Frequency-dependent Dielectric Maximum Research Articles

Energy storage performance of Nd3+-doped BiFeO3–BaTiO3-based lead-free ceramics

Lead-free ceramics 0.7(Bi1-xNdx)[Fe0.95(Li0.5Nb0.5)0.05]O3-0.3BaTiO3+0.1 wt% MnO2 (x = 0–0.05) solid solutions were synthesized through a solid state sintering route. Phase analysis showed the formation of a single/mixed perovskite structure for all samples. A morphotropic phase boundary between rhombohedral R3c and cubic Pm3‾m appeared in all the samples. The microstructure analysis revealed well-densified ceramics with clear grains and grain boundaries. The dielectric measurement showed broadened and frequency-dependent dielectric maxima, indicating relaxor behavior. With an increase in Nd3+ concentration, the temperature of maximum relative permittivity (Tm) shifted from 564 °C to 330 °C (x = 0.05). The breakdown strength (BDS) was significantly enhanced from 200 kV/cm (x = 0) to 290 kV/cm (x = 0.03). A maximum recoverable energy (Wrec = 3.2 J/cm3) and a high conversion efficiency (η = 73.7%) was achieved for sample x = 0.03, showing promise for use in pulse power systems.

Relaxor ferroelectricity and low microwave dielectric permittivity of Sr(1-x)CexTi(1-2/3y)MgyO3 ceramics

The structural instability, relaxor ferroelectricity and microwave dielectric (MWD) properties of Sr(1-x)CexTi(1-2/3y)MgyO3 (sintered in 5%H2 and 95%N2 atmosphere) samples were systematically studied. The ceramic sample with x = 0.05 shows cubic symmetry by x-ray diffraction (XRD). However, for x ≥ 0.1 the existence of superlattice and peaks splitting, clarify the existence of tetragonal symmetry. For x = 0.1, the SEM-EDX maps indicates the formation of a complete solid solution with a dense microstructure. For all samples, the presence of a frequency-dependent dielectric maxima (ε′−T plot) and intrinsic ferroelectricity (PUND) clarifies the relaxor ferroelectric nature. More interestingly, the sample with x = 0.15 shows a low microwave dielectric permittivity (εr) of 19, temperature coefficient of resonance frequency (TCF, τf) of +87 ppm/°C, and the Q × f value of 302 GHz, respectively.

Study of structural, dielectric and AC conductivity properties of SrMoO4

Strontium molybdate (SrMoO4) compound is synthesized using a solid-state reaction route. SrMoO4 was observed to form in tetragonal Scheelite structure with I41/a space group and is confirmed with the help of powder X-ray diffraction studies. The temperature-dependent dielectric constant measured at different frequencies indicated a maximum at around 795 K. The frequency-dependent dielectric maximum reveals the presence of a dielectric relaxation near 795 K. Further, the Nyquist plot analysis shows a depressed semi-circle and manifest the non-Debye type dielectric relaxation in SrMoO4. The SrMoO4 compound possesses a negative temperature coefficient of resistance and is confirmed by fitting the Nyquist plot with a suitable equivalent circuit. The AC conductivity studies ascertain that the observed conduction mechanism in the SrMoO4 as a translational type correlated barrier hopping. The temperature-dependent AC conductivity reveals that the obtained activation energies are comparable with the oxygen vacancies and are responsible for observed dielectric relaxation.

High Temperature Dielectric Relaxation And Impedance Spectroscopy Studies On BaBiO3

BaBiO3 (BBO) particles were successfully synthesized through solid-state route, to provide better understanding of its transport properties, which is not well studied yet. X-ray diffraction (XRD) measurement confirmed that the particles were crystallized with monoclinic structure in single phase. The Raman spectrum of BBO sample revealed the existence of two different Bi sites (the octahedral BiO6/3 and the triangular pyramidal BiO4/2 cluster). Subsequently, the observation of low resolution and lattice scale imaging through high resolution transmission electron microscope (HRTEM) indicated the formation of monoclinic BBO particles of size ~ 50-60 nm. The ring pattern obtained from selected area electron diffraction (SAED) inveterate polycrystalline nature of the sample and calculated structural parameters well harmonized with XRD results. As expected, BBO showed semiconducting behavior with resistivity of ~ 3.8 kΩ-cm at room temperature along with an excellent NTC (negative temperature coefficient) thermistor characteristic. The dielectric measurements and impedance spectroscopy studies reveal that BBO exhibit two typical characteristics, i.e., diffuse phase transition and frequency dependent dielectric maxima, of relaxor oxides; with negative dielectric constant above 550 K. Copyright © 2016 VBRI Press.

Dielectric and multiferroic properties of 0.75BiFeO3–0.25BaTiO3 solid solution

Solid solution 0.75BiFeO3–0.25BaTiO3 (BFO–25 % BT) was prepared by solid state reaction method. Powder X-ray diffraction showed the morphotropic phase boundary (MPB) with the coexistence of both rhombohedral and cubic phases due to splitting in the line at 2θ = 39.7°. Scanning electron micrographs indicated that the ceramic has compact and uniform microstructure with average grain size <3 μm. The polarization vs applied electric field analysis showed an unsaturated hysteresis loop with the remnant polarization 12.95 μC/cm2 at 22 kV/cm for 0.75BiFeO3–0.25BaTiO3 ceramic. The calculations of diffuse parameter i.e. slope γ = 1.63 suggested a high degree of diffusion in BFO–BT lattice. The room temperature magnetic measurements confirmed the weak ferromagnetism of magnetization ~0.1 emu/gm at an applied magnetic field of H = 5 kOe for 0.75BiFeO3–0.25BaTiO3 ceramic. The high temperature magnetic and dielectric analysis suggested a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition Tc ~ 310 °C, which was responsible for the broad frequency dependent dielectric maxima. The impedance spectroscopy and complex modulus analysis confirmed the conventional relaxor, NTCR (negative temperature coefficient of resistance), giant ferroelectricity and polydispersive non-Debye type dielectric relaxation behaviour for 0.75BiFeO3–0.25BaTiO3 ceramic at 170 °C on 1 kHz with activation energy 2.33 eV. The modulus analysis also confirmed the possibility of hopping mechanism for electrical transport process in material.

Evidences of magneto-electric coupling in BFO–BT solid solutions

Abstract Multiferroic properties viz antiferromagnetism and ferroelectricity of BiFeO3 (BFO) has been reported to be enhanced by forming solid solution with BaTiO3 (BT) designated by BFO–BT. In the present investigations a few compositions in the solid solution (1−x)BiFeO3–xBaTiO3 (x = 0.10, 0.15 and 0.30) have been synthesized by solid state ceramic route. Structural, magnetic and electrical properties of single phase solid solution compositions of BFO–BT have been studied in detail to understand their multiferroic properties. Powder X-ray diffraction confirms the formation of solid solution. All the samples show ferromagnetic behavior at room temperature having low coercivity and high saturation magnetization. Substitution of BaTiO3 into BiFeO3 enhances dielectric and ferromagnetic responses and reduces electrical leakage. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition, which is responsible for the broad frequency dependent dielectric maxima. The impedance spectroscopy also confirms the origin of the structure.

Studies of structural and electrical properties on four-layers Aurivillius phase BaBi4Ti4O15

BaBi4Ti4O15 (BBT) ceramic was synthesized using mixed oxide route and the structural and electrical properties were investigated systematically. The structural studies confirmed it to be an n=4 member of the Aurivillius oxide. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed. The dielectric relaxation obeyed the Vogel–Fulcher relation wherein f0=8.37E+14Hz, Ea=0.13eV, and Tf=608.18K. The diffuseness parameter γ established the relaxor nature and it was attributed to the A-site cationic disorder. The specimen exhibited the excellent reproducibility in the measurements of displacement current, a remnant polarization of 5.4μC/cm2, and a coercive field of 4.03MV/m. The room temperature piezoelectric coefficient d33 was found to be 23pC/N and the field-induced strain S was about 0.018% at the 8MV/m electric field.

Structure, magnetic, and dielectric properties of (1-x)BiFeO3-xBaTiO3 ceramics

Structure, magnetization, and dielectric permittivity of (1-x)BiFeO3-xBaTiO3 (BFO-BT) ceramics have been studied as a function of BT content (x = 0.0, 0.1, 0.2, and 0.3). In situ synchrotron x-ray diffraction result of BFO reveals a rhombohedral (R)–orthorhombic (O)–cubic (C) phase transition near 820 and 850 °C upon heating. BFO-10%BT and BFO-20%BT exhibit a R–C transition near 760 and 740 °C, respectively. A C(R)–C transition takes place near 680 °C in BFO-30%BT. C(R) represents that a minor R phase coexists in the C matrix. A local minimum of R distortion angle αR occurs upon heating and implies ionic displacements. This anomaly is likely resulted from the antiferromagnetic (AFM)–paramagnetic (PM) transition and is responsible for the broad frequency-dependent dielectric maximum. BFO and BFO-10−30%BT ceramics exhibit a similar AFM behavior with magnetic susceptibility of about 8.2 × 10-6 emu/g·Oe at room temperature. This work suggests that BTO-substitution can enhance dielectric response and reduce the dielectric loss.

Synthesis and Magnetic Properties of $\hbox{BiFeO}_{3}$, ${(\hbox{BiFeO}_{3})}_{0.95}{(\hbox{BaTiO}_{3})}_{0.05}$, and $(\hbox{Bi}_{0.95}\hbox{Ba}_{0.05})(\hbox{Fe}_{0.95}\hbox{Ti}_{0.05})\hbox{O}_{3}$ Ceramics

Magnetization, grain size, structure, and temperature-dependent dielectric permittivity of BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , (BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.95</sub> (BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.05</sub> -(BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> )0.05(5%BTO-BFO), and (Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.95</sub> Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.05</sub> )(Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.95</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.05</sub> )O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> [5%(Ba, Ti)-BFO] ceramics have been carried out. BFO and 5%BTO-BFO exhibit an typical antiferromagnetic behavior, whose magnetization curve is linear with magnetic field at room temperature. The magnetic hysteresis loop of 5%(Ba,Ti)-BFO ceramic shows a weak ferromagnetic behavior with a small remanent magnetization of about 0.01 emu/g possibly due to a higher density in the grain matrix. This result also implies that the A-and B-site substitutions with Ba <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> and Ti <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> could efficiently suppress the spiral magnetic modulation. The magnetic susceptibilities of BFO, 5%BTO-BFO, and 5%(Ba,Ti)-BFO ceramics are about 1.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> , 5.43 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> , and 8.67 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> emu/gOe, respectively. Frequency-dependent dielectric maxima were observed in BFO, 5%BTO-BFO, and 5%(Ba,Ti)-BFO ceramics upon heating. This dielectric response is likely triggered by the antiferromagnetic-paramagnetic transition near the Neel temperature.

Magnetoelectric coupling and phase transition in BiFeO3 and (BiFeO3)0.95(BaTiO3)0.05 ceramics

In situ high-resolution synchrotron x-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) near 400 and 350 °C in BiFeO3 (BFO) and (BiFeO3)0.95(BaTiO3)0.05 (BFO–5%BT), respectively. It suggests a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition, which is responsible for the broad frequency-dependent dielectric maxima. A rhombohedral (R)–orthorhombic (O)–cubic (C) transition sequence takes place near 820 and 850 °C in BFO upon heating. BFO–5%BT exhibits a R–C transition near 830 °C. The BaTiO3 substitution can enhance dielectric and ferromagnetic responses and reduce electric leakage. The dielectric loss of BFO–5%BT remains less than 0.04 below 150 °C.

Relaxor behavior of BaBi 4Ti 3Fe 0.5Nb 0.5O 15 ceramics

Monophasic BaBi 4Ti 3Fe 0.5Nb 0.5O 15 (BBTFN) which exhibited relaxor ferroelectric properties has been synthesized via the solid-state reaction route. X-ray powder diffraction (XRD) studies carried out at room temperature confirmed the phase to be an n = 4 member of the Aurivillius family of oxides. The XRD pattern was indexed to an orthorhombic cell associated with lattice parameters a = 5.463 ( 3 ) Å , b = 5.443 ( 3 ) Å and c = 41.77 ( 2 ) Å . A broad dielectric peak associated with the frequency dependent dielectric maximum temperature was observed. The high temperature slope of the dielectric peak was characterized by the Lorenz-type quadratic law for relaxors. The dielectric relaxation was modeled using the Vogel–Fulcher relationship with activation energy E a = 0.017 ± 0.002 eV and freezing temperature T VF = 558 ± 1 K . Relaxor behavior and the incidence of ferroelectric hystersis ( P vs E ) loop at room temperature suggested the coexistence of long-range polar ordering with the polar nanoregions induced by compositional fluctuations.

Investigation of frequency dependent and independent dielectric maxima in relaxor ferroelectric thin films

Highly oriented Pb(Sc0.5Nb0.25Ta0.25)O3 (PSNT) thin films were prepared by pulsed laser deposition. The transmission electron microscopy studies showed an epitaxial strain between the layers due to the in-plane oriented heterostructure. PSNT showed a decrease in the frequency dependent dielectric maximum temperature (Tm) compared to the bulk and a frequency independent dielectric maximum at 520K around the Burns temperature (Td). The linear fit of the modified Curie-Wiess law at Tm provides γ∼2 and Δ=90K, indicating diffuse phase transition and strong relaxor behavior, further supported by nonlinear fitting of Vogel-Fulcher law. Well-behaved hysteresis loops indicated ferroelectric relaxor nature of the PSNT thin films.

Relaxor behavior of (K0.5Bi0.5)TiO3 ceramics derived from molten salt synthesized single-crystalline nanowires

Single-crystalline K0.5Bi0.5TiO3 nanowires have been fabricated by a large scale and facile molten salt synthetic method in a KCl medium. Pristine nanowires have diameters of about 40nm and lengths exceeding 4μm, and they possess tetragonal perovskite structure. The K0.5Bi0.5TiO3 ceramics with a relative density above 98% can be fabricated from high quality nanowires. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed, which can be well fitted by a modified Curie-Weiss law and a Vogel-Fulcher relationship. The suggested relaxor behavior in K0.5Bi0.5TiO3 composition is possibly due to the A-site compositional fluctuations at the nanolevel.

Relaxor behavior of K0.5La0.5Bi2Nb2O9 ceramics

K 0.5 La 0.5 Bi 2 Nb 2 O 9 , a relaxor, was synthesized and the structural studies confirmed it to be an n=2 member of the Aurivillius oxides. The 12{h00} and 12{hk0} types of superlattice reflections in the electron diffraction patterns reflected the presence of ordered polar regions. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed. The dielectric relaxation obeyed the Vogel-Fulcher relation wherein Ea=0.04eV, Tf=428K,and ωo=1010Hz. The diffuseness parameter γ=2.003 established the relaxor nature and it was attributed to the A-site cationic disorder. The piezoelectric d31 coefficient was 0.5pC∕N at 300K and 2pC∕N at 480K.

Relaxor behavior of K 0.5La 0.5Bi 2Ta 2O 9 ceramics

Potassium lanthanum bismuth tantalate (K 0.5La 0.5Bi 2Ta 2O 9), a new relaxor ferroelectric was synthesized via the solid-state reaction route. X-ray structural studies along with Rietveld refinement confirmed it to be an n = 2 member of the Aurivillius family of oxides and the refined lattice parameters are a = 5.512 ( 2 ) nm , b = 5.504 ( 2 ) nm and c = 25.072 ( 4 ) nm . The appearance of 1 / 2 { h 00 } and 1 / 2 { h k 0 } type superlattice reflections in the electron diffraction patterns reflected the presence of ordered polar regions. A broad dielectric peak associated with frequency dependent dielectric maximum temperature was observed. The value of the diffuseness parameter γ = 1.93 , obtained from the fit of a modified Curie–Weiss law established the relaxor nature of the title compound. The dielectric relaxation obeyed the Vogel–Fulcher relation wherein E a = 0.06 eV and T v f = 396 K . The relaxor behavior was attributed to the local polar ordering on A-sites.

DEGREE OF DIFFUSED PHASE TRANSITION AND NON-DEBYE DIELECTRIC RELAXATION INBa(NdxTi1-2xNbx)O3CERAMICS

Dielectric measurements were made over the temperature range 80–300 K at different frequencies (10 kHz, 50 kHz, 100 kHz, 500 kHz and 1 MHz). The degree of relaxor behavior and diffuseness of phase transition were correlated to the cationic disorder at lattice site B. Non-Debye dielectric behavior was observed in the present samples and a modified Arrhenius relation proposed by Chen et al. was found to best describe the frequency dependent dielectric maxima temperature.

A micro-Brillouin scattering study of the acoustic properties of PLZT relaxorceramics

Acoustic properties of the transparent relaxor ferroelectric ceramics of PLZT-10/65/35 andPLZT-7.6/72/28 were studied by the high-resolution micro-Brillouin scattering technique.The ceramics showed significant softening in the elastic constant and velocity of thelongitudinal acoustic (LA) phonon mode, a broad anomaly in the attenuation of the LAmode, and a frequency-dependent dielectric maximum. The temperature dependences ofthe acoustic anomalies could be explained qualitatively by using electrostrictive coupling,quadratic in order parameter and linear in strain. The interaction between the polar microregions is more pronounced at some percolation limit below the Burns temperatureTB,where the shear deformation develops due to polarization fluctuations, local electrostrictivestrain fields and tilting of the oxygen octahedra.

Different dynamic behaviors of Pb(Mg1/3Ta2/3)O3 and Ba(Mg1/3Ta2/3)O3 single crystals studied by micro-Brillouin scattering and dielectric spectroscopy

Acoustic and dielectric properties of Pb(Mg1/3Ta2/3)O3 (PMT) and Ba(Mg1/3Ta2/3)O3 (BMT) single crystals with B-site disorder were obtained in a wide temperature range by micro-Brillouin scattering and dielectric spectroscopy. The temperature dependences of both the dielectric constant and the Brillouin shift of the longitudinal acoustic (LA) mode of BMT showed that there is no structural phase transition below 860 K, consistent with thermal expansion measurements. A low dielectric constant ε∼20 of BMT reflected the low-level flux contamination. PMT crystals showed frequency-dependent dielectric maximum, significant softening of the Brillouin shift of LA mode deviating from the high-temperature linear behavior. The temperature dependence of the maximum relaxation time could be obtained by combining dielectric and acoustic data, which followed the Vogel–Fulcher law with a freezing temperature of 119±6 K. This temperature coincides with that estimated from the frequency dependence of the temperature of the dielectric maximum, which is the evidence of the real freezing of the relaxation-time spectrum of PMT at a finite temperature.

Dielectric, hypersonic, and domain anomalies of (PbMg1/3Nb2/3O3)1−x(PbTiO3)x single crystals

Dielectric permittivities, Brillouin backscattering spectra, polarization-electric field hysteresis loops, and domain structures have been measured as a function of temperature in relaxor-based ferroelectric single crystals (PbMg1/3Nb2/3O3)1−x(PbTiO3)x(PMN-xPT) for x=0.24 and 0.34. For PMN-24%PT, a diffuse phase transition which is associated with a broad frequency-dependent dielectric maximum was observed near 380 K. As the temperature increases, the PMN-24%PT crystal gradually develops cubic regions and is fully converted into the cubic state near 375 K. An extra dielectric anomaly appears at 370 K, possibly due to the percolating polar cluster induced by an external electric field. PMN-34%PT exhibits a nearly normal ferroelectric phase transition near 445 K from the tetragonal to the cubic phase. In addition, a weak diffuse phase transition observed near 280 K may result from partial conversion of rhombohedral phase to tetragonal phase. The dielectric thermal hysteresis confirms that the transitions near 280 and 445 K are diffuse first order and first order, respectively. The dielectric permittivities of PMN-24%PT and PMN-34%PT obey the relation, εm′/ε′(f,T)=1+[T−Tm(f )]γ/2δγ2, above the temperature of permittivity maximum Tm.