The influence of hafnium impurities on the electrochemical performance of tantalum substituted Li7La3Zr2O12 solid electrolytes

Garnet-based Li7La3Zr2O12 (LLZO) is considered one of the most promising oxide-ceramic solid electrolyte materials for inorganic all-solid-state batteries. Dopants and substituents like Al, Ta, Nb, Ga, and W were shown to have a high impact on the total ionic conductivity, increasing it from 10−6 S/cm up to 10−3 S/cm. However, natural zirconium sources always contain a small amount of hafnium which could also act as dopant, but the separation of these two elements is complicated and expensive. In this work, we investigate the influence of various Hf-impurity concentrations on the performance of tantalum-doped LLZO. We synthesised Li6.45Al0.05La3Zr1.6−xHfxTa0.4O12 (LLZHO with x = 0 – 1.6) via conventional solid-state synthesis and have demonstrated that up to x = 0.1, hafnium impurities do not have a significant impact on the performance of the material. Above this concentration, the Li-ion conductivity is steadily reduced to around 70% when zirconium is fully substituted by hafnium resulting in Li6.45Al0.05La3Hf1.6Ta0.4O12. As the purity of Zr precursors has a great impact on their price, these findings can help to reduce the price of LLZO in general, as lower grade zirconium can be used in industrial scale applications.

A preliminary investigation of the molten salt mediated synthesis of Gd2TiO5 ‘stuffed’ pyrochlore

Refractory ‘stuffed’ pyrochlores such as Gd2TiO5 are of interest for nuclear applications, including as matrices for actinide disposition and as neutron absorbers in control rods. Here, we report the results of a preliminary comparative investigation of the synthesis of Gd2TiO5 by molten salt and conventional solid-state synthesis. We show that synthesis of Gd2TiO5 proceeds from the pyrochlore phase Gd2Ti2O7 which is first formed as a kinetic product. Molten salt synthesis afforded single phase Gd2TiO5 at 1300 °C in 2 h, via a template growth mechanism, and is effective for the synthesis of these refractory materials. This work demonstrates molten salt mediated synthesis of ‘stuffed’ pyrochlore for the first time. Graphic abstract

γ-Brass type structures with I- and P-cell in the ternary Cu–Zn–In system

Abstractγ-Brass type phases in Cu–Zn–In ternary system were synthesized from the highly pure elements by conventional solid-state synthesis and characterized by X-ray diffraction and EDX analysis. Diffraction analysis confirmed the existence of cubic γ-brass type phases with I- and P-cell having a significant homogeneity range in the ternary Cu–Zn–In system. The phase homogeneity is connected with structural disorder based on mixed site occupancies. Site specific In substitution was observed during single-crystal structure analysis. The γ-brass structures with body-centered cubic lattice (I$‾{4}$3m) are viewed as 26-atom γ-clusters. Like Cu5Zn8, the inner tetrahedron (IT), outer tetrahedron (OT) and octahedron (OH) sites in the 26-atom clusters of γ-brass structures with I-cell are occupied by Zn, Cu, Cu, respectively. Indium substitution is restricted to the cuboctahedral (CO) site and the CO site is assumed to be mixed with In, Cu and Zn throughout the homogeneity range. The structures of cubic γ-brass type (P$‾{4}$3m) phases with P-cell are built up with two independent 26‐atom γ‐clusters and centered at the special positions A (0, 0, 0) and B (½, ½, ½) of the unit cell. According to the single‐crystal X‐ray analyses, In substitutions are largely restricted to the cuboctahedral sited B clusters. In the cubic γ-phases with P-cell, site occupancy pattern of cluster positioned at A is similar to the γ-cluster in Cu5Zn8, whereas cluster B bears a close resemblance to Cu-poor γ-cluster (Cu14In12) of Cu9In4 (P$‾{4}$3m). The vec values for cubic γ-brass type phases in the Cu–Zn–In ternary system ranges between 1.57 and 1.64.

Effect of La3+ Substitution at Bi-Site on Transport Properties of Bi0.3-xLaxPr0.3Ca0.4Mn0.1Cr0.9MnO3

Magnetic and electronic transport properties of Bi0.3-xLaxPr0.3Ca0.4Mn0.1Cr0.9O3 (0≤x≤0.2) manganites have been investigated by measurements of AC-susceptibility, resistivity and magnetoresistance. The samples were prepared using conventional solid-state synthesis method. Magnetic susceptibility versus temperature measurements showed all samples exhibit ferromagnetic to paramagnetic transition with Curie temperature, Tc enhanced from 111 K (x=0) to 174 K (x=0.2). Electrical resistivity measurements of the samples in zero field showed increase of metal-insulator (MI) transition temperature from 58 K(x=0) to 88 K(x=0.2). The increase in both Tc and TMI indicates enhancement of double exchange (DE) interaction involving Mn3+ and Mn4+ ions as a result of weakening of the hybridization effect between Bi3+ 6s2 lone pair with O orbital due to La3+ substitution. La substitution in the Bi-based compound is suggested reduce MnO6 octahedral distortion hence increasing delocalization of charge carriers. The observed variation in MR behavior due to La substitution indicates the substitution influence the MR mechanism of extrinsic and intrinsic behavior in Bi0.3-xLaxPr0.3Ca0.4Mn0.1Cr0.9O3 .

Synthesis-Controlled Polymorphism, Magnetic and Electrochemical Properties of Li3Co2SbO6

<div>Li3Co2SbO6 is found to adopt two highly distinct structural forms: a hexagonal layered O3- LiCoO2 type phase with “honeycomb” 2:1 ordering of Co and Sb; and an orthorhombic superstructure of rock-salt type, isostructural with Li3Co2TaO6 but with the addition of significant Li/Co ordering. Pure samples of both phase scan be obtained by conventional solid-state synthesis from the same precursors, Li3SbO4 and CoO, by controlling particle size and reaction time. Both phases show relatively poor performance as lithium-ion battery cathode materials in their as-made states, but complex and interesting low-temperature magnetic properties. The honeycomb phase orders antiferromagnetically below TN = 14 K, but a positive Weiss constant θw = 18.1 K points to strong ferromagnetic interactions in the paramagnetic regime above TN; and isothermal magnetisation below TN shows evidence for a field-induced “spin-flop” transition at H ~ 0.7 T. The rock-salt type superstructure phase orders antiferromagnetically below TN = 112 K, then undergoes two more transitions at 80 K and 60, suggesting close competition between at least three ground states. Consistent with such competition, the Weiss constant θw = -181 K indicates some frustration, there is a strong field-cooled / zero field-cooled divergence below TN, and isothermal magnetisation shows it to be magnetically soft with low coercivity.<br></div>

Synthesis-Controlled Polymorphism, Magnetic and Electrochemical Properties of Li3Co2SbO6

<div>Li3Co2SbO6 is found to adopt two highly distinct structural forms: a hexagonal layered O3- LiCoO2 type phase with “honeycomb” 2:1 ordering of Co and Sb; and an orthorhombic superstructure of rock-salt type, isostructural with Li3Co2TaO6 but with the addition of significant Li/Co ordering. Pure samples of both phase scan be obtained by conventional solid-state synthesis from the same precursors, Li3SbO4 and CoO, by controlling particle size and reaction time. Both phases show relatively poor performance as lithium-ion battery cathode materials in their as-made states, but complex and interesting low-temperature magnetic properties. The honeycomb phase orders antiferromagnetically below TN = 14 K, but a positive Weiss constant θw = 18.1 K points to strong ferromagnetic interactions in the paramagnetic regime above TN; and isothermal magnetisation below TN shows evidence for a field-induced “spin-flop” transition at H ~ 0.7 T. The rock-salt type superstructure phase orders antiferromagnetically below TN = 112 K, then undergoes two more transitions at 80 K and 60, suggesting close competition between at least three ground states. Consistent with such competition, the Weiss constant θw = -181 K indicates some frustration, there is a strong field-cooled / zero field-cooled divergence below TN, and isothermal magnetisation shows it to be magnetically soft with low coercivity.<br></div>

Synthesis-Controlled Polymorphism, Magnetic and Electrochemical Properties of Li3Co2SbO6

<div>Li3Co2SbO6 is found to adopt two highly distinct structural forms: a hexagonal layered O3- LiCoO2 type phase with “honeycomb” 2:1 ordering of Co and Sb; and an orthorhombic superstructure of rock-salt type, isostructural with Li3Co2TaO6 but with the addition of significant Li/Co ordering. Pure samples of both phase scan be obtained by conventional solid-state synthesis from the same precursors, Li3SbO4 and CoO, by controlling particle size and reaction time. Both phases show relatively poor performance as lithium-ion battery cathode materials in their as-made states, but complex and interesting low-temperature magnetic properties. The honeycomb phase orders antiferromagnetically below TN = 14 K, but a positive Weiss constant θw = 18.1 K points to strong ferromagnetic interactions in the paramagnetic regime above TN; and isothermal magnetisation below TN shows evidence for a field-induced “spin-flop” transition at H ~ 0.7 T. The rock-salt type superstructure phase orders antiferromagnetically below TN = 112 K, then undergoes two more transitions at 80 K and 60, suggesting close competition between at least three ground states. Consistent with such competition, the Weiss constant θw = -181 K indicates some frustration, there is a strong field-cooled / zero field-cooled divergence below TN, and isothermal magnetisation shows it to be magnetically soft with low coercivity.<br></div>

Mechanochemically-Assisted Synthesis of Lead-Free Piezoelectric CaZrO3-Modified (K,Na,Li)(Nb,Ta)O3-Solid Solution

Lead-free piezoelectric 0.95(Na0.49K0.49Li0.02)(Nb0.8Ta0.2)O3–0.05CaZrO3 with 2 wt % MnO2 addition was prepared using mechanochemically-assisted solid-state synthesis. Upon mechanochemical activation of the mixture of reagents partial amorphization occurs which contributes to a significantly lower temperature of completion of the solid-state reaction, ~600 °C as opposed to ~700 °C for the conventional solid-state synthesis as determined by thermal analysis. The ceramic specimens prepared by the mechanochemically-assisted route exhibit improved compositional homogeneity and slightly enhanced piezoelectric properties, achieved in a considerably shorter processing time compared to the conventional solid-state synthesis route, which was studied as a reference.

Solid-State Synthesis and Characterization of Li7-3xGaxLa3Zr2O12 Solid Electrolyte for Li-Ion Battery Application

Conventional solid-state synthesis of Li7-3xGaxLa3Zr2O12 (LLZ) at x = 0.0 and 0.1 were performed in an attempt to investigate the microstructural and electrochemical properties of pure and Ga-doped LLZ as solid electrolyte material. The XRD patterns have shown that upon sintering at 1150°C the cubic-phased garnet LLZ were fully stabilized. Ga-doped LLZ exhibited a Li-ion conductivity up to 2.03 x 10-4 Scm-1 at 25°C. The relative densities of the pure and Ga-doped LLZ sintered at 1150°C for 15 h are 87.62% and 88.79%, respectively. This suggests that Ga dopant, even at small amount of x = 0.1, promotes densification. SEM-EDS confirmed the presence of Ga and homogenous distribution of elements in the synthesized material.

Studied on Structural Characterization of Lanthanum Doped Barium Titanium Ceramics

La-doped barium titanate (BaTiO3) was prepared using conventional solid state synthesis route. All peaks for sample x=0 are approaching the phase pure of BaTiO3 structure with tetragonal crystal structure (P4mm). Sintering of pressed powder are performed at 1300oC, 1400oC and 1450oC for overnight for pure BaTiO3 and 1350oC for 3 days for BaTiO3 doped lanthanum with intermittent grinding. Phase transition was studied by different x composition. The changes in the crystal structure of the composition x=0.1 and 0.2 were detected by using X-ray diffraction (XRD). The phase changes between tetragonal-cubic and cubic-tetragonal depending on the temperature. Rietveld Refinement analysis is carried out to determine the lattice parameter and unit cell for BaTiO3.