Cooperative Jahn-Teller Effect Research Articles

Compositional behavior of heat capacity and magnetic properties in double spinel ferrites

The purpose of the work is to identify the effects of the substitution of paramagnetic ions in ferromagnetic ferrites by diamagnetic components of zinc and aluminum. The following isomorphic spinel series are the object of review: Me(1-x)ZnxFe2O4 (Me – Ni, Co, Li, Cu, Mg) and Li0.5Fe2.5-xAlxO4 (x= 0-2.5). The single-phased samples were synthesized by ceramic procedure. Heat capacity near standard temperature Cp (298.15) was studied using calorimeter methods: drop calorimeter and DSC. Magnetic parameters – magnetic moments (M) and Curie temperatures (Tc) - were determined. All Me-Zn ferrite systems are characterized by dome-shaped correlations between heat capacity Cp(298) and composition (x), which have maximum values in the equimolecular region (x=0.4-0.6). This fact coincides with the nature of the compositional dependence of magnetic moments and indicates a significant effect of the excess magnetic contribution on the total heat capacity. A noticeable influence of the cooperative Jahn-Teller effect and the associated tetragonal distortion of the cubic lattice of Cu-Zn ferrites with a low Zn content (x<0.2) is observed, which causes overestimated values of the heat capacity of these compositions. Curie temperatures reveal the rectilinear decrease with increasing diamagnetic Zn and Al content in ferrite systems. The results are presented by graphs and tables.

Improving Rate Performance by Inhibiting Jahn–Teller Effect in Mn‐Based Phosphate Cathode for Na‐Ion Batteries

AbstractManganese‐based phosphate cathodes are promising candidates for developing advanced sodium‐ion batteries, primarily driven by their reliable elemental abundance, low toxicity, and desirable cycling performance. However, the cooperative Jahn–Teller effect of Mn3+ will inevitably lead to structural disorder and irreversible phase transition, thus greatly harming the reversible capacity, rate, and cycling performance. Herein, a stable NASICON‐type Na3MnHf(PO4)3 cathode is demonstrated with a volume variation of 1.9% upon the process of Na+ extraction/insertion based on the robust Hf─O bond and symmetrical MnO6 octahedron. Moreover, making full use of the stepwise redox reactions of Mn2+/Mn3+/Mn4+, this cathode reveals excellent cycling stability with a capacity retention of 85.4% after 2500 cycles at 10 C. Matching with commercial hard carbon anodes, the assembled full cell keeps a capacity retention of 92.1% with the Coulombic efficiency close to 100% after 600 cycles at 1 C. The research promises opportunities for the structural amelioration of manganese‐based phosphate cathodes toward the application in high‐performance sodium‐ion batteries.

Localised surface plasmon resonance inducing cooperative Jahn–Teller effect for crystal phase-change in a nanocrystal

The Jahn–Teller effect, a phase transition phenomenon involving the spontaneous breakdown of symmetry in molecules and crystals, causes important physical and chemical changes that affect various fields of science. In this study, we discovered that localised surface plasmon resonance (LSPR) induced the cooperative Jahn–Teller effect in covellite CuS nanocrystals (NCs), causing metastable displacive ion movements. Electron diffraction measurements under photo illumination, ultrafast time-resolved electron diffraction analyses, and theoretical calculations of semiconductive plasmonic CuS NCs showed that metastable displacive ion movements due to the LSPR-induced cooperative Jahn–Teller effect delayed the relaxation of LSPR in the microsecond region. Furthermore, the displacive ion movements caused photo-switching of the conductivity in CuS NC films at room temperature (22 °C), such as in transparent variable resistance infrared sensors. This study pushes the limits of plasmonics from tentative control of collective oscillation to metastable crystal structure manipulation.

Positive and negative magnetoresistance and charge transport anisotropy in RB12 (R - Ho, Er, Tm) antiferromagnets with dynamic charge stripes

Magnetization M and magnetoresistance Δρρ(H,T) (MR) were studied and MR analyzed quantitatively in the complicated low temperature Néel phase of RB12 (R - Ho, Er and Tm) antiferromagnets with structural (originating from cooperative Jahn-Teller effect) and electronic (coming from dynamic charge stripes) instabilities. It is shown, that well below the Néel field (HN) the magnetoresistance is determined by the concurrence of carriers' scattering by spin-density waves (leading to a linear positive contribution Δρρ(H) ∼ H) from one side, and by ferromagnetic nanoscale clusters (leading to a linear negative MR) from the other. The development of different kind instabilities in the critical region just below HN results into the emergence of an additional negative quadratic MR term, attributed to the carriers’ scattering on 4f-5d local electron density fluctuations. The anisotropy of both two linear and one quadratic MR components is analyzed in detail and compared for RB12 compounds with different magnetic structure.

Understanding Na+ ion diffusion in 1 T-MO2 (M = Mn, Fe, and Ni) via potential energy surface calculation

The cooperative Jahn-Teller effect (CJTE) plays a very important role in the study of sodium ion batteries with layered transition metal oxides 1 T-MO2 (M = Mn, Fe, and Ni) as electrodes. We have used the potential energy surface (PES) approach to describe the diffusion process of Na+ ion in these electrode materials. The successive distorting-and-hopping process was identified. For pure electrodes, the diffusion barrier of Na+ ion in FeO2 is smaller than MnO2 and NiO2. We have also investigated the diffusion mechanism of Na+ in the substitutional doped system. In MnO2, the Jahn-Teller (JT) effect of Mn3+ is modulated by the substitution of Ni and Co, and the diffusion barrier increases. In FeO2, the JT effect of Fe4+ is suppressed by the substitution of Co, Mn and Ni, and the diffusion barriers are reduced. We find that the substitutional doping of transition metal ions is an effective way to modulate the cooperative Jahn-Teller effect which helps to improve the batteries' cycling stability or rate performance.

Hall Effect Anisotropy in the Paramagnetic Phase of Ho0.8Lu0.2B12 Induced by Dynamic Charge Stripes.

A detailed study of charge transport in the paramagnetic phase of the cage-cluster dodecaboride Ho0.8Lu0.2B12 with an instability both of the fcc lattice (cooperative Jahn-Teller effect) and the electronic structure (dynamic charge stripes) was carried out at temperatures 1.9-300 K in magnetic fields up to 80 kOe. Four mono-domain single crystals of Ho0.8Lu0.2B12 samples with different crystal axis orientation were investigated in order to establish the singularities of Hall effect, which develop due to (i) the electronic phase separation (stripes) and (ii) formation of the disordered cage-glass state below T*~60 K. It was demonstrated that a considerable intrinsic anisotropic positive component ρanxy appears at low temperatures in addition to the ordinary negative Hall resistivity contribution in magnetic fields above 40 kOe applied along the [001] and [110] axes. A relation between anomalous components of the resistivity tensor ρanxy~ρanxx1.7 was found for H||[001] below T*~60 K, and a power law ρanxy~ρanxx0.83 for the orientation H||[110] at temperatures T < TS~15 K. It is argued that below characteristic temperature TS~15 K the anomalous odd ρanxy(T) and even ρanxx(T) parts of the resistivity tensor may be interpreted in terms of formation of long chains in the filamentary structure of fluctuating charges (stripes). We assume that these ρanxy(H||[001]) and ρanxy(H||[110]) components represent the intrinsic (Berry phase contribution) and extrinsic (skew scattering) mechanism, respectively. Apart from them, an additional ferromagnetic contribution to both isotropic and anisotropic components in the Hall signal was registered and attributed to the effect of magnetic polarization of 5d states (ferromagnetic nano-domains) in the conduction band of Ho0.8Lu0.2B12.

Structural phase transformation of quantum spin liquid herbertsmithite via pressure induced enhancement of the cooperative Jahn-Teller effect and antisite disorder.

Herbertsmithite, Cu3Zn(OH)6Cl2, serves as one of the most promising candidates for quantum spin liquids with a perfect quantum kagome Heisenberg antiferromagnetic system. It can comprise an ideal model system for studying the compression response of the unique structure as well as exotic properties of kagome quantum spin liquid materials, which is of fundamental importance from both scientific and technological viewpoints. In this work, the structural evolution of herbertsmithite was investigated via in situ X-ray diffraction and Raman scattering techniques up to 30 GPa. The trigonal herbertsmithite structure transformed into a monoclinic clinoatacamite-like structure at 12.6 GPa. High pressure seems to act in a reverse way as Zn-doping for herbertsmithite, with the distortion degree of the system changing continuously. The occurrence of the displacive and reversible phase transition between the polymorphs is a consequence of the interplay between the external pressure and cooperative Jahn-Teller (JT) effect, aided by the presence of antisite mutual substitution of magnetic Cu2+ ions and nonmagnetic Zn2+ ions between the kagome layer and interlayer sites.

Structural and Magnetic Properties of Nanosized Half-Doped Rare-Earth Ho0.5Ca0.5MnO3 Manganite

We investigated the structural and magnetic properties of 20 nm-sized nanoparticles of the half-doped manganite Ho0.5Ca0.5MnO3 prepared by sol-gel approach. Neutron powder diffraction patterns show Pbnm orthorhombic symmetry for 10 K < T < 290 K, with lattice parameters a, b, and c in the relationship c/√2 < a < b, indicating a cooperative Jahn–Teller effect, i.e., orbital ordering OO, from below room temperature. In contrast with the bulk samples, in the interval 250 < T < 300 K, the fingerprint of charge ordering (CO) does not manifest itself in the temperature dependence of lattice parameters. However, there are signs of CO in the temperature dependence of magnetization. Accordingly, below 100 K superlattice magnetic Bragg reflections arise, which are consistent with an antiferromagnetic phase strictly related to the bulk Mn ordering of a charge exchange-type (CE-type), but characterized by an increased fraction of ferromagnetic couplings between manganese species themselves. Our results show that in this narrow band half-doped manganite, size reduction only modifies the balance between the Anderson superexchange and Zener double exchange interactions, without destabilizing an overall very robust antiferromagnetic state.

Magnetoelectricity in Jahn–Teller Elastics

The magnetoelectric effects in Jahn–Teller crystals are discussed on the basis of phenomenology and microscopic theory. New magnetoelectric effects—metamagnetoelectricity—are analyzed. Formation of multiferroic crystal states as the consequence of the cooperative Jahn–Teller effect is discussed.

Cooperative Cluster Jahn-Teller Effect as a Possible Route to Antiferroelectricity

We report the observation of an antipolar phase in cubic GaNb_{4}S_{8} driven by an unconventional microscopic mechanism, the cooperative Jahn-Teller effect of Nb_{4}S_{4} molecular clusters. The assignment of the antipolar nature is based on sudden changes in the crystal structure and a strong drop of the dielectric constant at T_{JT}=31 K, also indicating the first-order nature of the transition. In addition, we found that local symmetry lowering precedes long-range orbital ordering, implying the presence of a dynamic Jahn-Teller effect in the cubic phase above T_{JT}. Based on the variety of structural polymorphs reported in lacunar spinels, also including ferroelectric phases, we argue that GaNb_{4}S_{8} may be transformable to a ferroelectric state, which would further classify the observed antipolar phase as antiferroelectric.

Theoretical evaluation of multivalent cation diffusion in the 1T-δ-MnO2 electrode via potential energy surface

Polymorphs of MnO2 have been studied extensively for their potential application in rechargeable batteries which provide attractive structures as the host for the cation insertion. In this study, the simplest form of δ-MnO2 has been taken as the representative of layered MnO2 and the ion diffusion performance is carefully examined. The potential energy surfaces of Li+, Na+, K+, NH4 +, Mg2+, Zn2+, Ca2+ and Al3+ ion diffusing in the 1T-δ-MnO2 are firstly obtained within the density functional theory framework, which give a comprehensive and detailed view of the diffusing process. We not only assess the 1T-δ-MnO2 as candidate electrode material quantitatively but also elucidate the influence of the cooperative Jahn–Teller effect which governs multivalent diffusion in the intuitive and clear view. Our findings are well matched with the reported results and lead to practical and implementable guidelines to find MnO2-based fast-diffusion multivalent ion conductors.

Electronic and magnetic properties of the Jahn-Teller active fluoride NaCrF3 from first-principles calculations

In perovskite-type compounds, the interplay of cooperative Jahn-Teller effect, electronic correlations and orbital degree of freedom leads to intriguing properties. $\mathrm{NaCrF_{3}}$ is a newly synthesized Jahn-Teller active fluoroperovskite where the $\mathrm{CrF_{6}^{4-}}$ octahedrons are considerably distorted. Based on the first-principles calculation, we analyze its electronic structure and magnetic properties. Our numerical results show that the $\mathrm{Cr^{2+}}$ ions adopt the high-spin $t_{2g\uparrow}^{3}e_{g\uparrow}^{1}$ configuration with $G$-type orbital ordering. We also estimate the magnetic exchange couplings and find that the in-plane and interplanar nearest-neighbor interactions are ferromagnetic and antiferromagnetic, respectively. The ground state of this material is $A$-type antiferromagnetic, in agreement with the experiments. Reasonable Curie-Weiss and $\mathrm{N\acute{e}el}$ temperatures compared to the experiments are given by mean-field approximation theory. Our results give a complete explanation of its electronic structure, magnetic and orbital order, and help to further comprehend the behaviors of Jahn-Teller active perovskite-type fluoride.

Manganese Spinel: Double the Capacity of Manganese Spinel for Lithium‐Ion Storage by Suppression of Cooperative Jahn–Teller Distortion (Adv. Energy Mater. 34/2020)

In article number 2000363 Jiaxin Zheng, Feng Pan and co-workers demonstrate that the capacity of lithium-ion manganese spinel can be doubled by the suppression of the cooperative Jahn-Teller effect. The basic suppression mechanism can be described by the image. When the dragon boat teammates work in a cooperative way just like the cooperative Jahn-Teller effect, the phase transition can be severe and result in the deterioration of the electrochemical performance. However, once the cooperative work is disturbed, like the non-coordination in the dragon boat, the phase transition can be suppressed, which makes it possible for the spinel to access double the capacity.

Physical study of PrCu1-xZnxO3 perovskite for 0.0 ≤ x ≤ 0.3

Bulk nanocrystalline samples of PrCu1-xZnxO3 (where x = 0.0, x = 0.1, x = 0.2 and x = 0.3) cuprates are prepared by the sol–gel based Pechini method. Samples were characterized by X-ray diffraction (XRD), differential scanning calorimetry DSC, FTIR, Raman spectroscopy, UV-VIS Diffuse Reflectance spectroscopic, Photoluminescence (PL), impedance spectroscopy and magnetization (M) measurements as a function of temperature and under magnetic fields. The XRD showed the single orthorhombic phase with space group Pnma. FTIR analysis confirmed the presence of Cu3+ and Cu2+ ions in our samples. Raman spectroscopy revealed the presence of many phonon modes, in particular, the B1g mode (120 cm−1) related to the existence of CuO6.The Tauc curves showed that the band gap decreased from 3.26 to 2.9 eV with Zn2+ amount. At room temperature, impedance spectroscopy in the range of 0.1 Hz–1 MHz revealed that electrical conductivity increases with Zn2+ amount. This result is linked with the observed increase of the Cu–O2–Cu angle which reflects the decrease of the cooperative Jahn-Teller effect. For x = 0.0, at temperature of 5 and 300K the M vs. H hysteresis loops exhibit an antiferromagnetic (AF) state and presented a low magnetocaloric effect at room temperature.

Structural, Magnetic, and Magneto-Caloric Properties of Cu-Substituted Nd0.67Ba0.33MnO3 Manganites

The crystal structure and magnetic properties of polycrystalline Nd0.67Ba0.33Mn1 – xCuxO3 (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.10) manganites are discussed. All the samples are crystallized into an orthorhombic crystal structure with Imma symmetry space group and the obtained lattice parameters confirm the presence of a co-operative Jahn–Teller effect for all the studied compounds. X-ray photoelectron spectra suggest the ratio of Mn3+/Mn4+ ions are observed to be decreasing systematically with the increase of Cu-content substitution and affects the Cu-ions oxidations states. The ferromagnetic (FM) to paramagnetic (PM) transition and magnetic moment is found to decrease systematically with the increase of Cu-content substitution leading to the suppression of double-exchange interactions. The theoretical and experimentally observed values of effective PM moment and saturation magnetic moment confirm the presence of inhomogeneous magnetic states containing FM and antiferromagnetic phases in all the samples. A magnetic phase change, i.e., from second-order transition to first-order transition is witnessed in between the 4 to 6 at wt % of the Cu substitution in Nd0.67Ba0.33MnO3 mixed-valence manganite.

Unusual magnetic phenomena in dynamic torsion studies of fullerene Rb3C60

In dynamic experiments using a highly sensitive torsion technique, the magnetic properties of the doped Rb3C60 single crystal are studied over a wide temperature range. The critical temperature of the superconducting transition Tc, the critical magnetic field Hc1, the pinning forces of both the Abrikosov vortices and the magnetic moments of dipoles at T >> Tc, at which relaxation processes are important, are determined and investigated. It was shown that the structural transition Fm3m-Pa3 at T = 260 K is accompanied by a reformation of the magnetic structure. Both the usual peaks at T ∼ 160–250 K and the not quite ordinary peaks of gigantic absorption of the energy of the oscillations, which shift to room temperature over time, were observed. The phenomenon is discussed in the framework of the cooperative Jahn-Teller effect, taking into account possible orbital and spin ordering. The relaxation processes at room temperatures (T ∼ 300 K) were studied. After many days of exposure (annealing) of fullerene at T ≥ 40 °C, in experiments with cooling from room temperatures, phenomena typical for a superconducting transition with giant pinning and damped oscillations were observed at T ∼ 200 K. The results of studies of magnetic phase transitions at T = 180–200 K in pure fullerite C60 (99.98% Term. Sublimed), which are related to the detected unusual magnetic phenomena in fullerene Rb3C60, are presented.

Interaction between Doubly Degenerate Centers through the Strain Field in a Weak-Anisotropy Cubic Lattice

Analytical expressions are obtained for the interaction between orbitally doubly degenerate states of ions through the strain field in weak-anisotropy cubic crystals. The arrangement of interacting pairs may be arbitrary. The energy of cooperative orbital ordering of the states of Fe2+ ions in FeCr2O4 crystal is calculated with regard to the local Jahn–Teller and the quadrupole–quadrupole interactions. It is found that the main contribution to the cooperative Jahn–Teller effect is made by the interaction through the strain field. The estimated critical phase transition temperature corresponds in order of magnitude to experimental data.

Collective infrared excitation in rare-earth GdxLa1−xB6 hexaborides

Using Fourier-transform infrared spectroscopy and optical ellipsometry, room temperature spectra of complex conductivity of single crystals of hexaborides Gd$_x$La$_{1-x}$B$_6$, $x$(Gd)$=0$, 0.01, 0.1, 0.78, 1 are determined in the frequency range 30$-$35000$~cm^{-1}$. In all compounds, in addition to the Drude free-carrier spectral component, a broad excitation is discovered with the unusually large dielectric contribution $\Delta$$\varepsilon$=5000 -- 15000 and non-Lorentzian lineshape. It is suggested that the origin of the excitation is connected with the dynamic cooperative Jahn-Teller effect of B$_6$ clusters. Analysis of the spectra together with the results of DC and Hall resistivity measurements shows that only 30$-$50$\%$ of the conduction band electrons are contributing to the free carrier conductivity with the rest being involved in the formation of an overdamped excitation, thus providing possible explanation of remarkably low work function of thermoemission of Gd$_x$La$_{1-x}$B$_6$ and non-Fermi-liquid behavior in GdB$_6$ crystals.

Parametrization of LSDA+U for noncollinear magnetic configurations: Multipolar magnetism in UO2

To explore the formation of noncollinear magnetic configurations in materials with strongly correlated electrons, we derive a noncollinear LSDA+$U$ model involving only one parameter $U$, as opposed to the difference between the Hubbard and Stoner parameters $U-J$. Computing $U$ in the constrained random phase approximation, we investigate noncollinear magnetism of uranium dioxide UO$_2$ and find that the spin-orbit coupling (SOC) stabilizes the 3$\textbf{k}$ ordered magnetic ground state. The estimated SOC strength in UO$_2$ is as large as 0.73 eV per uranium atom, making spin and orbital degrees of freedom virtually inseparable. Using a multipolar pseudospin Hamiltonian, we show how octupolar and dipole-dipole exchange coupling help establish the 3$\textbf{k}$ magnetic ground state with canted ordering of uranium $f$-orbitals. The cooperative Jahn-Teller effect does not appear to play a significant part in stabilizing the noncollinear 3$\textbf{k}$ state, which has the lowest energy even in an undistorted lattice. The choice of parameter $U$ in the LSDA+$U$ model has a notable quantitative effect on the predicted properties of UO$_2$, in particular on the magnetic exchange interaction and, perhaps trivially, on the band gap: The value of $U=3.46$ eV computed fully $ab$ $initio$ delivers the band gap of 2.11~eV in good agreement with experiment, and a balanced account of other pertinent energy scales.

Group-Theoretical Classification of Aristotypes of Cation and Anion Orders in Perovskites

A group-theoretical classification of cation and anion orders of crystals with a perovskite structure is presented. Aristotypes are idealized structures (phases), from which the low-symmetry ordered modifications of perovskites are formed as a result of rotations and deformation of octahedra, as well as the cooperative Jahn–Teller effect and other physical phenomena. Seven aristotype classes have been distinguished, which are characterized by the atomic ordering in each of Wyckoff positions and simultaneous atomic ordering in several positions. The critical and secondary (improper) order parameters, describing the formation of ordered structures, are determined. The classification proposed makes it possible to systematize a variety of known phases, establish genetic structural links between low-symmetry ordered structures, and design new materials.