CaTiO3 Ceramics Research Articles

Crystal structure and microwave dielectric properties of a novel rock-salt type Li3MgNbO5 ceramic

A new rock-salt type compound, namely Li3MgNbO5, was synthesized using traditional two-step sintering process for the first time. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermal dilatometer and network analyzer. The Li3MgNbO5 ceramic sintered at 1260 °C adopted a cubic structure with Fm-3 m space group and exhibited excellent microwave dielectric properties (MDPs) of er = 16.2, Q × f = 96796 GHz, and TCF = − 24.8 ppm/°C. The fitting results of the infrared spectrum indicated that the dielectric polarization of Li3MgNbO5 in microwave frequency band was contributed by phonon absorption in infrared band. Furthermore, the negative TCF value of Li3MgNbO5 ceramic was compensated with a traditional TCF compensator ~ CaTiO3. A near-zero TCF value of + 1.2 ppm/°C was achieved in the composite 0.96Li3MgNbO5–0.04CaTiO3 ceramics with er = 18.4 and high Q × f = 86625 GHz, exhibiting a great potential to be applied in microelectronics systems.

Structure, Raman spectra and properties of two low-εr microwave dielectric ceramics Ca3B2Ge3O12 (B = Al, Ga)

Ca3B2Ge3O12 (B = Al, Ga) cubic garnet ceramics with space group Ia-3d were synthesized by solid-state reaction. Ca3Al2Ge3O12 ceramic sintered at 1340 °C showed the optimal microwave dielectric performances with εr = 8.97, Q × f = 114,871 GHz and τf= −54.6 ppm/°C. The trace amount of secondary phase Ca2Ga2GeO7 was observed by XRD in Ca3Ga2Ge3O12 ceramic. The pure phase Ca3Ga2Ge3O12 could be obtained at 1320 °C by adding an excess of 3.3 mol% GeO2, which exhibited εr ~9.79, Q × f ~129,356 GHz and τf ~ −50.19 ppm/°C. The differences in microwave dielectric properties of Ca3B2Ge3O12 (B = Al, Ga) ceramics were discussed by Raman spectra, ionic polarizability, packing fraction and bond valence theories. Additionally, CaTiO3 was used to adjust the largely negative τf of Ca3B2Ge3O12 (B = Al, Ga) ceramics to near zero, and optimized performances of εr = 10.18, Q × f = 59,350 GHz and τf = +2.53 ppm/°C were obtained for the composite 0.88Ca3Al2Ge3O12-0.12CaTiO3 ceramics at 1360 °C for 8 h, with εr = 11.23, Q × f = 64,542 GHz and τf = −3.26 ppm/°C for 0.9Ca3Ga2Ge3O12-0.1CaTiO3 ceramics at 1320 °C.

Enhanced electrical energy storage performance of Pb-free A-site La3+-doped 0.85Na0.5Bi0.5TiO3-0.15CaTiO3 ceramics

A conventional preparation method of electroceramics was used to synthesise Pb-free 0.85Na0.5Bi0.5TiO3-0.15CaTiO3-xLa (NBT-CT-xLa) ceramics. La3+ doping effectively refined the grains and enhanced the dielectric breakdown strength (BDS) of the ceramics; this result was confirmed by numerical simulations, which revealed that grain refinement significantly contributed to the enhancement of the BDS. The energy storage density consequently improved when an appropriate amount of La3+ was added to the NBT-CT ceramics. In particular, the NBT-CT-0.75La ceramic displayed a maximum energy storage density of 2.15 J/cm3 and a high BDS of 210 kV/cm. This ceramic also possessed relatively excellent temperature and frequency stabilities (30–150 °C, 0.2–200 Hz). Moreover, the ceramics exhibited exceptional charge–discharge performances, with an outstanding power density of 43.87 MW/cm3, which is nearly twice of that of other NBT-based ceramics. On the basis of the findings, the NBT-CT-0.75La ceramic can be considered to be a promising candidate material for the pulsed power application.

Structure and dielectric properties of novel series of 3CaO–RE2O3–2WO3 (RE = La, Nd and Sm) microwave ceramics and the adjustment of τf value

Using the solid-state reaction method, novel series of 3CaO–RE2O3–2WO3 (RE = La, Nd and Sm) dielectric ceramics materials were fabricated, and the crystal structure and microstructure were studied through X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. The Ca3La2W2O12 (CLW) ceramic exhibited a single pure phase with a rhombohedral structure, and Ca3Nd2W2O12 (CNW) and Ca3Sm2W2O12 (CSW) ceramics had similar crystal structures with CLW. 3CaO–RE2O3–2WO3 (RE = La, Nd and Sm) ceramics are packed tightly, and the grains exhibited clear boundaries and uniform size. The CLW, CNW, and CSW ceramics sintered at 1375 °C for 4 h possessed excellent microwave dielectric properties: Ɛr = 19.1, Q × f = 34370 GHz, τf = − 80 ppm/°C; Ɛr = 19.3, Q × f = 36610 GHz, τf = − 74 ppm/°C and Ɛr = 18.8, Q × f = 23240 GHz, and τf = − 68 ppm/°C, respectively. Moreover, the (1 − x)CNW–xTiO2 (0.3 ≤ x ≤ 0.6) and (1 − y)CNW–yCaTiO3 (0.4 ≤ y ≤ 0.7) ceramics were designed and prepared to get a thermally stable material. The addition of TiO2 and CaTiO3 had a significant impact on the performances of ceramics. With increasing the TiO2 and CaTiO3 content, the relative permittivity (Ɛr) and temperature coefficient of resonance frequency (τf) values of ceramics increased, but the quality factor (Q × f) values of ceramics decreased. Especially, 0.55CNW–0.45TiO2 and 0.45CNW–0.55CaTiO3 ceramics sintered at 1375 °C for 4 h had microwave dielectric properties of Ɛr = 22.4, Q × f = 32,490 GHz, and τf = − 0.5 ppm/°C and Ɛr = 23.4, Q × f = 6440 GHz, and τf = − 1.5 ppm/°C, respectively.

Strain related curie temperature and improved piezoelectric properties of lead-free (1-x)Ba(Sn,Ti)O3-x(Ba,Ca)TiO3 ceramics

In this study, as a BaSnTiO3 structure based material, (1-x)Ba(Sn,Ti)O3-x(Ba,Ca)TiO3 piezoelectric ceramic was investigated for piezoelectric applications. Even though high piezoelectric properties, low Curie temperature is the obstacles for the applications. To increase Curie temperature of BaSnTiO3 material, (Ba,Ca)TiO3 ceramic was added. (Ba,Ca)TiO3 ceramic has shorter a-parameters compared with that of BaSnTiO3 ceramics, while c-parameter remains similar values of 4.02 Å. Due to the increased strain of (1-x)Ba(Sn,Ti)O3-x(Ba,Ca)TiO3, the Curie temperature can be controlled. Also, we have analyzed the structural and piezoelectric properties of a (1-x)Ba(Sn,Ti)O3-x(Ba,Ca)TiO3 system for application to an energy harvesting system. (1-x)Ba(Sn,Ti)O3-x(Ba,Ca)TiO3 ceramics with x = 0.4, 0.5, 0.55, 0.6, and 0.7 were synthesized and analyzed at sintering temperatures from 1455 to 1505 °C. We investigated the piezoelectric charge coefficient and P-E hysteresis loops. Results showed that the optimized composition of (1-x)Ba(Sn,Ti)O3-x(Ba,Ca)TiO3 ceramics was x = 0.55, sintered at 1480 °C. As lead-free piezoelectric ceramics, it is expected that (1-x)Ba(Sn,Ti)O3-x(Ba,Ca)TiO3 ceramics will be promising candidates for various applications.

CuO Modified CaTiO3 for NTCR Thermistor Application

CuO modified CaTiO3 ceramics exhibit logarithmic increase of resistance with decreasing temperature, which makes the compound well suited for use as a negative temperature coefficients resistance thermistor material in temperature sensing device applications. The source powder production, the experimental set-up, the process parameters and the resulting properties for each are presented and compared. Ca1−XCuXTiO3 (0.1, 0.3, 0.5 and 0.7) synthesized by High Energy Ball Mill. The phase purity of the source powder and the films was assessed by X-ray diffraction. The electrical properties were analysed by measuring the resistance–temperature characteristics. Steinhart and Hart model and time response analysis used for the verification and potential towards the thermistor industry. Experimental result shows potential of all samples in thermistor industry because of exponential electrical resistance with temperature. Time response analysis revels materials response potential to temperature also variation of response time due to effect of doping concentration variation. The sensitivity (β value found to be in the range of 4482–8001 K which is comparable to other potential thermistor industry material already in use. The aim of this experiment to introduce new thermistor material with matching electrical parameters.

Structure characterization and microwave dielectric properties of LiGa5O8 ceramic with low-εr and low loss

LiGa5O8 ceramics with inverse spinel structure were prepared in a temperature range of 1200–1300 ℃ by solid-state reaction method. LiGa5O8 ceramics crystallized in cubic structure with space group P4332, in which Li+ and Ga3+ distributed in the octahedral B sites with 1:3 ordering. The optimal microwave dielectric properties with εr =10.51, Q × f = 127,040 GHz, and τf = –60.16 ppm/℃ were achieved at 1260 ℃ for 6 h. Microwave dielectric properties were discussed in combination with the intrinsic characteristics of crystal structure by packing fraction, Raman spectra, and infrared reflectivity spectrum. Additionally, CaTiO3 was used to suppress τf of LiGa5O8 ceramics to near zero, and optimized performances of εr = 12.79, Q × f = 109,752 GHz and τf = +4.07 ppm/℃ were obtained for 0.94LiGa5O8‐0.06CaTiO3 ceramics at 1260 ℃. These bright spots make LiGa5O8 ceramic a potential candidate for 5 G and millimeter wave technology.

Structure evolution and improved microwave dielectric characteristics in CaTi1-x(Al0.5Nb0.5)xO3 ceramics

Enhanced microwave dielectric characteristics in (Al0.5Nb0.5)-co-substituted CaTiO3 ceramics were examined by means of structure evolution. CaTi1-x(Al0.5Nb0.5)xO3 solid solutions with orthorhombic structure in space group Pbnm were attained throughout the entire composition range x ≤ 0.75. The near-zero temperature coefficient of resonant frequency τf and significantly improved quality factor Qf value were achieved, while a tunable medium dielectric constant ϵr was achieved in the present ceramics. τf was tuned from 750 ppm/°C to 5 ppm/°C and became −80 ppm/°C finally (at x = 0.75), the Qf was first increased from 11,500 GHz up to 49,700 GHz due to the stable perovskite structure with increased bond strength and degree of covalency (%) and then slightly decreased to 43,100 GHz at x = 0.75. The best combination of significantly improved microwave dielectric characteristics was achieved at x = 0.45 (ϵr = 55.1, Qf = 49,700 GHz, τf = 5 ppm/°C). The present ceramics showed the great application potential in future wireless communication systems.

High‐throughput first‐principle calculations of the structural, mechanical, and electronic properties of cubic XTiO3 (X = Ca, Sr, Ba, Pb) ceramics under high pressure

AbstractHigh‐throughput first‐principle calculations are implemented to study the structural, mechanical, and electronic properties of cubic XTiO3 (X = Ca, Sr, Ba, Pb) ceramics under high pressure. The effects of applied pressure on physical parameters, such as elastic constants, bulk modulus, Young's modulus, shear modulus, ductile‐brittle transition, elastic anisotropy, Poisson's ratio, and band gap, are investigated. Results indicate that high pressure improves the resistance to bulk, elastic, and shear deformation for XTiO3 ceramics. Pugh's ratios B/G reveal that CaTiO3 and PbTiO3 ceramics are ductile, but SrTiO3 and BaTiO3 ceramics are brittle under the ground state. The brittle‐to‐ductile transition pressures are 24.26 GPa for SrTiO3 and 43.23 GPa for BaTiO3. Under high pressure, the strong anisotropy promotes the cross‐slip process of screw dislocations, and then enhances the plasticity of XTiO3 ceramics. Meanwhile, XTiO3 (X = Ca, Sr, Ba) is intrinsically an indirect‐gap ceramic, but PbTiO3 is a direct‐gap ceramic. High pressure increases the band gap of XTiO3 (X = Ca, Sr, Ba) ceramic, but decreases that of PbTiO3 ceramic. This work is helpful for designing and applying XTiO3 ceramics under high pressure.

Lattice structure and microwave dielectric properties of La[Al1−x(Mg0.5Ti0.5)x]O3 (x = 0‐0.2)‐based ceramics

AbstractLa[Al1−x(Mg0.5Ti0.5)x]O3 (LAMT, x = 0‐0.2) ceramics were synthesized by the conventional solid‐state reaction method and formed a solid solution. The pure solid solutions were recorded by X‐ray diffraction (XRD) in every range. Relative permittivity (εr) and structural stability were greatly affected because the Al3+ site was replaced by [Mg0.5Ti0.5]3+. The total ionic polarizability gradually increased with x, and εr gradually increased. The trend of τf is due to the change in structural stability. The variation in Q × f value increased firstly and then decreased due to the change in the symmetric stretching mode of Al/MgTi–O. The optimum microwave dielectric properties of LAMT were obtained at x of 0.1 after sintering at 1650°C for 5 hours, and εr = 24.9, Q × f = 79 956 GHz, and τf = −33 ppm/°C. The CaTiO3 have a large positive τf (+800 ppm/°C), thus, the τf achieved near zero when CaTiO3 and LAMT (x = 0.1) ceramics were mixed with a certain molar mass, and the optimum microwave dielectric properties of 0.65CaTiO3–0.35LaAl0.9(Mg0.5Ti0.5)0.1O3 were as follows: εr = 44.6, Q × f = 32 057 GHz, and τf = +2 ppm/°C.

Sintering Behaviors, Microstructure, and Microwave Dielectric Properties of CaTiO3-LaAlO3 Ceramics Using CuO/B2O3 Additions.

The effect of CuO/B2O3 additions on the sintering behaviors, microstructures, and microwave dielectric properties of 0.95LaAlO3–0.05CaTiO3 ceramics is investigated. It is found that the sintering temperatures are lowered efficiently from 1600 °C to 1350 °C, as 1 wt % CuO, 1 wt % B2O3, and 0.5 wt % CuO +0.5 wt % B2O3 are used as the sintering aids due to the appearance of the liquid phase sintering. The microwave dielectric properties of 0.95LaAlO3–0.05CaTiO3 ceramics with the sintering aid additions are strongly related to the densification and the microstructure of the sintered ceramics. At the sintering temperature of 1300 °C, the 0.95LaAlO3–0.05CaTiO3 ceramic with 0.5 wt % CuO + 0.5 wt % B2O3 addition shows the best dielectric properties, including a dielectric constant (εr) of 21, approximate quality factor (Q × f) of 22,500 GHz, and a temperature coefficient of the resonant frequency (τf) of −3 ppm/°C.

Dielectric and Impedance Studies of (Ba,Ca)TiO3 Ceramics Obtained from Mechanically Synthesized Powders

Mechanochemical synthesis offers unique possibility of perovskite phase formation at ambient conditions that is very attractive (simplifies production, allows strict stoichiometry control and brings economic benefits). In this work the mechanochemical synthesis has been used for preparation ofBa1−xCaxTiO3 (0.2 ≤ x ≤ 0.3) powders from simple oxides. The 20 h milled powders have been uniaxially pressed and sintered in order to get the ceramic samples. The sample morphologies have been observed by scanning electron microscopy. Dielectric and impedance studies have been performed on ceramics. The obtained results indicate that the two mechanism of doping occurred. The first one is observed for the lower calcium concentration (below 0.3) and consists of the introduction of calcium ion into the A site of the perovskite structure. The second one is observed for the higher calcium concentration (equal 0.3). In this case the calcium ions partially occupies the B site in the perovskite structure. Both cases have different influence on the final properties of the ceramics because they induce different defects.

A novel tungstate Li3Nd3W2O12 with garnet structure for low-temperature cofired ceramic technology

Microwave dielectrics sintered at low temperature are pursued for energy saving and cofiring with cost-effective metallic electrodes (e.g. Cu, Ag and Al). In this study, a novel tungstate low-firing microwave dielectric ceramic, Li3Nd3W2O12, which can realise co-firing with Ag electrode at 940 °C, was synthesised by the conventional solid-state reaction method. According to the X-ray diffraction and Rietveld refinement results, Li3Nd3W2O12 crystallised in the garnet structure with a space group of Ia3¯d and W6+ cations fully occupying the octahedral-coordinated site. The optimum microwave dielectric properties with permittivity of ∼9.8, quality factor of ∼36,800 GHz and temperature coefficient of resonant frequency of ∼ –30 ppm/°C were obtained after sintered at 940 °C. A near-zero temperature coefficient of resonant frequency of +3.6 ppm/°C was achieved in 0.96Li3Nd3W2O12-0.04CaTiO3 ceramics. These properties make tungstate Li3Nd3W2O12 a promising candidate for low-temperature co-fired ceramic technology.

Phase compositions, microstructures, and microwave dielectric properties of Li2Zn3Ti4O12-based temperature stable materials modified by CaTiO3 additions

In present work, the microwave dielectric properties of CaTiO3-added Li2Zn3Ti4O12 ceramics prepared by the conventional solid-state method have been investigated. The phase composition, microstructure and microwave dielectric properties of (1 − x) Li2Zn3Ti4O12–x CaTiO3 (x = 3, 4, 5, 6 and 7 wt%) ceramics were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), EDS and network analyzer. The XRD and EDS results indicated that the ceramics involved Li2Zn3Ti4O12 and CaTiO3 phases. The SEM micrographs shown that as the CaTiO3 contents increased, the average grain size of the composition ceramics decreased. The microwave dielectric properties of the composition ceramics can be effectively controlled by varying the CaTiO3 contents. The values of dielectric constant (er) and τf of the composition ceramics were increased, and the quality factor (Q × f) was decreased with increasing the CaTiO3 contents. Typically, a new temperature stable microwave dielectric material of 0.94 Li2Zn3Ti4O12–0.06 CaTiO3 with excellent microwave dielectric properties of er = 21.7, Q × f = 61,490 GHz, and τf = + 2.68 ppm/°C was attained when sintered at 1175 °C for 4 h.

Study on piezoelectric, dielectric and dispersive phase transition of BaTiO3–BaZrO3–CaTiO3 ceramics

The dielectric, piezoelectric properties and dispersive ferroelectric phase transitions of (0.84 − x) BaTiO3–0.16CaTiO3–xBaZrO3 ternary ceramics were investigated in this manuscript. The study found that the optimum BaZrO3 doping amount was 0.1 mol%. Compared to the binary system, the ternary system has a denser microstructure and a more uniform grain size, and more excellent electrical properties. The influence mechanism of BaZrO3 doping on the system was explained in detail by lattice theory and domain theory.

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

In this study, 0.95 Sr0.7Ba0.3Nb2O6-0.05CaTiO3-x wt% Er2O3 ceramics (SBNCTEx; x = 0–5) were synthesized using traditional solid-state method, and we investigated the microstructure, energy storage properties as well as the relationship between dielectric breakdown strength and interfacial polarization. As compared with pure 0.95 Sr0.7Ba0.3Nb2O6-0.05CaTiO3 ceramics, the Er2O3 dopants suppressed the grain growth of SBNCTEx, and the doped ones showed the dense microstructure. The secondary phase was found for x ≥ 1 according to the EDS results, and the influence of the secondary phase on relative dielectric breakdown strength has also been studied. The dielectric breakdown strength increased from 18.1 kV/mm to 34.4 kV/mm, which is good for energy storage. The energy storage density of 0.28 J/cm3 and the energy storage efficiency of 91.4% were obtained in the SBNCTE5 ceramics. The results indicate that SBNCTE ceramics can be used as energy storage capacitors.

Structure, Morphology and Electrical Properties of CaTiO3 Ceramics Synthesized by the Solid-State Reaction Method

Structure, Morphology and Electrical Properties of CaTiO3 Ceramics Synthesized by the Solid-State Reaction Method

CaTiO3 linear dielectric ceramics with greatly enhanced dielectric strength and energy storage density

AbstractCaTiO3 is a typical linear dielectric material with high dielectric constant, low dielectric loss, and high resistivity, which is expected as a promising candidate for the high energy storage density applications. In the previous work, an energy density of 1.5 J/cm3 was obtained in CaTiO3 ceramics, where the dielectric strength was only 435 kV/cm. In fact, the intrinsic dielectric strength of CaTiO3 is predicted as high as 4.2 MV/cm. Therefore, it should be a challenge issue to enhance the dielectric strength and energy storage density of CaTiO3 ceramics by optimizing the microstructures. In the present work, dense CaTiO3 ceramics with fine and uniform microstructures are prepared by spark plasma sintering, and the greatly enhanced dielectric strength (910 kV/cm) and energy storage density (6.9 J/cm3) are obtained. This can be ascribed to the improved resistivity and thermal conductivity, associated with the fine and uniform microstructures. The different post‐breakdown features of CaTiO3 ceramics prepared by different process well interpret why the enhanced dielectric strength is achieved in the SPS sample. The energy storage density can be further improved to 11.8 J/cm3 by introducing the amorphous alumina thin films as the charge blocking layer, where the dielectric strength is 1188 kV/cm.

Effects of Li2ZnTi3O8 addition on sintering behavior and microwave dielectric properties of the MgTiO3–CaTiO3 ceramic system

The effects of Li2ZnTi3O8 addition on the sintering behavior, phase formation, microstructure and microwave dielectric properties of 0.94MgTiO3–0.06CaTiO3 ceramics have been investigated. These results suggested that Li2ZnTi3O8 addition not only contributes in decreasing the sintering temperature, but also enhances grain growth. A new microwave dielectric ceramic, 0.94MgTiO3–0.06CaTiO3–0.015Li2ZnTi3O8 sintered at 1220 °C had optimal dielectric properties (er = 20.97, Q × f = 70,832 GHz, τf = 3.45 ppm/°C), which satisfies microwave applications in resonators, filters and antenna substrates.

Correlation between structure and microwave dielectric properties of low-temperature-fired Mg2SiO4 ceramics

Mg2SiO4–LiF ceramics were fabricated via a conventional solid-state process and sintered at 900 °C. The secondary phase, Li2SiO3, was observed with ≤6 wt% LiF, and the Li2MgSiO4 phase was detected with ≥8 wt% LiF. The relative density and secondary phase can account for the decrease in the εr with an increase in LiF. The degree of crystallization, unit cell volume, secondary phase, and microstructure correlated with the Q × f values. The value of the τf was related to the distortions in the Mg(1)O6 octahedron and the secondary phase. The sample exhibited excellent properties for Mg2SiO4–8 wt% LiF with εr = 6.1, Q × f = 109719 GHz, and τf = − 61 ppm/°C. The temperature stability of the Mg2SiO4–8 wt%LiF–6 vol%CaTiO3 ceramics was obtained with εr = 7.1, Q × f = 31091 GHz and τf = − 2.0 ppm/°C. Mg2SiO4–LiF–CaTiO3 ceramics provide excellent chemical compatibility with Ag.