Effects of thermal and electrical histories on structure and dielectric behaviors of(Li_(0.5)Nd_(0.5))^(2+)-modified(Bi_(0.5)Na_(0.5))TiO_(3)-BaTiO_(3) ceramics

The effect of thermal and electrical histories on structure and dielectric behaviors is studied using 0.95(Bi_(0.5)Na_(0.5))_(0.97)(Li_(0.5)Nd_(0.5))_(0.03)TiO_(3)-0.05BaTiO_(3)(abbreviated as BNTLN0.03-BT5)ceramic as a selected system.Subtle structure change caused by annealing treatment,and pronounced phase transition and domain switching by electrical poling,are observed to occur,respectively.The dielectric constant and its strong frequency dispersion in unpoled samples decrease evidently by electrical poling due to electric field-induced ordered domain.The high temperature Maxwell-Wagner relaxor behavior vanishes by annealing treatment due to the loss of electrical inhomogeneity with interface charging effects.Piezoelectric properties are improved evidently by annealing treatment at 900℃,implying a new appropriate method to improve piezoelectric properties.

Microstructures and microwave dielectric properties of (Ba1-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 solid solutions

(Bal-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 (x=0.02,0.04,0.06,0.08,0.1) solid solutions were prepared by the conventional solid-state reaction process.It was found that (Ba1-xSrx)4(Sm0.4Nd0.6)28/3 Ti18O54 ceramics are fully composed of BaSm2Ti4O12 and BaNd2TisO14 phases for all the compositions.The increasing x value (0.02 ≤ x ≤ 0.1) in (Ba1-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 ceramics can not only obtain high Q ×f value but also effectively enhance the permittivity (εr).The (Ba1-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 ceramic with x=0.08,sintered at 1440 ℃ for 4 h,shows excellent microwave dielectric properties of permittivity (εr) ≈ 93.19,quality factor (Q × f) ≈ 9770.14 GHz (at 3.415 GHz),and almost near-zero temperature coefficient of resonant frequency (rf)≈ +4.56 ppm/℃.

Photocurrent density and electrical properties of Bi_(0.5)Na_(0.5)Ti0_(3)-BaNi_(0.5)Nb_(0.5)0_(3) ceramics

In this work,the (1-x)Bi_(0.5)Na_(0.5)TiO_(3)-xBaNi_(0.5)Nb_(0.5)O_(3)(BNT-BNN;0.00≤x≤ 0.20)ceramics were prepared via a high-temperature solid-state method.The crystalline structures,photovoltaic effect,and electrical properties of the ceramics were investigated.According to X-ray diffraction,the system shows a single perovskite structure.The samples show the normal ferroelectric loops.With the increase of BNN content,the remnant polarization(P_(r))and coercive field(E_(c))decrease gradually.The optical band gap of the samples narrows from 3.10 to 2.27 eV.The conductive species of grains and grain boundaries in the ceramics are ascribed to the double ionized oxygen vacancies.The open-circuit voltage(V_(∝))of ~15.7 V and short-circuit current(J_(sc))of ~1450 nA/cm^(2) are obtained in the 0.95BNT-0.05BNN ceramic under 1 sun illumination(AM1.5G,100 mW/cm^(2)).A larger V_(∝) of 23 V and a higher J_(sc) of 5500 nA/cm^(2) are achieved at the poling field of 60 kV/cm under the same light conditions.The study shows this system has great application prospects in the photovoltaic field.

Enhanced energy storage properties of Bi0.5Li0.5TiO3 modified Sr0.1Bi0.45Na0.45TiO3 based ceramics

Lead-free (1-x)Sr0.1Bi0.45Na0.45TiO3-xBi0.5Li0.5TiO3 (x = 0-0.4) ceramics were successfully prepared by a solid-state reaction technique. The effects of amount of Bi0.5Li0.5TiO3 on structure and electrical properties were examined. The X-ray diffraction (XRD) analysis revealed that all the investigated specimens have a perovskite structure. An obvious change in microstructure with the increase of Bi0.5Li0.5TiO3 concentration was observed. This study demonstrated that relaxor could be stabilized in Sr0.1Bi0.45Na0.45TiO3 based ceramics by lowering the tolerance factor and electronegativity difference. Besides, a dielectric anomaly related to thermal evolution of crystallographic symmetry was emerged at the depolarization temperature. Upon incorporation of 26 mol% Bi0.5Li0.5TiO3, the specimens were able to withstand an electric field intensity of 106.9 kV/cm with an energy density of 0.88 J/cm(3) and an energy efficiency of 65%.

Dielectric behaviors and relaxor characteristics in Bi_(0.5)Na_(0.5)TiO_(3)-BaTiO_(3) ceramics

Microstructure and dielectric behaviors of heating/cooling and bias-field were investigated in lead-free ceramics(1-x)Bi_(0.5)Na_(0.5)TiO_(3)-xBaTiO_(3)(BNT-xBT,x=0,0.02,0.04,0.06,0.08 and 0.10).The relaxor characters and the Vogel–Fulcher law of frequency-dependent dielectric properties were analyzed.Three dielectric anomalies with pronounced frequency dispersion at Td,a maximum dielectric with variable frequency-dispersion at Tm and a third Maxwell–Wagner-type relaxation over a wide temperature range in high-temperature region were observed.The significant dielectric thermal hysteresis,low barrier energy,high freezing temperature in heating process and the maximum dielectric tunability appeared in x=0.4 ceramic.

A new insight into structural complexity in ferroelectric ceramics

The structure of the ferroelectrics has been widely studied in order to pursuing the origin of high electromechanical responses. However, some experiments on structure of ferroelectrics have yielded different results. Here, we report that the controversial phase structure is due to the adaptive diffraction of nanodomains which hides the natural crystal structure, and the electric-field-induced phase transition is that the natural crystal structure reappears due to the coalescent nanodomains or ordering nanodomains by applying a high electric field. The temperature dependence of dielectric constant with different measurement frequencies and X-ray diffraction (XRD) patterns of unpoled, poled, and annealing after poled ceramics in Bi0.5Na0.5TiO3–BaTiO3 (BNT–BT) ceramics authenticate the statement. These results provide a new insight into the origin of structural complexity in ferroelectric ceramics, which is related to the key role of nanodomains.