We conducted ion-substitution doping experiments on CsSnI3 to enhance its electrical properties for thermoelectric applications. While CsPbI3 is widely known as a printable semiconductor for solar cells, Sn-based halide perovskites are expected to be promising thermoelectric materials due to their inherently high carrier density, which originates from the characteristic self-doping effect caused by the instability of Sn2+. A CsSnI3 solution was spin-coated onto a glass substrate, and the resulting films exhibited electrical conductivity after annealing at 130 degrees C. Various dopants, including Bi, Sb, Ni, In, and Cu, were introduced at different concentrations to improve electrical conductivity, and the formation of Sn-based halide perovskites was confirmed by X-ray diffraction analysis. A positive correlation was observed between grain size and electrical conductivity, and it was found that dopants with smaller ionic radii play a significant role in promoting grain growth. Among the tested dopants, In-, Sb-, and Ni-doped samples exhibited higher electrical conductivity, whereas Bi-doped samples showed comparatively lower conductivity, which could be explained by the difference in grain size.

Lead-free hybrid perovskite CH3NH3SnI3 (MASnI3) is a promising light-absorbing material for optoelectronic energy-relevant optoelectronic applications owing to its favorable electronic properties and reduced environmental impact compared to lead-based counterparts. In this study, we systematically investigate the structural, optical, and electrical evolution of MASnI3 under combined high-pressure and elevated-temperature conditions. In situ synchrotron X-ray diffraction reveals that MASnI3 undergoes pressure-induced amorphization at room temperature, whereas concurrent heating and compression drive recrystallization into a stable orthorhombic (Pnma) phase. Post-treatment UV-Vis absorption and electrical resistivity measurements demonstrate pronounced enhancements in both light absorption and electrical conductivity, relative to pristine and room-temperature-processed samples. These improvements may be associated with defect suppression, enhanced crystallinity, and structural reordering involving SnI6 octahedral tilting in addition to metal-halide bond contraction, which may influence the band structure. Our findings establish high-pressure thermal processing as an effective strategy for providing a structure-guided route for stabilizing and optimizing lead-free halide perovskites for sustainable energy optoelectronics.

Tin-based organic-inorganic halide perovskites have emerged as promising lead-free candidates for photovoltaic applications due to their favorable optoelectronic properties. However, their practical deployment is limited by intrinsic instability arising from the native defect formation. In this work, we systematically investigate the defect chemistry of MASnX3 (MA = CH3NH3 +; X = I, Br, Cl) using a combination of density functional theory (DFT) calculations and experimental analysis. Formation energy calculations identify Sn vacancies and halide interstitials as the most thermodynamically favorable defects. Among the series, MASnCl3 exhibits the highest structural stability, attributed to its reduced tendency to form Sn vacancies. Furthermore, Cl doping in MASnI3 is shown to increase the formation energy of Sn vacancies, thereby mitigating defect-induced degradation. These findings offer critical insights into the defect tolerance of tin halide perovskites and highlight effective strategies for enhancing their stability and performance in solar cell applications.

This study focuses on the effect of high-density pulsed electric current (HDPEC) on the microstructure and mechanical properties of ultrafine-grained (UFG) Ti-6Al-7Nb (mass%) alloy. After the UFG Ti alloy prepared by high-pressure torsion (HPT), the samples exhibit high tensile yield strengths of 1200 MPa with total elongation of-20 %. Interestingly, an unusual improved elongation of-33 % with a yield strength of 1100 MPa was obtained in samples processed by HPT plus HDPEC. Quantitative evaluation shows that the improved ductility is attributed to the decreasing of dislocation density. The electron wind force played an important role to promote the movement of dislocation easier with the assistance of local Joule heating during HDPEC processing. It is shown that the bimodal structure with a low dislocation density leads to the high strength and high ductility. It indicated that HDPEC give an effective method to improve the ductility in UFG alloys.

A deep understanding of the effect of the A-site cation cross-exchange on the hot-carrier relaxation dynamics in perovskite quantum dots (PQDs) has profound implications on the further development of disruptive photovoltaic technologies. In this study, the hot carrier cooling kinetics of pure FAPbI3 (FA+ , CH(NH2 )2 + ), MAPbI3 (MA+ , CH3 NH3 + + ), CsPbI3 (Cs+ , Cesium) and alloyed FA0.5 MA0.5 PbI3 , FA0.5 Cs0.5 PbI3 , and MA0.5 Cs0.5 PbI3 QDs are investigated using ultrafast transient absorption (TA) spectroscopy. The lifetimes of the initial fast cooling stage (<1 ps) of all the organic cation-containing PQDs are shorter than those of the CsPbI3 QDs, as verified by the electron-phonon coupling strength extracted from the temperature-dependent photoluminescence spectra. The lifetimes of the slow cooling stage of the alloyed PQDs are longer under illumination greater than 1 sun, which is ascribed to the introduction of co-vibrational optical phonon modes in the alloyed PQDs. This facilitated efficient acoustic phonon upconversion and enhanced the hot-phonon bottleneck effect, as demonstrated by first-principles calculations.

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.

The microstructure and mechanical properties of materials saturate to steady states after severe plastic defor-mation (SPD). Despite the well-known effect of temperature on the steady-state microstructure, there is no general agreement on the significance of strain rate and the applicability of the Zener-Hollomon parameter in this regard. In this study, several pure metals (aluminum, copper, titanium, and iron) and a Cu-30Zn (wt%) brass alloy have been processed by a high-speed high-pressure torsion (HPT) equipment with controllable rotation speeds in the range of 0.06-60 rpm. It is found that crystallite/grain size, dislocation density, microhardness and shear stress at the steady state are reasonably rate-independent for the von Mises strain rates in the range of 0.004-20 s-1. Because both rates of grain refinement and of dynamic recrystallization are proportional to the strain rate, it is suggested that their balance, which determines the steady state, is rate-independent.

A powder mixture of Al-Ti-Mg with an equal atomic fraction was subjected to severe plastic deformation using high-pressure torsion (HPT) under 6 GPa at room temperature for full consolidation. Microstructural evolution with respect to straining and annealing was examined by X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy. The XRD analysis revealed that Ti prevails in the consolidated sample and a phase transformation occurs from alpha phase to omega phase during HPT processing while the total fraction of the omega phase increases with straining. Grain refinement to similar to 100 nm was achieved through the HPT processing for 100 revolutions as well as the formation of nanograined intermetallics such as Al3Ti, AlTi3 and TiAl. The hardness gradually increases with straining, and further increases by annealing at 573 K for 1.5 h due to the formation of an Al12Mg17 phase despite the fact that the harder omega phase was reversely-transformed to the softer alpha phase and grains were coarsened to similar to 450 nm. First-principles cal-culations show that Al and Mg elements are dissolved into the omega - Ti during HPT processing. (C) 2021 Elsevier B.V. All rights reserved.

TiO2 and ZnO, two semiconductors with promising optical properties, are considered as potential candidates for solar and photocatalytic applications. Although chemical methods have been primarily used to enhance the optical properties of these oxides, the current authors recently reported enhanced photocatalytic performance of pure TiO2 and ZnO by plastic straining due to the generation of high-pressure phases and oxygen vacancies. In this study, to improve the optical properties further, large fractions of ZnO/TiO2 interphase boundaries are also introduced by application of high-pressure torsion (HPT) straining to a mixture of anatase-TiO2 and wurtzite-ZnO powders. It was found that the amounts of oxygen vacancies and nanograined high-pressure TiO2-II and rocksalt-ZnO phases increase with increasing plastic strain. Moreover, due to the plastic strain effect, the rutile-TiO2 phase is formed at room temperature, which is at least 600 K below the reported anatase-to-rutile transition temperature. These structural features, together with the formation of large fraction of interphase boundaries, lead to electron spin resonance, optical bandgap narrowing, diminishing of the band-to-band photoluminescence and thus, improvement of photocatalytic hydrogen generation. Despite improvements in the photocatalytic activity of TiO2-ZnO composites after large straining, photocatalytic activity becomes poor by processing at ultra-large strains due to the significant reduction in crystallinity.

Tantalate perovskites are potential candidates for photocatalytic hydrogen production without cocatalyst addition; however, these oxides have large bandgaps, which result in their low photocatalytic activity. In this study, to enhance the photocatalytic activity, CsTaO3 as a potential photocatalyst and LiTaO3 as a well-known photocatalyst are subjected to severe plastic strain using the high-pressure torsion (HPT) method. Both superstrained tantalates exhibit optical bandgap narrowing and similar to 2.5 times enhancement of photocatalytic hydrogen production. Such bandgap narrowing is mainly due to the formation of oxygen vacancies, although nanocrystal formation and partial amorphization also occur by straining. These findings not only introduce CsTaO3 as a photocatalyst but also confirm the significance of strain-induced vacancies on the photocatalytic activity of perovskites.

Magnesium oxide (MgO), which is an insulator ceramic with high significance in geology and earth sciences, is not generally considered as a photocatalyst due to its wide bandgap as similar to 7.8 eV. Experimental studies show that nanocrystalline MgO can have optical bandgaps down to 5.25-5.95 eV and density functional theory calculations suggest that the introduction of oxygen vacancies can reduce the optical bandgap below 5 eV. In this study, oxygen monovacancies and divacancies (F, F+ and F-2(+) centers) are experimentally introduced in nanocrystalline MgO by severe plastic deformation via the high-pressure torsion (HPT) method. The overall optical bandgap is successfully reduced to 3.9 eV after HPT processing. The HPT-processed samples exhibit photocatalytic dye degradation, while the degradation rate improves with increasing the imposed strain. These results not only confirm that the simultaneous introduction of oxygen vacancies and nanocrystals is quite effective to tune the optical properties of nanocrystalline MgO as a nature-friendly photocatalyst, but also introduce a pressure-strain-based mechanism for the formation of vacancy defects in MgO-based minerals.

Phase transformation and optical properties of silica (silicon dioxide, SiO2) quartz sand under high pressure/temperature has been of interest in geology and optical physics for many years. In this study, besides high pressure/temperature, high plastic strain is simultaneously applied to the quartz sand by high-pressure torsion (HPT) processing. The material shows oxygen vacancy formation and transformation to (a) a denser nanocrystalline quartz phase, (b) a high-temperature amorphous phase and (c) a high-pressure coesite phase. These structural and microstructural changes lead to light absorbance, electron spin resonance, photoluminscence and photocatalytic activity, while these changes are enhanced by increasing strain. This study introduces a possible pressure-temperature-strain-based mechanism for the formation of naturally observed vacancies and coesite phase in SiO2-based minerals and sands.

Bismuth oxide (Bi2O3), a yellow semiconductor ceramic, is considered as an advanced photoactive energy material, but its activity still needs further improvement for practical applications. In this study, black Bi2O3 with nanocrystalline structure and large fraction of oxygen vacancies is synthesized by mechanical straining via the high-pressure torsion (HPT) method. The black oxide exhibits enhanced light absorbance under both UV and visible lights. It shows a bipolar photocurrent behavior with up to six times higher photocurrent density compared with the unprocessed yellow Bi2O3. This study shows the high potential of severely-strained black Bi2O3 for photovoltaic, photoconductivity and photocatalytic applications. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Titanium oxide (TiO2), with the anatase and rutile structures, has been widely studied for photovoltaic and solar cell applications, but its main drawback is large bandgap, which limits its activity to the UV light region. In this study, a high-pressure TiO2-II (columbite) phase, which has already been suggested to have low bandgap with downward-shifted Fermi level, is stabilized by the high-pressure torsion (HPT) method and its photovoltaic activity is examined. The TiO2-II formation by HPT processing leads to photocurrent generation under visible light, while the visible-light photocurrent is enhanced further after the recovery of oxygen vacancies by thermal annealing.

The introduction of high-entropy oxides (HEOs), i.e. compounds containing oxygen and five or more cations in their crystal structure, has led to interesting functional properties in recent years. In this study, the first high-entropy photocatalyst is synthesized by mechanical alloying via the high-pressure torsion (HPT) method followed by high-temperature oxidation. The synthesized oxide contains 60 mol% of AB(2)O(7) monoclinic perovskite and 40 mol% of A(6)B(2)O(17) orthorhombic perovskite, where A represents Ti, Zr and Hf and B represents Nb and Ta. This two-phase oxide with an overall composition of TiHfZrNbTaO11 and a d(0) electronic configuration shows an appreciable light absorbance in the visible-light region with a bandgap of 2.9 eV and appropriate valence and conduction bands for water splitting. The material successfully produces hydrogen by photocatalytic water splitting, suggesting the potential of HEOs as new low-bandgap photocatalysts.

Photocatalysis on semiconductors using solar energy sources provides a clean technology to produce hydrogen from water splitting. Although zirconia (ZrO2) is a semiconductor oxide, it is not generally considered as a photocatalyst owing to its poor light absorbance and wide bandgap (over 5 eV). In this study, black ZrO2 with a large concentration of lattice defects such as oxygen vacancies, dislocations and nanograin boundaries is stabilized by high-pressure torsion (HPT) straining. The black ZrO2, which experiences monoclinic-tetragonal phase transformations during the HPT process, shows large light absorption, a small bandgap, reduced conduction band energy and high photocatalytic activity for hydrogen evolution due the presence of oxygen vacancies. These results confirm that the introduction of strain-induced oxygen vacancies is a potential method to produce low-bandgap photocatalysts.

Electrocatalysis using renewable energy sources provides a clean technology to produce hydrogen from water. Titanium oxide is considered as a potential electrocatalyst not only for hydrogen production but also for CO2 conversion. In this study, to enhance the cathodic electrocatalytic activity of TiO2, the phase composition on TiO2 surface is modified by inclusion of high-pressure TiO2-II phase using high-pressure torsion (HPT) straining. Detailed spectroscopic studies revealed that the energy band gap is reduced and the valence band energy increased with increasing the TiO2-II fraction. The highest electrocatalytic activity for hydrogen production was achieved on an anatase-rich nanocomposite containing TiO2-II nanograins.