High lithium ionic conductivity in the garnet‐type oxide Li7−2xLa3Zr2−xMoxO12 (x=0‐0.3) ceramics by sol‐gel method

Lithium garnet‐type oxides Li_7?2xLa₃Zr_2?xMo_xO₁₂ (x=0, 0.1, 0.2, 0.3) ceramics were prepared by a sol‐gel method. The influence of molybdenum on the structure, microstructure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X‐ray diffraction, scanning electron microscopy, and impedance spectroscopy. The cubic phase Li₇La₃Zr₂O₁₂ has been stabilized by partial substitution of Mo for Zr at low temperature. The introduction of Mo (x≥0.1) can accelerate densification. Li_6.6La₃Zr_1.8Mo_0.2O₁₂ sintered at lower temperature 1100°C for 3 hours exhibits highest total ionic conductivity of 5.09 × 10^?4 S/cm. Results indicate that the Mo doping LLZO synthesized by sol‐gel method effectively lowers its sintering temperature and improves the ionic conductivity.     

Influence of Ln3+ and B3+ Ions Co‐Substitution on Thermophysical Properties of LnMB11O19‐type Magnetoplumbite LaMgAl11O19 for Advanced Thermal Barrier Coatings

Lanthanum hexaaluminate is a promising competitor to establish yttria partially stabilized zirconia as a thermal barrier coating material for Ni‐based superalloy due to its relative low intrinsic thermal conductivity and low sinterability at temperatures exceeding 1100°C. Sr²⁺ and Ti⁴⁺ were selected as two dopants to partially substitute the La³⁺ and Al³⁺ in LaMgAl₁₁O₁₉, respectively. The variation in thermal conductivity with Sr²⁺ and Ti⁴⁺ fractions was analyzed based on structure information provided by X‐ray diffraction and Raman spectroscopy. The average crystal size of LaMgAl₁₁O₁₉ sintered at 1600°C for 10 min by spark plasma sintering is in nanoscale. The fully dense La_1?xSr_xMgAl_11?xTi_xO₁₉ solid solution showed a minimum thermal conductivity value (λ = 1.12 W/(m K)^?1,T = 1273 K) at the composition of La_0.5Sr_0.5MgAl_10.5Ti_0.5O₁₉,which possibly reduces from the enhanced phonon scattering due to mass and strain fluctuations at the Ln³⁺ and B³⁺ sites.     

Tuning stoichiometry of high-entropy oxides for tailorable thermal expansion coefficients and low thermal conductivity

Thermal barrier coating materials with proper thermal expansion coefficient (TEC), low thermal conductivity, and good high-temperature stability are of great significance for their applications in next-generation turbine engines. Herein, we report a new class of high-entropy (La_0.2Sm_0.2Er_0.2Yb_0.2Y_0.2)₂Ce_xO_3+2x with different Ce⁴⁺ contents synthesized by a solid-state reaction method. They exhibit different crystal structures at different Ce⁴⁺ content, including a bixbyite single phase without Ce⁴⁺ doping (x = 0), bixbyite-fluorite dual-phase in the RE₂O₃-rich region (0 < x < 2), and fluorite single phase in the stoichiometric (x = 2) and CeO₂-rich region (x > 2). The high-entropy (La_0.2Sm_0.2Er_0.2Yb_0.2Y_0.2)₂Ce_xO_3+2x exhibit tailorable TECs at a large range of 9.04 × 10^–6–13.12 × 10^–6 °C^–1 and engineered low thermal conductivity of 1.79–2.63 W·m^–1·K^–1. They also possess good sintering resistance and high-temperature phase stability. These results reveal that the high-entropy (La_0.2Sm_0.2Er_0.2Yb_0.2Y_0.2)₂Ce_xO_3+2x are promising candidates for thermal barrier coating materials as well as thermally insulating materials and refractories.     

Chemical Bulk Diffusion Coefficient of a La0.5Sr0.5CoO3−δ Cathode for Intermediate‐Temperature Solid Oxide Fuel Cells

In the first part of this study, the characteristics of a La_0.5Sr_0.5CoO_3?δ cathode are described, including its chemical bulk diffusion coefficient (D_chem), and electrical conductivity relaxation experiments are performed to obtain experimental D_chem measurements of this cathode. The second part of this study describes two methods to improve the single‐cell performance of solid oxide fuel cells. One method uses a composite cathode, i.e., a mix of 30 wt% electrolyte and 70 wt% cathode; the other method uses an electrolyte‐infiltrated cathode, i.e., an active ionic‐conductive electrolyte with nano‐sized particles is deposited onto a porous cathode surface using the infiltration method. In this work, 0.2M Ce_0.8Sm_0.2O_1.9 (SDC)‐infiltrated La_0.5Sr_0.5CoO_3?δ exhibits a maximum peak power density of 1221 mW/cm² at an operating temperature of 700°C with a thick‐film SDC electrolyte (30 μm), a NiO + SDC anode (1 mm) and a La_0.5Sr_0.5CoO_3?δ cathode (10 μm). The enhancement in electrochemical performances using the electrolyte‐infiltrated cathode is attributed to the creation of electrolyte/cathode phase boundaries, which considerably increases the number of electrochemical sites available for the oxygen reduction reaction.     

Effects of La content on the densification,microstructure, and conductivity of doped La10−xGe6O26±δ electrolytes

In this study, the influence of La content on the characteristics of Nb‐, Mo‐, and W‐doped La_xGe₆O_26±δ electrolytes was investigated through sintering study, X‐ray diffraction, scanning electron microscopy, and conductivity measurement. The densification of La_xGe_5.5Nb_0.5O_26±δ and La_xGe_5.5W_0.5O_26±δ was retarded as the x reached 9.75, while that of La_xGe_5.5Mo_0.5O_26±δ improved with increasing La content. The average grain size slightly increased and weight loss due to evaporation of GeO₂ significantly reduced with increasing La content, ranging from 1.39% to 0.26%. Among the systems studied, La_9.33Ge_5.5Nb_0.5O_26.245, La_9.33Ge_5.5Mo_0.5O_26.045, and La_9.50Ge_5.5W_0.5O_26.75 electrolytes revealed great potential for use in SOFC applications.     

Tests for the Use of La2Mo2O9‐based Oxides as Multipurpose SOFC Core Materials

The mixed ionic–electronic conductivity under dilute hydrogen, the stability and the catalytic activity under propane:air type mixtures of a series of LAMOX oxide‐ion conductors have been studied. The effect of exposure to dilute hydrogen on the conductivity of the β‐La₂(Mo_{2 – y}W_y)O₉ series at 600 °C depends on tungsten content: almost negligible for the highest (y = 1.4), it is important for La₂Mo₂O₉ (y = 0). In propane:air, all tested LAMOX electrolytes are stable at 600–700 °C, but get reduced when water vapour is present. La₂Mo₂O₉ is the best oxidation catalyst of the series, with an activity comparable to that of nickel. The catalytic activity of other tested LAMOX compounds is much lower, (La_1.9Y_0.1)Mo₂O₉ showing a deactivation phenomenon. These results suggest that depending on composition, La₂(Mo_{2 – y}W_y)O₉ compounds could be either electrolytes in single‐chamber SOFC and dual‐chamber micro‐SOFC (y = 1.4) or anode materials in dual‐chamber SOFC (low y) or oxidation catalysts in SOFCs operating with propane (y = 0).     

Effect of Ba concentration on phase stability and mechanical and thermal properties of La2Mo2O9

Ba-substituted La₂Mo₂O₉ ((La_1−xBa_x)₂Mo₂O_9−δ, x = 0–0.12) was prepared and the thermal and mechanical properties were evaluated. The thermal expansion coefficients (TECs) were determined from high-temperature X-ray diffraction (XRD) analysis. Phase transition in La₂Mo₂O₉ was suppressed via substitution of Ba for La, as demonstrated by differential scanning calorimetry (DSC) analysis. The mechanical properties, such as the bulk modulus, shear modulus, Young’s modulus, compressibility, and Debye temperature were evaluated from the measured sound velocities. The thermal conductivity was evaluated from the thermal diffusivity, heat capacity, and density in the temperature range from room temperature to 1073 K. The thermal conductivity decreased with increasing Ba content. Theoretical calculations based on the Klemens–Callaway model were performed to analyze the thermal conductivity, and the results suggest that the reduction of the thermal conductivity was mainly attributed to oxygen defects in the anion sublattice of La₂Mo₂O₉.     

Effect of Tm3+ Ions on the White Light Emission of Dy3+–Tm3+ Codoped SrMg2La2W2O12 Phosphors

Dy³⁺–Tm³⁺ ions codoped SrMg₂La₂W₂O₁₂ (strontium magnesium lanthanum tungstate) phosphors were synthesized by conventional high‐temperature solid‐state reaction method. X‐ray analysis of the end products revealed the well‐crystallized phases with orthorhombic structure. The functional groups present in the phosphors were studied by the Fourier transform infrared measurements. To know the potential applicability of these phosphors for white light emission, the excitation and emission spectra were recorded. The excitation spectra exhibited an intense broad band at 313 nm, pertaining to the O → W ligand‐to‐metal charge‐transfer state (LMCT) of the host. With the excitation of LMCT band (313 nm), the decay curves of singly doped SrMg₂La₂W₂O₁₂:Dy phosphors exhibited single exponential, where as the codoped SrMg₂La₂W₂O₁₂:DyTm phosphors exhibited double exponential nature. The luminescence colors of these phosphors were estimated from Commission Internationale de L'Eclairage (CIE) coordinates using the photoluminescence data. The color of singly doped SrMg₂La₂W₂O₁₂:Dy phosphor has been tuned by codoping with Tm³⁺ ions. It has been noticed that the CIE chromaticity coordinates (x,y) determined from the luminescence spectrum of singly Dy³⁺ doped SrMg₂La₂W₂O₁₂ phosphor shifted toward the white light region, when codoped with Tm³⁺ ions. The increase in correlated color temperatures (T_cct) has been noticed with the increase of Tm³⁺ ions concentration in SrMg₂La₂W₂O₁₂:DyTm phosphors.     

Phase Structure Evolution and Thermo‐Physical Properties of Nonstoichiometry Nd2−xZr2+xO7+x/2 Pyrochlore Ceramics

Nonstoichiometry pyrochlore composites of Nd_2?xZr_2+xO_7+x/2 (x = 0, 0.1, 0.2) were synthesized by chemical‐coprecipitation and calcination method. The phase structure evolution and thermo‐physical properties of Nd_2?xZr_2+xO_7+x/2 were investigated. Structural analysis by Raman spectroscopy showed that Nd_2?xZr_2+xO_7+x/2 underwent an ordering degree decrease and a lattice distortion increase with increasing x value. Nd_1.9Zr_2.1O_7.05 and Nd_1.8Zr_2.2O_7.1 exhibited lower thermal conductivities than Nd₂Zr₂O₇, which might be related to the lower ordering degree and the enhanced phonon scattering due to lattice distortion. As ZrO₂ content increasing, the thermal expansion coefficients of Nd_2?xZr_2+xO_7+x/2 increased, which possibly arised from the decreased crystal energy due to reduced ordering degree.     

Effect of Ba Nonstoichiometry in Bax(Zr0.8Y0.2)O3−δ on Population of 5‐Coordinated Y

The local environments of Y in the Y‐substituted BaZrO₃ of the starting compositions of Ba_x(Zr_0.8Y_0.2)O_3?δ (x = 0.97, 1.0, 1.03, and 1.06) were analyzed by ⁸⁹Y magic angle spinning NMR spectroscopy. The result showed a strong population dependence of 5‐coordinated Y³⁺ ions mostly at the B site on the Ba contents. The enhancement of Ba contents by 9 at% (from 0.97 to 1.06 in the starting Ba contents) in a nominal composition increased the amount of 5‐coordinated Y³⁺ ions from 35% ± 7% to 49% ± 5%, suggesting the importance of maximizing the Ba contents to populate more oxygen vacancies which is related to the concentration of protons incorporated during the hydration process. The wide variation in the lattice parameter of yttrium‐substituted BaZrO₃ perovskite materials in previous reports was reinterpreted with the variation in the Ba contents resulting from the evaporation of BaO during the sintering processes. Y³⁺ ions were confirmed to replace mainly the Zr⁴⁺ ions, as expected, and a tendency of oxygen vacancy clustering near the Y³⁺ ions was discussed.     

Electrical conductivity and redox stability of La2Mo2−xWxO9 materials

A series of compounds La₂Mo_2−xW_xO₉ (x = 0-2) were synthesized using a freeze-dried precursor method at relatively low temperatures (673-823 K). These materials were characterised by thermogravimetric and differential thermal analysis (TG/DTA), differential scanning calorimetric (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM) and dilatometric measurements. Oxygen stoichiometry was evaluated by coulometric titration and thermogravimetric analysis at 873-1273 K. The ionic and electronic conductivities of these materials were analysed by impedance spectroscopy and a Hebb-Wagner ion-blocking method under moderately reducing conditions. The presence of W⁶⁺ leads to an increase of the stability range (about 10⁻¹⁶ Pa for La₂Mo_0.5W_1.5O₉ at 1073 K) and prevents oxygen loss and amorphisation. Within the stability range, the electronic conductivity increases gradually as the temperature increases and as the oxygen partial pressure reduces. This indicates that the electronic transport is mainly n-type as a result of the oxygen-content decreasing in the molybdate lattice. Further reduction of the oxygen partial pressure gave rise to the decomposition of La₂Mo_2−xW_xO₉, leading to the formation of new phases with molybdenum in lower oxidation states, which further enhances the electronic conductivity. The results of the coulometric titration and the thermogravimetric studies under a dry 5% H₂/Ar flow suggest that tungsten doped lanthanum molybdate materials can be used as electrolyte only at low temperature and under moderate reducing conditions.     

Some features of thermophysical properties of γ‐Gd2S3 ceramics based on real structure

The heat capacity C_p, thermal diffusivity χ_T, and lattice thermal conductivity κ_latt of ceramic solid solutions of sesquisulfides Gd_3‐xV_Gd,xS₄ (0 < x < 0.33) in the temperature range 300‐700 K has been studied. Changing the real structure, namely the concentrations of vacancies (N_V) and deformation (N_Dc) centers of polycrystals, significantly decreases κ_latt. A deviation of composition from the stoichiometry 2:3 is accompanied by an increase in the specific area of the crystallite boundaries per unit volume, and, hence, the concentration of deformation centers D_C increases. This observation was confirmed by examining the short‐range order disturbance of the lattice and symmetry environment of the Gd³⁺ and S^2? environment by Raman spectroscopy and the magnetic susceptibility Faraday method. Therefore the thermal diffusivity of gadolinium sesquisulfide is reduced because of the mean free path of phonons decrease. As a result, the thermal conductivity of the polycrystalline samples is reduced by 10%.     

Electrical and Thermal Conduction Behaviors in La‐Substituted GdBaCuFeO5+δ Ceramics

Gd_1?xLa_xBaCuFeO_5+δ polycrystalline ceramics have been prepared by a sol–gel method combined with the traditional ceramic processing. Analysis of the microstructure and phase composition reveals that the pure GdBaCuFeO_5+δ phase can be obtained even after the substitution of 50% La at Gd‐site. The band gap can be tuned from 1.47 to 1.36 eV by La substitution, resulting in a significant increase in the electrical conductivity. In addition, the total thermal conductivity can also be suppressed by the substitution of La at Gd‐sites. A ZT value of 0.02 at 1023 K is achieved in the 50% La‐substituted samples, which is over 20 times higher than that of the pure GdBaCuFeO_5+δ sample.     

Effect of Y3+-O2- partial substitution with Ca2+-F- on the luminescence enhancement of Y2Mo3O12:Sm3+ red-emitting phosphors

To improve the luminescence property of Sm³⁺ in Y₂Mo₃O₁₂, partial Ca²⁺-F^- co-substituted Y₂Mo₃O₁₂:Sm³⁺ phosphor, namely Y_2-xCa_xMo₃O_12-xF_x:Sm³⁺, was prepared using a solid-state method. The effect of introducing Ca²⁺-F^- ion pairs on structure and luminescence properties of Y₂Mo₃O₁₂:Sm³⁺ was studied in depth. XRD patterns not only manifested that all as-prepared Y_2-xCa_xMo₃O_12-xF_x:Sm³⁺ samples had standard Y₂Mo₃O₁₂ structure, but also indicated the introduction of Ca²⁺-F^- ion pairs did not cause the change of crystal structure. Under the near ultraviolet excitation of 404 nm, the emission peaks of Y₂Mo₃O₁₂:Sm³⁺ were located at 567 nm, 605 nm and 652 nm, respectively, resulting from the 4f→4f electron transitions of Sm³⁺ ions. Furthermore, the luminescence intensity of Sm³⁺ was obviously enhanced through the co-substitution of Y³⁺-O^2- ions with Ca²⁺-F^- ions in Y₂Mo₃O₁₂ structure, and the chromaticity coordinates moved towards red region, which due to the environmental effect of crystal field around Sm³⁺. Besides, the red LED device was manufactured for suitable chromaticity parameters. All results indicated that the as-prepared Y_1.84Ca_0.06Mo₃O_11.94F_0.06:0.10Sm³⁺ red-emitting phosphor could become a promising candidate for application of white light-emitting diodes and plant illumination.     

Thermal expansion and thermal conductivity of SmxZr1−xO2−x/2 (0.1 ≤ x ≤ 0.5) ceramics

A study was conducted of the effect of additions of samarium oxide on the thermal expansion and thermal conductivity of zirconium oxide for thermal barrier coatings. Sm_xZr_1?xO_2?x/2 (0.1 ≤ x ≤ 0.5) ceramic powders synthesized with a chemical-coprecipitation and calcination method were sintered at 1873 K for 15 h. Structures of the synthesized powders and sintered ceramics were identified by X-ray diffractometer. The morphologies of ceramic powders were observed by transmission electron microscope. The thermal expansion coefficients and thermal diffusion coefficients of Sm_xZr_1?xO_2?x/2 ceramics were studied with a high-temperature dilatometer and a laser flash diffusivity technique from room temperature to 1673 K. The thermal conductivity was calculated from thermal diffusivity, density and specific heat of bulk ceramics. Sm_0.1Zr_0.9O_1.95 ceramics consists of both monoclinic and tetragonal structures. However, Sm_0.2Zr_0.8O_1.9 and Sm_0.3Zr_0.7O_1.85 ceramics only exhibit a defect fluorite structure. Sm_0.4Zr_0.6O_1.8 and Sm_0.5Zr_0.5O_1.75 ceramics have a pyrochlore-type lattice. With the increase of Sm₂O₃ content, the linear thermal expansion of Sm_xZr_1?xO_2?x/2 ceramics increases except for Sm_0.1Zr_0.9O_1.95. The thermal conductivities of Sm_xZr_1?xO_2?x/2 ceramics ranged from 1.41 at 873 K to 1.86 W m^?1 K^?1 at room temperature in a test temperature range of room temperature to 1673 K, and the results can be explained by phonon scattering mechanism.     

Efficient red‐emitting phosphor of Eu3+‐activated (Na0.5Gd1.5)(TiSb)O7 derived via cation‐substitutions in Gd‐Pyrochlore

Rare‐earth (RE) titanate pyrochlore with perovskite‐layered structure is a well‐known engineering material in applied in many field. In this work, a red‐emitting phosphor of Gd_2?xNa_xTi_2?2xSb_2xO₇:Eu³⁺ (x = 0‐0.5) was developed via cation substitutions of (Sb⁵⁺→Ti⁴⁺) and (Na⁺→Gd³⁺) in Gd₂Ti₂O₇. The motivation is based on the fact that the introduction of cation‐disorders has been regarded to be an effective approach for improving the luminescent efficiency and thermal stability of RE‐activated materials. All the samples were synthesized via facile solid‐state reaction method. The morphology properties were measured via SEM and EDS measurements. The structural Rietveld refinement was performed to investigate the microstructure in pyrochlore lattices. The luminescence properties of Gd_2?xNa_xTi_2?2xSb_2xO₇:0.15Eu³⁺ (x = 0‐0.5) has a strict dependence on the cation substitution levels. The band energy of Gd₂Ti₂O₇ is 2.9 eV with a direct transition nature. The incorporation of Sb⁵⁺ and Na⁺ in the lattices moves the optical absorption to a longer wavelength. The cation disorder results in significant improvements of luminescence intensity, excitation efficiency in the blue region, longer emission lifetime and thermal stability.     

Enhanced Thermoelectric Properties in Cu‐Doped c‐Axis‐Oriented Ca3Co4O9+δ Thin Films

Highly c‐axis‐oriented Ca₃Co_4?xCu_xO_9+δ (x = 0, 0.1, 0.2, and 0.3) thin films were prepared by chemical solution deposition on LaAlO₃ (001) single‐crystal substrates. X‐ray diffraction, field‐emission scanning electronic microscopy, X‐ray photoelectron spectroscopy, and ultraviolet‐visible absorption spectrums were used to characterize the derived thin films. The solubility limit of Cu was found to be less than 0.2, above which [Ca₂(Co_0.65Cu_0.35)₂O₄]_0.624CoO₂ with quadruplicated rock‐salt layers was observed. The electrical resistivity decreased monotonously with increasing Cu‐doping content when x ≤ 0.2, and then slightly increased with further Cu doping. The Seebeck coefficient was enhanced from ~100 μV/K for the undoped thin film to ~120 μV/K for the Cu‐doped thin films. The power factor was enhanced for about two times at room temperature by Cu doping, suggesting that Cu‐doped Ca₃Co₄O_9+δ thin films could be a promising candidate for thermoelectric applications.     

Thermoelectric properties of La7Mo7O30 sintered by reactive spark plasma sintering

In this work, spark plasma sintering of La₂Mo₂O₉ powder was used to achieve dense ceramics of La₇Mo₇O₃₀ and explore their thermoelectric properties. SPS sintering of La₂Mo₂O₉ powder at 973 K for 10 min under 90 MPa leads to a bicoloured sample with white and black faces. XRD patterns of white and black faces are attributed to La₂Mo₂O₉ and La₇Mo₇O₃₀ phases, respectively. These experimental conditions allow observing the in-situ reduction of La₂Mo₂O₉ during the SPS process. With a longer sintering time of 30 min, a ceramic of La₇Mo₇O₃₀ is obtained. Its electrical conductivity exhibits a semiconducting behaviour and reaches a value of 1000 Sm^-1 at 1000 K. The negative Seebeck coefficient show a n-type conduction in this phase. La₇Mo₇O₃₀ exhibits a very low thermal conductivity, less than 1 Wm⁻¹K⁻¹ from room temperature up to 1000 K, similar to the values reported for La₂Mo₂O₉. A figure of merit of 0.04 is reached at 1000 K.     

Semiconductivity in Acceptor‐Doped BaTi1−xHoxO3−x/2−δ/2

Acceptor‐doped BaTiO₃ powders of formula: BaTi_1?xHo_xO_3?x/2?δ/2: x = 0.0001, 0.001, 0.01, 0.03, and 0.07, were prepared by sol‐gel synthesis, fired at 800°C–1500°C and either quenched or slow‐cooled to room temperature. Electrical properties of ceramics depended on firing conditions, Ho content, and cooling rate. Pellets of all x values fired at 800°C–1000°C were insulating and, from the presence of OH bands in the IR spectra, charge balance appeared to involve co‐doping of Ho³⁺ and H⁺ ions without necessity for oxygen vacancy creation. At higher firing temperatures, OH bands were absent. Pellets fired at 1400°C in air and slow cooled were insulating for both low x (0.0001) and high x (0.07) but at intermediate x (0.001 and 0.01) passed through a resistivity minimum of 20–30 Ω cm at room temperature, attributed to the presence of Ti³⁺ ions; it is suggested that, for these dilute Ho contents, each oxygen vacancy is charge compensated by one Ho³⁺ and one Ti³⁺ ion. At higher x, charge compensation is by Ho³⁺ ions and samples are insulating. A second, more general mechanism to generate Ti³⁺ ions, and a modest level of semiconductivity, involves reversible oxygen loss at high temperatures.     

Optimization of Lithium Content and Sintering Aid for Maximized Li+ Conductivity and Density in Ta‐Doped Li7La3Zr2O12

Ta‐doped cubic phase Li₇La₃Zr₂O₁₂ (LLZ) lithium garnet received considerable attention in recent times as prospective electrolyte for all‐solid‐state lithium battery. Although the conductivity has been improved by stabilizing the cubic phase with the Ta⁵⁺ doping for Zr⁴⁺ in LLZ, the density of the pellet was found to be relatively poor with large amount of pores. In addition to the high Li⁺ conductivity, density is also an essential parameter for the successful application of LLZ as solid electrolyte membrane in all‐solid‐state lithium battery. Systematic investigations carried out through this work indicated that the optimal Li concentration of 6.4 (i.e., Li_6.4La₃Zr_1.4Ta_0.6O₁₂) is required to obtain phase pure, relatively dense and high Li⁺ conductive cubic phase in Li_7?xLa₃Zr_2?xTa_xO₁₂ solid solutions. Effort has been also made in this work to enhance the density and Li⁺ conductivity of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ further through the Li₄SiO₄ addition. A maximized room‐temperature (33°C) total (bulk + grain boundary) Li⁺ conductivity of 3.7 × 10^?4 S/cm and maximized relative density of 94% was observed for Li_6.4La₃Zr_1.4Ta_0.6O₁₂ added with 1 wt% of Li₄SiO₄.