Effect of Composition on Polarization Hysteresis and Energy Storage Ability of P(VDF-TrFE-CFE) Relaxor Terpolymers

The temperature dependence of the dielectric permittivity and polarization hysteresis loops of P(VDF-TrFE-CFE) polymer films with different compositions are studied. Among them, the three compositions, 51.3/48.7/6.2, 59.8/40.2/7.3, and 70/30/8.1, are characterized for the first time. Relaxor behavior is confirmed for all studied samples. Increasing the CFE content results in lowering the freezing temperature and stabilizes the ergodic relaxor state. The observed double hysteresis loops are related to the field-induced transition to a ferroelectric state. The critical field corresponding to this transition varies with the composition and temperature; it becomes larger for temperatures far from the freezing temperature. The energy storage performance is evaluated from the analysis of unipolar polarization hysteresis loops. P(VDF-TrFE-CFE) 59.8/40.2/7.3 shows the largest energy density of about 5 J·cm−3 (at the field of 200 MV·m−1) and a charge–discharge efficiency of 63%, which iscomparable with the best literature data for the neat terpolymers.

Низкотемпературная аномалия диэлектрических свойств наночастиц магнетита

This paper is devoted to study the dielectric response of magnetic alkali borosilicate glasses containing single-domain magnetite nanoparticles in the temperature range 5 - 100 K on heating and on cooling in magnetic fields from 0 to 14 T in the frequency range from 1 Hz to 160 kHz. It is shown, that an anomaly in the dielectric response is observed in the temperature range 15 - 50 K for single-domain magnetite nanoparticles. The position of this peculiarity is in good agreement with the transition to the relaxor state observed in the bulk material. The temperature hysteresis of this anomaly has been observed on heating and cooling, and it decreases with decreasing measurement frequency.

Nature of polar state in 0.67BiFeO3–0.33BaTiO3

This study was conducted to further understand the nature of the polar state in 0.67BiFeO3–0.33BaTiO3 (0.67BF–0.33BT). A typical relaxor-type dielectric anomaly was observed (Tf = ~627 K, TB = ~820 K). The remnant polarization (Pr), maximum value of electrostrain (Sm) and magnitude strain at Ec in the bipolar mode (Sneg) increase clearly during heating (Pr, ~40 mC/cm2; Sm, 0.191 % under 40 kV/cm at 453 K). The first-cycle bipolar electrostrain loops indicate that the minimum strain on the negative side of the bipolar strain curves is negative. The slopes of the relative permittivity versus log frequency plots in unpoled (–21) and poled (–23) specimens are similar. The transition between the ergodic relaxor state and ferroelectric-like state does not involve a clear dielectric anomaly even in the poled specimen. Analyses based on the Rietveld refinement of XRD patterns, bright-field images and selected-area electron diffractions (SAED) demonstrate that the formation of the long-range ferroelectric domains is difficult under the poling field.

Electric-Field-Induced Phase Transformation and Frequency-Dependent Behavior of Bismuth Sodium Titanate–Barium Titanate

The electric field response of the lead-free solid solution (1−x)Bi0.53Na0.47TiO3–xBaTiO3 (BNT–BT) in the higher BT composition range with x = 0.12 was investigated using in situ synchrotron X-ray powder diffraction. An introduced Bi-excess non-stoichiometry caused an extended morphotropic phase boundary, leading to an unexpected fully reversible relaxor to ferroelectric (R–FE) phase transformation behavior. By varying the field frequency in a broad range from 10−4 up to 102 Hz, BNT–12BT showed a frequency-dependent gradual suppression of the field induced ferroelectric phase transformation in favor of the relaxor state. A frequency triggered self-heating within the sample was found and the temperature increase exponentially correlated with the field frequency. The effects of a lowered phase transformation temperature TR–FE, caused by the non-stoichiometric composition, were observed in the experimental setup of the freestanding sample. This frequency-dependent investigation of an R–FE phase transformation is unlike previous macroscopic studies, in which heat dissipating metal contacts are used.

Tuning the ferroelectric, dielectric and photoluminescence properties of 0.88(Na0.5Bi0.5)TiO3-0.12BaTiO3 ceramics by Sm ion doping

Solid solutions of the lead-free 0.88([Formula: see text][Formula: see text]TiO3-0.12([Formula: see text][Formula: see text]TiO3 (NBT-BT: [Formula: see text]Sm) ferroelectric ceramics were synthesized by solid state reaction. The doping of Sm promotes the structure of the ceramics to transform toward morphotropic phase boundary, and it decreases the grain size of the ceramics. With the increase of Sm content, the ferroelectric properties are improved gradually, where the ferroelectric polarization increases and the coercive field decreases. Sm doping induces a dielectric anomaly with obvious frequency dispersion at a low temperature, exhibiting the transition from the ferroelectric to relaxor state. Moreover, the photoluminescence spectra of NBT-BT:[Formula: see text]Sm ceramics exhibit a strong orange emission upon blue light excitation of the 400[Formula: see text]nm to 500[Formula: see text]nm. The emission intensities are strongly dependent on the Sm doping concentration, which reached the optimal value as the doping concentration is 0.7%. These results suggest that the NBT-BT:[Formula: see text]Sm ceramics may have significant technological promise in novel multifunctional devices.