Nb2O6 Relaxor Research Articles

Tailoring Zr-doped tungsten bronze (Sr,Ba,Gd)Nb2O6 relaxor ferroelectric with high electrical insulation interface for dielectric capacitor

Tetragonal tungsten bronze structure (TTB) compounds have attracted tremendous interest for their applications in energy storage, especially as dielectric capacitor mediums. However, constrained by the inverse correlation of polarization and electric breakdown field in relaxor ferroelectrics, there is still a major challenge in improving energy density. To addresse this challenge, a viable strategy of constructing relaxor behavior with robust electrical insulation in TTB-type Sr0.485Ba0.47Gd0.03Nb2-xZrxO6 (SBN-Gd-Zrx) by introducing ZrO2 during the preparation process was proposed. By introducing Zr4+ in the B-site, we have revealed how Zr4+ affects the dielectric and ferroelectric characteristics to explore the intrinsic relaxation. Based on the analysis of Rietveld refinement against synchrotron X-ray powder diffraction and Raman results, the substitution of Gd3+ and Zr4+ for Sr2+ and Nb5+ in Sr0.53Ba0.47Nb2O6 caused a decline in tetragonality and a shrinkage of the unit cell due to the lattice defect of [GdSr]• and [ZrNb]', which mutually compensates effectively alleviate the distortion of BO6 and then favors the balance of polarization and dielectric constant. The accrual of additional ZrO2 at grain boundaries significantly enhances electrical insulation characteristics, as validated by complex impedance spectroscopy. At near room temperature, all Zr-doped SBN-Gd compounds of the series exhibit heightened relaxation and undergo a phase transition from ferroelectric to paraelectric. As a result, in tandem with the synchronous augmentation in breakdown electric field (EB) and saturation polarization (Pm), optimal energy storage characteristic is realized in the SBN-Gd-Zr0.2 sample. It attains a remarkable Wrec of 2.67 J/cm3 and an efficiency ƞ of 91.21 %, showcasing excellent suitability in terms of different frequencies and temperatures, which far exceeds that of Gd-modified SBN ceramics and pure SBN ceramics. These results exemplify an efficacious strategy for designing novel TTB dielectrics by coupling relaxor modulation with electrical insulation, and position them competitively for implementation in dielectric storage capacitors utilized in pulsed power devices.

Enhanced Energy Storage Properties of La-Doped Sr0.6Ba0.4Nb2O6 Relaxor Ferroelectric Ceramics Prepared by Spark Plasma Sintering.

In this work, La-doped Sr0.6Ba0.4Nb2O6 ferroelectric ceramics were fabricated by the conventional solid state reaction method (CS) and spark plasma sintering (SPS), respectively. The microstructure, phase structure, dielectric properties, relaxor behavior, ferroelectric and energy storage properties were investigated and compared to indicate the effects of spark plasma sintering on their performances. The results show that the grain shape changes from columnar to isometric crystal and the grain size decreases obviously after spark plasma sintering. The dielectric constant of the CS sample and the SPS sample both show a typical relaxor behavior with obvious frequency dispersion. The diffusion parameters (γ) of both CS sample and SPS sample are close to 2 and all the samples present slim polarization–electric (P-E) loops, which verify the relaxor behavior. Moreover, the breakdown strength, Eb, and discharge energy storage density, Wrec, of La-doped Sr0.6Ba0.4Nb2O6 ferroelectric ceramics prepared by SPS are improved significantly. This work provides guidance for improving the energy storage performance of ferroelectric ceramics with tungsten bronze structures by decreasing the grain size through adopting a different sintering method.

Grain-size-insensitive dielectric properties of Sr0.6Ba0.4Nb2O6 relaxor ferroelectric ceramics with tetragonal tungsten bronze structure

The influence of grain size on the dielectric properties of Sr0.6Ba0.4Nb2O6 (SBN60) ceramics with a tetragonal tungsten bronze structure was examined. The conventional and two-step sintering procedures were used to fabricate dense and phase-pure SBN60 ceramics with grain sizes ranging from 2.2 μm to 17.3 μm. In the temperature dependence of the dielectric permittivity, all samples showed a relaxor-like broad dielectric peak with a maximum at around 60 °C. The maximum dielectric permittivity and dielectric maximum temperature of the SBN ceramics were found to be less dependent on the grain size. The reason for the grain-size-insensitive dielectric properties of the SBN60 ceramics is discussed based on the analysis of the dielectric properties and Raman spectra.

Random electric field strength distribution in lead-free relaxor ferroelectrics caused by barium content

Curie temperature behavior of BaxSr[Formula: see text]TiO3 ferroelectrics ceramic ([Formula: see text]) in dependence on bias field is detected by means of acoustic emission. Curie temperature exhibits nontrivial V-shape effect with threshold field of 0.3[Formula: see text]kV/cm, equivalent to random electric fields strength. This random field strength is compared with those in BaxSr[Formula: see text]TiO3 relaxor ferroelectrics ([Formula: see text], 0.7, 0.8) obtained previously, as well as with those determined from mean domain sizes in BaxSr[Formula: see text]Nb2O6 relaxor ferroelectrics ([Formula: see text], 0.39, 0.6). It is estimated that the random field strength of Ba[Formula: see text]Sr[Formula: see text]TiO3 is 30 times stronger than those of Ba[Formula: see text]Sr[Formula: see text]Nb2O6 and it is shown that the random field strengths of both BaxSr[Formula: see text]TiO3 and BaxSr[Formula: see text]Nb2O6 obey the same exponential law in dependence on barium content.

A comparative study of Sr0.7Ba0.3Nb2O6 relaxor ferroelectric ceramics prepared by conventional and microwave sintering techniques

Abstract Sr 0.7 Ba 0.3 Nb 2 O 6 (SBN70) ceramics were prepared by conventional sintering (CS) and microwave sintering (MWS) techniques. High-density ceramics were obtained by the MWS method in 2 h of cycle time, whereas it took 14 h by the CS method. Samples prepared by both sintering techniques showed single phase formation according to XRD results. It was observed that MWS SBN70 ceramics showed better densification and more uniform grain size than those of CS samples. The dielectric characteristics of both samples showed diffuse phase transition phenomenon features, which was confirmed by linear fitting of the modified Curie–Weiss law. Besides, the relaxor ferroelectric properties of both samples followed the Vogel–Fulcher relationship well. The value of spontaneous polarization ( P s ) and the P–E hysteresis loop for MWS samples were significantly higher and slimmer than those of the CS samples, respectively.

Dielectric maximum temperature non-monotonic behavior in unaxial Sr0.75Ba0.25Nb2O6 relaxor seen via acoustic emission

[100] oriented Sr0.75Ba0.25Nb2O6 relaxor crystals have been studied by means of acoustic emission (AE) over a wide 20–400 °C temperature range. Both the Burns temperature, Td = 350 °C, and the intermediate temperature, T* = 183°C, and the susceptibility maximum temperature, Tm (59 °C on heating and 47 °C on cooling), have been successfully detected. Dependent upon the external electric field, the Tm exhibits a local minimum near 0.25 kV/cm accompanied by pronounced AE maximum in a manner which had recently been detected in Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 by Dul’kin et al. [Appl. Phys. Lett. 94, 252904 (2009)] and in Pb(Sc1/2Ta1/2)O3 by Dul’kin et al. [Phys. Rev. B 82, 180101(R) (2010)], whereas the T* increases monotonically, similar to that which had recently been revealed in BaTiO3 by Dul’kin et al. [Appl. Phys. Lett. 97, 032903 (2010)] with a rate of 7.5 K cm/kV. An observed Tm behavior is discussed from the point of view of the existence of the random electric field components along the [100] direction in Sr0.75Ba0.25Nb2O6 crystals.

Comparison of Acoustic Behaviors Between the Perovskite and the Tungsten-Bronze Uniaxial Relaxors

The longitudinal acoustic mode behaviors of three cubic perovskite relaxors and one tungsten-bronze uniaxial relaxor were compared in a widest temperature range by Brillouin scattering. All investigated relaxors exhibited substantial softening of the Brillouin shift upon cooling and a sudden increase in the hypersonic damping at a temperature lower than the Burns temperature, from which four characteristic temperatures were defined in relation to the temperature evolution of polar nanoregions. The Brillouin shift of the uniaxial Sr0.61Ba0.39Nb2O6 relaxor showed a positive slope at temperatures above the Burns temperature, which indicates the existence of coupling between some persisting relaxation process and the acoustic waves propagating along the polar axis.

Nanopolar structures and local ferroelectricity of Sr0.61Ba0.39Nb2O6 relaxor crystal across Curie temperature by piezoresponse force microscopy

Nanopolar structures and local ferroelectricity of Sr0.61Ba0.39Nb2O6 relaxor crystal across Curie temperature have been investigated using piezoresponse force microscopy (PFM). The short-range nanopolar clusters are dominated by long-range ferroelectric order at room temperature, but exhibit themselves at higher temperature through the morphology change in written ferroelectric domains and persisting piezoresponse beyond Curie point. A maximum piezoresponse is observed at 80 °C, which is attributed to the peak in the dielectric permittivity near the ferroelectric phase transition. Substantial asymmetry in PFM hysteresis emerges above Curie temperature, indicating an internal bias field that becomes notable in the absence of long-range ferroelectric order.

Dielectric investigations in Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films

The dielectric properties of Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films were carefully analyzed. In contrast to bulk samples which present three distinct dielectric relaxation phenomena Sr0.75Ba0.25Nb2O6 thin films present only two of them. The suppression of the third anomaly can be mainly attributed to the narrow grain size distribution of nanograins and weak tensile strains imposed to the film from the substrate. The whole set of results point to the interpretation of a dielectric response characteristic of mesoscopic structure, which is composed of clusters and nanodomains.

Mesoscopic structure evidenced by AC dielectric nonlinearities inSr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films

The AC electric field and temperature dependences of the dielectric permittivity for strontium bariumniobate (Sr0.75Ba0.25Nb2O6) relaxor ferroelectric thin films have been investigated. The results indicate the existenceof a true mesoscopic structure evidenced by the nonlinear dielectric response of these films,which is similar to those observed for bulk relaxor ferroelectrics. A tendency for atemperature dependent crossover from a linear to a quadratic behaviour of thedielectric nonlinearity was observed, indicating an evolution from paraelectric toglass-like behaviour on cooling the samples towards the freezing temperaturetransition.

Investigation of nonlinear dielectric properties in Sr0.75Ba0.25Nb2O6 relaxor ferroelectric thin films

The ac and dc driving fields dependence of the dielectric permittivity for the strontium barium niobate relaxor ferroelectric thin films has been investigated. The nonlinear dielectric properties were obtained by using the measurements of the dielectric permittivity of the material as a function of the ac and dc “bias” electric field amplitude in wide frequency (100Hz–10MHz) and temperature (50–450K) intervals. The results hint the existence of a true mesoscopic dielectric relaxor response in the ferroelectric thin film, which is very similar to those observed in bulk relaxor ferroelectrics. An anomalous behavior of the NL dielectric response was observed when submitted to moderate dc electric fields levels, indicating a crossover from paraelectric to a glasslike behavior on cooling the sample toward the freezing transition. The obtained results were analyzed within the framework of the models proposed in the current literature.

Effect of gamma irradiation on the dielectric response of a Sr0.75Ba0.25Nb2O6 relaxor single crystal

The effect of gamma irradiation from a 60Co source at a dose D = 4.75 × 104 R on the dielectric properties of a Sr0.75Ba0.25Nb2O6 (SBN-75) single crystal with a smeared phase transition is investigated in the low-and infralow-frequency ranges. The behavior of the dielectric response is compared with the behavior of the depolarization currents induced in unirradiated and irradiated samples of the Sr0.75Ba0.25Nb2O6 compound. The observed changes in the electrical properties of the Sr0.75Ba0.25Nb2O6 single crystal in the temperature range of the smeared phase transition are associated with the stabilization of the ferroelectric phase of the material in an internal bias field generated by radiation-induced defects.

Dielectric and Magnetoelectric Characterization of CoFe2O4∕Sr0.5Ba0.5Nb2O6 Composites

Magnetoelectric composites were created through incorporating dispersed CoFe2O4 ferromagnetic grains into a Sr0.5Ba0.5Nb2O6 relaxor ferroelectric matrix. The two phases are chemically compatible and coexist in the dense, sintered composites. Unlike other relaxors, the Sr0.5Ba0.5Nb2O6-containing composites can be electrically poled. The apparent dielectric constant is enhanced by the conductivity in the ferrite phase and the space charge at the phase interface. A significant magnetoelectric effect was observed in all compositions investigated, with a maximum dE∕dH value of 24.8 mV/cm/Oe obtained for 0.4CoFe2O4∕0.6Sr0.5Ba0.5Nb2O6, which is much greater than that of magnetoelectric compounds and solid solutions. These results demonstrate that the Pb-free (Sr,Ba)Nb2O6 relaxor can be advantageously used as the matrix for ferromagnetic/ferroelectric composites in the future development of magnetoelectric materials.

Dielectric behavior and diffuse phase transition features of rare earth doped Sr0.61Ba0.39Nb2O6 ferroelectric ceramics

The dielectric behavior and the main features of the diffuse phase transition of nondoped and rare earth (La, Nd, or Gd) doped Sr0.61Ba0.39Nb2O6 relaxor ferroelectric ceramics were carefully investigated. The dopant incorporation gives rise to one continuous decrease of the temperatures of maximum dielectric permittivity. The whole set of the effects of rare earth (RE) doping on SBN diffuse phase transition and relaxation features can be attributed to the RE site distribution. In fact, the dopant incorporates into the tungsten bronze A2 sites, giving rise to the strong random field sources that act mainly on destroying the ferroelectric long-range interactions. This A2-sites occupation also affects the dielectric permittivity frequency response, whereas the relaxation strength (ΔTrs=Tm(1 MHz)−Tm(100 Hz)) increases with RE content increasing. This effect can be explained considering that the dopant roughens the free energy landscape, promoting strong changes in the volume size distribution of the interacting ferroelectric clusters.

Field-induced sharp ferroelectric phase transition in Sr0.66Ba0.34Nb2O6 relaxor ferroelectric

Field-induced sharp ferroelectric phase transition was observed in Sr0.66Ba0.34Nb2O6 single crystals. The peaks of the real and imaginary parts of dielectric permittivity arise upon cooling under weak dc bias electric fields and subsequently heating under zero fields or upon cooling under zero fields and subsequently heating under weak electric fields. The applied electric field cancels the random fields that destroy the phase transition and give rise to low temperature domain state if E=0. These results strongly suggest that the SBN system belongs to the random field Ising universality class, a rare case among structural phase transitions.

Memory effect at a (Sr0.61Ba0.39)Nb2O6single crystal

Abstract Relaxation experiments after switching out an electric field at low temperatures give evidence of the memory effect (ME) at the (Sr0.61Ba0.39)Nb2O6 relaxor ferroelectric.