Structural and thermoelectric properties of CH₃NH₃SnI₃ perovskites processed by applying high pressure with shear strain

CH3NH3SnI3 perovskites, which can be created using printing technology, are environmentally friendly thermoelectric materials, but their applications are limited by unsatisfactory thermoelectric efficiency and structural stability. In this work, CH3NH3SnI3 perovskites are processed by applying high pressure with shear strain for the first time, resulting in better structural stability, enhanced electrical conductivity and the Seebeck coefficient with CH3NH3SnI3 tube structures after processing. First-principles calculations verified the reasonable changes in lattice constants, electronic band structures, electrical conductivity and the Seebeck coefficient. The present study demonstrates a potential strategy to improve the structural and thermoelectric properties of CH3NH3SnI3 and uncovers the possible mechanism. Better structural stability and slightly improved thermoelectric properties are achieved in the CH3NH3SnI3 samples processed by high pressure with shear strain. DFT calculations disclose the possible mechanism.</p

Neutron Powder Diffraction Study on the Crystal and Magnetic Structures of BiCrO₃

The crystal and magnetic structures of polycrystalline BiCrO3 were determined by the Rietveld method from neutron diffraction data measured at temperatures from 7 to 490 K. BiCrO3 crystallizes in the orthorhombic system above 420 K (space group Pnma; Z = 4; a = 5.54568(12) Å, b = 7.7577(2) Å, and c = 5.42862(12) Å at 490 K) in the GdFeO3-type structure. Below 420 K down to 7 K, a monoclinic structure is stable with C2/c symmetry (a = 9.4641(4) Å, b = 5.4790(2) Å, c = 9.5850(4) Å, and β = 108.568(3)° at 7 K). A possible model for antiferromagnetic order below TN = 109 K is proposed with a propagation vector of k = (0, 0, 0). In this model, magnetic moments of Cr3+ ions are coupled antiferromagnetically in all directions, forming a G-type antiferromagnetic structure. Refined magnetic moments at 7, 50, and 80 K are 2.55(2)μB, 2.43(2)μB, and 2.09(2)μB, respectively. The structure refinements revealed no deviation from stoichiometry in BiCrO3

Bimetallic Sulfide SnS₂/FeS₂ Nanosheets as High-Performance Anode Materials for Sodium-Ion Batteries

Transition-metal sulfide SnS2 has aroused wide concern due to its high capacity and nanosheet structure, making it an attractive choice as the anode material in sodium-ion batteries. However, the large volume expansion and poor conductivity of SnS2 lead to inferior cycle stability as well as rate performance. In this work, FeS2 was in situ introduced to synchronously grow with SnS2 on rGO to prepare a heterojunction bimetallic sulfide nanosheet SnS2/FeS2/rGO composite. The composition and distinctive structure facilitate the rapid diffusion of Na+ and improve the charge transfer at the heterogeneous interface, providing sufficient space for volume expansion and improving anode materials’ structural stability. SnS2/FeS2/rGO bimetallic sulfide electrode boasts a capacity of 768.3 mA h g–1 at the current density of 0.1 A g–1, and 541.2 mA h g–1 at the current density of 1 A g–1 in sodium-ion batteries, which is superior to that of either single metal sulfide SnS2 or FeS2. TDOS calculation further confirms that the binding of FeS2/SnS2–Na is more stable than FeS2 and SnS2 alone. The superior electrochemical performance of the SnS2/FeS2/rGO composite material makes it a promising candidate for sodium storage

Relationship between Lattice Strain and Efficiency for Sn-Perovskite Solar Cells

In the composition of Q0.1(FA0.75MA0.25)0.9SnI3, Q is replaced with Na+, K+, Cs+, ethylammonium+ (EA+), and butylammonium+ (BA+), respectively, and the relationship between actually measured lattice strain and photovoltaic performances is discussed. The lattice strain evaluated by the Williamson–hall plot of X-ray diffraction data decreased as the tolerance factor was close to one. The efficiency of the Sn-perovskite solar cell was enhanced as the lattice strain decreased. Among them, EA0.1(FA0.75MA0.25)0.9SnI3 having lowest lattice strain gave the best result of 5.41%. Because the carrier mobility increased with a decrease in the lattice strain, these lattice strains would disturb carrier mobility and decrease the solar cell efficiency. Finally, the results that the efficiency of the SnGe-perovskite solar cells was gradually enhanced from 6.42 to 7.60% during storage, was explained by the lattice strain relaxation during the storage

Suppression of Charge Carrier Recombination in Lead-Free Tin Halide Perovskite via Lewis Base Post-treatment

Lead-free tin perovskite solar cells (PSCs) show the most promise to replace the more toxic lead-based perovskite solar cells. However, the efficiency is significantly less than that of lead-based PSCs as a result of low open-circuit voltage. This is due to the tendency of Sn2+ to oxidize into Sn4+ in the presence of air together with the formation of defects and traps caused by the fast crystallization of tin perovskite materials. Here, post-treatment of the tin perovskite layer with edamine Lewis base to suppress the recombination reaction in tin halide PSCs results in efficiencies higher than 10%, which is the highest reported efficiency to date for pure tin halide PSCs. The X-ray photoelectron spectroscopy data suggest that the recombination reaction originates from the nonstoichiometric Sn:I ratio rather than the Sn4+:Sn2+ ratio. The amine group in edamine bonded the undercoordinated tin, passivating the dangling bonds and defects, resulting in suppressed charge carrier recombination

Origin of the Monoclinic-to-Monoclinic Phase Transition and Evidence for the Centrosymmetric Crystal Structure of BiMnO₃

Structural properties of polycrystalline single-phased BiMnO3 samples prepared at 6 GPa and 1383 K have been studied by selected area electron diffraction (SAED), convergent beam electron diffraction (CBED), and the Rietveld method using neutron diffraction data measured at 300 and 550 K. The SAED and CBED data showed that BiMnO3 crystallizes in the centrosymmetric space group C2/c at 300 K. The crystallographic data are a = 9.5415(2) Å, b = 5.61263(8) Å, c = 9.8632(2) Å, β = 110.6584(12)° at 300 K and a = 9.5866(3) Å, b = 5.59903(15) Å, c = 9.7427(3) Å, β = 108.601(2)° at 550 K, Z = 8, space group C2/c. The analysis of Mn−O bond lengths suggested that the orbital order present in BiMnO3 at 300 K melts above TOO = 474 K. The phase transition at 474 K is of the first order and accompanied by a jump of magnetization and small changes of the effective magnetic moment and Weiss temperature, μeff = 4.69μB and θ = 138.0 K at 300−450 K and μeff = 4.79μB and θ = 132.6 K at 480−600 K

Neutron Powder Diffraction Study on the Crystal and Magnetic Structures of BiCoO₃

The crystal and magnetic structures of polycrystalline BiCoO3 have been determined by the Rietveld method from neutron diffraction data measured at temperatures from 5 to 520 K. BiCoO3 (space group P4mm; Z = 1; a = 3.72937(7) Å and c = 4.72382(15) Å at room temperature; tetragonality c/a = 1.267) is isotypic with BaTiO3 and PbTiO3 in the whole temperature range. BiCoO3 is an insulator with a Néel temperature of 470 K. A possible model for antiferromagnetic order is proposed with a propagation vector of k = (1/2, 1/2, 0). In this model, magnetic moments of Co3+ ions are parallel to the c direction and align antiferromagnetically in the ab plane. The antiferromagnetic ab layers stack ferromagnetically along the c axis, forming a C-type antiferromagnetic structure. Refined magnetic moments at 5 and 300 K are 3.24(2)μB and 2.93(2)μB, respectively. The structure refinements revealed no deviation from stoichiometry in BiCoO3. BiCoO3 decomposed in air above 720 K to give Co3O4 and sillenite-like Bi25CoO39

Facile Synthesis and Characterization of Sulfur Doped Low Bandgap Bismuth Based Perovskites by Soluble Precursor Route

The bismuth based perovskite with the structure (CH3NH3)3Bi2I9 (MBI) is rapidly emerging as eco-friendly and stable semiconducting material as a substitute for the lead halide perovskites. A relatively higher bandgap of MBI (about 2.1 eV) has been found to be a bottleneck in realizing the high photovoltaic performance similar to that of lead halide based perovskites. We demonstrate the bandgap engineering of novel bismuth based perovskites obtained by in situ sulfur doping of MBI via the thermal decomposition of Bi­(xt)3 (xt = ethyl xanthate) precursor. Colors of the obtained films clearly changed from orange to black when annealed from 80 to 120 °C. Formation of sulfur doped MA3Bi2I9 was confirmed by XRD and the presence of sulfur was confirmed through XPS. In this work, obtained sulfur doped bismuth perovskites exhibited a bandgap of 1.45 eV which is even lower than that of most commonly used lead halide perovskites. Hall-Effect measurements showed that the carrier concentration and mobility are much higher as compared to that of undoped MA3Bi2I9