Fabrication of 0.24Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 transparent ceramics by conventional sintering technique

0.24Pb(In_1/2Nb_1/2)O₃-0.42Pb(Mg_1/3Nb_2/3)O₃-0.34PbTiO₃ transparent ceramics were fabricated by a conventional sintering technique. Through optimization of sintering conditions of calcination and sintering temperatures and time, the obtained ceramics showed high optical transmittance of 53% and 71% at light wavelengths of 1300 and 2000 nm, respectively. The ceramics showed a rhombohedral to tetragonal phase transition at ~120°C and a tetragonal to cubic phase transition at 222°C. These transition temperatures were higher than those of 0.67Pb(Mg_1/3Nb_2/3)-0.33PbTiO₃ ceramics. In addition, the ceramics had a ferroelectric hysteresis loop, a large piezoelectric constant d₃₃ of 407 pC/N, and a planar electromechanical coupling factor k_p of 52%. These results suggest that the transparent ceramics may be used as a temperature-stable, linear electro-optic material.     

LaMgAl11O19 synthesis using non-hydrolytic sol-gel methods

Polycrystalline LaMgAl₁₁O₁₉ (LMA) was prepared by four different non-hydrolytic sol-gel methods. From stable solutions, four powder precursors containing an amorphous and nanocrystalline phase with specific reactivity were obtained. The particle size, morphology, thermal behaviour, and phase composition of the powder precursors were studied using DLS, TEM, DSC/TG and XRD. Bulk ceramic samples containing LMA were prepared at 1200?°C for 16?h and examined in terms of phase purity and microstructure using XRD, SEM, and TEM. Raman spectroscopy of pure LMA was used to study the structure in detail. A mechanism of LMA formation and a relation between powder precursor properties and final phase composition is proposed. These findings may be useful for designing modern technologies for fabrication of LMA for optical or protective coating applications.     

Composition-dependent xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 bulk ceramics for high energy storage applications

This work reports the composition dependent microstructure, dielectric, ferroelectric and energy storage properties, and the phase transitions sequence of lead free xBa(Zr_0.2Ti_0.8)O₃-(1-x)(Ba_0.7Ca_0.3)TiO₃ [xBZT-(1-x)BCT] ceramics, with x?=?0.4, 0.5 and 0.6, prepared by solid state reaction method. The XRD and Raman scattering results confirm the coexistence of rhombohedral and tetragonal phases at room temperature (RT). The temperature dependence of Raman scattering spectra, dielectric permittivity and polarization points a first phase transition from ferroelectric rhombohedral phase to ferroelectric tetragonal phase at a temperature (T_R-T) of 40?°C and a second phase transition from ferroelectric tetragonal phase - paraelectric pseudocubic phase at a temperature (T_T-C) of 110?°C. The dielectric analysis suggests that the phase transition at T_T-C is of diffusive type and the BZT-BCT ceramics are a relaxor type ferroelectric materials. The composition induced variation in the temperature dependence of dielectric losses was correlated with full width half maxima (FWHM) of A₁, E(LO) Raman mode. The saturation polarization (P_s) ≈8.3?μC/cm² and coercive fields ≈2.9?kV/cm were found to be optimum at composition x?=?0.6 and is attributed to grain size effect. It is also shown that BZT-BCT ceramics exhibit a fatigue free response up to 10⁵ cycles. The effect of a.c. electric field amplitude and temperature on energy storage density and storage efficiency is also discussed. The presence of high T_T-C (110?°C), a high dielectric constant (ε_r ≈?12,285) with low dielectric loss (0.03), good polarization (P_s ≈?8.3?μC/cm²) and large recoverable energy density (W?=?121?mJ/cm³) with an energy storage efficiency (η) of 70% at an electric field of 25?kV/cm in 0.6BZT-0.4BCT ceramics make them suitable candidates for energy storage capacitor applications.     

LaCr0.7Fe0.3O3-NiMn2O4 supported NTC composite ceramics with a sandwich-like structure

A novel sandwich-like structure was first proposed to adjust the electrical properties of NTC thermistors. The LaCr_0.7Fe_0.3O₃-NiMn₂O₄ supported composite ceramics with sandwich-like structure were initially fabricated via traditional solid-state reaction and uniaxial pressing methods, which allowed for the advantages of each component to be integrated into one material. X-Ray diffraction analysis indicates the ceramics mainly consisting of orthorhombic perovskite LaCr_0.7Fe_0.3O₃ and cubic spinel NiMn₂O₄ phases. SEM images manifest that the three layers adhered well to each other and exhibited high density. For electrical properties, the ρ_25°C was expanded to a wide range of 1182–110,233 Ω?cm and could be adjusted to the desired values by tuning the volume ratio of two basic layers, the B value was enhanced from 3358 K to 4167 K by NiMn₂O₄, and the thermal stability was improved by LaCr_0.7Fe_0.3O₃ with a resistance shift less than 0.55 % after annealing at 150 °C for 1500 h.     

Dual-phase rare-earth-zirconate high-entropy ceramics with glass-like thermal conductivity

A series of rare earth zirconates (RE₂Zr₂O₇) high-entropy ceramics with single- and dual-phase structure were prepared. Compared with La₂Zr₂O₇ and Yb₂Zr₂O₇, the smaller “rattling” ions (Yb³⁺, Er³⁺, Y³⁺) have been incorporated into pyrochlore lattice in (La_0.2Nd_0.2Y_0.2Er_0.2Yb_0.2)₂Zr₂O₇ (LNYEY) while larger ions (La³⁺, Nd³⁺, Sm³⁺, Eu³⁺) incorporated into fluorite lattice in (La_0.2Nd_0.2Sm_0.2Gd_0.2Yb_0.2)₂Zr₂O₇ (LNSGY). Due to high-entropy lattice distortion and resonant scattering derived from smaller ions Yb³⁺, Er³⁺, and Y³⁺, LNYEY shows a lower glass-like thermal conductivity (1.62-1.59 W m^-1 K^-1, 100-600℃) than LNSGY (1.74-1.75 W m^-1 K^-1, 100-600℃). Moreover, LNYEY and LNSGY exhibit enhanced Vickers’ hardness (LNYEY, H_v = 11.47 ± 0.41 GPa; LNSGY, H_v = 10.96 ± 0.26 GPa) and thermal expansion coefficients (LNYEY, 10.45 × 10^-6 K^-1, 1000℃; LNSGY, 11.02 × 10^-6 K^-1, 1000℃). These results indicate that dual-phase rare-earth-zirconate high-entropy ceramics could be desirable for thermal barrier coatings.     

Effects of Z-value on physicochemical and biological properties of β-SiAlONs ceramics

This study evaluated the effects of different Z-values on the physical, chemical, and biological properties of β-SiAlON ceramics. Increasing the Z-value of the β-Si₃N₄ solid solution's main phase resulted in the replacement of Si–N bonds with Al–O bonds. The number of columnar crystals decreased, bulk density increased, and porosity decreased, thus transforming the fine-particle microstructure of β-Si₃N₄ into the columnar structure of β-SiAlON. The compressive strength increased, which facilitated sintering at 1500 °C without sintering auxiliaries. H⁺ and OH⁻ ions in deionized water broke the covalent bonds on the β-SiAlON surface, thereby forming new Si–OH, Al–OH, and N–H bonds on the β-SiAlON surface and producing SiO₄⁴⁻, AlO₂⁻, and NH₄⁺ groups in the solution. Increasing the soaking time changed the compositions of ionized H⁺ and OH⁻ ions, thus increasing the pH. MC3T3-E1 cells were cultured on the β-SiAlON surface, and it was observed that the increase in the Z-value of β-SiAlON had no influence on cell adhesion and spreading, but it may slightly suppress cell proliferation at high Z-values. At low Z-values, the low AlO₂⁻ concentration helps promote osteogenic differentiation and mineralized nodule formation. Thus, β-SiAlON ceramics possess excellent physical, chemical, and biological properties and are considered excellent bone-repairing materials.     

Ultrahigh and field-independent energy storage efficiency of (1-x)(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-xBi(Mg0.5Ti0.5)O3 ceramics

Relaxor ferroelectrics are attracting an increasing interest in the application of pulse power systems due to their excellent energy storage performance. In this paper, the (1-x)(Ba_0·85Ca_0.15)(Zr_0·1Ti_0.9)O₃-xBi(Mg_0·5Ti_0.5)O₃ ((1-x)BCZT-xBMT, x ≤ 0.2) relaxor ceramics are prepared by the solid state method. The influence of BMT on the microstructure, dielectric and energy storage properties of the prepared ceramics is investigated. The XRD results show that the peak intensity of impurities (Bi₂O₃, TiO₂ and Ba₂Bi₄Ti₅O₁₈) is gradually stronger than that of BCZT phase with x increasing. Meanwhile, the grain size of (1-x)BCZT-xBMT ceramics gradually increases on account of the appearance of impurities Bi₂O₃. Influenced by the impurities and BMT, the dielectric constant of prepared ceramics gradually decreases with x increasing. A large W_rec value of 0.65 J/cm³ with an ultrahigh η value of 97.89% is achieved at x = 0.15 due to the high breakdown strength and slim P-E hysteresis loop. Meanwhile, the η is insensitive to the electric field. The ultrahigh η leads to lesser energy loss during the charge and discharge process. It makes the 0.85BCZT-0.15BMT ceramic more attractive in the application of pulse power systems.     

The effect of co-substitution on the microwave dielectric properties of Ba6-3xNd8+2xTi18O54(x=2/3) ceramics

In this work, the microwave dielectric properties of Ba₄(Nd_1-yBi_y)_28/3Ti_18-x(Al_1/2Ta_1/2)_xO₅₄(0≤x≤2, 0.05≤y≤0.2) ceramics co-substituted by A/B-site were studied. Firstly, (Al_1/2Ta_1/2)⁴⁺ was used for substitution at B-site. At 0≤x≤1.5, the above mentioned ceramic was found to exist in single-phase tungsten bronze structure, but at x = 2.0, the secondary phase appeared. Although the dielectric constant decreased by doping the (Al_1/2Ta_1/2)⁴⁺, but the quality factor was observed to improve by 40% and the temperature coefficient of resonant frequency decreased by 75%. Based on the above results, Bi³⁺ was introduced to Ba₄Nd_28/3Ti₁₇(Al_1/2Ta_1/2)O₅₄. The introduction of Bi³⁺ reduced the sintering temperature, greatly improved the dielectric constant, and ultimately decreased the temperature coefficient of resonant frequency, but it led to deterioration of quality factor. At last, with appropriate site-substitution content control (x = 1.0,y = 0.15), excellent comprehensive properties (ε_r = 89.0, Q × f = 5844 GHz @ 5.89 GHz，TCF = +8.7 ppm/°C) were obtained for the samples sintered at 1325 °C for 4 h.     

Influence of the stoichiometry,microstructure, and metallization method on the dielectric properties of 0.94 Na0.5Bi0.5TiO3-0.06 BaTiO3

The morphotropic composition of the lead-free solid solution between Na_0.5Bi_0.5TiO₃ and BaTiO₃ (0.94 Na_0.5Bi_0.5TiO₃-0.06 BaTiO₃ or NBT-6BT) is of particular interest for the next generation of high-temperature capacitors but remains plagued by the diversity of dielectric properties reported in the literature. In order to explain the apparent inconsistencies among the reported dielectric properties of NBT-6BT, we examine the influence of stoichiometry, phase separation, and metallization method. We show that the nominal stoichiometry has a crucial effect, since increasing the nominal Na/Bi ratio increases conductivity and dielectric losses (tan δ). It also increases the real part of the permittivity (ε’) and the frequency dispersion of both ε’ and tan δ, thereby altering the shape of the evolution with temperature of the dielectric properties. Moreover it increases the depolarization temperature (T_d) and decreases the temperature of maximum permittivity (T_m). Phase separation also occurs during the synthesis of NBT-6BT as Na evaporation leads to the formation of secondary Ba-containing phases. We report that these phases can have a positive impact on the dielectric properties: a moderate volume fraction (2.5 to 3.0%) and average grain surface (0.9 to 3.0 µm²) of these secondary Ba-containing phases increase the relative permittivity, decrease the dielectric losses, and increase the insulation resistance. We also show that the metallization method impacts the dielectric properties and therefore may contribute to the differences between various reports. The dielectric properties of NBT-6BT samples are measured during successive heating/cooling cycles and reveal that the permittivity value is lower during the first heating when silver paste, even cured, is used. These three components contribute to explaining the diversity of the reported dielectric properties of NBT-6BT.     

Fabrication and characterizations of Cr3+-doped ZnGa2O4 transparent ceramics with persistent luminescence

0.5 at.% Cr:ZnGa₂O₄ precursor was synthesized by the co-precipitation method with nitrates as raw materials, using ammonium carbonate as the precipitant. Low-agglomerated Cr:ZnGa₂O₄ powders with an average particle size of 43 nm were obtained by calcining the precursor at 900℃ for 4 h. Using the powders as starting materials, 0.5 at.% Cr:ZnGa₂O₄ ceramics with an average grain size of about 515 nm were prepared by presintering at 1150℃ for 5 h in air and HIP post-treatment at 1100℃ for 3 h under 200 MPa Ar. The in-line transmittance of 0.5 at.% Cr:ZnGa₂O₄ ceramics with a thickness of 1.3 mm reaches 59.5% at the wavelength of 700 nm. The Cr:ZnGa₂O₄ ceramics can be effectively excited by visible light and produce persistent luminescence at 700 nm. For Cr:ZnGa₂O₄ transparent ceramics, the brightness of afterglow was larger than 0.32 mcd/m² after 30 min, which is far superior to that of Cr:ZnGa₂O₄ persistent luminescence powders.