Structural Evolution in Hollandite Solid Solutions Across the A‐Site Compositional Range from Ba1.33Ga2.66Ti5.34O16 to Cs1.33Ga1.33Ti6.67O16

Hollandite solid solutions along the A‐site compositional range from the pure barium end‐member Ba_1.33Ga_2.66Ti_5.34O₁₆ to the pure cesium end‐member Cs_1.33Ga_1.33Ti_6.67O₁₆ have been synthesized using a solid‐state reaction technique. The crystal structure of the hollandite across the entire compositional range remained in the I4/m space group. Structural evolution was resolved by neutron diffraction, total scattering data, and density functional theory calculations. A trend of decreasing thermodynamic stability with smaller tunnel cations was attributed to increased structural distortion observed in the system. In addition, the tunnel cations' local environment was studied in the eightfold coordinated oxygen cavities. Local binding features of the tunnel cations reveals that the hollandite structure can strongly stabilize tunnel cations, even at elevated temperatures up to 500 K.     

The effect of cesium content on the thermodynamic stability and chemical durability of (Ba,Cs)1.33(Al,Ti)8O16 hollandite

Titanate-based hollandite ceramics are promising nuclear waste forms for Cs immobilization. In this work, a series of Al-substituted hollandite (Ba_,Cs)_1.33(Al,Ti)₈O₁₆ was investigated across a broad compositional range with varying Cs content. Powder X-ray diffraction showed that all samples exhibited a tetragonal hollandite phase. Enthalpies of formation determined by high-temperature melt solution calorimetry indicated enhanced thermodynamic stability with increased Cs content, which generally agreed with sublattice-based thermodynamic calculations. Moreover, enthalpies of formation of the samples were primarily affected by three factors: (a) relative sizes of cations on the A-sites and B-sites, (b) tolerance factor, and (c) optical basicity. Fractional element release revealed that Cs retention was significantly improved for the high Cs-containing hollandite compositions, which were supported by the evolution of microstructure of the pre and postleach particles. Elution studies of Al-substituted hollandite spiked with radioactive ¹³⁷Cs indicated that transmutation of Cs to Ba in the hollandite was accompanied by an increase in the retention of the Cs decay product, suggesting long-term stability of Al-substituted hollandite phase.     

Diffuse phase transition and ferroelectric study of (Ba,Bi)(Ti,Cr)O3 ceramics

Lead-free perovskite type (Ba_0.94Bi_0.06)(Ti_0.94Cr_0.06)O₃ (BBTC) ceramics have been prepared by the conventional mixed oxide method. The XRD results showed that BBTC ceramics have single phase tetragonal symmetry with space group P4mm. Dielectric studies exhibited a diffuse phase transition characterized by a strong temperature and frequency dispersion of permittivity. The quantitative characterization based on empirical parameters (ΔT_m, γ, ΔT_relax, and ΔT_dif) confirmed its relaxor nature. The origin of relax ferroelectric behavior is caused by the polar nanoclusters, which were arose due to the heterovalent substitutions of Bi³⁺ and Cr³⁺ at Ba²⁺ and Ti⁴⁺ sites. The P–E loops obtained at the temperature quite above T_m supported the diffuse phase transition behavior of the samples.     

A novel relaxor (Bi,Na,Ba)(Ti,Zr)O3 lead-free ceramic with high energy storage performance

Energy storage ceramic capacitors advance in high power density and working voltage, but challenge in simultaneously large recoverable energy density (W_rec), high energy efficiency (η), and good thermal stability. To achieve this, a novel lead-free ceramic system (1-x)(Bi_0.5Na_0.5)TiO₃-x(BaZr_0.3Ti_0.7O₃) [(1-x)BNT-xBZT] was explored by tailoring the ferroelectric relaxor states. The introduction of BZT gradually promotes the transformation of ferroelectric states into relaxor states at around the room temperature for x = 0.3-0.5 that presents a pinched P-E loop. The optimized composition of x = 0.45 possesses a large W_rec of up to 2.6 J/cm³ and ultrahigh ƞ of 94%, with only a small variation (±8%) in W_rec and the high ƞ (90%) over a broad temperature range (−30°C to 180°C), demonstrating the superior performances compared to many existing lead-free ceramics. The remarkable advantages of the novel BNT-BZT lead-free ceramics explored in this study are thus promising for the high-efficiency and temperature-stable energy storage capacitor applications.     

High piezoelectricity in CuO-modified Ba(Ti0.90Sn0.10)O3 lead-free ceramics with modulated phase structure

High piezoelectricity was achieved in Ba(Ti_0.90Sn_0.10)O₃ lead-free ceramics by optimizing CuO addition and sintering temperature. The phase structure of 1.0 mol% CuO-doped Ba(Ti_0.90Sn_0.10)O₃ ceramic is coexisting rhombohedral and tetragonal phases as sintered at 1300 °C. The coexistence of rhombohedral, tetragonal and orthorhombic phases appears in 1.0 mol% CuO-doped Ba(Ti_0.90Sn_0.10)O₃ ceramics as sintered at 1350–1450 °C, which leads to highly enhanced d₃₃ up to 650pC/N. This work demonstrates that high piezoelectric property (d₃₃ = 650pC/N) can be obtained in BaTiO₃-based lead-free piezoceramics with a simple composition modification by modulating phase structures, which also indicates that Ba(Ti,Sn)O₃ is a promising candidate to replace the lead-based piezoceramics.     

Flux crystal growth of Ba2[(UO2)2Ti2O8]: Structures,spectroscopies and implications

We report a flux crystal growth of Ba₂[(UO₂)₂Ti₂O₈] and subsequent structural and spectroscopic studies using multiple techniques. The layered crystal structure, built up with sheets of edge-sharing dimeric uranyl pentagonal bipyramids and dimeric TiO₅ square pyramids with interlayer Ba(II) ions, was revealed by synchrotron single crystal x-ray diffraction and confirmed with electron diffraction using a transmission electron microscope. The presence of only hexavalent uranium was confirmed by both diffuse reflectance and x-ray absorption near-edge structure spectroscopies, consistent with the bond valence sum calculations. Its vibrational modes were revealed by Raman spectroscopy. In addition, its implications as a potential hexavalent uranium waste form for the immobilization of uranium-rich radioactive wastes were discussed.     

Processing of 0.55(Ba0.9Ca0.1)TiO3-0.45Ba(Sn0.2Ti0.8)O3 lead-free ceramics with high piezoelectricity

We report a large piezoelectric constant (d₃₃), 720 pC/N and converse piezoelectric constant (d₃₃^*), 2215 pm/V for 0.55(Ba_0.9Ca_0.1)TiO₃-0.45Ba(Sn_0.2Ti_0.8)O₃ ceramics; the biggest value achieved for lead-free piezoceramics so far. The ceramic powders were calcined between 1050°C-1350°C and sintered at 1480°C. The best properties were obtained at a calcination temperature (CT) of 1350°C. The fitting combination of processing and microstructural parameters for example, initial powder particle size >2 µm, ceramics density ~95%, and grain size ~40 µm led to a formation of orthorhombic-tetragonal-pseudo-cubic (O-T-PC) mixed phase boundary near room temperature, supported by Raman spectra, pointed to the extremely high piezoelectric activity. These conditions significantly increase piezoelectric constants, together with high relative permittivity (ε_r) >5000 and a low loss tangent (tan δ) of 0.029. In addition, the d₃₃ value stabilizes in the range of 400-500 pC/N for all samples calcined between 1050°C and 1250°C. The results entail that the (Ba,Ca)(Sn,Ti)O₃ ceramics are strong contenders to be a substitute for lead-based materials for room temperature applications.     

Electrocaloric Effect in Ba(Zr,Ti)O3–(Ba,Ca)TiO3 Ceramics Measured Directly

In this paper, we report on studies of the electrocaloric (EC) effect in lead‐free (1?x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ ceramics with compositions range between 0.32 ≤ x ≤ 0.45. The EC effect was measured directly using a modified differential scanning calorimeter. The maximum EC temperature change, ΔT_direct = 0.33 K under an electric field of 2 kV/mm, was observed for the composition with x = 0.32 at ~63°C. We found that the EC effect peaks not only around the Curie temperature but also at the transition between the ferroelectric phases with different symmetries. A strong discrepancy observed between the results of the direct measurements and indirect estimations points out that using Maxwell's equations is invalid for the thermodynamic nonequilibrium conditions that accompany only partial (incomplete) poling of ceramics. We also observe a nonlinearity of the EC effect above the Curie temperature and in the temperature range corresponding to the tetragonal ferroelectric phase.     

Local structure study of phase transition behavior in Ba(Ti,Sn)O3 perovskite by X-ray absorption fine structure

In this work, BaTi_1−xSn_xO₃ (BST) powders (x=0–0.95) were synthesized by a conventional mixed-oxide method. The phase information was investigated by a combination of X-ray diffraction and X-ray absorption spectroscopy techniques. The XRD measurements indicated the global phase transition from tetragonal to cubic perovskite structure. From the synchrotron X-ray Absorption Near-Edge Structure (XANES) measurements at the Ti K-edge and Sn L₃-edge, it was seen that an increase of Sn content in BaTiO₃ affected the phase transition behavior and local structure of BST. In addition, the local structure of Ba(Ti,Sn)O₃ materials were experimentally determined and compared with that obtained from the simulation. The local structure obtained from the XANES technique provided additional structural information unavailable from XRD investigation. Finally, the phase transition behavior from relaxor ferroelectric to polar cluster in BST system was discussed and attributed mainly to the change in the local structure.     

离子交换法处理含Cr(Ⅵ)废水的研究

采用201×7强碱性阴离子交换树脂处理模拟含Cr(Ⅵ)废水,探讨了废水酸度、交换时间、浓度对Cr(Ⅵ)去除率的影响以及树脂再生所需的合适温度和再生剂浓度。结果表明,201×7强碱性阴离子交换树脂处理模拟含Cr(Ⅵ)废水,具有交换容量大、交换效果好、树脂再生条件较简单等优点。并对实际含铬废水进行了处理,废水中Cr(Ⅵ)的初始浓度为1 540 mg/L,处理量达52 BV(床体积)时,出水中Cr(Ⅵ)的浓度仍小于0.5 mg/L,达到国家排放标准。树脂交换容量约80 mg/g。用8%NaOH溶液,在50℃条件下进行再生效果较好,再生率大于95%,可实现树脂的重复使用。     

Accelerated Leach Testing of GLASS (ALTGLASS): I. Informatics approach to high level waste glass gel formation and aging

Glass corrosion data from the ALTGLASS^™ database were used to determine if gel compositions, which evolve as glass systems corrode, are correlated with the generation of zeolites and subsequent increase in the glass dissolution rate at long times. The gel compositions were estimated based on the difference between the elemental glass starting compositions and the measured elemental leachate concentrations from the long-term product consistency tests (ASTM C1285) at various stages of dissolution, ie, reaction progress. A well-characterized subset of high level waste glasses from the database was selected: these glasses had been leached for 15-20 years at reaction progresses up to ~80%. The gel composition data, at various reaction progresses, were subjected to a step-wise regression, which demonstrated that hydrogel compositions with Si^*/Al^* ratios of <1.0 did not generate zeolites and maintained low dissolution rates for the duration of the experiments. Glasses that formed hydrogel compositions with Si^*/Al^* ratios ≥1, generated zeolites accompanied by a resumption in the glass dissolution rate. The role of the gel Si/Al ratio, and the interactions with the leachate, provides the fundamental understanding needed to predict if and when the glass dissolution rate will increase due to zeolitization.     

Structure and disorder in Pb-Na metasilicate (PbO:Na2O:2SiO2) glasses: A view from high-resolution 17O solid-state NMR

Knowledge of the structure of lead (Pb)-bearing silicate glasses, such as degree of polymerization and arrangement among cations, provides improved prospects for understanding their macroscopic properties. Despite the importance, the detailed disorder in Pb-bearing silicate glasses with varying composition (i.e., Pb/alkali content) has not been systematically explored. Here, we reveal the first unambiguous structural information of PbO-Na₂O-SiO₂ glasses with varying PbO content [i.e., X_PbO = PbO/(Na₂O + PbO)], which are the fundamental model system for multicomponent Pb-bearing glasses, using high-resolution ¹⁷O solid-state NMR. ¹⁷O NMR spectra clearly show the resolved multiple oxygen sites, such as Na-O-Si, Si-O-Si, and [Na,Pb]-O-Si. As X_PbO increases, the fraction of [Na,Pb]-O-Si peak increases markedly at the expanse of substantial reduction in the fraction of Na-O-Si/total NBO. This trend indicates the relative predominance of the dissimilar pairs around non-bridging oxygen (NBO) and, therefore, can be explained well with the pronounced chemical ordering among Na⁺ and Pb²⁺. These results confirm that Pb is primarily a network-modifier in the glasses studied here. Atomic environments around both NBO and BO are affected by the change in Na/Pb ratio, while topological disorder due to cation mixing around NBO is much more prominent in Pb endmember. The structural details of short-range configurations around oxygen in alkali Pb-silicate glasses provide atomistic insights for understanding the properties of Pb-bearing multicomponent silicate glasses.     

A complex lead-free (Na,Bi, Ba)(Ti,Fe)O3 single phase perovskite ceramic with a high energy-density and high discharge-efficiency for solid state capacitor applications

We have investigated a series of compositions in the pseudo-ternary lead-free alloy system Na_1/2Bi_1/2TiO₃-BaTiO₃-BiFeO₃ with regard to its energy storage density and discharge efficiency. A composition 0.4(Na_0.5Bi_0.5TiO₃)-0.225BaTiO₃-0.375BiFeO₃ of this series was identified to give the best energy density and discharge efficiency. While conventional sintering gave energy density of 0.77 J/cm³ and discharge efficiency of 67%, we achieved a remarkable increase in energy storage density (∼1.4 J/cm³) and discharge efficiency (∼90%) by using spark plasma sintering of this composition. Our results suggest that this alloy system can be a potential lead-free candidate for high electric energy storage and discharge efficiency.     

Ferroelectric,dielectric, and impedance properties of Sm-modified Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 ceramics

To investigate the effect of Sm doping on the electrical properties of Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-xBCT) (x = 40, 50, 60) ceramics, three Sm-modified ceramics were prepared using the conventional solid-state reaction method. Related electrical measurements, including ferroelectric and dielectric investigations and impedance spectroscopy, were recorded for these ceramics. It was found that a tilted morphotropic phase boundary resulted from the addition of Sm, which induced the best piezoelectric properties and insulating behaviour in the Sm-BZT-60BCT sample. An abnormal P-E loop shrinkage appeared in the Sm-BZT-50BCT sample but not in the other two samples. This could be attributable to the different electronegativities between Ca²⁺ and Ba²⁺ and between Zr⁴⁺ and Ti⁴⁺, whose contents are different in varied samples and have an effect on defect-dipole alignment as well as spontaneous polarization. The activation energies for the bulk conductivity in the three composites were calculated to be 0.28 ± 0.01, 0.08 ± 0.01, and 0.36 ± 0.01 eV, confirming the existence of oxygen vacancies in our samples. The Sm dopant is responsible for the oxygen vacancies. This also leads to an increased Curie temperature in the three composites.     

A novel approach to sintering (Ba,Ca)(Ti,Zr)O3 multilayer ceramic capacitors with Ni electrodes

In this study, a novel sintering technique combining rapid heating and constrained sintering was adopted to fire multilayer ceramic capacitors (MLCCs). It was demonstrated that chamber development can be significantly minimized, leading to a small internal residual stress in MLCCs when they were fired by the novel sintering technique instead of free sintering. The magnitude of tensile stress was closely related to the heating rate and the thickness of the constraining layer. The presence of in-plane tensile stress resulted from the constrained sintering in the x–y plane of the MLCCs, which then modified both the densification rate of the dielectric materials and the inner electrode. The thin inner electrode (<1 μm) with high continuity (>98%) and the fine grain size (1.5 μm) with narrow distribution (±0.10 μm) of BCTZ-based MLCC with a concave-free morphology can be attained by using such a rapid constrained sintering technique when BT is used as a constraining layer laminated on both sides of the multilayer BCTZ-based MLCC.     

Creating adjoining polymorphic phase transition (PPT) regions in ferroelectric (Ba,Sr)(Zr,Ti)O3 ceramics

In this work, we report the polymorphic phase transitions(PPT) in ferroelectric Ba_0.95Sr_0.05Zr_xTi_(1-x)O₃ (BSZT, x = 0.01–0.10) ceramics synthesized by using a solid-state reaction method. The doping elements and composition ratios were selected to create adjoining PPT phase boundaries near room temperature, hence to achieve a broadened peak of piezoelectric performance with respect to composition. The temperature-composition phase diagram was constructed and the effects of PPT on the electromechanical and ferroelectric properties of the ceramics were investigated. It was revealed that the two adjacent PPT regions at room temperature showed different characteristics in property enhancement. However, due to the proximity of the phase boundaries, Ba_0.95Sr_0.05Zr_xTi_(1-x)O₃ ceramics in a fairly broad range of compositions (0.02 ≤ x ≤ 0.07) showed excellent piezoelectric properties, including a large piezoelectric constant (312 pC/N ≤ d₃₃ ≤ 365 pC/N) and a high electromechanical coupling coefficient k_p (0.42 ≤ k_p ≤ 0.49).     

Composition gradient (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 film with improved dielectric,piezoelectric and ferroelectric temperature stability

Lead-free (1-x)Ba(Ti_0.8Zr_0.2)O₃-x(Ba_0.7Ca_0.3)TiO₃ (BZT-BCT) possesses comparable piezoelectric constant with lead zirconate titanate (PZT), but its poor temperature electric performances stability and low Curie temperature limit its application. Here we designed composition graded BZT-BCT films with improved temperature stability of piezoelectric, ferroelectric, and dielectric performances over a wide temperature range, and the d₃₃ reaches 21 pm/V with hysteresis loop even at 180 °C, which is far above the Curie temperature of BZT-BCT ceramic and BZT-0.5BCT film. The excellent temperature stability is ascribed to the lattice distortion and strain gradient in the grains caused by ions diffusion, and could suppress phase transition. This work could bring forward a feasible design for dielectric/piezoelectric/ferroelectric devices operating in harsh temperature environment.     

Structure,dielectric properties of novel Ba(Zr,Ti)O3 based ceramics for energy storage application

(1-x) Ba(Zr_0.2Ti_0.8)O₃-x Na_0.5Bi_0.5TiO₃ (x = 0, 10, 20 30, 40, 50 mol%) (BZTN) ceramics are prepared by the traditional solid phase method. All BZTN ceramics exhibit a pseudo-cubic BZT based perovskite structure. Both the average grain size and the relaxor ferroelectricity of BZTN ceramics gradually increase with increasing NBT content. The W_rec of 3.22 J/cm³ and η of 91.2% is obtained for the BZTN40 ceramic at 241 kV/cm. BZTN40 ceramic also exhibits good temperature stability from room temperature to 150 °C and frequency stability from 1 Hz to 100 Hz. A P_D of 0.621 J/cm³ and a t_0.9 of 82 ns is obtained for the BZTN40 ceramic at 120 kV/cm. BZTN ceramics show application potential in energy storage and pulse power capacitors.     

Composition driven (Ba,Ca)(Zr,Ti)O3 lead-free ceramics with large quality factor and energy harvesting characteristics

A comprehensive study on energy harvesting characteristics as well as electro-mechanical properties of lead-free (1−x)(BaZr_0.2Ti_0.8)O₃—x(Ba_0.7Ca_0.3Ti)O₃ ceramics were systematically carried out. Raman and Rietveld analyses show a formation of rhombohedral-orthorhombic-tetragonal (R-O-T) phase boundary region between 4/6 BZT/BCT and 6/4 BZT/BCT compositional range. Raman modes shift toward lower frequencies with increased Zr/Ca stoichiometric ratio attributed to asymmetric Ti-O phonon vibrations, which caused local disorder, widening of energy band and reduced Curie temperature. The large mechanical quality factor Q_m = 556 is related to the hardening effect and significantly high energy conversion efficiency η = 96% was discovered for 3/7 BZT/BCT composition. Largely, the noblest electro-mechanical properties were retrieved for 5/5 BZT/BCT ceramics, in which d₃₃ = 500 pC/N (from quasi-static d₃₃ meter), d₃₃ = 540 pm/V (from field-dependent d₃₃ curves) indicating that the both methods are analogous with a deviation of 8%. The outstanding energy harvesting characteristics such as voltage constant g₃₃ = 27 × 10⁻³ Vm/N, transduction coefficient d₃₃ × g₃₃ = 13 301 × 10⁻¹⁵ m²/N, figure of merit under off-resonance conditions FOM_off = 12.1 × 10⁻¹⁰ m²/N and fairly large η of 94% were attained again for 5/5 BZT/BCT ceramics. These outstanding characteristics were ascribed to the R-O-T phase boundary region that comprises a low energy barrier, consequently facilitated easy polarization rotation and triggered an increased electro-mechanical conversion. These characteristics outperform other lead-free and even most commercially available lead-based ceramics, and thus suitable for sensors, actuators, resonators, and energy harvesting applications.     

Low-fire processing and microwave dielectric properties of LB glass-doped Ba3.75Nd9.5Ti17.5(Cr0.5Nb0.5)0.5O54 ceramic

The effects of LB glass on the sintering behavior, structure, and dielectric properties for the Ba_3.75Nd_9.5Ti_17.5(Cr_0.5Nb_0.5)_0.5O₅₄ (BNTCN) ceramic were investigated. The results showed that the LB glass, as an effective sintering aid, successfully lowered the sintering temperature of BNTCN ceramic by formation of the liquid phase. Furthermore, the change of the structure and decrease in grain size had influences on the electrical conductivity, thermal stability, and microwave dielectric properties for the BNTCN ceramics doped LB glass. Finally, the excellent microwave dielectric properties with ε_r = 73.4, Q × f = 5277 GHz, and τ_f = +7.1 ppm/°C were obtained for samples sintered at 950°C when x = 5, indicating the BNTCN ceramic doped with 5 wt% LB glass is a promoting LTCC material.