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Relevant academic research and scientific papers

Investigation of the phase diagrams of the Sm-Ni-Pb and Sm-Cu-Pb systems

The phase diagrams of the Sm-Ni-Pb and Sm-Cu-Pb systems were studied using X-ray phase analysis. The Sm-Ni, Sm-Cu, Sm-Pb, Ni-Pb and Cu-Pb binary systems bounding the Sm-Ni-Pb and Sm-Cu-Pb ternary systems were also investigated. The results showed that the

On the Origin of the Negative Thermal Expansion Behavior of YCu

Among the intermetallics and alloys, YCu is an unusual material because it displays negative thermal expansion without spin ordering. The mechanism behind this behavior that is caused by the structural phase transition of YCu has yet to be fully understood. To gain insight into this mechanism, we experimentally examined the crystal structure of the low-temperature phase of YCu and discuss the origin of the phase transition with the aid of thermodynamics calculations. The result shows that the high-temperature (cubic CsCl-type) to low-temperature (orthorhombic FeB-type) structural phase transition is driven by the rearrangement of three covalent bonds, namely, Y-Cu, Y-Y, and Cu-Cu, which compete for the bonding energy and phonon entropy. At low temperatures, the mixing of Y and Cu does not take place easily because of the weak attractive force between these atoms expected from the small negative mixing enthalpy. This causes all three interactions to take part in the bonding, and Y and Cu are segregated to form an FeB-type structure, which is stabilized by internal energy. At higher temperatures, Cu ions are bound loosely with Y ions due to the large Y-Cu distance (3.01 ?), which results in large vibration entropy and stabilizes a CsCl-type crystal structure. In addition, the CsCl-type structure is reinforced by the Y-Y interaction between next-nearest neighbors, resulting in a smaller unit cell volume. The crystal structure has the simple cubic framework of Y containing Cu ions bound loosely at the cavity sites. The calculated frequency of the Y-like phonon modes is much higher than that of the Cu-like modes, indicating the presence of Y-Y covalent interactions in the CsCl-type phase.

Changing phase equilibria: A method for microstructure optimization and properties improvement in preparing anisotropic Sm2Fe17N3 powders

Sm2Fe17N3 compound possesses excellent intrinsic permanent magnet properties. Sm2Fe17N3 is usually produced by nitridation of the Sm2Fe17 alloy; however, it is difficult to avoid the formation of α-Fe and SmFe3 phases in the Sm-Fe system, which may have adverse effects on the magnetic properties of the final magnets. In this study, the three-phase region of SmCu + SmCu2+Sm2Fe17 was determined experimentally and a partial isothermal section of the Sm-Fe-Cu phase diagram at 450 °C was established. Based on this newly determined three-phase region, a parent alloy free of α-Fe and SmFe3 phases was obtained and the effects of Sm-Cu assistant phases on the microstructure and magnetic properties of nitrided powder were investigated. Anisotropic Sm2Fe17N3 powders free of α-Fe and having a high (BH)max exceeding 31 MGOe and Hcj of 13.9 kOe were obtained using a parent alloy containing 3 at.% of Sm-Cu assistant phases. The magnetization reversal process of anisotropic Sm2Fe17N3 powders with and without α-Fe was investigated and the underlying mechanisms were analyzed.

The isothermal section of the phase diagram of Sm-Cu-Mg ternary system at 670 K

The isothermal section of the Sm-Cu-Mg system at 670 K was studied in the 0-50 at.% Mg concentration range. The phase analysis was carried out by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), wavelength dispersive spectrometry (WDS) and X-ray powder diffraction (XRPD) techniques. The X-ray single crystal and powder analysis were used for structure investigations. Of the nine ternary phases (τ1-τ9) which were found to exist in this section are seven new phases, τ1 - Sm60.1Cu26.4Mg13.5, τ3 - Sm22.5Cu74.3Mg3.2, τ4 - SmCu4Mg, τ5 - SmCuMg, τ6 -SmCuMg2, τ7 - Sm81.2Cu10.3Mg8.5 and τ8 - Sm4Cu10Mg3, and two known phases, τ2 - Sm2Cu2Mg and τ9 - SmCu9Mg2. As the result of our investigation the crystal structures of τ2, τ4, τ5, τ6 and τ8 phases have been established. Moreover, it has been found that the solubility of Mg and Cu in Sm-Cu and Sm-Mg binary phases, respectively, is insignificant, and that the maximum solubility takes place in the case of Cu2Mg phase, which dissolves up to 5 at.% Sm.