High temperature dielectrics in the ceramic system K0.5Bi0.5TiO3-Ba(Zr0.2Ti0.8)O3-Bi(Zn2/3Nb1/3)O3

Ceramics in the system (1-x)[0.5K_0.5Bi_0.5TiO₃-0.5Ba(Zr_0.2Ti_0.8)O₃]-xBi(Zn_2/3Nb_1/3)O₃ have been fabricated by a solid-state processing route for compositions x≤0.3. The materials are relaxor dielectrics. The temperature of maximum relative permittivity, T_m, decreased from 150 °C for composition x=0, to 70 °C for x=0.2. The x=0.2 sample displayed a wide temperature range of stable relative permittivity, ε_r, such that ε_r=805±15% from −20 to 600 °C (1 kHz). Dielectric loss tangent was ≤0.02 from 50 °C to 450 °C (1 kHz), but due to the tanδ dispersion peak, the value increased to 0.09 as temperatures fell from 50 °C to −20 °C. Values of dc resistivity were of the order of ~10⁹ Ω m at 300 °C. These properties are promising in the context of developing new high temperature capacitor materials.     

Lead-free BaTiO3-Bi0.5Na0.5TiO3-Na0.73Bi0.09NbO3 relaxor ferroelectric ceramics for high energy storage

A series of (1-x)(0.65BaTiO₃-0.35Bi_0.5Na_0.5TiO₃)-xNa_0.73Bi_0.09NbO₃ ((1-x)BBNT-xNBN) (x = 0–0.14) ceramics were designed and fabricated using the conventional solid-state sintering method. The microstructure, dielectric property, relaxor behavior and energy storage property were systematically investigated. X-ray diffraction results reveal a pure perovskite structure and dielectric measurements exhibit a relaxor behavior for the (1-x)BBNT-xNBN ceramics. The slim polarization electric field (P-E) loops were observed in the samples with x ≥ 0.02 and the addition of Na_0.73Bi_0.09NbO₃ (NBN) could decrease the remnant polarization (P_r) of the (1-x)BBNT-xNBN ceramics obviously. The sample with x = 0.08 exhibits the highest energy storage density of 1.70 J/cm³ and the energy storage efficiency of 82% at 172 kV/cm owing to its submicron grain size and high relative density. These results show that the (1-x)BBNT-xNBN ceramics may be promising lead-free materials for high energy storage density capacitors.     

Temperature–stable dielectrics based on Cu–doped Bi2Mg2/3Nb4/3O7 pyrochlore ceramics for LTCC

Temperature–stable dielectrics based on Cu–doped Bi₂Mg_2/3Nb_4/3O₇ pyrochlore ceramics were prepared by conventional solid–state reaction. Microstructure analysis indicates that all of the specimen maintain the cubic pyrochlore phase, a fluorite–like phase of Bi₃NbO₇ and a Bi₅Nb₃O₁₅ formed for Cu doping. The dielectric constant is dominated by densification of samples and secondary phases, while the dielectric loss is related by the secondary phases, grain boundaries, and leakage current characteristics. The (1-x)BMN - xCuO(x = 0.1 mol%) ceramic sintered at 925 °C shows excellent dielectric properties with dielectric constant of ~184.06, dielectric loss of ~0.0017 and near zero τ_ε (?20 ppm/°C) is obtained at sintering temperature of 925 °C, which could be a promising candidate for LTCC.     

Structure,Infrared Reflectivity and Microwave Dielectric Properties of (Na0.5La0.5)MoO4–(Na0.5Bi0.5)MoO4 Ceramics

A series of temperature‐stable microwave dielectric ceramics, (1?x)(Na_0.5La_0.5)MoO₄–x(Na_0.5Bi_0.5)MoO₄ (0.0 ≤ x ≤ 1.0) were prepared by using solid‐state reaction. All specimens can be well sintered at temperature of 580°C–680°C. Sintering behavior, phase composition, microstructures, and microwave dielectric properties of the ceramics were investigated. X‐ray diffraction results indicated that tetragonal scheelite solid solution was formed. Microwave dielectric properties showed that permittivity (ε_r) and temperature coefficient of resonant frequency (τ_f) were increased gradually, while quality factor (Q × f) values were decreased, at the x value was increased. The 0.45(Na_0.5La_0.5)MoO₄–0.55(Na_0.5Bi_0.5)MoO₄ ceramic sintered at 640°C with a relative permittivity of 23.1, a Q × f values of 17 500 GHz (at 9 GHz) and a near zero τ_f value of 0.28 ppm/°C. Far‐infrared spectra (50–1000 cm^?1) study showed that complex dielectric spectra were in good agreement with the measured microwave permittivity and dielectric losses.     

A novel low-temperature firable La2Zr3(MoO4)9 microwave dielectric ceramic

A novel low-temperature fired La₂Zr₃(MoO₄)₉ microwave dielectric ceramic was successfully fabricated by a conventional solid-state reaction method. The powder compact was densified in air in the temperature range of 700–800 °C for 4 h. X-ray diffraction analysis indicated that all studied samples presented a single phase structure. Rietveld refinement results further confirmed that La₂Zr₃(MoO₄)₉ belonged to a trigonal system with space group R$\overline{3}$c. Scanning electron microscopy results revealed dense and homogeneous microstructure of La₂Zr₃(MoO₄)₉ ceramics as sintered in the temperature range of 725–800 °C. The La₂Zr₃(MoO₄)₉ ceramic sintered at 775 °C for 4 h possessed excellent microwave dielectric properties of relative permittivity ε_r ～ 10.8, quality factor Qxf ～ 50,628 GHz (at 10.45 GHz), and temperature coefficient of the resonant frequency τ_f ～ ?38.8 ppm/°C, showing great potentials for applications of low temperature co-fired ceramic technology.     

Low-temperature sintering of Ti1−xCux/3Nb2x/3O2 (x = 0.23) microwave dielectric ceramics with CuO and B2O3 addition

The influence of CuO and B₂O₃ addition on the sintering behavior, microstructure and microwave dielectric properties of Ti_1?xCu_x/3Nb_2x/3O₂ (TCN, x = 0.23) ceramic have been investigated. It was found that the addition of CuO and B₂O₃ successfully reduced the sintering temperature of TCN ceramics from 950 to 875 °C. X-ray diffraction studies showed that addition of CuO-B₂O₃ has no effect on the phase composition. The TCN ceramics with 0.5 wt% CuO-B₂O₃ addition showed a high dielectric constant of 95.63, τ_f value of + 329 ppm/°C and a good Q × f value of 8700 GHz after sintered at 875 °C for 5 h, cofirable with silver electrode.     

Ultra‐low temperature sintering microwave dielectric ceramics based on Ag2O–MoO3 binary system

The Ag₂Mo₂O₇ and Ag₆Mo₁₀O₃₃ ceramics for ultra‐low temperature co‐fired ceramic application were prepared by the solid‐state reaction route. The optimized densification temperatures of Ag₂Mo₂O₇ and Ag₆Mo₁₀O₃₃ are 460°C and 500°C, respectively. The phase structures and microstructures of these ceramics were systematically studied. The Ag₂Mo₂O₇ ceramic sintered at 460°C/4 h exhibits excellent microwave dielectric properties with ε_r=13.3, Q×f=25 300 GHz and τ_f=?142 ppm/°C at 9.25 GHz. The Ag₆Mo₁₀O₃₃ ceramic sintered at 500°C/4 h shows the microwave dielectric properties with ε_r=14.0, Q×f=8500 GHz and τ_f=?50 ppm/°C at 9.00 GHz. Moreover, when Ag₂Mo₂O₇ samples are sintered at ultra‐low sintering temperatures of 420°C‐490°C, the Q×f values of them are all above 20 000 GHz. Besides, the Ag₂Mo₂O₇ ceramic does not react with silver powder or aluminum powder. The variation of relative permittivity, resonant frequency, and Q×f values as a function of operating temperature has been also studied. All the results indicate that the Ag₂Mo₂O₇ ceramic is a good candidate for ultra‐low temperature co‐fired microwave devices.     

Microwave dielectric properties of Pb2MoO5 ceramic with ultra-low sintering temperature

Ultra-low firing microwave dielectric ceramic Pb₂MoO₅ with monoclinic structure was prepared via a conventional solid state reaction method. The sintering temperature ranged from 530 °C to 650 °C. The relative densities of the ceramic samples were about 97% when the sintering temperature was greater than 570 °C. The best microwave dielectric properties were obtained in the ceramic sintered at 610 °C for 2 h with a permittivity ∼19.1, a Q × f value about 21,960 GHz (at 7.461 GHz) and a temperature coefficient value of −60 ppm/°C. From the X-ray diffraction, backscattered electron image results of the co-fired samples with 30 wt% silver and aluminum additive, the Pb₂MoO₅ ceramics were found not to react with Ag and Al at 610 °C for 4 h. The microwave dielectric properties and ultra-low sintering temperature of Pb₂MoO₅ ceramic make it a promising candidate for low temperature co-fired ceramic applications.     

Ultra‐low Sintering Temperature Microwave Dielectric Ceramics Based on Na2O‐MoO3 Binary System

The compounds in Na₂O‐MoO₃ system were prepared by the solid‐state reaction route. The phase composition, crystal structures, microstructures, and microwave dielectric properties of the compounds have been investigated. This series of compounds can be sintered well at ultra‐low temperatures of 505°C–660°C. The sintered samples exhibit good microwave dielectric properties, with the relative permittivities (ε_r) of 4.1–12.9, the Q × f values of 19900–62400 GHz, and the τ_f values of ?115 ppm/°C to ?57 ppm/°C. Among the eight compounds in this binary system, three kinds of single‐phase ceramics, namely Na₂MoO₄, Na₂Mo₂O₇ and Na₆Mo₁₁O₃₆ were formed. Furthermore, the relationship between the structure and the microwave dielectric properties in this system has been discussed. The average Na^I‐O and Mo^VI‐O bond valences have an influence on the sintering temperatures in Na₂O‐MoO₃ system. The large valence deviations of Na and Mo lead to a large temperature coefficient of resonant frequency. The X‐ray diffraction and backscattered electron image results show that Na₂MoO₄ doesn't react with Ag and Al at 660°C. Also, Na₂Mo₂O₇ has a chemical compatibility with Al at 575°C.     

0-3 type magnetoelectric 0.94Na0.5Bi0.5TiO3-0.06BaTiO3:CoFe2O4 composite ceramics with a deferred thermal depolarization

Developing Na_0.5Bi_0.5TiO₃-based magnetoelectric (ME) coupling composites with higher depolarization temperature is highly valuable for the environment-friendly smart electronic devices. We have developed a new kind of 0-3 type 0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃:xCoFe₂O₄ (NBTBT:xCFO, x = 0, 0.1, 0.2, 0.3) composite ceramics with a deferred depolarization temperature, together with an additional strong ME coupling of 9.2 mV/cm·Oe for the NBTBT:0.2CFO. The basic structure, ferroelectric/ferromagnetic properties, and the depolarization temperature of the NBTBT:xCFO composite ceramics were investigated. It was found that an enhancement of depolarization temperature (>25 °C) was obtained in these 0-3 type composites relative to the pure NBTBT ones (115 °C vs 90 °C). The mechanism of the enhanced depolarization temperature of the composites is discussed. The present results demonstrate that NBTBT:xCFO composites have great potential for ME devices.     

Structural evolution,grain growth kinetics and microwave dielectric properties of Li2Ti1-x(Mg1/3Nb2/3)xO3

Li₂Ti_1-x(Mg_1/3Nb_2/3)_xO₃ ceramics were prepared by conventional solid state process. Their structural evolution, grain growth kinetics and microwave dielectric properties have been studied in this paper. The results show that continuous solid solution could be formed within the experiment compositional range. The structure changed from long range ordered monoclinic into short range ordered cubic phase as the increase in x. Small levels of substitution for Ti⁴⁺by (Mg_1/3Nb_2/3)⁴⁺ slightly decreased the dielectric permittivity, while considerably improved the Q × f value. The temperature coefficient of resonant frequency changed from positive into negative value. The grain growth kinetics during sintering process and Q × f value of the sintered body were affected by different calcining temperature of mixed powders. Excellent combined microwave dielectric properties with ε_r ～21.0, Q × f ～ 200 000 GHz and τ_f value of ?1 ppm/ °C could be obtained after optimizing calcining temperature for the x = 0.24 composition after sintering at 1250 °C/2 h.     

Low-temperature-sintered Bi0.5Na0.5TiO3-based lead-free ferroelectric ceramics with good piezoelectric properties

Li₂CO₃ has been used as a sintering aid for fabricating lead-free ferroelectric ceramic 0.93(Bi_0.5Na_0.5TiO₃)-0.07BaTiO₃. A small amount (0.5 wt%) of it can effectively lower the sintering temperature of the ceramic from 1200 °C to 980 °C. Unlike other low temperature-sintered ferroelectric ceramics, the ceramic retains its good dielectric and piezoelectric properties, giving a high dielectric constant (1570), low dielectric loss (4.8%) and large piezoelectric coefficient (180 pC/N). The “depolarization” temperature is also increased to 100 °C and the thermal stability of piezoelectricity is improved. Our results reveal that oxygen vacancies generated from the diffusion of the sintering aid into the lattices are crucial for realizing the low temperature sintering. Owing to the low sintering temperature and good dielectric and piezoelectric properties, the ceramics, especially of multilayered structure, should have great potential for practical applications.     

Structural and electrical properties of Na0.5Bi4.0RE0.5Ti4O15 (RE=Tm,Yb and Lu) thin films

In the current study, a series of lanthanide ions, Tm, Yb and Lu, were used for doping at the Bi-site of the Aurivillius phase Na_0.5Bi_4.5Ti₄O₁₅ (NaBTi) to investigate the structural, electrical and ferroelectric properties of the thin films. In this regard, Na_0.5Bi_4.5Ti₄O₁₅ and the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5i₄O₁₅ (RE=Tm, Yb and Lu, denoted by NaBTmTi, NaBYbTi, and NaBLuTi, respectively) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of the Aurivillius phase orthorhombic structures for all the thin films were confirmed by X-ray diffraction and Raman spectroscopic studies. Based on the experimental results, the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5Ti₄O₁₅ thin films exhibited a low leakage current and the improved ferroelectric properties. Among the thin films, the NaBLuTi thin film exhibited a low leakage current density of 6.96×10⁻⁷ A/cm² at an applied electric field of 100 kV/cm and a large remnant polarization (2P_r) of 26.7 μC/cm² at an applied electric field of 475 kV/cm.     

A novel Li2TiO3–Li2CeO3 ceramic composite with excellent microwave dielectric properties for low-temperature cofired ceramic applications

A novel low-temperature sinterable (1 ? x)Li₂TiO₃-xLi₂CeO₃ (x = 0.08 ? 0.16 in molar) microwave dielectric ceramic was successfully prepared by a conventional solid-state reaction method. The X-ray diffraction and scanning electron microscopy analysis revealed the coexistence of two phases with different structures owing to their good chemical stability. Their relative content was easily adjusted to achieve near-zero temperature coefficient of the resonant frequency (τ_f) according to the mixing rule of dielectrics. The low-temperature sintering and desirable microwave dielectric properties can be simultaneously achieved by adding Li₂CeO₃ to the Li₂TiO₃ matrix owing to its low-firing characteristic and opposite-sign τ_f. The composite ceramics with x = 0.14 could be well sintered at 850 °C and exhibited excellent microwave dielectric properties of ε_r ～ 21.2, Qxf～ 59,039 GHz and τ_f ～?7.4 ppm/°C. In addition, no chemical reaction was identified between the matrix phase and Ag, suggesting that the Li₂TiO₃-Li₂CeO₃ ceramics might be promising candidates for low-temperature co-fired ceramic applications.     

Effects of annealing temperature on the microstructure,ferroelectric and dielectric properties of W-doped Na0.5Bi0.5TiO3 thin films

The effects of annealing temperature on the structure, morphology, ferroelectric and dielectric properties of Na_0.5Bi_0.5Ti_0.99W_0.01O_3+δ (NBTW) thin films are reported in detail. The films are deposited on indium tin oxide/glass substrates by a sol-gel method and the annealing temperature adopted is in the range of 560–620 °C. All the films can be well crystallized into phase-pure perovskite structures and show smooth surfaces without any cracks. Particularly, the NBTW thin film annealed at 600 °C exhibits a relatively large remanent polarization (P_r) of 20 μC/cm² measured at 750 kV/cm. Additionally, it shows a high dielectric constant of 608 and a low dielectric loss of 0.094 as well as a large dielectric tunability of 62%, making NBTW thin film ideal in the room-temperature tunable device applications.     

Sintering behaviour and microwave dielectric properties of BaAl2−2x(ZnSi)xSi2O8 ceramics

BaAl_2?2x(ZnSi)_xSi₂O₈ (x = 0.2–1.0) ceramics were prepared using the conventional solid-state reaction method. The sintering behaviour, phase composition and microwave dielectric properties of the prepared compositions were then investigated. All compositions showed a single phase except for x = 0.8. By substituting (Zn_0.5Si_0.5)³⁺ for Al³⁺ ions, the optimal sintering temperatures of the compositions decreased from 1475 °C (x = 0) to 1000 °C (x = 0.8), which then slightly increased to 1100 °C (x = 1.0). Moreover, the phase stability of BaAl₂Si₂O₈ was improved. A novel BaZnSi₃O₈ microwave dielectric ceramic was obtained at the sintering temperature of 1100 °C. This ceramic possesses good microwave dielectric properties with ε_r = 6.60, Q × f = 52401 GHz (at 15.4 GHz) and τ_f = ?24.5 ppm/°C.     

Synthesis and electrical properties of lead-free piezoelectric Bi0.5Na0.5TiO3 thin films prepared by Sol-Gel method

Lead-free Bi_0.5Na_0.5TiO₃ (BNT) piezoelectric thin films were deposited on Pt/TiO_x/SiO₂/Si substrates by Sol-Gel method. A dense and well crystallized thin film with a perovskite phase was obtained by annealing the film at 700 °C in a rapid thermal processing system. The relative dielectric constant and loss tangent at 12 kHz, of BNT thin film with 350 nm thickness, were 425 and 0.07, respectively. Ferroelectric hysteresis measurements indicated a remnant polarization value of 9 μC/cm² and a coercive field of 90 kV/cm. Piezoelectric measurements at the macroscopic level were also performed: a piezoelectric coefficient (d_33effmax) of 47 pm/V at E = 190 kV/cm was obtained. The piezoresponse force microscopy data confirmed that BNT thin films present ferroelectric and piezoelectric behavior at the nanoscale level.     

High performance lead-free piezoelectric 0.96(K0.48Na0.52)NbO3-0.03[Bi0.5(Na0.7K0.2Li0.1)0.5]ZrO3-0.01(Bi0.5Na0.5)TiO3 single crystals grown by solid state crystal growth and their phase relations

0.96(K_0.48Na_0.52)NbO₃-0.03[Bi_0.5(Na_0.7K_0.2Li_0.1)_0.5]ZrO₃-0.01(Bi_0.5Na_0.5)TiO₃ single crystals were grown for the first time by the solid state crystal growth method, using [001] or [110]-oriented KTaO₃ seed crystals. The grown single crystal shows a dielectric constant of 2720 and polarization-electric field loops of a lossy normal ferroelectric, with P_r = 45 μC/cm² and E_c = 14.9 kV/cm, while the polycrystalline samples with a dielectric constant of 828 were too leaky for P-E measurement due to humidity effects. The single crystal has orthorhombic symmetry at room temperature. Dielectric permittivity peaks at 26 °C and 311 °C, respectively, are attributed to rhombohedral-orthorhombic and tetragonal–cubic phase transitions. Additionally, Raman scattering shows the presence of an orthorhombic-tetragonal phase transition at ∼150 °C, which is not indicated in the permittivity curves but by the loss tangent anomalies. A transition around 700 °C in the high temperature dc conductivity is suggested to be a ferroelastic-paraelastic transition.     

Comparison of hot corrosion resistance of Sm2Zr2O7 and (Sm0.5Sc0.5)2Zr2O7 ceramics in Na2SO4+V2O5 molten salt

Sm₂Zr₂O₇ and (Sm_0.5Sc_0.5)₂Zr₂O₇ ceramics were fabricated by a chemical co-precipitation and calcination method, and their hot corrosion behaviors in Na₂SO₄+V₂O₅ molten salt were investigated. Hot corrosion tests were carried at 700 °C, 800 °C and 900 °C for 4 h, and corroded surfaces were investigated using X-ray diffractometer and scanning electron microscopy. The corrosion products of Sm₂Zr₂O₇ ceramics were composed of SmVO₄ and monoclinic-ZrO₂, while those of (Sm_0.5Sc_0.5)₂Zr₂O₇ ceramic consisted of SmVO₄ and Zr₅Sc₂O₁₃. Considering the fact that Zr₅Sc₂O₁₃ is more desirable than monoclinic-ZrO₂ for thermal barrier coating applications, (Sm_0.5Sc_0.5)₂Zr₂O₇ showed better corrosion resistance to Na₂SO₄+V₂O₅ salt than Sm₂Zr₂O₇. The hot corrosion mechanisms of Sm₂Zr₂O₇ and (Sm_0.5Sc_0.5)₂Zr₂O₇ in Na₂SO₄+ V₂O₅ salt were discussed in detail.