Active Lone Pair Of Electrons Research Articles

Stereo-Active Lone Pairs Induced Second Harmonic Generation Responses and Electrocatalytic Activity in Hybrid Material.

The lone pair electrons in the electronic structure of molecules have been a prominent research focus in chemistry for more than a century. Stable s2lone pair electrons significantly influence material properties, including thermoelectric properties, nonlinear optical properties, ferroelectricity, and electro(photo)catalysis.While major advances have been achieved in understanding the influence of lone pair electrons on material characteristics, research on this effect in organic-inorganic hybrid materials is in its initial stage. In this work, we successfully obtained a novel organic-inorganic hybrid material incorporating Ge with 4s2 lone pair electrons, (MeHDabco)2[GeBr3]4-H2O (MeHDabco = N-methyl-1,4-diazabicyclo[2.2.2]octane) (1). Driven by the stereochemically active lone pair electrons on the Ge2+,1 crystallizes in the noncentrosymmetric space group P21 at room temperature and exhibits good second harmonic generation (SHG) responses. Interestingly,1 also shows electrocatalytic activity for the hydrogen evolution reaction due to the existence of lone pair electrons on Ge2+ cations. The electrochemical experiment combined with the DFTcalculations revealed the lone pair electrons act as both an active site for proton adsorption and facilitate the ionization of water. This work not only emphasizes the important role of lone pair electrons in material properties and functions but also provides new insight for designing novel Ge-based hybrid materials.

Sb2O2SeO3 and Sb2O(SeO3)2: Two-Layered Antimony(III) Selenites with Enhanced Birefringence.

Two antimony selenites, Sb2O2SeO3 and Sb2O(SeO3)2, were synthesized by simultaneously incorporating stereochemically active lone pair electrons containing SeO32- and Sb3+. These compounds are structured with [SbOx] polyhedra and [SeO3] units within a two-dimensional framework. Both of them exhibit cutoffs at 300 and 330 nm within the ultraviolet (UV) range and demonstrate significant birefringence, with indices of 0.069 and 0.126 at 546 nm, respectively. These properties highlight their potential as UV birefringent materials. Structural analyses and theoretical calculations reveal that their exceptional birefringence results from the synergistic interactions between SeO32- anions and Sb3+ cations.

Enhance the performance of OER electrocatalyst via synergistic oxygen vacancies and NiFe2O4-phosphorene heterostructure

The exfoliated black phosphorus nanosheets (EBP, phosphorene) is considered as a highly anticipated electrocatalyst for oxygen evolution reaction (OER) because of its unique electron structure. However, the poor stability and conductivity of EBP limit its application potential. In this paper, a heterostructure of EBP and nickel ferrite with oxygen vacancies (NFO-V-EBP) is designed by using a simple ultrasound and electronic regulation of EBP. NFO-V forms P-Ni bonds and P-O-M (M=Ni/Fe) bonds by interacting with the active lone pair electrons on the surface of EBP, which passivates EBP to improve its stability and provide more active sites. In situ Raman testing is used to assist in demonstrating the cooperative effect of EBP and oxygen vacancy, which reduced the potential barrier of OER reaction. NFO-V-EBP heterostructure exhibits excellent electrocatalytic performance for alkaline OER, showing overpotential of 243 mV at current density of 10 mA cm-2 and Tafel slope of 39 mV dec-1. It also has excellent long-term stability, at a density of 10 mA cm-2 with no significant increase in overpotential observed after nearly 100 hours under the chronoamperometric method.

Interface-modulated kinetic differentials in electron and hole transfer rates as a key design principle for redox photocatalysis by Sb2VO5/QD heterostructures.

The efficient conversion of solar energy to chemical energy represents a critical bottleneck to the energy transition. Photocatalytic splitting of water to generate solar fuels is a promising solution. Semiconductor quantum dots (QDs) are prime candidates for light-harvesting components of photocatalytic heterostructures, given their size-dependent photophysical properties and band-edge energies. A promising series of heterostructured photocatalysts interface QDs with transition-metal oxides which embed midgap electronic states derived from the stereochemically active electron lone pairs of p-block cations. Here, we examine the thermodynamic driving forces and dynamics of charge separation in Sb2VO5/CdSe QD heterostructures, wherein a high density of Sb 5s2-derived midgap states are prospective acceptors for photogenerated holes. Hard-x-ray valence band photoemission spectroscopy measurements of Sb2VO5/CdSe QD heterostructures were used to deduce thermodynamic driving forces for charge separation. Interfacial charge transfer dynamics in the heterostructures were examined as a function of the mode of interfacial connectivity, contrasting heterostructures with direct interfaces assembled by successive ion layer adsorption and reaction (SILAR) and interfaces comprising molecular bridges assembled by linker-assisted assembly (LAA). Transient absorption spectroscopy measurements indicate ultrafast (<2ps) electron and hole transfer in SILAR-derived heterostructures, whereas LAA-derived heterostructures show orders of magnitude differentials in the kinetics of hole (<100ps) and electron (∼1ns) transfer. The interface-modulated kinetic differentials in electron and hole transfer rates underpin the more effective charge separation, reduced charge recombination, and greater photocatalytic efficiency observed for the LAA-derived Sb2VO5/CdSe QD heterostructures.

A particular mechanism of the effect of lone pair E TeIV dopant atoms on visible-light photocatalytic activity of anatase TiO2

It was found that small additives of E TeIV species (< 1 at%) notably enhance the visible-light photocatalytic activity of polycrystalline anatase TiO2. This effect can tentatively be attributed to the neutralization of the neighboring surface- located oxygen vacancy, acting as a recombination center for photogenerated holes and electrons, by the dopant stereochemically active lone electron pair E.

Characterization of the Pb Coordination Environment and Its Connectivity in Lead Silicate Glasses: Results from 2D 207Pb NMR Spectroscopy.

The Pb-O coordination environment in binary (PbO)x(SiO2)100-x glasses with 30 ≤ x ≤ 70 is probed by using two-dimensional 207Pb nuclear magnetic resonance (NMR) isotropic-anisotropic correlation spectroscopy. The isotropic 207Pb NMR spectra show little composition-dependent evolution of the Pb-O nearest-neighbor coordination environment. The systematic variation of the chemical shift tensor parameters offers a unique insight into their local site symmetry and suggests the presence of pyramidal PbO3 and PbO4 sites with sterically active electron lone pairs and with Pb-O bond lengths ranging between 0.23 and 0.25 nm. The PbO3/PbO4 ratio shows a small but monotonic increase from ∼70:30 to 80:20 as the PbO content increases from 30 to 70 mol %. When taken together, the isotropic and anisotropic 207Pb NMR spectra suggest that the majority of the PbOn (3 ≤ n ≤ 4) pyramids in these glasses are connected to the SiO4 tetrahedra via Pb-O-Si linkages. A significant fraction of Pb-O-Pb linkages, where the oxygen is linked only to Pb atoms, appears only in glasses with PbO ≥ 60 mol %. These oxygen atoms appear to be corner-shared between the PbOn pyramids in the structure, and no evidence for edge-sharing between these pyramids is observed in this composition range. We hypothesize that a substantial fraction of the constituent PbOn pyramids start to participate in edge-sharing only at higher PbO contents (>70 mol %), which diminishes the glass-forming ability of the network. This work illustrates the potential of isotropic-anisotropic correlation NMR spectroscopy in structural studies involving nuclides with large chemical shift ranges and anisotropy.

Synthesis and characterization of (Pb1−x Sr x )MnBO4: a structural and spectroscopic study

Abstract The presence of ns 2 stereo-chemical active lone electron pairs (LEPs) causes asymmetric atomic environments around a given p-block cation, leading to change the crystal chemistry of a respective system. Here we report a series of mullite-type compounds to understand at what extend Sr2+ replaces the stereochemical active Pb2+ cation in (Pb1−x Sr x )MnBO4. Each member of the solid solution has been synthesized by conventional solid-state method. The polycrystalline samples are characterized using X-ray powder diffraction followed by Rietveld refinement. Substitution of Pb2+ with Sr2+ leads to contraction of the a lattice parameter with slight elongation in the b and c direction. For a difference of 1 pm of the ionic radius between Sr2+ and Pb2+, the cell volume contracts about 4 % between the end members as the spatial requirement of the LEP activity in the MBO4 2− channels significantly decreases. Within the solid solution, two distinct Pb/Sr–O2 bond distances significantly differ, which gradually decreases with increasing strontium content leading to a more symmetric coordination around strontium. The calculated BVS of Pb2+/Sr2+ exhibits a linear correlation with the Wang–Liebau eccentricity parameter, indicating to an increased bonding ability cation. The vibrational properties are characterized by both Raman and FTIR spectroscopy, complementing the XPRD results. Electronic band gaps of selected (Pb1−x Sr x )MnBO4 samples were obtained from diffuse reflectance spectroscopy data. Additionally, the Sr containing samples show higher thermal stability than the Pb containing counterparts.

Nonlinear Optical Switching in a Tin-Based Multilayered Halide Perovskite Activated by Stereoactive Lone Pairs and Confined Rotators.

In recent years, there has been a surge in research enthusiasm on searching for solid-state nonlinear optical (NLO) switching materials in halide perovskites owing to their exceptional structural flexibility, compositional diversity, and broad property tenability. However, the majority of reported halide perovskite NLO switching materials contain toxic elements (e.g., Pb), which raise significant environmental concerns. Herein, we present a novel lead-free multilayered halide perovskite NLO switching material, (BA)2(EA)2Sn3Br10 (1, where BA is butylammonium and EA is ethylammonium). Driven by the stereochemically active lone-pair electrons of the Sn2+ cation and the cage-confined effect of EA rotators, 1 undergoes a phase transition with symmetry breaking from P4/mnc to Cmc21, which gives rise to a highly efficient modulation of the quadratic NLO property (0.7 times that of KH2PO4) at a high temperature of 353 K. Furthermore, crystallographic investigation combined with theoretical calculations reveals that the efficient modulation of NLO properties in 1 stems from the synergistic effects between stereochemically active lone pair-induced octahedral distortions and order/disorder transformation of organic cations. This study opens up an instructive avenue for designing and advancing environmentally friendly solid-state NLO switches in halide perovskites.

Novel antimony phosphates with enlarged birefringence induced by lone pair cations.

Phosphates, whose obvious disadvantage is the relatively small birefringence, can be overcome by the introduction of post-transition metal cations containing stereochemically active lone-pair electrons. In this paper, two new compounds were successfully explored in the A-Sb-P-O system, i.e. Cs2Sb3O(PO4)3 (CsSbPO) and (NH4)2Sb4O2(H2O)(PO4)2[PO3(OH)]2 (NH4SbPOH). Transmission spectra show that CsSbPO has a surprising transmission range with a UV cutoff edge of 213 nm. First-principles calculations show that both compounds have a wide band gap (5.02 eV for CsSbPO and 5.30 eV for NH4SbPOH) and enlarged birefringence (Δn = 0.034@1064 nm for CsSbPO and Δn = 0.045@1064 nm for NH4SbPOH). The results of real-space atom-cutting investigations show that the distorted [SbOx] polyhedra originating from the asymmetric lone pair electrons give the main contribution to the total birefringence and overcome the disadvantage of small birefringence of phosphates but maintain wide transition windows.

A2Hgx(SeO3)y (A = K, Rb, Cs): Three Alkali Metal Mercury Selenites Featuring Unique 1D [HgOm(SeO3)n]∞ Chains.

Herein, three alkali metal mercury selenites, K2Hg2(SeO3)3, Rb2Hg2(SeO3)3, and Cs2Hg3(SeO3)4, were successfully obtained by a hydrothermal method. The three compounds featured same one-dimensional (1D) [HgOm(SeO3)n]∞ chain structure that consisting of distorted Hg-O polyhedra and SeO3 triangular pyramids with stereochemically active lone pair (SCALP) electrons. Interestingly, the rich coordination environment of Hg atoms and the size difference of alkali metal cations lead to diverse arrangement of SeO3 groups, which makes them exhibit different birefringence. The band gaps of the three compounds indicate that they are potential ultraviolet (UV) optical materials. Detailed theoretical calculations demonstrate that the combined effects of SeO3 triangular pyramids and Hg-O polyhedra are responsible for the optical characteristics of the reported compounds.

Positive and Negative Contribution from Lead–Oxygen Groups and Halogen Atoms to Birefringence: A First Principles Investigation

Oxyhalides, containing oxygen and halogen atoms and combining the advantages of oxides and halides in geometry and optical response, have great potential in optical materials. In this study, the electronic structures and the optical properties of the Pb3O2X2 (X = Cl, Br, I) compounds have been investigated using the first principles method. The results show that these compounds have birefringence at 0.076, 0.078, and 0.059 @ 1064 nm, respectively. And, the asymmetric stereochemical active lone pair electrons were found around lead atoms, which were confirmed by the projected density of states, the electronic localization functions, and the crystal orbitals. The contribution of atoms and polyhedra to birefringence was further evaluated using the Born effective charge. The results show that halogen atoms give negative contribution, and lead—oxygen polyhedra give positive contribution. The spin—orbit coupling effect is also investigated, and the downshift of the conduction band and variation in the valence band are found after relevant spin—orbit coupling (SOC), which leads to a reduction in the band gap and birefringence.

Centrosymmetric Rb2Sb(C2O4)2.5(H2O)3 and Noncentrosymmetric RbSb2(C2O4)F5: Two Antimony (III) Oxalates as UV Optical Materials.

Herein, we have successfully synthesized two rubidium antimony (III) oxalates, namely, Rb2Sb(C2O4)2.5(H2O)3 and RbSb2(C2O4)F5, utilizing a low-temperature hydrothermal method. These two compounds share a similar chemical composition, consisting of Sb3+ cations with active lone pair electrons, alkali metal Rb+ ions, and planar π-conjugated C2O42- anions. However, they exhibit different symmetries, Rb2Sb(C2O4)2.5(H2O)3 is centrosymmetric (CS), while RbSb2(C2O4)F5 is noncentrosymmetric (NCS), which should be caused by the presence of F- ions. Notably, the NCS compound, RbSb2(C2O4)F5, demonstrates a moderate second-harmonic generation (SHG) response, approximately 1.3 times that of KH2PO4 (KDP), and exhibits a large birefringence of 0.09 at 546 nm. These characteristics indicate that RbSb2(C2O4)F5 holds promising potential as a nonlinear optical material for ultraviolet (UV) applications. Detailed structural analysis and theoretical calculations confirm that the excellent optical properties arise from the synergistic effects between Sb3+ cations with SCALP and planar π-conjugated [C2O4]2- groups.

Effect of Stereochemically Active Electron Lone Pairs on Magnetic Ordering in Trivanadates.

Stereoactive electron lone pairs derived from filled 5/6s2 states of p-block cations are an intriguing electronic and geometric structure motif that have been exploited for diverse applications such as thermoelectrics, thermochromics, photocatalysis, and nonlinear optics. Layered trivanadates are dynamic intercalation hosts, where the insertion of cations can be used to tune electron correlation, charge localization, and magnetic ordering. However, the interaction of 5/6s2 stereoactive electron lone pairs with layered trivanadates remains unexplored. In this study, we contrast s- and p-block trivanadates and map off-centering in the coordination environment and reduction in symmetry arising from the stereochemical activity of lone pair cations to the emergence of filled antibonding lone-pair 6s2-O 2p hybridized states. The former is studied by high-resolution single-crystal X-ray diffraction studies of TlV3O8 and isostructural RbV3O8 to probe distinct differences in Tl and Rb coordination environments and the resulting modulation of V-V interactions in V3O8 slabs. The latter has been probed by variable-energy hard X-ray photoelectron spectroscopy (HAXPES) measurements, which manifest orbital-specific contributions from bonding and antibonding interactions of stereoactive Tl 6s2 electron lone pairs in TlV3O8. The spectroscopic assignment of valence band states to stereoactive lone pairs is further corroborated by first-principles electronic structure calculations, crystal orbital Hamilton population analyses, and electron localization function maps. The presence of the Tl 6s2 electron lone pair in TlV3O8 brings about the off-centering of Tl+ cations, which leads to anisotropy in Tl-O bonds. The off-centering of Tl ions weakens V-O bonds in one direction, which subsequently strengthens directional V-V coupling. Magnetic measurements reveal ferromagnetic signatures for both RbV3O8 and TlV3O8. However, the differences in V···V interactions significantly affect the energy balance of the superexchange interactions, resulting in an ordering temperature of 140 K for TlV3O8 as compared to 125 K for RbV3O8. The results demonstrate the distinctive effects of stereochemically active lone pairs in modifying electronic structure near the Fermi level and for mediating superexchange interactions.

Hg3(SeO3)2(SO4): A UV Nonlinear Optical Mercury Selenite Sulfate Constructed by Neat [Hg6O8(SeO3)4]∞ Layers and SO4 Tetrahedra.

A novel mercury selenite sulfate named Hg3(SeO3)2(SO4) has been successfully synthesized under a mild hydrothermal method. Hg3(SeO3)2(SO4) crystallizes in a monoclinic space group P21 and features a unique three-dimensional (3D) frame structure formed by [Hg6O8(SeO3)4]∞ layers and SO4 tetrahedra, which enables it to exhibit a comprehensive performance of a moderate second-harmonic generation (SHG) response of approximately 1.3 times that of baseline KH2PO4 (KDP), a moderate birefringence (0.118@546 nm), and a wide band gap (4.70 eV), which indicates that it has potential for application as an ultraviolet (UV) nonlinear optical material. Detailed theoretical calculations show that the Hg2+-based polyhedra with large polarizability and deformability and the SeO3 groups with stereochemically active lone pair (SCALP) electrons are the main contributors to moderate optical properties.

Synthesis and physical characteristics of narrow bandgap chalcogenide SnZrSe 3.

Background: The development of organic/inorganic metal halide perovskites has seen unprecedent growth since their first recognition for applications in optoelectronic devices. However, their thermodynamic stability and toxicity remains a challenge considering wide-scale deployment in the future. This spurred an interest in search of perovskite-inspired materials which are expected to retain the advantageous material characteristics of halide perovskites, but with high thermodynamic stability and composed of earth-abundant and low toxicity elements. ABX 3 chalcogenides (A, B=metals, X=Se, S) have been identified as potential class of materials meeting the aforementioned criteria. Methods: In this work, we focus on studying tin zirconium selenide (SnZrSe 3) relevant physical properties with an aim to evaluate its prospects for application in optoelectronics. SnZrSe 3 powder and monocrystals were synthesized via solid state reaction in 600 - 800 °C temperature range. Crystalline structure was determined using single crystal and powder X-ray diffraction methods. The bandgap was estimated from diffused reflectance measurements on powder samples and electrical properties of crystals were analysed from temperature dependent I-V measurements. Results: We found that SnZrSe 3 crystals have a needle-like structure (space group - Pnma) with following unit cell parameters: a=9.5862(4) Å, b=3.84427(10) Å, c=14.3959(5) Å. The origin of the low symmetry crystalline structure was associated with stereochemical active electron lone pair of Sn cation. Estimated bandgap was around 1.15 eV which was higher than measured previously and predicted theoretically. Additionally, it was found that resistivity and conductivity type depended on the compound chemical composition. Conclusions: Absorption edge in the infrared region and bipolar dopability makes SnZrSe 3 an interesting material candidate for application in earth-abundant and non-toxic single/multi-junction solar cells or other infrared based optoelectronic devices.

The calcium oxidotellurates Ca2(TeIVTeVIO7), Ca2(TeIVO3)Cl2 and Ca5(TeIVO3)4Cl2 obtained from salt melts

Abstract The mixed-valent calcium oxidotellurate(IV,VI) Ca2(Te2O7) (= Ca2(TeIVTeVIO7)) and the two calcium oxidotellurate(IV) dichlorides Ca2(TeIVO3)Cl2 and Ca5(TeIVO3)4Cl2 were obtained from metal chloride salt melts. Structure determination from single crystal X-ray data revealed a unique crystal structure in each case. A common motif in the three crystal structures is the formation of a framework perforated by channels into which the stereochemically active 5s 2 electron lone pairs E of the TeIV atoms are directed. Ca2(Te2O7) belongs to category I of the Robin-Day classification of mixed-valent compounds. Its crystal structure features a double chain of condensed trigonal-pyramidal [TeIVO3] and octahedral [TeVIO6] units embedded within a framework of [CaO x ] polyhedra (x = 7–8). The Cl atoms in the crystal structures of Ca2(TeIVO3)Cl2 and Ca5(TeIVO3)4Cl2 act as spacers between isolated trigonal-pyramidal [TeO3] units and exhibit weak interactions with the 5s 2 electron lone pairs E, with Cl⋯E distances &lt;3.6 Å.

Highly active cobalt-free perovskites with Bi doping as bifunctional oxygen electrodes for solid oxide cells

Cobalt-containing perovskite materials have been intensively investigated as bifunctional oxygen electrodes for solid oxide cells because of their mixed ionic-electronic conducting nature. However, the direct application of these materials to the most widely used zirconia-based electrolytes has been limited because of their thermo-chemical incompatibility. Herein, we introduce a cobalt-free manganite-perovskite with significantly improved electrocatalytic activity by doping with Bi which possesses stereochemically active lone pair electrons. Replacing Bi with Pr in Pr0.8Sr0.2MnO3−δ increases the oxygen vacancy concentration and promotes oxygen ion incorporation and charge transfer processes at the electrode. Consequently, we apply Pr0.5Bi0.3Sr0.2MnO3−δ, to the interlayer-free yttria-stabilized zirconia electrolyte-based cells, which exhibits record high performance in the fuel cell (1.91 W∙cm−2) as well as electrolysis (1.90 A∙cm−2) modes at 700 °C along with remarkable long-term stability (450 h). Thus, our findings demonstrate that Pr0.5Bi0.3Sr0.2MnO3−δ is a highly promising bifunctional catalyst for solid-state energy storage and conversion applications.

2D/1D heterostructure of carbon nanotubes wrapping black phosphorus nanosheets with superior electrophilic property for improving oxygen evolution reaction

Black phosphorus (BP) is susceptible to oxidization under ambient conditions due to the exposed active lone pair electrons of P atoms, which will greatly decrease in activity and stability for oxygen evolution reaction (OER). Moreover, inferior adsorption property of BP partly restricts the OER activity. To solve these problems, BP is coupled with carbon nanotubes (CNTs) for constructing efficient metal-free BP/CNT (2D/1D) hetero-interface to transfer electrons and optimize the adsorption property. As is anticipated, characterization results reveal electrons transfer via this hetero-interface from BP NSs to CNTs occurs and alters interfacial electronic structure. Thus, this BP/CNT heterostructure displays high conductivity and superior electrophilicity. With this optimization of intrinsic electron-structure, the rate-determining step of electron transfer process is converted into chemical reaction process, and the activation energy towards OER dramatically is lowered. This effectively promotes the intrinsic activity and stability of BP/CNT hybrid. Moreover, here BP/CNT ratio, electrolytic time and electrolyte type are regulated to obtain best samples. The best BP/CNT prepared with TBACF3SO3 exhibits the lower overpotential of 35 mV than RuO2 at 10 mA cm−2. This work inspires us to design BP-based heterostructure and reveal the interfacial promotion effect for OER.

Experimental and Theoretical Study of Tetrel Bonding and Noncovalent Interactions in Hemidirected Lead(II) Phosphorodithioates: An Implication on Crystal Engineering

The importance of tetrel bonds (TtBs) in spontaneous self-assembly has been highlighted in two new lead(II) complexes: i.e. Pb[S2P{OC6H4(4-C(CH3)3)}2]2 (1) and Pb[S2P{OC6H4(4-C2H5)}2]2 (2), which were successfully isolated and characterized by FT-IR, UV–vis and multinuclear NMR (31P, 1H and 13C) spectroscopy. The structures of both complexes have been confirmed by single-crystal X-ray diffraction analyses. Interestingly, lead is coordinated by three sulfur atoms in 1 but by four sulfur atoms in 2, due to stereochemically active lone pair electrons, thus leading to trigonal-pyramidal and tetragonal-pyramidal geometries, respectively. Complex 1 is the first example of a lead(II) dithiophosphate wherein the lead(II) center is coordinated to three S atoms. These complexes are stabilized at a lower coordination number and display hemidirected structures that allow forming σ-hole bonds. The lead(II) center establishes short contacts with sulfur atoms to form Pb···S TtBs that contribute to the construction of a self-assembled dimer in 1 but to a supramolecular polymer in 2. The supramolecular assemblies are further stabilized by Pb···π TtB interactions. The attractive nature of TtBs has been studied by DFT calculations and characterized using a combination of Bader’s quantum theory of atoms-in-molecules (QTAIM) and noncovalent interaction plot (NCI plot) index based on a reduced density gradient (NCI-RDG) analysis. A systematic Hirshfeld surface analysis facilitates a comparison of intermolecular interactions such as C–H···π, π···π, Pb···S, and Pb···π in both complexes, which play a crucial role in the crystal engineering.

Synthesis and physical characteristics of narrow bandgap chalcogenide SnZrSe3

Background: The development of organic/inorganic metal halide perovskites has seen unprecedent growth since their first recognition for applications in optoelectronic devices. However, their thermodynamic stability and toxicity remains a challenge considering wide-scale deployment in the future. This spurred an interest in search of perovskite-inspired materials which are expected to retain the advantageous material characteristics of halide perovskites, but with high thermodynamic stability and composed of earth-abundant and low toxicity elements. ABX3 chalcogenides (A, B=metals, X=Se, S) have been identified as potential class of materials meeting the aforementioned criteria. Methods: In this work, we focus on studying tin zirconium selenide (SnZrSe3) relevant physical properties with an aim to evaluate its prospects for application in optoelectronics. SnZrSe3 powder and monocrystals were synthesized via solid state reaction in 600 – 750 °C temperature range. Crystalline structure was determined using single crystal and powder X-ray diffraction methods. The bandgap was estimated from diffused reflectance measurements on powder samples and electrical properties of crystals were analysed from temperature dependent I-V measurements. Results: We found that SnZrSe3 crystals have a needle-like structure (space group – Pnma) with following unit cell parameters: a=9.5862(4) Å, b=3.84427(10) Å, c=14.3959(5) Å. The origin of the low symmetry crystalline structure was associated with stereochemical active electron lone pair of Sn cation. Estimated bandgap was around 1.15 eV which was higher than measured previously and predicted theoretically. Additionally, it was found that resistivity and conductivity type depended on the compound chemical composition. Conclusions: Absorption edge in the infrared region and bipolar dopability makes SnZrSe3 an interesting material candidate for application in earth-abundant and non-toxic single/multi-junction solar cells or other infrared based optoelectronic devices.