Enhanced magnetic and dielectric properties of Ti‐doped YFeO3 ceramics

Polycrystalline YFeO₃ (YFO) and YFe_1?(4/3)xTi_xO₃(YFTO) ceramics were prepared using the powder synthesized from the sol‐gel route. X‐ray diffraction analyses of the polycrystalline ceramics revealed the crystallization of the phase in orthorhombic crystal structure associated with the space group Pnma. The magnetization versus magnetic field hysteresis loops were obtained at room temperature for YFO and YFTO ceramics. The magnetic property changes from weak ferromagnetic in YFO to ferromagnetic in YFTO ceramics. The dielectric constant recorded at room temperature for YFTO ceramics was six times higher than that of YFO, whereas the dielectric loss gets reduced to 0.06 from 0.3 for YFO at 1 kHz. Impedance spectroscopy study carried out on YFO and YFTO ceramics confirmed the existence of non‐Debye‐type relaxation. Observed single semicircle in Z′ vs ?Z′′ plot established the incidence of intrinsic (bulk) effect and ruled out any grain boundary or electrode effects. The mechanism for the dielectric relaxation and electrical conduction process observed in YFO and YFTO ceramics was discussed by invoking electric modulus formalisms. Activation energy obtained by ac conductivity study suggested that the conduction process in YFO was linked up with the existence of the polaron and oxygen vacancies, whereas only oxygen vacancies contribute to the conduction process in YFTO ceramics.     

Colossal permittivity and dielectric relaxations in Tl + Nb co-doped TiO2 ceramics

A series of Tl?+?Nb co-doped TiO₂ ceramics ((Tl_0.5Nb_0.5)_x%Ti_1-x%O₂ 0.5?≤?x?≤?10.0) were prepared by a solid-state reaction method under N₂ atmosphere. The evolution of their microstructures, and dielectric properties were systematically studied. The co-doped ceramics exhibited a tetragonal rutile structure wherein the Nb and Tl elements were homogeneously distributed. The cell volumes, grain size, and permittivity increased with doping x, whereas the impedance values of the grain and grain boundary decreased with an increasing x. The optimum dielectric performance (ε_r >?10⁴, tanδ?<?0.05) in the range of 10–10⁶ Hz was obtained for x?=?1.5 with a corresponding grain boundary active energy of 0.86?eV. Four types of dielectric relaxation were observed at different temperature ranges: 10–30?K, 30–200?K, 200–350?K and 350–475?K; those dielectric relaxtions were respectively caused by electron-pinned defect-dipoles, electron hopping, oxygen vacancy hopping, and Maxwell–Wagner polarization. The colossal permittivity is primarily a result of the electron-pinned defect-dipole polarization.     

The Lowered Dielectric Loss and Grain‐Boundary Effects in La‐doped Y2/3Cu3Ti4O12 Ceramics

The effects of La concentration on the electrical conductivity and electric modulus of Y_2/3?xLa_xCu₃Ti₄O₁₂ ceramics (0.00 ≦ x ≦ 0.20) were investigated in detail. Proper amount of La substitution in Y_2/3?xLa_xCu₃Ti₄O₁₂ ceramics made the dielectric loss decreased. When x = 0.10, Y_2/3?0.10La_0.10Cu₃Ti₄O₁₂ ceramics exhibited the highest grain‐boundary resistance (0.893 MΩ) and the lowest dielectric loss (about 0.025 at 1 kHz), meanwhile the samples exhibited a relatively high dielectric constant above 6000 over a wide frequency range from 40 Hz to 1 MHz. The decreased dielectric loss was attributed to the enhanced grain‐boundary resistance. With the increase in La concentration, the dielectric relaxation behaviors correlated with the grain‐boundary effects were significantly enhanced. By La doping, the activation energies for the conduction in grain boundaries were slightly depressed, and the activation energies for the relaxation process in grain boundaries were slightly changed. Based on the activation values, it can be concluded that the doubly ionized oxygen vacancies had substantial contribution to the conduction and relaxation behaviors in grain boundaries.     

Dielectric and electric relaxations induced by the complex defect clusters in (Yb+Nb) co‐doped rutile TiO2 ceramics

The effect of the Yb+Nb substitution for Ti on the microstructure, crystal structures, and dielectric properties of (Yb_1/2Nb_1/2)_xTi_1?xO₂ (0.01≤x≤0.1) ceramics is investigated in this study. The results reveal that the solid solubility limit of the (Yb_1/2Nb_1/2)_xTi_1?xO₂ ceramics is x=0.07, and the average grain sizes considerably decrease from 12 μm to 6 μm with x increasing from 0.01 to 0.1. Three types of dielectric relaxations are observed at temperature ranges of 10‐30 K, 80‐180 K, and 260‐300 K, caused by the electron‐pinned defect dipoles, polaron hopping, and interfacial polarizations, respectively. The conduction mechanism changes from nearest‐neighbor‐hopping to polaron hopping mechanism, which is confirmed by ac conductivity measurements. The present work indentifies the correlation between the colossal permittivity and polaron hopping process in the titled compound.     

Chemical interpretation,enhanced ferroelectric property and dielectric breakdown strength of CuO-added Sr2Nb2O7 ceramics

The structural interpretation and electrical properties of perovskite layer structured (PLS) Sr₂Nb₂O₇-xwt%CuO ceramics prepared by solid-state reaction method are investigated. The chemical interpretation of enhanced piezoelectricity is confirmed to be attributed to the rotation and/or distortion of oxygen octahedron caused by possible Cu²⁺ substitution at the A-site of Sr₂Nb₂O₇ by XRD refinement and variable-temperature Raman spectra. Sr₂Nb₂O₇-xwt%CuO (x?=?0.3, 0.5 and 0.7) ceramics shows enhanced ferroelectric properties with a larger P_r of ～4.1?μC/cm² and a smaller E_c of ～63.1?kV/cm. This study further explains the cations in A-site play a major structural role in the polarization process for PLS system. It was found that dielectric breakdown strength increases up to 258.8?kV/cm and then decreases gradually with the increase of CuO content. Impedance spectroscopy indicated that CuO addition could be helpful in increasing the grain boundary resistance then dielectric breakdown strength.     

Dielectric properties of strontium iron holmium niobate ceramics

Strontium iron holmium niobate (Sr(Fe_1?xHo_x)_0.5Nb_0.5O₃) ceramics were synthesized via a solid-state reaction technique. The undoped ceramic showed an orthorhombic phase, but it transformed to a pseudocubic phase for higher Ho concentrations. A low solubility limit of Ho in SFN caused a formation of second phase for the x=0.15 ceramic. Dielectric behavior of undoped ceramic exhibited high dielectric constant over a wide temperature range. However, the doping shifted this region to a higher temperature. The doping also shifted the peak of dielectric loss to a higher temperature. Activation energy of dielectric relaxation increased with increasing Ho concentration. In addition, complex impedance analysis was applied to determine the behaviors of grain boundary and grain after doping.     

Dielectric relaxation and electrical conductivity in Ca5Nb4TiO17 ceramics

The temperature dependence of dielectric properties and electrical conduction of Ca₅Nb₄TiO₁₇ ceramics were characterized in a broad temperature range. A dielectric anomaly with strong frequency dispersion was detected in the temperature range 700–1010 °C. This dielectric relaxation could be almost removed completely by annealing in an oxidizing atmosphere. Complex impedance analysis confirmed the electrical inhomogeneity of the ceramics with different contributions from the bulk and grain boundaries. This suggests that the main mechanism for the observed relaxation is the Maxwell–Wagner polarization. ac conductivity results revealed the variation of conduction mechanism with increasing temperatures from localized hopping to long-range motion of the doubly ionized oxygen vacancies.     

High dielectric constant and high‐Q in microwave ceramics of SrTiO3 co‐doped with aluminum and niobium

Al/Nb co‐doped SrTiO₃ microwave ceramics with the composition of SrTi_1–x(Al_0.5Nb_0.5)_xO₃ (x = 0.03, 0.05, 0.1, and 0.15) have been synthesized via a standard solid‐state reaction method. The substitution of (Al_0.5Nb_0.5)⁴⁺ in B‐site inhibits the reduction in Ti⁴⁺ ions and the growth of grain size, then the transport of mobile charge carriers is limited, and thus the Q value is improved. For the SrTi_0.9(Al_0.5Nb_0.5)_0.1O₃ ceramics, in addition to their high dielectric constant (ε_r ~185), they exhibit correspondingly a high Qf value (~ 9077 GHz) at 2.9 GHz, making the microwave ceramics suitable for myriad device miniaturization and high‐performance wireless communication.     

Origin of significantly enhanced dielectric response and nonlinear electrical behavior in Ni2+-doped CaCu3Ti4O12: Influence of DC bias on electrical properties of grain boundary and associated giant dielectric properties

CaCu_3-xNi_xTi₄O₁₂ (x?=?0, 0.05, and 0.10) powders were synthesized using a solid state reaction method. Phase structure and microstructure analyses revealed that all sintered CaCu_3-xNi_xTi₄O₁₂ ceramics were of a pure phase. The CaCu₃Ti₄O₁₂ ceramics had a dense microstructure and grain sizes were enlarged by doping with Ni²⁺. Interestingly, the dielectric permittivity was significantly enhanced, whereas the loss tangent was greatly suppressed to ～0.046–0.034 at 1?kHz. All sintered ceramics exhibited non-Ohmic characteristics. Clarification of the influences of DC bias showed that the dielectric permittivity and loss tangent values were increased by DC bias. The resistance of grain boundaries and the associated conduction activation energy of CaCu_3-xNi_xTi₄O₁₂ ceramics were reduced as the DC bias voltage increased. Therefore, the observed non-Ohmic behavior and significantly enhanced dielectric properties should be closely related to variation in the Schottky barriers at the grain boundaries.     

Correlation between crystal structure and modified microwave dielectric characteristics of Cu2+ substituted Li3Mg2NbO6 ceramics

Structural characteristics exert significant influences on microwave dielectric properties, and ion substitution is widely adopted to modify material performances by adjusting the crystal structure. In this work, low loss Li₃Mg_2-xCu_xNbO₆ (x?=?0–0.04) ceramics were prepared by Cu²⁺ substitution. The impacts of Cu²⁺ substitution for Mg²⁺ sites on the microwave dielectric characteristics and crystal structure were discussed in detail. Rietveld refinement results implied that a single Li₃Mg₂NbO₆ phase was formed. Additionally, a dense and homogeneous microstructure with grain sizes of 7–9?μm could be achieved, and moderate Cu²⁺ substitution could significantly promote the grain growth. The correlation between microwave dielectric characteristics and crystal structure was discussed by calculating some structural parameters. The ε_r was determined by the polarizability. The Q?×?f was influenced by the packing fraction. The τ_f value was dependent on the NbO₆ octahedron distortion, and the τ_f value could be adjusted to near zero for x?=?0.02. Typically, the Li₃Mg_2-xCu_xNbO₆ (x?=?0.02) composition exhibited remarkable microwave dielectric performances: ε_r?=?15.75, Q?×?f?=?92,134?GHz (9.86?GHz) and τ_f?=??2?ppm/°C, making it a promising candidate for temperature-stable millimeter-wave applications.     

Improvement of dielectric breakdown strength and energy storage performance in Er2O3–modified 0.95Sr0.7Ba0.3Nb2O6-0.05CaTiO3 lead-free ceramics

In this study, 0.95?Sr_0.7Ba_0.3Nb₂O₆-0.05CaTiO₃-x wt% Er₂O₃ ceramics (SBNCTEx; x?=?0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95?Sr_0.7Ba_0.3Nb₂O₆-0.05CaTiO₃ ceramics, the Er₂O₃ dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x?≥?1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1?kV/mm to 34.4?kV/mm, which is good for energy storage. The energy storage density of 0.28?J/cm³ and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors.     

Differentiated Electric Behaviors of La2/3Cu3Ti4O12 Ceramics Prepared by Different Methods

Microstructure and electric behaviors of La_2/3Cu₃Ti₄O₁₂ (LCTO) ceramics prepared by the sol‐gel method (SG) and solid‐state method (SS) have been systemically investigated. The results indicated that LCTO‐SG ceramics sintered at 1105°C for 15 h showed larger grain size, higher density, and especially higher dielectric constant up to about 0.9–1.6 × 10⁴ at 10²~10⁵ Hz compared to LCTO‐SS ceramics. The higher dielectric constant of the LCTO‐SG ceramics might be due to the stronger internal barrier layer capacitor (IBLC) effect. More notably, compared with LCTO‐SS ceramics, two kinds of dielectric anomalies, one conduction activation energy value and same activation energies for the conduction and relaxation process in LCTO‐SS ceramics, the LCTO‐SG ceramics showed three kinds of dielectric anomalies, two values of conduction activation energy, and decrease in conduction activation energy with increasing temperature. The activation energies for the conduction and relaxation process in LCTO‐SG ceramics showed great difference below about 210°C, suggesting that the mechanism of electrical conduction and dielectric relaxation seem to be different in LCTO‐SG ceramics. These remarkable differences in electric behaviors of LCTO ceramics prepared by sol‐gel and solid‐state methods were firstly found and analyzed.     

Enhanced relative permittivity in niobium and europium co-doped TiO2 ceramics

The appearance of colossal permittivity materials broadened the choice of materials for energy-storage applications. In this work, colossal permittivity in ceramics of TiO₂ co-doped with niobium and europium ions ((Eu_0.5Nb_0.5)_xTi_1-xO₂ ceramics) was reported. A large permittivity (ε_r ～ 2.01?×?10⁵) and a low dielectric loss (tanδ ～ 0.095) were observed for (Eu_0.5Nb_0.5)_xTi_1-xO₂ (x?=?1%) ceramics at 1?kHz. Moreover, two significant relaxations were observed in the temperature dependence of dielectric properties for (Eu, Nb) co-doped TiO₂ ceramics, which originated from defect dipoles and electron hopping, respectively. The low dielectric loss and high relative permittivity were ascribed to the electron-pinned defect-dipoles and electrons hopping. The (Eu_0.5Nb_0.5)_xTi_1-xO₂ ceramic with great colossal permittivity is one of the most promising candidates for high-energy density storage applications.     

Colossal dielectric response and relaxation behavior in novel system of Zr4+ and Nb5+ co-substituted CaCu3Ti4O12 ceramics

In this work, we developed a novel system of isovalent Zr⁴⁺ and donor Nb⁵⁺ co-doped CaCu₃Ti₄O₁₂ (CCTO) ceramics to enhance dielectric response. The influences of Zr⁴⁺ and Nb⁵⁺ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr⁴⁺ and Nb⁵⁺ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu₃Ti_3.8-xZr_xNb_0.2O₁₂ (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr⁴⁺ and Nb⁵⁺ ions than that of single-doped with Zr⁴⁺ or Nb⁵⁺ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~10⁵) at a frequency range of 10²–10⁵ Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr⁴⁺ and Nb⁵⁺ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus.     

Giant dielectric response and polaronic hopping in Al-substituted A5/3Sr1/3NiO4 (A=La,Nd) ceramics

The structures and dielectric properties of A_5/3Sr_1/3Ni_1−xAl_xO₄ (A=La, Nd; x=0.2, 0.3) ceramics were investigated. The single tetragonal phases were found in all ceramics. Giant dielectric responses were observed in these ceramics, and only one dielectric relaxation was found on the curve of the temperature dependence of dielectric constant. After comparing the activation energies of dielectric relaxation and electrical conduction, the giant dielectric response should be attributed to the adiabatic small polaronic hopping process in these ceramics.     

High energy storage performance of [(Bi0.5Na0.5)0.94Ba0.06]0.97La0.03Ti1-x(Al0.5Nb0.5)xO3 ceramics with enhanced dielectric breakdown strength

Novel lead-free [(Bi_0.5Na_0.5)_0.94Ba_0.06]_0.97La_0.03Ti_1-x(Al_0.5Nb_0.5)_xO₃ ceramics (BNBLT-xAN) were prepared by the conventional solid state sintering method. The dielectric, ferroelectric, ac impedance and energy-storage performance were systematically investigated. Temperature dependent permittivity curves showed that relaxation properties of sintered ceramics gradually diminished with the increase of AN. The introduction of AN gave rise to a slimmer polarization hysteresis loop (P-E) and an enhanced dielectric breakdown strength (DBS). Therefore, the optimum energy-storage performance were realized at x?=?0.05 with the energy-storage density (W_rec) of 1.72?J/cm³ and energy-storage efficiency (η) of 85.6% at 105?kV/cm, accompanied with the excellent temperature stability and fatigue performance. The results demonstrated that BNBLT-xAN system was a promising lead-free candidate for energy-storage applications.     

High dielectric permittivity and electrostrictive strain in a wide temperature range in relaxor ferroelectric (1-x)[Pb(Mg1/3Nb2/3)O3-PbTiO3]-xBa(Zn1/3Nb2/3)O3 solid solutions

High electric field-induced strain with ultralow hysteresis, which is often generated based on electrostrictive effects in ferroelectric materials, is highly desired due to its potential applications in high-precision displacement actuators. In this paper, (1-x)[Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃]-xBa(Zn_1/3Nb_2/3)O₃ [(1-x)(PMN-PT)-xBZN] ceramics were fabricated by a solid-state reaction method. The effect of Ba(Zn_1/3Nb_2/3)O₃ (BZN) content on dielectric and electrostrictive properties in relaxor ferroelectric PMN-PT solid solutions was investigated in detail by dielectric spectra, polarization-electric field (P-E) hysteresis loops and strain-electric field (S-E) curves. With an increasing BZN content, the temperature stability of the dielectric permittivity of (1-x)(PMN-PT)-xBZN is improved due to the formation of two coexistent phases. A high electrostrictive strain (~0.17% at 60?kV/cm) with an ultralow hysteresis (<10%) characteristic is obtained in a composition where x?=?0.1725. The strain versus polarization (S-P) curves measured from 30?°C to 130?°C can be well fitted based on a quadratic relation, suggesting the dominating role of the electrostrictive effect. The longitudinal electrostrictive coefficient Q₃₃ for this system ranges from 0.0254?m⁴/C² to 0.0318?m⁴/C². Our results suggest that (1-x)(PMN-PT)-xBZN ferroelectric ceramics are potential candidates for applications in capacitors and high-precision displacement actuators.     

Effect of compositional variations on phase transition and electric field-induced strain of (Pb,Ba) (Nb,Zr, Sn,Ti)O3 ceramics

(Pb_0.97Ba_0.02)Nb_0.02(Zr_0.55Sn_0.45?xTi_x)_0.98O₃ (PBNZST, 0.03≤x≤0.06) ceramics were prepared by conventional solid state synthesis and their crystal structure, ferroelectric, dielectric, and electric field-induced strain properties were systemically investigated. A transformation from antiferroelectric (AFE) phase to ferroelectric (FE) phase was observed at 0.05<x<0.06. Besides, with the increase of Ti content, the electric field-induced strain decreased, due to the larger strain of AFE ceramics compared to FE ceramics. Further, when the measuring frequency decreased, the strain improved, because the electric field at low frequency allows a more efficient switching of domains, resulting in larger strain. The maximum strain of 0.55% was obtained in (Pb_0.97Ba_0.02)Nb_0.02(Zr_0.55Sn_0.45?xTi_x)_0.98O₃ antiferroelectric ceramics with x=0.03 at 2 Hz.     

Crystal structure,microwave dielectric properties and low temperature sintering of (Al0.5Nb0.5)4+ co-substitution for Ti4+ of LiNb0.6Ti0.5O3 ceramics

The phase composition, microstructure, microwave dielectric properties of (Al_0.5Nb_0.5)⁴⁺ co-substitution for Ti site in LiNb_0.6Ti_0.5O₃ ceramics and the low temperature sintering behaviors of Li₂O-B₂O₃-SiO₂ (LBS) glass were systematically discussed. XRD patterns and EDS analysis result confirmed that single phase of Li_1.075Nb_0.625Ti_0.45O₃ solid solution was formed in all component. The increase of dielectric constant (ε_r) is ascribed to the improvement of bulk density. The restricted growth of grain has a negative influence on quality factor (Q×f) value. The τ_f value could be continuously shifted to near zero as the doping content increases. Great microwave dielectric properties were obtained in LiNb_0.6Ti_(0.5-x)(Al_0.5Nb_0.5)_xO₃ ceramics (x?=?0.10) when sintered at 1100?℃ for 2?h: ε_r =?70.34, Q×f =?5144?GHz, τ_f =?4.8?ppm/℃. The sintering aid, LBS glass, can effectively reduce the temperature and remain satisfied microwave performance. Excellent microwave dielectric properties for x?=?0.10 were obtained with 1.0?wt% glass: ε_r =?70.16, Q×f =?4153?GHz (at 4?GHz), τ_f =?-0.65?ppm/℃ when sintered at 925?℃ for 2?h.     

Effects of sintering method and BiFeO3 dopant on the dielectric and ferroelectric properties of BaTiO3–BiYbO3 based solid solution ceramics

(0.95–x) BaTiO₃–0.05 BiYbO₃–x BiFeO₃ (x?=?0, 0.01, 0.02, and 0.04) (abbreviated as (0.95–x) BT–0.05 BY–x BFO) ceramics were fabricated by conventional sintering (CS) and microwave sintering (WS) methods. Effects of sintering method and BFO dopant on the microstructure and electric properties of (0.95–x) BT–0.05 BY–x BFO ceramics were comparatively investigated. X-ray diffraction showed that all CS and WS samples presented a single perovskite phase. It was also found that WS ceramics possessed denser microstructure and finer grains compared to CS samples as indicated by the surface morphology characterization. Dielectric measurements revealed that all samples exhibited the weak relaxation behavior; however, the degree of relaxation behavior of BT–BY based ceramic could be strengthened by addition of BFO and by WS method. Moreover, the temperature and frequency stability could be improved with doped BFO. The density of 0.93BT–0.05BY–0.02BFO ceramic was found to be the largest while that of 0.94BT–0.05BY–0.01BFO ceramic was the smallest, thus, the dielectric constant of 0.93BT–0.05BY–0.02BFO was significantly larger than that of 0.94BT–0.05BY–0.01BFO and 0.94BT–0.05BY–0.04 BFO ceramics. minimum dielectric constant of (0.95–x) BT–0.05 BY–x BFO ceramic was obtained at x?=?0.01. Ferroelectric measurements indicated that all samples showed the slim hysteresis loop. The remnant polarization (P_r) and coercive field (E_C) of (0.95–x) BT–0.05 BY–x BFO ceramics first decreased and then increased with increasing x，the minimum values were obtained at x?=?0.01. Moreover, P_r and E_C of WS ceramics were slightly larger than those of CS ceramics, indicating that higher density and larger grain sizes contributed to enhancing the ferroelectric characteristic. These findings indicate that addition of moderate amount of BFO and use of WS technique can strengthen the degree of relaxation behavior and improve the ferroelectric properties of BT–BY based ceramics.