Effect Of LiF Addition Research Articles

Effects of LiF-Addition on Sintering Behavior and Dielectric Response of LaPO4 Ceramics at Microwave and Terahertz Frequency for LTCC Applications

This paper reports on the successful preparation of LaPO4-x wt.% LiF (x = 0–5) ceramics using the traditional solid-state reaction method. The crystal structures, sintering behaviors, and dielectric response at microwave and terahertz frequencies were investigated. XRD results indicate that all the diffraction peaks were attributed to LaPO4, and no secondary phase was observed. Rietveld refinement was conducted to analyze the variation of the crystal structure of LaPO4-x wt.% LiF. SEM indicates that the addition of LiF significantly decreased the grain size while increasing the apparent density of the ceramics. When x = 3, the optimum microwave dielectric properties εr = 10.03, Q × f = 81,467 GHz, and τf = −43.79 ppm/°C were achieved in LaPO4-3 wt.% LiF ceramic at 750 °C. The infrared reflectance spectrum and terahertz time-domain spectroscopy were analyzed and compared with the dielectric properties measured at microwave frequency to investigate the inherent dielectric response. The findings indicate that the dielectric constant attributed to ionic displacement polarization and oxygen vacancy is an essential factor affecting dielectric loss. Moreover, it is worth noting that the LaPO4-3 wt.% LiF ceramic demonstrates excellent compatibility with silver powders, suggesting its immense potential as a dielectric material in LTCC applications.

Effects of LiF addition on the densification and microwave dielectric properties of LiInO2 ceramics

Low-temperature co-fired ceramics (LTCC) LiInO2 + xwt% LiF (x = 0, 1, 2, 3, 4, 5) was synthesized by a traditional solid-state reaction method. XRD, TEM, and SEM show that all specimens form a pure-phase tetragonal structure with a space group of I41/amd. The addition of LiF can effectively optimize the microstructure and improve the relative density of LiInO2 ceramics. As x value increased, the εr increased from 9.6 to 13.6, Q×f increased from 39,600 GHz to 52,500 GHz, and all the specimens exhibit a positive τf value at the range of 9.6–19.1 ppm/°C. The low-εr and positive τf in LiInO2 ceramics was investigated by bond valence and P–V-L chemical bond theory, indicating that it was closely related to the rattling effect of In and Li. The concentration of oxygen vacancies was studied by dielectric spectroscopy, indicating that doping LiF can compensate for the volatilization of Li during high temperature sintering. Notably, excellent microwave dielectric properties (εr~13.6, Q×f = 52,500 GHz, and τf ~ 18.1 ppm/°C) were achieved in the LiInO2 + 3 wt% LiF sintered at 890 °C.

Effects of LiF addition on sintering characteristics and microwave dielectric properties of wolframite structure ZnWO4 ceramics

To perform low-temperature sintering and achieve excellent microwave dielectric properties of ZnWO4 ceramics, LiF was selected as sintering additive. Composite ceramics were prepared by conventional solid-state reaction. Effects of LiF addition on sintering behavior, microstructural features, vibration characteristics, and microwave dielectric properties of ZnWO4 + x wt %LiF (0 ≤ x ≤ 6) ceramics were investigated via X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and complex bond valence theory. Results of microstructure and relative density revealed that using appropriate amount of LiF additive enabled one to effectively improve sintering characteristics. Partial substitution of F− for O2− ions caused alterations in interionic interaction, which resulted in that structural characteristics became internal factor affecting the performance. The relatively satisfactory dielectric characteristics (εr = 15.943, Q × f = 36045 GHz, and τf = −69 ppm/°C) were detected in ceramics with x = 3, sintered at 900 °C, which was attributed to joint contribution of ionic substitution and the effect of secondary Li2WO4 phase.

Effect of LiF addition on sintering behavior and dielectric breakdown mechanism of MgO-based microwave dielectric ceramics

Glass-free MgO-based microwave dielectric ceramics (1-x) wt% (0.98 MgO-0.02 Al2O3)-x wt% LiF (x = 0.5, 1, 2, 3, 4) were synthesized where LiF and Al2O3 were utilized as sintering additive and reinforcement phase in MgO matrix respectively. It was found that ion substitution is apt to occur between LiF and MgO, leading to the formation of oxygen vacancies and MgF2. Nevertheless, different from ordinary liquid-phase sintering, morphologies of ceramics were distinctly altered with grains changing from polyhedron to sphere-like shape and densities underwent obvious decrease when excessive amount of LiF was introduced and we call it excessive liquid-phase sintering. Grain boundary weakening caused by this circumstance would exert an adverse effect on physical properties. Moreover, LiF addition dramatically reduced dielectric breakdown strength and altered the dielectric breakdown behavior of MgO-based ceramics, which is dominated by electrical breakdown mechanism. Combination of good properties were achieved in 1 wt% LiF modified MgO-based ceramics sintered at 950 °C which exhibited superior microwave properties (εr = 9.56, tanδ = 9.2 × 10−5, Qf = 124,600 GHz), high flexural strength (184.5 MPa), high thermal conductivity (21.3 W/(m⋅K)), high coefficient of thermal expansion (∼12 ppm/°C) and moderate electrical properties (Eb = 35.9 kV/mm, ρ = 4.9 × 1012 Ω cm).

LiF modified stable flexible PVDF-garnet hybrid electrolyte for high performance all-solid-state Li–S batteries

Polymer-based solid electrolytes are very promising for high energy density solid-state Li–S batteries owing to their flexibility and higher safety. However, poor room temperature Li-ion conductivity of polymer-based solid electrolyte is the biggest challenge for their practical utilization. Here, a flexible composite polymer-ceramic electrolyte (CPE) comprising of PVDF and garnet-type Li6.5La2.5Ba0.5ZrTaO12 for room temperature all-solid-state-Li-S battery (ASLSB) is demonstrated. The PVDF-garnet CPE exhibits a high Li-ionic conductivity of 0.34 mS cm−1 at 20 °C. PVDF-garnet-based CPEs are not electrochemically stable and undergoes severe dehydro-fluorination upon galvanostatic cycling with Li electrode. For the first time, PVDF-garnet-based CPEs are modified with LiF additive, evidenced by steady galvanostatic cycling at 0.2 mA cm−2 for more than 800 h. The effect of LiF addition on the stability of PVDF-based CPEs is explained by XPS studies and electrochemical measurements. ASLSB fabricated with the modified CPE displays a high specific capacity of 936 mA h g−1 with 0.1C rate at 20 °C, along with very good stable performances over 80 continuous cycles. The ASLSB also shows very good rate capability and high Coulombic efficicency. The performance of CPE vindicates the potential applications towards room-temperature operating all-solid-state-Li-S batteries.

Low temperature sintering of LiF-doped CoTiNb2O8 microwave dielectric ceramics

Rutile-structured CoTiNb2O8 ceramics were synthesized via traditional solid-state route. The effects of LiF addition on their sintering behavior, phase composition, microstructure and microwave dielectric properties were investigated systematically in this study. The sintering temperature was successfully lowered to 950 °C by a small amount (1 wt%) of sintering aid. XRD and EDS results indicated that chemical reaction between LiF and host ceramic took place during sintering process. And CoTiNb2O8 with Li0.8Co0.2Nb0.96O3 second phase coexisted in the entire composition range. The addition of LiF to the CoTiNb2O8 ceramics induced a limited degradation in microwave dielectric properties. The er and Q × f values of the low-fired CoTiNb2O8 ceramics ranged from 39.4 to 53.9 and 17,580 GHz to 20,147 GHz, respectively. While the τf decreased in negative values with increasing LiF content. When sintered at 950 °C, the CoTiNb2O8 ceramic doped with 1 wt% LiF had excellent microwave dielectric properties: er = 53.9, Q × f = 20,147 GHz, and τf = 77.2 ppm/°C, making them promising for LTCC applications.

Effects of Composition and Temperature on Current Efficiency for Aluminium Electrolysis from Cryolite-Based Molten Alumina Electrolytes

The current efficiency (CE) for aluminium electrolysis in modern cells can be as high as 96 %. The main reason for loss in current efficiency is the so-called back reaction between dissolved metal and the anode product of CO2. Decreasing temperature of the cell may give higher current efficiency. However, low superheat may cause solidification of melt. A laboratory cell to determine the current efficiency was recently modified to obtain more reliable results. Electrolysis was performed at constant current density and the current efficiency was determined from the weight of deposited aluminium. Effects of electrolyte composition by addition of LiF and temperature were studied. The loss in current efficiency is strongly related to the content of dissolved metal in the electrolyte. The effect of LiF addition on the current efficiency was discussed in this study.

Effects of LiF addition on microstructure and dielectric properties of CaCu3Ti4O12 ceramics

The effects of small amounts of lithium fluoride sintering aid on the microstructure and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics were investigated. CCTO polycrystalline ceramics with 0.5 and 1.0mol% LiF, and without additive were prepared by solid state synthesis. Good densification (>90% of the theoretical density) was obtained for all prepared materials. Specimens without the sintering aid and sintered at 1090°C exhibit secondary phases as an outcome of the decomposition reaction. The mean grain size is controlled by the amount of LiF in specimens containing the additive. Impedance spectroscopy measurements on CaCu3Ti4O12 ceramics evidence the electrically heterogeneous nature of this material consisting of semiconductor grains along with insulating grain boundaries. The activation energy for grain boundary conduction is lower for specimens prepared with the additive, and the electric permittivity reached 53,000 for 0.5mol% LiF containing CCTO.

Low-temperature sintering and microwave dielectric properties of LiF-doped Ba(Mg1/2W1/2)O3–TiO2 ceramics

The Ba(Mg1/2W1/2)O3 (BMW)–x wt% LiF (x = 2.0, 4.0, 6.0, 8.0) ceramics were prepared by a conventional solid-state route. The effects of LiF addition on the sinterability, crystal structure, microstructures and microwave dielectric properties of BMW ceramics were investigated. With an amount of LiF addition, the sintering temperature of the ceramics was reduced to below 960 °C from 1550 °C without degradation of microwave dielectric properties, due to the enhancement of the apparent density at low temperature by liquid phase sintering. On this basis, TiO2 was used to adjust the temperature coefficient of resonant frequency, optimized microwave dielectric properties with εr = 20, Q×f = 48,000 GHz, and τf = 1.2 ppm/°C for 0.96 BMW–0.04 TiO2–4.0 wt% LiF composition. With low sintering temperature and good dielectric properties, these LiF-doped ceramics are promising materials for LTCC integration applications.

Effects of LiF on microwave dielectric properties of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics

The effects of LiF addition on sinterability, microstructure and microwave dielectric properties of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics were investigated. The LiF addition enhanced the sintering temperature of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics from 1200 to 1300°C, because the LiF addition could compensate the evaporation of Li during the sintering process. It was found that the bulk density and dielectric constant ( ε r) gradually decreased, the quality factor (Q f) greatly increased and the temperature coefficient of resonant frequency (τ f) shifted to a near-zero value with the increase in LiF addition. Obviously, excess Li addition could efficiently improve the microwave dielectric properties. In addition, 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 + 4.0 wt% LiF ceramics sintered at 1350 ∘C for 4 h exhibited good microwave dielectric properties of ε r ∼123.4,Q f ∼ 2209 GHz (at 2.43 GHz) and τ f ∼ 12.3 ppm ∘C–1.

Effect of LiF addition on phase structure and piezoelectric properties of (Ba,Ca)(Ti,Sn)O3 ceramics sintered at low temperature

In this study, a series of (Ba0.95Ca0.05)(Ti0.90Sn0.10)O3–xLiF (BCTS–xLiF) (0≤x≤6mol%) lead-free piezoceramics were fabricated by a conventional solid-state reaction method. The incorporation of LiF could significantly improve the sinterability of BCTS ceramics by reducing the sintering temperature from 1480°C to 1250°C, where a relative density over 90% was achieved with grown grains of 5–20μm. X-ray diffraction and Raman spectroscopy experiments revealed that BCTS–xLiF ceramics are composed of coexisting R–O–T phases at 0≤x≤1 and R–T phases at 2≤x≤6 at room temperature. Optimal piezoelectric properties of d33=510pC/N, kp=40.9%, εr=5370, tanδ=0.019 and dS/dE=961pm/V were obtained at x=5, which is attributed to the coexistence of R and T phases with an optimum ratio at room temperature and dense structure with large grains.

Low temperature sintering properties of LiF-doped BaTiO3-based dielectric ceramics for AC MLCCs

The effects of LiF addition on phase evolution, microstructure and dielectric properties of BaTiO3 based ceramics were investigated. The LiF addition lowered the sintering temperature of BaTiO3 based ceramics effectively from 1,380 to 1,100 °C. Orthorhombic-to-pseudocubic phase transition appeared as increasing sintering temperature or LiF content. Li+ dissolved in the lattice of BaTiO3, replaced Ti4+ site, produced oxygen vacancies and further inhibited the grain growth. F− entered into O2− site, might cause weakening of oxygen bond strength, together with the low-melting-point liquid phase sintering of LiF, facilitated the formation of uniform dense and fine-grained structure and maintained good dielectric properties. Samples with 2 wt% LiF sintered at 1,100 °C showed excellent dielectric properties: er = 1,956, tanδ = 0.8 % (at 1 kHz), ΔC/C25 4.50 kV/mm.

Effect of LiF addition on spark plasma sintering of transparent Nd-doped Lu2O3 bodies

Transparent Nd-doped Lu2O3 bodies were fabricated by spark plasma sintering, and the effect of LiF addition on sintering, microstructure and transparency of Nd-doped Lu2O3 bodies were investigated. LiF promoted the densification at an early stage of sintering, resulted in high transparency of the Nd-doped Lu2O3 body. The optimal content of LiF was 0.2 wt% and that Nd-doped Lu2O3 body showed a transmittance of 81.8% (99.5% of theoretical) at 1080 nm after annealing in air for 21.6 ks.

Effects of LiF addition on sintering behavior and microwave dielectric properties of (Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4 ceramics

The effects of LiF addition on the sinterability and microwave dielectric properties of (Mg0.95Zn0.05)2(Ti0.8Sn0.2)O4 (MZTS) ceramics were investigated. A small amount of LiF addition can effectively lower the sintering temperature of MZTS from 1325°C to 1150°C due to the liquid phase effect and induce no apparent degradation of the microwave dielectric properties. With increasing LiF content, the apparent density and dielectric constant decreased gradually, the quality factor increased firstly and then decreased. In particular, MZTS–3.0wt% LiF ceramics sintered at 1150°C for 5h exhibited good microwave dielectric properties of ɛr=13.05, Q·f=119,310GHz (at 10GHz) and τf=−59.2ppm/°C.

Low-Temperature Sintering and Microwave Dielectric Properties of MgO Ceramic with LiF Addition

MgO ceramics with a nominal composition of (1-x)MgO–xLiF (x = 0.02–0.10) were synthesized and the effects of LiF addition and sintering conditions on the microwave dielectric properties of MgO ceramics were investigated in this study. With LiF addition, the MgO ceramics were well-sintered at 950 °C in a covered crucible, and the Q·f value of the LiF-added MgO ceramic strongly depended on the amount of LiF and sintering time. As a result, the MgO ceramics with a nominal composition of 0.96MgO–0.04LiF (x=0.04) exhibited the highest Q·f value of 751,500 GHz (εr = 9.6 and TCf= - 56 ppm/°C) when they were sintered at 950 °C for 100 h in a covered crucible. The endothermic reaction of the MgO ceramics was observed with LiF addition by differential thermal analysis and thermograviometry (DTA–TG), and it was considered that the partial melting of MgO with LiF addition to form the liquid phase enhances the sinterability of the MgO ceramics. The crystal structure analysis of the LiF-added MgO ceramics showed a slight increase in the lattice parameters of the MgO ceramics, suggesting the Li substitution for Mg in the MgO structure.

Low-Temperature Sintering and Microwave Dielectric Properties of MgO Ceramic with LiF Addition

MgO ceramics with a nominal composition of (1-x)MgO–xLiF (x = 0.02–0.10) were synthesized and the effects of LiF addition and sintering conditions on the microwave dielectric properties of MgO ceramics were investigated in this study. With LiF addition, the MgO ceramics were well-sintered at 950 °C in a covered crucible, and the Q·f value of the LiF-added MgO ceramic strongly depended on the amount of LiF and sintering time. As a result, the MgO ceramics with a nominal composition of 0.96MgO–0.04LiF (x=0.04) exhibited the highest Q·f value of 751,500 GHz (εr = 9.6 and TCf= - 56 ppm/°C) when they were sintered at 950 °C for 100 h in a covered crucible. The endothermic reaction of the MgO ceramics was observed with LiF addition by differential thermal analysis and thermograviometry (DTA–TG), and it was considered that the partial melting of MgO with LiF addition to form the liquid phase enhances the sinterability of the MgO ceramics. The crystal structure analysis of the LiF-added MgO ceramics showed a slight increase in the lattice parameters of the MgO ceramics, suggesting the Li substitution for Mg in the MgO structure.

Low-temperature firing and microwave dielectric properties of Ca[(Li0.33Nb0.67)0.9Ti0.1]O3−δ ceramics with LiF addition

The effects of LiF addition on sinterability, microstructure and microwave dielectric properties of Ca[(Li0.33Nb0.67)0.9Ti0.1]O3−δ ceramics were investigated. The LiF addition lowered the sintering temperature of Ca[(Li0.33Nb0.67)0.9Ti0.1]O3−δ ceramics effectively from 1180 to 840 °C. It was found that the bulk density and dielectric constant (εr) greatly decreased, the quality factor (Q·f) gradually increased, the temperature coefficient of resonant frequency (τƒ) shifted to a negative value with the increase amount of LiF addition. The dielectric properties (εr,Q·f, τf) of Ca[(Li0.33Nb0.67)0.9Ti0.1]O3−δ ceramics with 10 wt.% LiF sintered at 900 °C were 24.8, 19,300 GHz (at 4.16 GHz), −15.6 ppm/°C respectively. And those were 21.3, 20,450 GHz (at 4.59 GHz), −18.0 ppm/°C respectively for the specimen with 20 wt.% LiF at 840 °C.

Effect of LiF addition on the phase transition of sinterable β-spodumene precursor powders prepared by a sol-gel process

β-Spodumene (Li2O · Al2O · 4SiO2, LAS4) precursor powders were obtained through a sol-gel process using Si(OC2H5)4, Al(OC4H9)3, and LiNO3 as starting materials and LiF as a sintering aid. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy with a wavelength dispersive spectrometer, and electron diffraction analysis were utilized to study the phase transition of the β-spodumene glass–ceramics prepared from the gel-derived precursor powders with LiF additive. For the LAS4 precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4.0 wt% LiF and sintered at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution and β-eucryptite (Li2O · Al2O3 · 2SiO2, LAS2) solid solution. When the LiF content was 5.0 wt% and the sintering process was carried out at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution, β-eucryptite solid solution (triclinic), and eucryptite [rhombohedral (hex.)]. When the LiF addition attains 3.0 wt%, the fully densified grains are formed, accompanied with an increase in grain size for LiF addition. At the triple junction of grain boundaries a second phase segregates which is identified to be β-spodumene solid solution. In the sintering period of LAS4 precursor powders with LiF additive, the grains converted to β-eucryptite solid solution and β-spodumene solid solution remains at the grain boundaries.

Effect of LiF Addition on the Sintering of .BETA.-Spodumene Precursor Powders.

The effect of LiF addition on the sintering of β-spodumene (Li2O⋅Al2O3⋅4SiO2, LAS) powders prepared by a sol-gel process was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Upon sintering LAS precusor powders pellet samples without LiF addition, obtained the crystalline phase was merely β-spodumene. The intensity of the (102), (211), (222) and (303) refections of the β-spodumene phase decreases with increasing LiF additive content up to 4.0 mass% and some β-spodumene converts to β-eucryplite. The activation energies for grain growth were 26.0 and 23.0 kcal/mol for the calcined LAS precursor powders with 1.0 and 3.0 mass% LiF (sintered at various temperatures for 10 h), respectively. The slopes of the linear dependence of the grain size on the cubic root of time are 0.35 and 0.37 for the LAS precursor powders with 3.0 mass% LiF sintered at 1250 and 1350°C, respectively, showing a diffusion controlled growth.

Electrochemistry of Ta(V) in Lewis Basic TaCl5-EMIC Low Temperature Molten Salts

The electrochemical reduction of Ta(V) in a TaCl5-EMIC (1-ethyl-3-methylimidazolium chloride) low temperature molten salt was investigated by using various voltammetric techniques. The melt composition was 66.7 mol% of EMIC, and all experiments were carried out at 373 K. Cyclic voltammograms showed two reduction waves on the forward scan followed by two oxidation waves on the reverse scan at potentials nobler than that of EMI+ reduction. The stoichiometry and the number of electrons in the reaction for each cathodic wave were examined by wave shape analyses of normal pulse voltammograms and differential pulse voltammograms. The results indicated that the first cathodic wave corresponded to the reduction of Ta(V) to Ta(IV), then Ta(IV) was reduced to Ta(II) in the second one. The effects of LiF addition into the melt on the reduction mechanism of Ta(V) were also studied, and a possibility of a further reduction of Ta(II) to metallic tantalum in the LiF-added melt was obtained.