VA Elements Research Articles

Interfacial Passivation of Kesterite Solar Cells for Enhanced Carrier Lifetime: Ab Initio Nonadiabatic Molecular Dynamics Study

AbstractNonradiative recombination at the front contact interface of kesterite solar cells hinders the extraction of photo‐generated carriers, significantly restricting the efficiency enhancement. However, identifying the recombination centers and proposing effective passivation strategies remain open questions. First‐principles calculations combining with nonadiabatic molecular dynamics (NAMD) simulations unveil that the interfacial translational symmetry breaking in elemental valence states leads to a detrimental donor‐like Cu2ZnSnS4/CdS interface with deep states originating from the interfacial Sn‐5s orbital, which serve as significant nonradiative recombination centers. Here, two mechanisms are proposed for eliminating the deep interface states: 1) directly replacing Sn‐5s with higher outer orbital levels by substituting group IIIA elements (In and Ga) for the interfacial Sn atom; 2) introducing an extra defect‐level coupling with Sn‐5s by substituting group VA elements (N, P, and As) for the S atoms bonded with the interfacial Sn atom. The representative InSn and PS acceptor defects, which are energetically favorable at the detrimental donor‐like interface, effectively passivate the deep interface states, markedly improving the carrier lifetimes by weakening nonadiabatic coupling between the band edge and the interfacial states. This study reveals the origin of the interfacial nonradiative recombination of kesterite solar cells and offers insights into interfacial passivation in semiconductor devices.

Stable ferromagnetism and high Curie temperature in VGe2N4

The discovery of monolayer MA2Z4 (M = transition metals; A = IVA elements; Z = VA elements) [Hong et al 2020 Science 369 670] family has led another advance for facilitating and harnessing magnetism in low-dimensional materials. However, only Cr and V based MA2N4 compounds exhibit intrinsic magnetism yet with unsatisfied magnetic ordering temperature. Herein, we identify a stable ferromagnetic number of this family, i.e., VGe2Z4 monolayer, by means of first-principles calculations. It is found that the magnetic configuration sustains under both compression and tensile uniaxial in-plane strain, and the former can act as a positive modulator to enhance magnetic ordering temperature (T C). Electronic structure calculations reveal a large band gap in the spin down channel while band-gapless in the spin up channel, an impressive near-half-metallic character, which is a favorable candidate for spintronic device.

Beyond T-graphene: Two-dimensional tetragonal allotropes and their potential applications

Breakthrough of graphene dictates that decreasing dimensionality of the semiconducting materials can generate unusual electronic structures, excellent mechanical, and thermal characteristics with remarkable stability. Silicene, germanene, and stanene are the next 2D stable counterparts of other elements belonging to the same group. Since these monolayers possess hexagonal symmetry, scientists had already explored the possibility in the post graphene era of whether hexagonal symmetry was the main and utmost criterion for achieving Dirac cone. This motivation gave birth to T-graphene, a tetragonal network comprised of carbon atoms. However, T-graphene is not the only candidate for exhibiting Dirac fermion. In recent days, tetragonal monolayers of Si and Ge, i.e., T-Si and T-Ge, have been predicted to be stable. These 2D tetragonal allotropes remarkably possess double Dirac cones in their electronic band structure. As these monolayers possess buckling similar to silicene and germanene, the electronic bandgap can be easily introduced in the presence of an external electric field. Another technique to open bandgap is to apply strain in hydrogenated tetragonal networks. Tunable electronic properties in these tetragonal systems make them efficient for optoelectronics as well as thermoelectric applications. Moreover, due to delocalized π electrons, quantum dot systems comprised of tetragonal Si and Ge network show remarkable characteristics in the field of nonlinear optics. Recently, based on theoretical calculations, a bilayer T-graphene system is predicted with excellent mechanical strength relative to its monolayer variant. Not only group-IVA, group-VA elements also exhibit stable monolayer structures. Rather than T-graphene, T-Si, and T-Ge, these monolayers, however, possess intrinsic semiconducting properties, which enable them as a potential candidate for optoelectronic applications. Furthermore, several possible routes have been introduced to realize these systems experimentally. In this topical Review, we would critically explore the recent advancements of 2D tetragonal networks containing group-IVA and VA elements and their possible application perspectives in the field of thermoelectrics and nano-photonics.

Stability and passivation of 2D group VA elemental materials: black phosphorus and beyond

Since the successful isolation of graphene in 2004, two-dimensional (2D) materials have become one of the focuses in material science owing to their extraordinary physical and chemical properties. In particular, 2D group VA elemental materials exhibit fascinating thickness-dependent band structures. Unfortunately, the well-known instability issue hinders their fundamental researches and practical applications. In this review, we first discuss the degradation mechanism of black phosphorus (BP), a most studied group VA material. Next, we summarize the methods to enhance BP stability with the focus of multifunctional passivation. Finally, we briefly discuss the protection strategies of other emerging group VA materials in recent years. This review provides insight for the degradation mechanism and protecting strategy for 2D group VA elements materials, which will promote their potential applications in electronics, optoelectronics, and biomedicine.

Regulation of phase transition temperature and preparation for doping-VO2 smart thermal control films

Vanadium dioxide (VO2) is considered one of the most promising smart thermal control materials due to its insulator-metal temperature (IMT) reversible phase transition, accompanied by large changes in its optical properties. However, as the crystal defects on IMT change and the optical property of VO2 is still unclear, the preparation of doped VO2 films by magnetron sputtering is still a great challenge. In this work, the IMT of 41 kinds of doping-VO2 systems were studied by high throughput calculation based on density functional theory (DFT). It was found that the IMT increased with the decrease of the β angle in M phase and expansion of cell volume difference of M-phase and R-phase for IIA elements, VIIA elements, transition elements, and rare earth element doped VO2, and increased with the increase of the β angle in M phase and a decrease of cell volume difference of M-phase and R-phase for IA, IVA, VA, and VIA element doped VO2. According to the rule, the IMT, electronic structures, and optical properties of W doped VO2 were studied based on DFT. The results show that IMT and bandgap decrease with the increase of W6+ ion concentration, which is due to the increased cell volume difference of M-phase and R-phase in W doped VO2; each doped atom can reduce the IMT of 20.2 °C, and the IMT of V0.98W0.02O2 is close to room temperature (Tc ≈ 27 °C). The rate of infrared emissivity (∆ɛ) of V0.98W0.02O2 is about 0.2 at 8–14 μm (0.088–0.155 eV) and the average solar absorption (αs) of M phase and R phase is about 0.53 and 0.59 at 0.3–1.5 μm (0.496–4.13 eV), respectively. Finally, radio frequency magnetron sputtering was used to achieve precise doping, which solved the problem of oxygen partial pressure in reactive magnetron sputtering, and V1-xWxO2 films with IMT close to room temperature and narrow hysteresis width were prepared. This is due to the fact that higher W doping content will greatly increase the density of defect-induced nucleation sites and promote nucleation. At the same time, the experimental results of IMT were consistent with the calculated results, which proved the reliability of the calculation. This will provide a theoretical basis for the development of new thermal control materials and a new method for the preparation of doping-VO2 films in the future.

ABX6 Monolayers: A new Dirac material family containing high Fermi velocities and topological properties

Dirac materials have received attracting attentions due to their intriguing properties and potential applications in advanced electronics. In this work, we reported 44 new two-dimensional Dirac materials, named ABX6 monolayers, by constructing group IVA, VA, and VIA elements with the same structural prototype. Our first principle calculations revealed that they show excellent dynamical stability, mechanical stability, and thermodynamics stability. Those monolayers possess the elastic constant from 23.93 to 245.57 N/m, attributing to broadly used mechanical strength materials. The electronic calculations show that the Dirac cones in all ABX6 monolayers are both located at K points in Brillouin zone and mainly contributed from the pz orbital of group IVA atoms and group VIA atoms. Their Fermi velocities are from 3.44 × 105 to 6.83 × 105 m/s, which is benefiting for the potential applications in high-speed electric devices. Moreover, it is interesting to notice that the ABX6 monolayers with heavy atoms, such as the ISbSn6 monolayer, exhibit a large band gap of ∼ 0.106 eV, due to the spin-orbital coupling effect. The further calculations reveal their nontrivial topological nature with topological edge states, indicating they could be used as potential dissipationless transport devices at room temperature.

The lattice thermal conductivity in monolayers group-VA: from elements to binary compounds

The lattice thermal conductivity () of the monolayers of partial group-VA elements and binary compounds are systemically investigated by the first-principles calculations and phonon Boltzmann transport equation (PBTE), including aW-antimonene, α-arsenene, black phosphorus, α-SbAs, α-SbP and α-AsP. The values decrease with the increasing of atomic mass for these materials with similar geometry and valence structures. It is ascribed to phonon branches softening, low phonon group velocity, and large Grüneisen parameters. Due to the neutralization of phonon group velocity and phonon lifetime, of binary compounds is between their corresponding elements. As the atomic radius and mass increase, the bond strength and the phonon group velocity decreases. Furthermore, the dimensionless parameter , which comes from the Slack equation and only has the dependence of Grüneisen parameter, grows up with the atomic mass rising, which indicates that a larger anharmonicity is present in the heavier V-V monolayers. For SbAs and SbP compounds, the thermal conductivity anisotropy mainly results from the anisotropy of elastic coefficients along armchair and zigzag directions. Our results highlight the impact of atomic arrangement on the thermal conductivity of group VA binary compounds. This work paves a way to modulate the thermal conductivity of 2D VA elements by incorporation atoms with suitable mass and may guide to improve thermoelectrical performance via the alloying method.

(Invited) Two-Dimensional Pnictogens: Van Der Waals Growth, Stability, and Phase Transformation

Pnictogens (P, As, Sb, Bi) emerged as a new class of elemental 2D materials displaying a wide range of electronic and topological properties. With their ns2 np3 valence electronic configuration and sp3 hybridization, group VA elements are the only elemental group which forms vdW and quasi-vdW structures throughout the entire group, thus providing a rich allotropic system. Light group VA elements crystallize in the semiconducting orthorhombic layered phase (A17) and heavier group VA elements prefer the semi-metallic rhombohedral layered phase (A7). At nanoscale thicknesses, group VA materials undergo various electronic phase transitions. For instance, A17 P – black phosphorus – is a high mobility 2D semiconductor with a thickness-dependent direct band gap gradually varying between 0.3-2 eV as its thickness decreases from bulk to single layer. Similarly, A7 Sb is predicted to exhibit topological semimetal, topological insulator, quantum spin Hall and indirect band gap semiconductor phases at thicknesses between 1 and 22 layers.Despite their highly attractive scientific and technological potential, 2D materials remain scarcely implemented in scalable devices and technologies due to several challenges including among others the lack of large-area and uniform synthesis methods. In fact, many 2D materials exist only in the realm of theoretical predictions and most 2D materials can only be produced by mechanical or chemical exfoliation from bulk crystals, yielding 2D flakes with limited dimensions and poor thickness control. Developing epitaxial growth methods is therefore a crucial step to enable the integration of 2D materials in emerging technologies. With this perspective, this presentation will address the development of the molecular beam epitaxy (MBE) growth of group VA 2D materials on semiconducting and vdW substrates. Furthermore, thermal, ambient and phase stability of these emerging 2D materials is studied using in situ low-energy electron microscopy, transmission electron microscopy, x-ray photoelectron emission microscopy, and ab initio calculations. MBE growth of 2D-Sb and 2D-AsSb is demonstrated on Ge(111) and graphene. Real-time LEEM measurements of the growth dynamics combined with in situ STM allow to determine the nucleation and growth mechanisms on semiconductor and vdW substrates. Subtle behavior during growth or thermal annealing was revealed based on these in situ studies including the metastability and layered-to-layered phase transformation mechanisms of A17 2D-Sb, which was previously considered as an unstable Sb phase. These results provide a deeper understanding of vdW growth of group VA 2D materials and layered-to-layered phase transformation mechanisms.

Effects of atomic substitutional doping on electronic structure of monolayer Janus WSeTe

Based on the first principles calculations, the effects of substitutional doping of nitrogen, halogen and 3d transition metal elements on the electronic structure of monolayer Janus transition metal dichalcogenides WSeTe are studied in this paper, where the VASP software package is used based on density functional theory to perform calculations through using both the projector augmented wave method and the GGA-PBE functional method. A monolayer WSeTe hexagonal crystal system with 4 × 4 supercells is established, which contains 48 atoms. When VA (VIIA) element substitutes for monolayer WSeTe, one of the Se atoms is replaced with a nitrogen (halogen) atom; when the 3d transition metal element substitutes for monolayer WSeTe, one of the W atoms is replaced with a transition metal atom. Through the analysis of band structure, charge transfer and magnetism, it is found that VA (VIIA) nonmetallic elements doped monolayer WSeTe due to the introduction of the hole (electronic) doped, makes the Fermi level shift downward (upward), thus transforming into a p(n) type semiconductor. The Ti and V element substitutional doped monolayer WSeTe will present semiconductor-metal transformation. A doping for each of Cr, Co, Mn, Fe element doesn’t lead semiconductor material properties to change, but the each of Co, Mn, Fe element doped monolayer WSeTe can create a band gap of less than 20 meV. The VIIA (VA) non-metallic element and 3d transition metal element doped monolayer WSeTe will not have a huge influence on the original geometric structure of the material. Due to the charge transfer and doped atoms on the top of the valence band hybridization phenomenon, the Rashba spin splitting intensity near the <i>Γ</i> point of the top valence band increases with the increase of the atomic number of the doped atoms in the same main group when VIIA and VA non-metallic elements are doped. Moreover, the increase in atomic number and charge transfer have a greater influence on the strength of Rashba spin-orbit coupling than the change in electronegativity. The 3d transition metal element substitution doped single-layer WSeTe has obvious spin polarization phenomenon, which produces valley polarization near the Fermi level and introduces magnetism. In particular, since Cr-doped WSeTe retains the original semiconductor properties of WSeTe and has a large energy valley polarization, it may have a wide range of applications, such as in the field of spintronic devices. The monolayer WSeTe doped separately with Cr, Mn and Fe element produces an impurity band with fully polarized spin electrons in the band gap. The results are of great significance in systematically understanding the properties of monolayer WSeTe doping model and can provide theoretical reference for designing the monolayer WSeTe based electronic devices.

Elastic and Optoelectronic Properties of Cs2NaMCl6 (M = In, Tl, Sb, Bi)

In this article, elpasolite perovskites, Cs2NaMCl6 (M = In, Tl, Sb, Bi), are investigated using density functional theory (DFT). Structural properties like lattice constants and bond lengths are in agreement with the available experimental data. Electronic properties are calculated by several DFT exchange-correlation approximations, and it is found that a modified Becke–Johnson (mBJ) approximation along with the inclusion of spin orbit coupling (SOC) gives the most promising results. The M-site cation decides the nature of the band gap; i.e. direct band gaps are obtained for group IIIA elements (In, Tl), and indirect band gaps are experiential for group VA elements (Sb, Bi). Narrow discrete energy bands are observed in the valence and conduction bands, which make these compounds suitable for scintillation applications. SOC induces splitting of Bi/Sb p orbitals in the conduction band and reduces the band gaps of these double perovskite halides. Obtained values of mechanical parameters confirm that these compounds are ductile and anisotropic. Optical properties, i.e. dielectric functions, energy loss function and refractive index, are also calculated, and interesting variations are found which can play a important role in scintillation and other optoelectronic applications of these materials.

Pnictogens Allotropy and Phase Transformation during van der Waals Growth.

With their ns2 np3 valence electronic configuration, pnictogens are the only system to crystallize in layered van der Waals (vdW) and quasi-vdW structures throughout the group. Light pnictogens crystallize in the A17 phase, and bulk heavier elements prefer the A7 phase. Herein, we demonstrate that the A17 of heavy pnictogens can be stabilized in antimonene grown on weakly interacting surfaces and that it undergoes a spontaneous thickness-driven transformation to the stable A7 phase. At a critical thickness of ∼4 nm, A17 antimony transforms from AB- to AA-stacked α-antimonene by a diffusionless shuffle transition followed by a gradual relaxation to the A7 phase. Furthermore, the competition between A7- and A17-like bonding affects the electronic structure of the intermediate phase. These results highlight the critical role of the atomic structure and substrate-layer interactions in shaping the stability and properties of layered materials, thus enabling a new degree of freedom to engineer their performance.

Alloy Anode Materials for Rechargeable Mg Ion Batteries

AbstractRechargeable magnesium ion batteries are interesting as one of the alternative metal ion battery systems to lithium ion batteries due to the wide availability and accessibility of magnesium in the earth's crust. On the one hand, electrolyte solutions in which Mg metal anodes are fully reversible are not suitable for the use of high voltage/high capacity transition metal oxide cathodes due to complex surface phenomena. On the other hand, Mg metal anodes cannot work reversibly in conventional electrolyte solutions in which high voltage/high capacity Mg insertion cathodes can work because of passivation phenomena that fully block them. Replacing Mg metal with alternative anodes that can work reversibly in conventional electrolyte solutions could provide a promising route to elaborate high voltage and high capacity rechargeable Mg battery systems. Herein, the recent progress in alloy anodes based on group IIIA, IVA, VA elements is summarized. The theoretical evaluations, achievable capacities, synthetic strategies, battery test configurations, electrochemical properties, and underlying reaction mechanisms are systematically summarized and discussed. The key issues and challenges impeding their current use are identified and some valuable suggestions for their future development as practical reversible anodes for Mg batteries are provided.

Bioaccumulation of vanadium (V), niobium (Nb) and tantalum (Ta) in diverse mangroves of the Indian Sundarbans

Vanadium (V), niobium (Nb), and tantalum (Ta), recognized as Technology-Critical Element (TCE), are highly growing in demand for industrial development. Despite their economic relevance, little is known about their environmental concentrations, especially in marine ecosystems like mangroves. This paper describes concentrations and distribution patterns of Group Va elements (V, Nb and Ta) in plant organs and sediments from diverse mangroves of the Indian Sundarbans. Sediment cores and plant organs of eight dominant mangrove species were sampled and analyzed for V, Nb and Ta by ICP-MS. Stable carbon isotope (δ13C) in mangrove leaves were analyzed by EA-IRMS. Mean concentrations (mg kg−1) of V, Nb and Ta decreased in the order V (84.7 ± 12.5) > Nb (37.5 ± 4) > Ta (3 ± 0.8) in the sediment and V (0.6 ± 0.6) > Nb (0.02) > Ta (0.002) in the mangrove plants. Species-specific variability in bioaccumulation factor (V: 0.012–0.035; Nb: 0.001–0.003; Ta: 0.001–0.005), translocation factor (V: 0.5–5.1; Nb: 0.26–7.06; Ta: 0.22–2.56) and enrichment factor (V: 0.008–0.027; Nb: 0.0002–0.001; Ta: 1.0 × 10−5-3.0 × 10−6) indicated different partitioning of Group Va elements within the plant organs and varying degree of mangrove uptake efficiency. Results showed a general decrease in V, Nb and Ta concentrations with their increasing atomic weight. Their total concentrations in plants were related to the degree of enrichment of substrate sediments. The phytoextraction capacity varied amongst mangrove species depending on their CO2 uptake efficiency. Given increased demand for TCEs, results may have important implications for bioremediation processes.

Lattice dynamics and phase stability of rhombohedral antimony under high pressure

The high pressure lattice dynamics of rhombohedral antimony have been studied by a combination of diffuse scattering and inelastic x-ray scattering. The evolution of the phonon behavior as function of pressure was analyzed by means of two theoretical approaches: density functional perturbation theory and symmetry-based phenomenological phase transition analysis. This paper focuses on the first structural phase transition, SbI-SbIV, and the role of vibrations in leading the transition. The phonon dispersion exhibits complex behaviour as one approaches the structural transition, with the branches, corresponding to the two transitions happening at high pressure in the Va elements (A7-to-BCC and A7-to-PC) both showing softening.

Interfacial Effects on the Growth of Atomically Thin Film: Group VA Elements on Au(111)

AbstractThe understanding of growth mechanism at atomic scale is a key issue for realizing wafer‐scale, high‐quality 2D materials, in which their interfaces play a crucial role. Here, the adsorption and the aggregation of group VA elements within the first layer on Au(111) are investigated. Together with recent results for group VA elements on Cu and Ag(111), this study leads to a comprehensive understanding of the interfacial effects on the surface structures. Blue phosphorene forms the typical (4 × 4) honeycomb structure on Au(111) regardless of the coverage. Sb assembles into multiple intermediate phases comprising dimer pairs and coin‐shaped aggregates depending critically on the coverage. Increasing the coverage and annealing temperature converts these dimer pairs to AuSb2 surface alloy. The honeycomb structure and periodic stripes are the most stable of Bi on Au(111). Notably, neither P nor Bi prefers surface alloy under the similar growth conditions even though they have the smaller and larger atomic radius, higher and lower electronegativity than Sb, respectively. This difference is correlated with the relativistic effect that tightly bound inner 6s2 electrons make Bi inert. These model systems provide guidance framework for selection of elements and substrates to synthesize monoelemental and binary 2D materials.

Achieving giant spin-orbit splitting in conduction band of monolayer WS2 via n-p co-doping

Large spin-orbit splitting in the conduction band minimum (CBM) of monolayer transition metal dichalcogenides (TMDs) is in great demand for suppressing the intervalley scattering. Here we propose a new scheme to significantly enhance the spin-orbit splitting at the K point in the CBM of WS2 monolayer, via the n-p co-doping of fluorine and group VA elements (N, P, As and Sb). Based on the first-principles calculations, a giant spin-orbit splitting of 101.86 meV is theorized in the F-Sb co-doped system. This is evidenced to originate from the enhanced spin-orbit interaction, intimately related to the strengthened trigonal prismatic ligand field and the increased asymmetric surface charge. The giant spin-orbit splitting in the CBM can strongly suppress the intervalley scattering, which will enhance the spin-valley coupling and is beneficial for longer spin and valley lifetimes. This theoretical work provides a key to designing the high-performance monolayer TMD-based spintronic devices.

Delocalized Carriers and the Electrical Transport Properties of n-Type GeSe Crystals

Recent discovery of a high thermoelectric figure of merit in n-type SnSe single crystal stimulates further research on the analogue compounds. In this work, n-type GeSe is predicted to have a significantly higher normalized power factor along the cross-plane direction based on density functional theory (DFT) calculations and Boltzmann transport theory. This high normalized power factor is due to the high normalized electrical conductivity, which originates from the more delocalized interlayer carrier density. Furthermore, the effects of several potential n-type dopants (group VA and group VIIA elements) on the electronic structure and electrical transport properties of GeSe have been studied. We find that the group VA dopants decrease the density of states near the conduction band minimum and result in a decrease of the Seebeck coefficient of GeSe. As a result, n-type GeSe doped with group VIIA elements is predicted to have a higher normalized power factor than that doped with group VA elements.

Structural design of Ge-based anodes with chemical bonding for high-performance Na-ion batteries

Ge-based anodes for Na-ion batteries (NIB) usually suffer from sluggish reaction kinetics, low initial Coulombic efficiency, poor reversible capacity, and short cycling life due mainly to its rigid diamond-like structure. Here we report our findings in characterization and application of a GeP anode with a flexible layered structure, synthesized by a simple mechanochemical method. When tested as the anode for NIBs, the GeP undergoes a self-healing Na-storage process that involves intercalation, conversion, and alloying, as co-revealed by ex-situ X-ray diffraction, HRTEM, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis. The peculiar self-healing phenomenon derives from its ultra-low formation energy (−0.19 eV) for reconstruction of the original layered structure, as confirmed by first-principle calculations. The low formation energy also enables the formation of chemical bonding between layered GeP and graphite, thus achieving unprecedented performances among all reported anode materials based on Group IVA- and Group VA elements. The structural design strategy guided by formation energy of desirable phases is also applicable to the development of other energy-storage materials.

Tunable electronic and magneto-optical properties of monolayer arsenene: From GW0 approximation to large-scale tight-binding propagation simulations

Monolayers of group VA elements have attracted great attention with the rising of black phosphorus. Here, we derive a simple tight-binding model for monolayer grey arsenic, referred as arsenene (ML-As), based on the first-principles calculations within the partially self-consistent GW0 approach. The resulting band structure derived from the six p-like orbitals coincides with the quasi-particle energy from GW0 calculations with a high accuracy. In the presence of a perpendicular magnetic field, ML-As exhibits two sets of Landau levels linear with respect to the magnetic field and level index. Our numerical calculation of the optical conductivity reveals that the obtained optical gap is very close to the GW0 value and can be effectively tuned by external magnetic field. Thus, our proposed TB model can be used for further large-scale simulations of the electronic, optical and transport properties of ML-As.

Ferromagnetic Shape Memory Heusler Materials: Synthesis, Microstructure Characterization and Magnetostructural Properties.

An overview of the processing, characterization and magnetostructural properties of ferromagnetic NiMnX (X = group IIIA–VA elements) Heusler alloys is presented. This type of alloy is multiferroic—exhibits more than one ferroic property—and is hence multifunctional. Examples of how different synthesis procedures influence the magnetostructural characteristics of these alloys are shown. Significant microstructural factors, such as the crystal structure, atomic ordering, volume of unit cell, grain size and others, which have a bearing on the properties, have been reviewed. An overriding factor is the composition which, through its tuning, affects the martensitic and magnetic transitions, the transformation temperatures, microstructures and, consequently, the magnetostructural effects.