TiO3 Ceramics Research Articles

High quality of LiMg0.9Zn0.06Ni0.04PO4-TiO2 microwave ceramic and its application for 5G dielectric waveguide bandpass filter

A new microwave dielectric composite ceramic (1-x) wt%LiMg0.9Zn0.06Ni0.04PO4-x wt%TiO2 (0 ≤ x ≤ 18 wt%) was synthesized in the low sintering temperature range of 850 °C − 975 °C by the solid-state reaction method. The XRD diffractogram confirmed the coexistence of LiMg0.9Zn0.06Ni0.04PO4 and TiO2, and no second phase was detected. Due to their opposite τf values, the τf values of LiMg0.9Zn0.06Ni0.04PO4 solid solution ceramics were adjusted by adding different volume fractions of TiO2. The composite ceramic with x = 15 wt% sintered at 975 °C shows desirable microwave dielectric properties of εr∼10.30, Q×f ∼ 58,400 GHz (tan δ = 2.093 ×10−4), and τf ∼ + 4.04 ppm/ °C (at ∼12 GHz). Based on the 85 wt% LiMg0.9Zn0.06Ni0.04PO4-15 wt% TiO2 ceramics, a fourth order dielectric waveguide filter filled with composite ceramics is designed and packaged for the RF front-end of the China Mobile 5 G base station. The test results show that the center frequency of the filter is 4.65 GHz, the working bandwidth is 300 MHz, the filter has a good out of band rejection capability, and the insertion loss in band is 0.18 dB. Combined with the filter test data and material performance, the designed dielectric waveguide filter meets the communication requirements of the base station, and the higher Q×f microwave dielectric ceramic material can achieve low insertion loss and excellent frequency selection performance of the filter.

Optimized dielectric energy storage performance in ZnO-modified Bi0.5Na0.5TiO3-Sr0.7Bi0.2□0.1TiO3 ceramics with composite structure and element segregation

In this work, ZnO is introduced into the 0.55Bi0.5Na0.5TiO3-0.45Sr0.7Bi0.2□0.1TiO3 (BNT-SBT) to optimize the dielectric energy storage performance. ZnO is not only used as a sintering aid to decrease the sintering temperature and ceramic grain size, but also enhances the random fields and polar nanoregions activity in the ceramics by Zn2+ doping. Intriguingly, the ZnO-modified BNT-SBT ceramics present a 0–3 type composite structure containing the TiZn2O4 and Bi2Ti2O7 linear dielectrics. Moreover, obvious element segregation is generated in the BNT-based matrix grains showing different Sr2+/(Bi3+, Na+) ratios and polarization magnitudes. The significant variations in composition distribution, grain and domain configurations cause the overall optimization of energy storage properties, reflected in the enhanced breakdown strength, delayed polarization saturation, and reduced polarization hysteresis. As a result, the optimized Wrec ∼ 5.84 J/cm3 and η ∼ 93 % at 40 kV/mm is obtained in the BNT-SBT-0.10ZnO ceramic, superior to that of the BNT-SBT ceramic (Wrec ∼ 3.35 J/cm3 and η ∼ 89 % at 28 kV/mm).

The grain growth mechanisms for 0.8(Bi,Na)TiO3-0.2(Sr,Ti)O3 ceramics prepared using a two-step sintering process

ABSTRACT In this study, lead-free 0.8(Bi,Na)TiO3-0.2(Sr,Ti)O3 piezoelectric ceramics were prepared using a two-step sintering process to analyze their sintering mechanisms. Two-step sintering process has benefits of being able to be conducted at lower temperatures than conventional sintering process, but the complicated sintering mechanisms involved in this process have not been yet fully investigated. Therefore, in the present study, two-step sintering mechanism for lead-free piezoelectric ceramics was analyzed by estimating the activation energy required depending on the sintering conditions. Using the two-step sintering process, the piezoelectric charge and electromechanical coupling coefficients improved from 146 pC/N and 0.347 to 163 pC/N and 0.377, respectively. By comparing the grain-growth mechanisms for the conventional and two-step sintering processes, it appeared that the sintering mechanisms differed. By introducing the two-step sintering process, piezoelectric ceramics with improved piezoelectric charge and electromechanical coupling coefficients were produced.

Investigation of TiO2 and SiO2 Filled Polybutadiene Composite Substrates and Their Dielectric Properties

AbstractPolybutadiene‐based (PB) composite substrates filled with TiO2 and SiO2 ceramics were fabricated in this work. The total content of ceramic components modified by vinyltrimethoxysilane (A171) was fixed at 80 wt.% with TiO2 amount varying from zero to 8 wt.%. The differences of characteristics of ceramic fillers before and after surface modification were analyzed comprehensively and the treated ceramic fillers were uniformly distributed in the polymer matrix. The effects of TiO2 filler addition on the performances of SiO2/PB composite substrates, such as microstructure, moisture absorption, dielectric and thermal properties were also systematically studied. The composite filled with 4 wt.% TiO2 and 76 wt.% SiO2 exhibited excellent dielectric properties with proper dielectric constant (ϵr=3.2), ultra‐low dielectric loss (tanδ=0.0017) at 10 GHz and a near‐zero τϵ (0.5 ppm/°C) was obtained at filler content of 8 wt.% TiO2 and 72 wt.% SiO2.

Suppression of intrinsic thermal conductivity in Sr1-x Gd x TiO3 ceramics via phonon-point defect scattering for enhanced thermoelectric application.

A substantial reduction in the thermal conductivity for strontium titanate (ABO3) perovskite structure was realized for the A-site substitution of gadolinium (rare earth element) in SrTiO3 ceramics. The effect of Gd3+ substitution on the structure, composition, and thermoelectric properties of SrTiO3 was investigated. The substitution of Gd3+ in the SrTiO3 matrix resulted in the minimalization of thermal conductivity. The thermal conductivity followed a similar trend as that of thermal diffusivity, but specific heat capacity exhibited a non-monotonic trend. The thermal conductivity is reduced to 1.05 W m-1 K-1 for the minimal substitutional composition (Sr0.99Gd0.01TiO3) which is 30% less than that of SrTiO3 at 303 K. The variation in the ionic radii and atomic mass of the heavier rare earth Gd3+ substituted over Sr2+ resulted in the reduction of thermal conductivity of SGTO ceramics caused by the corresponding boundary scattering at low temperatures and temperature-independent phonon-impurity scattering at high temperatures.

The origin of dielectric relaxation behavior in TiO2 based ceramics co-doped with Zn2+, W6+ ions under a N2/O2 sintering atmosphere.

Dense (Zn0.5W0.5)xTi1-xO2 (ZWTOx) ceramics were fabricated using a conventional solid state reaction method with sintering under a nitrogen atmosphere (ZWTOx-N2) and an oxygen atmosphere (ZWTOx-O2), respectively. Colossal permittivity (ε > 104) and low loss (tan δ < 0.1) were simultaneously achieved in ZWTOx-N2 ceramics, and two types of dielectric relaxation behaviors observed were interpreted to be due to interface polarization and disassociation between oxygen vacancies and trivalent titanium ions, respectively. The impedance plots suggested that the ZWTOx-N2 ceramics are electrical heterostructures composed of semiconductor and insulator grain boundaries, which proved that the CP performance of ZWTOx-N2 ceramics almost originates from the internal barrier layer capacitance (IBLC) effect. In addition, a series of anomalous dielectric behaviors such as low permittivity and low frequency dispersion were observed for ZWTOx-O2 ceramics; polarization (P)-electric field (E) hysteresis loop curves were obtained for ZWTOx-O2 ceramics, and that impedance plots have shown that the ZWTOx-O2 ceramics display higher insulation resistivity. Density functional theory (DFT) calculations illustrated that the Zn2+-W6+ ion pairs are easy to form in ZWTOx-O2 ceramics, which causes destruction of the local lattice and thus leads to abnormal dielectric behavior. This work will provide a new strategy for defect engineering in TiO2 and other CP materials.

The effects of microstructure on the dielectric, ferroelectric and impedance properties of 0.5Ba(Zr0·2Ti0.8)O3-0.5(Ba0·7Ca0.3)TiO3 ceramics

0.5Ba(Zr0·2Ti0.8)O3-0.5(Ba0·7Ca0.3)TiO3 (BCZT) ceramics with average grain sizes from 3.26 to 18.15 μm were synthesized by adjusting the sintering temperature in the solid-state-reaction process. The effects of various grain sizes on the dielectric, ferroelectric, and impedance properties of BCZT ceramics were studied, and the liquid phase in the grain boundary was observed. When a solid solution exists in the grain boundary, both the maximum dielectric constant εmax and loss tangent tanδ are affected by the competition between the grain size effect and liquid phase in the grain boundary morphology. The energy storage efficiency increases and the energy density decreases owing to the improved compactness and hindered grain boundary conduction. The contributions of grain and grain boundary are demonstrated by two arc curves in impedance spectra. The effects of different grain boundary morphologies on the electrical properties of BCZT ceramics were quantitatively obtained by high-temperature impedance patterns and DC conductivity fluctuations. These results help to prepare different targeted functional ceramics by designing specific microstructures.

Enhanced energy storage performance achieved in Na0.5Bi0.5TiO3–Sr0.7Bi0.2TiO3 ceramics via domain structure and bandgap width tuning

Dielectric capacitors have attracted considerable attention owing to their excellent performance, including high charge-discharge rate as well as good temperature stability and fatigue resistance. Na0.5Bi0.5TiO3(NBT)-based ceramics are considered to be one of the most prospective lead-free dielectric materials because of their unique phase transition and relaxation characteristics. However, the energy storage performance obtained in the currently available materials is not satisfactory. We propose a synergetic optimization strategy through composition design and domain engineering in 0.74Na0.5Bi0.5TiO3-0.26Sr0.7Bi0.2TiO3 (NBSBT) ceramic, i.e., by simultaneously refining the grain size and widening the bandgap width, which facilitates a large breakdown strength and ΔP (Pm–Pr). A high dielectric constant and low remnant polarization is beneficial for obtaining improved energy storage properties. Piezoelectric force microscopy revealed that the introduction of NaNbO3(NN) disrupts the microdomains of the NBSBT ceramics and promotes the generation of polar nano-regions. An excellent energy storage density (Wrec) of 4.83 J/cm3 and a moderate efficiency (η) of 87.4% are obtained at the optimum composition of 0.85NBSBT-0.15NN. These characteristics demonstrate that (1-x)NBSBT-xNN based ceramics are promising candidate materials for high-temperature energy storage devices and provide an effective strategy for the design of next-generation dielectric capacitors.

Enhanced Energy Storage Performance by Relaxor Highly Entropic (Ba0.2Na0.2K0.2La0.2Bi0.2)TiO3 and (Ba0.2Na0.2K0.2Mg0.2Bi0.2)TiO3 Ferroelectric Ceramics

Dielectric ceramic capacitors have attained considerable attention due to their energy storage performance in the field of advanced high/pulsed power capacitors. For such a purpose, configurationally disordered composite material engineering, with the substitution of suitable oxide cations at a single lattice site have demonstrated a strong dielectric relaxor phase with the ability to show high performance capacitive properties. Herein, two prominent high-entropy ceramics systems (Ba0.2Na0.2K0.2A0.2Bi0.2)TiO3, (with A = La and Mg) were fabricated to evaluate their structural, ferroelectric and dielectric properties. XRD patterns and Rietveld refinement of the XRD analysis confirmed the cubic structure Pm3¯m space group of the ceramics. The relative dielectric analysis of Ba0.2Na0.2K0.2La0.2Bi0.2TiO3 (BNKLBT) and Ba0.2Na0.2K0.2Mg0.2Bi0.2TiO3 (BNKMBT) ceramics were demonstrated with relaxor ferroelectric behavior having diffusion coefficients of 1.617 and 1.753, respectively. Moreover, BNKLBT and BNLMBT ceramics presented better stored energy density (1.062 J/cm3 and 0.8855 J/cm3, respectively) and high energy conversion efficiency (80.27% and 82.38%, respectively) at an electric field of 100 kV/cm. The results clearly demonstrate that such high-entropy configured ceramics have the potential to be used in efficient energy storage devices.

Fabrication, microstructure, dielectric, and ferroelectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3 nanograined ceramics via cold-sintering-assisted sintering

(Bi0.5Na0.5)0.94Ba0.06TiO3 nanograined ferroelectric ceramics were successfully fabricated via a simple cold-sintering-assisted sintering method. Here, the cold-sintering-assisted sintering method includes two steps, i.e., cold-sintering and post-annealing. The cold-sintered samples were prepared via moistening (Bi0.5Na0.5)0.94Ba0.06TiO3 powders with de-ionized water followed by compressing under various pressures at 180 °C, which exhibit densities as high as 83.7% ∼ 93.6% of the theoretical value. Effects of cold-sintering time and pressure on densification and microstructure of the cold-sintered samples were studied. The cold-sintered samples were then annealed at 800 °C–900 °C, which are far below the temperatures for sintering (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics via the conventional solid-state reaction method. After being annealed, the relative densities of the post-annealed ceramics are all higher than 96%. The dielectric and ferroelectric behaviors of the post-annealed ceramics were compared with those of the ceramics with the same composition and various mean grain sizes. The cold-sintering-assisted sintering mechanism was discussed based on the transmission electron microscopy measurement. The study provides a simple and efficient cold-sintering-assisted sintering method for obtaining dense (Bi0.5Na0.5)0.94Ba0.06TiO3 nanograined ferroelectric ceramics at relatively low temperatures with excellent dielectric and ferroelectric properties.

Influence of Sintering Temperature Strategy on Structural, Dielectric, and Resistive Switching in Bulk Ba0.7Sr0.3TiO3 Ceramics

Influence of Sintering Temperature Strategy on Structural, Dielectric, and Resistive Switching in Bulk Ba0.7Sr0.3TiO3 Ceramics

Enhanced energy storage efficiency of Ba0.8Sr0.2TiO3 ceramics modified by BiTaO3

Lead-free (1-x)Ba0.8Sr0.2TiO3-xBiTaO3 (BST-xBTA) ceramics were prepared via a solid-state reaction process. The effect of BTA addition on the energy storage properties of BST ceramics was investigated. The pure perovskite phases were found in the BST-xBTA ceramic samples as x ≤ 0.12. With the increasing BTA content, the maximum breakdown strength (Eb) reached 130 kV/cm at x = 0.12, twice that of the undoped samples. The large Eb and slim ferroelectric loops of the 0.88BST-0.12BTA ceramics indicated an advantageous energy density of Wrec ∼0.526 J/cm3 and a high energy efficiency of η ∼98% at 130 kV/cm. The low dielectric loss and high η make this ceramic system a promising material applying pulsed-powder devices.

Effect of substitution of (NiNb)4+ into B-sites on the phase formation, microstructure and electrical properties of Bi0.47Na0.47Ba0.06TiO3 ceramics

Bi0.47Na0.47Ba0.06Ti1-x(Ni1/3Nb2/3)xO3 ceramics (abbreviated as BNBT1-x(NN)x, x = 0, 0.01, 0.03 and 0.05) were synthesized by solid-state combustion. The effect of x on the phase formation, microstructure and electrical properties of BNBT1-x(NN)x ceramics was examined. The XRD pattern indicated the coexistence of rhombohedral and tetragonal phases in all the specimens. Moreover, Rietveld refinement confirmed that the tetragonal phase increased from 47 to 71% when x increased from 0 to 0.05. The morphology of BNBT1-x(NN)x ceramics was observed by SEM and the ceramics grains showed polygonal shapes and the grain growth tended to be anisotropic. With (NiNb)4+ substitution, the average grain sized decreased rapidly from 1.7 to 1.0 µm and the grain size distribution was narrower as the amount of (NiNb)4+ increased. The density, remnant polarization (Pr) and coercive field (Ec) rapidly decreased with increasing x. A significant decrease in the ferroelectric properties was caused by the increasing tetragonal phase.

Phase formation, microstructure and electrical properties of Ba0.9Ca0.1TiO3 ceramics fabricated via the solid-state combustion technique

In this research, the effects of calcination temperature in a range of 1050–1200 °C for 2 h and sintering temperature in a range of 1325-1400 °C for 2 h on phase formation, microstructure and electrical properties of lead-free Ba0.9Ca0.1TiO3 (BCT) ceramics fabricated via the solid-state combustion technique were investigated. For the XRD result, all the ceramics exhibited a coexisting phase between tetragonal and orthorhombic. The ceramic grain size tended to increase with increase of the sintering temperature. For BCT ceramic produced by the optimum sintering temperature (1375 °C for 2 h), the dielectric, ferroelectric and piezoelectric properties of ε C=7393, P r=7.60 μC/cm2 , E C=5.99 kV/cm and d 33=158 pC/N, respectively, were obtained.

Effect of electric field induced structural ordering on photo-luminescence and piezoelectric response of praseodymium doped (Na0.41K0.09Bi0.5)TiO3 ceramics

A correlation of the ferroelectric and photoluminescence response to the structural ordering of praseodymium doped (Na0.41K0.09Bi0.5)TiO3 has been investigated. It has been observed that the ferroelectric and photoluminescence response lacks one-to-one correlation. The ferroelectric response is generally driven by long-range polar ordering. On the contrary, photoluminescence response is concomitant to the local site symmetry around the praseodymium ion. The optimum ferroelectric response has been observed for 1.0 at. % praseodymium doped (Na0.41K0.09Bi0.5)TiO3, whereas for the sample with higher doping concentration, it diminishes gradually due to disruption of the long-range ordering. On the other hand, with the establishment of long-range ordering, no noticeable shift in the position and shape of the photoluminescence lines has been observed. However, a quenching in the photoluminescence intensity of the hypersensitive transitions (1D2 → 3H4) takes place, which has been associated with the modification in the local site symmetry. It has been argued that structural modification has an influence on the photoluminescence intensity but does not affect the energy levels of these transitions. The observed dielectric, piezoelectric, and photoluminescence response has been explained on the basis of the amphoteric nature of praseodymium in (Na0.41K0.09Bi0.5)TiO3.

Optimization of Processing Steps for Superior Functional Properties of (Ba, Ca)(Zr, Ti)O3 Ceramics.

Lead-free piezoelectric ceramics with nominal composition at morphotropic phase boundary Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCTZ) prepared by different processing routes and sintered either by conventional solid-state reaction or by spark plasma sintering (SPS) techniques were comparatively investigated to observe the role of structural modifications and of microstructures on the dielectric, ferroelectric, piezoelectric and electrocaloric responses. The ceramics presented relative densities from 75% to 97% and showed variations in their phase composition as a result of variable mixing and different synthesis and sintering parameters providing local compositional heterogeneity. As result, all of the ceramics showed diffuse phase transition and ferroelectric switching responses, with parameters affected mostly by density (Pr between 3.6 to 10.1 μC/cm2). High values for the electrocaloric response in the Curie range were found for the ceramics with predominantly orthorhombic character. Field-induced structural modifications were probed by tunability anomalies and by XRD experiments in remanence conditions. Piezoelectric effects with notably high figure of merit values were assigned to the better densification and poling efficiency of BCTZ ceramics.

Giant comprehensive energy storage performance in Pb-doped Bi0.25Na0.25Sr0.5TiO3 ceramics via multiscale regulation of grain size and relaxation behavior

Developed ceramic capacitors with excellent recoverable energy storage density (Wrec) and efficiency (η) are greatly desired for next-generation pulsed power devices but challenge as well. Herein, outstanding Wrec of 5.2 J/cm3 and η of 82% are achieved in the PbO-doped fine grain Bi0.25Na0.25Sr0.5TiO3 (BNST-P) based relaxor ferroelectric ceramics. The corresponding mechanism is that A-site Pb-doping increases maximum polarization and breakdown strength, and suppresses remnant polarization simultaneously. Meanwhile, the energy storage property possesses excellent temperature and frequency stability, and the variation of Wrec and η is less than 5% within the range of 25–100 °C and 2–100 Hz. Encouragingly, superior charge-discharge performance with fast discharge speed t0.9 of 24 ns and high power density PD of 296 MW/cm3 is obtained. These striking comprehensive results suggest BNST-P ceramics possess potential prospects for applications.

Good temperature stability and colossal permittivity in TiO2 ceramics doped with Cu2+ and W6+ ions

The rutile TiO2 ceramics substituted with acceptor and donor ions are regarded to be promising candidate materials for energy storage because of their colossal permittivity (CP). In this work, a good CP performance (ϵr>104) was achieved in all of (Cu0.5W0.5)xTi1-xO2 (CWTOx) ceramics fabricated by a traditional solid reaction method. Remarkably, CWTO0.015 ceramic obtained an acceptable temperature stability accompanied a low dielectric loss (tan δ < 0.1) within a broad frequency/temperature range, which satisfies the application requirement of X8R. Two kinds of abnormal dielectric relaxation at low and high temperature region were interpreted by interface polarization and ionization of oxygen vacancies, respectively. Data of complex impedance combined XPS and EPR results proved that the IBLC effect is dominant to the CP performance of CWTOx ceramics. The finding in this work is expected to promote the further development and application of CP materials.

Enhanced unipolar electrical fatigue resistance and related mechanism in grain-oriented Pb(Mg1/3Nb2/3)O3-Pb(Zr, Ti)O3 piezoceramics

Piezoceramics with high and fatigue-resisted piezoelectric properties are strongly desired for actuator applications. In this work, textured Pb(Mg1/3Nb2/3)O3-Pb(Zr, Ti)O3 ceramics with Lotgering factor F001∼98% were fabricated by templated grain growth technique. Strong [001]c-grain orientation (f∼90% and r∼0.22) of the textured ceramics effectively produced about 230% enhanced piezoelectric coefficient d33* (i.e., Smax/Emax) and substantially improved unipolar electrical fatigue resistance. Unipolar polarization Pmax and d33* of the textured ceramics were nearly maintained up to 106 unipolar cycles, while 19% and 14% degradations were respectively observed from randomly oriented counterparts. Especially, normalized d33* of the textured ceramics shows better unipolar fatigue resistance than those of piezoceramics reported previously. Much lower bipolar strain asymmetry γs (∼4%) was observed from the textured samples fatigued after 106 unipolar cycles as compared to γs∼23% for randomly oriented counterparts. While charged defect accumulation model described the serious fatigue deteriorations in randomly oriented ceramics, the current work revealed that substantially enhanced unipolar fatigue resistance of the textured ceramics is mainly associated with the inherent fatigue anisotropy, weakened local bias fields owing to both enhanced domain mobility and lower defect density near grain boundaries/interfaces, and increased intrinsic contribution due to more tetragonal content. These superior characteristics suggest the great potential of textured ceramics for high-performance and robust actuator applications.

High-entropy MTiO3 perovskite oxides with glass-like thermal conductivity for thermoelectric applications

High-entropy oxides with complex compositions can be designed to lower the thermal conductivity of SrTiO3-based thermoelectric materials to optimize their properties. High-entropy (Sr0.25Ca0.25Ba0.25RE0.25)TiO3 (RE=Nd, Sm, Eu, Gd, Dy, Ho) ceramics were designed to systematically investigate the effects of critical average ionic radius (rA̅), atomic size disorder factor (δAr), and the mass difference factor (δAm) of A-site elements on the single-phase formation, disorder microstructure, and the thermoelectric properties. The successful synthesis of single-phase perovskite-type ceramics of (Sr0.25Ca0.25Ba0.25Nd0.25)TiO3, (Sr0.25Ca0.25Ba0.25Sm0.25)TiO3, and (Sr0.25 Ca0.25Ba0.25Eu0.25)TiO3 by a solid-state reaction method were reported. When rA̅ ＜1.377 Å, indicator of δAr≥ 12.86, and δAm≥ 18.6, the pyrochlore phase of Gd2Ti2O7, Dy2Ti2O7, and Ho2Ti2O7 precipitated. Importantly, the obtained temperature- independent low glass-like lattice thermal conductivity of 2.27 W/(m∙K) was significantly reduced by 68.2–21.4% compared with the majority values ranging from 7.16 W/(m∙K) at 300 K to 2.89 W/(m∙K) at 1073 K of SrTiO3-based polycrystal system. The temperature independence of thermal conductivity over the whole range of 323–1073 K realizes the concept of ‘phonon-glass electron crystal’. Evidence strongly confirmed that large lattice distortion, TiO6 octahedral twist, dislocations, and complex strain field coexisted by Raman, HRTEM combined with GPA analysis in the high-entropy perovskite structures.