Dielectric properties of PIN–PT ceramics under compressive stress

Lead indium niobate, Pb(In_1/2Nb_1/2)O₃ or (PIN), is an interesting ferroelectric material, because it can be changed from a disordered state to ordered state by long-time thermal annealing. However, the temperature related to the maximum dielectric constant (T_max) of PIN in relaxor phase is low (at 1 kHz, T_max = 66 °C). In this study, to increasing T_max of PIN, lead titanate, PbTiO₃(PT) was thus added to PIN with compositions (1 − x)PIN–xPT (for x = 0.1–0.5). The influence of stress on the dielectric properties of (1 − x)PIN–xPT ceramics was then investigated. The dielectric properties were measured under various uniaxial compressive stress up to 400 MPa. The results showed that the superimposed compression load reduced the dielectric constant in 0.9PIN–0.1PT. For the other compositions, the dielectric constants first increased with the compressive stress, and then decreased when the stress was further increased up to 400 MPa. The dielectric loss tangent of all composition was found to decrease with increasing compressive stress.     

Dielectric and electromechanical properties of (1−x)PMN-xPZT ferroelectric ceramics

The dielectric and electromechanical characteristics of the (1?x)PMN-xPZT ferroelectric ceramics have been obtained at different temperatures, amplitudes, and frequencies of the measuring field and at different bias field strengths. It is shown that this ferroelectric ceramics at low and infralow frequencies possesses pronounced relaxor properties in a certain temperature range and ferroelectric properties in other temperature range. The temperature and amplitude ranges have been determined, in which the permittivity ?′ either only decreases or first increases and then decreases with an increase in the measuring field amplitude E ₀. The temperature ranges of existing the phases similar to the superparaelectric phase, dipole glass phase, and ferroelectric phase are evaluated from the temperature dependences of the coercive field E _c (T) and the remanent polarization P _r (T) and also from the reverse dependences of ?* and the electromechanical characteristics. The PZT concentration in the PMN-PZT system is determined, at which the electrostrictive constant M ₁₁ is maximum. It is demonstrated that, in the neighborhood of the temperature at a maximum of ?′, the strain S ₃ is quadratic in the field E ₌; that is, S ₃=M ₁₁ E ².     

Dielectric properties of potassium–sodium niobate ceramics at low frequencies

ABSTRACT

A study of the effects of ageing history on the electrical properties of lead-free ferroelectric ceramics of (K_0.5Na_0.5)(Nb_1?xSb_x)O₃ + 0.5 mol% MnO₂ and (K_0.5Na_0.5)(Nb_1?xTa_x)O₃ + 0.5 mol%MnO₂ for x = 0.05 is reported. The samples after storage at a constant temperature have been subject to infra-low-frequency electric field and radiation. Differences of the photoelectric response between the two examined compounds were found and the restoration of polarisation in the aged ceramic materials by cycles of applied field is discussed.     

Dielectric and magnetic properties of Bi1−xYxFeO3 ceramics

Y doped BiFeO₃ polycrystalline ceramics were prepared by sol–gel method. Crystal structure examined by X-ray diffraction indicates that the samples were single-phase and crystallize in rhombohedral structure. An anomaly in the dielectric constant and dielectric loss in the vicinity of the antiferromagnetic Neel temperature (T_N) was observed. Saturated magnetization loops were observed for all sample with saturated magnetization M_s=0.678 emu/g and remnant magnetization M_r=0.084 emu/g for x=0.3.     

Dielectric, ferroelectric and piezoelectric properties of 0-3 barium titanate–Portland cement composites

In this work, barium titanate (BT) and cement composites of 0-3 connectivity were produced with BT concentrations of 30%, 50% and 70% by volume using the mixing and pressing method. The dielectric constant (ε _r ) and the dielectric loss (tan δ) at room temperature and at various frequencies (0.1–20 kHz) of the ferroelectric BT-Portland cement composites with different BT concentrations were investigated. The results show that the dielectric constant of BT-PC composites was found to increase as BT concentration increases, and that the highest value for ε _r —of 436—was obtained for a BT concentration of 70%. In addition, the dielectric loss tangent decreased with increasing BT concentration. Moreover, several mathematical models were used; the experimental values of the dielectric constants are closest to those calculated from the cube model. The 0-3 cement-based piezoelectric composites show typical ferroelectric hysteresis loops at room temperature. The instantaneous remnant polarization (P _ir ), at an applied external electrical field (E ₀) of 20 kV/cm (90 Hz) of 70% barium titanate composite, was found to have a value ≈3.42 μC/cm². Furthermore, the piezoelectric coefficient (d ₃₃) was also found to increase as BT concentration increases, as expected. The highest value for d ₃₃ was 16 pC/N for 70% BT composite.     

Electrical properties of ferroelectric BiMnO3–PbTiO3 under tailored synthesis and ceramic processing

Conductivity is a main issue in research on multiferroic perovskite oxides, which makes the characterization of their ferroelectric properties difficult, and for several compounds even to unambiguously state their ferroelectric nature. In this report, we use ferroelectric BiMnO₃–PbTiO₃ as a model system to study the relationships among synthesis, processing, and conductivity in ABO₃ perovskite oxides with magnetically active cations in the B-site. Three single phase, dense ceramic materials processed by conventional sintering, hot pressing, or spark plasma sintering (SPS) of powders synthesized by either wet chemistry or mechanochemical activation were studied. Impedance spectroscopy analysis was carried out to obtain grain and grain boundary conductivities for the three materials, along with activation energies. Mechanosynthesis is shown not to modify the mechanism of bulk or boundary conductivity, but only the carrier concentration, while SPS processing results in a low temperature, additional conduction mechanism.     

Oxygen transport properties of dense and porous (La0.8Sr0.2)0.99Co0.8Ni0.2O3-δ

We have determined k_ex and D_chem for (La_0.8Sr_0.2)_0.99Co_0.8Ni_0.2O_3-δ by the use of electrical conductivity relaxation on a dense sample and by applying the ALS model to measured AC impedance spectrum on a porous electrode. Extracting k_ex and D_chem from the methods resulted in comparable values. k_ex and D_chem also agreed well with literature values on La_0.8Sr_0.2CoO_3-δ, indicating that nickel substitution does not change the oxygen transport properties. k_ex of the porous sample was further found to decrease with a five times higher rate than D_chem when measured by using an Electrochemical Impedance Spectroscopy (EIS) over several days.     

Effect of sintering temperature on luminescence properties of borosilicate matrix blue–green emitting color conversion glass ceramics

The color conversion glass ceramics which were made of borosilicate matrix co-doped(SrBaSm)Si_2O_2N_2:(Eu~(3+)Ce~(3+)) blue–green phosphors were prepared by two-step method in co-sintering. The change in luminescence properties and the drift of chromaticity coordinates(CIE) of the(SrBaSm)Si_2O_2N_2:(Eu~(3+)Ce~(3+)) blue–green phosphors and the color conversion glass ceramics were studied in the sintering temperature range from 600℃ to 800℃. The luminous intensity and internal quantum yield(QY) of the blue–green phosphors and glass ceramics decreased with the sintering temperature increasing. When the sintering temperature increased beyond 750℃, the phosphors and the color conversion glass ceramics almost had no peak in photoluminescence(PL) and excitation(PLE) spectra. The results showed that the blue–green phosphors had poor thermal stability at higher temperature. The lattice structure of the phosphors was destroyed by the glass matrix and the Ce~(3+) in the phosphors was oxidized to Ce~(4+), which further caused a decrease in luminescent properties of the color conversion glass ceramics.     

Effects of Zr/Ti ratio on dielectric and ferroelectric properties of 0.8Pb(ZrxTi1−x)O3–0.2Pb(Co1/3Nb2/3)O3 ceramics

The influences of Zr/Ti ratio on electrical properties of the 0.8Pb(Zr_xTi_1−x)O₃–0.2Pb(Co_1/3Nb_2/3)O₃ ceramics prepared by a mixed-oxide method (with x = 0.46, 0.48, 0.50, 0.52, and 0.54) have been investigated in order to identify the morphotropic phase boundary composition in this system. With XRD analysis, the crystal structure of dense specimens appeared to change gradually from tetragonal to rhombohedral with increasing Zr content. The dielectric properties measurements showed a maximum dielectric constant at x = 0.50, while the transition temperature decreased with increasing Zr content in the system. Moreover, all ceramics showed diffused phase transition behaviors with a minimum diffusivity at x = 0.50. In addition, the Polarization–Electric field (P–E) hysteresis loops of the ceramic systems also changed significantly with the Zr content. Interestingly, the loop squareness parameter reached maximum around x = 0.50. Other ferroelectric hysteresis parameters showed noticeable change at x = 0.50. These results clearly showed the significance of Zr/Ti ratio in controlling the electrical properties of the PZT–PCN ceramic systems.     

Composition-dependent ferroelectric properties of Ba1− x Sr x TiO3 ceramics

Pure and homogeneous nanopowders of Ba_{1? x} Sr _x TiO₃ with compositions x?=?0, 0.10, 0.20, 0.25, 0.30 and 0.35 were prepared by a polymerized complex method based on the Pechini-type reaction route, wherein mixed solutions of citric acid, ethylene glycol, titanium isopropoxide, barium carbonate and strontium carbonate were polymerized to form transparent resins used as precursors for the final oxide powders. X-ray diffraction data indicated the formation of tetragonal BaTiO₃ and cubic (Ba,?Sr)TiO₃ solid solutions, free from secondary phases. Ceramics with relative densities of 85–93% were obtained after sintering for 3?h at 1300°C and 1350°C, respectively. The Sr content influences the microstructure of the ceramic samples and their ferroelectric characteristics. The P(E) loops are strongly composition-dependent, with reducing the remnant polarization and coercive fields with increasing the Sr addition. The First Order Reversal Curve (FORC) analysis is used for describing the local switching properties and the ac-tunability characteristics. The maximum of the FORC distribution is located at low fields, meaning that small fields are necessary to switch the large majority of the domains of these systems. The tunability determined in the FORC experiment depends not only on the actual field, but also on the reversal field. For two compositions, higher FORC tunability at room temperature was found for the sample closer to its ferro-para phase transition. This result was interpreted in relationship with the domain walls mobility, which is higher for the ferroelectric sample close to its ferro-para phase transition.     

Dielectric,ferroelectric and piezoelectric properties of (1−x)[K0.5Na0.5NbO3]−x[LiSbO3] ceramics

Lead-free (1?x)[K_0.5Na_0.5NbO₃]?x[LiSbO₃] (x=0, 0.04, 0.05 and 0.06)/(KNN-LS) ceramics were prepared by conventional solid-state reaction route (CSSR). For dense morphology pure KNN ceramic was sintered at 1120 °C and LS modified KNN ceramics were sintered at 1080 °C for 4 h, respectively. The structural study at room temperature (RT) revealed the transformation of pure orthorhombic to tetragonal structure with the increase in LS content in KNN-LS ceramics. Temperature dependent dielectric study confirmed the increase of diffuse phase transition nature with the increase in LS content in KNN-LS ceramics. The presence of orthorhombic to tetragonal (T_O?T) polymorphic phase transition temperature (PPT) ～43 °C confirmed the presence of two ferroelectric (orthorhombic and tetragonal) phases in 0.95KNN-0.05LS ceramics at RT. 0.95KNN-0.05LS ceramics showed better ferroelectric and piezoelectric properties i.e., remnant polarization (P_r)～18.7 μC/cm², coercive field (E_c)～11.8 kV/cm, piezoelectric coefficient (d₃₃)～215 pC/N, coupling coefficient (k_p)～0.415 and remnant strain ～0.07% were obtained.     

Magnetic and magneto-transport properties of (Ba0.8Sr0.2)2−xNdxFeMoO6

The variation in structural, magnetic and magneto-transport properties of the double perovskite system (Ba_0.8Sr_0.2)_2?xNd_xFeMoO₆ {0.0<X<0.5} induced by Nd³⁺ doping (electron doping) has been studied and compared. The samples were prepared by standard solid state reaction method in a reducing atmosphere. The parent compound showed a saturation magnetic moment value of 3.75 μ_B/f.u. at an applied field of 0.5 T and a change in magnetoresistance value up to 26% (77 K, 0.8 T). The Rietveld refinement of the X-ray diffraction data showed a continuous decrease in lattice parameters and Fe–Mo ordering with increasing Nd³⁺ doping. The Curie temperature was found to increase with Nd³⁺ doping (3 K per % of Nd) while the saturation magnetic moment values and magnetoresistance values were found to decrease. The observed variations in magnetic and magneto-transport properties of the system are explained on the basis of increasing antisite disorder defects and band filling effects induced by electron doping. We have observed the dominant role of band filling in determining the low field magnetoresistance of these systems.     

Influence of CuO and sintering temperature on the microstructure and magnetic properties of Mg–Cu–Zn ferrites

The synthesis of a series of Mg–Cu–Zn ferrites with the substitution of Cu for Mg has been obtained by solid-state reaction method. Microstuctural and structural analyses were carried out using a scanning electron microscope and X-ray diffraction (XRD), respectively. The lattice parameter is found to increase with increasing copper content. A remarkable densification is observed with the addition of Cu ions in the ferrites. Microstructural analyses indicate that CuO influences the microstructure of the ferrites by the formation of liquid phase during sintering. The grain size significantly increases with increasing copper content. Exaggerated grain growth is observed for the samples of x=0.25–0.35. The initial magnetic permeability (μ′) increases sharply with increasing concentration of Cu ions. This increase in μ′ is explained with the grain growth mechanism and enhanced densification of the ferrites. The resonance frequency of all the samples shifts toward the lower frequency as the permeability increases with Cu content. Sintering temperature T_s also affects the densification, grain growth and initial magnetic permeability of the samples.     

Dielectric properties and specific heat of the (1 ? x)PbNi1/3Nb2/3O3-xPbTiO3 ferroelectric ceramics

The temperature dependences of the permittivity and specific heat of a mixed (1 ? x)PbNi_1/3Nb_2/3O₃-xPbTiO₃ system (where x = 0.3, 0.4, 0.5) have been studied over a wide temperature range 290?C700 K. It has been shown that the composition with x = 0.3 undergoes a diffuse phase transition at T _m ?? 315 K. A specific heat anomaly that is characteristic of the phase transition has been revealed at T ?? 315 K in all the compositions under study.     

Complex impedance analyses and magnetoelectric effect in ferrite–ferroelectric composite ceramics

Magnetoelectric (ME) composites yBa_0.8Pb_0.2TiO₃–(1−y$1-y$)CuFe₂O₄ are prepared by ceramic method. The component phases are prepared from two different routes, viz. CuFe₂O₄ (ferrite phase) is prepared by oxalate precursor route and Ba_0.8Pb_0.2TiO₃ (ferroelectric phase) by solid-state reaction route. No intermediate phases are observed in the composites containing these ferrite and ferroelectric phases. ME conversion factor (measure of ME effect) is found to be enhanced compared to those reported in the composites, in which the component phases were prepared by only one route, i.e. solid-state reaction route. The results on ME conversion are well accounted by measuring the complex impedance and analyzing their Nyquist plots.     

Structural,dielectric and ferroelectric study of (1−ϕ)(NBT–KNN)–ϕSBexT ceramics

(1−ϕ)(0.93 Na_0.5Bi_0.5TiO₃–0.07K_0.5Na_0.5NbO₃)-ϕSr_0.8Bi_2.15Ta₂O₉/(1−ϕ)(NBT–KNN)–ϕSB_exT (ϕ=0, 2, 4, 8, 12, 16 wt%) ceramic samples were synthesized by conventional solid state reaction route. Secondary phases started developing for higher SB_exT content in the (1−ϕ)(NBT–KNN)–ϕSB_exT ceramic samples. Decrease of transition temperature (T_m) with the increase of SB_exT content in (1−ϕ)(NBT–KNN)–ϕSB_exT ceramics was attributed to the increase of internal stress. Remnant polarization (P_r), leakage current density and polarization degradation values reduced with the increase of SB_exT content in (1−ϕ)(NBT–KNN)–ϕSB_exT ceramic samples. Retention of good ferroelectric properties and enhancement of fatigue-free behavior with the incorporation of SB_exT phase in (1−ϕ)(NBT–KNN)–ϕSBexT ceramic samples suggested their usefulness for ferroelectric memory applications.     

Dielectric, modulus and impedance analysis of lead-free ceramics Ba0.8La0.133Ti1−x Sn x O3 (x=0.15 and 0.2)

Titanate barium (BaTiO₃)-type oxide ceramics Ba_0.8La_0.133Ti_1?x Sn _x O₃ (BLTS) (here x=0.15 and 0.2) have been synthesized by the standard solid-state reaction method. Preliminary room temperature X-ray study confirms the formation of single-phase compounds in a rhombohedral crystal system. The electrical properties of BLTS were studied using the ac impedance spectroscopy technique over a wide range of temperature (120–320 K) in the frequency range of 40 Hz to 10 MHz. The presence of a single arc in the complex modulus spectrum at different temperatures confirms the single-phase character of the BLTS compounds.     

Processing of gadolinium–iron garnet under non-equilibrium conditions

We have investigated the mechanosynthesis of gadolinium iron garnet (GdIG) by high-energy ball-milling of 3.(Gd₂O₃)?+?10.(α-Fe) followed by thermal annealing conducted at moderate temperatures (1100 °C). The samples were characterized by X-ray diffraction and Mössbauer spectroscopy in order to determine the influence of the milling time on the final products. For as-milled samples the results revealed the enlargement of the magnetic component belonging to iron and a discrete paramagnetic component. The formation of a garnet phase was observed in all as-annealed samples treated at 1100 °C for 6 h in quantities proportional to the time of grinding the precursors. Evidently, high-energy ball milling of Gd₂O₃?+?α-Fe powders is an important step in GdIG synthesis by a ceramic method. Single-phase garnet is observed for the samples milled for 12 and 24 h treated at 1100 °C for 6 h.     

Enhancing magnetoelectric properties of 0–3 particulate composite ceramics by introducing nano-sized sintering aids via self-combustion method

The 0.55Pb(Ni_1/3Nb_2/3)O₃-0.05PbHfO₃-0.4PbTiO₃/Ni_0.875Zn_0.125Fe₂O₄ (PNNHT/NZF) 0–3 particulate composite ceramics were prepared by the conventional solid-state reaction method via introducing the nano-sized WO₃ and CuO sintering aids by the self-combustion method. Due to the introducing of nano-sized sintering aids, densified PNNHT/NZF composite ceramics are synthesized sintered at low sintering temperature. Furthermore, the nano-sized sintering aids act effectively as blocking layers, leading to compact composite ceramics with homogenously dispersed and isolated microstructure morphology, inhibiting inter-phase diffusion, avoiding interfacial chemical reaction, and achieving strong inter-phase coupling. Therefore, the synthesized PNNHT/NZF composite ceramics exhibit enhanced magnetoelectric properties.     

Dielectric properties of magnetic-ferroelectric CoO–NaNO2–porous glass nanocomposite

Physics of the Solid State - Dielectric properties of the nanostructured multiferroic composite on the basis of silicate porous glass simultaneously filled with ferromagnetic (cobalt oxide CoO) and...