Room Temperature Relative Permittivity Research Articles

Enhanced room temperature relative permittivity and low dielectric loss ferroelectric double perovskite for energy storage applications

The polycrystalline ceramic oxide, BaBi1.2Fe0.8TiO6 is synthesized by a mixed oxide method at 1000 °C. XRD and Rietveld's analysis suggests a tetragonal system and P4mm space group. The closely spaced dense micro grains of various shapes and sizes in scanning electron micrograph (SEM) image support the polycrystalline single-phase compound. The UV–Visible spectroscopy results in a convenient value of threshold wavelength (610 nm), absorption bandgap energy (2.23 eV), and reflectance bandgap energy (2.31 eV) which are good responses to the IR and visible range and its possible application in photocatalytic devices. The room temperature (RT) polarization loop shows non-zero remanent polarization, i.e. ferroelectric property of the compound. Relatively higher room temperature dielectric permittivity (ɛr = 2455) with low loss tangent (tanδ) = 0.247 at 100 Hz, phase transition (Td > 200 °C), and Curie (Tc > 470 °C) temperature values are supporting to be as good dielectric material for ceramic capacitors. Transport property shows lower RT current density is in order of 1E-9 at 300 V/cm. The compound follows the Arrhenius equation and results in imminent values of activation energy in ac conductivity (Ea = 0.847 eV at 100 Hz) and dc conductivity (Ea = 0.838 eV) analysis. Based on the results, the present compound is likely to be used as a dielectric material in ceramic capacitors, energy and memory storage devices, and photocatalytic devices.

Effect of spark plasma sintering on the dielectric response of Sm and La co-doped barium titanate

Samarium and Lanthanum co – doped barium titanate ceramic (Ba0.96Sm0.02La0.02TiO3) was synthesized by an ethylene glycol polymerization route followed by both conventional and spark plasma sintering. A small amount of grain growth was observed after the spark plasma sintering, which could be due to the high heating rate during the process which causes agglomeration. The spark plasma sintered ceramic showed a significant increase in room temperature relative permittivity value from 247.76 to 4129.355 respectively at 1 kHz respectively. Temperature dependent permittivity showed a shift in curie temperature to 393 K for the SPS ceramic.

Structural, thermal and dielectric behaviour of exfoliated graphite nanoplatelets (xGnP) filled EVA/EOC blend composites

Nano-composites of xGnP filled ethylene vinyl acetate (EVA)/ethylene-octene copolymer (EOC) (80–20) blend with 0, 1, 3, 5, 9, 11 wt % of xGnP were fabricated by solution casting followed by compression moulding. The room temperature X-ray diffraction (XRD) pattern and field emission scanning electron microscope (FESEM) of the investigated samples reflect distribution of exfoliated graphite nanoplatelets (xGnP) in the EVA/EOC matrix. The thermo-physical properties of the composites were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC analysis shows that with increase in xGnP contents, crystallisation temperature increase and act as a nucleating agent. TGA analysis data validates the stability of composites with increase in xGnP wt % in the composites. The dielectric and conducting behaviours of the studied samples were investigated by computer controlled impedance analyser within the frequency range of 100 Hz to 5 MHz. The room temperature relative permittivity (εr) value increases with rise in wt % of xGnP loading and achieved maximum at 9 wt % and then it falls. Similar behaviour also noticed in ac conductivity study. The nature of charge carriers in the composites were investigated by utilising non-destructive impedance spectroscopy technique. The theoretical fitting of experimental data of Nyquist plot reveals all the compounds perform the bulk behaviour. Additionally, ac conductivity study validates Johnsher’s universal power law which confirms motions of the charges are translational one. I ∼ V characteristics of the studied samples were carried out by using Keithly electrometer which confirms that conduction behaviour was non-Ohmic at lower wt % xGnP loading but Ohmic conduction was achieved at higher wt % xGnP loading. From both impedance and I ∼ V study we have also confirmed the increases in conductance with increase in wt % of xGnP loading and shows similar phenomena as observed in dielectric study.

Structural, Dielectric, and Energy Storage Properties of Citric Acid and Ethylene Glycol Assisted Hydrothermally Synthesized Y2FeCoO6

Citric acid and ethylene glycol assisted hydrothermal synthesis of pure‐phase double perovskite oxide Y2FeCoO6 is reported. The Rietveld refinement confirm the orthorhombic phase formation with Pnma space group symmetry and lattice parameters as, a = 5.5039 Å, b = 7.4734 Å, and c = 5.2094 Å. The high‐resolution transmission electron micrographs exhibit formation of flakes, composed of agglomerated crystallites, oriented in [121] direction. The oxidation states of Fe as Fe3+ and Co as Co2+/Co3+ are observed by X‐ray photoelectron spectroscopy. The room temperature relative permittivity, 6.8 × 104, is found to increase to 1.3 × 107 at 473 K and frequency 500 Hz. The specific capacitance of ≈31.32 F g−1 is obtained at the current density of 1 A g−1. The effective charge storage involve the redox reactions of Fe2+/Fe3+, Co2+/Co3+, and Co3+/Co4+, and excellent capacitance retention of ≈99% is achieved after 5000 charging/discharging cycles at current density of 6 A g−1.

High permittivity BaTiO3 and BaTiO3-polymer nanocomposites enabled by cold sintering with a new transient chemistry: Ba(OH)2∙8H2O

Cold sintering process (CSP) offers a promising strategy for the fabrication of innovative and advanced high permittivity dielectric nanocomposite materials. Here, we introduce Ba(OH)2∙8H2O hydrated flux as a new transient chemistry that enables the densification of BaTiO3 in a single step at a temperature as low as 150 °C. This remarkably low temperature is near its Curie transition of 125 °C, associated with a displacive phase transition. The cold sintered BaTiO3 shows a relative density of 95 % and a room temperature relative permittivity over 1000. This new hydrated flux permits the fabrication of a unique dense BaTiO3-polymer nanocomposite with a high volume fraction of ceramics ((1-x) BaTiO3 – x PTFE, with x = 0.05). The composite exhibits a relative permittivity of approximately 800, at least an order of magnitude higher than previous reports on polymer composites with BaTiO3 nanoparticle fillers that are typically well below 100. Unique high permittivity dielectric nanocomposites with enhanced resistivities can now be designed using polymers to engineer grain boundaries and CSP as a processing method opening up new possibilities in dielectric materials design.

Rapid synthesis of dielectric tantalum-based oxynitrides

Perovskite-type oxynitride with a general formula of ATa(O,N)3 (A = Sr, Ba) is a class of promising dielectric material due to their very high permittivity. Conventional synthesis routes for these materials always require multiple processing steps, long durations and elevated temperatures. In this study, thermodynamic calculations were employed to predict the feasible synthesis reactions, possible impurities and reasonable processing parameters. Then, ceramic powders of SrTaO2N and BaTaO2N were fabricated through direct calcination of SrCO3/BaCO3 and Ta2O5 with urea as nitrogen source by using a modified pressureless spark plasma sintering set-up. High-purity oxynitrides can be obtained within 10 min. Thermal stability, corrosion resistance and dielectric property were evaluated. The results showed that SrTaO2N was thermally stable up to 475 °C in air while that temperature for BaTaO2N was 605 °C. The oxynitrides possessed a good resistance to hot water and strong acid/alkali. BaTaO2N had a very high room-temperature relative permittivity up to 9550 with a dielectric loss down to 0.001 at 100 Hz, while the values for SrTaO2N were 3141 and 0.017 respectively. The temperature dependence of permittivity for BaTaO2N was weak at −10–200 °C. The efficient synthesis method enabled the fast preparation of the tantalum-based oxynitride materials for energy storage applications.

Low loss tunable dielectric BaNd2Ti5O14 - (Ba0.5Sr0.5)TiO3 composite thick films

An alternative low cost flexible processing is utilized to fabricate tunable dielectric thick-films with low loss. By using a combination of electrophoretic deposition with chemical solution deposition, 9 μm-thick BaNd2Ti5O14-Ba0.5Sr0.5TiO3 (BNT-BST) composite films are fabricated with a room-temperature relative permittivity of 287 and a loss tangent of 0.0013 at 1 MHz. Moreover, a dielectric tunability and a figure of merit of 12% and 96 at 33 kV/cm, respectively, are obtained by the incorporation of highly tunable ferroelectric BST in a non tunable BNT matrix, thus fitting the requirements of tunable dielectrics for such agile systems as band pass filters.

Cold sintering and electrical characterization of lead zirconate titanate piezoelectric ceramics

This paper describes a cold sintering process for Pb(Zr,Ti)O3 ceramics and the associated processing-property relations. Pb(Zr,Ti)O3 has a very small, incongruent solubility that is a challenge during cold sintering. To circumvent this, a Pb(NO3)2 solution was used as the transient liquid phase. A bimodal lead zirconate titanate powder was densified to a relative density of 89% by cold sintering at 300 °C and 500 MPa. After the cold sintering step, the permittivity was 200, and the dielectric loss was 2.0%. A second heat-treatment involving a 3 h anneal at 900 °C increased the relative density to 99%; the resulting relative dielectric permittivity was 1300 at room temperature and 100 kHz. The samples showed well-defined ferroelectric hysteresis loops, having a remanent polarization of 28 μC/cm2. On poling, the piezoelectric coefficient d33 was ∼200 pC/N. With a 700 °C 3 h post-annealing, samples show a lower room temperature relative permittivity (950 at 100 kHz), but a 24 h hold time at 700 °C produces ceramics where there is an improved relative dielectric constant (1050 at 100 kHz).

Structural, dielectric, electromechanical, piezoelectric, elastic and ferroelectric properties of lanthanum and sodium co-substituted barium titanate ceramics

In this paper, the polycrystalline ceramics Ba(1-x) (La, Na)xTiO30≤x≤0.08 were synthesized by microwave assisted heating of the starting materials. Room temperature X-ray diffraction along with Rietveld refinement analysis confirmed the formation of single-phase polycrystalline compound with the tetragonal crystal structure. A dense microstructure with several grains having different size distribution throughout the sintered pellet has been observed. The incorporation of La3+ and Na+ ions in BaTiO3 enhanced the room temperature relative permittivity. The studies of the temperature dependence of dielectric permittivity indicate ferroelectric-paraelectric phase transition with a clear shift in the Curie temperature (Tc) of BaTiO3 towards lower temperature side on co-substitution. The co-substituted sample with x = 0.08 exhibited superior dielectric constant (ɛ' = 4226) with low dielectric loss (tanδ = 0.0113) which is highly essential for the fabrication of ceramic capacitors. Resonance and antiresonance characteristics of impedance and phase for poled Ba(1-x)(La,Na)xTiO3 samples have been investigated in the frequency range of 300 kHz-1 MHz. Based on IRE standards for piezoelectric ceramics the piezoelectric response has been discussed. The room temperature P-E loop is investigated at an applied electric field of 80 kV/cm at 33 Hz frequency using Precision Premier II.

Band gap narrowing in ferroelectric KNbO3-Bi(Yb,Me)O3 (Me=Fe or Mn) ceramics

The direct optical bandgap in ferroelectric KNbO3-Bi(Yb,Me)O3 (Me = Fe or Mn) ceramics fabricated by the solid state reaction method varies from 3.2 eV for KNbO3 down to 2.2 eV for 0.95KNbO3-0.05BiYbO3, as revealed by optical spectroscopic ellipsometry. This narrowing of bandgap is accompanied by an apparent increase of the room-temperature relative permittivity from 320 for KNbO3 to 900 for 0.95KNbO3-0.05BiYbO3. All compositions studied exhibit dielectric anomalies associated with structural phase transitions, and their ferroelectric nature is corroborated by the presence of a sharp mixed mode (at ∼190 cm−1) and by a Fano-type resonant dip in their Raman spectra.

Formation mechanism and characteristics of lanthanum-doped BaTiO3 powders and ceramics prepared by the sol–gel process

Pure and lanthanum-doped barium titanate nanopowders described by two different formulae, as Ba1−xLaxTiO3, for lower La concentrations (0≤x≤0.005) and Ba1−xLaxTi1−x/4O3 for higher La concentration (x=0.025) were prepared by an alkoxide sol–gel method. Single phase compositions were obtained after annealing at 900°C for 2h, in air. The increase of the lanthanum content causes structural and morphological changes in the oxide powders, including the evolution of the unit cell from tetragonal toward a cubic symmetry, the particle size decrease and a higher aggregation tendency.SEM investigations of the ceramics sintered at 1300°C for 4h indicate significant changes of the microstructural features (strong decrease of the average grain size and increase of the intergranular porosity) with the raise of La amount. Lanthanum addition to barium titanate prepared by sol–gel induces a more significant shift of the Curie temperature toward lower values, than that one reported in literature for ceramics of similar compositions, but processed by the conventional solid state method. The compositions with smaller La amount (x≤0.005) show semiconducting properties at room temperature and high relative dielectric permittivity values, while the undoped ceramics and those doped with higher La content (x=0.025) are good dielectrics. The ceramic with x=0.025 exhibits acceptable low losses, a very diffuse ferroelectric–paraelectric transition and Curie temperature closed to the room temperature, being thus susceptible for high tunability applications.

Preparation and X-Ray diffraction, dielectric, and Mössbauer characterization of Co1 − x Cu x Cr2O4 ceramics

Co1 − xCuxCr2O4 (0 ≤ x ≤ 1) ceramic samples have been characterized by room-temperature X-ray diffraction and relative dielectric permittivity ɛ(T) and loss tangent tanδ(T) measurements (at frequencies from 0.1 to 200 kHz) in the range 100–350 K. The samples were shown to consist of spinel solid solutions with a cubic (0 < x < 0.53) or tetragonal (0.53 < x < 1) structure. Increasing the Cu content of the samples increases their tanδ and electrical conductivity and produces anomalies in the temperature dependences ɛ(T) and tanδ(T) due to dielectric relaxation processes. Co1−xCuxCr2O4:0.0157Fe2O3 samples were characterized by Mossbauer spectroscopy in the range 77–290 K and shown to be in a magnetically ordered state at 77 K.

Study of Electrical and Aging Properties on the La-Doped Aurivillius Phase Ferroelectrics BaBi4Ti4O15

Aurivillius phase ferroelectrics Ba(Bi1−xLax)4Ti4O15(x=0-0.05) (BBiLxT) was synthesized by a modified high-temperature solid-phase route.The structure, the dielectric, the ferroelectric and the aging properties were investigated systematically. With the La3+doping, the room temperature relative permittivity of the samples is increased, and dielectric loss is decreased. For the BBiLxT phase, only a weak variation with respect to the F2mm space group can be suggested from single crystal X-ray diffraction. The microstructure confirms the samples have a well-proportioned grain size and a higher density. The substitution also results in a marked improvement in the remnant polarization. The doping of La3+in BBiLxT ceramics increased the room temperature relative permittivity aging properties.

Phase transition, microstructure and electrical properties of Fe doped Ba0.70Ca0.30TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of Ba 0.70 Ca 0.30 Ti 1− x Fe x O 3 ( x =0–0.03) have been synthesized by a conventional solid state reaction method. The influence of Fe content on the microstructure, phase transition, dielectric, ferroelectric, and piezoelectric properties is investigated systematically. The ceramics with x ≤0.02 are diphasic composites of tetragonal Ba 0.80 Ca 0.20 TiO 3 :Fe and orthorhombic Ba 0.07 Ca 0.93 TiO 3 :Fe solid solutions. The tetragonal phase is gradually suppressed as x increases, the ceramic with x =0.03 is found to have diphasic pseudocubic and orthorhombic phases. And the grain size is dependent on Fe content significantly. Introduction of Fe at B-sites improves the densification and decreases the sintering temperature. As x increases from 0 to 0.03, the room temperature relative dielectric permittivity enhances, dielectric loss decreases, and the Curie temperature decreases monotonically from 128 °C to 58 °C. However, the ferroelectricity enhances slightly and reaches the maximum near x =0.005, and then weakens with increasing x . On the other hand, the piezoelectric coefficient ( d 33 ) and the electromechanical coupling coefficient ( k p ) decrease simultaneously with increasing x , whereas the mechanical quality factor ( Q m ) increases significantly. The structure–electrical properties relationship is discussed intensively to give more information on (Ba,Ca)TiO 3 -based lead-free piezoelectric ceramics.

High Energy Density, High Temperature Capacitors Utilizing Mn‐Doped 0.8CaTiO3–0.2CaHfO3 Ceramics

Single layer air co‐fired capacitors with Pt internal electrodes were prototyped for the compositions 0.8CaTiO3–0.2CaHfO3 (CHT) and 0.5 mol% Mn‐doped 0.8CaTiO3–0.2CaHfO3 (CHT + Mn) to yield a material with a room‐temperature relative permittivity of εr ~170, thermal coefficient of capacitance (TCC) of ±15.8% to ±16.4% from −50°C to 150°C, and a band gap of ~4.0 eV. Impedance spectroscopy revealed that doping with Mn reduces both the ionic and electronic conductivity. Undoped CHT single layer capacitors exhibited ambient energy densities as large as 9.0 J/cm3, but showed a drastic decrease in energy density above 100°C. When doped with 0.5 mol% Mn, the temperature dependence of the breakdown strength was minimized, and energy densities similar to ambient values (9.5 J/cm3) were observed up to 200°C. At 300°C, energy densities as large as 6.5 J/cm3 were measured. The design rationale for these dielectrics centered on materials with large band gaps, linear or weakly nonlinear permittivities, and high breakdown strengths. These observations suggest that with further reductions in grain size and dielectric layer thickness, the CaTiO3–CaHfO3 system is a strong candidate for integration into future power electronics applications.

Effects of average and local structure on the dielectric behavior of (1−x)BaTiO3–xLaYO3 (≤x≤0.40) ceramics

The dielectric properties of dense ceramics of (1−x)BaTiO3–xLaYO3 (LBTY) (0≤x≤0.40) were characterized in the temperature range 10 to 450 K. The Curie temperature, Tc, of LBTY ceramics decreases at a rate of −23 K/at. % (La,Y) for x&amp;lt;0.10 but increases at +7 K/at. % (La,Y) for x≥0.20. The room temperature relative permittivity, εRT, decreases from ∼2000 for x=0.10 to ∼57 for x=0.40. This variation is accompanied by a substantial reduction in the temperature dependence of the relative permittivity, εr, and also by the emergence of relaxor ferroelectric-like behavior at x&amp;gt;0.05. The gradual transition from a classical ferroelectric to a relaxor-type response results from disruption of the long-range ferroelectric order, believed to be caused by a nanoclustering phenomenon. x=0.10 exhibits all the characteristic features of a relaxor-ferroelectric, i.e., εr decreases and tan δ increases with increasing frequency. For x&amp;gt;0.20 the relaxor behavior becomes progressively more subtle, suggesting a weaker coupling between the polar nanoregions. The poor microwave dielectric properties of LBTY ceramics, in particular for x=0.40, which exhibit εRT∼57 and a quality factor of ∼755 GHz are attributed to phase separation on the nanometer scale.

Microstructure and properties of Co-, Ni-, Zn-, Nb- and W-modified multiferroic BiFeO 3 ceramics

BiFeO 3 polycrystalline ceramics were prepared by the mixed oxide route and a chemical route, using additions of Co, ZnO, NiO, Nb 2O 5 and WO 3. The powders were calcined at 700 °C and then pressed and sintered at 800–880 °C for 4 h. High density products up to 96% theoretical were obtained by the use of CoO, ZnO or NiO additions. X-ray diffraction, SEM and TEM confirmed the formation of the primary BiFeO 3 and a spinel secondary phase (CoFe 2O 4, ZnFe 2O 4 or NiFe 2O 4 depending on additive). Minor parasitic phases Bi 2Fe 4O 9 and Bi 25FeO 39 reduced in the presence of CoO, ZnO or NiO. Additions of Nb 2O 5 and WO 3 did not give rise to any grain boundary phases but dissolved in BiFeO 3 lattice. HRTEM revealed the presence of domain structures with stripe configurations having widths of typically 200 nm. In samples prepared with additives the activation energy for conduction was in the range 0.78–0.95 eV compared to 0.72 eV in the undoped specimens. In co-doped specimens (Co/Nb or Co/W) the room temperature relative permittivity was ∼110 and the high frequency dielectric loss peaks were suppressed. Undoped ceramics were antiferromagnetic but samples prepared with Co or Ni additions were ferromagnetic; for 1% CoO addition the remanent magnetization ( M R) values were 1.08 and 0.35 emu/g at temperatures of 5 and 300 K, respectively.

Possible incipient ferroelectricity in Mn-doped Na1/2Bi1/2Cu3Ti4O12

The grain semiconductivity of Na1/2Bi1/2Cu3Ti4O12 ceramics is suppressed by several orders of magnitude by Mn-doping and Na1/2Bi1/2Cu2.82Mn0.18Ti4O12 ceramics exhibit high room temperature relative permittivity, εr, ∼140. εr data at 100 kHz fit the Barrett equation over the range ∼10–320 K and the magnitude and temperature dependence of εr are consistent with incipient ferroelectricity in this compound.

The influence of nanometric phase separation on the dielectric and magnetic properties of (1 − x)BaTiO3–xLaYbO3(0 ≤ x ≤ 0.60) ceramics

X-Ray diffraction analysis shows the co-solubility of La3+ and Yb3+ into BaTiO3 according to the formulae LaxBa1−xTi1−xYbxO3 (LBTYb) to be as high as x = 0.45. Raman spectroscopy analysis suggests the occurrence of continuous ion clustering with increasing x, which culminates with nanometric phase separation at x ≥ 0.35, as revealed by dark-field transmission electron microscopy. The room temperature relative permittivity, eRT, of LBTYb ceramics decreases from ∼1600 for x = 0 to ∼62 for x = 0.45. The Curie temperature, Tc, of LBTYb ceramics decreases at a average rate of ∼ 23 K/at% La/Yb for x ≤ 0.20. Relaxor-type behaviour is observed for 0.10 ≤ x ≤ 0.35. A nearly linear dielectric response is observed for 0.40 ≤ x ≤ 0.45, but below 25 K, er decreases sharply, whereas the magnetic susceptibility increases. The microwave dielectric properties of x = 0.40 ceramics are eRT ∼ 65 and tan δ ∼ 0.01 at ∼5 GHz. The high dielectric loss may be primarily associated with anharmonic phonon interactions resulting from the phase separation.

Processing and properties of 0.65Pb(Mg 1/3Nb 2/3)O 3–0.35PbTiO 3 thick films

We have investigated the processing of 0.65Pb(Mg 1/3Nb 2/3)O 3–0.35PbTiO 3 (PMN–PT) thick films on platinised alumina substrates. Nanosized PMN–PT powder with 2 mol% of excess PbO was prepared by high-energy milling and deposited on the substrate using screen-printing technology. The films were then sintered at 950 °C in a PbO-rich atmosphere. The influence of the sintering time and the amount of PbO-containing packing powder was studied and related to the structural, microstructural, dielectric and piezoelectric properties of the film. In order to obtain a homogeneous and dense thick film without any secondary phase, the PMN–PT films had to be sintered in the presence of a PbO-based liquid phase that had to be completely removed from the thick film during the final stage of the sintering. Under optimal sintering conditions we obtained a room temperature relative dielectric permittivity of 3600, dielectric losses of 0.036, a T m of 174 °C, a permittivity at the T m of 21,000 and a d 33 of 140 pC/N.