Effect of ZnO on sintering and microwave dielectric properties of 0.5CaTiO3-0.5 (Li0.5La0.5) TiO3 ceramics

The novel calcium titanate-lithium lanthanum titanate doped with zinc oxide (0.10, 0.30, and 0.50 mol. %) ceramic samples were prepared by solid-state reaction route. The phase formation, microstructure, densification, and microwave dielectric properties were investigated. It was found that the doping with zinc oxide led to a decrease in sintering temperature by 25 ^oC as compared with pure calcium titanate lithium lanthanum titanate due to the liquid phase effect. Also, the calcium titanate lithium lanthanum titanate (10ZCTLLT&30ZCTLLT)) doped with lower zinc oxide (0.10 and 0.30 mol. %) led to higher densification parameter. This was followed by increasing the zinc oxide doping up to (0.50 mol. %) which resulted in a decrease in densification and microwave dielectric properties which may be attributed to increase in porosity and grain growth upon the evaporation of zinc and oxygen vacancy. This led to the increase in dielectric loss (≈10 × 10^?4) value with 50ZCTLLT. Hence, the best result of microwave dielectric characteristics was obtained for 0.5CaTiO₃–0.5(Li_0.5La_0.5)TiO₃ with (0.10 and 0.30 mol. % ZnO) 10ZCTLLT and 30ZCTLLT ceramic samples sintered at 1175 ^oC/2h, with low dielectric constant (ε_r) = 4.4–10.5, very low dielectric loss = 1.07-2.23 × 10^?4 and high quality factor (Q x ?) ≈59-55 × 10⁴ at 8 GHz. Consequently, they can be used not only in wireless satellite communications technology but also can be used in the fifth-generation telecommunication 5G technology construction.     

Bi0·5K0·5TiO3-based lead-free relaxor ferroelectric with high energy storage performances via the grain size and bandgap engineering

Dielectric capacitors with high energy storage performance show a huge competitive advantage for use in vehicles and power electronics. Here, the (1-x) (0.75Bi_0·5K_0·5TiO₃?0.25BiFeO₃) – xSr_0.7Bi_0·2TiO₃ (BKT-BF-xSBT) materials were designed based on the dual optimization strategy of grain size and bandgap. The optimal performance was obtained in the BKT-BF-0.4SBT sample, achieving high energy storage density W_rec of 5.21 J/cm³ and high energy storage efficiency η of 90.87% at 360 kV/cm. The addition of SBT optimized the microstructure and relaxation behavior of BKT-BF ceramic, giving rise to the formation of polar nanoregions (PNRs), small grain size (G), compact grain boundaries, and wide bandgap (E_g) synchronously. Encouragingly, prominent stabilities against temperature, frequency, and cycle numbers, and favorable charge/discharge performance (power density P_D ≈ 64.5 MW/cm³, τ_0.9 ≈ 90 ns) are also accomplished in designed BKT-based ceramics. These findings indicate that the BKT-BF-xSBT ceramic system has excellent potential in the dielectric energy storage field and also provides a viable prospect for engineering design of high-efficiency lead-free dielectrics via bandgap and grain size.     

Effects of niobium doping on lead zirconate titanate films deposited by a sol–gel route

Niobium (Nb)-doped lead zirconate titanate (PZT) films have been prepared on platinized silicon substrates using a sol–gel method. The Zr/Ti ratios of the films are 53/47 and 40/60, and the Nb doping level ranges from 0 mol% to 3 mol%. Similar to the cases in bulk ceramics, after the doping with Nb, the remanent polarization P_r, effective transverse piezoelectric coefficients e_31,c and pyroelectric coefficient p of the PZT films increase; but the longitudinal effective piezoelectric coefficient d_33,c remains roughly unchanged. At the optimum Nb doping levels, the observed P_r, −e_31,c and p reach a maximum value of 30 μC/cm², 18 C/m² and 350 μC/m² K, respectively, for the PZT (53/47) films, and 37 μC/cm², 7.9 c/m² and 370 μC/m² K for the PZT (40/60) films. Our results also reveal that there exist linear relations between p, e_31,c/ε_r and P_r.     

Dielectric behavior and impedance analysis of lead-free CuO doped (Na0.50K0.50)0.95(Li0.05Sb0.05Nb0.95)O3 ceramics

Pure (Na_0.50K_0.50)_0.95(Li_0.05Sb_0.05Nb_0.95)O₃ (NKNLS) and CuO doped NKNLS perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. x wt% of CuO (x = 0.2–0.8 wt%) was added in the NKNLS ceramics. X-ray diffraction patterns indicate that single phase was formed for pure NKNLS while a small amount of second phase (K₆Li₄Nb₁₀O₃₀ ∼ 3%) was present in Cu²⁺ doped NKNLS ceramics. Dielectric anomalies around the temperatures of 120 °C and 350 °C have been identified as the ferroelectric–paraelectric transition (orthorhombic to tetragonal and tetragonal to cubic) temperatures for pure NKNLS compound. The electrical behavior of the ceramics was studied by impedance study in the high temperature range. Impedance analysis has shown the grain and grain boundary contribution using an equivalent circuit model. The impedance response in pure and Cu²⁺ doped NKNLS ceramics could be resolved into two contributions, associated with the bulk (∼grains) and the grain boundaries. From the conductivity studies, it is found that activation energies are strongly frequency dependent. The activation energy obtained from dielectric relaxation data may be attributed to oxygen ion vacancies.     

Electrical,dielectric and pyroelectric behavior of neodymium substituted barium zirconium titanate

Neodymium (Nd) substituted barium zirconium titanate with nominal composition (Ba_1−xNd_x)(Zr_0.52Ti_0.48)O₃ [x = 0.1, and 0.2] were synthesized using solid state reaction method. X-ray analysis confirmed the formation of perovskite structure along with minor pyroclore phase of neodymium. The change in grain size revealed the influence of Nd-ions on the microstructure. The sintered samples exhibited negative temperature coefficient of resistance (NTCR) and superior semiconducting behavior. Addition of Nd³⁺varies the room temperature resistivity of Ba(Zr_0.52Ti_0.48)O₃. As the concentration of Nd-ion increased, the value of temperature dependent dielectric constant decreased whereas the Curie temperature of the ceramics shifted toward higher temperature side showing diffuse phase transition. This is attributed to decrease in average grain size. Temperature dependent pyroelectric current exhibited combination of primary and secondary pyroelectric effect.     

Enhanced energy-storage performance and thermal stability in Bi0.5Na0.5TiO3-based ceramics through defect engineering and composition design

Dielectric ceramics have been widely used in advanced microelectronics systems due to their inherent rapid charging/discharging capabilities and superb power density. However, concurrently attaining high energy storage density (W_rec), superior efficiency (η), and excellent thermal stability are arduous tasks for actual applications in dielectric ceramics. Herein, the introduction of predictable defects A-site vacancies (V_A) and oxygen vacancies (V_O) into the morphotropic phase boundary (MPB) of (Bi_0.45La_0.05Na_0.5)_0.94Ba_0.06TiO₃ (BLNBT) ceramics leads to a pinning effect in the grain boundary to improve the breakdown strength and energy storage performance. According to this strategy, the novel Sr_0.8Bi_0.1□_0.1Ti_0.8Zr_0.2O_2.95 (SBTZ)-modified BLNBT ceramics are designed and manufactured, which include SBTZ with a high relaxation behavior gene and BLNBT with an inherently high maximum polarization gene. As a result, a large W_rec of 3.84 J/cm³ with an excellent η of 90.8%, and outstanding charge/discharge capabilities (C_D ～ 584.99 A/cm², P_D ～ 40.94 MW/cm³ and τ_0.9 ～ 95 ns) in the 0.75BLNBT-0.25SBTZ ceramic are achieved. Notably, the corresponding ceramic shows a slight degradation of W_rec with a variation of less than 8% (RT ～ 200 °C), while the η remains at over 90%. The predictable defect engineering strategy proposed in this work is an effective way to develop new Bi_0.5Na_0.5TiO₃-based systems with good energy storage performances.     

Microstructure,dielectric and piezoelectric properties of (Pb1−xSrx)Nb1.96Ti0.05O6 ceramics

(Pb_1−xSr_x)Nb_1.96Ti_0.05O₆ with 2 wt% excess PbO (x = 0, 0.02, 0.04, 0.06, 0.08) piezoelectric ceramics with high Curie temperature were fabricated via the conventional solid state reaction method. Effects of Sr²⁺ amount on crystallite structure, microstructure, dielectric and piezoelectric properties were studied. The substitution of Sr²⁺ ions for Pb²⁺ ions is effective to lower sintering temperatures. X-ray diffraction patterns indicate that all ceramics form the single orthorhombic ferroelectric phase. The doping of Sr²⁺ ions facilitates improving densification of the ceramics. Grain size and lattice parameters of the ceramics vary with the change of the Sr²⁺ contents. Both Curie temperature and maximum dielectric constant change with increasing the Sr²⁺ amounts. The dielectric constant data were also studied using the Curie–Weiss law and modified Curie–Weiss law. The ceramic with x = 0.04 possesses excellent piezoelectric and dielectric properties, presenting a high potential to be used in high-temperature applications as piezoelectric transducers.     

Ferroelectric properties and ac conductivity studies of yttrium modified Pb(Fe0.5Nb0.5)O3 ceramics

Using a high-temperature standard solid-state reaction (i.e., mixed oxide) method several yttrium modified ferroelectric ceramics of type Pb_1−xY_x(Fe_0.5Nb_0.5)_1−x/4O₃ (PYFN)with different concentration (x = 0.00, 0.02, 0.04, 0.06, 0.08) were prepared. Preliminary X-ray structural analysis reveals that all the samples were crystallized in monoclinic crystal system. The crystal structure is almost invariant with small Y-concentration. Microstructure of the samples exhibits grain growth on increasing Y content. Curie temperature of Y-substituted samples decreases slightly as compared to that of PFN (Pb(Fe_1/2Nb_1/2)O₃). However, Y substitution results in a notable enlargement of remnant polarization (2P_r). The 2P_r of PYFN (x = 0.02) reaches to a large value (23 μC/cm²) which is nearly 5 times greater than that of x = 0.00 (4.6 μC/cm²). A phenomenological model (i.e., ferroelectric capacitor model) used to simulate hysteresis loops was found to be suitable to explain experimental results. Jonscher's single power law (σ_ac(ω) = σ(0) + Aωⁿ) was well fitted to the frequency dependence of conductivity for all the samples.     

Phase,crystal struture and sintering behavior of shock-synthesized Pb(Zr0.95Ti0.05)O3 powders

With a cylindrical shock-wave-loading technique, the single perovskite-phase Pb(Zr_0.95Ti_0.05)O₃ powders (PZT 95/5) were synthesized by shock-induced chemical reactions in heterogeneous multi-material powder mixtures of Pb₃O₄, ZrO₂ and TiO₂. The phase and crystal structure of as-synthesized powders were characterized by X-ray diffraction (XRD) and fourier transform infrared (FT-IR) analysis. And the microstructure and electrical properties of PZT 95/5 ceramics prepared with as-synthesized PZT powders at different sintering temperature were analyzed. The results showed that the shock-wave-induced a large quantity of lattice defects and distortion of the crystal structure in the shock-synthesized PZT powders, which could enhance the sintering activity. Thus, the optimal density and electrical properties of PZT ceramics prepared with as-synthesized powders could be obtained at a sintering temperature of 1200–1225 °C for 3 h, significantly lower than the sintering temperature of PZT 95/5 ceramics prepared by conventional solid-state reaction.     

Annealing effects on the morphology and luminescence of cubic boron nitride based ceramics

Cubic boron nitride based ceramics with silicon were sintered at 1350 °C under a pressure of 5.0 GPa. The effects of post-annealing on grain morphology, surface morphology, and photoluminescence of Si–cBN ceramics were investigated by scanning electron microscope and room temperature photoluminescence measurements. The results showed that the annealing treatment had great influence on cBN grain morphology, rather than the surface morphology. The luminescence intensity increased with annealing temperature and annealing time. The void-net structure formed by continuous distribution of SiO_x particulate on the ceramic surface resulted in the emission band peaking at about 701.2 nm, and the tense passivation of Si by SiO_x led to the peak's low intensity. The near ultraviolet emission band peaking at about 317 nm was attributed to the oxygen vacancies formed in cBN grain surface, caused by the scavenging of oxygen from the cBN grain surface by the added Si.     

Effects of Charge Compensation on Colossal Permittivity and Electrical Properties of Grain Boundary of CaCu3Ti4O12 Ceramics Substituted by Al3+ and Ta5+/Nb5+

The effects of charge compensation on dielectric and electrical properties of CaCu₃Ti_4-x(Al_1/2Ta_1/4Nb_1/4)_xO₁₂ ceramics (x = 0−0.05) prepared by a solid-state reaction method were studied based on the configuration of defect dipoles. A single phase of CaCu₃Ti₄O₁₂ was observed in all ceramics with a slight change in lattice parameters. The mean grain size of CaCu₃Ti_4-x(Al_1/2Ta_1/4Nb_1/4)_xO₁₂ ceramics was slightly smaller than that of the undoped ceramic. The dielectric loss tangent can be reduced by a factor of 13 (tanδ ~0.017), while the dielectric permittivity was higher than 10⁴ over a wide frequency range. Impedance spectroscopy showed that the significant decrease in tanδ was attributed to the highly increased resistance of the grain boundary by two orders of magnitude. The DFT calculation showed that the preferential sites of Al and Nb/Ta were closed together in the Ti sites, forming self-charge compensation, and resulting in the enhanced potential barrier height at the grain boundary. Therefore, the improved dielectric properties of CaCu₃Ti_4-x(Al_1/2Ta_1/4Nb_1/4)_xO₁₂ ceramics associated with the enhanced electrical properties of grain boundaries. In addition, the non-Ohmic properties were also improved. Characterization of the grain boundaries under a DC bias showed the reduction of potential barrier height at the grain boundary. The overall results indicated that the origin of the colossal dielectric properties was caused by the internal barrier layer capacitor structure, in which the Schottky barriers at the grain boundaries were formed.     

Electrical conductivity and Hf4+ ion substitution range in NaSICON system

In this paper, we present the synthesis and characterizations of NaSICON-type ionic conducting ceramics of the general formula Na_1+xM_1.775Si_x−0.9P_3.9−xO₁₂ with 1.8 ≤ x ≤ 2.2 and M = Zr or Hf. The effect of the total substitution of zirconium by hafnium on electric properties has been studied. The various compositions were prepared by using the sol–gel method and the synthesized precursors were characterized by coupled DTA–TG. The oxides obtained after pyrolysis of the precursors were identified by X-ray diffraction. A sintering study by thermodilatometry permits to select the best thermal cycle adapted to our ceramics. Furthermore, the electric conductivity of the sintered ceramic samples was characterized by complex impedance spectroscopy. These results show that ceramics containing Zr synthesized by soft method, present a higher total conductivity than those obtained in literature (to be around 10⁻⁴ S cm⁻¹). The total substitution of Zr by Hf still improves this conductivity for some compositions.     

Preparation and functional characterization of BiFeO3 ceramics: A comparative study of the dielectric properties

In the present study, the electrical properties of BiFeO₃ ceramic specimens prepared by solid-state sintering method by using two thermal treatment strategies are comparatively investigated. The room temperature XRD pattern shows perovskite single-phase, in the limit of XRD accuracy, for BiFeO₃ ceramic prepared by single-step method. For two-step sintering method sample small amounts of secondary Bi₂Fe₄O₉ phases were identified. The ceramics show a non-homogeneous microstructure, consisting of ceramic grains with irregular morphology and interconnected porosity mainly in the grain boundary regions in the case of two-step sintering sample. The most interesting feature is the conduction anomaly observed on the conductivity in the low-frequency range close to dc-conductivity. The Arrhenius plot of the dc-conductivity determined at the lowest frequency vs. 1/T shows two distinct linear regions separated by the mentioned temperature range of (189–244) K, for which the dc conductivity could not be determined from the present impedance spectroscopy data only. It is clear that in the mentioned temperature range (for both samples), a conduction anomaly takes place.     

Colossal dielectric constant in PrFeO3 semiconductor ceramics

The perovskite PrFeO₃ ceramics were synthesized via sol–gel method. The dielectric properties and impedance spectroscopy (IS) of these ceramics were studied in the frequency range from 100 Hz to 1000 kHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant value of ∼10⁴ at room temperature. The response is similar to that observed for relaxorferroelectrics. IS data analysis indicates the ceramics to be electrically heterogeneous semiconductor consisting of semiconducting grains with dielectric constant 30 and more resistive grain boundaries with effective dielectric constant ∼10⁴. We conclude, therefore that grain boundary effect is the primary source for the high effective permittivity in PrFeO₃ ceramics.     

Structural variations and cation distributions in Mn3−xCoxO4 (0 ≤ x ≤ 3) dense ceramics using neutron diffraction data

Single phase ceramics of cobalt manganese oxide spinels Mn_3?xCo_xO₄ were structurally characterized by neutron powder diffraction over the whole solid solution range. For x < 1.75, ceramics obtained at room temperature by conventional sintering techniques are tetragonal, while for x ≥ 1.75 ceramics sintered by Spark Plasma Sintering are of cubic symmetry. The unit cells, metal–metal and metal–oxygen average bonds decrease regularly with increasing cobalt content. Rietveld refinements using neutron data show that cobalt is first preferentially substituted on the tetrahedral site for x < 1, then on the octahedral site for increasing x values. Structural methods (bond valence sum computations and calculations based on Poix's work in oxide spinels) applied to our ceramics using element repartitions and [M–O] distances determined after neutron data refinements allowed us to specify the cation distributions in all phases. Mn²⁺ and/or Co²⁺ occupy the tetrahedral site while Mn³⁺, Co²⁺, Co^III (cobalt in low-spin state) and Mn⁴⁺ occupy the octahedral site. The electronic conduction mechanisms in our highly densified ceramics of pure cobalt and manganese oxide spinels are explained by the hopping of polarons between adjacent Mn³⁺/Mn⁴⁺ and Co²⁺/Co^III on the octahedral sites.     

Effect of silver content on the phase transition and electrical properties of 0.95[(K0.5Na0.5)NbO3]–0.05LiSbO3 ceramics

Lead free 0.95[(K_0.5Na_0.5)_1−xAg_xNbO₃]–0.05LiSbO₃ (KNAN–LS) ceramics with x = 0, 0.02, 0.04, 0.06 and 0.08 have been synthesized by conventional solid state reaction route (CSSR). X-ray diffraction (XRD) analysis confirmed the transformation of mixed structure to pure tetragonal structure with the increase in Ag content in KNN–LS ceramics. The Curie temperature (T_c) of the ceramics decreased from 385.5 °C to 331 °C with the increase in silver (Ag) content. The poling temperature was optimized for better piezoelectric properties. The KNAN–LS ceramics with x = 0.06 showed better piezoelectric and ferroelectric properties (d₃₃ = 227 pC/N, k_p = 42.5%, T_c = 368 °C and P_r = 21.9 μC/cm²).     

Size confinement and magnetization improvement by La3+ doping in BiFeO3 quantum dots

Nanometric multiferroic samples Bi_1−xLa_xFeO₃; 0.05 ≤ x ≤ 0.40 were prepared using ceramic method. Structural and magnetic properties were investigated using XRD, TEM, magnetic susceptibility and M–H loop. The decrease in the lattice parameters is due to the difference between the ionic radii of Bi and La and this effect is compensated by the change in the atomic weight of the two elements which is reflected as a decrease in the density. The obtained results showed that all samples were antiferromagnetic in character. The small values of remnant and saturation magnetization indicated the canted type antiferromagnetism. Maximum coercivity H_c = 5265 Oe was obtained at x = 0.25. The magnetic susceptibility measurements show its size dependence due to long range spin arrangement. Improvement of the magnetization of BiFeO₃ is achieved by La³⁺ at different doping levels. The obtained quantum dot size of the crystallites enhances their use in spintronic devices.     

Effects of metal salts on the thermal decomposition of edta-gel precursors for ferroelectric ceramic powders

Raw chemicals such as metal nitrates and chlorides were found to affect the thermal decomposition behaviour of EDTA-gel precursors used for the production of ceramic powders. Fine, homogeneous ceramic powders were produced from nitrate solutions while chlorides gave segregated phases. In studies on the production of lead zirconate titanate (PZT) using chlorides, the segregation and loss of lead was observed and shown to be caused by the formation and evaporation of PbCl₂. Thermal analysis (DTA/TG) quantitatively proved the suggested reaction mechanism for this phase segregation. Crystallization of the desired perovskite phase of lead zirconate titanate (PZT) and barium titanate (BT) initiated at temperatures as low as 250°C in the nitrate-EDTA precursors. Water of crystallization and formation of BaCO₃ in the barium titanate precursor were suggested to account for differences in the observed decompositional behaviours of the BT and PZT precursors.     

Influence of sintering method on microstructure,electrical and magnetic properties of BiFeO3–BaTiO3 solid solution ceramics

The (1-x)BiFeO₃-xBaTiO₃ (short for (1-x)BFO-xBTO, x = 0.2–0.4) ceramics were prepared by solid-state reaction with microwave sintering (MWS) and conventional sintering (CS) methods. The crystal structure, microstructures, dielectric properties, ferroelectric properties, and magnetic properties of BFO-BTO ceramics sintered by MWS and CS were systematically investigated. It is found that the MWS can effectively decrease the grain size and enhance the compactness of BFO-BTO ceramics. The X-ray diffraction (XRD) results confirm that all ceramics exhibit a single perovskite structure, and the phase transforms from rhombohedral in BiFeO₃-rich compositions to pseudo-cubic phase gradually as x increases. Introducing BTO into BFO can strengthen its dielectric relaxation behavior. Compared with CS, the MWS samples have a lower remanent polarization (P_r) and a smaller coercive field (E_c) under the same electric field. Therefore, MWS contributes to the decrease of dielectric loss. Addition of BTO can contribute to the reduction of the coercive force (H_c) of BFO-based ceramic, and so decrease the hysteresisloss. At the same time, its remanent magnetization (M_r) value can be decreased by introducing BTO into BFO and using MWS method. The present research provides a route for decreasing the dielectric loss and hysteresis loss of BiFeO₃-based ceramics using the MWS method.     

Synthesis and electrical properties of (LiCo3/5Fe1/5Mn1/5)VO4 ceramics

(LiCo_3/5Fe_1/5Mn_1/5)VO₄ ceramic was synthesized via solution-based chemical method. X-ray diffraction analysis was carried out on the synthesized powder sample at room temperature, which confirms the orthorhombic structure with the lattice parameters of a = 10.3646 (20) Å, b = 3.7926 (20) Å, c = 9.2131 (20) Å. Field emission scanning electron microscopic analysis was carried out on the sintered pellet sample that indicates grains of unequal sizes (～0.1 to 2 μm) presents average grains size with polydisperse distribution on the surface of the ceramic. Complex impedance spectroscopy (CIS) technique is used for the study of electrical properties. CIS analysis identifies: (i) grain interior, grain boundary and electrode–material interface contributions to electrical response (ii) the presence of temperature dependent electrical relaxation phenomena in the ceramics. Detailed conductivity study indicates that electrical conduction in the material is a thermally activated process. The variation of A.C. conductivity with frequency at different temperatures obeys Jonscher's universal law.