Polar Strength Research Articles

Evaluation of Processes Related to Stratosphere–Troposphere Coupling in GEFSv12 Subseasonal Hindcasts

Abstract The representation of the stratosphere and stratosphere–troposphere coupling processes is evaluated in the subseasonal Global Ensemble Forecast System, version 12 (GEFSv12), hindcasts. The GEFSv12 hindcasts develop systematic stratospheric biases with increasing lead time, including a too strong boreal wintertime stratospheric polar vortex. In the tropical stratosphere, the GEFSv12 winds and temperatures associated with the quasi-biennial oscillation (QBO) tend to decay with lead time such that they underestimate the observed amplitudes; consistently, the QBO-associated mean meridional circulation is too weak. The hindcasts predict extreme polar vortex events (including sudden stratospheric warmings and vortex intensifications) about 13–14 days in advance, and extreme lower-stratospheric eddy heat flux events about 6–10 days in advance. However, GEFSv12’s ability to predict these events is likely affected by its zonal-mean circulation biases, which increases the rates of false alarms and missed detections. Nevertheless, GEFSv12 shows stratosphere–troposphere coupling relationships that agree well with reanalysis and other subseasonal forecast systems. For instance, GEFSv12 reproduces reanalysis relationships between polar vortex strength and the Northern Annular Mode in the troposphere. It also exhibits enhanced weeks 3–5 prediction skill of the North Atlantic Oscillation index when initialized during strong and weak polar vortex states compared to neutral states. Furthermore, GEFSv12 shows significant differences in Madden–Julian oscillation (MJO) amplitudes and enhanced MJO predictive skill in week 4 during easterly versus westerly QBO phases, though these results are sensitive to the level used to define the QBO. Our results provide a baseline from which future GEFS updates may be measured.

Octahedron distortion-triggered dipole–spin interaction in multiferroic magnetoelectric perovskites

The design of perovskite structures with multiferroic magnetoelectric coupling effects opens up new opportunities in fields such as the creation of next-generation spin-dependent multistate information storage technologies. In this work, we prepared a transition metal-implanted perovskite with multiferroic magnetoelectric coupling, in which both magnetoelectric coupling and a blueshift of photoluminescence were observed. The introduction of transition metal-generated polarized spin interacts with the electronic orbit through spin–orbital coupling to lead to a pronounced octahedron distortion, where the temperature dependence of the dielectric constant undergoes a ferroelectric polarization transition. An external magnetic field could enhance the strength of spin polarization to further affect the magnitude of electric polarization. Moreover, applying an electric field tunes the distortion of the octahedron dependence of electric polarization to feed back to the change in spin polarization. Overall, the spin polarization-induced electric polarization in perovskites provides a unique approach to realizing the room-temperature magnetoelectric coupling of multiferroic materials.

Enhanced resistivity and strain stability of BiFeO3–BaTiO3 ceramics by hot‐press sintering in oxygen atmosphere

AbstractEven though BiFeO3–BaTiO3 (BF–BT) with high Curie temperature and excellent piezoelectric properties is very suitable for high‐temperature applications, its rapid reduction in resistivity with temperature limits its further application. So far, there is no effective method to improve the resistivity of BF–BT at a high‐temperature state. In this work, hot‐press sintering combined with an oxygen atmosphere was used to prepare (1 − x)BF–xBT (x = 0.2–0.33) ceramics for the first time, which reduced the sintering temperature from 1000 to 920°C. The controllable grain size can be achieved by adjusting the sintering temperature and the applied pressure. The X‐ray photoelectron spectroscopy results confirmed that using hot‐press sintering effectively avoided the generation of heterovalent Fe ions, and the resistivity of BF–BT ceramics at the high‐temperature stage was improved by two orders of magnitude. It was found that hot‐press sintering can cause the oriented growth of the sample along the (1 1 0) direction, and further refined X‐ray diffraction was used to accurately analyze the changes in the lattice structure. The hot‐press sintered samples obtained larger polarization strength, especially the electro‐induced strain showed excellent temperature stability in the wide temperature range of 30–170°C. Hot‐pressing sintering combined with an oxygen atmosphere is more suitable for preparing high insulation and electrical breakdown resistance ceramics.

A novel way to prepare PbZrO3 nanocomposite films for increasing electrical properties and energy storage performance

The energy storage performance of dielectric materials depends largely on their polarization properties and electric breakdown strength. Nanocomposites have emerged as an effective method for improving these properties. In this study, we propose a novel method to prepare PbZrO3-Al2O3 nanocomposite films by combining chemical solution deposition with thermal evaporation of a metal Al layer. The resulting composite films exhibit a layered distribution of Al2O3 nanoparticles (NPs) on the PbZrO3 matrix, which can be used to control the shape and characteristics of the polarization-electric field (P-E) hysteresis loop by varying the thickness of the Al layer. We thoroughly investigated the effects of Al2O3 NPs on the microstructure, polarization, leakage current, and energy storage properties of the composite films. Our results show that as the content of Al2O3 NPs increases, the property of the composite films gradually evolves from antiferroelectric characteristics to ferroelectric characteristics. Specifically, the maximum polarization, remanent polarization, and electrical breakdown strength increase, while the leakage current decreases. Compared to PbZrO3 thin films, the electrical breakdown strength (1850 kV/cm) and energy storage density (25.0 J/cm3) of the nanocomposite thin films increased by 189% and 93%, respectively. Our study presents a new method to prepare dielectric nanocomposite films and opens up a new avenue for designing energy storage capacitor materials using nanocomposites.

Reconstruction of Multiscale Electromagnetic Sources from Multifrequency Electric Far Field Patterns at Sparse Observation Directions

We introduce a multistep scheme for reconstructing multiscale sources from multifrequency sparse electric far field patterns. The unknown source is a combination of electric dipoles, magnetic dipoles and extended sources. The dipoles are shown to be uniquely identified by the multifrequency electric far field patterns at properly chosen sparse observation directions. Motivated by the constructive uniqueness, two indicator functions are then designed for locating the magnetic dipoles and the electric dipoles. After locating all the dipoles, the formulas for computing the corresponding polarization strengths are proposed. The stability of the formulas with respect to the frequency band is also derived. Finally, an indicator for the support of the extended sources is introduced once the dipoles are identified. Some numerical examples are presented to show the validity and robustness of the proposed algorithm.

Research on Improving Energy Storage Density and Efficiency of Dielectric Ceramic Ferroelectric Materials Based on BaTiO3 Doping with Multiple Elements

In order to promote the research of green energy in the situation of increasingly serious environmental pollution, dielectric ceramic energy storage materials, which have the advantages of an extremely fast charge and discharge cycle, high durability, and have a broad use in new energy vehicles and pulse power, are being studied. However, the energy storage density of ordinary dielectric ceramic ferroelectric materials is low, so, in this paper, we have divided eight components based on BaTiO3 (BT). Through the traditional solid phase sintering method, AB positions were replaced with various elements of different proportions to improve their energy storage density and the energy storage efficiency of BT-based ferroelectric materials. In this paper, we studied the results of XRD, Raman, ferroelectric, dielectric, and impedance tests of doped samples, and the best components were determined. The (1−x)BT−xBi(Mg1/3Zn1/3Ta1/6Nb1/6)O3 series of ceramics are made by the incorporation of five elements, Bi3+, Mg2+, Zn2+, Ta5+, and Nb5+. With the rising electric hysteresis loop of the doping amount x thin, the saturation polarization strength and residual polarization strength decrease, and the energy storage density rises first and then decreases. The dielectric characteristic after x = 0.08 showed a flat dielectric peak, indicating that the ferroelectric relaxation had been formed. The energy storage density and efficiency of the best component x = 0.12 reached 1.75 J/cm3 and 75%, respectively, and the Curie temperature was about −20 °C, so it has the potential to be used at room temperature.

Stabilizing polar P21ma phase in Bi0.5Na0.5TiO3-Na0.91Bi0.09Nb0.94Mg0.06O3 relaxors by CaTiO3 additive to promote energy storage density, efficiency and discharge rate

Eco-friendly Bi0.5Na0.5TiO3 relaxor ferroelectric has attracted considerable attention for pulsed power capacitor applications due to its large saturation polarization. However, high remnant polarization and low breakdown strength (Eb) restrict its application. Herein, linear dielectric CaTiO3 (CT) is introduced into Bi0.5Na0.5TiO3-Na0.91Bi0.09Nb0.94Mg0.06O3 (BNT-NBNM) ceramic to enhance its Eb. Interestingly, CT additive can stabilize polar orthorhombic P21ma phase. As a result, a high recoverable energy density of 6.4 J/cm3 and a high efficiency of 92% at 400 kV/cm as well as an ultrafast discharge rate of 57 ns are obtained in 0.63BNT-0.27NBNM-0.1CT ceramic. Furthermore, temperature dependent Raman spectra reveal that the superior temperature stability of energy storage properties over the temperature span of 30–150 °C is due to insensitive B-O vibration to temperature. The results demonstrate an effective strategy to construct superior and stable BNT-based energy storage materials for pulsed power capacitor applications.

Improved energy storage performance of Bi(Mg0.5Ti0.5)O3 modified Ba0.55Sr0.45TiO3 lead-free ceramics for pulsed power capacitors

(1–x)Ba0.55Sr0.45TiO3–xBi(Mg0.5Ti0.5)O3 (x = 0, 0.08, 0.1, 0.12, 0.15, 0.2) ceramics were fabricated via a solid-state reaction route. The ultrahigh recoverable energy density (Wrec = 4.05 J cm−3), efficiency (η = 78%), maximum polarization (Pmax = 51.40 μC cm−2), and high dielectric breakdown strength (BDS = 230 kV cm−1) were achieved for the 0.9BST−0.1BMT ceramic. The fast discharge rate (t0.9∼0.14 μs), current density (CD∼637.02 A cm−2), high power density (PD∼38.70 MW cm−3), good temperature stability (20−180 °C), frequency stability (10−500 Hz), and fatigue endurance for cycling (105) of 0.9BST−0.1BMT ceramic make it suitable for the development of energy-storage devices. The relaxor behavior with a high Wrec (3.06 J cm−3) and η (93%) at BDS (220 kV cm−1) was also achieved for the 0.8BST−0.2BMT ceramic. This study systematically investigates the correlation among the structural, dielectric, impedance, and energy storage properties of BMT-doped BST ceramics.

Influence of Inner Surface Roughness on the Spectral Induced Polarization Response—A Numerical Study

AbstractSpectral induced polarization (SIP) laboratory measurements on water‐saturated rocks show a strong correlation between the electrical polarization strength and the inner surface area of rocks. We investigate the influence of inner surface roughness on the SIP response by simulating the frequency‐dependent complex conductivity of micro‐scale rock models. Starting with smooth grain models, we introduce surface roughness using two different approaches: increasing the surface roughness in a fractal‐like manner, and creating random surface structures, resulting in more natural‐looking surfaces. We find that surface roughness has two distinct effects on the SIP response: (a) a shift in the position and magnitude of the primary relaxation frequency to lower frequencies and lower magnitudes, respectively, and (b) the formation of secondary polarizations above the polarization frequency of the primary polarization. We also compare the relaxation time and normalized chargeability obtained by Debye decomposition and the imaginary conductivity at 1 Hz of our models with mechanistic models and empirical relations. We point out the congruences and offer explanations for the discrepancies between our models and the empirical observations. We conclude that the results of our study are applicable to real rocks and that the SIP method has the potential to detect inner surface roughness. However, the SIP method it not able to discriminate between signals from rough particles and a distribution of smooth particles.

Cover Image, Volume 140, Issue 26

Wenlong Yang and Yu Wang designed the cover image that shows flexible all-organic polyimide-poly(amidic acid)/poly(vinylidene fluoride) hybrid films. The incorporation of polyvinylidene fluoride and poly(amidic acid) with high intrinsic polarization strength into polyimide could significantly enhance the energy density and suppress the dielectric loss of PI-based composites. The authors propose a simple and low-cost approach to fabricate films with excellent dielectric performance, which can provide a contribution to the next generation of dielectric capacity. DOI: 10.1002/app.54043

Microstructure and mechanical properties of BT/PVTC composite ferroelectric thin films.

Ferroelectric ceramic polymer composites have become the preferred electrocaloric materials due to their light weight and high polarization strength. But the mechanical properties were desired to be improved. In this study, the polyvinylidene fluoride trifluoro ethylene chloride (PVTC) and barium titanate (BT) composites were prepared, and the microstructure and mechanical properties were investigated by molecular dynamics simulations and experiments. It was found that with the increase of BT ceramic content in the composites, the yield stress is significantly reduced, which can be reduced by 16.07%. By comparing with the experimental data, the agglomeration and stress mechanism of the composites were proposed. The microstructure of the composite was analyzed using radial distribution function, self-diffusion coefficient, and glass transition temperature. The agglomeration mechanism of the composite was revealed from the microscopic point of view, and the rationality of the agglomeration behavior was verified by experiments. The calculations were performed by Material Studio 2019 software and the COMPASS force field was adopted.

Constructing Novel High-Performance Dipolar Glass Polymer Dielectrics by Polar Rigid/Flexible Side Chains.

Developing new polymer dielectrics with superior dielectric and energy storage properties is urgent to meet the demand for electronic devices in the field of microminiaturization or harsh environments. In this paper, two dipolar glass polymers based on polynorbornene main chain and flexible/rigid cyano side chain were synthesized by ring opening metathesis polymerization method: polymer PCEMT with flexible side chains and polymer PCPMT with rigid side chains. The backbone is built from two rigid five-membered rings, which not only avoids the narrow band gap caused by π-π conjugation of traditional aromatic main chains, but also maintains high thermal stability and high glass transition temperature (Tg). The introduced polar cyano groups on the side chain gave high dielectric constants (εr) for both polymers, where the εr of PCEMT and PCPMT reached 7.9 and 4.6 at room temperature and 1 kHz, respectively. Due to high polarization and high breakdown strength, the PCPMT obtains a maximum discharge energy density (Ud) of 4.47 J/cm3 at room temperature, which is 1.61 and 1.57 times of biaxially oriented polypropylene and polyimide (Kapton). The supernal Tg of 229 °C makes the energy storage performance of PCPMT almost unaffected at 100 °C. The charge-discharge efficiency (η) always keeps over 90% and an Ud of 5.2 J/cm3 at 480 MV/m is achieved, which is much better than Kapton (Ud = 1.77 J/cm3, η = 42.5%) under the same conditions. This work provides a new idea for preparing the high-performance polymer dielectrics via introducing rigid polar side chains.

Enhanced energy storage performance of polyethersulfone-based dielectric composite via regulating heat treatment and filling phase

Polyethersulfone (PESU) has distinctive features of great breakdown strength and low dielectric loss. However, some factors limit the practical application of PESU dielectric materials in the field of energy storage, for instance, the low energy storage density, polarization strength and dielectric constant of PESU. In this work, ZnO nano-shell and BFSTO nano-shell coated BZCT are successfully synthesized, respectively, using the hydrothermal method. Compared to the pure PESU and BZCT/PESU, discharged energy density and efficiency are obviously improved by adding the core-shell structural nanofibers (NFs) into the PESU matrix. Particularly, a remarkably suppressed dielectric loss in 2 wt% BZCT@BFSTO/PESU composites with an outstanding dielectric energy density and an excellent charging-discharging efficiency are simultaneously achieved. The results demonstrate that the discharge energy density of the 2 wt% BZCT@BFSTO/PESU can reach 10.5 J/cm3 under the electric field of 500 kV/mm, and the charge-discharge efficiency is 84%. This in-depth research on PESU-based composite dielectrics has laid an experimental and theoretical basis for the improvement of the dielectric properties and energy storage performance of polymer-based composite, resulting in promoting the development of new dielectric capacitors, and paving the way for the applications of it in the field of energy storage.

All organic polyimide‐based composite films with high intrinsic polarization for superior energy density and low dielectric loss

AbstractA simple and low‐cost approach was proposed to fabricate poly(vinylidene fluoride) (PVDF) and polyimide‐poly(amidic acid) (PI‐PAA) all‐organic hybrid films with excellent dielectric performance by solution casting and thermal imidization process. The results showed that the introduction of PVDF and PAA molecular chains into PI matrix significantly enhanced the dielectric permittivity and energy density of PI‐based composites. The permittivity and energy density of 15 wt% PI‐PAA/PVDF composites were 4.83 at 103 Hz and 5.55 J cm−3, which were 52% and 107% higher than that of PI (3.18 at 103 Hz, 2.68 J cm−3). In addition, the dielectric loss of 15 wt% PI‐PAA/PVDF composites was still maintained at a low level (0.009 at 103 Hz). The molecular dynamics results showed that the polarization strength of composites mainly originated from the intrinsic polarization strength. The intrinsic polarization strength of PI‐PAA/PVDF in the composites was 1010 times higher than interfacial polarization strength, and interfacial polarization was negligible. There was no significant difference between the self‐diffusion coefficients of 15 wt% PI‐PAA/PVDF and PI‐PAA, indicating that the relaxation polarization of polymer molecular chains was suppressed. This work provides an effective way for the preparation of dielectric for all organic high voltage direct current system.

Voltage Modulation of Nanoplasmonic Metal Luminescence from Nano-Optoelectrodes in Electrolytes.

Metallic nanostructures supporting surface plasmon modes can concentrate optical fields and enhance luminescence processes from the metal surface at plasmonic hotspots. Such nanoplasmonic metal luminescence contributes to the spectral background in surface-enhanced Raman spectroscopy (SERS) measurements and is helpful in bioimaging, nanothermometry and chemical reaction monitoring applications. Although there is growing interest in nanoplasmonic metal luminescence, its dependence on voltage modulation has received limited attention in research investigations. Also, the hyphenated electrochemical surface-enhanced Raman spectroscopy (EC-SERS) technique typically ignores voltage-dependent spectral background information associated with nanoplasmonic metal luminescence due to limited mechanistic understanding and poor measurement reproducibility. Here, we report a combined experiment and theory study on dynamic voltage-modulated nanoplasmonic metal luminescence from hotspots at the electrode-electrolyte interface using multiresonant nanolaminate nano-optoelectrode arrays. Our EC-SERS measurements under 785 nm continuous wavelength laser excitation demonstrate that short-wavenumber nanoplasmonic metal luminescence associated with plasmon-enhanced electronic Raman scattering (PE-ERS) exhibits a negative voltage modulation slope (up to ≈30% V-1) in physiological ionic solutions. Furthermore, we have developed a phenomenological model to intuitively capture the plasmonic, electronic, and ionic characteristics at the metal-electrolyte interface to understand the observed dependence of the PE-ERS voltage modulation slope on voltage polarization and ionic strength. The current work represents a critical step toward the general application of nanoplasmonic metal luminescence signals in optical voltage biosensing, hybrid optical-electrical signal transduction, and interfacial electrochemical monitoring.

On the Influence of ENSO on Sudden Stratospheric Warmings

AbstractUsing the extended ERA5 reanalysis and three state‐of‐the‐art models, this study explores how El Niño‐Southern Oscillation (ENSO) can influence the total frequency, seasonal cycle and preconditioning of sudden stratospheric warmings (SSWs). Reanalysis data shows that in the last seven decades, winters with SSWs were more common than winters without, regardless El Niño (EN) or La Niña (LN) occurrence or the ENSO/SSW definitions. In agreement with previous studies, our models tend to simulate a linear ENSO‐SSW relationship, with more SSWs for EN, around mid‐winter (January–February) as in reanalysis, and less for LN when compared to neutral conditions. Independently of ENSO, the main tropospheric precursor of SSWs appears to be an anomalous wave‐like pattern over Eurasia, but it is dominated by wavenumber 1 (WN1) for EN and shows an enhanced wavenumber 2 (WN2) for LN. The differences in this Eurasian wave pattern, which is largely internally generated, emerge from the distinct configuration of the background, stationary wave pattern induced by ENSO in the North Pacific, favoring a stronger WN1 (WN2) component during EN (LN). Our results suggest that the ENSO‐forced signal relies on modulating the seasonal‐mean polar vortex strength, becoming weaker and more displaced (stronger and more stable) for EN (LN), while ENSO‐unforced wave activity represents the ultimate trigger of SSWs. This supports the view that ENSO and SSWs are distinct sources of variability of the winter atmospheric circulation operating at different time‐scales and may reconcile previous findings in this context.

Multi-symmetry high-entropy relaxor ferroelectric with giant capacitive energy storage

Relaxor ferroelectric ceramics with remarkable energy storage performance, which is dominantly determined by polarization and breakdown strength, are one of the bottlenecks for next generation high/pulsed power dielectric capacitors. Herein, we report that high-entropy composition Li2CO3-densified Bi0.2Na0.2Ba0.2Sr0.2Ca0.2TiO3 achieves a giant recoverable energy density (Wrec) of 10.7 J/cm3 and an ultrahigh efficiency (η) of 89 %. To understand the mechanism, the influence of the high-entropy effect on atomic-scale polarization configuration and macroscale electrical properties has been investigated systematically. Randomly distributed A-site ions and B-site ions form complex interactions, which lead to coexisted atomic-scale low crystallographic symmetries, and thus, high-dynamic polar nanoregions as well as “intermediate polarization”, such multiple symmetry polarization configuration ensures fast and strong polarization response. On the other hand, the high-entropy system exhibits a wide band gap, helping to reduce conductivity and delay breakdown. Moreover, stable high-entropy structure brings great advantages for enhancing the thermal/frequency stability of energy storage performance. This work not only provides a material candidate with outstanding comprehensive energy storage performance but also affirms high-entropy approach is a shortcut to optimizing functional property by multi-scale interactions between polarization, microstructure and crystal structure.

Tunable Phase Structure in Mn-Doped Lead-Free BaTiO3 Crystalline/Amorphous Energy Storage Thin Films

For dielectric energy storage materials, high polarization and high breakdown strengths are a long-standing challenge. A modulating crystalline/amorphous phase structure strategy is proposed by Mn-doping and annealing temperature to enhance the energy storage performance of pure BaTiO3 (BT) films. In this study, lead-free Mn-doped BT films were prepared on Pt/Ti/SiO2/Si substrates via the sol-gel method, and the effects of the crystalline/amorphous phase ratio on polarization and electric properties were analyzed. A small amount of Mn-doping in BT could reduce the annealing temperature and enhance polarization with an Mn content of 8%. In addition, the energy storage properties of BT-8%Mn films achieve the best energy storage performance in terms of energy density and efficiency of 72.4 J/cm3 and 88.5% by changing the annealing temperature to 640 °C. BT-8%Mn energy storage films also possess good stability over a wide temperature range of 20 °C–200 °C, which demonstrates that crystalline/amorphous engineering is a simple and effective way to enhance energy storage applications of dielectric films.

Enhanced optical transmittance and energy‐storage performance in NaNbO3‐modified Bi0.5Na0.5TiO3 ceramics

AbstractDielectric ceramics with both excellent energy storage and optical transmittance have attracted much attention in recent years. However, the transparent Pb‐free energy‐storage ceramics were rare reported. In this work, we prepared transparent relaxor ferroelectric ceramics (1 − x)Bi0.5Na0.5TiO3–xNaNbO3 (BNT–xNN) by conventional solid‐state reaction method. We find the NN‐doping can enhance the polarization and breakdown strength of BNT by suppressing the grain growth and restrained the reduction of Ti4+ to Ti3+. As a result, a high recoverable energy‐storage density of 5.14 J/cm3 and its energy efficiency of 79.65% are achieved in BNT–0.5NN ceramic at 286 kV/cm. Furthermore, NN‐doping can promote the densification to improve the optical transmittance of BNT, rising from ∼26% (x = 0.2) to ∼32% (x = 0.5) in the visible light region. These characteristics demonstrate the potential application of BNT–xNN as transparent energy‐storage dielectric ceramics.

Room-Temperature Ionic Liquid Cation Effects on the Structure and Stability of Anionic Lanthanide Complexes.

Room-temperature ionic liquids (RTILs) are a subset of molten salts that are liquids at room temperature and may offer an elegant, low-temperature route to predicting the properties of solvated metal complexes in their high-temperature analogues. This work studied the chemistry of chloride anion-containing RTILs to determine their similarity to inorganic molten chloride salts. The behaviors of complexes of Mn, Nd, and Eu were evaluated in a variety of chloride RTILs by absorption spectrophotometry and electrochemistry to elucidate trends in cation effects on the coordination geometry and redox properties of the solvated species. Spectrophotometric data indicated the metals are present as anionic complex (e.g., MnCl42- and NdCl63-) analogous to those observed in molten chloride salts. Strongly polarizing, charge-dense RTIL cations induced distortions to the symmetry of these complexes, resulting in lower oscillator strengths and red-shifted energies for the observed transitions. Cyclic voltammetry experiments were used to characterize the Eu(III/II) redox couple producing diffusion coefficients on the order of 10-8 cm2 s-1 and heterogeneous electron transfer rate constants ranging between 6 × 10-5 and 2 × 10-4 cm s-1. The E1/2 potentials for Eu(III/II) were also found to shift positively with increasing cation polarization power, stabilizing the Eu(II) oxidation state by removing electron density from the metal center over chloride bond networks. Both the optical spectrophotometry and electrochemistry results suggest that the polarization strength of an RTIL cation plays a major role in the geometry and stability of a metal complex.