CaTiO3 Ceramics Research Articles

Structural, Microstructural, Dielectric and Ac-conductivity of CaTi1-xFexO3 Multiferroic Materials Synthesized by Solid State Method

In this study, the structural, microstructural, dielectric and conductivity properties of Fe-doped CaTiO3 (CT) ceramic were investigated. These ceramics were successfully synthesized using the conventional solid-state method. The X-ray diffraction and Rietveld refinement results showed that the ceramics at x=0.0, 0.1, 0.2 and 0.3 crystalized in the orthorhombic phase with the Pmmm space group. While for x=0.4, 0.5 and 0.6, the phase formation changes from orthorhombic to tetragonal phase with P4/mmm group space. The SEM results revealed a semi-spherical shape of grain for lower Fe content (≤0.4), while at x=0.5 and 0.6 an agglomeration phenomenon is observed and the observed density of the sample at x=0.5 is higher than the other ceramics. The dielectric properties were studied as function of frequency and temperature. The dielectric permittivity (ɛ’r) decreases as function of frequency at lower frequency region and remain almost independent of frequency at high frequency region in the whole temperature range of R.T–520 °C. Each converges at high frequency (>105 Hz) for all the temperatures. The evolution of ɛ’r as function of temperature for pure CT ceramic showed a stability at large range of temperature (from R.T to 250°C). For substituted ceramics, we obtained a phase transition which shifted to the lower temperature with the increase of Fe content. And the value of ɛ’r, increases for Fe-doped CT ceramics and reaches a maximal value for x=0.5 which is 50 time bigger than the pure ceramic. The AC conductivity, σAC, is found to increase rapidly as a function of frequency, at low frequency region, and increases linearly at high frequency region, which confirms the hopping of electrons related to the conduction mechanism. The σAC evolution is found to follow the Jonscher’s law and the s exponent decreased with the increasing temperature which is related to the correlated barrier height (CBH) model. And the σAC values increase with the increases of Fe content.

CaTiO3-rich precipitates and their impacts on ferroelectric domains during heating in (Ba,Ca)TiO3 ceramics

CaTiO3-rich precipitates and their impacts on ferroelectric domains during heating in (Ba,Ca)TiO3 ceramics

Electric field response of ferroelectric domains near non-polar precipitates in BaTiO3-based ceramics

Precipitates have recently been found to significantly enhance the mechanical quality factor in piezoelectric ceramics. Such a piezoelectric hardening effect was attributed to strong interactions between ferroelectric domains and precipitates. In the present work, the response of domains to applied electric fields is observed in situ via transmission electron microscopy in aged (Ba, Ca)TiO3 ceramics with precipitates to reveal the underlying mechanism of this phenomenon. Ferroelectric domains in the Ba-rich matrix grain are observed to be more concentrated near non-polar Ca-rich precipitates. With increasing applied voltage, domains separate from precipitates merge together first, while those near precipitates persist to higher voltages. During ramping down, domains nucleate from precipitates. These direct observations confirm the strong interactions between ferroelectric domains and precipitates in piezoelectric ceramics.

Sintering behavior of 0.95MgTiO3-0.05CaTiO3 ceramics with high densification, high Q and enhanced mechanical properties for 5G massive MIMO technology: Effect of particle gradation

An increase in the requirements for microwave dielectric materials was brought on by the quick growth of communication technologies. In this study, the sintering problems including the narrow sintering densification range and high sintering temperature of 0.95MgTiO3-0.05CaTiO3 (95MCT) ceramics with high densification and high Q, as one of the candidate materials for 5G filters, were discussed and overcome through the particle gradation with sub-micrometric and micrometric powders according to closest packing models. It was found that sub-micrometric (0.7–1 μm) 95MCT powder particles agreed well with the Andreasen model, while micrometric (1–3 μm) particles agreed better with the Dinger-Funk model. With increasing of sub-micrometric powders, the activation energy decreased from 926.01 ± 75.49 to 569.49 ± 31.57 kJ/mol, and the relative density of samples which contained 20–60% fine powders were increased to 98%. The average grain size and grain homogeneity decreased from 7.36 μm to 2.54 μm and 3.36 to 1.79, respectively, to improve the mechanical properties. The results show that the powder grading further improved the comprehensive performance of 95MCT, and the best performance point was J1 which exhibited excellent microwave dielectric properties with εr = 21.1, Qf = 82000 GHz, τf = −0.9 ppm/°C, RD = 98.2%, σf = 178.7 MPa and HV = 8.78 GPa after sintering at 1225 °C for 3h.

A high-performance, temperature-stable Mg1.99Ga0.01Si0.99Al0.01O4-CaTiO3 microwave dielectric ceramic and its 5 G/6 G waveguide filter

New ultra-low loss, temperature-stable composite ceramics, (1-x) Mg1.99Ga0.01Si0.99Al0.01O4-xCaTiO3, have been developed with a view to expanding the portfolio of low-cost, MW dielectrics available for 5 G/6 G telecommunications, currently dominated by 95 wt%MgTiO3-5 wt%CaTiO3, (Mg,Ca)TiO3 (relative permittivity, εr ∼ 21, quality factor, Q×f ∼ 56,000 GHz and temperature coefficient of resonant frequency, τf ∼ 0 ppm/°C). Compared with (Mg,Ca)TiO3, 89 wt%Mg1.99Ga0.01Si0.99Al0.01O4-11 wt%CaTiO3 ceramics are also temperature stable (τf = −2.72 ppm/°C) but have lower εr (∼8.55) and a higher Q×f (∼ 72,900 GHz @ 12 GHz and 80,900 GHz @ 26 GHz), better suited to the higher frequencies earmarked for 6 G millimeter-wave (mm-wave) applications. To demonstrate its potential for 5 G/6 G telecommunications, a waveguide filter with novel negative coupling structure was fabricated based on simulated results. The filter had low insertion loss (0.43 dB) at the center frequency (4.8 GHz) and high selectivity with a roll-off rate of 576/375 dB/GHz. The S-parameters matched well at 25 °C and 85 °C, demonstrating that the filter had excellent temperature stability and was therefore suitable for future 5 G/6 G microwave and mm-wave communication devices.

Evolving energy-storage performances during temperature-induced antiferroelectric P–R phase transition in NaNbO3-based lead-free ceramics

Temperature-driven antiferroelectric (AFE) P to AFE R phase transition in MnO2-doped 0.90NaNbO3-0.10CaTiO3 ceramics was investigated through polarization-field response, energy-storage and charge-discharge properties as well as ex/in-situ multiscale structure characterization. Both room-temperature AFE P and high-temperature AFE R phases show double polarization-electric field hysteresis loops, indicating a reversible field-driven AFE to ferroelectric (FE) phase transition. An abnormal variation of critical fields for the AFE-FE and FE-AFE phase transition and a faster polarization-field response contribute to the reduced polarization hysteresis for both AFE P and R phases but an obviously expanded linear polarization-field response only for AFE R phase, being responsible for a two-time significant enhancement in energy-storage properties from P phase to P–R phase boundary and then to R phase. The variation of unit cell anisotropy and domain morphology with temperature was found to play crucial roles in the modulated field-driven phase transition behavior and polarization-field response on heating.

Low-temperature sintering and phase component modulation of 0.95MgTiO3–0.05CaTiO3 microwave dielectric ceramics

This study prepared glass doped 0.95MgTiO3–0.05CaTiO3 (95MCT) ceramics with excellent microwave dielectric properties via phase constituent regulation. Based on XRD and semi-quantitative analysis, it is found that the types of glass, addition amounts of glass, and sintering method can introduce different phase compositions. With the aid of the low softening point for glass materials and the liquid phase sintering mechanism, the 95MCT ceramics can be densified at a relatively low temperature. Meanwhile, based on the mixture rule, adjusting the proportion of each phase structure by altering the sintering method, the optimum temperature (1200 °C) for 95MCT ceramics is reduced by about 200 °C without deteriorating performance. Typically, the 95MCT ceramic doped with 1 wt % ZnO–B2O3–SiO2 glass demonstrates excellent microwave dielectric properties: εr = 18.3, Q × f = 50824 GHz (@7.9 GHz).

Modification of high-temperature electrical properties in CaTiO3 ceramics by Sm3+ and Al3+ doping

Modification of high-temperature electrical properties in CaTiO3 ceramics by Sm3+ and Al3+ doping

Investigation of impact of Zr-doping on the structural and microwave dielectric properties of CaTiO3 ceramics

A new lead-free composition of Ca(Ti1-xZrx)O3, 0.0 ≤ x ≤ 1.0 ceramics was fabricated by a conventional method. The effects of B-site Zr substitution on the structure and microwave dielectric properties of CaTiO3 ceramics were investigated using X-ray diffraction, scanning electron microscopy, and impedance analyzers. Rietveld's refinement of the XRD pattern revealed that all the ceramics has an orthorhombic structure with space group Pbnm. The SEM micrographs revealed that the samples have a dense microstructure and spherical grain shape. The dielectric constant value (ϵr) decreased to 27 with increasing Zr4+ concentrations and the maximum dielectric constant (175) was reported for CaTi0·5Zr0·5O3 ceramics. The quality factor (Q) value of CaZrO3 ceramics reached 3267 GHz even though pure CaTiO3 ceramics possesses relatively smaller quality factor values equal to 2622.0 GHz and the maximum quality factor (∼8400 GHz) was achieved for x = 0.5.

Influence of MnO2 addition on the dielectric properties of 0.95MgTiO3-0.05CaTiO3 ceramics sintered in a reducing atmosphere

The increasing cost of palladium has demonstrated the significant value of using inexpensive base metals as inner electrodes for RF/microwave multilayer ceramic capacitors. However, solving the co-sintering problem of dielectric ceramics with base metals such as copper is highly challenging, as sintering in a reducing atmosphere is required to prevent the oxidation of the base metals. In this work, the feasibility of sintering nonreducible MnO2-doped 0.95MgTiO3-0.05CaTiO3 (95MCT) ceramics in a reducing atmosphere (H2-N2, pO2=1×10−10∼1×10−11MPa) at 1000 °C was investigated. The effects of the MnO2 additive (1.6–2.4 mol%) on the phase structures, dielectric properties, and thermal stability were studied. Thermally stimulated depolarization current (TSDC) analysis and X-ray photoelectron spectroscopy (XPS) were conducted to characterize the oxygen vacancies and Mn ion valence state in MnO2-doped ceramics, indicating that Mn plays an important role in the dielectric properties, especially the extrinsic dielectric loss. With the optimized addition of 2.0 mol% MnO2, due to the decrease in oxygen vacancy concentration, the samples with εr=20.22 exhibited the attractive properties of a high insulation resistivity of IR =3.65×1014 Ω∙cm and a low dielectric loss of tanδ=0.036%, meeting the C0G specifications. The results show that the 2.0 mol% MnO2-doped 0.95MgTiO3-0.05CaTiO3 ceramic is an outstanding nonreducible dielectric material for base-metal electrode RF/microwave multilayer ceramic capacitor applications with low cost, excellent dielectric properties, and high reliability.

Temperature stable dielectric properties of Mg2TiO4–MgTiO3–CaTiO3 Ceramics Over a Wide Temperature range

The zero resonant frequency temperature coefficient (τf) of microwave dielectric ceramics (MWDCs) at high and low temperature have attracted great attention in the development of microwave communication equipment. In this work, the Mg2TiO4–MgTiO3–CaTiO3 (MMC) ceramics with meeting the application requirements of 5G communication were prepared by traditional solid-phase sintering after investigating the relationship among phase compositions of xMg2TiO4-(0.931-x)MgTiO3-0.069CaTiO3 and 0.34Mg2TiO4-0.591MgTiO3-yCaTiO3, sintering process, and dielectric properties in detail. The results show that the dielectric properties of MMC ceramics are strongly affected by the phase relative contents of MgTiO3, Mg2TiO4 and CaTiO3. For instance, MMC ceramics with approximate τf = 0 is contributed by mutual compensation of Mg2TiO4 and MgTiO3, in which the Mg2TiO4 phase plays an important role in decreasing the τf value; and the increase of CaTiO3 will greatly increase the εr value for MMC ceramics, while has a negative effect in the Q × f value. After three-phase regulation, the 0.32Mg2TiO4-0.611MgTiO3-0.069CaTiO3 microwave dielectric ceramic has a better dielectric temperature stability, associated with dielectric properties of εr = 19.7, Q × f = 55,400 GHz (at 8.43 GHz), τf- = 4.5 ppm/°C (−40 °C–25 °C), and τf+ = −5.1 ppm/°C (25 °C–90 °C).

Lattice disorder effect on the structural, ferroelectric and electrocaloric properties of (Ba, Sr, Ca)TiO3 ceramics

We report the effect of A-site disorder σ2 on the structural, dielectric, ferroelectric (FE) and electrocaloric (EC) properties of lead-free Ba1-x-ySrxCayTiO3 (0.025 ≤ x ≤ 0.3, 0.275 ≤ y ≤ 0.113) perovskites. We have synthesized a series of samples with the same A-site cationic mean radius but different A-site ionic radii variance (i.e., A-site disorder) σ2. The tetragonal distortion and FE Curie temperature TC are found to decrease with decreasing A-site disorder σ2. The temperature of the maximum EC effect decreases from ~120–27 °C with decreasing disorder σ2. The highest adiabatic temperature change ΔT obtained using both the direct and indirect methods reaches ~0.8 K for the sample with optimized A-site disorder σ2. Our results suggest that, in addition to the lattice distortion, the lattice disorder might be a new and effective parameter for promoting the EC effect.

Microwave hybrid sintering of 0.95(Mg0.95Zn0.05)TiO3-0.05CaTiO3 ceramics and its microwave dielectric properties

Microwave dielectric ceramic powder of 0.95(Mg0.95Zn0.05)TiO3-0.05CaTiO3 (MCT) has been prepared by solid-state reaction method through single-step calcination at 1150 °C. The green bodies prepared from the calcined powder have been sintered by conventional, susceptor-aided, and hybrid microwave sintering techniques followed by annealing. XRD of calcined and sintered ceramics show (Mg,Zn)TiO3 as a major phase with CaTiO3 as a minor secondary phase. Fractographs of fired ceramics obtained by SEM show similar features in conventional and hybrid microwave types of sintering. Microwave dielectric properties such as relative permittivity(εr), temperature coefficient of resonant frequency(τf), and unloaded quality factors (Qu) for conventional sintered at 1325 °C for 4 h are—εr~19.8, τf< –6 ppm/°C and Qu.f 69,600 GHz at 6 GHz. Ceramics obtained through susceptor-aided microwave sintering at 1325 °C for 4 h show poor fired density. But ceramics got by microwave-hybrid sintering (resistive + microwave) at the same temperature show εr~20.6, Qu.f~81,600 GHz at 6 GHz and τf~−6.9 ppm/°C. The effect of hybrid microwave sintering on the dielectric properties of MCT ceramics is found to be more subtle than microstructural.

Dielectric properties, microstructure and phase evolution of non-stoichiometric 0.9Mg2+xSiO4+x-0.1CaTiO3 microwave dielectric ceramics

In the present work, non-stoichiometric 0.9Mg2+xSiO4+x-0.1CaTiO3 ceramics with nero-zero τf were prepared by using the conventional solid-phase reaction method. The effects of additional magnesium contents on the sintering behavior, phase evolution, microstructure, and microwave dielectric properties of the ceramics were investigated. Based on the XRD analysis, the relationship between phase composition and microwave dielectric properties was investigated. The τf value was closely related to secondary phase, such as MgSiO3 and Mg2TiO4. The Q × f and εr depended on the grain size distribution and porosity. Optimally, samples with a x value of 0.075 and sintering at 1425 °C for 3 h showed microwave dielectric characteristics of εr = 9.78, high Q × f = 68,048 GHz and near-zero τf = + 4.57 ppm/°C. As a result, the 0.9Mg2+xSiO4+x-0.1CaTiO3 ceramics are regarded a potential candidate for microwave dielectric applications.

Grain size engineered 0.95MgTiO3–0.05CaTiO3 ceramics with excellent microwave dielectric properties and prominent mechanical performance

AbstractMicrowave communication systems are being developed with the goal to achieve miniaturization and high reliability. There are urgent requirements for microwave dielectric materials to exhibit low sintering temperatures, excellent microwave dielectric properties, and prominent mechanical performance. However, simultaneously achieving these requirements is a significant challenge. These concerns have been addressed in the uniform ultrafine‐grained 0.95MgTiO3–0.05CaTiO3 ceramics with an average grain size of ~0.6 µm via a grain size engineering strategy. Interestingly, the sintering temperature in the unique two‐step sintering method of 1250℃/1 min and 1130℃/10 h is much lower (200–300℃) than that obtained in the conventional sintering method reported previously (1400–1450℃). Excellent dielectric properties are achieved, with relative permittivity εr = 20.11, quality factor Q × f = 68 613 GHz, and temperature coefficient of resonant frequency τf = 1.81 ppm/℃. The bending strength , Vickers hardness Hv, and elastic modulus E reach up to 212.4 MPa, 10.1 GPa, and 200.7 GPa, respectively. These values are significantly enhanced over those of samples obtained via the conventional sintering method with an average grain size of ~2.5 µm. For the first time, uniform ultrafine‐grained microwave dielectric materials with excellent microwave dielectric properties and prominent mechanical performance were synthesized. This work provides a guideline for developing other high‐performance microwave dielectric materials and makes a significant contribution to the miniaturization and high reliability of microwave dielectric devices.

Effect of Zr4+ on the structural and microwave dielectric properties of CaTiO3 ceramics

The new ceramic composite of Ca(ZrxTi1-x)O3 had been prepared using the conventional mixed oxide solid state reaction method. The effects of Zr4+ ions substation over Ti4+ ions on the microwave dielectric properties of the CaTiO3 ceramics were investigated. The phase analysis showed that the specimens Ca(ZrxTi1-x)O3 presented single phase with orthorhombic structure in the range of x = 0.0–0.7 when sintered at 1300 °C for 3 h. The addition of Zr4+ facilitated the formation of large round-like grains with porous microstructure. The solid solution with x = 0.7 sintered at 1300 °C for 3 h showed a good combination of dielectric properties: and (at 2.5 GHz).

Impedance spectroscopy, B-site cation ordering and structure–property relations of (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 ceramics for 5G dielectric waveguide filters

Dense (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 ceramics were synthesized via solid-state reaction. The crystal structure and microwave dielectric properties of the ceramics were systematically investigated. Rietveld refinement revealed that when x ≤ 0.2, the ceramics had a rhombohedral structure with an R-3c space group. When x ≥ 0.5, the ceramics had an orthorhombic structure with a Pbnm space group. Selected area electron diffraction and Raman spectroscopy analyses proved that the microwave dielectric ceramics had a B-site order, which accounted for the great improvement in microwave dielectric properties. The content of oxygen vacancies was identified through X-ray photoelectron spectroscopy, and the change rule of Q × f was closely related to oxygen vacancy content. The perturbation of A-site cations had an important influence on dielectric constant. Specifically, with the increase in Ti4+ content, the perturbation effect of the A-site cations was enhanced and dielectric constant increased. When x = 0.65, the temperature coefficient of resonant frequency of the (1 − x) La[Al0.9(Mg0.5Ti0.5)0.1]O3–x CaTiO3 microwave dielectric ceramics was near zero. The optimal microwave dielectric properties of 0.35LaAl0.9(Mg0.5Ti0.5)0.1O3–0.65CaTiO3 were εr= 44.6, Q × f = 32,057 GHz, and τf= +2 ppm/°C.

Effects of octahedral tilting on the site of substitution of manganese in CaTiO3

Electron paramagnetic resonance (EPR) and X-ray absorption fine structure measurements were combined with first principles calculations to investigate the substitutional behavior of Mn ions in perovskite CaTiO3 ceramics. While transition-metal dopants in perovskite-structured oxides often act as aliovalent defects, Mn in CaTiO3 is amphoteric and concurrently occupies both Ca and Ti sites as Mn2+ and Mn4+, respectively. Contrary to the behavior of Mn in SrTiO3 and BaTiO3, which exhibit larger geometric perovskite tolerance factors, in CaTiO3, it is determined that Mn2+ prefers A-site substitution. Density functional theory (DFT) calculations provide insight to the unique defect chemistry of Mn-doped CaTiO3 compared to SrTiO3 and BaTiO3, highlighting the role of octahedral rotations which accommodate ionic size mismatch between the larger host and smaller dopant cations on the cuboctahedral sites without significant dopant-ion displacements. Superposition models of the EPR zero-field splitting parameters for multiple types of Mn defect centers were considered based on the structural parameters of DFT calculations, and these results, combined with the EPR, DFT, and X-ray absorption analysis, were used to determine the point defect substitution mechanisms of Mn-CaTiO3.

Preparation, structure and microwave dielectric properties of novel La2MgGeO6 ceramics with hexagonal structure and adjustment of its τf value

A novel La2MgGeO6 ceramic was synthesized through a solid-state reaction process within a sintering temperature range of 1450–1550 °C. By a combination of X-ray diffraction and Rietveld refinement analyses, the ceramics were found to have a pure hexagonal phase structure belonging to space group R3/146. The scanning electron microscopy images revealed that the ceramic grains were closely connected. The effects of internal (lattice energy, valence bond, and fraction packing) and external factors (density) on the microwave properties of ceramics were also studied. The ceramic exhibited excellent microwave dielectric performances, with a relative permittivity (Ɛr) of 21.2, a quality factor (Q × f) of 52 360 GHz, and a temperature coefficient of resonant frequency (τf) of −44.2 ppm/°C, when sintered at 1500 °C for 4 h. The τf value of the La2MgGeO6 ceramic doped with CaTiO3 could be adjusted to zero. Particularly, 0.2La2MgGeO6-0.8CaTiO3 ceramics have good microwave dielectric properties with τf = +2.1 ppm/°C, Q × f = 15 610 GHz, and Ɛr = 40.3.

Effect of pre-sintering process on 95MCT for microwave antenna

The original magnesium titanate powders were pre-sintered, and the 0.95MgTiO3-0.05CaTiO3 (95MCT) ceramics were prepared by the pre-sintered magnesium titanate showed better dielectric properties than by the original powders. Because the magnesium titanate (MgTi2O5) phase was not detected. Then the microwave patch antenna was designed by the prepared ceramic measured at 2.8 GHz exhibited a 4.83% bandwidth (return loss ≤ −3 dB) of the center frequency.