Transport Properties Of Solid Solutions Research Articles

Molecular Dynamics Simulation of Structural and Transport Properties of Solid Solutions of Double Perovskites Based on PrBaCo2O5.5

The oxygen diffusion has been simulated by the molecular dynamics method in the solid solutions of PrBaCo2O5.5-based double perovskites: PrBa0.5Sr0.5Co2O5.5 with random substitution of half of Ba atoms by Sr atoms, PrBa0.5Sr0.5CoFeO5.5 with random substitution Ba → Sr and Co → Fe, PrBa0.5Sr0.5CoCuO5.5 with random substitution Ba → Sr and Co → Cu, and PrBa0.5Sr0.5CuFeO5.5 with random substitution Ba → Sr and random substitution of Co atoms by Fe and Cu atoms. It is shown that, varying the oxygen nonstoichiometry and/or chemical composition of solid solutions based on PrBa0.5Sr0.5Co2O5.5, one can significantly change the coefficient of thermal expansion of the materials. It is established for the first time that the maximum difference between the mobilities of oxygen atoms of different types observed in PrBa0.5Sr0.5Co2O5.5 significantly decreases at partial substitutions of cobalt by iron and copper. In the PrBa0.5Sr0.5CuFeO5.5 solid solution, the oxygen atom mobility in the (Cu,Fe)–O layers becomes somewhat higher than that in the Pr–O layers.

Transport properties of solid solutions of хKYF4–(1–х)PbF2 system

In the system (1–x)PbF2–x YF3–x KF, solid solutions of aliovalent substitution with fluorite structure at 0.47 < x < 0.69 are formed, in which the fluorine ions are found to be in three structurally nonequivalent positions that differ in the local environment and mobility. There are immobile, locally mobile, and highly mobile anions. The conductivity of the synthesized polycrystalline samples is ensured by highly mobile interstitial fluoride ions, whose concentration and hence electrical conductivity increase on heating. The contribution of the surface conductivity of crystallites is not detected. The electronic component is two orders of magnitude lower than the ionic one.

Transport properties of solid solutions PbF2–SnF2–SbF3 prepared by solid state techniques

The ionic mobility and electrical conductivity in solid solutions with the fluorite structure obtained by the solid-phase method in the system PbF2–SnF2–SbF3 with composition close to PbSnF4 have been investigated using the methods of 19F NMR and impedance spectroscopy. It has been established that parameters of 19F NMR spectra, types of ionic motions in the fluoride sublattice and the value of ionic conductivity are determined by temperature and the composition of the solid solutions. Transport properties of solid solutions under study are similar to those of tetragonal phase β-PbSnF4. It suggests that fluorite phase in solid solutions under study is metastable and formed by elementary fluorite-type blocks typical of the structure of β-PbSnF4. Introduction of Sb3+ into the structure leads to decrease in the conductivity. Nevertheless, the specific conductivity of solid solutions in the system and PbF2–SnF2–SbF3 at 400K attains the values of 10−2–10−3S/cm, which enables one to consider them as promising materials for electrochemical applications.

Magnetic and anomalous electronic transport properties of the quaternary Heusler alloys Co2Ti1−xFexGe

The half-metallic Heusler alloy Co2TiGe has a ferromagnetic ground state with a low magnetic moment (2μB). It is free of atomic antisite disorder but has low Curie temperature (~390K). In contrast the other cobalt based Heusler alloy Co2FeGe has high Curie temperature (~980K) and high magnetic moment (5.6μB) while exhibiting antisite disorder and lack of half-metallicity. Hence it is of interest to investigate the magnetic and transport properties of solid solutions of these two materials with contrasting characteristics. We report the structural, magnetic and electronic transport properties of quaternary Co2Ti1−x FexGe (x=0.2, 0.4, 0.6, 0.8) Heusler alloys. The alloys crystallize in L21 structure but with antisite disorder. The magnetization measurements revealed that the alloys were of soft ferromagnetic type with high Curie temperatures. Deviation from Slater-Pauling behavior and drastic change in electronic transport properties with some anomalous features were observed.The complex electronic transport properties have been explained using different scattering mechanisms.

Synthesis processes and transport properties of solid solutions in the Bi2O3-GeO2-V2O5 system

The results of studies of solid solutions with the overall composition of Bi4V2 − xGexO11 − δ and Bi4Ge3 − xVxO12 + δ are presented. The process of phase formation are studied during the synthesis of solid solution using the ceramic method and through liquid precursors. Crystallochemical parameters of the obtained compounds are determined. The size distribution of the particles is studied. Conductivity of annealed of polycrystalline samples as a function of temperature and composition is studied using the impedance spectroscopy method. The shape of impedance complex plane plots of the samples obtained in different ways is studied and analyzed.

Influence of point-defect scattering on the lattice thermal conductivity of solid solutionCo(Sb1−xAsx)3

We have investigated the transport properties of solid solutions of skutterudites based on $\mathrm{Co}{({\mathrm{Sb}}_{1\ensuremath{-}x}{\mathrm{As}}_{x})}_{3}$. Homogeneous solid solutions were prepared with As content $x\ensuremath{\leqslant}0.1$. The influence of point-defect scattering on the lattice thermal conductivity has been studied in detail. The lattice thermal conductivity decreases with the increasing content of As at all temperatures from $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}700\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Theoretical analysis indicates that the reduction of the lattice thermal conductivity with increasing As concentration can be explained by the enhanced point-defect scattering due to mass fluctuations and strain field fluctuations as As atoms substitute on the Sb sublattice.

Oxygen in the Earth's core: a first-principles study

First-principles electronic structure calculations based on DFT have been used to study the thermodynamic, structural and transport properties of solid solutions and liquid alloys of iron and oxygen at Earth's core conditions. Aims of the work are to determine the oxygen concentration needed to account for the inferred density in the outer core, to probe the stability of the liquid against phase separation, to interpret the bonding in the liquid, and to find out whether the viscosity differs significantly from that of pure liquid iron at the same conditions. It is shown that the required concentration of oxygen is in the region 25–30 mol%, and evidence is presented for phase stability at these conditions. The Fe/O bonding is partly ionic, but with a strong covalent component. The viscosity is lower than that of pure liquid iron at Earth's core conditions. It is shown that earlier first-principles calculations indicating very large enthalpies of formation of solid solutions may need reinterpretation, since the assumed crystal structures are not the most stable at the oxygen concentration of interest.