Co-doped BaTiO3 Ceramics Research Articles

Synergistic enhancement of electrical characteristics in Sr2+ and Zr4+ Co-doped BaTiO3 ceramics through multiphase coexistence regulation at room temperature

BaTiO3 (BT)-based ceramics have recently become one of the most promising lead-free piezoelectric ceramics. However, its overall performance still falls short of meeting the demands for multifunctional applications. Although phase boundary regulation can enhance the piezoelectric properties, BT ceramics have very separate phase transition temperatures for different phases. This leads to the difficulty of achieving multiphase coexistence at room temperature (RT). In this work, based on doping 0.08 mol Zr4+, the lead-free Ba1-xSrxTi0.92Zr0.08O3 [x = 0, 0.04, 0.08, 0.12, 0.16, 0.20 (mol), B1-xSxTZ] piezoelectric ceramics were prepared using the solid-state reaction method, and the effect of the Sr2+ doping level on the multiphase structural evolution and piezoelectric properties was systematically investigated. The results demonstrated that with the increase in the Sr2+ doping content, multiphase coexistence within the B1-xSxTZ ceramics was successfully achieved at RT. Moreover, it showed significant synergistic improvements in piezoelectric, dielectric, and electric-field-induced strain properties. At the doping level of about x = 0.16 mol, the key performance metrics of the piezoelectric ceramics were optimal. The d33 at room temperature reached ∼447 pC/N, kp ∼0.49, and εr ∼4649. Under an applied electric field of 10 kV/cm, Spos was ∼0.092 %, and d33∗ was ∼895 p.m./V. Therefore, this study provides new insights into the progress of advanced lead-free piezoelectric materials for multifunctional applications.

Investigation of Ga–Nb co-doped barium strontium titanate ceramics for DC-bias free dielectrics

The Ba0.8Sr0.2Ti1−2x Ga x Nb x O3 (0 ≤ x ≤ 0.10) ceramics were fabricated and the electrical properties were evaluated regarding DC-bias and temperature characteristics of the dielectric properties. The ceramics with x = 0.10 exhibited a stable dielectric constant with a change of–40% within 25 °C–150 °C. The dielectric loss of all the co-doped ceramics was below 2% within 25 °C–200 °C. The Ba0.8Sr0.2Ti1−2x Ga x Nb x O3 ceramics showed a higher dielectric constant with a lower DC-bias dependence as compared to previous study on co-doped BaTiO3 ceramics. The Ba0.8Sr0.2Ti0.20Ga0.10Nb0.10O3 ceramics exhibited the best results of DC-bias dependence ≈−24%, dielectric constant at 100 kV cm−1 ≈ 560, and the dielectric constant at 0 kV cm−1 ≈ 735. The better results for the Ga–Nb co-doped BST ceramics might be due to the higher contribution of the ionic polarization in the BST base matrix resulting in a shallower potential energy curve.

Temperature-dependent Raman and dielectric studies of Sm and Zr Co-doped BaTiO3 ceramics

Temperature-dependent Raman and dielectric studies of Sm and Zr Co-doped BaTiO3 ceramics

Enhancement of dielectric and ferroelectric properties of (Sr, Ni) Co-doped BaTiO3 ceramics

In the present study, systematic investigations on dielectric and ferroelectric properties of pure and (Sr, Ni) co-doped BaTiO3 nanocrystalline powder samples fabricated via microwave-assisted co-precipitation method have been reported. XRD patterns divulge the formation of mono-phase tetragonal crystal structure with P4mm space group. The fingerprint bands in the FTIR spectra further assure the formation of desired crystal structure. The dielectric responses have been examined by virtue of the universal dielectric response mechanism with remarkable improvement in the dielectric properties for the (Sr, Ni) co-doped sample. The P-E loop measurement corroborates ferroelectricity in the system and augmentation in the maximum polarization for the co-doped sample. The improved dielectric and ferroelectric properties in (Sr, Ni) co-doped BaTiO3 suggest its potential in various technological applications.

Dielectric relaxations without colossal permittivity in Mg and Nb co-doped BaTiO3 ceramics

Magnesium (Mg) and Niobium (Nb) co-doped BaTiO3 ceramics are prepared using a solid-state reaction method under an air atmosphere, and their crystal structures, microstructures, valence states and dielectric properties are studied. The ceramics adopt a cubic perovskite structure, and the lattice parameter increases with doping content owing to the larger ionic radii of dopants. The complex permittivity and electric modulus as a function of frequency and temperature are analyzed. Dielectric relaxations without colossal permittivity are observed. The relaxation processes are thermally activated and their variations with temperature are analyzed. The activation energy values for the relaxation processes are determined by the Arrhenius relationship and increase with doping content. By analyzing the electric modulus, the activation values for high-frequency relaxation are found to be associated with the electrical properties of grain, and the contribution of grain boundary could be neglected based on internal barrier layer capacitor (IBLC) model. The electron hopping between the different Ti valences, which is confirmed by X-ray photoelectron spectroscopy, is supposed to play an important role in high-frequency relaxation. The permittivity plateaus are related to the inhomogeneous structures of grain and grain boundary, and the low-frequency permittivity plateau is attributed to the space-charge polarization at grain boundaries. By comparing with Cu/Nb co-doped BaTiO3, the absence of colossal permittivity is ascribed to high resistivity of the samples. Charge density and migration as well as the insulating grain boundaries are critical for the formation of space charge and a high permittivity.

Tetragonal-structural changes influenced the magnetic and ferroelectric properties of (Y, Fe)-codoped BaTiO3 ceramics

We present a detailed study on the structural characterization, electronic structure, and magnetic/electric-polarization properties of Ba1-xYxTi1-xFexO3 (BYxTFxO, x = 0–0.1) ceramic samples. These samples mainly crystalized in a tetragonal structure, and a small amount of a YFeO3-related secondary phase constituted as x ≥ 0.08. With increasing x, the lattice constant a increases while c decreases. Such structural changes reduce rapidly the intensity of characteristic Raman modes. Magnetization data have proved all BYxTFxO samples exhibiting ferromagnetism at room temperature. Both the saturation magnetization and coercivity tend to increase with increasing x. This is ascribed to an enhanced exchange interaction between Fe3+ ions, and the YFeO3-phase formation. Herein, the Fe3+ presence has been confirmed upon analyzing X-ray absorption spectra. Though all the samples exhibit ferroelectricity, the electric-polarization slightly decreases with increasing x. This is associated with an increased symmetry due to the changes in the lattice parameters towards the cubic structure.

Internal Friction and Mechanical Spectroscopy (IFMS-19). Concluding remarks

The BaTiO3 perovskite is widely used in the electronic technology due to its dielectric, piezoelectric and ferroelectric properties and is a well-known base for obtaining a promising multifunctional material. In this paper we report the extensive studies on the Co-doped BaTiO3 ceramics for the wide range cobalt content. Full structural characterization of studied samples in a 20–450 K range was provided. The results of research on spectroscopic, dielectric, electronic, optical, magnetic and elastic properties are presented. The superior dielectric properties to those exhibited by the parent compound have been found. Namely, the reduction of dielectric losses and stability of the dielectric permittivity in the vicinity of the room temperature are reported. Additionally, our research revealed: broadening of the dielectric anomalies related to the ferroelectric-paraelectric phase transition, shifting the Curie point towards lower temperatures, displacive mechanism of Curie phase transition with order-disorder contributions; maximum value of the real part of dielectric permittivity of about 5000 at Curie point for 0.05 wt% of Co-doping, value of the activation energy ∼ 0.9 eV as the result of the migration of oxygen vacancies that are generated due to charge compensation, and the occurrence of magnetoelectric response. At last, the Co-doped BaTiO3 shows potential to use in non-linear optoelectronic devices, while no evidence of multiferroic properties, suggested in the literature, was found.

Magnetoelectric, spectroscopic, optical and elastic properties of Co-doped BaTiO3 ceramics

Magnetoelectric, spectroscopic, optical and elastic properties of Co-doped BaTiO3 ceramics

Structural evolution and coexistence of ferroelectricity and antiferromagnetism in Fe, Nb co-doped BaTiO3 ceramics

Multiferroics are materials that exhibit two or more primary ferroic properties within the same phase and have potential applications in sensors, spintronics and memory devices. Here, the dielectric, ferroelectric and magnetic properties of novel multiferroics derived from BaTi1−x(Fe0.5Nb0.5)xO3 (BTFN, 0.01 ≤ x ≤ 0.10) ceramics are investigated. Multiferroism in these ceramics is manifested by the coexistence of ferroelectric long-range ordering and antiferromagnetism. With increasing x-value, there is a structural evolution from a tetragonal perovskite to a mixture of tetragonal and cubic phases, accompanied by a decrease in the temperature of maximum permittivity. At room temperature, ferroelectric behaviour is evidenced by the presence of current peaks corresponding to domain switching in the current-electric field loops, while the observation of non-linear narrow magnetic hysteresis loops suggests dilute magnetism. The results indicate that in the x = 0.07 composition the antiferromagnetic order is established through an indirect super-exchange interaction between adjacent Fe ions.

Implementing a sol-gel route to adjust the structural and dielectric characteristics of Bi and Fe co-doped BaTiO3 ceramics

The present work explores the impact of Fe insertion on the physical properties of Ba0.95Bi0.05Ti1-xFexO3 (x = 0.025, 0.050, and 0.075) prepared via sol gel method. The resulting samples crystallize in the tetragonal structure with space group P4mm and their morphological features point out the variation of the microstructure with Fe content. In turn, the dielectric constant versus temperature plot reveals the existence of two transition phases: the first one is ferroelectric-paraelectric transition phase (TF-P) and the second one is ferroelectric orthorhombic - ferroelectric tetragonal phase (TO-T). Analysis of conductivity curves using Jonscher’s augmented equation (for x = 0.025) and Jonscher’s power law (for x = 0.075) suggests the Non-Overlapping Small Polaron Tunneling (NSPT) model as a conduction mechanism.

Optimization of Sintering Conditions to Enhance the Dielectric Performance of Gd3+ and Ho3+ Codoped BaTiO3 Ceramics

BaTiO3 dielectric capacitors, one of the important energy storage devices, play critical roles in storing electricity from renewable energies of water, wind, solar, etc. The synthesis of BaTiO3 ceramics with weak temperature dependence and a high dielectric constant at room temperature (εRT') is an urgent problem to meet the miniaturization and large capacity of dielectric capacitors. Doping rare earth elements into BaTiO3 can solve this problem, but it is still challenging. In this work, we adopt a synergistic strategy of increasing εRT' and improving the temperature stability by codoping Gd3+ and Ho3+, respectively, to address this challenge. By carefully adjusting the synthesis conditions in the solid-state reaction, codoping 7% Gd3+ and 7% Ho3+ in BaTiO3 (BGTH7) ceramics were synthesized. The temperature-dependent dielectric constant reveals that the obtained optimal BGTH7 ceramic satisfies the X7U specification and displays a stable ε' in the temperature range of -55~125 °C. The optimal BGTH7 ceramic after sintering at 1400 °C for 6 h exhibits a high dielectric constant of 5475 and low dielectric loss (tan δ) of 0.0176, hitherto exhibiting the best performance in X7U ceramics. The findings in this work are conducive to the miniaturization and stabilization of dielectric energy storage devices.

Role of A-site (Sr), B-site (Y), and A, B sites (Sr, Y) substitution in lead-free BaTiO3 ceramic compounds: Structural, optical, microstructure, mechanical, and thermal conductivity properties

Strontium and Yttrium-doped and co-doped BaTiO3 (BT) ceramics with the stoichiometric formulas BaTiO3, B1-xSrxTiO3, Ba1-xYxTiO3, BaTi1-xYxO3, Ba1-xYxTi1-xYxO3, and Ba1-xSrxTi1-xYxO3 (x = 0.075) noted as BT, BSrT, BYT, BTY, BYTY, and BSrTY have been synthesized through sol-gel method. X-ray diffraction (XRD) patterns of the prepared ceramics, calcined at a slightly low temperature (950 °C/3h), displayed that BT, BSrT, and BYT ceramics possess tetragonal structures and BTY, BYTY, and BSrTY have a cubic structure. The incorporation of the Ba and/or Ti sites by Sr2+ and Y3+ ions in the lattice of BaTiO3 ceramic and the behaviors of the crystalline characteristics in terms of the Y and Sr dopant were described in detail. The scanning electron microscopy (SEM) images demonstrated that the densification and grain size were strongly related to Sr and Y elements. UV–visible spectroscopy was used to study the optical behavior of the as-prepared ceramic samples and revealed that Sr and Y dopants reduce the optical band gap energy to 2.74 eV for the BSrTY compound. The outcomes also demonstrated that the levels of Urbach energy are indicative of the created disorder following the inclusion of Yttrium. The measurements of the thermal conductivity indicated the influence of the doping mechanism on the thermal conductivity results of the synthesized samples. Indeed, the thermal conductivity of BaTiO3 is decreased with Sr and Y dopants and found to be in the range of 085–2.23 W.m-1. K−1 at room temperature and decreases slightly with increasing temperature from 2.02 to 0.73-W.m-1. K−1. Moreover, the microstructure and grains distribution of the BT, BSrT, BYT, BTY, BYTY, and BSrTY samples impacted the compressive strength, hence; the compressive strength was minimized as the grain size decreased.

Cathodoluminescence evaluation of the degradation of Mg, Ca and Dy Co-doped BaTiO3 Ceramics

Mg, Ca and Dy co-doped BaTiO3 ceramics were prepared by conventional solid-state method. About 25% of grains possessed core-rim structure, which was caused by different Ca and Mg solutions. Cathodoluminescence, an efficient tool to obtain defect information with high spatial and spectral resolution, was applied to investigate the degradation mechanism of the ceramics. Oxygen vacancy concentration in the core is higher than that in the rim due to the higher Ca content in the rim. In the initial stage of degradation, oxygen vacancies mainly migrated within the core region. In the middle stage, oxygen vacancies migration in the grains with core-rim structure was confined to the grains, from the core to the rim. In contrast, oxygen vacancies in the grains without core-rim structure migrated across the grain boundaries to the cathodic region. Core-rim structure could delay oxygen vacancy migration to prolong the lifetime.

Influence of Sr ions on the structure and dielectric properties of Cu/Nb Co-doped BaTiO3 ceramics

Sr-modified Cu/Nb co-doped BaTiO3 ceramics were prepared using solid-state reactions and the structures and dielectric properties were studied. All the samples had single-phase perovskite structures with no detectable secondary phases. In the low-temperature range, the dielectric constant decreased as the Sr content increased in the high- and low-frequency ranges. Two dielectric constant plateaus accompanied by dielectric relaxation peaks were present in the loss curves, and the relaxation process deviated from the Arrhenius law at low temperatures. The dielectric constants of different plateaus were related to inhomogeneous structures such as grain interiors and grain boundaries. The polarization strength of the grain boundaries in the low-frequency range increased with the temperature and that of the grain interiors demonstrated paraelectric behaviour in high-temperature ranges. An analysis of the electric modulus spectra indicated a close relationship between the relaxation process and resistivity of the grains for high-frequency relaxation. The impedance spectra at high temperatures consist of three electrical responses, corresponding to the effects of grains, grain boundaries, and electrodes. The dielectric relaxation appeared in high temperature range was related to the electrical properties of the grain boundaries.

Enhanced dielectric and ferroelectric properties of the hybrid-doped BaTiO3 ceramics by the semi-solution method

In the present study, an industrially viable ceramics fabrication way based on solid-state reaction method–semi-solution method was used to improve the dielectric and ferroelectric properties of acceptor-donor co-doped BaTiO3 ceramics. Unlike the conventional solid-state reaction method, additives in the semi-solution method were introduced in the form of the aqueous solution rather than oxide powders. Experiment results show that higher peak dielectric constant εmax (140–150%), larger maximum polarization Pmax (24 μC cm−2), and less apparent aging phenomena were achieved by the semi-solution method. A comprehensive microscopic analysis was carried out to explore the origin of property enhancement. Results show that enhanced properties could be ascribed to the higher level of compositional homogeneity and lower content of oxygen vacancies. This study provides a new method to control aging phenomena and achieve property enhancement in acceptor-donor co-doped ceramics. Moreover, this simple and cost-effective method may also find its application in other extensive-doped ceramics.

Colossal permittivity (Nb, Mg) co-doped BaTiO3 ceramics with excellent temperature stability and high insulation resistivity

High performance colossal permittivity ceramic materials are indispensable for the development of electronic devices. In this work, Mg and Nb co-doping BaTiO3 ceramics were prepared by solid-state reaction under reducing atmosphere. The polarization mechanism, dielectric properties and insulation mechanism were investigated. The defect dipoles ([MgTi″−VO••]× and [MgTi″−2NbTi•]×) could be formed inside co-doping BaTiO3 ceramics with various content of MgO, which is the source of colossal permittivity. Appropriate MgO content doping is favorable to enhance short-range hopping, thus improve grain resistance, grain boundary resistance and grain boundary activation energy. The 1.0 at% MgO modified BaTiO3-0.01Nb2O5 ceramics possess excellent performance at room temperature with colossal dielectric constant (ԑr = 4.5 × 104), low dielectric loss (tanδ<0.018), and high insulation resistivity (ρv = 6.52 × 1011 Ω cm). Meanwhile, good temperature stability is obtained in 1.0 at% MgO modified BaTiO3-0.01Nb2O5 ceramics, which satisfies the Electronic Industries Association (EIA) X8R (−55–150 °C, △εr/ε25≤ ±15%) specification. This study suggests that the defect-dipoles related polarization mechanism can be used to design the colossal permittivity BaTiO3-based ceramics.

Enhanced electrocaloric effect in the Sm and Hf co-doped BaTiO3 ceramics

In this work, the electrocaloric (EC) effect was studied in the (100-x)BaHf0.2Ti0.8O3-xBa0.94Sm0.04TiO3 (BHT-xBST) ceramics fabricated by the conventional solid-reaction method. By tuning composition to their diffuse phase transition (DPT), invariant critical point (ICP) and first-order phase transition (FPT), the large electrocaloric response with a temperature change of ΔT = 0.46 °C (at 64 °C) under 30 kV/cm and an electrocaloric strength of ΔT/ΔE = 0.18 K mm/kV under 12 kV/cm were achieved in BHT-70BST. In addition, BHT-50BST shows a broad EC working temperature window from 28 °C to 68 °C because of its diffusion behavior near the ferroelectric-to-paraelectric phase transition and multiphase coexistence. The maximum ΔT of BHT-50BST is larger than that of BHT-40BST with only diffusion character but no multiphase coexistence. This work may provide a design strategy to enhance EC performance with a broad working temperature region in lead-free rare-earth doped BaTiO3-based ceramics by combining the diffusion behavior, multiphase coexistence and heterovalent substitution.

High temperature stability and mechanical quality factor of donor-acceptor co-doped BaTiO3 piezoelectrics

Low temperature stability has limited the applications at elevated temperature for ABO3-type lead-free ceramics. And multi-grade resonances of piezoelectric ceramics are hardly obtained although the resonances are very important in some applications such as filter and resonator. High piezoelectric properties and large mechanical quality factors with multi-grade resonances can be obtained in (Li+-La3+) co-doped BaTiO3 ceramics, and excellent temperature stabilities are achieved in the ceramics. It has been shown that the thermal treatments both with and without electric field at 200 °C improve the piezoelectric properties and thermal stability further. Large piezoelectric constant (272 pC N1) and huge mechanical quality factor (2010) was obtained after thermal-electrical treatment, which is caused by Li+-La3+ ionic pair aligning along the external electric filed during thermal-electrical treatment. Moreover, the present study provides an effective method to design combination properties with high temperature stability for ABO3 perovskite ferroelectric ceramics.

Ferroelectric characteristics of Fe/Nb co-doped BaTiO3

[Formula: see text] ceramics ([Formula: see text] mol.%, [Formula: see text]:[Formula: see text] = 1:3, 2:3, 3:2, 3:1) were successfully prepared using the traditional solid-phase sintering method. The effects of the proportion doping (Fe/Nb) components on various properties of BaTiO3ceramics were studied. The X-ray diffraction showed that all solid solutions have the single cubic phase at room temperature, and that dielectric permittivity exhibits a maximum, Curie’s temperature at the peak. The ceramics have obvious peak shift effect: Curie’s temperature shifts to low temperature as Fe/Nb ratio increases. The high Fe/Nb ratio BaTiO3ceramic showed also an enhancement of the broadening effect for dielectric constant curve with respect to temperature, and dielectric permittivity peak reflected phase transition from rhombohedral to tetragonal polar-nano regions. Dielectric and ferroelectric properties of Fe/Nb co-doped BaTiO3ceramics have obvious enhanced ferroelectric properties and have slender hysteresis loop beneficial for energy storage materials.

Dense Sm and Mn Co-Doped BaTiO₃ Ceramics with High Permittivity.

The structure, valence state, and dielectric properties of (Ba1−xSmx)(Ti0.99Mn0.01)O3 (BSTM) (x = 0.02‒0.07) ceramics prepared via a high temperature (1400 °C/12 h) solid state reaction were investigated. A homogeneous and dense microstructure was observed in all samples. With increasing Sm content, the crystal structure changed from tetragonal (x ≤ 0.06) to cubic (x = 0.07) and unit cell volume (V0) decreased continuously, which was mainly due to the substitution of Ba2+ ions by smaller Sm3+ ions in the perovskite lattice. Electron paramagnetic resonance investigation revealed that Mn ions were reduced from high valence to low valence under the role of Sm3+ donor, and only Mn2+ ions were observed at x = 0.07. The Curie temperature (Tc) moved to lower values, from 105.5 down to 20.4 °C, and the x = 0.07 sample satisfied Y5V specification with high permittivity (ε′RT > 13,000) and low loss (tan δ < 0.03).