Intermetallic phases in the Sc–Ir–In system – synthesis and structure of Sc1.024Ir2In0.976 and Sc3Ir1.467In4

The intermetallic scandium compounds Sc1.024Ir2In0.976 and Sc3Ir1.467In4 were synthesized by reactions of the elements in sealed tantalum ampoules at high temperature followed by annealing for crystal growth. Both structures were refined from single-crystal X-ray diffractometer data: MnCu2Al type, F m 3 ‾ m $Fm‾{3}m$ , a = 639.97(19) pm, wR2 = 0.0376, 41 F 2 values, seven variables for Sc1.024Ir2In0.976 and P 6 ‾ $P‾{6}$ , a = 769.99(5), c = 684.71(4) pm, wR2 = 0.0371, 967 F 2 values, 33 variables for Sc3Ir1.467In4. Sc1.024Ir2In0.976 is a new Heusler phase with a small homogeneity range due to Sc/In and In/Sc mixing. The structure of Sc3Ir1.467In4 is closely related to that of Sc3Rh1.594In4 and belongs to the large family of ZrNiAl superstructures. The striking structural motif is the ordered stacking of empty In6 and filled Ir@In6 prisms with Ir–In distances of 269 pm.

Development of new Fe–Al–Nb(–B) alloys for structural applications at high temperatures

It is known for Fe–Al–Ta alloys, that a homogeneous distribution of strengthening Laves phase precipitates in the matrix and aligned at the grain boundaries can be obtained when the formation of the stable Laves phase is preceded by the formation of the metastable Heusler phase. Several Fe–Al–Nb alloys with different Al and Nb contents and with or without boron doping are studied to elucidate whether comparable microstructures can be obtained in this system. It was found that the Heusler phase only occurs within a limited composition range. The time-dependent evolution of the microstructure shows that the transformation proceeds faster in Fe–Al–Nb alloys. Microhardness was measured in dependence on the microstructural evolution with increasing annealing time, and compressive yield stress was determined for alloys annealed 700 °C/1000 h to evaluate the influence of microstructure and composition. Graphic Abstract

Study of the structural, electrokinetic and magnetic characteristics of the Er1-xZrxNiSb semiconductor

Peculiarities of the structural, electrokinetic, energetic, and magnetic characteristics of Er1-xZrxNiSb semiconductive solid solution, х=0–0.10, were studied. It was suggested that when Zr (4d25s2) atoms were introduced into the structure of the ErNiSb half-Heusler phase by substitution of Er (5d06s2) atoms in 4a position, Zr atoms can also simultaneously occupy the 4c position of Ni (3d84s2) atoms. As a result, in Er1-xZrxNiSb semiconductor, the structural defects of donor nature in position 4a and ones of acceptor nature in position 4c were generated simultaneously. In this case, in the band gap of Er1-xZrxNiSb, the energy states of impurity donor and acceptor bands (donor-acceptor pairs) appear and determine the electrical conductivity mechanism of the semiconductor.

Synthesis of Cu–Ti–Al-based intermetallic alloy. Structural phase analysis and electrophysical properties

For the first time, an intermetallic alloy based on the Heusler phase – Cu2TiAl – was obtained by self-propagating high-temperature synthesis (SHS) in the Cu–Ti–Al reaction mixture. The frontal combustion modes of green mixture compositions and phase formation processes during synthesis were studied. The products obtained were studied by X-ray diffraction analysis including high-temperature diffractometry with stage heating up to 900 K, scanning electron microscopy, differential thermal analysis (DTA), and some physical properties were studied. Also, electrophysical and magnetic measurements were carried out for the obtained alloy. The results of X-ray analysis and SEM using energy-dispersive analysis (EDA) showed that the Heusler phase content in the synthesized product is at least 82 %. The product also contains copper (Cu9Al4) and titanium (Ti3Al2) aluminides. The temperature dependence of the synthesized product electrical resistivity was measured for a wide temperature range of 90–1000 K, which was 0.3 μmm at T = 300 K. The metallic type of the conductivity for the samples obtained and the abnormal behavior of the electrical resistance temperature curve in the region of Т = 770÷790 K were revealed. Thermal analysis was used to measure the melting point of the synthesized product and to reveal additional heat effects at Т = 788, 848 and 1248 К associated with possible phase transitions in the Cu2TiAl intermetallic compound. A possible mechanism of phase transitions is considered in accordance with the Cu–Ti–Al system phase diagram. Magnetic measurements results showed that intermetallic samples obtained by the SHS method feature by weak ferromagnetic properties with residual magnetization of 0.069 A·m2/kg.

Phase Boundary Mapping in ZrNiSn Half-Heusler for Enhanced Thermoelectric Performance

The solubility range of interstitial Ni in the ZrNi1+xSn half-Heusler phase is a controversial issue, but it has an impact on the thermoelectric properties. In this study, two isothermal section phase diagrams of the Zr-Ni-Sn ternary system at 973 K and 1173 K were experimentally constructed based on the binary phase diagrams of Zr-Ni, Zr-Sn, and Ni-Sn. The thermodynamic equilibrium phases were obtained after a long time of heating treatment on the raw alloys prepared by levitation melting. Solubilities of x<0.07 at 973 K and x<0.13 at 1173 K were clearly indicated. An intermediate-Heusler phase with a partly filled Ni void was observed, which is believed to be beneficial to the lowered lattice thermal conductivity. The highest ZT value~0.71 at 973 K was obtained for ZrNi1.11Sn1.04. The phase boundary mapping provides an important instruction for the further optimization of ZrNiSn-based materials and other systems.

Synthesis, Structural, Electrical Transport and Energetic Characteristics of ZrNi1-хVxSn Solid Solution

The samples of ZrNi1-хVxSn solid solution (x = 0 – 0.10) based on the ZrNiSn half-Heusler phase (MgAgAs structure type) were synthesized by direct arc-melting with homogenous annealing at 1073 K. The electrokinetic and energy state characteristics of the ZrNi1-хVxSn semiconducting solid solution were investigated in the temperature range T = 80 - 400 K. An analysis of behavior of the electrokinetic and energetic characteristics, in particular, the motion rate of the Fermi level, ΔεF/Δx for ZrNi1-хVxSn, allows to assume about the simultaneous generation of the structural defects of donor and acceptor nature in the crystal. The additional researches are required to establish the mechanisms of donor generation.