High-temperature impedance spectroscopy of BaFe0.5Nb0.5O3 ceramics doped with Bi0.5Na0.5TiO3

Bi_0.5Na_0.5TiO₃ (BNT)-doped BaFe_0.5Nb_0.5O₃ (BFN) ceramics were synthesized by a two-step solid-state reaction. Temperature dependence of dielectric properties measured at different frequencies was investigated over broad temperature and frequency ranges. Impedance spectroscopy and universal dielectric response were employed to study the relaxation behavior and conductivity mechanism of the ceramics in a frequency range from 40 Hz to 100 MHz and a temperature range from 300 K to 800 K. The complex plane impedance data revealed the bulk and grain boundary contributions toward conductivity processes in the form of semicircular arcs. The high-temperature conductivity of ceramics is attributable to thermally activated second ionized oxygen vacancy.     

Structural and electrical properties characterization of (1–x)PbZr0.52Ti0.48O3–xBaFe0.5Nb0.5O3 system

The structural and electrical properties of (1-x)PbZr_0.52Ti_0.48O₃–xBaFe_0.5Nb_0.5O₃ ceramics system with the composition near the morphotropic phase boundary were investigated as a function of the BaFe_0.5Nb_0.5O₃ content by X-ray diffraction (XRD) and dielectric measurement technique. Studies were performed on the samples prepared by solid state reaction for x=0.1, 0.2, 0.3, 0.4 and 0.5. The XRD analysis demonstrated that with increasing BFN content in (1-x)PZT–xBFN, the structural change occurred from the tetragonal to the cubic phase at room temperature. Changes in the dielectric behavior were then related to these structural depending on the BFN content. PACS 77.84.Dy; 77.22.Ch; 77.22.Gm     

Microwave dielectric properties of the 5.5Li<Subscript>2</Subscript>O–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–7TiO<Subscript>2</Subscript> ceramics

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 5.5:1:7 was prepared by solid state reaction route. The phase and structure of the ceramic were characterized by X-ray diffraction and scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The microwave dielectric ceramic has low sintering temperature (∼1075°C) and good microwave dielectric properties of ε _r=42, Q×f=16900 GHz (5.75 GHz), and τ _f =63.7 ppm/°C. The addition of B₂O₃ can effectively lower the sintering temperature from 1075 to 875°C and does not induce degradation of the microwave dielectric properties. Obviously, the LNT ceramics can be applied to microwave low temperature-cofired ceramics (LTCC) devices.     

Optimizing conditions of fabrication and the properties of BaNb2O6-SrNb2O6 binary ceramics

Conditions for fabricating (Ba_0.5Sr_0.5)Nb₂O₆ ceramics are optimized. It is shown that materials synthesized at T = 1250°C and sintered at T = 1375–21400°C exhibit the best ceramic characteristics. The (Ba_0.5Sr_0.5)Nb₂O₆ solid solution is found to be a ferroelectric with a diffuse phase transition. The possibility of fabricating Ba_0.5Sr_0.5Nb₂O₆ thin films from ceramic targets prepared in the resulting optimum regimes is shown.     

Structure evolution and microwave dielectric response of (Ca0.5+xSr0.5−x)[(Al0.5Nb0.5)0.5Ti0.5]O3 solid solutions

The phase assemblage, crystal structure evolution and microwave dielectric response of (Ca_0.5+xSr_0.5−x)[(Al_0.5Nb_0.5)_0.5Ti_0.5]O₃ ceramics (abbreviated as CSANT hereafter) are investigated. Single perovskite solid solution is formed in the CSANT ceramics in Sr-rich composition range of x < −0.05, however, Ca₄Ti₃O₁₀-type layered perovskite phase begins to segregate after x = −0.05. The CSANT perovskites crystallized in Fm3m cubic symmetry in the composition range of x ≤ −0.2, however, as the Ca²⁺ content in A-site increased, the oxygen octahedral began to be anti-phase tilted at x = −0.1 and the crystal structure transited to P2₁/n pseudo-orthorhombic space group thereafter. The microwave dielectric response of the CSANT ceramics is elaborately discussed in terms of their crystallographic structure and chemical composition. When sintered at 1500 °C for 4 h, a dielectric constant ɛ_r of 52.5, a Qf product of 28000 GHz and a τ_f of +25.4 ppm/°C microwave dielectric ceramic can be obtained in the CSANT ceramics at x = 0.3.     

Evolution of microstructure and dielectric properties of (LiCe)-doped Na0.5Bi2.5Nb2O9 Aurivillius type ceramics

Aurivillius type (NaBi)_0.5?x(LiCe)_xBi₂Nb₂O₉ ceramics were prepared by the standard ceramics route. The single crystal structural ceramics were achieved for all compositions and lattice distortion was decreased by (LiCe) dopants. The temperature dependent dielectric properties revealed that all compositions possess a high Curie-temperature (>780 °C). A modified Curie–Weiss relationship is used to study the diffuseness behavior of a ferroelectric phase transition indicating the degree of diffuseness of NBN-based ceramics increased with (LiCe) modifications. The degradation of resistance implied a plausible model that Ce⁴⁺ ions entered into the B-site of the pseudo-perovskite structure and acted as acceptor doping. Further investigation demonstrated that both electrical conduction and dielectric relaxation processes were associated with the oxygen vacancies produced by the substitution of Nb⁵⁺ ions by the Ce⁴⁺ ions.     

Influence of heat treatment on structure and some physical properties of lithium boro-niobate glass

The glass composition (90?mol% Li₂B₄O₇–10?mol% Nb₂O₅) was prepared by the melt quenching technique. The quenched sample was heat treated at 480°C, 545°C and 630°C for 5?h and heat treated at 780°C with different time. The times were 5, 10, 15, 20, 28, and 36?h. The glass and glass ceramics were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and dc conductivity as a function of temperature. Lithium niobate (LiNbO₃) and lithium diborate (Li₂B₄O₇) were the main phases in glass ceramic addition to traces from LiNb₃O₈. Crystallite size of the main phases determined from the X-ray diffraction peaks are in the range <100?nm. The fraction of crystalline (LiNbO₃) phase increases with increase the heat treatment temperature and time. The relation between physical properties and structure were studied.     

Preparation and ferroelectric properties of pyrochlore-free Pb(Ni1/3Nb2/3)O3-based solid solutions

Polycrystalline ceramics of the perovskite solid solution 0.5Pb(Ni_1/3Nb_2/3)O₃-(0.5-x)-Pb(Zn_1/3Nb_2/3)O₃–xPb(Zr_1/2Ti_1/2)O₃; x=0.0–0.5 (PNN–PZN–PZT) were synthesized by a modified columbite method. Highly dense ceramics lacking parasitic pyrochlore phases were prepared at a calcination temperature of 950 °C by using a double-crucible configuration, excess PbO (2 mol %), and a fast heating/cooling rate (20 °C/min). The ceramics were characterized by a variety of techniques including X-ray diffraction, ferroelectric hysteresis loop measurements, field-induced longitudinal strain measurements, and electron microscopy. It was observed that the remanent polarization exhibited a significant increase with increasing x. In addition, the squareness of the hysteresis loop increased quasi-linearly as the molar fraction of PZT increased. The maximum spontaneous polarization and remanent polarization for the x=0.5 composition were 31.9 μC/cm² and 25.2 μC/cm², respectively. Moreover, the data were analyzed to show the evolution of the micro-domain state as a function of the molar fraction of PZT. PACS 77.22.-d; 77.80.Bh; 77.84.Dy; 61.10.Nz; 77.80.Dj     

Enhancement microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by substituting La3+ with Sm3+

The microwave dielectric properties of La_1?xSm_x(Mg_0.5Sn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La_1?xSm_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. Apparent density of 6.59 g/cm³, dielectric constant (ε_r) of 19.9, quality factor (Q×f) of 70,200 GHz, and temperature coefficient of resonant frequency (τ_f) of ?77 ppm/°C were obtained for La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1500 °C for 4 h. The dielectric constant, and τ_f of La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃ ceramics were almost independent with the sintering temperature as the sintering temperature varied from 1450 to 1600 °C.     

Peculiarities of low- and infralow-frequency dielectric response of layered ferroelectrics

The low-and infralow-frequency dielectric properties of layered BaBi₂Nb₂O₉, Na_0.5Bi_8.5Ti₂Nb₄O₂₇, Na_0.5Bi_8.5Ti₂Ta₄O₂₇, and K_0.5Bi_8.5Ti₂Nb₄O₂₇ ferroelectrics have been investigated in a wide temperature range. Anomalies of the dielectric response of these materials have been found in the vicinity of 100°C; possible reasons for these anomalies are discussed.     

Preparation of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials by electrospinning

LiNi_0.5Mn_1.5O₄ cathode material was prepared by electrospinning using lithium hydroxide, manganese acetate, nickel acetate, acetic acid, ethanol, and poly(vinyl pyrrolidone) as raw materials. The effect of calcination temperature on the structure, morphology, and electrochemical properties was investigated. XRD results indicate that the LiNi_0.5Mn_1.5O₄ composite is well crystallized as a spinel structure at calcination temperature of 650 °C for 3 h. SEM results reveal that this composite has a nanofiber shape with average size of about 300–500 nm. Electrochemical performance tests reveal that this composite shows the initial discharge capacity of 127.8 and 105 mAhg^?1 at 0.1 and 3 C rates, respectively, and exhibits good cycling performance.     

Ferroelectric and magnetic properties of ferroelectromagnetic PbFe1/2Nb1/2O3 type ceramics

PbFe_1/2Nb_1/2O₃ (PFN) ceramics, to which an admixture of manganese oxide (MnO₂) was added, was obtained by calcination of the powder in a single stage synthesis. Compacting was made by a free sintering method. Results of investigations of microstructure, magnetic, magnetoelectric, dielectric and piezoelectric properties and electric conductivity vs. temperature are presented. The influence of manganese admixture on the physical properties of the PFN ceramics is presented. The admixtures decrease the electric conduction of the PFN ceramic specimens.     

The effect of some transition metal oxides on the physical properties of K0.5Na0.5Nb0.95Ta0.05O3 ceramics

Abstract

Both K_0.5Na_0.5Nb_0.95Ta_0.05O₃ (KNNTO) and (K_0.5Na_0.5Nb_0.95Ta_0.05O₃)_0.99-M_0.01, M = Co₃O₄ and Mn₂O₃ (M/KNNTO) Ferromagnetic behaviour was observed for some M/KNNTO compounds. The hardness and compressive strength of all investigated samples are given. Comparisons with similar materials are discussed. Ceramics were synthesised using a solid-state reaction method. X-ray diffraction patterns of all samples revealed that the crystal structure is orthorhombic. Field-emission scanning electron microscopy was performed. Polarisation hysteresis curves indicated a disruption of ferroelectric order with the addition of M into KNNTO ceramics. The dielectric properties of the investigated ceramics have been studied as a function of frequency and temperature.     

The improvement in dielectric and ferroelectric performance of PZT–PZN ceramics by thermal treatment

Pyrochlore-free lead zirconate titanate – lead zinc niobate ceramics have been systematically investigated in the as-sintered condition as well as after annealing. The ceramics were characterized by dielectric spectroscopy and Sawyer–Tower polarization (P–E) measurements. The powders of Pb[(Zr_1/2Ti_1/2)_(1−x)–(Zn_1/3Nb_2/3)_x]O₃, where x = 0.1, 0.3 and 0.5 were prepared using the columbite–(wolframite) precursor method. The general trend seems to indicate that the annealed samples become more normal-ferroelectric-like behavior as opposed to the relaxor-ferroelectric-like behavior observed in the as-sintered state. The as-sintered 0.9PZT–0.1PZN ceramic exhibited weak relaxor-ferroelectric behavior, with a relatively low dielectric constant maximum of 14,000 measured at 1 kHz. Annealing resulted in a transition to normal-ferroelectric-like behavior, a shift in the dielectric maximum temperature from 360 °C to 350 °C, and a dramatic increase in the dielectric constant at 1 kHz to a maximum value of 35,000 for the longer anneal. After thermal annealing at 900 °C for one week a strong enhancement of remanent polarization (P_r) was observed.     

Synthesis and characteristics of KTa0.5Nb0.5O3 thin films

KTa_0.5Nb_0.5O₃ thin films were synthesized via a metal-organic solution. Characteristics were measured, such as X-ray diffraction pattern, surface morphology and roughness, and electric properties. The synthesized films have a (100) preferential growth orientation on Si (100) substrate. The homogeneous microstructure and smooth surface benefit to the good electric properties of the thin films. The current density-voltage characteristic shows an unexpected feature of the transition from linear to nonlinear, which can be explained by the space-charge-limited mode. Dielectric constant and loss of the thin films decrease with the increase of frequency. The decrease of dielectric loss is related to the decrease of net polarization in material. The decrease of dielectric constant can be explained by Debye formula. The phase transition temperature T _c is about 102 °C for KTa_0.5Nb_0.5O₃ materials.     

Electrical properties of complex tungsten bronze ceramics

This paper highlights the electrical properties of two new complex tungsten bronze ceramics (K₂Pb₂Eu₂W₂Ti₄Nb₄O₃₀ and K₂Pb₂Pr₂W₂Ti₄Nb₄O₃₀) which were prepared by high temperature mixed oxide method. Variation of impedance parameters with temperature (27–500 °C) and frequency (1 kHz to 5 MHz) shows the grain and grain boundary effects in the samples. The variation of dielectric parameters with frequency is also studied. The ac conductivity variation with temperature clearly exhibits that the materials have thermally activated transport properties of Arrhenius type.     

Microstructure,dielectric, and piezoelectric properties of Ce‐modified Na0.5Bi4.5Ti4O15 high temperature piezoceramics

The cerium modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics have been prepared by using the conventional mixed oxide method. X‐ray diffraction analysis revealed that the cerium modified NBT ceramics have a pure four‐layer Aurivillius phase structure. The piezoelectric activity of NBT ceramics was found significantly improved by the modification of cerium. The Curie temperature T_c, and piezoelectric coefficient d₃₃ for the NBT ceramics with 0.50 wt% cerium modification were found to be 655 °C, and 28 pC/N respectively. The Curie temperature gradually decreased from 668 °C to 653 °C with the increase of cerium modification. The dielectric spectroscopy showed that the samples possess stable piezoelectric properties, demonstrating practical potential that for high temperature applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetoelectricity in the PbFe1/2Nb1/2O3 Ceramics

The magnetodielectric effect (the influence of a magnetic field H on the dielectric constant ?) and the magnetoelectric effect (the influence of an electric field E on the magnetoelectric constant ??) of the PbFe_1/2Nb_1/2O₃ ceramics have been investigated at temperatures T in the range from 50 to 200°C, including the Curie point T _C ? 98°C. It has been demonstrated that there is a correlation of these effects with the shift of the ferroelectric-paraelectric phase transition temperature in a magnetic field.     

Enhanced dielectric and nonohmic properties of SrTiO3-modified CaCu3Ti4O12 ceramics

Dielectric and nonohmic properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics can be modified by addition of SrTiO₃ (STO) in different molar proportions which were fabricated by a modified sol-gel method. XRD results indicated that all modified ceramics showed mixed phase consisting of both CCTO and STO. SEM images and grain size distribution probability also presented the change of microstructure with the addition of STO. The dielectric loss of the CCTO/0.4STO ceramics sintered at 1000 °C can be lower than 0.02 in a wide frequency (1 kHz–10 kHz), especially at 1 kHz, the dielectric loss of this sample is as low as 0.012. Furthermore, excellent nonlinear I–V electrical characteristic (high breakdown voltage to 54.15 kV/cm for CCTO/0.4STO sintered at 1000 °C) was observed as well. All the results indicated that the addition of STO does improve the dielectric properties and nonohmic characteristics of CCTO ceramics dramatically.     

Effect of Ba-substitution on the structure and properties of Pb<Subscript>0.8</Subscript>Ba<Subscript>0.2</Subscript>[(In<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)<Subscript>1-x</Subscript>Ti<Subscript>x</Subscript>]O<Subscript>3</Subscript> ceramics

Ferroelectric ceramics with formula Pb_0.8Ba_0.2[(In_1/2Nb_1/2)_1-xTi_x]O₃ (PBINT) (x=0.0,0.1,0.2,0.3,0.4 and 0.5) were prepared via a two-step solid state reaction method. It was found that ceramics with compositions in the range of x=0.0∼0.3 showed a pseudo-cubic structure, whereas the ceramic with x=0.5 displayed a tetragonal structure. All compositions showed significant frequency dispersion in their dielectric properties. The remanent polarization P_r as well as the coercive field E_c, measured at room temperature, increases with the Ti content. The experimental results obtained in this system are summarized into a phase diagram, with the morphotropic phase boundary (MPB) located at x=0.4. Compared with the Pb[(In_1/2Nb_1/2)_1-xTi_x]O₃ solid solution system, incorporating Ba in the A-site leads to a significant decrease in the dielectric maximum temperature T_max, a suppression of the dielectric relaxation parameter γ, and a shift of the MPB composition to a higher Ti content. PACS 77.84.Dy; 77.80.Bh; 77.22.Ch