Effects of Tb doping on structural and electrical properties of 47(Ba0.7Ca0.3)TiO3–0.53Ba(Zr0.2Ti0.8)O3 thin films at various annealing temperature by pulsed laser deposition

The ceramic thin films of 47(Ba_0.7Ca_0.3)TiO₃–0.53Ba(Zr_0.2Ti_0.8)O₃ (BCZT) + x (x = 0.2, 0.3, 0.4 and 0.5) mol% Tb were grown on Pt(111)/Si substrates with various annealing temperature by pulsed laser deposition. The XRD spectra confirm that Tb element can enhance the (l10) and (111) orientations in ceramic films. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that Tb-doping can increase particle size effectively. The surface of Tb-doped film annealed at 800 ℃ is uniform and crack-free, and the average particle size and mean square roughness (RMS) are about 280 nm and 4.4 nm, respectively. Comparing with pure BCZT, the residual polarization (P_r) of 0.4 mol% Tb-doped film annealed at 800 ℃ increase from 3.6 to 9.8 μC/cm². Moreover, the leakage current density value of Tb doped films are one order of magnitude (5.33 × 10^?9?1.97 × 10^?8 A/cm² under 100 kV/cm) smaller than those of pure BCZT films (1.02 × 10^?7 A/cm²).     

Co2O3 substitution effects on the structure and microwave dielectric properties of low-firing (Zn0.9Mg0.1)TiO3 ceramics

Low-firing (Zn_0.9Mg_0.1)_1?xCo_xTiO₃ (x = 0.02–0.10) (ZMC_xT) microwave dielectric ceramics with high temperature stability were synthesized via conventional solid-state reaction. The influences of Co₂O₃ substitution on the phase composition, microstructure and microwave dielectric properties of ZMC_xT ceramics were discussed. Rietveld refinement results show the coexistence of ZnTiO₃ and ZnB₂O₄ phases at x = 0.02–0.10. (Zn_0.9Mg_0.1)_1?xCo_xTiO₃ ceramic with x = 0.06 (ZMC_0.06T) obtains the best combination microwave dielectric properties of: ε_r = 21.58, Q × f = 53,948 GHz, τ_f = ? 54.38 ppm/°C. For expanding its application in LTCC field, 3 wt% ZnO-B₂O₃-SiO₂ (ZBS) and 9 wt% TiO₂ was added into ZMC_0.06T ceramic, great microwave dielectric properties were achieved at 900 °C for 4 h: ε_r = 26.03, Q × f = 34,830 GHz, τ_f = ? 4 ppm/°C, making the composite ceramic a promising candidate for LTCC industry.     

Evaluation of rare-earth element dopants (Sm and Er) on ablation resistance of ZrB2/SiC-sintered billets

In this paper, how rare-earth element dopants (samarium and erbium) affect the scale development of sintered ZrB₂/SiC (ZBS) samples during ablation testing was investigated. ZBS billets with five different Sm to Er ratios, with a nominal total amount of 3 mol% dopant incorporated, were prepared by sintering in vacuum to 2000°C and subjected to 60 and 300 seconds ablation cycles. Differences in surface temperatures between ZBS samples with different dopant ratios suggests differences in spectral absorptance/emittance between each of the five compositions investigated. ZBS billets co-doped with Sm and Er form a beneficial c₁-(Sm/Er)_0.2Zr_0.8O_1.9 oxide scale as the majority phase, with some glassy phase observed. The crystalline c₁-(Sm/Er)_0.2Zr_0.8O_1.9 oxide scale is more thermally stable than the m-ZrO₂ oxide scale typically formed in oxidized ZBS systems, resulting in a more adherent oxide scale to the unreacted material. The crystalline oxide scale and the amorphous phase are formed by a convection cell mechanism where the c₁-(Sm/Er)_0.2Zr_0.8O_1.9 crystalline islands precipitate, grow, and coalesce.     

Effect of spherical porosity on co-fired dense/porous zirconia bi-layers cambering

Geometrical instability leading to cambering is recorded during co-sintering of zirconia dense/porous bi-layered planar structures. Sintering strain in the bi-layers rises mainly from mismatch between the different porosity volume fractions at the layers and their interface. In this paper, we analyze the model case of dense taped of 8 mol% Y₂O₃-stabilized ZrO₂ laminated on ca. 400 μ thick 3 mol% Y₂O₃ doped zirconia porous tapes, with homogenous spherical porosity of 13 vol%, 46 vol%, and 54 vol%. Sintering stress during densification is evaluated from the shrinkage rates and viscoelastic behavior during sintering by thermo-mechanical analysis, using cyclic loading dilatometry. The camber development of the bi-layers is measured by in-situ optical dilatometry. In accordance with the model prediction, cambering can be controlled tuning the porosity while achieving a synergetic effect between densification and formation of open porosity at the bilayers.     

Multiplicity of photoluminescence in Raman spectroscopy and defect chemistry of (Ba1−xRx)(Ti1−xHox)O3 (R = La,Pr, Nd,Sm) dielectric ceramics

(Ba_1?xR_x)(Ti_1?xHo_x)O₃ (R = La, Pr, Nd, Sm; x ≥ 0.04) (BRTH) ceramics were prepared using a mixed oxides method. The solubility limits in BRTH with R = La, Pr, Nd, Sm were determined by XRD to be x = 0.11, 0.12, 0.06, and 0.14, respectively. The ionic radius of R at Ti-site plays a decisive role in the solubility limit in BRTH. Only BRTH with R = La satisfied Vegard's law. The multiplicity of photoluminescence (PL) signals of Nd³⁺/Ho³⁺ and Sm³⁺/Ho³⁺ in Raman scattering under 532-nm excitation laser and the high-permittivity abnormality for the denser BRTH with R = Sm and at x = 0.07 were reported. The PL provided the evidence of a small number of Ho³⁺ at Ba-site in BRTH and it was determined that the number of Ba-site Ho³⁺ ions increased from 0.05 at% at R = La to 0.19 at% at R = Sm with increasing atomic number of light rare earth. BRTH exhibited a much broadened dielectric-temperature characteristics, marked by ×5 T, ×6 T, ×7 T, and ×8 S dielectric specifications for BRTH with R = La, Pr, Nd, Sm and at x = 0.06, respectively, and they exhibited lower dielectric loss (tan δ < 0.015) at room temperature. The dielectric-peak temperature (T_m) of BRTH decreased linearly at a rate of less than ?21 °C/%(R/Ho). The defect chemistry, solubility limit, lower dielectric loss, and dielectric abnormality are discussed.     

Fabrication and photocatalytic performance of Sn-doped titania hollow spheres using polystyrene as template

Sn-doped anatase hollow spheres were fabricated using a template method involving polystyrene spheres as core and anatase coating as shell. The synthesis route included the preparation of PS spheres, followed by their coating by Sn-doped TiO₂ sol-gel precursor and subsequent removal of the PS cores by pyrolysis and recrystallization at 500 °C for 2 h. The observation of minor amounts of rutile suggests that Sn promotes the anatase → rutile phase transformation. At doping levels of ≤ 1.0 mol% Sn, the unsaturated solubility and increasing defect densities enhanced nucleation. At 1.0–2.0 mol% Sn, the solubility remained unsaturated but increasing Sn incorporation reduced crystallinity owing to lattice deformation and partial amorphization. At 2.0–3.0 mol% Sn, solid solution saturation occurred, resulting in excess dopant precipitation, leading to grain boundary pinning and partial blockage of surface-active sites. Ionic radii, thermodynamic, phase equilibria, intervalence charge transfer, and defect chemistry considerations suggest that Sn⁴⁺ exhibits substitutional solid solubility in the TiO₂ lattice. The photocatalytic performance was in the order 1.0 > 1.2 > 1.5 ≈ 0.7 > 2.0 > 0.0 > 3.0 mol% Sn. This ranking is consistent with the dominant role of crystallinity such that, at ≤ 1.0 mol% Sn, the performance increased owing to enhanced nucleation from low defect density and increasing crystallinity while, at 1.0–2.0 mol% Sn, the performance decreased from increased lattice strain and effective partial amorphization, and, at 2.0–3.0 mol% Sn, it decreased from maximal lattice strain and blockage of active sites.     

Fabrication of dense Ce0.9Mg0.1P2O7-PmOn composites by microwave heating for application as electrolyte in intermediate-temperature fuel cells

In the present work, we report a method of fabrication of dense 10 mol% Mg²⁺-doped cerium pyrophosphate-phosphate (Ce_0.9Mg_0.1P₂O₇-P_mO_n; CMP-P) composites by microwave heat-treatment of the preformed Ce_0.9Mg_0.1P₂O₇ substrates in the presence of phosphoric acid. The composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The microwave heating at 375 °C for 5 min resulted in the formation of dense CMP-P composites which retained most of the pyrophosphate phase. The electrical conductivity was extracted from the EIS data and for the CMP-P composite prepared by H₃PO₄ loading for 10 h and microwave heat-treatment for 5 min it was found to be >10^?2 S m^?1 in 100–250 °C range with a maximum of 0.062 S cm^?1 at 190 °C, which was significant for its application as electrolyte in intermediate temperature fuel cells.     

Characterization of nickel manganite NTC thermistor films prepared by aerosol deposition at room temperature

NiMn₂O_4+δ thermistor thick films have been successfully deposited by the so-called Aerosol Deposition Method (ADM) at room temperature on alumina substrates, Si-wafers, as well as on special planar four-wire interdigital electrode structures for high-precision electrical characterization. The NTCR films are homogeneous, completely dense and scratch resistant. Both as-deposited and tempered, the NTCR films exhibit a cubic spinel structure. Between 25 °C and 90 °C, the NTCR film resistance behaves as it is typical for variable range hopping (VRH) with parabolic density of states. As a result of moderate film tempering, the thermistor constant B and the specific resistance at 25 °C (ρ₂₅) decrease from 4250 K to 4020 K and 65 Ω·m to 40 Ω·m respectively, and are close to bulk values. In combination with the excellent reproducibility of the ρ₂₅ and B values, AD processing of films appears to be a promising alternative for classical ceramic bulk processes.     

Low temperature cofirable Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ microwave dielectric ceramic with ZnO–B2O3–SiO2 frit

The sintering properties and microwave dielectric properties of Ca[(Li_1/3Nb_2/3)_1?xZr_3x]O_3+δ (x = 0.05, abbreviated as CLNZ) ceramic doped with ZBS frit are investigated for LTCC applications. XRD patterns and SEM photographs show that dense and single perovskite phase ceramics can be obtained with ZBS doping content of less than 10 wt%, before the Ca₂Nb₂O₇ pyrochlore phase begins to segregates. The results show that ZBS vitreous phase stays at the grain boundary in the final sintered ceramics, suggesting it acts as liquid phase lubrication during sintering, and has effectively lowered the sintering temperature of CLNZ ceramics from 1170 °C to 940 °C. The preferred orientation of CLNZ solid solution varies from (1 2 1) plane to (1 0 1) plane as ZBS content and sintering temperature increase. The optimal microwave dielectric properties of ?_r = 32.0, Q_f = 6.64 THz and τ_f = ?27.1 ppm/°C can be obtained in 15 wt% ZBS doped CLNZ ceramic when sintered at 940 °C for 4 h. The Ag-cofiring experiment clearly shows that no chemical reaction takes place between Ag and the ZBS-doped CLNZ ceramic, indicating its great potential applications in LTCC field.     

Influence of MnO2 and Co3O4 dopants on dielectric properties of Pb(Fe2/3W1/3)O3 ceramics

Dielectric properties of Pb(Fe_2/3W_1/3)O₃ ceramic doped with 0.05–1 mol% of MnO₂ or Co₃O₄ were investigated in a wide temperature range from −160 to 450 °C at frequencies 10 Hz–1 MHz. Besides the maxima corresponding to the ferroelectric–paraelectric transition, at higher temperatures other peaks in temperature dependencies of relative electrical permittivity and dissipation factor were observed, attributed to dielectric relaxation. The location and height of these peaks are strongly related to frequency and the dopant level. Both MnO₂ and Co₃O₄ addition caused a significant increase in the resistivity of PFW ceramic—from 10⁶ Ω cm for undoped samples to 10¹¹ Ω cm for those with 1 mol% of a dopant. The activation energies of relaxation calculated on the basis of dielectric measurements are very close to the conduction activation energies determined in similar temperature range.     

Near room temperature giant negative and positive electrocaloric effects coexisting in lead–free BaZr0.2Ti0.8O3 relaxor ferroelectric films

BaZr_0.2Ti_0.8O₃ (BZT) relaxor ferroelectric (FE) films with tetragonal structure were deposited on Pt/TiO₂/SiO₂/Si(100) substrates via a sol-gel technique. A giant electrocaloric effect (ECE) was observed in the compact films with ΔT = 43.6 K and ΔS = 61.9 J/K kg at near room temperature of 366.5 K, which was attributed to the high breakdown electric field of E = 1010 kV/cm. Meanwhile, large negative ECE (ΔT = ? 5.2 K and ΔS = ? 8.8 J/K kg at room temperature of 305 K, ΔT = ? 5.1 K and ΔS = ? 7.2 J/K kg at near room temperature of 375 K) were achieved. The abnormal negative ECE is originated from structural transformation in relaxor ferroelectrics. The coexisting of giant negative and positive electrocaloric effects makes it more effective to realize the refrigeration during the application or removal of an electric field. The maximum electrocaloric coefficient (ζ_max = 0.043 K cm/kV) and refrigeration efficiency (COP = 35.18) of the films were obtained at near room temperature of 366.5 K. The giant electroelectric effect makes BZT films promising as lead-free materials for application in environment-friendly refrigeration equipment at near room temperature.     

CMAS (CaO–MgO–Al2O3–SiO2) resistance of Y2O3-stabilized ZrO2 thermal barrier coatings with Pt layers

Calcium–magnesium–alumina–silicate (CMAS) corrosion significantly affects the durability of thermal barrier coatings (TBCs). In this study, Y₂O₃ partially stabilized ZrO₂ (YSZ) TBCs are produced by electron beam-physical vapor deposition, followed by deposition of a Pt layer on the coating surfaces to improve the CMAS resistance. After exposure to 1250 °C for 2 h, the YSZ TBCs were severely attacked by molten CMAS, whereas the Pt-covered coatings exhibited improved CMAS resistance. However, the Pt layers seemed to be easily destroyed by the molten CMAS. With increased heat duration, the Pt layers became thinner. After CMAS attack at 1250 °C for 8 h, only a small amount of Pt remained on the coating surfaces, leading to accelerated degradation of the coatings. To fully exploit the protectiveness of the Pt layers against CMAS attack, it is necessary to improve the thermal compatibility between the Pt layers and molten CMAS.     

Ablation behavior and mechanism of boron nitride - magnesium aluminum silicate ceramic composites in an oxyacetylene combustion flame

In the present study, ablation behavior and properties of BN-MAS (magnesium aluminum silicate) composites impinged with an oxyacetylene flame at temperatures up to 3100 °C were investigated. As ablation time ranged from 5 to 30 s, the mass and linear ablation rates increased from 0.0027 g/s and 0.001 mm/s to 0.0254 g/s and 0.087 mm/s, respectively. A SiO₂-rich protective oxide layer formed during the ablation process, which contributed to the oxidation resistance of the composites. Ablation products mainly consisted of magnesium-aluminum borosilicate glass, mullite, spinel and indialite. The thermal oxidation of h-BN during flame ablation and scouring of MAS by high-speed gas flow were the main ablation mechanisms.     

Constrained sintering of YSZ/Al2O3 composite coatings on metal substrates produced from eletrophoretic deposition

Yttria stabilized zirconia/alumina (YSZ/Al₂O₃) composite coatings were prepared from electrophoretic deposition (EPD), followed by sintering. The constrained sintering of the coatings on metal substrates was characterized with microstructure examination using electron microscopy, mechanical properties examination using nanoindentation, and residual stress measurement using Cr³⁺ fluorescence spectroscopy. The microstructure close to the coating/substrate interface is more porous than that near the surface of the EPD coatings due to the deposition process and the constrained sintering of the coatings. The sintering of the YSZ/Al₂O₃ composite coating took up to 200 h at 1250 °C to achieve the highest density due to the constraint of the substrate. When the coating was sintered at 1000 °C after sintering at 1250 °C for less than 100 h, the compressive stress was generated due to thermal mismatch between the coating and metal substrate, leading to further densification at 1000 °C because of the ‘hot pressing’ effect. The relative densities estimated based on the residual stress measurements are close to the densities measured by the Archimedes method, which excludes an open porosity effect. The densities estimated from the hardness and the modulus measurements are lower than those from the residual stress measurement and the Archimedes method, because it takes account of the open porosity.     

Fabrication of porous fibrous alumina ceramics by direct coagulation casting combined with 3D printing

A novel forming method for preparing porous alumina ceramics using alumina fibers as raw materials by direct coagulation casting (DCC) combined with 3D printing was proposed. Porous fibrous alumina ceramics were fabricated through temperature induced coagulation of aqueous-based DCC process using sodium tripolyphosphate (STPP) as dispersant and adding K₂SO₄ as removable sintering additives. The sacrificial coated sand molds was fabricated by 3D printing technology, followed by the infiltration of silica sol solution for the subsequent suspension casting. Stable alumina suspension of 40 vol% solid loading was obtained by adding 2.0 wt% STPP and 40 wt% K₂SO₄. The controlled coagulation of the suspension could be realized after heating at 90 °C for about 35 min. The ceramic sample sintered at 1450 °C for 2 h showed the highest compressive strength of 24.33 MPa with porosity of 57.38%. All samples sintered at 1300–1450 °C had uniform pore size distributions with average pore size of 7.2 µm, which indicated the good structure stability when sintered at high temperature.     

The effect of sintering temperature and time on microwave properties of Sm(Zn1/2Ti1/2)O3 ceramics for resonators

The microwave dielectric properties of Sm(Zn_1/2Ti_1/2)O₃ ceramics have been investigated. Sm(Zn_1/2Ti_1/2)O₃ ceramics were prepared by conventional solid-state route with various sintering temperatures and times. The prepared Sm(Zn_1/2Ti_1/2)O₃ exhibited a mixture of Zn and Ti showing 1:1 order in the B-site. Higher sintered density of 7.01 g/cm³ can be produced at 1310 °C for 2 h. The dielectric constant values (ɛ_r) of 22–31 and the Q × f values of 4700–37,000 (at 8 GHz) can be obtained when the sintering temperatures are in the range of 1250–1370 °C for 2 h. The temperature coefficient of resonant frequency τ_f was a function of sintering temperature. The ɛ_r value of 31, Q  ×  f value of 37,000 (at 8 GHz) and τ_f value of −19 ppm/°C were obtained for Sm(Zn_1/2Ti_1/2)O₃ ceramics sintered at 1310 °C for 2 h. For applications of high selective microwave ceramic resonator, filter and antenna, Sm(Zn_1/2Ti_1/2)O₃ is proposed as a suitable material candidate.     

The effect of Sm2O3 on the microstructure and electrical properties of SiO2-doped SnO2-Zn2SnO4 ceramic varistors

In this work, Sm₂O₃- and SiO₂-codoped SnO₂-Zn₂SnO₄ ceramic varistors were prepared through traditional ceramic processing, and the effect of Sm₂O₃ on the resulting microstructure and electrical properties was investigated. The results demonstrated that the ceramics were composed mainly of SnO₂ and Zn₂SnO₄, and Sm was distributed homogeneously in the grains and along the grain boundaries. With 0.2 mol% Sm₂O₃ doping, the grain growth was obviously promoted. Further increases in Sm₂O₃ to 0.4 mol% resulted in trace amount of SiO₂ and segregations containing elemental Sm via X-ray diffraction patterns and microstructure photos, respectively. In the sample doped with 0.3 mol% Sm₂O₃, optimal electrical characteristics of α=9.4, E_B=10 V/mm, J_L=46 μA/cm² and ε′=1.2×10⁴ were obtained. Simultaneously, the sample doped with 0.3 mol% Sm₂O₃ had the lowest conductance activation energy of 0.16 eV at temperatures lower than 110 °C. This good performance indicates that Sm₂O₃- and SiO₂-codoped SnO₂-Zn₂SnO₄ composite ceramics are viable candidate for the manufacture of capacitor-varistor functional devices.     

Interfacial origin of enhanced energy density in SrTiO3-based nanocomposite films

SrTiO₃-based films doped with different Al-precursors were prepared by sol-gel methods and the dielectric strengths and leakage currents of the materials were investigated. The best performance was found in SrTiO₃ films doped with Al₂O₃ nanoparticles (nano-Al₂O₃). When 5 mol% of nano-Al₂O₃ was added to SrTiO₃ films with Al electrodes, the dielectric strength was enhanced to 506.9 MV/m compared with a value of 233.5 MV/m for SrTiO₃ films. The energy density of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films was 19.3 J/cm³, which was also far higher than that of the SrTiO₃ films (3.2 J/cm³). These results were attributed to interfacial anodic oxidation reactions, which were experimentally confirmed by cross-sectional transmission electron microscope studies and theoretically modelled based on Faraday's laws. The films with added nano-Al₂O₃ featured many conducting paths at the interfaces between the host phase and the guest nano-Al₂O₃, which promoted ion transport and contributed to the strong anodic oxidation reaction capability of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films.     

Optimal synthesis and new understanding of P2-type Na2/3Mn1/2Fe1/4Co1/4O2 as an advanced cathode material in sodium-ion batteries with improved cycle stability

A sol-gel method with ethylene diamine tetraacetic acid and citric acid as co-chelates is employed for the synthesis of P2-type Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ as cathode material for sodium-ion batteries. Among the various calcination temperatures, the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ with a pure P2-type phase calcined at 900 °C demonstrates the best cycle capacity, with a first discharge capacity of 157 mA h g^?1 and a capacity retention of 91 mA h g^?1 after 100 cycles. For comparison, the classic P2-type Na_2/3Mn_1/2Fe_1/2O₂ cathode prepared under the same conditions shows a comparable first discharge capacity of 150 mA h g^?1 but poorer cycling stability, with a capacity retention of only 42 mA h g^?1 after 100 cycles. Based on X-ray photoelectron spectroscopy, the introduction of cobalt together with sol-gel synthesis solves the severe capacity decay problem of P2-type Na_2/3Mn_1/2Fe_1/2O₂ by reducing the content of Mn and slowing down the loss of Mn on the surface of the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, as well as by improving the activity of Fe³⁺ and the stability of Fe⁴⁺ in the electrode. This research is the first to demonstrate the origin of the excellent cycle stability of Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, which may provide a new strategy for the development of electrode materials for use in sodium-ion batteries.     

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.