Dielectric Peak Temperature Research Articles

Structural evolution and dielectric properties of (Ba1−xNdx)(Ti1−yFey)O3 ceramics

Abstract The influence of donor and acceptor co-doping on structure and dielectric properties of (Ba 1− x Nd x )(Ti 1− y Fe y )O 3 (BNTF) ( x = 0.05, y = 0.01–0.07; and x = 0–0.08, y = 0.05) ceramics was investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), Raman spectroscopy, and dielectric measurements. When x y , two types of Nd 3+ –Fe 3+ and Fe 3+ – V O –Fe 3+ defect complexes formed and could not coexist, leading to the mixed phases of cubic and hexagonal. A single-phase ceramic with a cubic or tetragonal structure formed for x ⩾ y and the dielectric-peak temperature ( T m ) in BNTF with x = 0.05 decreased linearly with increasing y at a rate of −5 °C/mol% Fe ions. A high-k Y5V behavior can be realized at x = y = 0.05 (i.e., C-N5F5). The same concentrations of Nd 3+ and Fe 3+ formed Nd 3+ –Fe 3+ complexes, which could effectively suppress the dielectric loss and silence the 840 cm −1 band called “Raman charge effect” associated with Nd 3+ donors. C-N5F5 exhibited a cubic structure, medium-sized grains (3.3 μm), low dielectric loss ( e RT ′ = 6790). Defect chemistry associated with structure evolution is discussed.

Magnetic control of relaxor features in BaZr0.5Ti0.5O3 and CoFe2O4 composite

We report the effect of magnetic field on the dielectric response in a relaxor ferroelectric and ferromagnetic composite (BaZr0.5Ti0.5O3)0.65-(CoFe2O4)0.35. Relaxor characteristics such as dielectric peak temperature and activation energy show a dependence on applied magnetic fields. This is explained in terms of increasing magnetic field induced frustration of the polar nanoregions comprising the relaxor. The results are also consistent with the mean field formalism of dipolar glasses. It is found that the variation of the spin glass order parameter q(T) is consistent with increased frustration and earlier blocking of nanopolar regions with increasing magnetic field.

Ferroelectric Relaxor Behavior in Co-doped BCZT Ceramic

Ferroelectric relaxor behavior of Ba0.92-xCa0.08Ndx(Zr0.18Ti0.815Y0.0025Mn0.0025)O3 (x = 0, 0.5%, 1.0% and 2.0% mol) ceramics has been investigated. All the compositions have only tetragonal perovskite structure at room temperature. The dielectric peak constant of samples decrease and broaden, dielectric peak temperature (Tm ) shifts toward lower temperature as the content of Nd increases. Diffuse phase transition (DPT) and strong frequency dispersion can be observed. When Nd varied from 0 to 2.0% mol, the degree of deviation from the Curie-Weiss law (△Tm ) is from 62 to 108 and the parameter γ from 1.588 to 1.853 respectively. The ferroelectric relaxor behavior is discussed using the random field model.

DC field effect on dielectric property of Ba(ZrxTi1−x)O3 ceramics

Barium zirconate titanate Ba(ZrxTi1−x)O3 (BZT) ceramics have been fabricated by conventional solid state route. The dielectric properties and ferroelectric relaxor behavior were investigated as a function of Zr content and DC bias field. It was found that the relaxor behavior of BZT is enhanced with the increase in Zr content. The temperature of maximum dielectric peak (Tm) of BZT ceramic is greatly increased with DC bias field (E) up to a certain threshold field Et, below which Tm starts to increase gradually. This behavior could be associated with the size of domain. The relationship between temperature and dielectric tunability is also discussed in details.

Observation of relaxor ferroelectricity and multiferroic behaviour in nanoparticles of the ferromagnetic semiconductor La2NiMnO6

We report a diffuse phase transition (extending over a finite temperature range of ∼50 K) in sol–gel derived nanoparticles (∼25 nm) of the ferromagnetic double perovskite La2NiMnO6. The macroscopic polarization (P–E hysteresis loop), validity of the Vogel–Fulcher relation and high dielectric permittivity (∼9 × 102) confirm relaxor ferroelectric phenomena in these magnetic nanoparticles. Compared to the corresponding bulk sample, appreciably large enhancement of the magnetocapacitive effect (MC ∼ 30%) is observed even under low magnetic field (0.5 T) around the broad relaxor dielectric peak temperature (∼220 K), which is close to the ferromagnetic transition temperature (θf ∼ 196 K). All of these features establish the multiferroic character of the La2NiMnO6 nanoparticles. The inhomogeneities arising from chemical and valence mixing in the present La2NiMnO6 nanoparticles and the inter-site, Ni/Mn-site disorder along with surface disorder of the individual nanoparticles resulting in local polar regions are attributed to the observed dielectric behaviour of the nanoparticles. The wave vector dependent spin-pair correlation is considered to be the plausible cause of the colossal magnetocapacitive response near the transition temperature. High permittivity and large magnetocapacitive properties make these ferromagnetic La2NiMnO6 nanoparticles technologically important.

High‐permittivity and conduction mechanism of La‐doped Ba0.67Sr0.33TiO3 ceramics

AbstractHigh permittivity La‐doped Ba0.67Sr0.33TiO3 ceramics (BSTL) with cubic perovskite structure, i.e., BaxSr1−xTiO3 (BST) + x at.% La, where x = 0–1, were prepared by conventional ceramic processing techniques. Dielectric characteristics, X‐ray diffraction, scanning electron microscopy (SEM), and J–V (leakage current density–voltage) behaviors were measured. Doping with the La in the BST host lattice resulted in a large‐grained (1–3 µm) and fine‐grained (0.3–1 µm) microstructure, marked raising, and broadening of the Curie peak. The temperature of dielectric peak (Tm) at 10 kHz decreased rapidly with a doping concentration of <0.7 at.% La. By means of doping with La, high dielectric constant ceramics (BSTL: 0.2 ≤ x ≤ 0.7) with permittivity at room temperature (εRT) > 110 000 at 10 kHz have been achieved. The plots of leakage current density versus voltage show the different electrical conduction mechanism in different voltage ranges.

Diffuse Phase Transition of Ba0.92Ca0.08(Ti0.82Zr0.18)O3 Based Ceramics

Ba0.9175Ca0.08Nd0.0025(Zr0.18Ti0.8175-xYxMn0.0025)O3(x = 0, 0.5%, 0.75%, 1.0%, 1.5% and 2.0% mol) ceramics are synthesized by the conventional solid state processing. X-ray diffraction patterns show that all the compositions have an only tetragonal BaTiO3 structure at room temperature. The dielectric constant of samples decrease, dielectric peak temperature (Tm ) shifts toward lower temperature and the frequency dispersion becomes strong and the more pronounced DPT (Diffuse Phase Transitions) behavior as the content of Y increases. The degree of deviation from the Curie–Weiss law is found to increase and the value of the parameter γ is from 1.82 to 1.96 with the increasing amount of Y3+.

Characterization of Dielectric Relaxation of Relaxor Ferroelectrics

The concept ‘relaxativity’ is proposed to describe the degree of dielectric relaxor in relaxor ferroelectrics, like the ‘fragility’ in supercooled liquid in describing glass forming ability during vitrification process. The calculated results of Pb(Mg1/3Nb2/3)O3-PbTiO3 relaxors and BaTiO3-BaZrO3 relaxors exhibit good coincidences with the intervals between their dielectric peak temperatures. The larger relaxativity is corresponding to larger configurational entropy and smaller spatial correlation length, or stronger local interactions for a relaxor.

Low-temperature polaronic relaxations with variable range hopping conductivity in FeTiMO6(M=Ta,Nb,Sb)

Low-temperature dielectric measurements on FeTiMO(6) (M = Ta,Nb,Sb) rutile-type oxides at frequencies from 0.1 Hz to 10 MHz revealed anomalous dielectric relaxations with frequency dispersion. Unlike the high-temperature relaxor response of these materials, the low-temperature relaxations are polaronic in nature. The relationship between frequency and temperature of dielectric loss peak follows T(-1/4) behavior. The frequency dependence of ac conductivity shows the well-known universal dielectric response, while the dc conductivity follows Mott variable range hopping (VRH) behavior, confirming the polaronic origin of the observed dielectric relaxations. The frequency domain analysis of the dielectric spectra shows evidence for two relaxations, with the high-frequency relaxations following Mott VRH behavior more closely. Significantly, the Cr- and Ga-based analogs, CrTiNbO(6) and GaTiMO(6) (M = Ta,Nb), that were also studied, did not show these anomalies.

Single Phase Formation and Electric Properties of Bismuth Niobium Based Perovskite-Type Oxides

The structural, and dielectric and piezoelectric properties of (1-x)BaTiO3 – x Bi1/2K1/2(X1/3Nb2/3)O3(X=Cu, X=Mg or X=Zn) ceramic were studied. The single perovskite phase was observed when x≤0.5 for X=Cu and Mg and x≤0.2 for X=Zn. As x increased, the dielectric constant peak temperature and piezoelectric properties continuously decreased for X=Mg and Zn. On the other hand, those of X=Cu possessed a local maxima at x=0.7 and the peak temperature was 200°C and the large field piezoelectric constant,d33*, was 94 pC/N.

The Phase Transition Behavior of (1−x)Pb(Sc0.5Ta0.5)O3-(x)PbHfO3 Ceramics

The phase transition behavior of (1−x)Pb(Sc0.5Ta0.5)O3–(x)PbHfO3 [PSTH(x), x=0, 0.05, and 0.10] ceramics was investigated by transmission electron microscopy (TEM), dielectric properties under dc bias, and hysteresis loop measurements at several temperatures. TEM showed 5–10 nm cation-ordered regions were embedded in a disordered matrix for PSTH(0.10), which indicated it was a typical relaxor ferroelectric. By fitting the dielectric constant-temperature characteristics, it was found that application of an electric field could induce the relaxor ferroelectric transforming into normal ferroelectric. The maximum dielectric constant of the PSTH(x) ceramics exhibited different trends under dc bias, which was because PSTH(0) underwent the first-order-like phase transition, PSTH(0.10) underwent the second-order-like transition, while PSTH(0.05) lied somewhere in between. The argument was confirmed by the different changes of hysteresis loops above dielectric peak temperature under 40 kV/cm.

Dielectric properties and depolarization temperature of Bi 0.5(Na, K) 0.5TiO 3–BiFeO 3 lead-free ceramics

The (1− x− y)Bi 0.5Na 0.5TiO 3– xBi 0.5K 0.5TiO 3– yBiFeO 3 lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method. The microstructure, dielectric properties, phase transition temperature and depolarization temperature of the ceramics were investigated. The phase structure of the ceramics is a pure perovskite phase at x≤0.21, and a second phase of K 4Ti 3O 8 is observed at x>0.21. A method to obtain depolarization temperature by temperature dependence of electromechanical coupling factor k p, poling phase angle θ max has been proposed. The relation of temperature between depolarization and phase transition was studied by temperature dependence of dielectric properties. It is found that depolarization temperature is very close to the temperature of dielectric loss peak, and both temperatures are lower than that of ferroelectric to anti-ferroelectric phase transition. The depolarization temperature of the ceramics decreases linearly with the increase of BiFeO 3, and first decreases and then increases with the increase of Bi 0.5K 0.5TiO 3. The temperature of ferroelectric to anti-ferroelectric phase transition shifts insignificantly with the increase of BiFeO 3.

Phase Transitions of the Mixed System (Rb1−x Cs x )2MnI4

The mixed system (Rb 1 − x Cs x ) 2 MnI 4 was synthesized over full range of x by Bridgman method and the phase transitional properties was investigated. The melting point T m , α-β phase transition point T α−β and dielectric peak temperature T C of both Rb 2 MnI 4 and Cs 2 MnI 4 were obtained as the function of x. Obtained results were discussed in connection with supercooling of α−β phase transition.

Ag2O가 첨가된 0.65PbMg1/3Ta2/3)O3-0.35PbTiO3고용체의 유전, 초전 특성

Ferroelectric samples of the 0.65Pb modified with were prepared by sintering at for 4 h. The fractured surface of sintered pellets were examined by scanning electron microscopy(SEM). The dielectric constant, loss, and pyroelectric coefficient of the ceramics samples were determined. The dielectric and pyroelectric properties could be improved with the addition of small amount of up to 0.2 mol%. The dielectric and pyroelectirc peak temperatures are continuously shifted to lower temperature with addition of small amounts of .

ZrO2첨가에 따른 Pb(Mg1/3Ta2/3)O3-PbTiO3고용체의 강유전 특성 연구

The 0.65Pb(Mg1/3Ta2/3)O3-0.35PbTiO3 (PMT-PT)ceramics were near morphotropic phase boundary. The dielectric constant, the loss, and pyroelectric coefficient of the ceramics were measured as a function of temperature (25 ℃ ~ 250 ℃). The dielectric constant, the loss, and the pyroelectric coefficient could be improved with the addition of small amounts of ZrO2 up to 0.2 mol%. The dielectric and pyroelectric peak temperature are slightly shifted to lower temperatrues with the addition of amount of ZrO2.

Diffuse phase transition of BaTi0.6Zr0.4O3 relaxor ferroelectric ceramics

BaTi0.6Zr0.4O3 ceramic was prepared through solid state reaction route. X-ray diffraction showed that the composition has cubic perovskite structure with space group Pm-3m at room temperature. Temperature dependency dielectric study of the ceramic has been investigated. Bulk density was determined using Archimedes principle and found to be ∼97% of X-ray density. The average grain size in the pallet is measured by an optical microscope and found to be 22.23 µm. The dielectric measurement revealed diffuse phase transition of second-order, where dielectric peak temperature (T m) is dependent of frequency showing relaxor-type behaviour. A clear deviation from Curie–Weiss law is observed in the paraelectric region. The dielectric relaxation rate follows the Vogel–Fulcher relation with E a = 0.1020 eV, T f = 106 K, ν0 = 8.5 × 1011 Hz.

High-temperature relaxor ferroelectric behavior in Pr-dopedSrTiO3

Temperature-dependent Raman scattering, dielectric, and powder x-ray diffraction studies have been carried out on Pr-doped $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ ceramic samples. Activation of $\mathrm{T}{\mathrm{O}}_{2}$ and $\mathrm{T}{\mathrm{O}}_{4}$ polar modes indicated increasing degree of polar distortion by Pr doping. Dielectric measurements revealed that the system exhibits dielectric relaxation peaks at $\ensuremath{\sim}500\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The softening tendency of the polar $\mathrm{T}{\mathrm{O}}_{1}$ soft mode decreases with increasing Pr doping. X-ray diffraction results show no evidence of symmetry breaking across the dielectric peak temperatures. The system exhibits features of high-temperature relaxor ferroelectrics.

A novel high-k ‘Y5V’ barium titanate ceramics co-doped with lanthanum and cerium

Structural, dielectric, and ferroelectric properties of a novel high-k ‘Y5V’ (Ba 1− x La x )(Ti 1− x /4− y Ce y )O 3 ceramics (where x=0.03 and y=0.05, denoted by BL3TC5) with the highest ‘Y5V’ dielectric response ( ε′>10 000) among rare-earth-doped BaTiO 3 ceramics to date are investigated in detail using SEM, TEM, XRD, DSC, EPR, Raman spectroscopy (RS), temperature and frequency, electric field dependences of dielectric permittivity ( ε′), and temperature and electric field dependences of ferroelectric hysteresis loops. The BL3TC5 diffusion of ferroelectric phase transition occurs around dielectric peak temperatures ( T m) near a room temperature characteristic of dielectric thermal relaxation. Powder XRD data and defect complex model were given. “Relaxor” behavior associated with an order/disorder model and formation of a solid solution were discussed. The EPR results provided the evidence of Ti vacancies as compensating for lattice defects. High-k relaxor nature of BL3TC5 is characterized by an average cubic structure with long-range lattice disordering and local polar ordering; a slow change of the ε′ ( T) and P r( T) curves around T m; no phase transition observed by DSC; and a broad, red-shifted A 1 (TO 2) Raman phonon mode at 251 cm −1 accompanying the disappearance of the “silent” mode at 305 cm −1 and a clear anti-resonance effect at 126 cm −1 at room temperature.

Phase Transitions of the Mixed System of (Rb1 − xCsx)2ZnI4

The mixed system of (Rb 1− x Cs x ) 2 ZnI 4 was prepared over full range of x by Bridgman method and the phase transitional properties were investigated. The melting point T m , α − β phase transition point Tα −β and dielectric peak temperature T C of both Rb2ZnI4 and Cs 2 ZnI 4 were obtained as the function of x. Obtained results were discussed in connection with supecooling of α − β phase transition.

Powder neutron diffraction study of phase transitions in and a phase diagram of(1−x)[Pb(Mg1∕3Nb2∕3)O3]−xPbTiO3

Dielectric, piezoelectric resonance frequency, and powder neutron diffraction studies as a function of temperature have been performed on several compositions of $(1\ensuremath{-}x)[\mathrm{Pb}({\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}){\mathrm{O}}_{3}]\text{\ensuremath{-}}x\mathrm{Pb}\mathrm{Ti}{\mathrm{O}}_{3}$ $(PM\mathrm{N}\text{\ensuremath{-}}x\mathrm{PT})$ ceramics in and outside the morphotropic phase boundary (MPB) region to investigate the phase transitions and phase stabilities in this mixed system. Anomalies in the temperature dependence of piezoelectric resonance frequency and dielectric constant are correlated with structural changes using Rietveld analysis of powder neutron diffraction data. The frequency dependent dielectric studies reveal relaxor ferroelectric behavior for $x<0.35$ and a normal ferroelectric behavior for $x\ensuremath{\geqslant}0.35$. The dielectric peak temperature and the Vogel-Fulcher freezing temperature are found to increase linearly with ``$x$'' while their difference, after decreasing linearly with $x$, vanishes at $x=0.35$ suggesting a crossover form relaxor ferroelectric to normal ferroelectric behavior at this composition. A phase diagram of the $\mathrm{PMN}\text{\ensuremath{-}}x\mathrm{PT}$ system showing the stability fields of ergodic relaxor, monoclinic ${M}_{B}$, monoclinic ${M}_{C}$, tetragonal and cubic phases is presented. Our results suggest the presence of a succession of three phase transitions, not reported earlier, corresponding to structural changes from the monoclinic ${M}_{B}$ to the monoclinic ${M}_{C}$ to the tetragonal to the cubic phases for $0.27\ensuremath{\leqslant}x\ensuremath{\leqslant}0.30$ on heating above room temperature. In addition, our studies confirm the earlier findings on transitions from the monoclinic ${M}_{C}$ to the tetragonal to the cubic phases for $0.31\ensuremath{\leqslant}x\ensuremath{\leqslant}0.34$ on heating above room temperature and tetragonal to monoclinic ${M}_{C}$ phase on cooling below room temperature for $x=0.36$. All these transitions are found to be accompanied with anomalies either in the temperature dependence of dielectric constant or the piezoelectric resonance frequency or both. Rietveld analyses of the powder neutron diffraction data at various temperatures on a pseudorhombohedral composition with $x=0.25$ suggest that the short range ${M}_{B}$ type monoclinic order present at room temperature grows to long range monoclinic order on lowering the temperature. The temperature variations of the unit cell parameters and atomic shifts are also presented to throw light on the nature of the various phase transitions in this mixed system.