Temperature Of Maximum Dielectric Constant Research Articles

Low-Temperature Sintering of Bi(Ni0.5Ti0.5)O3-BiFeO3-Pb(Zr0.5Ti0.5)O3 Ceramics and Their Performance.

A low-temperature sintering strategy was realized for preparing 0.21Bi(Ni0.5Ti0.5)O3-0.05BiFeO3-0.74Pb(Zr0.5Ti0.5)O3 (0.21BNT-0.05BF-0.74PZT) ceramics by conventional ceramic processing by adding low melting point BiFeO3 and additional sintering aid LiBO2. Pure perovskite 0.21BNT-0.05BF-0.74PZT ceramics are prepared at relatively low sintering temperatures, and their structure presents tetragonal distortion that is affected slightly by the sintering temperature. The 1030 °C sintered samples have high densification accompanied by relatively large grains. All ceramics have excellent dielectric performance with a relatively high temperature of dielectric constant maximum, and present an apparent relaxation characteristic. A narrow sintering temperature range exists in the 0.21BNT-0.05BF-0.74PZT system, and the 1030 °C sintered 0.21BNT-0.05BF-0.74PZT ceramics exhibit overall excellent electrical performance. The high-temperature conductivity can be attributed to the oxygen vacancies' conduction produced by the evaporation of Pb and Bi during sintering revealed by energy dispersive X-ray measurement.

Investigation of Dielectric, Ferroelectric, and Strain Responses of (1- x)[0.90(Bi0.5Na0.5)TiO3 - 0.10SrTiO3] - xCuO Ceramics.

The low-temperature sintering of (Bi0.5Na0.5)TiO3-based ceramics can be achieved by sintering aid CuO. Piezoelectric ceramics (1 - x)[0.90(Bi0.5Na0.5)TiO3 - 0.10SrTiO3] - xCuO (BNT-ST-Cu) with x = 0, 0.01, 0.02, 0.03, and 0.04 were prepared through the mixed oxide route. A tetragonal structure was indexed for the undoped sample. Its structure was found to be changed to a pseudocubic when Cu was added. For undoped Cu samples, the sintering temperature (T s) for sufficient densification was 1160 °C. However, T s was reduced to 1090-1120 °C for Cu-added specimens. Field emission scanning electron microscopy (FE-SEM) showed a uniform and dense grain morphology for all samples. The maximum dielectric constant temperature (T m) was decreased with the doping concentration of Cu and applied frequency. The strain was increased with Cu concentration and had the maximum value of 500 pm/V for the sample x = 0.02 with symmetric and slim strain loops.

Non-trivial Behavior of Temperature of Dielectric Constant Maximum in (Pb/La)(Zr/Ti)O3 9/65/35 Relaxor Ferroelectric Ceramics Detected by Acoustic Emission

9/65/35 PLZT relaxor was studied under a bias electric field using the acoustic emission method. It was established that the temperature of smeared dielectric constant maximum exhibits the V-shape, lying fully within the ergodic phase, as well as that the threshold electric field is found to be approximately the same as in both PMN-0.24PT and PFN-0.02PT relaxors. A reason of the latter phenomena is discussed from the viewpoint of incorporated ions properties.

Investigations on structural, dielectric, and impedance properties of ecofriendly Ho3+ / Nb5+ co-substituted Na0.5 Bi0.5TiO3

The lead-free, 0.5 mol% of Ho3+ substituted Na0.5 Bi0.5TiO3 (Na0.5Bi0.495Ho0.005TiO3) has been modified by Nb+5 substitution at the Ti-site to improve the relaxor nature and physical properties. Enhancement in relaxor characteristics was found through polarization loop and the bipolar strain studies. The slanted polarization loop showed slightly better recoverable energy storage density as compared to the square loop at the moderate electric field of ≈ 85 kV/cm. Maximum dielectric constant temperature (Tm) and depolarization temperature (Td) shifted towards the lower region with Nb5+ substitution along with decreased average grain size. The Cole-Cole plots portrayed the single semicircle for all the compositions at higher temperatures which confirms the Debye-type behavior due to the grain interiors. The decrement in the grain resistance with increase in temperature depicted the negative temperature coefficient of resistance (NTCR) behavior like the semiconductor materials. The 3 mol% of Nb5+ substituted composition exhibited improved insulating character at higher temperatures as compared to Na0.5Bi0.495Ho0.005TiO3. It is advantageous to use the material for high-temperature dielectric applications.

Relaxor-normal ferroelectric transition in (1−x)Sr0.75Ba0.25Nb2O6–xNaNbO3 ceramics

(1−x)Sr0.75Ba0.25Nb2O6–xNaNbO3 (x = 0–0.8) ceramics were prepared by the traditional solid-state reaction method. The x = 0–0.4 ceramics preserve the tungsten bronze phase with a gradually unfilled–filled structure evolution accompanying a relaxor-normal ferroelectric transition. This transition process is accompanied by an increase in the maximum dielectric constant temperature or Curie temperature (Tc), enhancement of room temperature ferroelectric and piezoelectric properties, and appearance of the stripe domain. On the other hand, ceramics with x > 0.4 consist of coexisting tungsten bronze and perovskite phases, for which Tc slightly fluctuates, and the ferroelectric and piezoelectric properties decrease with increasing x. This work provides a feasible way to manipulate the relaxor-normal ferroelectric transition and the electrical properties of the tungsten bronze family.

Influence of weak ac electric field on the temperature of dielectric maximum of (1-x)PbMg1/3Nb2/3O3-xPbTiO3 relaxor ferroelectric single crystals based on acoustic emission data studies

(1-x)PbMg1/3Nb2/3O3-xPbTiO3, [100]-oriented relaxor ferroelectric crystals were studied by means of dielectric and acoustic emission methods in dependence on temperature and under ac measuring electric field with several values and frequencies. The dependence of temperature of dielectric constant maximum on and without ac field value and frequency was plotted. Also a scatter of the temperature of dielectric constant maximum was calculated in dependence on ac field frequency. Such the phenomenon was discussed from a point of view of growth of the polar nanoregions on cooling.

Composition-dependent electrical property of (1-x)Sr0.75Ba0.25Nb2O6-xPbZr0.52Ti0.48O3 solid solution ceramics

Solid solution ceramics of (1-x)Sr0.75Ba0.25Nb2O6-xPbZr0.52Ti0.48O3 (x = 0−0.4) were prepared and investigated. The phase evolves from tungsten bronze for x = 0, coexisted tungsten bronze and pyrochlore at x = 0.3, to pyrochlore for x> 0.3. As the results, the ceramics show dramatically composition dependent microstructure and electrical property. The grain shape changes from anisotropic pillar-like with maximum length-diameter ratio of 3.3 at x = 0.2 to isotropic cubic-like for x> 0.2. At the same time, the maximum dielectric constant temperature tends to decrease with an exceptional increase at x = 0.3 due to the coexisted phases. Interestingly, the x = 0.3 ceramic endures ultrahigh breakdown strength of 340 kV/cm, which, together with enhanced polarization, results in maximum recoverable energy storage density of 3.0 J/cm3and energy storage efficiency of 81.5 % at room temperature.

Dielectric, ferroelectric, and strain properties of lead-free (1−y)BNT–yST ceramics

Lead-free ceramics (1−y) (Bi1/2Na1/2)TiO3–ySrTiO3 (1−y)BNT–yST with y = 0, 0.1, 0.20, 0.25, 0.28, 0.30, and 0.32 were synthesized via a solid-state reaction process. A uniform grain morphology was obtained, and the mean grain size was around 2.0 μm for y = 0, which decreased slightly for y > 0. The undoped compound displayed a crystal structure with rhombohedral symmetry, and increasing amounts of ST gradually transformed the material to cubic phase. The maximum dielectric constant temperature (Tm) was observed to decrease from 305 °C for sample y = 0 to 135 °C for sample y = 0.30. Remnant polarization (Pr) decreased with increasing ST, and the ferroelectric loops narrowed. The coercive field (Ec) was also observed to decrease with enhanced ST content; however, Ec and Pr increased for y = 0.30. The electric field-induced strain gradually increased up to y = 0.28 but decreased for y > 0.28. The loops of strain became slimmer and saturated with increasing ST ratio to attain the maximum dynamic strain of 624 pm/V.

Effect of BaZr0.4Ti0.6O3 addition on electrical and magnetic properties of multiferroic (1-x)BiFeO3-xBaTiO3 ceramics

The composite 0.75(1-x)BiFeO3-xBaTiO3-0.25BaZr0.4Ti0.6O3 or 0.75(BFO-BTO)-0.25BZT ceramics (x = 0.23–0.27) have been prepared by solid state reaction method to studied the relationship between phase formation, dielectric and magnetic properties. The results found that the phase formations of calcined BFO-BTO and BZT powders are distorted rhombohedral and cubic structure, respectively. Moreover, the addition of BZT in BFO-BTO-BZT ceramics affected to the phase change dramatically according to increasing of BZT content compared to calcined BFO-BTO powders. All the samples showed cubic perovskite structure. The room temperature dielectric properties decreased with increasing of BTO content, the highest dielectric constant with low losses observed in 0.75(0.77BFO-0.23BTO)-0.25BZT ceramic. Furthermore, the ceramics displayed maximum dielectric constant temperature (Tm) above 360 °C. Interestingly, all ceramic compositions exhibited typical ferromagnetic hysteresis loop and the highest remanent magnetization observed in 0.75(0.77BFO-0.23BTO)-0.25BZT ceramic.

Preparation and dielectric properties of Ba4RFe0.5Nb9.5O30 (R = La, Nd, Eu, Gd) unfilled tungsten bronze ceramics

Lead-free relaxor ferroelectrics with the general structural formula Ba4RFe0.5Nb9.5O30 (R = La, Nd, Eu, Gd) (BRFN) were prepared using a standard solid-state sintering route, and the influence of the A site ion occupation on their electrical properties and dielectric characteristics was systematically discussed based on their structure. All compounds presented tetragonal tungsten bronze (TTB) structure with space group P4bm, where the A1 sites were exclusively occupied by R3+ ions and the A2 sites were exclusively occupied by Ba2+ ions, while the Fe3+ and Nb5+ ions were randomly distributed between the B1 and B2 sites. Furthermore, frequency and temperature caused BRFNs to present a broad permittivity peak accompanied by wide frequency dispersion. The maximum dielectric constant temperature gradually increased and the frequency dispersion gradually decreased as the A1-site ion size decreased. Complex impedance spectroscopy indicated that only the grain boundaries contributed to the conductive behavior of BRFN ceramics at high temperature, and the activation energy increased as the A1-site ion size decreased. The direct current (DC) conductivity of all compounds originated from the electrons generated by the second ionization of the oxygen vacancies and might have been caused by the hybrid conduction mechanism of the oxygen-vacancy ions and electrons. Raman spectra of the BRFN ceramics mostly contained multi-component and broad bands related to the internal vibrations of the octahedral NbO6, and as the size of the A1-site ion decreased, the Nb-O stretching changed.

Enhanced dielectric and piezoelectric properties in Na0.5Bi4.5Ti4O15 ceramics with Pr-doping

The bismuth layer-structured Na0.5Bi4.5-xPrxTi4O15 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) (NBT-xPr3+) ceramics were fabricated using the traditional solid reaction process. The effect of different Pr3+ contents on dielectric, ferroelectric and piezoelectric properties of Na0.5Bi4.5Ti4O15 ceramics were investigated. The grain size of Pr3+-doping ceramics was found to be smaller than that of pure one, the maximum dielectric constant and Curie temperature Tc gradually decreased with increasing Pr3+ contents, and the dielectric loss decreased at high temperature by Pr3+-doping. Moreover, the activation energy (Ea), resistivity (Z’), remanent polarization (2Pr) and piezoelectric constant (d33) increased by Pr3+-doping. The NBT-xPr3+ ceramics with x = 0.3 achieved the optimal properties with the maximum dielectric constant of 1109.18, minimum loss of 0.00822 (250 kHz), Ea of 1.122 eV, Z’ of 7.9 kΩ cm (725 ºC), d33 of 18 pC/N, 2Pr of 12.04 μC/cm2. The enhancement was due to the addition of Pr3+ which suppressed the decreasing of resistivity at high temperature and made it possible for NBT-xPr3+ ceramics to be poled in perpendicular direction, implying that it is a great improvement for Na0.5Bi4.5Ti4O15 ceramics in electrical properties.

Dielectric and piezoelectric properties of Cr2O3-doped PLZT (7/65/35) hot pressed ceramics

Single phase PLZT (7/65/35) ceramics doped with Cr2O3 [0,0.05, 0.08, 0.18, 0.30 0.50, 0.75 and 1.0 wt%] were synthesized by high temperature solid-state reaction technique accompanied by hot pressing. XRD studies revealed that the chromium doping reduces the lattice parameter of PLZT (7/65/35) without changing its crystal structure. A relaxor like behavior with decrease in temperature of dielectric constant maxima (Tm) was observed with increase in chromium content. A sharp rise in the conductive losses were observed for higher chromium (≥0.08 wt%) contents. The room temperature dielectric constant (ε′RT) and electromechanical coupling coefficient (k31) showed maxima value for 0.08 wt% Cr2O3 doped PLZT (7/65/35) ceramic. The results were interpreted on the basis of multiple valence nature of chromium.

Effect of ZnO addition on ferroelectric properties of 0.94Pb(Fe1/2Nb1/2)O3-0.06PbTiO3 and 0.9Pb(Fe1/2Nb1/2)O3-0.1PbTiO3 ceramics

ABSTRACTRelaxor and ferroelectric materials are outstanding for electronic application, indicating kind of ferroelectric material is still ambiguously due to different behavior of stoichiometric ratio of precursors. The samples of 0.94Pb(Fe1/2Nb1/2)O3-0.06PbTiO3 (PFNT94/6) and 0.9Pb(Fe1/2Nb1/2)O3-0.1PbTiO3 (PFNT90/10) were mixed with ZnO at 0, 1, 2, and 3 wt.%, and were synthesized using mixed oxide. Phase transition and microstructure were analyzed by using X–ray diffractometer (XRD) and SEM technique, respectively. The results showed that PFNT94/6-xZnO and PFNT90/10-xZnO shifted to tetragonal phase and suppressed pyrochlore phase when increasing ZnO content. Grain size decreased with increasing ZnO contents in range of 0.89–2.18 µm of PFNT94/6 due to coarsening processes dominate, the production of a highly porous is easily be found and decreased the average grain size, conversely, grain size increased with increasing ZnO contents in range of 3.15–11.52 µm of PFNT90/10. The PFNT94/6 exhibits broaden peak of dielectric constant, meanwhile, the dielectric constant maximum temperature at 144°C of PFNT90/10. The dispersion of dielectric constant decreases with increasing ZnO contents. The relaxor ferroelectric of PFNT90/10 ceramic shifted to normal ferroelectric with increasing ZnO contents. Ferroelectric properties were investigated on polarization electric field, polarization of PFNT94/6 exhibited relaxor ferroelectric at low field, PFNT90/10 showed normal ferroelectric as well as endurable breakdown. The relaxor ferroelectric material can be modified to ferroelectric material by adding ZnO.

Effect of Cr2O3 modification on dielectric, ferroelectric and field-induced strain properties of 0.18Pb(Mg1/3Nb2/3)O3–0.82Pb(Zr0.49Ti0.51)O3 ceramics

A systematic investigation was performed to study the effect of Cr2O3 on dielectric, ferroelectric and field-induced strain properties of 0.18Pb(Mg1/3Nb2/3)O3–0.82Pb(Zr0.49Ti0.51)O3 (0.18PMN–0.82PZT) ceramics. The PMNZT/xCr2O3 (with x = 0, 0.1, 0.15, 0.2, 0.25, 0.30, 0.50 wt%) ceramics were prepared by solid state reaction and sintering process. Dielectric properties of the as-prepared ceramics were characterized, wherein the maximum dielectric constant (ɛ m) presents an increasing trend when x < 0.15, followed by a down-trend with an abrupt increase at x = 0.50. The temperature of maximum dielectric constant (T m) appears to display a slight change from 297 °C (x = 0.50) to 310 °C (x = 0.30). At 1 kHz, the sample with composition of x = 0.15 has the largest room temperature dielectric constant ɛ r of 1599 and maximum dielectric constant ɛ m of 25813 at T m, while the sample with composition of x = 0.3 possess the maximum dielectric relaxor factor of γ = 1.93. The remnant polarization gradually decreased from 37.3 to 23.10 μC/cm2 with increasing Cr2O3 content. Meanwhile, compared with pure 0.18PMN–0.82PZT, the coercive field (E c) of the 0.18PMN–0.82PZT+xCr2O3 ceramics are found to be significantly improved when x > 0.10. Furthermore, the field-induced strain of 0.18PMN–0.82PZT+xCr2O3 ceramics appeared to be lower than that of pure 0.18PMN–0.82PZT. However, an up-trend is observable in the field-induced strain of 0.18PMN–0.82PZT+xCr2O3 ceramics with increasing Cr2O3 content up to x = 0.15, which corresponds to a peak value of 0.158%.

Relaxor nature in Ba5RZr3Nb7O30 (R = La, Nd, Sm) tetragonal tungsten bronze new system

AbstractBa5RZr3Nb7O30(R = La, Nd, Sm) lead‐free relaxor ferroelectrics were prepared by a standard solid‐state reaction process, and the influence of A and B site ion occupation on the dielectric characteristics especially the relaxor nature were investigated systematically. Tetragonal tungsten bronze structure with space group P4/mbm was determined for all compositions, ion cross distribution by Ba2+ and R3+ in A1 site was observed, while A2 site was only occupied by Ba2+. Selected area electron diffraction patterns confirmed the existence of incommensurate superlattice modulation. Furthermore, temperature and frequency dependences of the dielectric properties showed a broad permittivity peak with strong frequency dispersion, following well the Vogel‐Fulcher relationship. The maximum dielectric constant temperature increased gradually with decreasing A1 site ion size. Slim P‐E hysteresis loops were obtained at room temperature for all compositions. Meanwhile, micro ferroelectric domains were observed in Ba5SmZr3Nb7O30. For Ba4R2Zr4Nb6O30 and Ba5RZr3Nb7O30 (R = Nd, Sm), the transition from normal ferroelectric to relaxor behavior originates from the increased tA1, which is a result of cross distribution at A1 site. Compared with Ba5RTi3Nb7O30, Zr substitution at B site enhances the relaxor nature.

Composition-dependent structural, dielectric and ferroelectric responses of lead-free Bi0.5Na0.5TiO3-SrZrO3 ceramics

The influence of SrZrO3 (SZ) addition on the crystal structure, piezoelectric and the dielectric properties of lead-free Bi0.5Na0.5TiO3 (BNT−SZ100x, with x = 0 − 0.10) ceramics was systematically investigated. A significant reduction in the grain size was observed with SZ substitution. The X-ray diffraction analysis of the sintered BNT−SZ ceramics revealed a single perovskite phase with a pseudocubic symmetry; however, electric poling indicated a non-cubic distortion in the poled BNT−SZ ceramics. With increase in the SZ content, the temperature of maximum dielectric constant (T m ) shifted towards lower temperatures, and the curves became more diffuse. Enhanced piezoelectric constant (d 33 = 102 pC/N) and polarization response were observed for the BNT−SZ5 ceramics. The results indicated that SZ substitution induced a transition from a ferroelectric to relaxor state with a field-induced strain of 0.24% for BNT−SZ9 corresponding to a normalized strain of 340 pm/V.

Composition‐Dependent Microstructures and Properties of La‐, Zn‐, and Cr‐Modified 0.675BiFeO3–0.325BaTiO3 Ceramics

Pure and 1.0 mol% La2O3, ZnO, and Cr2O3‐modified 0.675BiFeO3–0.325BaTiO3 (BF–BT) multiferroic ceramics were prepared and comparatively investigated. For pure and La‐, Zn‐, and Cr‐modified BF–BT, the average grain size is 415, 325, 580, and 395 nm, and the maximum dielectric constant temperature is 460°C, 430°C, 465°C, and 445°C, respectively. All additives weaken the ferroelectricity slightly. Zn‐ and Cr‐modifications dramatically enhance the room‐temperature magnetic properties, whereas La‐modification has almost no effect on magnetic property. Especially, the Cr‐modified BF–BT ceramics show switchable polarization and magnetization of 4.9 μC/cm2 and 0.27 emu/g at room temperature, the magnetoelectric coupling is confirmed by the magnetization‐magnetic field curves measured on ceramics before and after electric poling. The mechanism responsible for the different effects of additive on microstructures and properties are discussed based on additive‐induced point defect and second phase as well as diffusion‐induced substitution. These results not only provide a promising room‐temperature multiferroic material candidate, but also are helpful to design new multiferroic materials with enhanced properties.

Improvement in dielectric and ferroelectric property of dysprosium doped barium bismuth titanate ceramic

The dysprosium doped barium bismuth titanate ceramic with general formula BaBi4−xDyxTi4O15 (BBDT) were prepared by solid-state reaction process. The effect Dy3+ on Bi3+ sites on the structural, microstructure, dielectric, conductivity and ferroelectric behaviour of BaBi4Ti4O15 ceramics were investigated. X-ray diffraction and Raman analysis confirmed the above compositions to be monophasic with orthorhombic structure and belonged to the m = 4 member of the Aurivillius family of oxides. The SEM micrographs show well define grains in all ceramics. From the dielectric behavior as a function of temperature it was observed that the maximum dielectric constant decreases and transition temperature increases with an increase in Dy content. The diffuse nature of the dielectric behavior of BBDT ceramics obtained from the modified Curie–Weiss law and it was attributed to the A site cationic disorder. The frequency dependence AC conductivity obeys the power law and the DC conductivity shows a thermally activated process. Ativation energies were obtained from the Arrhenius law and it is observed that oxygen vacancy (\({\text{V}}_{\text{O}}^{ \cdot \cdot }\)) are mainly responsible for the conduction mechanism in the systems. The ferroelectric properties were studied by P–E hysteresis loop and it observed that the remnant polarization increases with Dy doping.

Structural, Ferroelectric and Field-Induced Strain Response of Nb-Modified (Bi0.5Na0.5)TiO3-SrZrO3 Lead-Free Ceramics

Lead-free ceramics system of 0.96[Bi0.5Na0.5Ti(1−x)NbxO3]-0.04SrZrO3 BNT-SZ-Nb100x (with Nb100x = 0–4) were prepared by a solid-state reaction method. X-ray diffraction analysis revealed the formation of pure perovskite phase with x ≤ 0.03. The temperature dependence of dielectric curves showed that maximum dielectric constant temperature (Tm) shifted towards lower temperatures and the curves become more diffuse with increasing Nb doping. Ferroelectric curves indicated a disruption of ferroelectric order upon Nb addition. From Nb0 to Nb2 ceramics, maximum values for the field-induced strain (Smax) was enhanced from 0.09 to 0.22%. The corresponding normalized strain (Smax/Emax) was increased from 125 to 315 pm/V.

Enhancement of dielectric and ferroelectric properties of dysprosium substituted SrBi2Ta2O9 ceramics

Aurivillius polycrystalline Dy3+ substituted SrBi2Ta2O9 ceramics were prepared using solid state reaction method, with general formula Sr1−xDy3x/2Bi2Ta2O9 (x = 0.0, 0.025, 0.05, 0.075, 0.1). X-Ray diffraction patterns reveal a single phase orthorhombic (A21am) structure for x ≤ 0.05 composition and a secondary phase is obtained for higher compositions. Scanning electron microscope figures show well defined anisotropic grains in all compositions. Temperature dependent dielectric study shows that the maximum dielectric constant increases and transition temperature decreases with increase in Dy3+ content. The dielectric loss decreases with increase in Dy content may be due to reduction in oxygen vacancy. The diffusivity decreases up to x ≤ 0.05 obtained from modified Curie–Weiss law and then increases for higher doping. The hysteresis loop shows enhanced ferroelectric properties with Dy3+ content.