Effects of Yb3+ doping on phase structure,thermal conductivity and fracture toughness of (Nd1-xYbx)2Zr2O7

To investigate the effects of Yb³⁺ doping on phase structure, thermal conductivity and fracture toughness of bulk Nd₂Zr₂O₇, a series of (Nd_1-xYb_x)₂Zr₂O₇ (x?=?0, 0.2, 0.4, 0.6, 0.8, 1.0) ceramics were synthesized using a solid-state reaction sintering method at 1600?°C for 10?h. The phase structures were sensitive to the Yb³⁺ content. With increasing doping concentration, a pyrochlore-fluorite transformation of (Nd_1-xYb_x)₂Zr₂O₇ ceramics occurred. Meanwhile, the ordering degree of crystal structure decreased. The substitution mechanism of Yb³⁺ doping was confirmed by analyzing the lattice parameter variation and chemical bond of bulk ceramics. The thermal conductivities of (Nd_1-xYb_x)₂Zr₂O₇ ceramics decreased first and then increased with the increase of Yb³⁺ content. The lowest thermal conductivity of approximately 1.2?W?m^?1 K^?1 at 800?°C was attained at x?=?0.4, around 20% lower than that of pure Nd₂Zr₂O₇. Besides, the fracture toughness reached a maximum value of ~1.59?MPa?m^1/2 at x?=?0.8 but decreased with further increasing Yb³⁺ doping concentration. The mechanism for the change of fracture toughness was discussed to result from the lattice distortion and structure disorder caused by Yb³⁺ doping.     

Influence of LiBO2 addition on the microstructure and lithium-ion conductivity of Li1+xAlxTi2−x(PO4)3(x = 0.3) ceramic electrolyte

Concerning the safety problems of conventional Li-ion batteries with liquid electrolytes, it is crucial to develop reliable solid-state electrolytes with high ionic conductivity. Li_1+xAl_xTi_2?x(PO₄)₃ (LATP, x = 0.3) is regarded as one of the most promising solid electrolytes due to its high ionic conductivity and excellent chemical stability to humidity.Herein, a new strategy is proposed for improving the sintering behavior and enhancing the ionic conductivity of LATP by using LiBO₂ as the sintering aid via liquid phase sintering. The as-prepared sample LATP with homogeneous microstructure and high relative density of 97.1% was successfully synthesized, yielding high total ionic conductivity of 3.5 × 10^?4 S cm^?1 and low activation energy of 0.39 eV at room temperature. It was found that the addition of LiBO₂ could effectively enhance the densification and increase the ionic conductivity of LATP electrolyte, proving an effective way to synthesis LATP ceramics by a simple and reliable route.     

Study of structure and conductivity of Li3/8Sr7/16-3x/2LaxZr1/4Nb3/4O3 solid electrolytes

Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0, 0.05, 0.10, 0.15, 0.20) were synthesized using the conventional solid-state reaction method. In order to increase the vacancy concentration, La³⁺ was doped on the Sr²⁺ site. Crystal structures of doped samples were characterized by X-ray diffraction. Except, perovskite-type Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0, 0.05, 0.10, 0.15) samples were fabricated by heat treatment at 1250 °C, 1275 °C, 1275 °C and 1275 °C, respectively, for 15 h. Lattice sizes decreased with the increase of doping amounts because of the smaller ion radius of La³⁺ compared to that of Sr²⁺. Ionic conductivities of the samples were measured by AC impedance spectroscopy. The results showed that the ionic conductivity increases at first and then decreases with raising doping amounts and sintering temperatures. So the optimized composition Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0.05) sintered at 1275 °C was selected with the highest total conductivity of 3.33 × 10^?5 S cm^?1at 30 °C and an activation energy of 0.27 eV. Additionally, potentiostatic polarization test was used to evaluate the electronic conductivity. The optimal composition Li_3/8Sr_7/16-3x/2La_xZr_1/4Nb_3/4O₃ (x = 0.05) as a possible Li-ion conducting solid electrolyte has an electronic conductivity of only 8.39 × 10^?9 S cm^?1.     

Synthesis and electrochemical properties of Co-doped Li3V2(PO4)3 cathode materials for lithium-ion batteries

Co-doped Li₃V_2−xCo_x(PO₄)₃/C (x = 0.00, 0.03, 0.05, 0.10, 0.13 or 0.15) compounds were prepared via a solid-state reaction. The Rietveld refinement results indicated that single-phase Li₃V_2−xCo_x(PO₄)₃/C (0 ≤ x ≤ 0.15) with a monoclinic structure was obtained. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the cobalt is present in the +2 oxidation state in Li₃V_2−xCo_x(PO₄)₃. XPS studies also revealed that V⁴⁺ and V³⁺ ions were present in the Co²⁺-doped system. The initial specific capacity decreased as the Co-doping content increased, increasing monotonically with Co content for x > 0.10. Differential capacity curves of Li₃V_2−xCo_x(PO₄)₃/C compounds showed that the voltage peaks associated with the extraction of three Li⁺ ions shifted to higher voltages with an increase in Co content, and when the Co²⁺-doping content reached 0.15, the peak positions returned to those of the unsubstituted Li₃V₂(PO₄)₃ phase. For the Li₃V_1.85Co_0.15(PO₄)₃/C compound, the initial capacity was 163.3 mAh/g (109.4% of the initial capacity of the undoped Li₃V₂(PO₄)₃) and 73.4% capacity retention was observed after 50 cycles at a 0.1 C charge/discharge rate. The doping of Co²⁺into V sites should be favorable for the structural stability of Li₃V_2−xCo_x(PO₄)₃/C compounds and so moderate the volume changes (expansion/contraction) seen during the reversible Li⁺ extraction/insertion, thus resulting in the improvement of cell cycling ability.     

Effect of Sn doping on the electrochemical performance of NaTi2(PO4)3/C composite

In this paper, NaTi_2-xSn_x(PO₄)₃/C (x?=?0.0, 0.2, 0.3, and 0.4) composites were fabricated via facile sol-gel method, and employed as anodes for aqueous lithium ion batteries. Effect of Sn doping with various content on electrochemical properties of NaTi₂(PO₄)₃/C was investigated systematically. Sn doping on Ti site has no obvious effect on the lattice structure and morphology of NaTi₂(PO₄)₃/C. Among all samples, NaTi_1.7Sn_0.3(PO₄)₃/C (NC-Sn-3) demonstrates the best electrochemical properties. NC-Sn-3 exhibits the outstanding rate performance, delivering a discharge capacity of 103.3, 95.2, and 87.4?mAh?g^?1 at 0.5, 7, and 20?°C, respectively, 1.7, 30.5, and 56.2?mAh?g^?1 larger than those of pristine NaTi₂(PO₄)₃/C. In addition, NC-Sn-3 shows excellent cycling performance with the capacity retention of 80.6% after 1000 cycles at 5?°C. This work reveals that Sn doped NaTi₂(PO₄)₃/C with outstanding electrochemical properties are potential anode for aqueous lithium ion batteries.     

Phase composition,microstructure and thermophysical properties of the Srx(Zr0.9Y0.05Yb0.05)O1.95+x ceramics

Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8, 0.7) ceramics were prepared by solid state reaction sintering. The sintered Sr_1.0(Zr_0.9Y_0.05Yb_0.05)O_2.95 is a single-phase solid solution while the sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=0.9?0.7) are composites, and a significant grain growth inhibition is observed in the sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9). Rare-earth elements distribution in the bulk materials indicates that Yb and Y preferentially substitute Zr-sites in SrZrO₃, and the highest solubility of RE₂O₃ in pure SrZrO₃ is ～0.8 mol%. The sintered Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x have high thermal expansion coefficients up to ～11.0×10^?6 K^-1 (1200°C). Sr_0.8(Zr_0.9Y_0.05Yb_0.05)O_2.75 has the lowest thermal conductivity of 1.38 W·m^-1·K^-1 at 800°C. Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8) show no phase transition from 600 to 1400°C, whereas Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=0.9, 0.8) have excellent high-temperature phase stability over the whole investigated temperature range. Therefore, Sr_x(Zr_0.9Y_0.05Yb_0.05)O_1.95+x (x=1.0, 0.9, 0.8) are considered as promising TBCs materials that might be operated at higher temperatures compared to YSZ.     

Effect of Zn addition on the structure and electrochemical properties of co-doped BaCe0.6Zr0.2Ln0.2O3-δ (Ln=Y,Gd, Yb) proton conductors

In this work, BaCe_0.6Zr_0.2Y_0.2-xYb_xO_3-δ and BaCe_0.6Zr_0.2Gd_0.2-xYb_xO_3-δ (x?=?0–0.20), proton conducting materials are prepared by the freeze-drying precursor method. The sintering conditions were optimized by adding Zn(NO₃)₂·6H₂O as sintering additive. The materials are thoroughly characterized by different structural and microstructural techniques, including X-ray diffraction, scanning and transmission electron microscopy, and thermogravimetric-differential thermal analysis. The addition of Zn favours the phase formation and densification at lower sintering temperatures; however, it leads to the segregation of a Zn-rich secondary phase, with general formula BaLn₂ZnO₅ (Ln?Y, Gd and Yb), which is identified and quantified for the first time. All samples with Zn as sintering aid exhibit cubic structure; however, the samples without Zn crystallize with orthorhombic or cubic structure, depending on the composition and thermal treatment. The electrical properties are studied by impedance spectroscopy. A deep analysis of the bulk and grain boundary contributions to the conductivity has revealed that the bulk conductivity remains almost unchanged along both series over Yb-doping; however, the grain boundary resistance decreases. The highest conductivity values are found for the intermediate members of both series, BaCe_0.6Zr_0.2Y_0.1Yb_0.1O_3-δ and BaCe_0.6Zr_0.2Gd_0.1Yb₁O_3-δ, with 33 and 28?mS?cm^?1 at 750?°C, respectively.     

Highly transparent Yb:Y2O3 ceramics obtained by solid-state reaction and combined sintering procedures

(Y_0.87-xLa_0.1Zr_0.03Yb_x)₂O₃ (x?=?0.02, 0.04, 0.05) transparent ceramics were obtained by solid-state reaction and combined sintering procedures with La₂O₃ and ZrO₂ as sintering additives. A method based on two-step intermediate sintering in air followed by vacuum sintering was applied in order to control the densification and grain growth of the samples during the final sintering process. The results indicate that La₂O₃ and ZrO₂ co-additives can improve the microstructure and optical properties of Yb:Y₂O₃ ceramics at relatively low sintering temperature. On the other hand, the addition of Zr⁴⁺ ions leads to the formation of dispersed scattering volumes in the ceramic bodies. Transmittance of 78.8% was measured for the 2.0?at% Yb:Y₂O₃ ceramic sample at the wavelength of 1100?nm. The spectroscopic properties of Yb:Y₂O₃ ceramics were investigated at room temperature. The obtained results show that the absorption cross-section at 978?nm is in the range of 2.08?×?10^–20 to 2.36?×?10^–20 cm², whereas the emission cross-section at 1032?nm is ~1.0?×?10^–20 cm².     

Silicon and its effect on the electrochemical properties of Li3V2(PO4)3 cathode material

In this study, silicon and its effect on the properties of Li₃V₂(PO₄)₃ were studied for lithium-ion battery applications. The composite material was synthesized and found to show enhanced capacity and cyclability. The presence of silicon in the composites was confirmed. Furthermore, large particles with rough, corroded-like structures formed, and these were distributed well with the silicon particles. The Li₃V₂(PO₄)₃-Si battery had good properties showing improved cyclability, an improved high performance rate, smaller impedance values and improved lithium-ion diffusion coefficients, as determined by cyclic voltammetry. Furthermore, the optimization of the silicon content led to a Li₃V₂(PO₄)₃-Si battery with a 2?wt% silicon loading that had a discharge capacity of 181?mA?h?g^?1. At 2?C, Li₃V₂(PO₄)₃-Si (2?wt%) still demonstrated a capacity of 111.8?mA?h?g^?1, which was 83.8% of its original capacity (compared with 70.3?mA?h?g^?1 and 63.8% for Li₃V₂(PO₄)₃) after 400 cycles.     

Sc3+-doping effects on porous Li3V2(PO4)3/C cathode with superior rate performance and cyclic stability

An enhanced sol-gel combustion method was used to synthesize different porous Sc³⁺-doped Li₃V_2-xSc_x(PO₄)₃/C (x = 0.00, 0.05, 0.10 and 0.15) compounds. The substitution of Sc³⁺ into the V³⁺ sites of Li₃V_2-xSc_x(PO₄)₃/C expands the lattice volume along with the enlargement of Li⁺ diffusion channel, which is beneficial for Li⁺ transportation and ionic conductivity improvement. Besides, the Sc³⁺ doping content exhibits a great impact on the morphology of Li₃V_2-xSc_x(PO₄)₃/C composite. The pristine Li₃V₂(PO₄)₃/C are constituted of porous particles and nanorods, and the ratio of nanorods to particles can be controlled by adjusting the amount of Sc³⁺ doping since the ratio of nanorods to particles decreases with increasing Sc³⁺ doping content. When Sc³⁺ doping content increases to a certain level (x = 0.15, Li₃V_1.85Sc_0.15(PO₄)₃/C), the nanorods are hardly seen. Li₃V_1.90Sc_0.10(PO₄)₃/C with higher tapped density, better reversibility, smaller resistance and larger Li⁺ diffusion coefficient demonstrates outstanding rate performance and cyclic stability, together with high specific discharge capacities of 130.2 and 92.9 mAh g⁻¹ at 0.5 and 20 C, respectively. Furthermore, a superior specific discharge capacity of 85.8 mAh g⁻¹ was retained at 20 C following 1000 cycles. Overall, a novel approach for the preparation of high-performance Li₃V_2-xSc_x(PO₄)₃/C cathodes with different morphologies for lithium-ion batteries is provided.     

Phase stability and thermo-physical properties of ZrO2-CeO2-TiO2 ceramics for thermal barrier coatings

The properties of ZrO₂ co-stabilized by CeO₂ and TiO₂ ceramic bulks were investigated for potential thermal barrier coating (TBC) applications. Results showed that the (Ce_0.15Ti_x)Zr_0.85-xO7 (x?=?0.05, 0.10, 0.15) compositions with single tetragonal phase were more stable than the traditional 8YSZ at 1573?K. These compositions also showed a large thermal expansion coefficient (TEC) and a high fracture toughness, which were comparable to those of YSZ. However, the phase stability, fracture toughness and sintering resistance of the CeO₂-TiO₂-ZrO₂ system showed a decline tendency with the increase of TiO₂ content. The TEC of the ceramic bulks decreased with increase of TiO₂ content as well because the crystal energy was enhanced with increasing substitution of Zr⁴⁺ by smaller Ti⁴⁺. The (Ce_0.15Ti_0.05)Zr_0.8O₂ had the best comprehensive properties among the (Ce_0.15Ti_x)Zr_0.85-xO₂ compositions as well as a low thermal conductivity. Therefore, it can be explored as a TBC candidate material for high-temperature applications.     

Aluminothermal synthesis and characterization of Li3V2−xAlx(PO4)3 cathode materials for lithium ion batteries

Monoclinic Li₃V_2−xAl_x(PO₄)₃ with different Al³⁺ doping contents (x = 0, 0.05, 0.08, 0.10 and 0.12) have been prepared by a facile aluminothermal reaction. Aluminum nanoparticles have been used as source for Al³⁺ and nucleus for Li₃V_2−xAl_x(PO₄)₃ nucleation as well as reducing agent in the aluminothermal strategy. The products were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and electrochemical methods. The XRD results show that the as-obtained Li₃V_2−xAl_x(PO₄)₃ has a phase-pure monoclinic structure, irrespective of the Al³⁺ doping concentration. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results reveal that the charge-transfer resistance of the Li₃V₂(PO₄)₃ is reduced and the reversibility is enhanced after V³⁺ substituted by Al³⁺. In addition, The Li₃V_2−xAl_x(PO₄)₃ phases exhibit better cycling stability than the pristine Li₃V₂(PO₄)₃.     

Tuning the phase transition temperature of Cr2(MoO4)3 by A-site substitution of scandium

A series of Cr_2-xSc_x(MoO₄)₃ solid solutions with tunable monoclinic-to-orthorhombic phase transition temperature have been synthesized via solid-state reaction. X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results show that all synthesized Cr_2-xSc_x(MoO₄)₃ (0?< x?≤?1.4) solid solutions are single phased with no impurities identified, which reveals that Cr³⁺ has been substituted by Sc³⁺ in Cr₂(MoO₄)₃. Monoclinic to orthorhombic phase transition temperature of Cr_2-xSc_x(MoO₄)₃ can be effectively tuned from 372?°C to room temperature as the substituted Sc³⁺-content (x) varies from 0 to 1.4. The synthesized Cr_0.6Sc_1.4(MoO₄)₃ crystalizes in an orthorhombic structure at room temperature, exhibiting anisotropic negative thermal expansion throughout the testing temperature range. The coefficient of thermal expansion measured by thermal mechanical analyzer (TMA) for Cr_0.6Sc_1.4(MoO₄)₃ is ?11.17?×?10^?6 °C^?1 in the testing temperature range of 30–600?°C. Moreover, the crystallization, micromorphology, density and coefficient of thermal expansion of Cr_0.6Sc_1.4(MoO₄)₃ are obviously sensitive to the twice sintering temperature, whereas none of such sensitivity is found for the phase transition temperature.     

High densification and Li-ion conductivity of Al-free Li7-xLa3Zr2-xTaxO12 garnet solid electrolyte prepared by using ultrafine powders

Ta-doped Li₇La₃Zr₂O₁₂ (Ta-LLZO) is considered as a promising solid electrolyte due to high Li-ion conductivity and good chemical stability against electrode materials. In this work, Ta-LLZO was prepared by a conventional solid-state reaction. Ultrafine powders were obtained by ball-milling to improve the surface activity. Ta-LLZO is sintered in ZrO₂ crucibles to avoid introducing Al into the samples. The particle size distribution, phase structure, morphology, ionic conductivity, electronic conductivity, density and electrochemical performance of semi-solid battery were characterized by laser diffraction particle size analyzer, X-ray diffraction, scanning electron microscope, AC-impedance, DC polarization, Archimedes method and a battery testing system, respectively. The results show that the ball milling to reduce the particle size is an effective way to solve the problem of relatively low density and Li-ion conductivity for Al-free Li_7-xLa₃Zr_2-xTa_xO₁₂. For Al-free Li_7-xLa₃Zr_2-xTa_xO₁₂, the increase of x (0.2?≤?x?≤?0.4) promotes the grain growth and sintering densification, but the increase of x (0.4?<?x?≤?0.6) has an adverse effect. Li_6.7La₃Zr_1.7Ta_0.3O₁₂ sintered at 1180?°C for 12?h shows the relative density of 92% and the highest Li-ion conductivity of 1.03?×?10^?3 S/cm at ³0?°C with the activation energy of about 0.37?eV, while Li_6.6La₃Zr_1.6Ta_0.4O₁₂ sintered at 1180?°C for 12?h shows the highest relative density of 96% and the Li-ion conductivity of 6.68?×?10^?4 S/cm at 30?°C with the activation energy of about 0.46?eV. The electronic conductivity of Al-free Li_7-xLa₃Zr_2-xTa_xO₁₂ is 10^?9 S/cm orders of magnitude. The semi-solid battery shows the first discharge capacity of 104.6 mAh/g and 92.5% capacity retention after 20 cycles.     

Mechanical and thermal expansion studies on Ca0.5Sr0.5Zr4-xTixP6O24 ceramics

Ca_0.5Sr_0.5Zr_4-xTi_xP₆O₂₄ (x?=?0?0.2) ceramics belonging to the NZP family were prepared and dense ceramics with no microcracks were obtained. All of the ceramic samples were still composed of the typical NZP structure with a small amount of Ti⁴⁺ substitution for Zr⁴⁺. The mechanical and thermal expansion properties of the ceramics were characterized and the result showed that the flexural strength monotonically increased to 66.5?MPa. The thermal expansion coefficient varied from 1.8 to 3.4?×?10^?6/°C with Ti⁴⁺ content increasing. Thus, it was clear that the substitution of Ti⁴⁺ for Zr⁴⁺ had obvious effects on the sinterability, mechanical and thermal expansion properties of Ca_0.5Sr_0.5Zr_4-xTi_xP₆O₂₄ ceramics, which were discussed in detail.     

Improvement of Al3+ ion conductivity by F doping of (Al0.2Zr0.8)4/3.8NbP3O12 solid electrolyte for mixed potential NH3 sensors

New Al³⁺ ion conducting solid electrolytes (Al_0.2Zr_0.8)_4/3.8NbP₃O_12-xF_2x(0?≤x?≤?0.4) with Nasicon-structure are successfully prepared by solid state reaction method. The influences of the doped F^- content on the properties of the (Al_0.2Zr_0.8)_4/3.8NbP₃O_12-xF_2x samples are investigated using X-ray powder diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The results show that F^- doping can effectively improve the sinterability and the total conductivity of the (Al_0.2Zr_0.8)_4/3.8NbP₃O_12-xF_2x samples. Among the solids series, (Al_0.2Zr_0.8)_4/3.8NbP₃O_11.7F_0.6 shows the highest conductivity of 1.53?×?10^?3 S?cm^?1at 500?°C, which is approximately 7.9 times higher than that of the undoped (Al_0.2Zr_0.8)_4/3.8NbP₃O₁₂. The ion transference number of the samples is higher than 0.99 at 300–700?°C. On the basis of the promising properties, a mixed-potential type NH₃ sensor based on (Al_0.2Zr_0.8)_4/3.8NbP₃O_11.7F_0.6 electrolyte and In₂O₃ sensing electrode has been developed. The sensing performance of the sensor is evaluated. The mixed-potential type sensor can work at relatively low temperatures of 200–350?°C and an excellent sensitivity of 99.71?mV/decade at 250?°C is obtained. The sensor also displays excellent stability and reproducibility, accompanied by low cross-sensitivities to CO₂, CH₄ and H_2.     

Preparation and electrochemical performance studies on Cr-doped Li3V2(PO4)3 as cathode materials for lithium-ion batteries

Cr-doped Li₃V_2−xCr_x(PO₄)₃/C (x = 0, 0.05, 0.1, 0.2, 0.5, 1) compounds have been prepared using sol–gel method. The Rietveld refinement results indicate that single-phase Li₃V_2−xCr_x(PO₄)₃/C with monoclinic structure can be obtained. Although the initial specific capacity decreased with Cr content at a lower current rate, both cycle performance and rate capability have excited improvement with moderate Cr-doping content in Li₃V_2−xCr_x(PO₄)₃/C. Li₃V_1.9Cr_0.1(PO₄)₃/C compound presents an initial capacity of 171.4 mAh g⁻¹ and 78.6% capacity retention after 100 cycles at 0.2C rate. At 4C rate, the Li₃V_1.9Cr_0.1(PO₄)₃/C can give an initial capacity of 130.2 mAh g⁻¹ and 10.8% capacity loss after 100 cycles where the Li₃V₂(PO₄)₃/C presents the initial capacity of 127.4 mAh g⁻¹ and capacity loss of 14.9%. Enhanced rate and cyclic capability may be attributed to the optimizing particle size, carbon coating quality, and structural stability during the proper amount of Cr-doping (x = 0.1) in V sites.     

Phase composition,Raman spectra,infrared spectra and dielectric properties of Li2MgTi1-x(Mg1/3Nb2/3)xO4 ceramics at microwave frequency

The Li₂MgTi_1-x(Mg_1/3Nb_2/3)_xO₄ (0?≤x?≤?0.5) ceramics were prepared by the conventional solid-state method. The relationship among phase composition, substitution amount and microwave dielectric properties of the ceramics was symmetrically investigated. All the samples possess the rock salt structure with the space group of Fm-3m. As the x value increases from 0 to 0.5, the dielectric constant linearly decreases from 16.75 to 15.56, which can be explained by the variation of Raman spectra and infrared spectra. The Q·f value shows an upward tendency in the range of 0?≤x?≤?0.3, but it then decreases when x?>?0.3. In addition, the temperature coefficient of resonant frequency (τ_f) is shifted toward zero with the increasing (Mg_1/3Nb_2/3)⁴⁺ addition. By comparison, the Li₂MgTi_0.7(Mg_1/3Nb_2/3)_0.3O₄ ceramics sintered at 1400?°C can achieve an excellent combination of microwave dielectric properties: ε_r=?16.19, Q·f =?160,000?GHz and τ_f =??3.14?ppm/°C.     

The synergistic effect of dual substitution of Al and Sb on structure and ionic conductivity of Li7La3Zr2O12 ceramic

Li₇La₃Zr₂O₁₂ (LLZO) with cubic garnet type structure is a promising solid electrolyte. In this work, Li_6.925-3xAl_xLa₃Zr_1.925Sb_0.075O₁₂ (0 ≤ x ≤ 0.1) electrolytes were prepared by conventional solid-state reaction. The influence of Sb-Al cosubstitution on the structure, microstructure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and impedance spectroscopy. Single cubic phase has been achieved for Li_6.925-3xAl_xLa₃Zr_1.925Sb_0.075O₁₂ (x = 0–0.075). Suitable amount of Al-Sb cosubstitution accelerates densification and improves the ionic conductivity. Li_6.775Al_0.05La₃Zr_1.925Sb_0.075O₁₂ exhibits highest relative densities (96.7%) and total ionic conductivity (4.10 × 10^?4 S/cm at 30 °C).     

On the way to understand the keys for the stabilization of the conductive phase in doped- NASICON-type materials

A family of doped-NASICON-type structures according to the chemical compositions: Li_1.2 Zr_1.9M_0.1(PO₄)₃ [with M = Ca²⁺, Mg²⁺, Zn²⁺]; Li_1.1 Zr_1.9Y_0.1(PO₄)₃ and Li_1.0 Zr_1.9Ce_0.1(PO₄)₃ have been synthesized by solid state reaction. The modification on the thermal treatment proposed in this work makes possible to obtain a high purity phase confirmed by XRD, SEM, microRaman-confocal and FTIR. Rietveld refinement evidences how the LZP lattice parameters are affected by each of those five different dopant cations incorporated into the pristine structure. Impedance spectroscopy proves how the relationship radius - charge of each dopant-ion affects the ionic conductivity. Unravelling that the partial replacement of Zr⁴⁺ in the LZP by a dopant improves the conductivity behavior. When the dopant cation has a lower charge and a larger size than the Zr⁴⁺ the developed structure favours the lithium-ion mobility at room temperature and the lithium conductivity increases.