Impedance spectroscopy studies on PbFe0.5Nb0.5O3 –BiFeO3 multiferroic solid solution

(1-x) PbFe_0.5Nb_0.5O₃ (PFN) – (x) BiFeO₃ (BFO) (PFN – BFO) multiferroic solid solution (x = 0.1, 0.2, 0.3 and 0.4) were synthesized by single step solid state reaction method. Single phase was confirmed in all the samples through room temperature (RT) X-ray Diffraction (XRD) with monoclinic structure (Cm space group). Transmission Electron Microscopy (TEM) studies confirm the high crystallinity of the materials with the average particle size of 100 nm. The temperature (313–528 K) and frequency (100 Hz – 5 MHz) dependent impedance, modulus and DC conductivity of PFN – BFO solid solutions were investigated. An impedance spectroscopy result shows a significant contribution from the grains (bulk) to the conductivity and exhibits non-Debye type of relaxation. The bulk (grain) resistance reduces as the temperature increases corresponds to negative temperature coefficient of resistance (NTCR) behaviour. Electric modulus exhibits thermally dependent relaxation phenomena in the material. The Bergmann modified KWW function fitted to the imaginary modulus with non-Debye type of relaxation. DC conductivity of PFN – BFO solid solutions was found to follow the Arrhenius behaviour.     

High-temperature 0.5BiFeO3–0.5PbFe0.5Nb0.5O3 multiferroic: Microstructure,ferroelectric properties,and Mössbauer effect

Research findings of the microstructure, dielectric, ferroelectric characteristics, and Mössbauer effect of solid solution ceramics with 0.5BiFeO₃–0.5PbFe_0.5Nb_0.5O₃ composition in a wide temperature range are presented. The examined ceramic chip surface allows one to draw conclusions about the internal homogeneity of grains and the absence of pores inside them. It was shown that Fe³⁺ iron cations in the material are valence and they are found only in seven locally different states, which is associated with disorder in the solid solution structure. The Néel temperature is T_N ~ 445 K. The anomalous behavior at T < 30 K becomes clear when analyzing the dielectric spectra of 0.5BiFeO₃–0.5PbFe_0.5Nb_0.5O₃ ceramics in the range of 10 … 1000 K. It is explained by the appearance of a spin-glass state in the object. The presence of contributions to the dielectric response in ceramics at T > 300 K is revealed. It is claimed that the ferroelectric–relaxor → paraelectric phase transition caused the low-temperature contribution, and the second one is a manifestation of the Maxwell–Wagner polarization and the corresponding non-Debye type dielectric relaxation. The causes of the revealed regularities and the prospects for using the material in the thin films form are discussed.     

Structure,microstructure, dielectric and piezoelectric properties of (1-x-y)BiFeO3-xPbFe0.5Nb0.5O3-yPbTiO3 ceramics

Ceramics of seven quasi-binary concentration sections of the ternary solid solution system (1-x-y)BiFeO₃-xPbFe_0.5Nb_0.5O₃-yPbTiO₃ were prepared by the conventional solid-phase reaction method in the range of 0.05 ≤ x ≤ 0.325; 0.05 ≤ y ≤ 0.325. By using x-ray diffraction technique, the phase diagram of the system was constructed which was shown to contain the regions of tetragonal and rhombohedral symmetry and the morphotropic phase boundary between them. Grain morphology, dielectric and piezoelectric properties of selected solid solutions were investigated. The highest piezoelectric coefficient d₃₃ = 50 pC/N was obtained. Dielectric characteristics of ceramics revealed ferroelectric relaxor behavior and region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 600–800 K.     

Mg0.5Ni0.5Fe2O4 nanoparticles as heating agents for hyperthermia treatment

In the present work, Mg_0.5Ni_0.5Fe₂O₄ nanopowders were prepared by a sol-gel combustion method. The magnetic properties, heat generation ability in an AC magnetic field and cytotoxicity of the mixed ferrite nanopowders were investigated. The results showed that the powders have crystalline spinel structure with a particle size in the range of 20-90 nm. Maximum saturation magnetization (Ms) of 51 emu/g was obtained for the Mg_0.5Ni_0.5Fe₂O₄ nanoparticles calcined at 900°C. The results showed that, the coercivity (Hc) of the Mg_0.5Ni_0.5Fe₂O₄ initially increases up to 700°C and then decreases with increasing temperature, whereas the Ms of the samples continuously increases. The Mg_0.5Ni_0.5Fe₂O₄ sample exhibited a temperature increase up to 45°C during 10 minutes in the exposure of magnetic field of 200 Oe. By increasing the viscosity of ferrofluid, the heat generation ability of nanoparticles reduced up to 9% at magnetic field of 200 Oe. Cell compatibility of the ferrite powders was studied by MTT assay using MG63 cell line proliferation. MTT results showed that calcination temperature of the Mg_0.5Ni_0.5Fe₂O₄ nanoparticles significantly affects the cell compatibility.     

Piezoelectric properties of (Na0.5K0.5)(Nb1‐xSbx)O3‐SrTiO3 ceramics with tetragonal‐pseudocubic PPB structure

CuO‐added 0.96(Na_0.5K_0.5)(Nb_1‐xSb_x)O₃‐0.04SrTiO₃ ceramics sintered at the low temperature of 960°C for 10 hours showed dense microstructures and high relative densities. The specimens with 0.0 ≤  x ≤ 0.04 had orthorhombic‐tetragonal polymorphic phase boundary (PPB) structure. Tetragonal‐pseudocubic PPB structure was observed in specimens with 0.05 ≤  x ≤ 0.07, while the specimen with x = 0.08 has a pseudocubic structure. The structural variation in the specimens is explained by the decreases in the orthorhombic‐tetragonal transition temperature and Curie temperature with the addition of Sb⁵⁺ ions. The specimens with 0.05 ≤  x ≤ 0.07, which have tetragonal‐pseudocubic PPB structure, had large electric field‐induced strains of 0.14%‐0.016%. Moreover, these specimens also showed increased d₃₃ values between 280 pC/N and 358 pC/N. In particular, the specimen with x = 0.055 showed particularly enhanced piezoelectric properties: d₃₃ of 358 pC/N, k_p of 0.45, and the electric field‐induced strain of 0.16% at 4.5 kV/mm.     

Room-temperature ferromagnetism in (K0.5Na0.5)NbO3-xBaNi0.5Nb0.5O3-δ ferroelectric ceramics with narrow bandgap

In this paper, a simple, reproducible and cost-effective solid-state reaction sintering process is developed to fabricate (K_0.5Na_0.5)NbO₃-xBaNi_0.5Nb_0.5O_3-δ (KNN-xBNN) ceramics with a narrow bandgap and room-temperature ferromagnetism. Here, we report a systematic investigation of the influence of the BaNi_0.5Nb_0.5O_3-δ (BNN) concentration on the properties of KNN-xBNN ceramics. All ceramics form orthorhombic perovskite structures with a space group Amm2 and a weak peak at the wavelength of 550 cm^?1 that is characteristic of the pillow shoulder of the orthorhombic phase. KNN-xBNN ceramics with x between 0.02 and 0.08 have a narrow bandgap of about 2.5 eV—much smaller than the 3.5 eV of its parent (K_0.5Na_0.5)NbO₃ (KNN) ceramic—which is attributed to Ni²⁺-oxygen vacancy combinations (Ni²⁺-V_O) raising the valence electron energy level of the KNN ceramic. Furthermore, doping BNN into KNN ceramics can significantly convert the magnetism from diamagnetism to ferromagnetism and the component of x = 0.08 achieves both maximum saturation magnetisation intensity (14 memu/g) and minimum coercive magnetic field (80 Oe). Our findings provide a systematic insight into the bandgap tunability and ferromagnetism induction at room temperature in lead-free perovskite KNN-xBNN ceramics, as well as demonstrate their potential applications in perovskite solar cells and multiferroic devices.     

Subsolidus phase equilibria in the La2O3–Fe2O3–Sb2O5 system and characterization of layered ternary oxide LaFe0.5Sb1.5O6

Phase equilibria in the La₂O₃-Fe₂O₃–Sb₂O₅ system have been studied. The isothermal section was constructed at T=900 °С. The existence of the ternary oxide LaFe_0.5Sb_1.5O₆ was confirmed. The structure of this compound was solved using Rietveld refinement of synchrotron radiation-based powder XRD data. LaFe_0.5Sb_1.5O₆ crystallizes in a trigonal layered structure relating to PbSb₂O₆ type (space group P-31m, a=b=5.2446(3) Å, c=5.1930(3) Å, Z=1). The fine powder of LaFe_0.5Sb_1.5O₆ was prepared by molten salt synthesis. The compound was characterized by diffuse reflection and Mossbauer spectroscopy, magnetic measurements, scanning electron microscopy and photocatalytic tests. The magnetic behavior of LaFe_0.5Sb_1.5O₆ in the applied magnetic field H=5000 Oe is entirely paramagnetic. By contrast, in the small magnetic field H=100 Oe the magnetic data of LaFe_0.5Sb_1.5O₆ indicates an unusual critical behavior near phase transition at T<2 K.     

The effect of B-site Y substitution on cubic phase stabilization in (Ba0.5Sr0.5)(Co0.8Fe0.2)O3−δ

The cubic phase mixed ionic-electronic conductor (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3−δ (BSCF) is well-known for its excellent oxygen ion conductivity and high catalytic activity. However, formation of secondary phases impedes oxygen ion transport and consequentially a widespread application of BSCF as oxygen transport membrane. B-cation substitution by 1, 3 and 10 at.% Y was employed in this work for stabilization of the cubic BSCF phase. Secondary phase formation was quantified on bulk and powder samples exposed to temperatures between 640 and 1100°C with annealing time up to 44 days. The phase composition, cation valence states, and chemical composition of all samples were analyzed by high-resolution analytical electron microscopic techniques. Y doping effectively suppresses the formation of Ba_n+1Co_nO_3n+3(Co₈O₈) (n ≥ 2) and Co_xO_y phases which would otherwise act as nucleation centers for the highly undesirable hexagonal BSCF phase. This work validates for 10 at.% Y cation substitution perfect stabilization of the cubic BSCF phase at temperatures ≥800°C, while a negligible small volume fraction of the hexagonal BSCF phase was found at lower temperatures. A newly developed model describes the effect of Y doping on the formation of secondary phases and their effective suppression with increasing Y concentration.     

Effect of electric poling on structural,magnetic and ferroelectric properties of 0.8PbFe0.5Nb0.5O3-0.2BiFeO3 multiferroic solid solution

The effect of electric poling on structure, magnetic and ferroelectric properties of 0.8PbFe_0.5Nb_0.5O₃-0.2BiFeO₃ (0.8PFN-0.2BFO) multiferroic was studied through XRD, Raman, magnetic and ferroelectric measurements. Single step solid state reaction method was adopted to synthesize single phase 0.8PFN-0.2BFO multiferroic at lower calcination and sintering temperature. Room temperature (RT) XRD pattern before and after poling confirmed the monoclinic structure with Cm space group. Rietveld refined XRD for poled and unpoled sample shows the influence of electric poling on Fe-O1, Fe-O2, Nb-O and Bi-O modes. There is a small variation in the lattice parameters after electric poling. The structural properties were also studied in detail for the poled and unpoled 0.8PFN-0.2BFO using Raman spectroscopy. Raman measurements were carried out over a wide range of temperature (250–550 K) for both poled and unpoled samples. At RT unpoled 0.8PFN-0.2BFO multiferroic exhibit 8 active modes at 211, 263, 440, 484, 571, 706, 785 and 1120 cm^-1 in the frequency range 100–1200 cm^-1. The Raman peaks exhibits significant changes in intensity as well as shape of the spectra at the characteristic temperature T_C (470 K) and T_N (310 K). Poled Raman spectra show major changes in the Fe/Nb-O modes intensities around T_N and are due to dynamic nature of spin phonon coupling. Changes observed in the temperature dependent magnetic measurements i.e. ZFC/FC and M − H loop evidence the existence of converse magneto-electric coupling (CME) and this is due to the poling effects on Fe-O, Nb-O active modes. Due to rotation of the oxygen octahedral the electric field induced strain will originate in the system. P-E loops after poling show an increase in remnant polarisation and coercive field due to an improvement in domain ordering. The potential tunability of magnetisation with electric poling is an ideal tool for realisation of application in practical devices.     

Catalytic performance of LaCo0.5M0.5O3 (M = Mn,Cr, Fe,Ni, Cu) perovskite-type oxides and LaCo0.5Mn0.5O3 supported on cordierite for CO oxidation

Catalytic combustion of CO over perovskite-type oxides LaCo_0.5M_0.5O₃ (M = Mn, Cr, Fe, Ni, Cu) and LaCo_0.5Mn_0.5O₃ supported on cordierite were investigated. The catalysts were synthesized by impregnation method with citrate and characterized by XRD, SEM and TPR. The LaCo_0.5Mn_0.5O₃ catalyst showed much higher activity in CO oxidation compared with LaCo_0.5M_0.5O₃ (M = Cr, Fe, Ni, Cu) due to different kinds of valence state and lattice oxygen content. When LaCo_0.5Mn_0.5O₃ was supported on cordierite, the activity was improved significantly. However, calcining temperature and the presence of water vapor affected the catalytic activity due to sintering and competition of H₂O with CO for adsorption, respectively.     

Eu-substitution-induced commensurate phase with enhanced ferroelectric property in Ba4(EuxLa1−x)2Fe2Nb8O30 multiferroics

Effects of Eu-substitution on the crystal structure, dielectric, ferroelectric, and magnetic properties have been systematically studied for Ba₄(Eu_xLa_1−x)₂Fe₂Nb₈O₃₀ (x = 0, 0.3, 0.5, 0.7, 0.9, 0.95, 1) tungsten bronze ceramics. The tetragonal bronze structure is confirmed in all compositions. With the increase of x, Ba₄(Eu_xLa_1−x)₂Fe₂Nb₈O₃₀ ceramics transform from paraelectric to ferroelectric. The compositions of x = 0.9, 0.95, and 1 show first-order ferroelectric phase transitions above room temperature (391 K for x = 0.9, 404 K for x = 0.95, and 425 K for x = 1). The ferroelectric behavior is associated with a commensurate octahedral tilting, which is caused by large A2-A1 ionic-radius difference. Magnetic hysteresis loops for all compositions at room temperature have been obtained, which could be ascribed to both the secondary phase and tungsten bronze structure per se. It is confirmed that the radius difference between A2 and A1 cations plays a critical role on the structure, dielectric, and ferroelectric characteristics.     

Tuning of electrical properties of xBi(Zn0.5Ti0.5)O3-(1-x) (Ba0.5Sr0.5)TiO3 ceramics by composition design and bandgap engineering

Herein, the xBi(Zn_0.5Ti_0.5)O₃-(1-x) (Ba_0.5Sr_0.5)TiO₃ (x = 0.05, 0.10, 0.15, 0.20) novel negative temperature coefficient (NTC) ceramic materials were fabricated by solid-state method. X-ray diffraction revealed that xBi(Zn_0·5Ti_0.5)O₃-(1-x) (Ba_0.5Sr_0.5)TiO₃ successfully formed solid solution. The UV–vis diffuse spectra of the samples indicate that the band gap increases with the increasing Bi(Zn_0·5Ti_0.5)O₃ content. The resistance temperature curve showed that with the increase of Bi(Zn_0·5Ti_0.5)O₃ content, the resistivity ρ of the ceramics at 400 °C increased from 5.96 × 10⁶ to 2.67 × 10⁷ Ω cm, as well as an increase in the B_400/800 from 12374.6 to 13469.1 K. The enhanced resistivity is attributed to the increased band gap and reduced carrier pairs caused by the Bi(Zn_0.5Ti_0.5)O₃ modification. The impedance data indicates that the conduction process is activated by thermal. The ceramic samples exhibit the excellent NTC characteristics over a range of 400 °C–1000 °C. Hence, the xBi(Zn_0.5Ti_0.5)O₃-(1-x) (Ba_0.5Sr_0.5)TiO₃ ceramics have the potential to become high temperature NTC ceramics that can operate in a wide temperature range.     

Piezoelectric performance of 0.5BaZr0.2Ti0.8O3-0.5Ba1-xCaxTiO3 at triple phase point

0.5BaZr_0.2Ti_0.8O₃-0.5Ba_1-xCa_xTiO₃ ceramic samples with x = 15–35% have been fabricated to investigate the composition-driven phase evolution, ferroelectric, and piezoelectric properties. X-ray diffraction and temperature-dependent permittivity studies reveal the structural phase transition from the rhombohedral (R) to R + orthorhombic (O) and then O + tetragonal (T) having a tricritical triple phase points consisting of the R + O + T at x = 29.6%. The average grain size tends to increase with x but there is an exception of reducing grain size for x = 29.6%. The triple phase point displays the outstanding properties, such as minimum relaxation time (τ = 6.4 ms), large piezoelectric response (d₃₃ = 543 pC/N), high saturation polarization (P_S = 16.5 μC/cm²), small coercive field (E_c = 0.6 kV/cm), and high dielectric permittivity, over 8700 peaking at 21,765. These parameters reduce drastically at the O/R and O/T phase boundaries. Our studies indicate the important role of multiphase coexistence for enhancing the piezoelectric properties.     

Preparation of multiferroic composites of BaTiO3–Ni0.5Zn0.5Fe2O4 ceramics

Magneto-electric coupling in ceramic composites formed by ferroelectric and ferromagnetic phases can be obtained via an adequate mechanical coupling between the individual piezoelectric and magnetostrictive phases (product property). In the present work, the possibility of forming diphase ferroelectric–ferromagnetic ceramics has been investigated. Composites of xBaTiO₃–(1 − x)Ni_0.5Zn_0.5Fe₂O₄ with x = 0.5, 0.6 and 0.7 were prepared according two different procedures: (i) by direct mixing powders of perovskite BaTiO₃ and Ni_0.5Zn_0.5Fe₂O₄ spinel prepared by solid state and (ii) by coprecipitating Fe^III–Ni^II–Zn^II nitric salts in a NaOH solution in which the BaTiO₃ powders were previously dispersed. Optimum processing parameters for good homogeneity, densification and for a reduction of the chemical reactions at the interfaces ferroelectric-ferrite were found. A temperature and composition-dependent magnetic order is present in all the composites, with a dilution effect of the magnetisation due to the presence of the non-ferromagnetic phase. A diffuse ferroelectric–paraelectric transition due to the BaTiO₃ phase was identified by the temperature-dependence of the permittivity and losses, showing that at room temperature the material preserves a ferroelectric order. The interfaces play important roles in the dielectric properties, causing space charge effects and Maxwell–Wagner relaxation, particularly at low frequencies and high temperatures. The combined ferroelectric and magnetic ordering will result in magneto-electric coupling in this material; further investigations are necessary.     

Strong Red Emissions in Pr3+‐Doped (K0.5Na0.5)NbO3–CaTiO3 Diphase Ceramics

The photoluminescence and temperature sensing properties based on down‐shifting emission of Pr³⁺‐doped (K_0.5Na_0.5)NbO₃–yCaTiO₃ (KNN: yCT) diphasic materials were systematically investigated. Under 447‐nm excitation, Pr³⁺‐doped KNN: yCT samples exhibited significantly enhanced red emission at 603 nm assigned to ¹D₂→³H₄ transitions of Pr³⁺ ions. The red emission intensities reached the optimum value with y = 0.05 near the polymorphic phase transition region. The origin of the enhanced red emission is mainly ascribed to the doping‐induced lattice symmetry change. The energy level transitions from the typical f–f transitions to the valence‐to‐conduction transitions were observed as CaTiO₃ concentration increases above a critical concentration of y = 0.05. Furthermore, the sample with y = 0.05 also possessed excellent temperature response properties in a wide temperature range 300–473 K and the maximum sensing sensitivity was 0.016 K^?1. The Pr³⁺‐doped (K_0.5Na_0.5)NbO₃–yCaTiO₃ red emission materials with admirable intrinsic piezoelectric properties may have important technological promise in novel multifunctional devices.     

The complexity of structural phase transitions in Pb(Hf0.92Sn0.08)O3 single crystals

Pb(Hf_1−xSn_x)O₃ single crystals with x = 0.08 were characterized using single-crystal X-ray diffraction and Raman scattering, in a wide temperature range. The information concerning the structure of two intermediate phases (IMs), situated between low-temperature antiferroelectric A1 and high-temperature paraelectric PE phases, was obtained. The lower temperature IM, A2, is characterized by incommensurate displacive modulations in the Pb sublattice. The higher temperature IM, is characterized by tilting of oxygen octahedra, and serious disorder coming from lead ions represented by X-ray diffuse scattering. Optical phonons and phase transitions in Pb(Hf_1−xSn_x)O₃ single crystals were investigated by temperature-dependent Raman spectra. It was found that several soft modes control the phase transition between two antiferroelectric phases indicating its displacive character, whereas, in the paraelectric phase, both soft modes and Rayleigh scattering were observed.     

Raman and dielectric spectroscopic analysis of magnetic phase transition in Y(Fe0.5Cr0.5)O3 multiferroic ceramics

Here, we report the Raman and dielectric spectroscopic studies as a function of temperature of orthorhombically distorted Y(Fe_0.5Cr_0.5)O₃ (YFC) ceramics, measured from 80 to 300 K. The dc-magnetization measurements under field cooled (FC)-zero field cooled (ZFC) protocol indicate a small onset of magnetic ordering at T_N∼270 K. The field dependent magnetization plot recorded at 50 K, 150 K and 200 K show a clear opening in hysteresis loops. The linear dependence of magnetization plot at high field without any saturation of magnetization indicates the coexistence of weak ferromagnetic (WFM) component within the canting antiferromagnetic (CAFM) matrix. Temperature evolution of Raman line-shape parameter of B_2g(4) phonon mode clearly exhibits an anomalous behavior of phonon shift near T_N∼270 K, indicating the spin-phonon coupling in the ceramics. From the temperature dependent dielectric permittivity (ε(T)) study, two dielectric relaxation peaks are detected below 200 K and above 250 K. The appearance of former relaxation peak is responsible for polaronic conduction mechanism, while the later one is associated with magnetic phase transition which might be relevant to the presence of magnetoelectric coupling in YFC ceramics. The observed P-E hysteresis loops at room temperature indicate weak ferroelectric nature of the ceramics.     

Novel B-site scheelite structure ceramic Bi(Ge0.5Mo0.5)O4 and its dielectric properties

Scheelite structure phase inorganic oxides show their irreplaceable role in numerous application areas due to their clear structure and superior properties, especially in dielectrics. Scheelite structure phase BiVO₄ has been permanently studied but substitutions, modifications, and explorations of novel phases persist hitherto and inspire more interest. In this work, we report a novel Scheelite structure phase of Bi(Ge_0.5Mo_0.5)O₄ and a detailed study of both structural analysis and dielectric properties investigation. Bi(Ge_0.5Mo_0.5)O₄ adopts the monoclinic Scheelite structure, identical to BiVO₄, with a dielectric permittivity of ∼ 35, Qf value of ∼20 000 GHz, and TCF value of ‒46 ppm/°C. No secondary ferroelastic transition was seen in Bi(Ge_0.5Mo_0.5)O₄ till 600°C, close to its synthetical temperature. The results indicate the success of discovering a new Scheelite structure phase and its prior engineering potential in modifying and substituting BiVO₄ over the dielectric area, photocatalyst, ion conductor, and so forth.     

Phase structure and electrochemical performance of layered-spinel integrated LiNi0.5Mn0.5O2-LiMn1.9Al0.1O4 composite cathodes for lithium ion batteries

In recent years, multi-component integrated composite cathodes for lithium ion batteries have attracted considerable attention. In this work, novel layered-spinel integrated cathode materials of (1−x)LiNi_0.5Mn_0.5O₂-xLiMn_1.9Al_0.1O₄ were synthesized by a sol-gel method, and their phase structures, morphologies and electrochemical performance were investigated. The crystal structure of the (1−x)LiNi_0.5Mn_0.5O₂-xLiMn_1.9Al_0.1O₄ is changed from layered to spinel structure with increasing x. All the samples exhibit nanoscale grains with the minimum grain size of ~130 nm when x = 0.5. The composite electrode with x = 0.5 exhibits the optimal discharge capacity, presenting a large initial discharge capacity of 236 mAh g⁻¹ at the current density of 20 mA g⁻¹. Good rate capability is also obtained at the composite electrode with x = 0.5 where the electrode displays the relatively high discharge capacity of 64.9 mAh g⁻¹ at the high rate of 5 C. The improved electrochemical performance is related to the introduction of spinel structure into layered structure and small grain size. The spinel structure can stabilize the layered structure, which leads to the improvement in the electrochemical performance of the composites; and the small grain size in the sample with x = 0.5 provides short lithium ion diffusion way and thus enhances the electrochemical performance.     

Investigations of BaFe0.5Nb0.5O3 nano powders prepared by a low temperature aqueous synthesis and resulting ceramics

A facile method to prepare nanoscaled BaFe_0.5Nb_0.5O₃ via synthesis in boiling NaOH solution is described herein. The nano-crystalline powder has a high specific surface area of 55 m² g⁻¹ and a crystallite size of 15 nm. The as-prepared powder does not show any significant crystallite growth up to 700 °C. The activation energy of the crystallite growth process was calculated as 590 kJ mol⁻¹. Dense ceramics can be obtained either after sintering at 1200 °C for 1 h or after two-step sintering at 1000 °C for 10 h. The average grain sizes of ceramic bodies can be tuned between 0.23 μm and 12 μm. The thermal expansion coefficient was determined as 11.4(3)·10⁻⁶ K⁻¹. The optical band gap varies between 2.90(5) and 2.63(3) eV. Magnetic measurements gave a Néel temperature of 20 K. Depending on the sintering regime, the ceramic samples reach permittivity values between 2800 and 137,000 at RT and 1 kHz.