transfer between various ions. The combined effect of a degraded antiferromagnetic order and reduced JT activity weakens the ``Mottness'' of the system, leading to the emergence of superconductivity at higher temperatures.

Effect of Jahn-Teller distortion on physical properties of Y2CuMnO6

The effect of Jahn-Teller distortion in Y2CuMnO6 on crystal symmetry, magnetic and dielectric property has been investigated. In this material, Cu2+ ions enable coupling of dielectric property with magnetic field. X-ray diffraction pattern indicates that Y2CuMnO6 exhibits Pbam type symmetry. As response of this, alternate patterns of MnO6 and CuO6 are broken due to the Jahn-Teller activity and polyhedra are distributed randomly. The magnetic interaction among randomly distributed Cu2+ and Mn4+ is antiferromagnetic interaction below 18 K which is much lower than the ordered Y-based double perovskite. As response of magnetic dilution, the system undergoes a magnetic frustration due to occupation of triangular sites by magnetic ions. The interaction between triangularly arranged magnetic ions leads the magnetocapacitance.

Jahn–Teller distortions in (Co1–xCux)Cr2O4 (x = 0.5, 0.25) nanoparticles: Structural, magnetic and electronic properties

The spinel ferrimagnetic compound CoCr2O4 demonstrates a spin spiral (TS) ordering at 25 K, as well as an anomaly at 15 K termed as lock-in transition (TL). From crystallographic perspective CoCr2O4 retains the cubic phase down to 11 K. On the other hand, the normal spinel CuCr2O4 crystallizes into the cubic phase above 850 K, below which Jahn-Teller (J-T) activity of the Cu reduces the crystal symmetry by transforming it to a tetragonal phase. Contraction of CuO4 tetrahedra towards the formation of a square planar structure accounts for the tetragonal to orthorhombic structural transition at ∼ 130 K associated with the ferrimagnetic Curie temperature (TC). Considering the differences in crystal structure and magnetism of these two compounds, the current work investigates the modification in crystal structure and magnetic behaviour by mixing Co site with Cu in CoCr2O4. To achieve this, (Co1–xCux)Cr2O4 (x = 0.5, 0.25 and 0.75) nanoparticles were prepared by chemical routes. X-ray diffraction (XRD) revealed the retention of cubic structure for the samples calcined at a temperature of 600 °C for x = 0.25 and 0.5. On the other hand, J-T distortion becomes prominent for x = 0.75. Hence, only the compositions with x = 0.25 and 0.5 were studied in detail as unusual cubic phase retention is observed in these compounds. The temperature dependent magnetization studies revealed that the TC values of both the samples, 103 K for (Co0.5Cu0.5)Cr2O4 and 99 K for (Co0.75Cu0.25)Cr2O4, compare well with the value reported for CoCr2O4. However, the feature related to TS is quite prominent for x = 0.25, whereas it is suppressed for x = 0.5. The electronic properties of the cations associated with these compounds, probed using X-ray photoelectron spectroscopy (XPS), indicate that Cu and Co mostly has a 2+ oxidation state whereas that of Cr is 3+.

Enhanced Spontaneous Polarization by V4+ Substitution in a Lead-Free Perovskite CaMnTi2O6.

Spontaneous polarization (Ps) of novel order-disorder type lead-free ferroelectric CaMnTi2O6 was successfully enhanced by partial V4+ substitution for Ti4+. A synchrotron X-ray diffraction study revealed that the polar displacement of octahedrally coordinated (Ti, V) in CaMn(Ti1-xVx)2O6 (0 ≤ x ≤ 0.4) increases with V4+ substitution having Jahn-Teller activity owing to the d1 electronic configuration. Our magnetic study suggested the presence of antisite disorder between Ca2+ and square planar coordinated Mn2+ associated with Mn-V intermetallic charge transfer for x ≥ 0.4, resulting in decreases in spontaneous polarization and the ferroelectric-paraelectric transition temperature. This is the first report on the enhanced polarization owing to the Jahn-Teller distortion of V4+ without stereochemical Pb2+ or Bi3+.

(Invited) Reversible Asymmetric Structure Evolution and Battery Performance in Layered Sodium Transition Metal Oxides

Layered sodium transition metal oxide system of NaMO2 (M = 3d transition metal ions and their mixtures) forms a unique material platform to study the interactions between transition metal, oxygen and sodium sublattices. Specifically, Fe and Mn, which are not stable in layered LiMO2, become much more stable in NaMO2. In this talk, I will show that the interplay between these different sublattices at low Na composition modulates the electrochemical performance of NaxMO2 through the generation of novel high voltage phases. A combined in situ (synchrotron) XRD, X-ray absorption spectroscopy, atomic resolution (scanning) TEM, neutron diffraction and density functional theory (DFT) simulation techniques are used to understand the structural and functional details in crystallographic, electronic and magnetic properties. For the Fe containing mixed transition metal system of Na(FexTM1-x)O2, a rippling phase at high voltage was developed due to the unique electronic property of FeO6­ octahedra, while at low voltage it goes back to the normal flat phase through an asymmetric structural evolution pathway, giving high discharge rate capability. For NaMnO2 a unique phenomenon of super charge separation is reported, where an emergent structural unit of charge superplane related to the collective Jahn-Teller activity of Mn3+ was found to dominate the entire electrochemical evolution, giving asymmetric charge discharge behavior and high discharge capacity. The underlying connection between these reversible asymmetric systems will be discussed to further facilitate the design of advanced cathode materials for sodium ion batteries. [1]Advanced Functional Materials, 1805105 (2018) [2]Advanced Functional Materials, 1803896 (2018)

Jahn-Teller Distortion and Disproportionation in Spinel Lithium Manganese Oxides from First Principles

Spinel lithium manganese oxide (LMO) is a promising cathode material for Li-ion batteries. Dissolution of manganese from LMO into the electrolyte, however, limits its cycle life. The widely accepted mechanism of dissolution requires charge disproportionation of Mn(III), but the atomistic details of such processes have remained elusive. The dissolution has also been loosely correlated with the Jahn-Teller activity of Mn, especially when LMO is over-lithiated. Using first-principles simulations, we provide insights into the mechanism of both Jahn-Teller activity and disproportionation and discuss possible connections between the two.

Jahn–Teller Assisted Na Diffusion for High Performance Na Ion Batteries

Na energy storage technology is strategically attractive for large scale applications such as grid energy storage. We show in this paper that there is a clear relation between the Jahn–Teller activity of a transition metal ion at the end of charge and the mobility of Na in a cathode material. This is particularly important as mobility at the end of charge limits the capacity of current materials. Hence, by using this classical piece of physics in the battery world, it is possible to create higher capacity Na-cathode materials. Even more exciting is that the ideal element to impart this effect on cathodes is Fe, which is the least expensive of the transition metal oxides and can therefore enable low cost cathode materials.

Conductivity Limits of Extrinsically Doped SnO2 Supports

Supported catalyst technologies made Pt-based Polymer-Electrolyte Membrane Fuel Cell (PEMFC) electrodes cost-competitive. It has, however, become clear that current standard supports (i.e., high surface area carbons) might not provide the corrosion resistance needed to achieve life-time targets for stationary and/or automotive applications [1]. This has sparked strong interest in alternatives in recent years. Research ranges from exploring different allotropes of carbon (e.g., graphitised carbons, carbon-nano-tubes, and graphene) to new chemistries such as oxides [2]. Especially, oxides in their highest valence state appear attractive for their likely stability under strongly oxidising conditions. Indeed a number of metal oxides promise thermodynamic stability over the full operating range of a PEFC [3]; amongst them TiO2, Bi2O3, and SnO2also appear economically attractive. Being fully oxidised, all of them are intrinsic wide band-gap semi-conductors or even insulators. Hence, achieving and retaining near metallic conductivity over the life-time of a PEFC is a major challenge for oxide supports. We have investigate the possibility of extrinsic n-type doping to tailor the conductivity of SnO2 using Hybrid Density-Functional-Theory (DFT) as implemented in Crystal09. We find that Ta-doping provides limited potential to tailor conductivity of SnO2 for two reasons: (1) the stoichiometric ternary SnTa2O6 competes for thermodynamic stability along the rutile SnO2-TaO2 pseudo-binary potentially limiting the solubility of Ta in SnO2, and (2) collaborative Jahn-Teller distortions [4] tend to localise the Ta donor state leading to a freezing out of the donor state with increasing dopant concentration. Our calculations indicate that the maximum extrinsic carrier concentration should be around 1% Ta-doping. The use of B3LYP as function provided a significantly more accurate description of the band gap of SnO2than semi-local approximations to DFT produce. This enabled accurate description of electron localisation of the donor state without erroneous resonances with the conduction band. Electron localisation is accompanied with a strong Jahn-Teller distortion. Therefore, Ta centres interact via long-ranged elastic effects providing relatively large stabilisation of ordered superlattices. A cluster expansion based search strategy was implemented to bias the search towards these low energy orderings. This can be seen as a collaborative distortion of the crystal structure that leads to a freezing out of the donor state with increasing Ta concentration. Further, the Ta donor state is predicted to be a deep donor state that can only contribute to conductivity at room temperature if secondary defects provide a significant lowering of the conduction band. Using thin-film deposition techniques [5], we have synthesised doped SnO2 thin films. Consistent with our First Principles calculations, we find a declining conductivity in the range 1.0% to 7.1% Ta-doping. Interestingly, our experiments indicate that Nb as an alternative donor impurity shows an increase in conductivity up to at least 2.1% Nb-doping. Given the similarity between the two ions (same ionic radii, same d1 state in four-valent configuration, both are known for Jahn-Teller activity), we currently try to identify the underlying reason for the markedly different behaviour using the methodology described above. This work was supported by CCEM Switzerland and Umicore AG & Co KG within the project DuraCat. The authors acknowledge the use of the ARCHER UK National Supercomputing Service. [1] Tang et al., J. Power Sources 158 (2006) 1306-1312[2] A. Rabis, P. Rodriguez, T.J. Schmidt, ACS Catalysis 2 (2012) 864-890[3] K. Sasaki et al., ECS Transactions 33 (1) (2010) 473-482[4] G. Gehring and K. Gehring, Reports on Progress in Physics 38 (1) (1975) 1-89[5] A. Rabis, D. Kramer, E. Fabbri, M. Worsdale, R. Kötz, and T.J. Schmidt, The Journal of Physical Chemistry C 118 (2014) 11292-11302

Spin-state responses to light impurity substitution in low-spin perovskite LaCoO3

We studied the spin-state responses to light impurity substitution in low-spin perovskite LaCoO${}_{3}$ (Co${}^{3+}$: ${d}^{6}$) through magnetization, x-ray fluorescence, and electrical resistivity measurements of single-crystal LaCo${}_{0.99}{M}_{0.01}$O${}_{3}$ ($M$ $=$ Cr, Mn, Fe, Ni). In the magnetization curves measured at 1.8 K, a change in the spin-state was not observed for Cr, Mn, or Fe substitution but was observed for Ni substitution. Strong magnetic anisotropy was also found in the Ni-substituted sample. The fluorescence measurements revealed that the valences were roughly estimated to be Cr${}^{3+}$, Mn${}^{(4\ensuremath{-}\ensuremath{\delta})+}$, Fe${}^{(3+{\ensuremath{\delta}}^{\ensuremath{'}})+}$, and Ni${}^{3+}$. From the observed chemical trends, we propose that the chemical potential is a key factor in inducing the change of the low-spin state. By expanding a model of the ferromagnetic spin-state heptamer generated by hole doping [Podlesnyak et al., Phys. Rev. Lett. 101, 247603 (2008)], the emergence of highly anisotropic spin-state molecular ferromagnets induced by low-spin Ni${}^{3+}$ with Jahn-Teller activity is suggested. We also discuss applicability of the present results to other materials with Fe (${d}^{6}$).

Structure refinements of members in the brownmillerite solid solution series Ca2Alx(Fe0.5Mn0.5)2−xO5+δ with 1/2≤x≤4/3

Four different brownmillerite solid solutions Ca2Alx(Fe0.5Mn0.5)2−xO5+δ with 1/2≤x≤4/3 were synthesized by a solid oxide ceramic method. The phases crystallize either in a primitive centered orthorhombic cell with space group Pnma or in a body centered cell with space group I2mb dependent on the aluminum concentration present in the solid solution. Mn3+ ions occupy exclusively site 4a coordinated by six oxygen anions. Increasing Mn3+ concentrations cause a remarkable distortion of the octahedron and indirectly of the tetrahedron, resulting in twisted and tilted octahedral layers as well as buckled tetrahedral chains. The influences are discussed on the site 4a of trivalent manganese due to its Jahn-Teller activity, with regard to the occupation of octahedron and tetrahedron with different sized iron and aluminum ions.

Chemical control of polar behavior in bicomponent short-period superlattices

Using first-principles density functional calculations, we study the interplay of ferroelectricity and polar discontinuities in a range of 1--1 oxide superlattices, built out of ferroelectric and paraelectric components. Studies have been carried out for a varied choice of chemical composition of the components. We find that, when polar interfaces are present, the polar discontinuities induce off-centric movements in the ferroelectric layers, even though the ferroelectric is only one unit cell thick. The distortions yield nonswitchable polarizations, with magnitudes comparable to those of the corresponding bulk ferroelectrics. In contrast, in superlattices with no polar discontinuity at the interfaces, the off-centric movements in the ferroelectric layer are usually suppressed. The details of the behavior and functional properties are, however, found to be sensitive to epitaxial strain, rotational instabilities and second-order Jahn-Teller activity, and are therefore strongly influenced by the chemical composition of the paraelectric layer.

Relativistic Jahn-Teller effect in tetrahedral systems

It is shown that orbitally degenerate states in highly symmetric systems are split by Jahn-Teller forces which are of relativistic origin (that is, they arise from the spin-orbit coupling operator). For the example of tetrahedral systems, the relativistic Jahn-Teller Hamiltonians of orbitally degenerate electronic states with spin $1/2$ are derived. While both electrostatic and relativistic forces contribute to the Jahn-Teller activity of vibrational modes of $E$ and ${T}_{2}$ symmetry in ${}^{2}{T}_{2}$ states of tetrahedral systems, the electrostatic and relativistic Jahn-Teller couplings are complementary for ${}^{2}E$ states: The $E$ mode is Jahn-Teller active through electrostatic forces, while the ${T}_{2}$ mode is Jahn-Teller active through the relativistic forces. The relativistic Jahn-Teller parameters have been computed with ab initio relativistic electronic-structure methods. It is shown for the example of the tetrahedral cluster cations of the group V elements that the relativistic Jahn-Teller couplings can be of the same order of magnitude as the familiar electrostatic Jahn-Teller couplings for the heavier elements.

Frustration effects in spinel compound GeCo2O4 studied by ultrasound velocity measurements

Ultrasound velocity measurements of the cubic spinel GeCo2O4 in the single crystal have been performed for the investigations of shear and compression moduli. The shear moduli reveal the absence of Jahn-Teller activity despite the presence of the orbital degeneracy in the Co2+ ions. This Jahn-Teller inactivity indicates that the intersite orbital-orbital interaction is much stronger than the Jahn-Teller coupling. The compression moduli reveal that the dominant path of the exchange interactions for the antiferromagnetic transition lies in the [111] direction. This exchange-path anisotropy is consistent with the antiferromagnetic structure with the wave vector q ∥ [111], suggesting the presence of bond frustration among several ferromagnetic and antiferromagientic interactions. In the JT-inactive condition, the bond frustration can be induced by geometrical orbital frustration of t2g-t2g interaction between the Co2+ ions which can be realized in the pyrochlore lattice of the high spin Co2+ with t2g -orbital degeneracy. In GeCo2O4, the tetragonal elongation below TN releases the orbital frustration by quenching the orbital degeneracy.

Jahn-Teller inactivity and magnetic frustration inGeCo2O4probed by ultrasound velocity measurements

Ultrasound velocity measurements of cubic spinel ${\text{GeCo}}_{2}{\text{O}}_{4}$ in single crystal were performed for the investigation of shear and compression moduli. The shear moduli in the paramagnetic state reveal the absence of Jahn-Teller activity despite the presence of orbital degeneracy in the ${\text{Co}}^{2+}$ ions. Such a Jahn-Teller inactivity indicates that the intersite orbital-orbital interaction is much stronger than the Jahn-Teller coupling. The compression moduli in the paramagnetic state near the N\'eel temperature ${T}_{N}$ reveal that the most relevant exchange path for the antiferromagnetic transition lies in the [111] direction. This exchange-path anisotropy is consistent with the antiferromagnetic structure with the wave vector $q\ensuremath{\parallel}[111]$, suggesting the presence of bond frustration due to competition among a direct ferromagnetic interaction and several distant-neighbor antiferromagnetic interactions. In the Jahn-Teller-inactive condition, the bond frustration can be induced by geometrical orbital frustration of ${t}_{2g}\text{\ensuremath{-}}{t}_{2g}$ interaction between the ${\text{Co}}^{2+}$ ions, which can be realized in the pyrochlore lattice of the high-spin ${\text{Co}}^{2+}$ with ${t}_{2g}$-orbital degeneracy. In ${\text{GeCo}}_{2}{\text{O}}_{4}$, the tetragonal elongation below ${T}_{N}$ releases the orbital frustration by quenching the orbital degeneracy.

Experimental investigation of the Jahn-Teller effect in the ground and excited electronic states of the tropyl radical. Part II. Vibrational analysis of the ÃE3″2-X̃E2″2 electronic transition

Laser-induced fluorescence (LIF) and laser-excited dispersed fluorescence (LEDF) spectra of the cycloheptatrienyl (tropyl) radical C7H7 have been observed under supersonic jet-cooling conditions. Assignment of the LIF excitation spectrum yields detailed information about the A-state vibronic structure. The LEDF emission was collected by pumping different vibronic bands of the A 2E"3<--X 2E"2 electronic spectrum. Analysis of the LEDF spectra yields valuable information about the vibronic levels of the X 2E"2 state. The X- and A-state vibronic structures characterize the Jahn-Teller distortion of the respective potential energy surfaces. A thorough analysis reveals observable Jahn-Teller activity in three of the four e'3 modes for the X 2E"2 state and two of the three e'1 modes for the A 2E"3 state and provides values for their deperturbed vibrational frequencies as well as linear Jahn-Teller coupling constants. The molecular parameters characterizing the Jahn-Teller interaction in the X and A states of C7H7 are compared to theoretical results and to those previously obtained for C5H5 and C6H6+.

Combined Ligand Field and Density Functional Theory Analysis of the Magnetic Anisotropy in Oligonuclear Complexes Based on FeIII−CN−MII Exchange-Coupled Pairs

Magnetic anisotropy in cyanide-bridged single-molecule magnets (SMMs) with Fe(III)-CN-M(II) (M = Cu, Ni) exchange-coupled pairs was analyzed using a density functional theory (DFT)-based ligand field model. A pronounced magnetic anisotropy due to exchange was found for linear Fe(III)-CN-M(II) units with fourfold symmetry. This results from spin-orbit coupling of the [Fe(III)(CN)6](3-) unit and was found to be enhanced by a tetragonal field, leading to a (2)E g ground state for Fe(III). In contrast, a trigonal field (e.g., due to tau 2g Jahn-Teller angular distortions) led to a reduction of the magnetic anisotropy. A large enhancement of the anisotropy was found for the Fe(III)-CN-Ni(II) exchange pair if anisotropic exchange combined with a negative zero-field splitting energy of the S = 1 ground state of Ni(II) in tetragonally compressed octahedra, while cancellation of the two anisotropic contributions was predicted for tetragonal elongations. A recently developed DFT approach to Jahn-Teller activity in low-spin hexacyanometalates was used to address the influence of dynamic Jahn-Teller coupling on the magnetic anisotropy. Spin Hamiltonian parameters derived for linear Fe-M subunits were combined using a vector-coupling scheme to yield the spin Hamiltonian for the entire spin cluster. The magnetic properties of published oligonuclear transition-metal complexes with ferromagnetic ground states are discussed qualitatively, and predictive concepts for a systematic search of cyanide-based SMM materials are presented.

The Jahn–Teller and pseudo‐Jahn–Teller effects in the anion photoelectron spectroscopy of B3 cluster

The photodetachment spectroscopy of B3- anion is theoretically studied with the aid of a quantum dynamical approach. The theoretical results are compared with the available experimental photoelectron spectra of B3-. Both B3- and B3 possess D(3h) symmetry at the equilibrium configuration of their electronic ground state. Distortion of B3 along its degenerate vibrational mode nu2 splits the degeneracy of its excited C2E' electronic manifold and exhibits (E [symbol: see text] e)-Jahn-Teller (JT) activity. The components of the JT split potential energy surface form conical intersections, and they can also undergo pseudo-Jahn-Teller (PJT) crossings with the X2A1' electronic ground state of B3 via the degenerate nu2 vibrational mode. The impact of the JT and PJT interactions on the nuclear dynamics of B3 in its X2A1'-C2E' electronic states is examined here by establishing a diabatic model Hamiltonian. The parameters of the electronic part of this Hamiltonian are calculated by performing electronic structure calculations and the nuclear dynamics on it is simulated by solving quantum eigenvalue equation. The theoretical results are in good accord with the experimental data.

Magnetism and electronic transport in Sr4−xLaxRu2−xMnxO9: Interplay of Mn and Ru redox chemistry

Sr 4 Ru 2 O 9 has a P6¯2C space group and differs from the Ruddelsden–Popper series of the strontium ruthenate family where Ru is distinctly present in Ru+5 state with no Jahn–Teller activity. A significant increase in magnetic moment and coercivity is observed along with lowering of resistivity, especially around a critical concentration of x=0.2 in Sr4−xLaxRu2−xMnxO9. Such an unusual effect is correlated to the mixed magnetic pair effect arising out from the variable oxidation states of Ru as suggested by x-ray photoelectron spectroscopic studies. Our results substantiate the long-range ferromagnetism observed for Ruthenium-substituted three-dimensional manganites.