Influence of Powder Milling and Annealing Parameters on the Formation of Cubic Li7La3Zr2O12 Compound

Li-ion batteries are widely used as energy storage devices due to their excellent electrochemical performance. The cubic Li7La3Zr2O12 (c-LLZO) compound is regarded as a promising candidate as a solid-state electrolyte for lithium-ion batteries due to its high bulk Li-ion conductivity, excellent thermal performance, and chemical stability. The standard manufacturing procedure involves the high-temperature and lengthy annealing of powders. However, the formation of the tetragonal modification of LLZO and other undesired side phases results in the deterioration of electrochemical properties. The mechanical milling of precursor powders can enhance the powders’ reactivity and can result in an easier formation of c-LLZO. The aim of this work was to study the influence of selected milling and annealing parameters on c-LLZO compound formation. The starting powders of La(OH)3, Li2CO3, and ZrO2 were subjected to milling in various ball mills, under different milling conditions. The powders were then annealed at various temperatures for different lengths of times. These studies showed that the phase transformation processes of the powders were not very sensitive to the milling parameters. On the other hand, the final phase composition and microstructure strongly depended on heat treatment conditions. Low temperature annealing (750 °C) for 3 h produced 90% of c-LLZO in the powder structure.

Investigation of the influence of the mode of heat treatment of the initial powder on the efficiency of sintering zirconium ceramics by dilatometry

Using methods of synchronous thermal and X-ray structural analyzes applied to zirconium dioxide powders partially stabilized with yttrium obtained by chemical coprecipitation the processes of dehydration of these powders during annealing in air have been investigated. Using the dilatometry method, the regularities of compaction of powder compacts have been investigated with thermal sintering. It was found that the resulting powders mainly consist of the tetragonal modification zirconium dioxide and are nano-sized. The average particle size was 25 nm. The resulting powders are characterized by a high degree of agglomeration. It is shown that an increase in the thermal annealing temperature from 500 to 700ºС leads to partial baking of individual particles inside the agglomerate, and causes the formation of hard agglomerates, the presence of which complicates the processes of compaction and subsequent sintering. The presence of such agglomerates prevents the production of ceramics with high mechanical characteristics: density and porosity. Thermal annealing temperature increase leads to a decrease in the density of the sintered ceramic and a decrease in its hardness.

Single-crystal structures of A 2SiF6 (A = Tl, Rb, Cs), a better structure model for Tl3[SiF6]F, and its novel tetragonal polymorph

We report on the syntheses and single-crystal structure determinations of the compounds A 2SiF6 (A = Tl, Rb, Cs). In comparison to the previous powder-based structure models we achieved more precise atom positions and distances. The compounds crystallize in the K2PtCl6 structure type, space group Fm 3 ‾ $‾{3}$ m (No. 225, cF36) with a = 8.4749(10) Å, V = 608.7(2) Å3, Z = 4 at T = 100 K for Tl2SiF6, a = 8.3918(10) Å, V = 591.0(2) Å3, Z = 4 at T = 100 K for Rb2SiF6, and a = 8.8638(11) Å, V = 696.4(3) Å3, Z = 4 at T = 200 K for Cs2SiF6. For the compound Tl3[SiF6]F we present a previously unknown tetragonal modification and correct the crystal structure of its trigonal modification to hexagonal. The tetragonal one crystallizes in the (NH4)3[SiF6]F structure type, space group P4/mbm (No. 127, tP22) with a = 8.0313(8), c = 5.8932(6) Å, V = 380.13(7) Å3, Z = 2, T = 298 K, and the crystal structure of the hexagonal modification is best described in space group P63 mc (No. 186, hP22) with a = 7.8248(4), c = 6.8768(4) Å, V = 364.64(4) Å3, Z = 2, T = 100 K.

Electronics of Anion Hot Injection-Synthesized Te-Functionalized Kesterite Nanomaterial

Metal chalcogenides such as copper zinc tin sulfide (CZTS) have been intensively studied as potential photovoltaic cell materials, but their viability have been marred by crystal defects and low open circuit potential (Voc) deficit, which affected their energy conversion efficiency. Strategies to improve on the properties of this material such as alloying with other elements have been explored and have yielded promising results. Here, we report the synthesis of CZTS and the partial substitution of S with Te via anion hot injection synthesis method to form a solid solution of a novel kesterite nanomaterial, namely, copper zinc tin sulfide telluride (CZTSTe). Particle-size analyzed via small angle X-ray scattering spectroscopy (SAXS) confirmed that CZTS and CZTSTe materials are nanostructured. Crystal planes values of 112, 200, 220 and 312 corresponding to the kesterite phase with tetragonal modification were revealed by the X-ray diffraction (XRD) spectroscopic analysis of CZTS and CZTSTe. The Raman spectroscopy confirmed the shifts at 281 cm−1 and 347 cm−1 for CZTS, and 124 cm−1, 149 cm−1 and 318 cm−1 for CZTSTe. High degradation rate and the production of hot electrons are very detrimental to the lifespan of photovoltaic cell (PVC) devices, and thus it is important to have PVC absorber layer materials that are thermally stable. Thermogravimetric analysis (TGA) analysis indicated a 10% improvement in the thermal stability of CZTSTe compared to CZTS at 650 °C. With improved electrical conductivity, low charge transfer resistance (Rct) and absorption in the visible region with a low bandgap energy (Eg) of 1.54 eV, the novel CZTSTe nanomaterials displayed favorable properties for photovoltaics application.

ISOTHERMAL SECTION STRUCTURE THE ZrO2-La2O3-Gd2O3 SYSTEM AT 1500 °С

Using the methods of physicochemical analysis (XRD, petrography, scanning electron microscopy analyses) phase equilibria were firstly investigated in the ternary system ZrO2–La2O3–Gd2O3 system at 1500 ºС. It was established that in the system there exist fields of solid solutions based on hexagonal (A) modification of La2O3 and cubic with fluorite-type structure (F) and tetragonal (Т) modification ZrО2 , cubic (С) and monoclinic (M) modification Gd2O3 and ordered intermediate phase with pyrochlore-type structure lanthanum zirconate La2Zr2O7 (Py). No new phases were found. The refined lattice parameters of the unit cells for solid solutions for the systems were determined. In the zirconia-rich corner, the solid solutions based on tetragonal modification of ZrO2 are formed. The phase field T-ZrO2 is narrow and elongated (0–18 mol% CeO2) along the ZrO2–CeO2 side of the binary system. The solubility of La2O3 in the T-ZrO2 is low and amounts to ~ 0.5 mol%, as evidenced by XRD analysis results. It is worth noting that the solid solutions based on tetragonal modification of zirconia cannot be quenched from high temperatures due to low stability of T-ZrO2 under cooling with furnace conditions. The diffraction patterns recorded at room temperatures included the peaks of monoclinic phase M-ZrO2. The homogeneity field of solid solution based on A-La2O3 extends to 31 mol% Gd2O3 and 12 mol% ZrO2 in the corresponding binary systems and locates near the composition 6,7 mol % ZrO2–90 mol% La2O3–3.3 mol% Gd2O3 on the section La2O3–(67 mol % ZrO2–33 mol % Gd2O3). It should be noted that the samples with a higher lanthanum oxide content after annealing and cooling rapidly absorb water in humid air and become hydrated. Hence, according to XRD, the hexagonal A-La(OH)3 modification forms instead of the hexagonal A-La2O3 phase. The lattice parameters for A-La(OH)3 phase vary from а = 0.6513 nm, c = 0.3847 nm the sample containing 3.35 mol % ZrО2–95 mol % La2O3–1.65 mol % Gd2O3 to а = 0.6508 nm, c = 0.3847 nm in the two-phase sample (Py+А ) containing 6.7 mol % ZrО2–90 mol % La2O3–3.3 mol % Gd2O3 and to а = 0.6477 nm, c = 0.3725 nm in the three-phase sample (Py+F+А) containing 40.2 mol % ZrО2–40 mol % La2O3–19.8 mol % Gd2O3 The isothermal section of the ZrO2–La2O3–Gd2O3 system at 1500°C contains four three-phase regions (F+Py+A, F+B+A, F+C+B, T+F+Py) and ten two-phase regions (Py+A, A+F, A+B, F+B, B+C, C+F, F+Py, Py+T, T+F, Py+F).

Effect of Al2O3 nanofibers on compaction, phase composition, and mechanical properties of ZrO2-based composites obtained by vacuum pressureless sintering

This work studies the effect of the relative content of Al2O3 nanofibers on the compaction, phase composition, and physicomechanical properties of composites based on ZrO2 obtained by free vacuum sintering. It was found that in the process of manufacturing composites, nanofibers are sintered into Al2O3 grains of complex, elongated shape, which form a solid, frame-reinforcing structure. The relative density of composites with 5 wt. % and 10 wt. % of nanofibers, decreases up to 95%. It is shown that in all sintered samples the tetragonal modification of ZrO2 acts as the main phase, and the different content of nanofibers affects the amount of cubic and monoclinic modifications of ZrO2. It was found that addition of 5 wt. % and 10 wt. % of Al2O3 nanofibers increases the microhardness of the composite by 11% and crack resistance by 46%.

EFFECT OF MODIFYING ZIRCONIUM OXIDE ADDITIVE ON THE PROPERTIES OF CERAMIC MATERIALS OF THE Y2O3–Al2O3–SiO2 SYSTEM OBTAINED BY THE SOL-GEL METHOD

The effect of the modifying additive ZrO2 on the rheological properties, the processes of structure and phase formation of the compositions of the Y2O3–Al2O3–SiO2 system obtained by the sol-gel method has been investigated. It was found that the temperature range of crystallization of the compositions of the Y2O3–Al2O3–SiO2 system with the addition of ZrO2 is 1020–1270 °C and with an increase in the concentration of zirconium oxide, the amount of the main crystalline phase of yttrium pyrosilicate (β-Y2Si2O7) decreases and the concentration of the zirconium-containing phase – the tetragonal modification of zirconium oxide and zirconium silicate ZrSiO4 -increases.

Ternary Aluminides of a New Homologous Series—CePt2Al2 and CePt3Al3: Crystal Structures and Thermal Properties

In the process of studying the Ce–Pt–Al system, we identified CePt2Al2 and CePt3Al3, two new ternary intermetallic compounds. CePt2Al2 aluminide undergoes a structural phase transition from a low-temperature orthorhombic modification (of its own structure type, Cmme, a = 5.84138(2) Å, b = 6.39099(3) Å, c = 10.11611(5) Å) to a high-temperature tetragonal modification (CaBe2Ge2 type, P4/nmm, a = 4.3637(9) Å, c = 10.0925(14) Å) at 280(1) °C. CePt3Al3 crystallizes with a new type of structure (Cmme, a = 6.36548(6) Å, b = 5.78301(6) Å, c = 13.36245(19) Å) built of structural units of low-temperature orthorhombic CePt2Al2-type and CsCl-type.

Study of Structural and Catalytic Properties of Pt/WOх/ZrO₂, Modified by Lanthanum Cations

The effect of the addition of La3+ cations on the structural properties of Pt/WOх/ZrO₂ catalysts and the characteristics of catalytic activity in the process of hydroisomerization of n-heptane and benzene mixture was studied. The phase composition of the catalysts is represented by a solid solution of lanthanum cations in nanocrystalline zirconia of tetragonal modification with localization of lanthanum in the surface layers predominantly. The positive effect of La3+ additives on the selectivity and yield of isomerized products was shown

Оптические свойства кристаллов (ZrO-=SUB=-2-=/SUB=-)-=SUB=-1-x-=/SUB=-(Y-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-)-=SUB=-x-=/SUB=- (x=0-0.037), полученных направленной кристаллизацией расплава

The luminescent and optical properties of materials based on zirconium oxide obtained by the crystallization of ZrO2 with 0, 2.0, 2.5, 2.8, and 3.7% mol Y2O3 melts were studied. Using Raman spectroscopy, it was found that when the Y2O3 content in the mixture is less than 2 % mol. the material is predominantly a monoclinic ZrO2 structure. For such crystal, a blue-green band with the maximum energy of 2.4 eV was observed in the photoluminescence spectra. This fact, together with the peculiarities of the refractive index and absorption dispersion spectra, indicates the presence of a high concentration of oxygen vacancies and polyvacancies in the sample. With a higher content of Y2O3 in the mixture, the tetragonal modification of ZrO2 dominates in the studied materials; the intensity of blue-green luminescence decreases. A comparative analysis of experimental optical spectra with the first-principle calculations for ideal ZrO2 crystals in the cubic, tetragonal and monoclinic phases was performed.