Temperature stability and high-Qf of low temperature firing Mg2SiO4–Li2TiO3 microwave dielectric ceramics

In this work, a series of low-temperature-firing (1−x)Mg₂SiO₄–xLi₂TiO₃–8 wt% LiF (x = 35–85 wt%) microwave dielectric ceramics was prepared through conventional solid state reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that the Li₂TiO₃ phase was transformed into cubic phase LiTiO₂ phase and secondary phase Li₂TiSiO₅. Partial substitution of Mg²⁺ ions for Ti³⁺ ions or Li⁺Ti³⁺ ions increased the cell volume of the LiTiO₂ phase. The dense microstructures were obtained in low Li₂TiO₃ content (x ≤ 65 wt%) samples sintered at 900 °C, whereas the small quantity of pores presented in high Li₂TiO₃ content (x ≥ 75 wt%) samples sintered at 900 °C and low Li₂TiO₃ content (x = 45 wt%) sintered at 850 and 950 °C. Samples at x = 45 wt% under sintering at 900 °C for 4 h showed excellent microwave dielectric properties of ε_r = 10.7, high Q × f = 237,400 GHz and near-zero τ_f = − 3.0 ppm/°C. The ceramic also exhibited excellent chemical compatibility with Ag. Thus, the fabricated material could be a possible candidate for low temperature co-fired ceramic (LTCC) applications.     

Improved thermoelectric performances in textured Bi1.6Pb0.4Ba2Co2Oy/Ag composites

Bi_1.6Pb_0.4Ba₂Co₂O_y thermoelectric ceramics with small Ag additions (0, 1, 3, and 5 wt%) have been textured using the laser floating zone method. Microstructure has shown a slight decrease on the secondary phases content and a better grain alignment in Ag added samples. These microstructural features are reflected in the thermoelectric properties, which have shown a significant decrease of electrical resistivity, when the Ag content is raised. In spite of a corresponding decrease of Seebeck coefficient, all the Ag-containing samples possess higher Power Factor values than the Bi_1.6Pb_0.4Ba₂Co₂O_y ones. Moreover, the maximum Power Factor values (about 0.36 mW/K².m at 650 °C) have been measured in Bi_1.6Pb_0.4Ba₂Co₂O_y+3 wt% Ag samples, which are the best results reported in this family of materials.     

Ag enhanced electrochemical performance for Na2Li2Ti6O14 anode in rechargeable lithium-ion batteries

Due to the characteristics of an electronic insulator, Na₂Li₂Ti₆O₁₄ always suffers from low electronic conductivity as anode material for lithium storage. Via Ag coating, Na₂Li₂Ti₆O₁₄@Ag is fabricated, which has higher electronic conductivity than bare Na₂Li₂Ti₆O₁₄. Enhancing the Ag coating content from 0.0 to 10.0 wt%, the surface of Na₂Li₂Ti₆O₁₄ is gradually deposited by Ag nanoparticles. At 6.0 wt%, a continuous Ag conductive layer is formed on Na₂Li₂Ti₆O₁₄. While, particle growth and aggregation take place when the Ag coating content reaches 10.0 wt%. As a result, Na₂Li₂Ti₆O₁₄@6.0 wt% Ag displays better cycle and rate properties than other samples. It can deliver a lithium storage capacity of 131.4 mAh g⁻¹ at 100 mA g⁻¹, 124.9 mAh g⁻¹ at 150 mA g⁻¹, 119.1 mAh g⁻¹ at 200 mA g⁻¹, 115.8 mAh g⁻¹ at 250 mA g⁻¹, 111.9 mAh g⁻¹ at 300 mA g⁻¹ and 109.4 mAh g⁻¹ at 350 mA g⁻¹, respectively.     

Silver cofirable (Ca0.9, Mg0.1)SiO3 microwave dielectric ceramics with Li2CO3–Bi2O3 additive

The effects of Li₂CO₃–Bi₂O₃ (LB) additive on the microstructure, phase formation, microwave dielectric properties and applicability for low-temperature co-fired ceramics (LTCC) technology of (Ca_0.9Mg_0.1)SiO₃ (CMS) ceramics were investigated. The sintering temperature of the CMS ceramics was reduced from 1290 °C to 890 °C by the addition of LB. Secondary phases SiO₂ and Bi₄(SiO₄)₃ were detected when LB content was less than 9 wt%. Low melting point liquid phases were formed when LB content was 11–14 wt%. The Q_f value initially increased with the addition of LB and attained the maximum value for the 9 wt% LB-doped CMS ceramic. When the LB content exceeded 9 wt%, the Q_f value decreased because of the presence of liquid phase and abnormal growth of grains. ?_r of 6.92, Q_f of 27,600 GHz and τ_f of ?43.6 ppm/°C were obtained for 9 wt% LB-doped CMS ceramics sintered at 890 °C for 2 h. Also the ceramics can be well co-fired with Ag electrode.     

Microwave dielectric properties of low-fired Li2MnO3 ceramics co-doped with LiF–TiO2

Li₂MnO₃ ceramics co-doped with 2 wt% LiF and x wt% TiO₂ (x=0, 3, 5, 7, 10) were prepared by solid-state reaction for low-temperature co-fired ceramics (LTCC) applications. The sintering temperatures of Li₂MnO₃ ceramics were successfully lowered to 925°C due to the formation of a LiF liquid phase. Their temperature stability was improved by doping with TiO₂. A typical Li₂MnO₃-2 wt% LiF-5 wt% TiO₂ sample with well-densified microstructures displayed optimum dielectric properties (ε_r=13.8, Q×f= 23,270 GHz, τ_f=1.2 ppm/°C). Such sample was compatible with Ag electrodes, which suggests suitability of the developed material for LTCC applications in wireless communication systems.     

Effect of NiO additive on microstructure,mechanical behavior and electrical properties of 0.2PZN–0.8PZT ceramics

A NiO-added Pb((Zn_1/3Nb_2/3)_0.20(Zr_0.50Ti_0.50)_0.80)O₃ system is prepared and investigated. The results reveal that Ni doping induces a phase transformation from the morphotropic phase boundary to the tetragonal phase side. Above the solubility limit of 0.3 wt% in NiO form, excess Ni ions segregate at the grain boundaries and triple junctions, which facilitate the formation of a liquid phase with excess PbO and lead to remarkable grain growth. The mechanical behavior (Vickers hardness (H_v) and fracture toughness (K_IC)) can be tailored by controlling the content of additive; this is accompanied by a transition in the fracture mode changed from transgranular without NiO additive to intergranular with 1.0 wt% NiO additive. Moreover, the NiO addition weakens the dielectric relaxor behavior and improves the piezoelectric properties simultaneously. The 0.2PZN–0.8PZT with 0.5 wt% NiO addition shows good transduction coefficient (d₃₃·g₃₃ = 10,050 × 10^?15 m²/N) and large fracture toughness (K_IC = 1.35 MPa m^1/2).     

A rare 2D coordination polymer of graphite-like structure extended by infinite silver–oxygen–silver bonds

The reaction of AgNO₃ and H₃btb (H₃btb = 1,2,3-benzenetricarboxylic acid) leads to the isolation of {[Ag(μ₂-H₂O)(μ₂-H₂btb)]}_n · 1.5nH₂O (1), which crystallizes in the orthorhombic space group Fddd with a = 11.436(2) Å, b = 6.876(1) Å, c = 58.837(1) Å, V = 4626.5(2) Å³, Z = 32. Silver ions are connected by both strong Ag?Ag interaction and μ₂-H₂O bridges to form hexagonal Ag₆ subunits, and are further assembled into a high ordered 2D grid, presenting an interesting graphite-like 6³ net. Both the fluorescence and the crystal transformation after dehydration are studied.     

Enhanced transport critical current density of (Bi,Pb)-2223/Ag superconductor tapes added with nano-sized Bi2O3

Ag sheathed superconductor tapes with starting composition (Bi, Pb)-2223(Bi₂O₃)_0.01 were prepared. Bi₂O₃ with average size 150 nm was used in this work. The Bi₂O₃ amount was chosen based on our initial study on nano-sized Bi₂O₃ added pellets which showed an optimal superconducting property for 0.01 wt% addition. Non-added tapes were also prepared for comparison. The tapes were investigated by X-ray diffraction method, scanning electron microscopy and transport critical current density, J_c measurements (30 K to 77 K). The influence of different sintering times (50, 100, and 150 h) on J_c under applied magnetic field (0–0.75 T at 77 K) parallel and perpendicular to the surface of the tapes was also investigated. J_c of added tapes was found to increase significantly as compared with the non-added tapes. The Bi₂O₃ added tapes sintered for 150 h exhibited the highest J_c at 30 K of 57,900 A/cm² as compared with 19,400 A/cm² for the non-added tapes sintered for 100 h. The improvements in flux pinning and connectivity between grains due to nano Bi₂O₃ addition led to the enhancement of J_c.     

Effect of WC content on microstructure and mechanical properties of Ni3Al-bonded cermets

The effect of WC content on microstructure and mechanical properties of the TiC–Ni₃Al system cermets was investigated. Ni₃Al-bonded cermets showed a core–rim structure with carbide particle coupled with rim embedded in Ni₃Al binder. With WC content increasing, TiC grains were refined and the white rim became complete and got thicker gradually. Interface between core and rim showed a completely coherent relationship. The rim enriched in W constituted an ideal coherence between hard phase and Ni₃Al binder phase. With WC content increasing, the densification of cermets was enhanced, and hardness and TRS were increased firstly and then reduced, reaching peak values 90.9 HRA (HV₃₀ 15 GPa) and 1629 MPa, respectively in cermet N5 (25 wt% WC). Similarly, fracture toughness got a peak value (11.6 MPa m^1/2), at the composition with 20 wt% WC.     

Effects of glass additions on the microstructure and dielectric properties of barium strontium titanate (BST) ceramics

Commercial glass frits (lead borosilicate glasses) were employed as the sintering aids to reduce the sintering temperatures of BST ceramics. The effects of the glass content and the sintering temperature on the microstructures, dielectric properties and tunabilities of BST ceramics have been investigated. Densification of BST ceramics of 5 wt% glass content becomes significant from sintering temperature of 1000 °C. The glass content shows a strong influence on the Curie temperature T_c, permittivity and the diffuse transition. X-ray results show all BST ceramics exhibit a perovskite structure and also the formation of a secondary phase, Ba₂TiSi₂O₈. The shift of BST diffraction peaks towards higher angle with increasing the glass content indicates the substitution of Pb²⁺ in Ba²⁺ site, which mainly accounts for the diffuse transition observed in these BST ceramics. BST ceramics with 10 wt% glass additives possess the highest tunability at all four sintering temperatures. A tunability of 12.2% at a bias field of 1 kV/mm was achieved for BST ceramics with 10 wt% glass content sintered at 900 °C.     

Electrical and thermal properties of low permittivity Sr2Al2SiO7 ceramic filled HDPE composites

The feasibility of low permittivity Sr₂Al₂SiO₇ (SAS) ceramic filled high density polyethylene (HDPE) composites for substrate and packaging applications has been investigated in this paper. The composites were prepared by the melt mixing and hot pressing techniques. Scanning electron microscopic images of SAS filled HDPE showed the increased connectivity with filler loading. The composites showed excellent relative density (>98%) with low bulk density (<2.40 g cm^?3) and very low moisture absorption (<0.10 wt%). The relative permittivity (ε_r) and the dielectric loss (tan δ) at 1 MHz and at 5 GHz were found to be low and found to increase with filler volume fraction (V_f). The experimentally observed relative permittivity at 5 GHz was correlated with the values proposed by different theoretical models. Among them, effective medium theory (EMT) gave better fit with experimental values except at the highest filler loading (0.50 V_f). Improvement in the thermal properties was also observed with filler content. The coefficient of linear thermal expansion (CTE) was found to decrease with filler content. Thermal conductivity (TC) of the composite was greatly enhanced as a function of filler volume fraction. The composite with 0.50 filler volume fraction showed balanced thermal and dielectric properties with ε_r=4.2, tan δ=3.9×10^?3, TC=2.2 W m^?1 K^?1 and CTE=101 ppm/°C.     

Three Ag(I)–cyanide coordination polymers with metal bonds tuned by N-heterocyclic ligands

Hydrothermal reactions of AgNO₃, K₃[Fe(CN)₆] with N-heterocyclic ligands afforded three novel Ag(I)–cyanide coordination polymers, [Ag₂(CN)₂(tpt)]_n (1), {[Ag(CN)(bpe)_0.5][Ag(CN)]}_n (2) and [Ag(CN)(btmb)_0.5]_n (3) (tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine, bpe = 1,2-bis(4-pyridyl)ethane, btmb = 1,2-bis(1,2,4-triazol-1-ylmethyl)benzene). In complex 1, two Ag(CN) linear chains are bridged by bidentate tpt ligand to form a ladder-like structure, which are further connected by AgAg metal bond to generate a 2D polymeric network. Complex 2 is an interesting 3D supramolecular architecture assembled by 2D [Ag¹(CN)(bpe)_0.5]_n network and linear [Ag²(CN)]_n chain combined by strong AgAg metal bond. Complex 3 is a 1D ladder-like double-chain polymer constructed from Ag–cyanide linear chains and btmb spacer, which is further extended to a 2D supramolecular network by Ag–Ag weak interaction. The Ag–Ag metal interactions play important roles in the construction of three coordination polymers. Complexes 1 and 2 are respectively thermally stable at 300 and 180 °C. Complexes 1 and 3 emit strong blue luminescence.     

Role of cement content on the properties of self-flowing Al2O3 refractory castables

In this work, Al₂O₃ self-flowing castables (SFCs) were produced based on various cement contents. The SFCs were sintered at 1273 K, 1573 K and 1773 K and the exhibited properties were experimentally determined. Among the properties determined in this work are bulk density (BD), apparent porosity (AP), water absorption (WA), cold crushing strength (CCS), modulus of rupture (MOR) and fracture toughness (K_IC). It is found that additions of 5% cement lead to SFCs with maximum MOR and K_IC values after firing at 1773 K. Firing at 1573 K leads to a reduction in both, MOR and K_IC. In SFC containing 3% cement, maximum K_IC values of 3.53 MPa m^1/2 were achieved after firing at 1573 K. In the low cement SFCs (1 wt%) after firing at 1773 K the exhibited K_IC values were below those obtained in either the SFC-3 or SFC-5, but they were significantly high (3.43 MPa m^1/2).     

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.     

Densification and biocompatibility of sintering 3.0 mol% yttria-tetragonal ZrO2 polycrystal ceramics with x wt% Fe2O3 and 5.0 wt% mica powders additive

The densification and biocompatibility of sintered 3.0 mol% yttria-tetragonal zirconia polycrystal (3Y-TZP) ceramics, with X wt% Fe₂O₃ and 5.0 wt% mica powders (denoted by 3Y-TZP: X-5.0 wt% mica) have been studied. When the pellets of 3Y-TZP: X-5.0 wt% mica were sintered at 1300 °C for 1 h, the relative shrinkage increases from 19.20–19.43% with the X increased from 0.3 to 1.0. The relative shrinkage of pellets containing 1.0 wt% Fe₂O₃ (X=1.0) increased from 19.43–19.59% when sintering temperatures were raised from 1300 °C to 1450 °C. X-ray diffraction results show that the pellets of 3Y-TZP: X-5.0 wt% mica sintered at 1400 °C for 1 h only contained single phase of tetragonal ZrO₂ (t-ZrO₂). When the sintering temperature was higher than 1400 °C, the Vickers microhardness was greatest in the pellets with X=0.5. Within pellets with the same Fe₂O₃ content, the dominant wavelength (λ_d) was only slightly different for pellets sintered at 1300 °C and those sintered at 1450 °C. The results of the materials were evaluated in vitro cytotoxicity tests reveals that the powders and sintered pellets are safe materials. The oral mucosa irritation tests did not find erythema or histopathological change including normal epithelium, and was free from leucocyte infiltration, vascular congestion and oedema.     

Piezoelectric properties of Pb(Zr,Ti)O3-Pb(Ni,Nb)O3 ceramics and their application in energy harvesters

The piezoelectric properties of (1-x-y)PbZrO₃-xPbTiO₃-yPb(Ni_1/3Nb_2/3)O₃ ceramics were investigated. Specimens with a large Pb(Ni_1/3Nb_2/3)O₃ content, which have compositions close to the triple point, show small g₃₃ and d₃₃ × g₃₃ values because of their large ε^T₃₃/ε₀. These values increased with a decrease in y (amount of Pb(Ni_1/3Nb_2/3)O₃) and the specimen with x = 0.39 and y = 0.29 showed the largest g₃₃ of 43 × 10⁻³ V·m/N and d₃₃ × g₃₃ of 25.2 × 10⁻¹² m²/N. Cantilever-type energy harvesters were fabricated using specimens with 0.38 ≤ x ≤ 0.41 and y = 0.29. The output power densities of the energy harvesters were related to the d₃₁ × g₃₁ × k₃₁² value of the piezoelectric ceramics. The energy harvester fabricated using a specimen with x = 0.39 and y = 0.29, which has a maximum d₃₁ × g₃₁ × k₃₁² value, showed the maximum output power density of 1.01 mW/cm³.     

Effect of Li2O–V2O5 on the low temperature sintering and microwave dielectric properties of Li1.0Nb0.6Ti0.5O3 ceramics

Li₂O–Nb₂O₅–TiO₂ based ceramic systems have been the candidate materials for LTCC application, due to their high dielectric constant and Q × f value and controllable temperature coefficient in the microwave region. However, the sintering temperature was relatively higher (above 1100 °C) for practical application. In this study, dielectric properties of Li_(1+x−y)Nb_(1−x−3y)Ti_(x+4y)O₃ solid solution were studied with different x and y contents and among them, the Li_1.0Nb_0.6Ti_0.5O₃ composition (x = 0.1, y = 0.1) was selected, due to its reasonable dielectric properties to determine the possibility of low temperature sintering. The effects of 0.17Li₂O–0.83V₂O₅, as a sintering agent, on sinterability and microwave dielectric properties of Li_1.0Nb_0.6Ti_0.5O₃ ceramics were investigated as a function of the sintering agent content and sintering temperature. With addition of 0.17Li₂O–0.83V₂O₅ above 0.5 wt%, the specimens were well densified at a relatively lower temperature of 850 °C. Only slight decrease in apparent density was observed with increasing 0.17Li₂O–0.83V₂O₅ content above 0.75 wt%. In the case of 0.5 wt% 0.17Li₂O–0.83V₂O₅ addition, the values of dielectric constant and Q × f reached maximum. Further addition caused inferior microstructure, resulting in degraded dielectric properties. For the specimens with 0.5 wt% 0.17Li₂O–0.83V₂O₅ sintered at 850 °C, dielectric constant, Q × f and TCF values were 64.7, 5933 GHz and 9.4 ppm per °C, respectively.     

Microstructure and mechanical properties of Ti (C,N) based cermets reinforced with different ceramic particles processed by spark plasma sintering

The addition effect of different ceramic particles such as TiB₂, TiN and nano-Si₃N₄ on the microstructure and mechanical properties of TiCN-WC-Co-Cr₃C₂ based cermets, which are prepared by spark plasma sintering, was studied. Microstructural characterization of the cermets was done by scanning electron microscope. X-ray diffraction was performed to study the crystal structures. Mechanical properties such as hardness and fracture toughness were measured for the different developed cermets. The hardness and fracture toughness of the TiCN-WC-Co-Cr₃C₂ cermets without TiN, TiB₂, and nano-Si₃N₄ were 8.4 GPa and 3.4 MPa m^1/2, respectively. It was found that 5 wt% TiB₂ addition alone improved the corresponding hardness and fracture toughness to 19.2 GPa and 6.9 MPa m^1/2, respectively. The addition of 5 wt% TiN, improved the hardness and fracture toughness to 16.7 GPa and 6.9 MPa m^1/2, respectively. With the combination of 5 wt% TiN and 5 wt% TiB₂, the hardness and fracture toughness were improved to 15.5 GPa and 6.6 MPa m^1/2, respectively. But, the addition of 5 wt% Si₃N₄ showed a balanced improvement in both hardness (17.6 GPa) and toughness (6.9 MPa m^1/2). Fracture toughness did not change much for all the above cermets with different ceramic inclusions.     

Synthesis and characterization of LTCC compositions with middle permittivity based on CaO-B2O3-SiO2 glass/CaTiO3 system

CaTiO₃ ceramics with the addition of CaO-B₂O₃-SiO₂ (CBS) glass (45–55 wt%) composites were sintered at 830 °C, 850 °C, 875 °C and 900 °C. To illustrate influence mechanism of the different glass contents and sintering temperatures on the properties of the composites, we focused on the multiple performances of the composites by employing different qualitative and quantitative instruments. Composites with 50 wt% glass sintered at 875 °C presented fairly ideal performance: the bulk density was 3.20 g/cm³, the dielectric constant was 25.7 and the dielectric loss was 0.0009 at 7 GHz. Micro-Structure analysis of the composites showed a dense and pore-less microstructure except for few pores with size around 1 μm. In addition, the composite could meet the shrinkage requirement of Ag electrodes and could not possibly react with Ag electrodes any more. This makes them suitable for various dielectric applications at low sintering temperature.     

Temperature-stable and high-ɛ dielectric ceramics based on Ag (Nb1−xTax)O3

The dielectric properties of novel dielectric system AgNb_1−xTa_xO₃ (ANT) have been studied in this paper. In this system, the temperature coefficient of capacitance (TCC) can be adjusted to 0 ± 30 × 10⁻⁶/°C by choosing proper molar ratio of Nb⁵⁺ to Ta⁵⁺. When 2 wt% glass is added to the ceramics, the sintering temperature is reduced to 960 °C, which restrains Ag⁺ decomposition in ambient atmosphere. It is noted that the dielectric loss reduces further after adding 2.5 wt% Sb₂O₅. The dielectric properties of the resultant samples are as follows: dielectric constant ɛ ≈ 512, loss tangent tan δ ≈ 5.2 × 10⁻⁴, and TCC ≈ 10 × 10⁻⁶/°C.