Electron Diffraction Study of the Space Group Variation in the Al–Mn–Pt T-Phase

Binary high temperature “Al3Mn” (T-phase) and its extensions in ternary systems were the subjects of numerous crystallographic investigations. The results were ambiguous regarding the existence or lack of the center of symmetry: both Pna21 and Pnam space groups were reported. Our research on the Al–Mn–Pt T-phase allowed concluding that inside a continuous homogeneity region, the structure of the Al-rich T-phase (e.g., Al78Mn17.5Pt4.5) belongs to the non-centrosymmetric Pna21 space group, while the structure of the Al-poor T-phase (such as Al71.3Mn25.1Pt3.6) is centrosymmetric, i.e., Pnam. Following metallurgical and crystallographic considerations, the change in the symmetry was explained.

Calculation of the nonstoichiometry area of nanocrystalline palladium (II) oxide films

Nanocrystalline palladium (II) oxide films were synthesised using thermal oxidation in the oxygen atmosphere of the initial ultradispersed metal palladium layers with a thickness of ~ 35 nanometres that were obtained on SiO2/Si (100) substrates using the method of thermal sublimation in high vacuum. Using X-ray analysis, it was established that during thermal oxidation in the oxygen atmosphere within the temperature range T = 670–970 K the values of the a and c parameters of the tetragonal lattice as well as the unit cell volume of nanocrystalline PdO films increased monotonously with the rise of the temperature reaching the maximum values at T = 950–970 K. It was found that the parameters of the tetragonal lattice and the unit cell volume of nanocrystalline PdO films decreased as the oxidation temperature increased up to T > 970 KBased on the ratio of the c/a parameters, it was shown that the main contribution to the deformation phenomena of the tetragonal lattice were mostly due to the increase in the elementary translations along the coordination axes OX and OY. Based on an assumption that the ionic component of the chemical bond is essential to the palladium (II) oxide structure, we suggested a method for the calculation of the range of the nonstoichiometry area for nanocrystalline PdO films, using the reported data on the radii of cation Pd2+ and anion O2- taking into account their coordination environment. The results of the calculations showed that nanocrystalline PdO films synthesised with an oxygen pressure of ~ 105 kPa are characterisedby the two-sided homogeneity region in relation to the stoichiometric ratio of the components. The homogeneity region of nanocrystalline PdO films is characterised by the retrograde solidus line in the range of the temperatures T = 770–1070 K.

Variants of the X-phase in the Mn–Co–Ge system

We report two new variants of the X-phase (orthorhombic, space group Pnnm) derived from the Mn–Co–Ge system. Two compositionally related crystals were investigated by means of single-crystal X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The Mn14.9Co15.5Ge6.6 and Mn14Co16.2Ge6.8 intermetallic compounds are part of the homogeneity region of the X-phase and adopt the Mn14(Mn0.11Co0.64Si0.25)23 structure type. The composition obtained from refinement of the XRD data is in agreement with the EDS results. In the present study, chemical disorder was only detected on the 8h positions. The ordering is compared with other members of the X-phase family and shows that the degree of disordering depends on the chemical composition. No completely ordered variants of the X-phase have yet been reported.

Effect of zinc doping on electrical properties of LaAlO3 perovskite

New solid solution with the general formula of LaAl1-xZnxO3-1/2x was prepared by a solid-state reaction route. According to XRD, the crystal structure of LaAlO3 is rhombohedral, while the solid solution possesses cubic symmetry. Homogeneity region of the solid solution LaAl1-xZnxO3-1/2x was narrow and limited to the maximum concentration of 5 mol. %. Computer simulations using crystalochemistry and density functional theory approaches showed that LaAlO3 has high energy barriers for O2–-ion transport (2.79 eV). These results are in good agreement with the low values of electrical conductivity obtained experimentally. The electrical conductivity of LaAl1-xZnxO3-1/2x was measured by impedance spectroscopy in the temperature range of 200–1000 °C. The partial substitution of Al3+ by Zn2+ was found to increase the electrical conductivity by ~2 order of magnitude. The electrical conductivity of doped phase LaAl0.95Zn0.05O2.975 as a function of oxygen partial pressure was measured, and the partial contributions (oxygen-ionic and electronic) were determined. It was found that the sample has mixed ionic and p-type electronic conductivity, while the electronic contribution increases with the rise of the temperature.

Yttrium effect on the structural-phase state in situ of Mo – 15.3 V – 10.5 Si composite

The effect of yttrium on the structural-phase state of the Mo – 15.3 V – 10.5 Si hypereutectic alloy has been investigated using X-ray phase analysis and scanning electron microscopy with energy-dispersive X-ray analysis. It has been established that the main phases of Mo – (14.3 – 15.4) V – (9.8 – 10.6) Si – (0.3 – 5.3) Y alloys obtained under nonequilibrium crystallization are the metal solid solution (Mo1 – xVx)ss-matrix, silicide solid solution (Mo1 – xVx)3Si and silicide Y5Si3. In alloys doped with yttrium up to 1.0 at. %, the space between the dendrites of the (Mo1 – xVx)ss metal phase is filled with (Mo1 – xVx)3Si solid solution, and Y5Si3 is located at the boundaries of the metal solid solution. At a concentration of yttrium in alloys above 3.0 at. % the space between (Mo1 – xVx)ss dendrites is filled with Y5Si3 silicide, inside which (Mo1 – xVx)3Si grains are formed. Triple or quaternary compounds containing yttrium were not detected. Elemental composition of alloy phases of the Mo – (14.3 – 15.4) V – (9.8 – 10.6) Si – (0.3 – 5.3) Y alloys is almost identical and is characterized by non-stoichiometry with respect to silicon. According to well-known literature data, the silicon contents in the (Mo1 – xVx)ss and (Mo1 – xVx)3Si phases are within the acceptable limits of the homogeneity region, and the silicon concentration in Y5Si3 (≈ 35.4 at.%) is beyond the established limits. Doping of the Mo – 15.3 V – 10.5 Si alloy with yttrium increases the dispersion of the structure. Particles of the main structural components become close in size. Wherein the volume ratio of the metallic phase to the silicide with increasing yttrium content in the alloys increases. The density of alloys varies between 8.7 – 9.0 g/cm3.

Er-Cr-Ge Ternary System

The isothermal section of the phase diagram of the Er–Cr–Ge ternary system was constructed at 1070 K over the whole concentration range using X-ray diffractometry, metallography and electron microprobe (EPM) analysis. The interaction between the elements in the Er−Cr−Ge system results in the formation of two ternary compounds: ErCr6Ge6 (MgFe6Ge6-type, space group P6/mmm, Pearson symbol hP13; a = 5.15149(3), c = 8.26250(7) Ǻ; RBragg = 0.0493, RF = 0.0574) and ErCr1-хGe2 (CeNiSi2-type, space group Cmcm, Pearson symbol oS16, a = 4.10271(5), b = 15.66525(17), c = 3.99017(4) Ǻ; RBragg = 0.0473, RF = 0.0433) at investigated temperature. For the ErCr1-xGe2 compound, the homogeneity region was determined (ErCr0.28-0.38Ge2; a = 4.10271(5)-4.1418(9), b = 15.6652(1)-15.7581(4), c = 3.99017(4)-3.9291(1) Ǻ).

Limited solid solution Li(Ni0,33Mn0,33Co0,33)1-xFexO2 with structure α-NAFEO2

In the framework of this work, the compositions Li (Ni0.33Mn0.33Co0.33)1-xFexO2 (0 ≤ x ≤ 1) of the tetrahedron LiNiO2-LiMnO2-LiCoO2-LiFeO2 were investigated. The samples were synthesized by the gel combustion method with starch. For the first time it was obtained without admixtures LiNi0.2Mn0.2Co0.2Fe0.4O2 solid solution with a layered crystalline structure a-NaFeO2, which can be used as a cathode material of lithium-ion batteries. An electrochemical testing of the homogeneous sample LiNi0.2Mn0.2Co0.2Fe0.4O2 and the sample with a minimum iron content LiNi0.3Mn0.3Co0.3Fe0.1O2 was conducted. The results show feasibility of further studying the homogeneity region and the properties of the solid solution Li (Ni, Mn, Co, Fe)O2.

About the crystalline structure of vanadates Ca1.5±0.1Mn0.5±0.1V2O7 and Ca1.5Cd0.5V2O7

The crystal structures of Ca1.5Mn0.5V2O7 (I) and Ca1.5Cd0.5V2O7 (II) synthesized by the citrate method and by a conventional solid-state reaction, respectively, were determined using X-ray powder diffraction data. It was found that the compound I has a monoclinic crystal structure a = 4.88563(9) Å, b = 11.21279(22) Å, c = 5.69643(11 Å), β = 96.376(7)°, V = 310.132(10) Å3 (space group P21/c), Z = 2). Compound I has a narrow homogeneity region Ca1.5±0.1Mn0.5±0.1V2O7. The vanadate Ca1.5Cd0.5V2O7 crystallizes in the triclinic system with the parameters a = 6.66139(6) Å, b = 6.93019(7) Å, c = 7.02211(6) Å, α = 85.4404(9)°, β = 63.7505(7)°, γ = 82.5515(10)° и V = 288.201(5) Å3 (space group P$\bar 1$, Z = 2). It is one of the formulations of the primary solid solution, formed as a result of the substitution of part of the calcium cations for cadmium cations in Ca2V2O7.