High Vacancy Concentration Research Articles

In Situ Carbon Thermal Reduction to Enrich Sulfur-Vacancy in Nickel Disulfide Cathode for Efficient Synthesizing Hydrogen Peroxide.

Transition metal catalysts are widely used in the 2e- ORR due to their cost-effectiveness. However, they often encounter issues related to low activity. Defect engineering are used on developing highly active catalysts, which can effectively modify active sites and promote electron transfer. Here, carbon-coated Ni3S2 (Ni3S2@C), where the additional sulfur vacancies (VS) is prepared induced by the carbon layer is coupled with active nickel sites. Through in situ and ex situ experiments combined with DFT calculations, it is demonstrated that the carbon layer can regulate the quantity of VS in Ni3S2. Materials with a higher concentration of VS exhibit enhanced 2e- ORR activity and higher H2O2 selectivity. In situ Raman spectroscopy confirms that Ni serves as the key active site in this catalyst. DFT calculations indicate that the OOH binding energy (ΔG) decreases with an increase in the number of VS, favoring the protonation of *OOH to generate H2O2. Upon performance testing, the average H2O2 selectivity is 92.3%, with the highest yield reaching up to 3860mmolgcat-1h-1. It is noteworthy that Ni3S2@C exhibits high stability, with only a slight decrease in 2e- pathway selectivity after 5000 cycles of ADT.

Boosting the Thermoelectric Properties of Ge0.94Sb0.06Te via Trojan Doping for High Output Power.

GeTe stands as a promising lead-free medium-temperature thermoelectric material that has garnered considerable attention in recent years. Suppressing carrier concentration by aliovalent doping in GeTe-based thermoelectrics is the most common optimization strategy due to the intrinsically high Ge vacancy concentration. However, it inevitably results in a significant deterioration of carrier mobility, which limits further improvement of the zT value. Thus, an effective Trojan doping strategy via CuScTe2 alloying is utilized to optimize carrier concentration without intensifying charge carrier scattering by increasing the solubility of Sc in the GeTe system. Because of the high doping efficiency of the Trojan doping strategy, optimized hole concentration and high mobility are obtained. Furthermore, CuScTe2 alloying leads to band convergence in GeTe, increasing the effective mass m* in (Ge0.84Sb0.06Te0.9)(CuScTe2)0.05 and thus significantly improving the Seebeck coefficient throughout the measured temperature range. Meanwhile, the achievement of the ultralow lattice thermal conductivity (κL ∼ 0.34 W m-1 K-1) at 623 K is attributed to dense point defects with mass/strain-field fluctuations. Ultimately, the (Ge0.84Sb0.06Te0.9)(CuScTe2)0.05 sample exhibits a desirable thermoelectric performance of zTmax ∼ 1.81 at 623 K and zTave ∼ 1.01 between 300 and 723 K. This study showcases an effective doping strategy for enhancing the thermoelectric properties of GeTe-based materials by decoupling phonon and carrier scattering.

The thermodynamic effects of solute on void nucleation in Mg alloys.

Replica exchange transition interface sampling simulations in Mg-Al alloys with high vacancy concentrations indicate that the presence of a solute reduces thermodynamic barriers to the clustering of vacancies and the formation of voids. The emergence of local minima in the free energy along the reaction coordinate suggests that void formation may become a multi-step process in the presence of a solute. In this scenario, vacancies agglomerate with solute before they coalesce into a stable void with well-defined internal surfaces. The emergence of vacancy-solute clusters as intermediate states would imply that classical nucleation theory is unlikely to adequately describe void formation in alloys at high vacancy concentrations, a likely precursor for alloy strengthening through nanoscale precipitation.

Advancing the ethanol pathway during the competitive photocatalytic CO2 reduction in a defective transition metal dichalcogenide

The photocatalytic carbon dioxide (CO2) reduction is a very promising approach for harvesting solar energy and recycling carbon resources. However, the native defects induced competition among different pathways for photocarriers is inevitable and negatively affects the selectivity. This work studies the competition between the vacancy induced pathway and the normal in a molybdenum sulfide selenide during photocatalytic CO2 reduction. It has been revealed that the high concentration of chalcogen vacancies can open up the carbene pathway by lowering the free energy and adjusting the adsorptions for the critical intermediates of *CH2 to attract the neighboring *CO for the C-C coupling in the ethanol production, and therefore improve the ethanol production obviously. We propose that in the design of photocatalysts for C2+ production, construction of variant active sites for the coupling of matching intermediates should be fully considered when choosing the basic materials, dopants and native defects.

Ball milling-engineered nanostructured MoSe2/graphite electrocatalyst: Achieving superior hydrogen evolution with a high density of active sites

Nanostructured MoSe2 and its composites with graphite nanoparticles were prepared by a simple, inexpensive, and productive ball-milling method, demonstrating their superior effectiveness as electrocatalysts for the hydrogen evolution reaction (HER). The study revealed that the ball-milling duration significantly influences the prepared nanomaterials' morphology and electrocatalytic properties. The materials prepared in this way are characterized by significant delamination of both components and high defectiveness of molybdenum diselenide. The introduction of graphite nanoparticles into the molybdenum diselenide composition significantly enhances the material's electrocatalytic properties. It has been established that the electrocatalyst based on gMoSe2/Gr(2h) is characterized by a Tafel slope of 40 mV/dec and a potential of −75 mV at a current density of 10 mA/cm2. The electrode modified with gMoSe2/Gr(2h) demonstrates exceptional stability for over 20 hours while maintaining a high current density of approximately 450 mA/cm2 at −300 mV. The study establishes that the high electrocatalytic activity of materials obtained in this manner is directly related to the presence of a high concentration of selenium vacancies in their structure, which can act as catalytically active centers in HER.

Role of S-Vacancy Concentration in Air Oxidation of WS2 Single Crystals.

Semiconducting transition metal dichalcogenides (TMDs) are a class of two-dimensional materials with potential applications in optoelectronics, spintronics, valleytronics, and quantum information processing. Understanding their stability under ambient conditions is critical for determining their in-air processability during device fabrication and for predicting their long-term device performance stability. While the effects of environmental conditions (i.e., oxygen, moisture, and light) on TMD degradation are well-acknowledged, the role of defects in driving their oxidation remains unclear. We conducted a systematic X-ray photoelectron spectroscopy study on WS2 single crystals with different surface S-vacancy concentrations formed via controlled argon sputtering. Oxidation primarily occurred at defect concentrations ≥ 10%, resulting in stoichiometric WO3 formation, while a stable surface was observed at lower concentrations. Theoretical calculations informed us that single S-vacancies do not spontaneously oxidize, while defect pairing at high vacancy concentrations facilitates O2 dissociation and subsequent oxide formation. Our XPS results also point to vacancy-related structural and electrostatic disorder as the main origin for the p-type characteristics that persists even after oxidation. Despite the complex interplay between defects and TMD oxidation processes, our work unveils scientifically informed guidance for working effectively with TMDs.

S-NiSe/HG Nanocomposites with Balanced Dielectric Loss Encapsulated in Room-Temperature Self-Healing Polyurethane for Microwave Absorption and Corrosion Protection.

Exploring anticorrosion electromagnetic wave (EMW) absorbing materials in harsh conditions remains a challenge. Herein, S-NiSe/HG nanocomposites encapsulated in room-temperature self-healing polyurethane (S-NiSe/HG/SPU) were exploited as superior anticorrosion EMW absorbing materials. A dual-defect engineering collaborative Schottky interface construction endows S-NiSe/HG with a high vacancy concentration, abundant defects, and moderate conductivity. These structural merits synergistically balance dielectric loss by enhancing dipole-interface polarization loss and optimizing conduction loss. As a result, S-NiSe/HG demonstrates the optimal EMW absorption performance with a minimum reflection loss (RLmin) of -54.8 dB and an adequate absorption bandwidth (EAB) of 7.1 GHz. Besides, S-NiSe/HG/SPU combines the maze effect of S-NiSe/HG with the active repair capability of SPU, thereby providing long-term corrosion resistance for the Mg alloy. Even under corrosion for 10 days, S-NiSe/HG/SPU affords a low corrosion current density (1.3 × 10-5 A) and high charge transfer resistance (3796 Ω cm2). Overall, this work provides valuable insights for in-depth exploration of dielectric loss and development of multifunctional EMW-absorbing materials.

The influence of defects on conduction processes in chalcogenide semiconductor compounds

Due to the strong dependence on the intrinsic defectiveness of structures, semiconductor compounds based on metal chalcogenides have a wide spread in kinetic properties and high growth temperatures of materials, as well as a tendency to self-compensation of defects. It has been shown that an increase in defectivity in the cation sublattice leads to a decrease in ionic conductivity in copper chalcogenides, and an increase in temperature leads to an increase in ionic conductivity due to a change in mobility. The low activation energy indicates a strong intrinsic disorder of the cation part of the lattice. In copper chalcogenides, the presence of hopping conductivity at small deviations from stoichiometry is explained by compensation and a high concentration of vacancies. Under such conditions, this activation energy is the activation energy for the movement of copper ions throughout the crystal and almost all metal ions contribute to the ionic electrical conductivity. In semiconductor compounds based on metal chalcogenides with deviations from stoichiometry, the activation energy of cationic conductivity does not change, since the defects that arise in this case do not introduce large changes in ionic conductivity with temperature. The increase in ionic conductivity with increasing temperature is due to a change in mobility, since the carrier concentration remains unchanged. The latter is determined only by the structural features of the phases. Deviation from stoichiometry in compounds makes it necessary to take into account the movement of the main charge carriers in the allowed zones, and the movement of carriers along vacancies. The properties of metal chalcogenides are largely determined by the characteristics of their preparation and depend on the relative ratio of metal and chalcogen atoms, as well as the presence of intrinsic defects and their influence on the mechanism of behavior of charge carriers and transfer phenomena.

Tuning surface defects of WO3-x for enhanced photothermal catalytic propane combustion

Photothermal synergistic catalysis for volatile organic compounds has been widely exploited due to its low energy consumption and high-efficiency advantages. However, little is known about how the defect concentration affects the photothermal catalytic performance. Herein, the regulated surface oxygen defects of Pt/WO3-x via calcined under various atmospheres were synthesized, showing an excellent photothermal catalytic propane combustion over the Pt/WO3-x with high oxygen vacancies concentration under light without any external heat source. The experiments and theory simulation unveiled a new photothermal reaction mechanism in which surface defects are conducive to broadening the adsorption light and trapping the photogenerated electrons to boost the activation of O2. This work bodes well for opto-surface defects engineering strategy in advancing and implementing a “solar remove VOCs” process.

Large mechanical properties enhancement in ceramics through vacancy-mediated unit cell disturbance

Tailoring vacancies is a feasible way to improve the mechanical properties of ceramics. However, high concentrations of vacancies usually compromise the strength (or hardness). We show that a high elasticity and flexural strength could be achieved simultaneously using a nitride superlattice architecture with disordered anion vacancies up to 50%. Enhanced mechanical properties primarily result from a distinctive deformation mechanism in superlattice ceramics, i.e., unit-cell disturbances. Such a disturbance substantially relieves local high-stress concentration, thus enhancing deformability. No dislocation activity involved also rationalizes its high strength. The work renders a unique understanding of the deformation and strengthening/toughening mechanism in nitride ceramics.

Thermoelectric performance of indium-rich thiospinels [formula omitted] ([formula omitted] ≈ 0.16, 0.22 and x ≈ 0.1, 0.2)

Powder x-ray diffraction and Raman spectroscopy studies showed In-rich thiospinels with the chemical formula In1−y□yIn2S4−xTex (y ≈ 0.16, 0.22 and x ≈ 0.1, 0.2) to be composed of the cubic α-modification [space group (SG) Fd3̅m] with a minor admixture of tetragonal β-phase (SG I41/amd). Tellurium incorporation in the crystal structures is confirmed by Rietveld refinements, energy dispersive x-ray- and Raman spectroscopies. All samples are found to be indirect band gap semiconductors with an Egopt≈ 2 eV, which decreases with increasing Te-content. The thiospinels with y ≈ 0.16, 0.22 and x ≈ 0.1 revealed by two orders of magnitude enhanced charge carrier concentration (i.e., n≈ 1018 cm−3) and ≈ 6–9 times larger charge carrier mobilities (μ) than corresponding binary specimens. A kink at 200 K in ρT is found to originate from a stepper increase of n. The Seebeck coefficient is negative for all samples indicating electrons to be the dominant charge carriers. The total thermal conductivity of the compounds is almost completely phonon (κph) mediated. The Debye-Callaway fits of κph reveal an enhanced point-defect scattering in the In2.78S4−xTex series compared to In2.84S4−xTex, in accordance with the higher vacancy concentration (i.e., smaller y). The Balkanski-Klemens analysis of the temperature dependent Raman shifts indicated domination of three-phonon scattering mechanism agreeing with the lowered κph values. The appearance of low-energy optical modes confirms the In1-atoms, randomly occupying [In1S4]-tetrahedra, to reveal a ‘rattling’ motion and thus, to be a probable source of enhanced anharmonic effects limiting κph. Te-doping of In-rich thiospinels (y ≈ 0.16, 0.22) results in the improvement of the electrical transport characteristics and simultaneously in an increase of their thermal conductivities due to smaller vacancy concentration. The possible reduction of κph and the improvement of the TE performance are discussed.

Two-step phase manipulation by tailoring chemical bonds results in high-performance GeSe thermoelectrics

In thermoelectrics, phase engineering serves a crucial function in determining the power factor by affecting the band degeneracy. However, for low-symmetry compounds, the mainstream one-step phase manipulation strategy, depending solely on the valley or orbital degeneracy, is inadequate to attain a high density-of-states effective mass and exceptional zT. Here, we employ a distinctive two-step phase manipulation strategy through stepwise tailoring chemical bonds in GeSe. Initially, we amplify the valley degeneracy via CdTe alloying, which elevates the crystal symmetry from a covalently bonded orthorhombic to a metavalently bonded rhombohedral phase by significantly suppressing the Peierls distortion. Subsequently, we incorporate Pb to trigger the convergence of multivalence bands and further enhance the density-of-states effective mass by moderately restraining the Peierls distortion. Additionally, the atypical metavalent bonding in rhombohedral GeSe enables a high Ge vacancy concentration and a small band effective mass, leading to increased carrier concentration and mobility. This weak chemical bond along with strong lattice anharmonicity also reduces lattice thermal conductivity. Consequently, this unique property ensemble contributes to an outstanding zT of 0.9 at 773 K for Ge0.80Pb0.20Se(CdTe)0.25. This work underscores the pivotal role of the two-step phase manipulation by stepwise tailoring of chemical bonds in improving the thermoelectric performance of p-bonded chalcogenides.

Effects of vacancy concentration on the edge dislocation motion in copper by atomic simulations

Nonequilibirum vacancy concentration widely appears in crystals under many extreme loading conditions, but receives relatively few attentions. In this work, we systematically explore the influence of a serial of different vacancy concentrations on the edge dislocation motion in copper using molecular dynamics (MD) simulations. Our result shows that the vacancy would hinder the dislocation motion, but the mechanism depends on the detailed dislocation motion regions. In thermally activated region, its influence is mainly reflected by modifying the dynamic and static threshold stresses required for edge dislocation initiation and continuous motion. In the linear region, the hindering mechanism is gradually transformed from phonon damping to vacancy pinning with the increasing vacancy concentration. In contrasts, the dislocation structure is almost unchanged under different vacancy concentrations in the non-linear region. Under high applied stress, high vacancy concentration will cause the dislocation velocity to jump back and forth between transonic and subsonic velocities more frequently. It has been attributed to the reactions between the dislocation and vacancies. The latter may result in dislocation local constriction and climbing. Moreover, a mobility equation suitable for describing edge dislocations at different non-equilibrium vacancy concentrations is proposed, which fits the MD results well. Finally, the roles of the nonequilibirum vacancy concentration on the edge dislocation motion is interpreted using the degrading elastic property and stacking fault energy.

Effects of grain boundaries and temperature on spinodal decomposition in a binary Fe-Cr alloy: A phase-field simulation

Due to its excellent oxidation resistance, corrosion resistance and mechanical properties, Fe-Cr based stainless steel is a promising candidate for advanced nuclear power systems. At the temperature of 300–600 °C, spinodal decomposition usually occurs in Fe-Cr alloys. However, irradiation can greatly accelerate this process. Fe-Cr based stainless steel decompose into a Cr-enriched α′ phase and a Fe-enriched α phase during spinodal decomposition, and the Cr-enriched α′ phase plays an important role in the hardening/embrittlement of Fe-Cr based stainless steels. In the present work, the evolution of vacancy and the Cr-enriched α′ phase in Fe-Cr alloy is investigated using phase-field method. The simulation results show that the vacancy concentration has a great influence during the spinodal decomposition. The Cr-enriched α′ phase occurs initially at the positions with high vacancy concentration. During spinodal decomposition, the vacancy forms a defect concentration loop around the Cr-enriched α′ phase. In addition, with the increase of temperature, the concentration of Cr atoms in the center of the Cr-enriched α′ phase decreases, and the coarsening rate increases, while the number of the Cr-enriched α′ phase formed in the alloy decreases. At low temperature, α′ phase is mainly coarsened by interlinking; while at high temperature, α′ phase is mainly coarsened by Oswald maturation. Moreover, the Cr-enriched α′ phase occurs at the grain boundary (GB) and the Fe-enriched α phase occurs at both sides of the GB during the spinodal decomposition. At the same time, in polycrystalline system, GB movement during grain growth is inhibited during the spinodal decomposition.

Vacancy-Driven Stabilization of Sub-Stoichiometric Aluminate Spinel High Entropy Oxides

Despite significant recent developments in the field of high entropy oxides, previously reported HEOs are overwhelmingly stoichiometric structures containing a single cationic site and are stabilized solely by intermixing increasing numbers of cations. For the first time, we demonstrate here that cationic vacancies can significantly increase configurational entropy and stabilize phase-pure HEOs. Aluminate spinel HEOs with AB2O4 stoichiometry are used as a model crystal structure. These spinels tolerate large divalent cation deficiencies without changing phase, allowing for high concentrations of cationic vacancies. Stoichiometric and sub-stoichiometric spinels (with A:B molar ratios <0.5), which contained various mixtures of Co, Cu, Mg, Mn, Ni, and cationic vacancies in nominal equimolar concentration, were systematically compared as a function of heat treatment temperature and number of unique cationic species. We found that the same number of cationic species were needed to stabilize both stoichiometric and sub-stoichiometric nickel-containing spinels at 800 °C calcination, as exemplified by (CoCuMgNi)Al2O4 and (CoMgNi)0.75Al2Ox samples, signifying that vacancies stabilize phase-pure spinels similarly to cations. The chromatic, structural, and chemical properties of these complex spinels were highly tunable via incorporation of cationic vacancies and multiple divalent metals, promoting their potential application as unique pigments, catalysts, and thermal coatings.

The Effect of Oxygen Vacancies on the Diffusion Characteristics of Zn(II) Ions in the Perovskite SrTiO3 Layer: A Computational Study.

A highly polar perovskite SrTiO3 (STO) layer is considered as one of the promising artificial protective layers for the Zn metal anode of aqueous zinc-ion batteries (AZIBs). Although it has been reported that oxygen vacancies tend to promote Zn(II) ion migration in the STO layer and thereby effectively suppress Zn dendrite growth, there is still a lack of a basic understanding of the quantitative effects of oxygen vacancies on the diffusion characteristics of Zn(II) ions. In this regard, we comprehensively studied the structural features of charge imbalances caused by oxygen vacancies and how these charge imbalances affect the diffusion dynamics of Zn(II) ions by utilizing density functional theory and molecular dynamics simulations. It was found that the charge imbalances are typically localized close to vacancy sites and those Ti atoms that are closest to them, whereas differential charge densities close to Sr atoms are essentially non-existent. We also demonstrated that there is virtually no difference in structural stability between the different locations of oxygen vacancies by analyzing the electronic total energies of STO crystals with the different vacancy locations. As a result, although the structural aspects of charge distribution strongly rely on the relative vacancy locations within the STO crystal, Zn(II) diffusion characteristics stay almost consistent with changing vacancy locations. No preference for vacancy locations causes isotropic Zn(II) ion transport inside the STO layer, which subsequently inhibits the formation of Zn dendrites. Due to the promoted dynamics of Zn(II) ions induced by charge imbalance near the oxygen vacancies, the Zn(II) ion diffusivity in the STO layer monotonously increases with the increasing vacancy concentration ranging from 0% to 16%. However, the growth rate of Zn(II) ion diffusivity tends to slow down at relatively high vacancy concentrations as the imbalance points become saturated across the entire STO domain. The atomic-level understanding of the characteristics of Zn(II) ion diffusion demonstrated in this study is expected to contribute to developing new long-life anode systems for AZIBs.

Effects of Nb/TiC/TaC/VC and Co addition on the microstructure and properties of WC‐based cemented carbides

AbstractA series of WC‐based cemented carbides with Nb/TiC/TaC/VC and Co was prepared through spark plasma sintering (SPS) at a low sintering temperature of 1300°C, and their microstructures and mechanical properties were investigated. The nonstoichiometric multicomponent carbide Nb/TiC/TaC/VC with a rock‐salt structure () has a high atomic solution capacity. In the sintering process, partial WC and Co may dissolve in Nb/TiC/TaC/VC. With a high concentration of carbon vacancies, Nb/TiC/TaC/VC plays a beneficial role as a mass transfer intermediary. Good mass transfer facilitates the formation of a more accommodating and stable bonding between WC, Nb/TiC/TaC/VC, and Co, thereby preserving the hardness of the sintered bulks and preventing the initiation and propagation of cracks. When 6 wt.% Nb/TiC/TaC/VC and 4 wt.% Co are added to WC, the sintered bulk with fine grains exhibits superior hardness (23.27 ± .63 GPa) and toughness (10.45 ± .56 MPa·m1/2).

Coupling stress fields and vacancy diffusion in phase-field models of voids as pure vacancy phase

High vacancy concentrations in crystals may lead to formation and growth of voids, which is connected to swelling under irradiation and degradation of material properties. Recent experimental work suggests that vacancy condensation may also be involved in nucleation and evolution of porosity in early stages of ductile fracture. Mostly in the realm of irradiation effects, void formation and growth has been simulated with phase-field methods, where voids are treated as pure vacancy phases. Since vacancies induce an eigenstrain field, it is well-known that the evolution of vacancy concentrations is coupled to the elastic stress field. However, the few existing elastically coupled diffuse interface models of void growth seem to face a conceptual problem in the diffuse interface; in the center of which they predict the highest eigenstrains, which results in unrealistically high, fluctuating stresses. In the current work, we present a new model for coupling elastically driven vacancy diffusion with a diffuse interface model of void surfaces, which overcomes the named short-comings and closely reproduces the sharp interface solution. This is achieved by making the eigenstrain a function of the non-conserved order parameter used to distinguish the crystal and void phase. The model is verified for two-dimensional example problems by comparison to the analytical solution of the according sharp interface model. Eventually, the model is used to show the impact of elasto-diffusional coupling on void growth in mechanically loaded systems. We analyze the model with regard to the bi-stable energy landscape and discuss limitations and future prospects of the approach.

Temperature-dependent thermal conductivity of Ge2Sb2Te5 polymorphs from 80 to 500 K

We report the thermal conductivity of amorphous, cubic, and hexagonal Ge2Sb2Te5 using time-domain thermoreflectance from 80 to 500 K. The measured thermal conductivities are 0.20 W m−1 K−1 for amorphous Ge2Sb2Te5, 0.63 W m−1 K−1 for the cubic phase, and 1.45 W m−1 K−1 for the hexagonal phase at room temperature. For amorphous Ge2Sb2Te5, the thermal conductivity increases monotonically with temperature when T &amp;lt; 300 K, showing a typical glass-like temperature dependence, and increases dramatically after heating up to 435 K due to partial crystallization to the cubic phase. For hexagonal Ge2Sb2Te5, electronic contribution to thermal conductivity is significant. The lattice thermal conductivity of the hexagonal phase shows a relatively low value of 0.47 W m−1 K−1 at room temperature and has a temperature dependence of T−1 when T &amp;gt; 100 K, suggesting that phonon–phonon scattering dominates its lattice thermal conductivity. Although cubic Ge2Sb2Te5 has a similar grain size to hexagonal Ge2Sb2Te5, its thermal conductivity shows a glass-like trend like that of the amorphous phase, indicating a high concentration of vacancies that strongly scatter heat-carrying phonons. These thermal transport mechanisms of Ge2Sb2Te5 polymorphs help improve the thermal design of phase change memory devices for more energy-efficient non-volatile memory.

Assessing the high concentration of vacancies in refractory high entropy alloys

Accurate determination of monovacancy formation enthalpy is vital for work on diffusion, melting point determination of high temperature materials, radiation damage, and thermophysical stability of alloys. These enthalpies take on a single value in pure metals but is made more complex in concentrated solid solutions due to the local chemical environments possible around each vacancy. Herein, using first-principles density functional theory, we report the distributions of vacancy formation enthalpies in 21 equiatomic 5-component solid-solution alloys from the Hf-Mo-Nb-Ta-Ti-W-Zr system. Chemical disorder is treated using the special quasi-random structure method, and the chemical potential of vacant element is treated by approximating it to its total energy in its standard state. We find that the highest vacancy formation enthalpies belong to the MoNbTaTiW alloy (which incidentally is the most reported in literature) and the lowest belongs to HfNbTaTiZr, with other alloys in-between. We use the whole distribution of formation enthalpies to estimate the equilibrium concentration of vacancies as a function of temperature.