Due to specific highly distorted crystalline structure, high-entropy alloys (HEAs) are expected to demonstrate interesting behavior under high pressures. However, this issue is not yet well studied. ...Here we address pressure effects on electronic structure and electrical conductivity of TiZrHfNb alloy. Among the multiplicity of single-phase HEAs explored so far, the TiZrHfNb one is an exemplar of thermally stable metallic material that crystallizes into body-centered cubic (BCC) structure and demonstrates excellent mechanical, corrosion, and friction properties compared to conventional alloys. We synthesize this material with BCC structure and analyze its electrical, superconducting, and magnetic properties. The alloy is a Curie-Weiss paramagnet and a type-II superconductor with the critical temperature of about 6.3 K. The estimated upper critical field and critical current density in the HEA are rather moderate compared to those observed in the superconductors based on Ti–Nb alloys. In the normal state, the alloy demonstrates high electrical resistance that practically independent of temperature but significantly dependent on pressure; it decreases linearly by 12.5% as the pressure increases up to 5.5 GPa. By analyzing the experimental data, we suggest that alloy resistance is mainly determined by two contributions: the residual resistance and Mott's s-d scattering. We show that a cooperative effect from changes in both the Debye temperature and electronic band structure near the Fermi level are the main factors responsible for the electrical resistance behavior of the HEA under pressure. Ab initio calculations performed at different pressures support this conclusion. The results show that TiZrHfNb alloy is a promising material for designing resistance pressure gauges.
•Electrical, superconducting and magnetic properties of TiZrHfNb HEA are analyzed.•Electrical resistivity decreases by 12.5% in the pressure range of 0–5.5 GPa.•The electronic structure of the HEA is examined via ab initio calculations.•Pressure behavior of resistivity is determined by variations in DOS and Debye parameter.•The HEA can be considered as a promising material for designing pressure/strain gauges.
Development of magnetic cooling technology needs effective and suitable solid state refrigerants whose properties meet rigorous functional and market requirements. One of the important issues ...hindering progress in this field is the lack of a clear understanding of the mechanisms underlying the giant magnetocaloric effect that some materials demonstrate. Considering systems based on one magnetic component seems to be a promising and effective way to unraveling this puzzle. This study is aimed at partially filling this gap by inspecting the magnetic and magnetocaloric properties of a series of GdSc alloys containing up to 25 at.% Sc. It has been established that all obtained alloys form single-phase disordered solid solutions with an hexagonal closed-packed crystal lattice. We found that doping with scandium induces strong distortion effects in the crystal structure due to huge atomic size mismatch. The studied GdSc alloys are ultra-soft ferromagnets with high Curie points. The magnetocaloric response in the alloys is not large in magnitude compared to Gd but the magnetocaloric effect (MCE) extends over a wide temperature interval exceeding 135 K, resulting in the relative cooling power of 930 – 986 J/kg in a magnetic field of 5 T. Such behavior in the MCE is associated with the strongly distorted crystalline structure which provokes complicated magnetic exchange correlations. High density of structural defects in GdSc alloys, induced by large atomic size mismatch, is probably the determining factor in improving the refrigerant capacity.
•The magnetic and magnetocaloric properties of a series of GdSc alloys are studied.•The fabricated materials are single-phase solid solutions with an HCP structure.•The alloys are ultra-soft ferromagnets with high Curie points.•The relative cooling power in the materials reaches values of 930 – 986 J/kg at 5 T .
Magnetic energy conversion systems based on magnetocaloric effect promise to be an efficient and eco-friendly alternative to widespread gas cooling systems. Progress in this field initiates an active ...search for high-performance magnetic refrigerants with suitable characteristics. Among various caloric materials, rare-earth multi-principal element alloys are of particular interest to achieve these purposes. Since structure and properties in these materials strongly depend on synthesis conditions and fabrication prehistory, these issues need to be considered for each multi-element systems. This study is aimed to address structure formation, magnetic and magnetocaloric properties in ScGdTbDyHo high-entropy alloy fabricated under different conditions. We analyze the liquid and solid phases in this system using the ab initio molecular dynamics simulations and find that the alloy has a strong tendency to form a single-phase solid solution. Within the experimental study, as-cast, rapidly quenched, thermally annealed and severely cold-deformed alloy samples have been examined. We have found that all the fabricated specimens are single-phase hexagonal close-packed solid solutions characterized by different density of structural defects. The magnetic measurements reveal a complex magnetic structure in these materials. The Neel point in the studied alloys varies in the range of 139–144 K. A field-induced metamagnetic transition from antiferromagnetic to ferromagnetic state is observed in the alloy samples at all temperatures below the Neel point. In the magnetically ordered state, all the materials demonstrate large coercive force, reaching 4 kOe. Despite of the magnetic hysteresis, the alloys demonstrate the largest values of relative cooling power (920–984 J/kg at 5 T magnetic field) among similar rare-earth high-entropy systems reported so far. Analysis of the experimental results obtained for the alloy samples fabricated under different synthesis conditions allows us to conclude that there is a correlation between structural defectiveness and refrigerant capacity in this rare-earth system.
•The liquid and solid phases in the system are analyzed with the ab initio molecular dynamics simulations.•The fabricated materials are single-phase solid solutions with HCP crystalline structure.•The alloys exhibit a complex magnetic structure and a pronounced field-induced metamagnetic transition.•The relative cooling power in the alloys reaches values of 920–984 J/kg at 5 T magnetic field.•A correlation between structural defectiveness and the refrigerant capacity is revealed.
Volumetric characteristics of high-entropy alloys (HEAs) are among the main ones when considering possible practical applications of these materials. Low specific gravity is an important parameter ...providing the use of these alloys in industry. Density of AlNiCoCuZr HEAs with different component ratios has been experimentally investigated in the present work in a wide temperature range, including liquid state. Molar volume in liquid state and temperature coefficients of expansion in full temperature range (from room temperature up to 1800 K) were calculated basing on the experimental data. Structure of the alloys and thermal reactions during heating and cooling were studied. Two BCC - solid solutions, as well as solution based on (half)-Heusler phase ZrNi2Al were found. The presented results can provide a basis for further experimental study of AlNiCoCuZr HEAs and numerical modeling of their properties.
•Al–Ni–Co–Cu–Zr high-entropy alloys were synthesized.•Structure and phase composition of AlNiCoCuZr HEAs were determined.•Density of AlNiCoCuZr HEAs in solid and liquid states was studied experimentally.
We study the structural, magnetic, and optical properties of double manganites LnBaMn
2
O
6
with Ln = Pr, Nd, Sm, Nd
1 –
x
Sm
x
(
x
= 0.25, 0.5, 0.75). Analysis of the temperature dependences of ...transmission in the near IR range has shown the difference in the responses of the charge subsystem for different types of charge/orbital ordering in the system. In PrBaMn
2
O
6
manganite, the orbital ordering of the
type leads to an insulator state at low temperatures. The charge subsystem of manganites NdBaMn
2
O
6
, Nd
0.75
Sm
0.25
BaMn
2
O
6
, and Nd
0.5
Sm
0.5
BaMn
2
O
6
is sensitive to the orbital ordering type: in the temperature interval
T
CO2
<
T
<
T
CO1
, where pairwise alignment of layers with
/
ordered orbitals is realized, the semiconductor character of charge carriers is observed, while upon a transition to the layer-by-layer alignment of orbitally ordered layers for
T
<
T
CO2
, charge carriers are of the metal character. In manganites Nd
0.25
Sm
0.75
BaMn
2
O
6
and SmBaMn
2
O
6
, the absence of clearly manifested metal nature of the charge subsystem at
T
<
T
CO2
is associated with the formation of the antiferromagnetic ordering of the CE type.
Equiatomic Al–Ni–Co–Cu–Zr alloy was produced by arc melting. Rapidly quenched rods were prepared by suction casting method. Density, electrical resistivity and thermal analysis of the alloy were ...investigated experimentally. Basing on X-ray diffraction it was shown that the structure of the alloy consists of two competing solid solutions: BCC-ZrNi2Al (Heusler-type phase) and γ-phase Cu9Al4. In addition, pure cooper and Cu3Al, Cu5Zr7Ni5 intermetallic compounds were determined. Rapid quenching of this alloy leads to the formation of solid solutions based on BCC-ZrNi2Al and high-temperature Cu3Al phase. It is shown that the alloy in crystalline state has a linear density change up to solidus temperature. A region of resistivity decrease with increasing temperature is found out for the first time. The melting process goes in a wide temperature range (above 250 K) where 4 thermal reactions were detected. Density and electrical resistivity changes here non-linearly. In liquid state there are no thermal effects in the alloy and temperature dependencies of density and electrical resistivity can be fitted by linear functions.
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•A novel AlNiCoCuZr equiatomic alloy was synthesized.•Rapidly quenched bulk AlNiCoCuZr samples were prepared by vacuum suction method.•Structure and phase composition of Al20Ni20Co20Cu20Zr20 alloy was determined for the first time.•Density, electrical resistivity and DSC of AlNiCoCuZr alloy were investigated experimentally.
The study investigated the dependences of the structural, magnetic, and optical properties of double manganites NdBaMn
2
O
6
on the degree of order of Nd and Ba atoms in the A-position. Analysis of ...the temperature dependences of light transmission showed the changes of the charge carrier subsystem in the region of structural and magnetic phase transitions. If there was a metal–insulator transition, the magnetotransmission near the Curie temperature was detected.
Metallic glasses are of permanent fundamental and technological interest due to their unique functional properties. Why does one alloy composition tend to vitrify while another one does not? What are ...the reasons underlying the glass formation mechanisms responsible for the existence of pinpoint compositions in metallic systems? All these questions still remain among the principal and complex issues that need to be addressed for a deeper understanding of the physical processes that determine the glass-forming ability in various alloy systems. Despite decades of intensive research, so far there are no reliable and physically substantiated methods capable of predicting narrow composition ranges of easy vitrification in multi-element alloys. In this study, we propose a phenomenological approach for predicting glass formers, which implies that a glass-forming alloy in its equilibrium crystalline state is a mixture of intermetallic phases in equal or almost equal proportions. In accordance with this strategy, we analyze glass-forming ability of a series of Gd–Co–Al alloys near the composition corresponding to the one generated by combining an equal ratio of intermetallic phases. To do that, we fabricate bulk amorphous samples by melt quenching technique into a variable-section copper mold and inspect their structure, thermal properties and critical casting size.
•We suggest a simple phenomenological approach for locating glass formers.•This method allows interpreting the existence of several pinpoints in a metallic system.•Competing multiple frustrated phases are the driving force initiating vitrification.
Structural, magnetic and optical properties of double manganites PrBaMn
2
O
6
and NdBaMn
2
O
6
are studied depending on the degree of ordering in the A-position. It is shown that, annealing induced ...disordering goes in an initial stage throw formation of a two-phase state: a phase with a high A-site ordering with
T
C
∼ 280–300 K and a phase with a low ordering of ~30% with significantly lower
T
C
coexist. In partially ordered PrBaMn
2
O
6
samples there are metal-insulator transitions near
T
C
of the each coexisting phases. In partially ordered NdBaMn
2
O
6
in a highly A-site ordered high-temperature phase, there is no metal-insulator transition due to the destruction of the channels for metallic conductivity formed by the ordering of the
x
2
‒
y
2
orbitals. If a metal-insulator transition takes place, the application of a magnetic field leads to the effect of magnetotransmission near
T
C
, which is associated with a change in the concentration of delocalized charge carriers.
The sorption properties of the MnO
2
/mechanically activated graphite composite with respect to As(III) compounds were studied. The static sorption capacity relative to As(III) compounds of the MnO
2
.../mechanically activated graphite composite was 22.7 mg g
–1
, which exceeds the sorption properties of MnO
2
. The effect of solution pH in the range of 1–5, sorbent dose, and sorption time on the recovery of As(III) compounds was studied. It is shown that the process of As(III) sorption on the composite is described by the Freundlich model. The MnO
2
/mechanically activated graphite composite can be recommended for the removal of As(III) compounds from aqueous solutions.
