Antiferroelectricity in tantalum doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06(Ti_1−xTa_x)O₃ (x=0.00–0.04) lead-free polycrystalline ceramics were synthesized using the solid state reaction route, and their crystal structures and electrical properties were systematically studied. With the introduction of Ta substitution, the relaxor antiferroelectric phase with tetragonal P4bm symmetry is stabilized. The representative double polarization hysteresis loops and sprout shaped strain curves for antiferroelectric ceramics are observed at higher Ta contents with x=0.01–0.02 at room temperature. x=0.01 shows the largest strain of 3.81‰ under 60 kV/cm, indicating a good candidate for actuator applications. The polarization and strain hysteresis loops are also evaluated to verify the temperature-induced normal ferroelectric phase to relaxor antiferroelectric phase transition at temperature up to 120 °C. The energy storage density and efficiency at various temperatures are calculated and analyzed in the compositions of x=0.00–0.02. The results indicate that the energy storage density becomes more temperature independent with the increase of Ta concentration, which are promising for applications in high-temperature capacitors.     

Enhanced energy storage properties and large electrostrictive effect of Bi0.35Na0.35Ba0.09Sr0.21Ti(1-x)(Al0.5Nb0.5)xO3 relaxor ceramics

Ferroelectric ceramics have good piezoelectric and ferroelectric properties and can be used for energy storage equipment and actuators. Nevertheless, current research on dielectric capacitors has only focused on the energy storage density, but ignored efficiency. Moreover, conventional piezoelectric materials have a large strain hysteresis. In this work, (Al_0.5Nb_0.5)⁴⁺ (AN) complex ions doped 0.7Bi_0.5Na_0.5TiO₃-0.3Ba_0.3Sr_0.7TiO₃ (BNBST) ceramics were prepared. Doping AN destroyed the long-range ordered ferroelectric domains and generated polar nano regions, resulting in a gradual thinning and inclination of polarization hysteresis loops and an increase in relaxor degree. For BNBST-3AN ceramics, a W_rec of 1.52 J/cm³ and a η of 92.1% were achieved at 150 kV/cm. Meanwhile, BNBST-3AN ceramics had good energy storage temperature stability and cycling performance. The AN doping reduced the strain hysteresis in BNBST ceramics. BNBST-2AN ceramics exhibited a longitudinal electrostrictive coefficient Q₃₃ ～ 0.0292 m⁴/C² and a field-induced strain of 0.25% with low strain hysteresis (6.67%). Furthermore, BNBST-4AN ceramics had superior dielectric temperature stability from 24 to 270 °C. All results show that BNBST-100xAN ceramics have great promise for energy storage devices and actuators.     

Bi0·5Na0·5TiO3–Sr0.85Bi0·1TiO3 ceramics with high energy storage properties and extremely fast discharge speed via regulating relaxation temperature

Bi_0·5Na_0·5TiO₃-based relaxor ferroelectric ceramics have recently gained increasing attention due to their outstanding energy storage properties. However, the trade-off between the recoverable energy storage density/efficiency and discharge rate resulted from the hysteresis of domain switching process, severely limits their applications. Herein, a strategy realizing synergistic excellent energy storage properties and fast discharge rate is proposed through regulating relaxation temperature. The relaxation temperature was decreased to below room temperature by introducing Sr_0·85Bi_0·1TiO₃ into Bi_0·5Na_0·5TiO₃ [(1-x)Bi_0·5Na_0·5TiO₃-xSr_0.85Bi_0·1TiO₃, x = 0.5–0.7)], enabling the small size and weak correlation polar nanoregions (PNRs) with relatively high polarization. The trade-off was overcome by reducing the hysteresis of electrical switching of weak correlation PNRs. Thus, large recoverable energy storage density of 2.32 J/cm³ and high efficiency of 80.1% (250 kV/cm) were achieved simultaneously for x = 0.7 ceramics. Meanwhile, extremely rapid discharge rate (<30 ns) and remarkable power density of 63.7 MW/cm³, which were superior to the previously reported lead-free ceramics were realized. Besides, the 0.3BNT-0.7SBT ceramics also possess good thermal stability over 25 °C–115 °C at 100 kV/cm and good frequency stability (5–100 Hz). These properties make the 0.3BNT-0.7SBT ceramic an ideal candidate for energy storage applications.     

NaNbO3-based short-range antiferroelectric ceramics with ultrahigh energy storage performance

Lead-free NaNbO₃ (NN) antiferroelectric ceramics provide superior energy storage performance and good temperature/frequency stability, which are solid candidates for dielectric capacitors in high power/pulse electronic power systems. However, their conversion of the antiferroelectric P phase to the ferroelectric Q phase at room temperature is always accompanied with large remnant polarization (P_r), which significantly reduces their effective energy storage density and efficiency. In this study, to optimize the energy storage properties, short-range antiferroelectric (0.95-x)NaNbO₃-xBi(Mg_2/3Nb_1/3)O₃-0.05CaZrO₃ (xBMN) ceramics were designed to stabilize the antiferroelectric phase, in which the local random fields were simultaneously constructed. The results showed that the antiferroelectric orthorhombic P phase was transformed into the R phase, and the local short-range random fields were generated, which effectively inhibited the hysteresis loss and P_r. Of great interest is that the 0.12BMN ceramics displayed a large recoverable energy storage density (W_rec) of 5.9 J/cm³ and high efficiency (η) of 85% at the breakdown strength (E_b) of 640 kV/cm. The material also showed good frequency stability in the frequency range of 2–300 Hz, excellent temperature stability in the temperature range of 20–110 ℃, and a very short discharge time (t_0.9∼4.92 μs). These results indicate that xBMN ceramics have great potential for advanced energy storage capacitor applications.     

Effect of Sr(Zn1/3Nb2/3)O3 modification on the energy storage performance of BaTiO3 ceramics

Lead-free (1-x)BaTiO₃-xSr(Zn_1/3Nb_2/3)O₃ (abbreviated as BT-xSZN, x = 0–0.08) relaxor ferroelectric ceramics were prepared using the traditional solid phase technology, and the effects of SZN modification on their phase structures, microstructures, dielectric performance, ferroelectricity and energy storage performance were studied in detail. A pure perovskite phase was observed in the BT-xSZN ceramics. The BT-based ceramics modified by SZN exhibited refined grain size. As the SZN content was increased, the breakdown strength initially increased and then decreased, and the ferroelectric loops gradually became ‘slim’. The BT-xSZN (x = 0.07) ceramics demonstrated a favourable energy storage performance with high recoverable energy density (W_rec = ~1.45 J/cm³) and energy storage efficiency (η = ~83.12%) at 260 kV/cm. Results indicate that the energy storage performance of BaTiO₃ ceramics modified by SZN can be remarkably improved, widening their applications in energy storage at low temperatures.     

Lead-free BaTiO3-Bi0.5Na0.5TiO3-Na0.73Bi0.09NbO3 relaxor ferroelectric ceramics for high energy storage

A series of (1-x)(0.65BaTiO₃-0.35Bi_0.5Na_0.5TiO₃)-xNa_0.73Bi_0.09NbO₃ ((1-x)BBNT-xNBN) (x = 0–0.14) ceramics were designed and fabricated using the conventional solid-state sintering method. The microstructure, dielectric property, relaxor behavior and energy storage property were systematically investigated. X-ray diffraction results reveal a pure perovskite structure and dielectric measurements exhibit a relaxor behavior for the (1-x)BBNT-xNBN ceramics. The slim polarization electric field (P-E) loops were observed in the samples with x ≥ 0.02 and the addition of Na_0.73Bi_0.09NbO₃ (NBN) could decrease the remnant polarization (P_r) of the (1-x)BBNT-xNBN ceramics obviously. The sample with x = 0.08 exhibits the highest energy storage density of 1.70 J/cm³ and the energy storage efficiency of 82% at 172 kV/cm owing to its submicron grain size and high relative density. These results show that the (1-x)BBNT-xNBN ceramics may be promising lead-free materials for high energy storage density capacitors.     

Significantly enhanced energy storage performance in Sm-doped 0.88NaNbO3-0.12Sr0·7Bi0·2TiO3 lead-free ceramics

Lead-free antiferroelectric (AFE) ceramic materials have attached increasing attention in application of high-power capacitors for the past few years, due to their high energy storage density and environmental protection. However, the related applications are seriously restricted because of the limited number of environment friendly AFE candidate materials, high cost and low energy storage efficiency. In this work, the A-site ion Sm³⁺ doped 0.88NaNbO₃-0.12Sr_0·7Bi_0·2TiO₃ lead-free AFE P phase ceramics (0.88Na_1-3xSm_xNbO₃-0.12Sr_0·7Bi_0·2TiO₃, abbreviated as NN-SBT-100xSm) were prepared and characterized. With the increase of Sm doping amount, a relaxor-like behavior was found in the dielectric-temperature curves of NN-SBT-100xSm, indicating the AFE orthorhombic P phase is gradually replaced by an AFE orthorhombic R phase. As a result, double-like and slim P-E curve with near-zero residual polarization and suppressed hysteresis loss was obtained at x > 0.01. More encouragingly, a good discharge energy storage density (W_rec = 3.58 J/cm³) and a high efficiency (η = 82%) at a low electric field (E = 200 kV/cm) has been recorded simultaneously for NN-SBT-2Sm relaxor AFE ceramic, which are better than the other lead-free energy storage ceramics under the same E. In addition, the energy storage properties of NN-SBT-2Sm ceramics exhibit outstanding temperature and frequency stability. These results indicate that NN-SBT-2Sm relaxor AFE ceramic has a great practical value in pulse power capacitors.     

Highly-reliable dielectric capacitors with excellent comprehensive energy-storage properties using Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics

The development of capacitors with high reliability and good comprehensive performances is of great significance for practical applications. In this work, lead-free relaxor ferroelectric (FE) ceramics of (1-x)(0.5(Bi_0.5Na_0.5)TiO₃-0.5SrTiO₃)-xBi(Mg_2/3Nb_1/3)O₃ ((1-x)(BNT-ST)-xBMN) were prepared by a conventional solid-state reaction method. The introduction of BMN was found to enhance local structure disorder, leading to the significantly reduced size of FE nanodomains, which is responsible for the slim polarization-electric field hysteresis loops. A giant energy-storage density of 6.62 J/cm³ and a high efficiency of 82 % can be achieved simultaneously under a moderate electric field of 34 kV/mm at x = 0.08. It also exhibits high discharge density ～ 2.74 J/cm³, large power density ～ 248 MW/cm³ and ultrafast discharge rate ～ 28 ns at 20 kV/mm in addition to excellent temperature (10–130 °C) and frequency (1–100 Hz) stabilities. These results demonstrate that the (1-x)(BNT-ST)-xBMN ceramic system is a promising lead-free candidate for advanced pulsed power capacitor applications.     

Enhanced energy storage property achieved in Na0.5Bi0.5TiO3-based ferroelectric ceramics via composition design and grain size tuning

Dielectric energy storage capacitors have been explored to obtain excellent energy storage density along with high energy storage efficiency with the development of electronic devices. In this work, linear dielectric CaTi_0.5Zr_0.5O₃ is introduced into Bi_0.5Na_0.5TiO₃-NaNbO₃ matrix to form 0–3 type composites to vary the size and conductivity of the composite grain, which lead to ultra-high breakdown electric field of 410 kV/cm and the quasi-linear hysteresis loops. Meanwhile, linear dielectric does not change the characteristic of ferroelectric, and thus composites maintain high maximum polarization of 26.4 μC/cm². Integrating the advantages of linear dielectric and ferroelectric, an excellent recoverable energy density of 4.93 J/cm³ with an efficiency of 93.3% have been achieved in BNT-NN/7 wt%CZT ceramics. This work contributes to the development of dielectric energy storage capacitors for practical applications in pulsed power devices.     

Ultrahigh energy storage density and charge-discharge performance in novel sodium bismuth titanate-based ceramics

Lead-free ferroelectric ceramics are very suitable for electrostatic energy storage capacitors due to their outstanding characteristics of high charge-discharge speed, high power density, and environmental friendliness. Herein, a novel material system as (1−x)Na_0.5Bi_0.5TiO₃-xCaZr_0.5Ti_0.5O₃ (NBT-CZT, x = 0, 0.05, 0.10, 0.12, 0.15, and 0.20) was designed and prepared for dielectric energy storage ceramics. It demonstrated that the CZT additives induced a phase transition for the NBT ceramics, from ferroelectric to relaxor ferroelectric. In particular, extremely high stored energy storage density (6.92 and 5.37 J/cm³), high recoverable energy storage density (4.77 and 4.37 J/cm³), and moderate efficiency (69.0% and 81.4%) were achieved in both the samples of x = 0.12 and x = 0.15, respectively. The ceramics exhibited excellent stability of energy storage performance covering a wide temperature (25°C–200°C) and frequency (0.5–50 Hz) range, and also fatigue cycles up to 10⁵. Additionally, the NBT-CZT ceramics had a fast discharge speed (t_0.9 < 100 ns) and high power density (24.2 MW/cm³, E = 100 kV/cm, x = 0.15), and the charge-discharge process remained stable even when the measured temperature was up to 160°C. Therefore, the NBT-CZT ceramics have the potential to be utilized in electrostatic energy storage applications.     

High recoverable energy storage density and large energy efficiency simultaneously achieved in BaTiO3–Bi(Zn1/2Zr1/2)O3 relaxor ferroelectrics

Relaxor ferroelectrics have attracted much attention as electric energy storage materials for intermittent energy storage because of their high saturated polarization, near-zero remnant polarizations, and considerable dielectric breakdown strength (BDS). Despite the numerous efforts, the dielectric energy storage performance of relaxor ferroelectric ceramics is incomplete or unsatisfactory. The enhancement of recoverable energy storage density W_rec usually accompanies with the sacrifice of discharge-to-charge energy efficiency η; therefore, it is an important issue to achieve high recoverable W_rec and large efficiency η simultaneously. In this work, the (1-x)BaTiO₃-xBi(Zn_1/2Zr_1/2)O₃ (abbreviated as BT-100xBZZ, 0 ≤ x ≤ 0.20) ferroelectric ceramics were prepared using the conventional solid-state reaction method. The phase structure, microstructural morphology, dielectric and ferroelectric properties, relaxation behaviors, and energy storage properties of BT-BZZ ceramics were investigated in detail. X-ray powder diffraction, dielectric spectra, and ferroelectric properties confirm the transformation of tetragonal phase for normal ferroelectrics (BT) to pseudo-cubic phase for relaxor ferroelectrics (BT-8BZZ). A high recoverable energy storage density W_rec of 2.47 J/cm³ and a large energy efficiency η of 94.4% are simultaneously achieved in the composition of BT-12BZZ, which presents typical weakly coupled relaxor ferroelectric characteristics, with an activation energy E_a of 0.21 eV and a freezing temperature T_f of 139.7 K. Such excellent energy storage performance suggests that relaxor ferroelectric BT-12BZZ ceramics are promising dielectric energy storage materials for high-power pulsed capacitors.     

Effect of layered structure on dielectric properties and energy storage density in xBa0.7Sr0.3TiO3-SrTiO3 multilayer ceramics

xBa_0.7Sr_0.3TiO₃-SrTiO₃ (BST-ST) multilayer ceramics with different BST layers (x=1, 3, 5) were designed and fabricated by lamination of Ba_0.7Sr_0.3TiO₃ (BST) and SrTiO₃ (ST) tapes. Dielectric and energy storage properties of the multilayer ceramics were investigated. BST-ST multilayer ceramics exhibited enhanced temperature- and frequency-stability of dielectric properties, accompanying high permittivity (~2000) and low dielectric loss (<0.005) at room temperature. P-E loops revealed that BST-ST multilayer ceramics displayed low remnant polarization and favorable maximum polarization. The optimal energy storage performance was obtained in the composition of x=5 with dielectric breakdown strength of 220 kV/cm and energy storage density of 2.3 J/cm³. These results indicate that BST-ST multilayer ceramics can be a favorable candidate for dielectric capacitor applications.     

Effective strategy to realise excellent energy storage performances in lead-free barium titanate-based relaxor ferroelectric

High-performance capacitors, which possess a high energy storage density, large power density and fast charge/discharge rate, are in high demand in pulsed power systems. Although several studies have been conducted to obtain excellent energy storage performances, the scientific and feasible guidance is lacking on how to quickly and efficiently find a material system with high recoverable energy storage density (W_rec), large energy storage efficiency (η), and excellent thermal stability. Herein, a strategy is proposed to concurrently regulate the temperature corresponding to the maximum dielectric constant (T_m) to around room temperature and enhance the relaxor characteristic. To our satisfaction, excellent energy storage performances with a high W_rec of 3.05 J/cm³, large η of 95%, and wide temperature stability (20–180 °C) were achieved in 0.85BaTiO₃-0.15Bi(Mg₀₅Sn_0.5)O₃ (0.15BMS) ceramics. In addition, these ceramics also exhibited a large discharge energy density (W_dis = 0.74 J/cm³) and fast discharge time (t_0.9 = 105 ns) over a broad temperature range (20–180 °C), which confirms their significant application potential in the high-temperature field. These results indicate that this work can provide an effective guideline approach to attain high-performance capacitors for application in pulsed power capacitors.     

(1-x)Bi0.5Na0.47Li0.03TiO3-xNaNbO3 lead-free ceramics with superior energy storage performances and good temperature stability

Dielectric capacitors show great potential in superior energy storage devices. However, the energy density of these capacitors is still inadequate to meet the requirement of energy storage applications. In this study, the Bi_0.5Na_0.47Li_0.03TiO₃-xNaNbO₃ (BNLT-xNN) ceramics were prepared via conventional solid-phase reaction. Results showed that NN can efficaciously enhance the breakdown strength (E_b) and the relaxation behavior of the BNLT ceramic because of the broken ferroelectric long-range order. When x = 0.3, the maximum E_b reached 350 kV/cm, at which the 0.7BNLT-0.3NN ceramic exhibited the high recoverable energy storage density (W_rec) of 4.83 J/cm³ and great efficiency (η) of 78.9%. The ceramic demonstrated good temperature stability at 20 °C-160 °C and excellent fatigue resistance. Additionally, the 0.7BNLT-0.3NN ceramic presented high power density (P_D; ～77.58 MW/cm³), large current density (C_D; ～861.99 A/cm²), and quite short discharge time (t_0.9; ～0.090 μs). These results indicated that the 0.7BNLT-0.3NN material has excellent energy storage properties and various application prospects.     

Antiferroelectric‐ferroelectric phase transition in lead‐free AgNbO3 ceramics for energy storage applications

The high‐energy storage density reported in lead‐free AgNbO₃ ceramics makes it a fascinating material for energy storage applications. The phase transition process of AgNbO₃ ceramics plays an important role in its properties and dominates the temperature and electric field dependent behavior. In this work, the phase transition behavior of AgNbO₃ ceramics was investigated by polarization hysteresis and dielectric tunability measurements. It is revealed that the ferrielectric (FIE) phase at room temperature possesses both ferroelectric (FE)‐like and antiferroelectric (AFE)‐like dielectric responses prior to the critical AFE‐FE transition point. A recoverable energy storage density of 2 J/cm³ was achieved at 150 kV/cm due to the AFE‐FE transition. Based on a modified Laudau phenomenological theory, the stabilities among the AFE, FE and FIE phases are discussed, laying a foundation for further optimization of the dielectric properties of AgNbO₃.     

Giant energy storage efficiency and low strain hysteresis in lead-free relaxor ferroelectrics by designing the dynamic behavior of PNRs

Lead-free ferroelectric ceramics have aroused widespread concerns, due to their properties of rapid charge/discharge and electric-induced strain without harming the environment. However, compared with thin-film capacitors, ceramics have a larger energy loss. In addition, the large time lag between electric field and strain also reduces its accuracy as an actuator. Therefore, the relaxor ternary solid solution (BaTiO₃–Bi_0.48Na_0.48La_0.03TiO₃–NaNbO₃) was constructed in this work, aiming to obtain large energy storage efficiency and low time delay. The strategy and optimization aim to improve the relaxation degree and reduce the maximum permittivity temperature to room temperature, building a special crossover region where high and low dynamic polar nano regions co-existence. Thus a recoverable energy density of 1.24 J/cm³ under a low electric field (135 kV/cm) and a high energy storage efficiency (96%) are obtained and low hysteresis electrostriction with a large electrostriction coefficient (Q₃₃ = 0.0367 m⁴/C²) is also achieved in this system. This work suggests that this system can be considered promising materials as high-efficiency capacitors and high-precision actuators. It also attracts interest in the basic research on the dynamic changes of polar nano regions.     

High energy-storage properties of [(Bi1/2Na1/2)0.94 Ba0.06] La(1−x) ZrxTiO3 lead-free anti-ferroelectric ceramics

Energy-storage properties of [(Bi_1/2Na_1/2)_0.94Ba_0.06]La_(1−x)Zr_xTiO₃ (BNT-BLZT, x=0, 0.02, 0.04, and 0.06) lead-free anti-ferroelectric ceramics fabricated via the conventional sintering technique were first investigated. Calculation from the X-ray diffraction results reveals that BNT-BLZT ceramic possesses a single perovskite structure phase. In addition, the P–E hysteresis loops measured at room temperature show that the BNT-BLZT (x=0.02) ceramics obtain the maximum P value of 37.5 μC/cm² and the largest energy-storage density W_max is 1.58 J/cm³. The temperature dependence of dielectric permittivity ε_r and dielectric loss tanδ illustrate that the addition of Zr can improve the piezoelectric properties of BT-BLZT ceramics. These properties indicate that BNT-BLZT ceramics might be a promising lead-free anti-ferroelectric material for energy storage application.     

Enhanced energy-storage properties of (1-x)(0.7Bi0.5Na0.5TiO3-0.3Bi0.2Sr0.7TiO3)-xNaNbO3 lead-free ceramics

A series of (1-x)(0.7Bi_0.5Na_0.5TiO₃-0.3Bi_0.2Sr_0.7TiO₃)-xNaNbO₃ (BNT-BST-100xNN) lead-free ceramics were fabricated using conventional solid-state reaction technique. The phase behavior, microstructure, dielectric, ac impedance and energy-storage properties of the sintered ceramics were systematically investigated. XRD patterns and surface SEM micrographs revealed the introduction of NaNbO₃ didn't change the perovskite structure of BNT-BST at low doping level. The NaNbO₃ doping gave rise to slimmer P-E loops and thus gained enhanced energy storage properties. Therefore, a maximum energy storage density of 1.03 J/cm³ was achieved at 85 kV/cm at x = 0.01 via increasing the dielectric breakdown strength (DBS). Temperature-dependent dielectric permittivity illustrated the enhanced relaxor characteristics, implying the long-rang ferroelectric order was further damaged due to the introduction of NaNbO₃. The results above indicate the sintered ternary ceramics can be a promising lead-free candidate for energy storage capacitors.     

Achieving high energy storage performance below 200 kV/cm in BaTiO3-based medium-entropy ceramics

A small applied electric field is particularly crucial in the practical application of dielectric ceramic capacitors, since it means a longer lifetime of the capacitors in practical energy storage applications. Based on the traditional ferroelectric BaTiO₃, the (1-x)(Ba_0.6Na_0.2Bi_0.2)TiO₃-xNaNbO₃ medium-entropy material is designed in this paper, which correlates configuration entropy with energy storage performance. The findings demonstrate that the BNBT-0.15NN ceramic synchronously achieves high energy storage density (2.95 J/cm³) and the energy storage efficiency (95.2%) at 180 kV/cm when the configuration entropy rises to 1.43R. The idea of medium-entropy energy storage under low electric field is proposed for the first time, opening up a new avenue for research into the preparation of high energy storage dielectric ceramics via exploring medium-entropy composition.     

Structural evolution and coexistence of ferroelectricity and antiferromagnetism in Fe,Nb co-doped BaTiO3 ceramics

Multiferroics are materials that exhibit two or more primary ferroic properties within the same phase and have potential applications in sensors, spintronics and memory devices. Here, the dielectric, ferroelectric and magnetic properties of novel multiferroics derived from BaTi_1?x(Fe_0.5Nb_0.5)_xO₃ (BTFN, 0.01 ≤ x ≤ 0.10) ceramics are investigated. Multiferroism in these ceramics is manifested by the coexistence of ferroelectric long-range ordering and antiferromagnetism. With increasing x-value, there is a structural evolution from a tetragonal perovskite to a mixture of tetragonal and cubic phases, accompanied by a decrease in the temperature of maximum permittivity. At room temperature, ferroelectric behaviour is evidenced by the presence of current peaks corresponding to domain switching in the current-electric field loops, while the observation of non-linear narrow magnetic hysteresis loops suggests dilute magnetism. The results indicate that in the x = 0.07 composition the antiferromagnetic order is established through an indirect super-exchange interaction between adjacent Fe ions.