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.     

A new multiferroic ternary solid solution system: NdFeO3–Pb(Fe1/2Nb1/2)O3–PbTiO3

Ceramic materials were sintered from powders of the NdFeO₃–Pb(Fe_1/2Nb_1/2)O₃–PbTiO₃ (NF–PFN–PT) ternary system synthesized by the conventional solid reaction method and their multiferroic properties investigated. The structure, electric and magnetic properties of the ternary system have been investigated. The introduction of Pb(Fe_1/2Nb_1/2)O₃ into the NdFeO₃–PbTiO₃ binary system can effectively increase its electric properties. The ternary system exhibits enhanced piezoelectric property with optimal piezoelectric constants d₃₃=143 pC/N, reduced coercive fields E_C=5.78 kV/cm and remnant polarization P_r=12.8 μC/cm² for 0.10NF–0.56PFN–0.34PT, near tetragonal phase region. The Curie temperature (T_C) of the NdFeO₃–Pb(Fe_1/2Nb_1/2)O₃–PbTiO₃ ceramics varies in the range from 108.7 °C to 67.9 °C. The magnetic hysteresis loops show that the ternary system is paramagnetic originating from canting of paramagnetic sublattices in NF–PFN–PT, due to the rare earth ions Nd³⁺ influencing on the exchange interaction between Fe³⁺ ions at the octahedral sites.     

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.     

Effect of annealing temperature on the multiferroic properties of 0.7BiFeO3–0.3Bi0.5Na0.5TiO3 solid solution prepared by sol–gel method

Room-temperature multiferroic 0.7BiFeO₃–0.3Bi_0.5Na_0.5TiO₃ solid solution ceramics have been prepared by the sol–gel method. We have discussed the annealing temperature dependence of the multiferroic properties. The samples are annealed at 1023, 1123, 1223 and 1323 K for 3 h, respectively. X-ray diffraction patterns identify that all samples are pure. Scanning electron micrographs present the increasing grain size with higher annealing temperature. Magnetic, ferroelectric and dielectric properties are enhanced obviously with the increase in annealing temperature. The coexistence of ferroelectric and ferromagnetic properties is also proved at room temperature. In addition, it reveals that the optimal annealing temperature accompanied with favorable multiferroic properties of 0.7BiFeO₃–0.3Bi_0.5Na_0.5TiO₃ solid solution ceramics is near 1223 K.     

Magnetic and electrical properties of single-phase multiferroic (1-x)Pb(Zr0.52Ti0.48)O3–xPb(Fe0.5Nb0.5)O3 thin films prepared by sol-gel route

Single-phase multiferroic (1-x)Pb(Zr_0.52Ti_0.48)O₃-xPb(Fe_0.5Nb_0.5)O₃ (0≤x≤0.5) thin films were synthesized by sol-gel route and characterized to understand their structural, electrical, and magnetic properties. The films were thermally treated by conventional furnace (CFA) and rapid thermal annealing (RTA). A pyrochlore-free perovskite phase is stabilized only by RTA in samples with high Fe³⁺/Nb⁵⁺ content. The films displayed excellent dielectric and ferroelectric properties in the whole concentration range, with saturated hysteresis loops and remanent polarization values of ～15μC/cm². Films with x>0.3 showed ferromagnetic behavior at room temperature. Consequently, the multiferroic behavior in the films occurs in a different concentration range than that observed in bulk ceramics. The origin of the weak ferromagnetism is discussed.     

Room temperature multiferroic properties of BiFeO3–MnFe2O4 nanocomposites

The novel functionalities of multiferroic magneto-electric nanocomposites have spawned substantial scope for fast-paced memory devices and sensor applications. Following this, herein we report the development of nanocomposites with soft ferromagnetic MnFe₂O₄ and ferroelectric BiFeO₃ to fabricate a system with engineered multiferroic properties. A modified sol-gel route called Pechini method is demonstrated for the preparation of the (1-x) BiFeO₃-x MnFe₂O₄ (x = 10%, 30%, 50%, 70%) nanocomposites. The crystallographic phase, structure, and morphology are characterized by XRD, FESEM, and HRTEM. The accurate crystallite size and lattice strain are determined by Williamson-Hall plot method and a comparative study with Scherer's equation is carried out. TEM image evidences the interface between BiFeO₃ and MnFe₂O₄ nanoparticles in the composite. The room temperature magnetic response reveals the strong dependence of magnetic saturation, remanent magnetization, and coercivity of the nanocomposites on MnFe₂O₄ addition. The dielectric response and impedance analysis of the prepared nanocomposites are observed. The electrical performance of the composite is affected by grain, grain boundaries, and oxygen vacancies. The unsaturated P-E loops exhibit the leaky ferroelectric behavior for the nanocomposite. The intrinsic magnetoelectric coupling between ferroelectric BiFeO₃ and ferromagnetic MnFe₂O₄ has been determined by varying H_dc/H_ac and its maximum coupling coefficient (α) is found to be 25.39 mV/cmOe for 70% BiFeO₃ -30% MnFe₂O₄ nanocomposite. These distinctive and achievable characteristics of the nanocomposite would enable the designing of magnetic field sensors, spintronic devices, and multiferroic memory devices.     

Synthesis,structural evolution,and dielectric properties of a new perovskite solid solution (Pb0.5Sr0.5)(Zr0.5Ti0.5)O3–PbTiO3

To explore lead-reduced dielectric materials in the SrTiO₃–PbTiO₃–PbZrO₃ ternary system, a novel solid solution between relaxor ferroelectric (Pb_0.5Sr_0.5)(Zr_0.5Ti_0.5)O₃ and ferroelectric PbTiO₃, namely (1 − x)(Pb_0.5Sr_0.5) (Zr_0.5Ti_0.5)O₃–xPbTiO₃ (lead–strontium–zirconate–titanate [PSZT]–PT), has been synthesized in the perovskite structure by high-temperature solid-state reaction method in the form of ceramics. The crystal structure and phase symmetry of the materials synthesized were analyzed and resolved based on X-ray powder diffraction (XRD) data through both the Pawley and Rietveld refinements. The results of the structural refinements indicate that at low PT-concentration end of the solid solution system, for example, x = 0.05, the PSZT–PT solid solution exhibits a cubic structural symmetry (with the space group Pm-3m). As the PT concentration (x) increases, the structure of (1 − x)PSZT–xPT gradually transforms from the cubic to a tetragonal (P4mm) phase. In the composition range of x = 0.10–0.25, a mixture of the cubic and tetragonal phases was identified. As the concentration of PT increases, the proportion of the tetragonal phase increases at the expense of the cubic phase. For a composition of x > 0.25, a pure tetragonal phase is observed. The dielectric properties of the materials were studied by measuring the permittivity as a function of temperature at various frequencies. For the composition of x = 0.05, the temperature dependence of dielectric constant shows typical relaxor behavior. For x = 0.35, the dielectric peaks indicate a normal ferroelectric phase transition. Overall, a structural transformation from a central-symmetric, nonpolar cubic phase to a non-centrosymmetric, polar tetragonal phase is induced by the substitution of PT for PSZT in the pseudo-binary solid solution of (1 − x)PSZT–xPT, which also reveals an interesting relaxor to ferroelectric crossover phenomenon.     

Investigation on ferromagnetic and ferroelectric properties of (La,K)-doped BiFeO3–BaTiO3 solid solution

Multiferroic materials of BiFeO₃–BaTiO₃ solid solution have been fabricated in order to improve ferromagnetic and ferroelectric properties. The effects of La (1 mol%) and K (varied from 0.5–5 mol%) doped 0.75BiFeO₃–0.25BaTiO₃ on phase formation, ferromagnetic and ferroelectric properties have been investigated and discussed. The rhombohedral perovskite phase of specimens was characterized by XRD technique. Fracture morphology reveals the grain growth characteristics with increasing K content. (La, K)-doped 0.75BiFeO₃–0.25BaTiO₃ with La=1 mol% and K=3 mol% exhibits the highest remnant polarization and remnant magnetization.     

Magnetoelectric properties of 0.5BiFeO3–0.5Pb(Fe0.5Nb0.5)O3 solid solution

Magnetoelectrics are materials that join magnetic and electric orderings in the same phase. They exhibit magnetoelectric coupling which is important from the fundamental and practical point of view. The subject of the paper is a presentation of magnetic, electric and magnetoelectric properties of 0.5BiFeO₃–0.5Pb(Fe_0.5Nb_0.5)O₃ solid solution. The obtained material belongs to oxide perovskite magnetoelectrics of relatively high magnetic and electric ordering temperatures. Both temperatures are considerably above room what suggests potential application possibilities of the material. The magnetic properties were investigated using Mössbauer spectroscopy and magnetization measurements. The solid solution is an antiferromagnet with incomplete compensated magnetic moments. The electrical properties were determined using impedance spectroscopy analysis. There is an observed change of the electrical properties at the magnetic ordering temperature what indicates magnetoelectric coupling in the system. The electrical conductivity mechanism is also proposed. Magnetoelectric voltage coefficient was determined and possible explanation of its changes was proposed.     

Dielectric properties and related ferroelectric domain configurations in multiferroic BiFeO3–BaTiO3 solid solutions

Dielectric properties and ferroelectric domain configurations of multiferroic xBaTiO₃–(1 ? x)BiFeO₃ (x = 0.10–0.33) solid solutions synthesized by conventional solid-state reaction, were reported. A structural transition from rhombohedral to pseudo-cubic structures appeared around x = 0.33, and the formation of impurity phase of Bi₂Fe₄O₉ was effectively depressed by doping BaTiO₃. Dielectric constants of xBaTiO₃–(1 ? x)BiFeO₃ solid solutions decreased with increasing the frequency, and the degree of decrease was related to the doping content of BaTiO₃. Transmission electron microscopy images revealed that the ferroelectric domain configurations in the multiferroic BiFeO₃–BaTiO₃ solid solutions with rhombohedral symmetry, exhibited a wavy character whereas a predominant intricate domain structure with fluctuating mottled contrast was observed in the multiferroic BiFeO₃–BaTiO₃ solid solution with pseudo-cubic phase structure. The presence of 1/2{1 1 1} superlattice spots in the selected area electron diffraction patterns taken from the multiferroic BiFeO₃–BaTiO₃ solid solutions with rhombohedral symmetry indicated that the ordered regions have a doubled perovskite unit cell.     

Structure and multiferroic properties of ternary (1−x)(0.8BiFeO3-0.2BaTiO3)-xK0.5Na0.5NbO3 (0 ≤ x ≤ 0.5) solid solutions

The ternary (1?x)(0.8BiFeO_3-0.2BaTiO₃)-xK_0.5Na_0.5NbO₃ (0?≤?x?≤?0.5) solid solutions have been successfully synthesized by a solid-state reaction route. X-ray diffraction and Rietveld refinement studies reveal the phase transition from the rhombohedral and tetragonal phases to the single tetragonal phase with x increasing. The average grain size decreases initially and then increases as x increases, whereas the remnant magnetization shows an opposite trend and reaches the maximum value of ~2.09?emu/g at x?=?0.3. An enhanced remnant polarization of ~8.6?μC/cm² appears at x?=?0.3 due to the structure distortion and the decrement of defects. Moreover, the remanent polarization and the relative permittivity reach the maximum value of ~20.14 μC/cm² (10?Hz) and ~644 (1?kHz) at x?=?0.5, respectively, and the corresponding dielectric loss decreases to the lowest value of ~0.022 (1?kHz). These results indicate that the properties of ternary BFO-BTO-KNN solid solutions can be modulated by adjusting the K_0.5Na_0.5NbO₃ content to adapt to different application needs.     

Improvement of temperature-stability and piezoelectric performance of Pb(In0.5Nb0.5)O3–PbTiO3 crystals via Nd doping

High-performance relaxor-PbTiO₃ ferroelectric crystals have been widely applied in transduces, sensors and so on. The ferroelectric phase transition temperature restricts their application in automobile, deep oil-well detection and aerospace which requires high thermal stability. Decreasing the effects of ferroelectric phase transition is a promising strategy for improving the thermal stability. Here, the design strategy is structural regulation via rare earth doping tetragonal Pb(In_1/2Nb_1/2)O₃–PbTiO₃ (PIN-PT) crystals. The d₃₃, k₃₃ and T_C of [001]_c-oriented Nd-PIN-PT crystals are 750 pC/N, 87%, 250 °C. Compared with the d₃₃ of tetragonal 0.61PIN-0.39 PT crystals (540 pC/N) and tetragonal 0.35PIN-0.26 Pb(Mg_1/3Nb_2/3)O₃ (PMN)-0.39 PT crystals (530 pC/N), the d₃₃ of Nd-PINT crystals enhance by 39% and 41%. In addition, Nd-PIN-PT crystals have Q_m of 110, which is larger than rhombohedral relaxor-PbTiO₃ ferroelectric crystals (~50). Although the d₃₃ of Nd-PIN-PT crystals is lower than that of rhombohedral relaxor-PT ferroelectric crystals, the d₃₃ and k₃₃ are stable up to 250 °C, which is higher than tetragonal PIN-PMN-PT crystals (210 °C). The high thermal stability of piezoelectric properties is related to the high thermal stability of domain after poling. This work provides a design strategy for high thermal stability ferroelectric crystals.     

Structural,strong magnetic exchange,and room temperature multiferroic properties of single-phase 0.75BiFeO3–BaFe1/2Nb1/2O3 bulk ceramics

The ceramic 0.75BiFeO₃–BaFe_1/2Nb_1/2O₃ (0.75BF–BaFN) exhibits enhanced magnetisation and polar order regions at room temperature. This study investigated the microscopic structure and the magnetic, ferroelectric, magneto-ferroelectric, and optical properties of 0.75BF–BaFN by conducting experiments and performing density functional theory (DFT) calculations. Evidence of weak amplitude R-type octahedral rotations was observed using transmission electron microscopy (TEM). X-ray diffraction (XRD) refinement revealed that the P1 space group more appropriately described the structure of 0.75BF–BaFN. The weak influence of the magnetic field H on the polarisation of 0.7BF–BaFN and 0.75BF–BaFN ceramics was investigated. A notable magnetic enhancement was observed in 0.75BF–BaFN ceramics with a saturation magnetisation of 0.19 μB per Fe. DFT calculations predicted that the stable magnetic configuration of 0.75BF–BaFN is a G-type antiferromagnetic (AFM) structure. This study found stronger magnetic interactions between first-neighbour Fe ions (Ja = 12 meV) compared to pure BiFeO₃. With a significant remanent moment, strong exchange coupling, and magnetic field control of polarisation, 0.75BF–BaFN may facilitate the development of room temperature single-phase magnetoelectric components.     

Orientation-dependent electrical property and domain configuration of Mn-doped Pb(In0.5Nb0.5)O3–PbTiO3 single crystal

Orientation dependence of electrical properties and domain configurations of 8 mol% Mn-doped rhombohedral PIN-PT (0.68Pb(In_0.5Nb_0.5)O₃–0.32Pb(Ti_0.92Mn_0.08)O₃) rhombohedral single crystals were investigated with an emphasis on studying the variations of coercive field (E_C), internal field (E_i) on domain patterns. Our results showed that for both [001] and [110]-oriented samples, the coercive field and internal field decreased with temperature (T) increasing in rhombohedral phase, and a peak appeared above rhombohedral-tetragonal phase transition temperature (T_RT). The abnormal peaks between T_RT and Curie temperature on E_C-T and E_i-T plots are explained by taking into consideration the ferroelectric phase transition and variation of defect polarization, which provides assistant comprehension on the dynamic of defect dipoles during phase transition at high temperature. Bubble- and ribbon-like domain patterns were observed in (001)- and (110)-plane, respectively, and smaller value of short-length correlation radius in (001)- plane indicates less aggregation of polar nanoregions in this crystallographic plane than that in (110)-plane.     

Electrical properties and phase of BaTiO3–SrTiO3 solid solution

It has been known that ABO₃ type perovskite ferroelectrics, such as BaTiO₃ (BTO) and SrTiO₃ (STO), form a complete solid solution. In this study, Ba_1?xSr_xTiO₃ (BST, x=0.0–1.0) solid solution were sintered by a solid-state reaction method using BTO and STO raw powders with appropriate chemical composition. The crystal structure was investigated by a Rietveld refinement method; Fullprof, using X-ray diffraction data. Within the reasonable goodness of fit, tetragonal symmetry was found in BST with x≤0.2, while BST with x≥0.4 were found to be cubic symmetry. However, Ba_0.7Sr_0.3TiO₃ was difficult to decide whether it is cubic or tetragonal because of large uncertainties after final fitting. The composition ratios calculated from the fitted occupancies match well with those measured by EDS within experimental uncertainties. Remnant polarizations of BST with x<0.3 decrease with increasing Sr concentration. Furthermore, measured phase transition temperatures and maximum dielectric constant decrease as increasing Sr concentration. Measured electrical properties of BST were match well with the structural refinement investigations.     

Effect of mechanical milling on structural,dielectric and magnetic properties of BaTiO3–Ni0.5Co0.5Fe2O4 multiferroic nanocomposites

The coexistence of ferroelectricity and ferromagnetism has triggered great interest in multiferroic materials. Multiferroic with strong room temperature magnetoelectric (ME) coupling can provide a platform for future technologies. In this paper, we have investigated the effect of mechanical milling on the properties of multiferroic nanocomposites synthesized by mixing barium titanate (BaTiO₃) (BT) and nickel cobalt ferrite (Ni_0.5Co_0.5Fe₂O₄) (NCF). This process has resulted into reliable disposal of a given quantity of NCF nanoparticles in BT grid and composite samples of different particle sizes (<500 nm) have been obtained by varying the duration of ball-milling for 12, 24, and 48 h. The presence of NCF within BT powder has been confirmed by X-ray Diffraction (XRD) and magnetization measurements (MH). Structural analysis was performed by using Reitveld refinement method that shows that the tetragonality of BaTiO₃ structure get reduced in submicron range. Variations in ferroelectric and dielectric properties with reduction in particle size/milling duration have been studied by P-E loop tracer and Impedance analyzer. The dielectric constant value of 400 has been observed for BT-NCF0 that increases to 9.7 K for composite sample ball mill at 48 h whereas remnant polarization increases to 4.2 μC/cm². These composites with high dielectric constant that changes with temperature and particles size find application in energy storage devices, sensor and memory devices.     

Understanding the microwave dielectric properties of (Pb0.45Ca0.55)[Fe0.5(Nb1−xTax)0.5]O3 ceramics via the bond valence

Microwave dielectric properties of the (Pb_0.45Ca_0.55)[Fe_0.5(Nb_1−xTa_x)_0.5]O₃ ceramics were investigated in the range of 0.0⩽x(mol)⩽1.0. With increasing Ta₂O₅, the dielectric constant and the temperature coefficient of the resonant frequency (TCF) decreased, while the Q·f value of the specimens increased. The change of dielectric constant was evaluated by the correlation between ionic polarizability and bond valence. TCF of the specimens decreased with the tilting of oxygen octahedra due to an increase of bond valence of the B-site. The Q·f values were studied by infrared reflectivity spectra from 50 to 4000 cm⁻¹, and calculated by the Kramers-Kronig analysis and classical oscillator model. The specimens with 0.4 mol of Ta₂O₅ sintered at 1150 °C for 3 h showed ε_r of 82, Q·f of 7650, and TCF of −5 ppm/°C.     

Effect of compositional modifications on microstructure development and dielectric properties of Pb(Mg1/3Nb2/3)O3–PbTiO3 solid solutions

The effect of minor additions of excess MgO and PbO on the sintering characteristics, microstructure development and dielectric properties of perovskite-based Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ solid solutions was investigated. Both MgO and PbO are compatible with the Pb(Mg_1/3Nb_2/3)O₃-based solid solutions and thus, these phases co-exist with one another during sintering at elevated temperatures. On sintering a solid solution composition Pb[(Mg_1/3Nb_2/3)_0.9Ti_0.1]O₃ with minor additions of MgO, the excess MgO remained as a discrete phase in the ceramics at temperatures up to 1230 °C and inhibited grain growth. Above this temperature, MgO combined with the solid solution to form a liquid phase, which caused an enhancement of the densification process. On sintering the solid solution with excess PbO, a low-temperature melting PbO-rich liquid phase was formed, which promoted the densification process with inhomogeneous grain growth. Simultaneous additions of 1.0 wt.% MgO and 2.0 wt.% PbO to the Pb[(Mg_1/3Nb_2/3)_0.9Ti_0.1]O₃ solid solution and sintering the resulting material at 1000 °C for 3 h led to the formation of a dense and homogeneous microstructure consisting of evenly distributed grains with an average grain size of 10 μm. The peak dielectric constant of this composition (at ≈38 °C), measured at a frequency of 1 kHz, was 18,000 with a dissipation factor of <2%.