Distortion Of Crystal Structure Research Articles

High Phase Stability in CsPbI3 Enabled by Pb-I Octahedra Anchors for Efficient Inorganic Perovskite Photovoltaics.

CsPbI3 inorganic perovskite has exhibited some special properties particularly crystal structure distortion and quantum confinement effect, yet the poor phase stability of CsPbI3 severely hinders its applications. Herein, the nature of the photoactive CsPbI3 phase transition from the perspective of PbI6 octahedra is revealed. A facile method is also developed to stabilize the photoactive phase and to reduce the defect density of CsPbI3 . CsPbI3 is decorated with multifunctional 4-aminobenzoic acid (ABA), and steric neostigmine bromide (NGBr) is subsequently used to further mediate the thin films' surface (NGBr-CsPbI3 (ABA)). The ABA or NG cation adsorbed onto the grain boundaries/surface of CsPbI3 anchors the PbI6 octahedra via increasing the energy barriers of octahedral rotation, which maintains the continuous array of corner-sharing PbI6 octahedra and kinetically stabilizes the photoactive phase CsPbI3 . Moreover, the added ABA and NGBr not only interact with shallow- or deep-level defects in CsPbI3 to significantly reduce defect density, but also lead to improved energy-level alignment at the interfaces between the CsPbI3 and the charge transport layers. Finally, the champion NGBr-CsPbI3 (ABA)-based inorganic perovskite solar cell delivers 18.27% efficiency with excellent stability. Overall, this work demonstrates a promising concept to achieve highly phase-stabilized inorganic perovskite with suppressed defect density for promoting its optoelectronic applications.

Effect of co-substitution of Zn2+/Zr4+ on Surface Morphology, Structure and Magnetic Properties of BaZnxZrxFe12-2xO19

The effect of co-doping of Zn2+/Zr4+ ions on surface morphology, structure and magnetic properties of BaZnxZrxFe12-2xO19 (x=0.00, 0.20,0.40,0.60,0.80, 1.00) synthesized using Pechini method has been investigated. XRD data reveals that the samples are phase pure and have no intermittent phase. The c/a parameter is <3.98 for all samples implying that they are M-type hexaferrites. The grain size increases with an increase in the composition of Zn2+/Zr4+ dopant seen using FE-SEM micrographs. The local crystal structure distortion with increasing Zn2+/Zr4+ dopant composition is confirm by Raman measurements. M vs H plots reveal that all the samples shows magnetic ordering. The highest Ms value has been noticed to be 68.43 emu/g in x=0.20 sample. The Hc value varies from 5350 Oe to 763 Oe with increase in dopant concentration. These materials have strong potential in magnetic recording applications.

Effect of high-energy ball milling on the magnetocaloric properties of La0.7Ca0.2Sr0.1MnO3

We report an experimental–theoretical analysis of the large magnetocaloric effect observed in the compound La0.7Ca0.2Sr0.1MnO3, synthesized by high-energy ball milling assisted by heat treatment. We demonstrated that this method induces crystal structure distortions and defects, which are responsible for the excellent MC properties. X-ray diffraction and Rietveld refinement allowed quantification of the high levels of microstrain and distortion of the synthesized orthorhombic structure (Pnma). Temperature-dependent magnetization measurements reveal a Curie temperature of approximately 310 K; furthermore, a large value of magnetic entropy change |ΔSM|= 4.11 Jkg−1 K−1 and relative cooling power of 61.12 Jkg−1 were estimated by means of Maxwell's equations under an applied field (H) of 18 kOe, making this manganite a promising material for refrigeration applications. Electron paramagnetic resonance spectra of the doped manganite show the presence of Mn4+ ions, which strengthen the double-exchange interaction (ferromagnetic). It is demonstrated that the high-energy ball milling process assisted by heat treatment is an easy, economic, and fast method for synthesizing doped manganites, showing improved magnetocaloric properties compared to those of the same material synthesized by other methods.

Origin of itinerant carriers in antiferromagnetic LaFe1−xMoxO3 studied by x-ray spectroscopies

We report on the electronic structure of doped $\mathrm{LaFe}{\mathrm{O}}_{3}$ at the crossover from an insulating-to-metallic phase transition. Comprehensive x-ray spectroscopic methodologies are used to understand core and valence electronic structure as well as crystal structure distortions associated with the electronic transition. Despite the antiferromagnetic (AFM) ordering at room temperature, we show direct evidence of itinerant carriers at the Fermi level revealed by resonant photoemission spectroscopy (RPES) at the Mo ${L}_{3}$ edge. RPES data taken at the Fe ${L}_{3}$ edge show spectral weight near the valence band edge and significant hybridization with O $2p$ states required for AFM ordering. Resonant inelastic x-ray scattering spectra taken across Fe ${L}_{2,3}$ edges show electron correlation effects ($U$) driven by Coulomb interactions of $d$ electrons as well as broad charge-transfer excitations for $x\ensuremath{\ge}0.2$ where the compound crosses over to a metallic state. Site substitution of Fe by Mo ions in the Fe-${\mathrm{O}}_{6}$ octahedra enhances the separation of the two Fe-O bonds and Fe-O-Fe bonding angles relative to the orthorhombic $\mathrm{LaFe}{\mathrm{O}}_{3}$, but no considerable distortions are present to the overall structure. Mo ions appear to be homogeneously doped, with average valency of both metal sites monotonically decreasing with increasing Mo concentration. This insulator-to-metal phase transition with AFM stability is primarily understood through intermediate interaction strengths between correlation ($U$) and bandwidth ($W$) at the Fe site, where an estimation of this ratio is given. These results highlight the important role of extrinsic carriers in stabilizing a unique phase transition that can guide future efforts in antiferromagnetic-metal spintronics.

Study on the mechanical activation of malachite and the leaching of complex copper ore in the Luanshya mining area, Zambia

Mechanical activation (MA) of malachite was carried out by dry planetary grinding (DPG) and wet Isa grinding (WIG) methods. When the rotational speed was increased to 400 r/min in DPG, the specific surface area of malachite reached the maximum and the particle size reached the minimum of 0.7–100 µm. Agglomeration occurred between mineral particles when the rotational speed was increased to 580 r/min in DPG. However, no agglomeration was observed among particles with sizes 0.4–3 µm in WIG. X-ray diffraction analysis showed that, at a 580 r/min rotational speed in DPG, the amorphization degree of malachite was 53.12%, whereas that in WIG was 71.40%, indicating that MA led to amorphization and distortion of crystal structures. In addition, in the Fourier transform infrared (FT-IR) spectra of activated malachite, the bands associated with −OH, CO 3 2− and metal lattice vibrations of Cu-O and Cu-OH were weakened, and a new H-O-H bending mode and peaks of gaseous CO2 appeared, indicating that MA decreased the band energy, enhanced dihydroxylation, and increased the chemical reactivity of the malachite. Furthermore, the leaching behavior of copper ore was greatly improved by MA.

Metal-Insulator Transitions in β′-CuxV2O5 Mediated by Polaron Oscillation and Cation Shuttling

Summary Silicon circuitry has dominated the semiconductor industry for decades but is constrained in its power efficiency by the Fermi-Dirac distribution of electron energies. Electron-correlated transition metal oxides exhibiting metal-to-insulator transitions (MITs) are excellent candidates for energy-efficient computation, which can further emulate the spiking behavior of biological neural circuitry. We demonstrate that β′-CuxV2O5 exhibits a pronounced nonlinear response to applied temperature, voltage, and current, and the response can be modulated as a function of Cu stoichiometry. We show that polaron oscillation, coupled to the real-space shuttling of Cu ions across two adjacent sites, underpins the MIT of this material. These results reveal the interplay between crystal structure distortions and electron correlation in underpinning the metal-insulator transition of a strongly correlated system. The utilization of coupled cation diffusion and polaron oscillation further demonstrates a means of using ionic vectors to obtain highly nonlinear conductance switching as required for neuromorphic computing.

The State of Platinum in Pyrite Studied by X-Ray Absorption Spectroscopy of Synthetic Crystals

Abstract Pyrite (FeS2) is a typical container of Pt in ores of magmatic and hydrothermal origin and in some carbonrich ores of sedimentary-diagenetic origin. Knowledge of the state of Pt disseminated in the matrix of pyrite, including local atomic environment (type of atoms in the nearest and distant coordination shells, coordination numbers, interatomic distances) and oxidation state, is necessary for physical-chemical modeling of platinum group element mineralization and for the improvement of Pt ore extraction and processing technologies. Here we report results of an investigation of local atomic structure of synthetic Pt-bearing pyrites by means of X-ray absorption spectroscopy (XAS). Synthesis experiments, performed at 580° and 590°C in a Pt-saturated system by means of salt-flux method, yielded crystals of pyrite with concentrations of Pt up to 4 wt %. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) showed that the distribution of Pt within the pyrite grains is of zonal character, but within the distinct zones Pt is distributed homogeneously. Negative correlation between the concentrations of Pt and Fe was observed in the synthesized pyrite grains. The slope of the correlation line corresponds to the formation of the solid solution in the Pt-Fe-S system and/or to the formation of PtS2. The XAS experiments revealed the existence of two forms of Pt in pyrite. The main form is the solid solution Pt(IV), which isomorphically substitutes for Fe. The Pt-S distance in pyrite is ~0.1 Å longer than that of Fe-S in pure pyrite. The distortion of the pyrite crystal structure disappears at R &gt;2.5 Å. The second Pt-rich form was identified by means of high-resolution transmission electron microscopy (HRTEM) as nanosized inclusions of PtS2. Heating experiments with in situ registration of X-ray absorption spectra resulted in partial decomposition (dissolution) of PtS2 nanosized inclusions with the formation of the solid solution (Fe1–xPtx)S2. Therefore, the PtS2 nanosized particles can be considered as a quench product. Our data demonstrate that both Pt solid solution and PtS2 nanosized inclusions (at high Pt content) can exist in natural Pt-bearing pyrites.

Silver vacancy concentration engineering leading to the ultralow lattice thermal conductivity and improved thermoelectric performance of Ag1-xInTe2

AgInTe2 compound has not received enough recognition in thermoelectrics, possibly due to the fact that the presence of Te vacancy (VTe) and antisite defect of In at Ag site (InAg) degrades its electrical conductivity. In this work, we prepared the Ag1-xInTe2 compounds with substoichiometric amounts of Ag and observed an ultralow lattice thermal conductivity (κL = 0.1 Wm−1K−1) for the sample at x = 0.15 and 814 K. This leads to more than 2-fold enhancement in the ZT value (ZT = 0.62) compared to the pristine AgInTe2. In addition, we have traced the origin of the untralow κL using the Callaway model. The results attained in this work suggest that the engineering of the silver vacancy (VAg) concentration is still an effective way to manipulate the thermoelectric performance of AgInTe2, realized by the increased point defects and modified crystal structure distortion as the VAg concentration increases.

Electron Microscopy Study of Silver Nanoparticles Obtained by Thermal Evaporation

Metallic nanoparticles are promising objects of study, since their properties greatly differ from the properties of bulk material. In analyzing nanoparticles, it is important to investigate their size, stability, structural features, and spatial arrangement. In this study, initial and annealed silver nanoparticles from ∼2 to 10 nm in size formed on a carbon substrate by vacuum thermal evaporation are investigated by high resolution transmission electron microscopy and their shape and structure are classified. The examined nanoparticle types include faceted ellipsoid ones with a polycrystalline structure, coarse ones with a single-crystal structure and twins, icosahedral and decahedral ones with multiple twinning, and fine single-crystal nanoparticles smaller than 3.5 nm. It is established that, after annealing, the total number of nanoparticles decreases by a factor of ~1.3, the number of fine nanoparticles almost halves, and the fraction of nanoparticles with icosahedral and decahedral cross sections increases by a factor of ~1.5. It is shown that nanoparticles smaller than 5 nm become unstable already after a few seconds of exposure to high-energy electrons. For fine single-crystal nanoparticles smaller than 3.5 nm, the average crystal-lattice parameter is found by precise determination of the centers of atomic columns in their images and calculation of the local distances between atoms located in the mutually perpendicular (200) and (022) planes. It is shown that, in such nanoparticles both before and after annealing, there are no noticeable crystal-structure distortions and their lattice parameter is similar to the value characteristic of bulk silver.

Raman Characterization of polycrystalline barium hexaferrite nanoparticles: SERS of nanoparticles in powder form

Raman Characterization of Materials in powder form has always remained challenging because of low signal to noise ratio. We, herein, propose a method to make use of Surface Enhanced Raman Scattering (SERS) technique to improve the usefulness of Raman study of powder samples containing particles of sub wavelength size. As a case study, we have successfully applied the method to barium hexaferrite (BHF) synthesized by the modified citrate sol-gel method. The crystal structure and surface morphology of the prepared BHF powder were characterized by X-ray diffraction (XRD) and scanning electron microscopy. As many as 19 Raman peaks in a single spectrum with unpolarized laser were observed in the present work, against the commonly observed (in literature) 10–12 peaks for BHF. This report, as it is believed, will enable the research community to probe further into the distortions in crystal structure through Raman studies.

Characterization and Wear Properties of Fe3Al and (Fe,Ti)3Al Intermetallic Claddings Produced by GTAW Process

In this study, Fe3Al and (Fe,Ti)3Al intermetallic coatings were applied on the surface of CK45 steel by GTAW process. For this purpose, Fe3Al and (Fe,Ti)3Al intermetallic powders were synthesized by mechanical alloying. Phase analysis of powders and coatings was carried out by X-ray diffractometery. The microstructure of the coatings was evaluated by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The wear behavior of the coatings was characterized by reciprocal wear test. It was found that Fe3Al and (Fe,Ti)3Al coatings were deposited successfully on the surface of substrate. The addition of Ti into Fe–Al system enhanced the hardness of the coating due to the dissolution of Ti in lattice and therefore distortion of crystal structure. In FA2 coating (Fe75Al25, 2 weldings) synergic effect of abrasive and adhesive wear mechanisms increased the wear of coating as compared with FAT2 coating (Fe50Al25Ti25, 2 weldings), while the main wear mechanism of FAT2 coating was microcutting abrasive wear.

Lattice Structure and Dynamics of Two-Layer Heterostructures of Barium–Strontium Titanate and Layered Bismuth Titanate of Various Thicknesses on a Magnesium Oxide Substrate

The lattice structure and dynamics of single-crystal Bi4Ti3O12 with a thickness from 4 to 430 nm on a (001)MgO substrate with a previously deposited Ba0.4Sr0.6TiO3 sublayer (4 nm) have been studied. The two-layer structures were prepared by radio-frequency sputtering of ceramic targets of the corresponding compositions. The X-ray diffraction studies performed at room temperature have shown that, in this heterostructure, axis c of the Bi4Ti3O12 unit cell is perpendicular to the substrate, and direction [100] has an angle of ±45° to the [100]MgO direction. At the thicknesses of Bi4Ti3O12 to ~40 nm, the film unit cell is compressed in the direction of a normal to the substrate plane and extended in the conjugate plane, and the sign of the deformation is changed at large thicknesses. It is found that the phonon mode frequency in the Bi4Ti3O12 film shift and additional peaks appear in the Raman spectra, which demonstrates an increase in the degree of monoclinic distortion of the film crystal structure as compared to the crystal structure.

Effect of the Shear Component of Loading on the Damage and Microrelief of Fractures of Specimens of Low-Carbon Steel

Special features of the microrelief of fractures of notched specimens of steel 20 tested under shear, opening and mixed loading modes are studied by x-ray diffraction analysis and analysis of fracture surfaces. The degree of the damage of the specimens is assessed. It is shown that increase in the contribution of the shear component lowers the degree of distortion of crystal structure on the fracture surface, which agrees with reduction of the area of the plastic zone, of the depth of the fracture microrelief, and of the relative width of the shear region. The physical broadening of the x-ray diffraction line obtained from the fracture surface is shown to be correlated with the mode of loading of the specimen.

Low-temperature magnetostriction and distortions in the rare-earth Laves phases

The effects of partial substitution of dysprosium in Tb0.2Dy0.8Co2 by terbium and gadolinium on the structure and magnetic properties have been studied. Two compositions, Tb0.3Dy0.7Co2 and Tb0.2Dy0.7Gd0.1Co2 have been synthesized. Their crystal structure, in contrast to the structure of the original compound, has both tetragonal distortions and rhombohedral distortions at lower temperatures. Anomalies of magnetostriction and magnetocaloric effect near the observed magnetic phase transitions have been studied. The sign-alternating temperature dependences of the longitudinal and transverse magnetostrictions associated with various types of crystal structure distortions of the alloys are revealed.

The Optimization of the Reduction Temperature and the Local Crystal Structure in Titanium-Oxide Nanosheets Model-Electrode to the Oxygen Reduction Reaction in Acidic Environmental

Non-platinum metal-oxide catalyst is expected to the next generation catalyst of polymer electrolyte fuel cell (PEFC). Because the metal oxide catalyst has high natural abundance and long service time. However, the activity of metal oxide catalyst has not achieved that of practical Pt/C catalyst, yet. This means a lot of oxide catalyst needs to the operation of PEFC if it alternatives to Pt/C, at this time. Thus, the enhancement of catalytic activity in metal oxide is urgently needed. To enhance the catalytic activity, we should know well about the reaction mechanism on metal oxide at the first. In reality, the active site of oxygen reduction reaction (ORR) in metal oxide has not been unclear. One possibility was reported that the active site of ORR is the distortion site formed by the oxygen vacancy site in the titanium-based oxide [1]. Past research used the supported catalyst to investigate the active site. The supported catalyst has a complex substance diffusion path, which is attributed to the complicated pore structure. As a result, we should take considerations not only the catalytic reaction but also the diffusion resistivity of oxygen and generation water. However, we cannot focus attention on only the ORR on the oxide catalyst besides to remove the other phenomena in the reaction system. One of the solutions is using the model electrode which can be negligible some diffusion resistivities. In this study, in order to understand the active site, the model electrode composed by titanium oxide nanosheet was prepared and introduced the distortion site by heat treatments. And the ORR activity and the local crystal structure as an index of the distortion site were related in the each calcination temperatures. Titanium oxide nanosheet was prepared according to previous literature [2]. The model electrode was prepared by the layer by layer method. First, the GC plate was dipped into the PDDA solution, and then it rinsed by the ultra-pure water. Next, it dipped into the titanium nanosheet solution. After the rinsing, we obtained a monolayer titanium nanosheet electrode. The distortion site was introduced by the calcination under mixture gas of 10%H2 and 90%Ar. The crystal structure was evaluated by in-plan XRD, and the electron structure was confirmed by XPS and XAFS. The ORR activity was judged from difference curve of cyclic voltammograms between oxygen flow and argon flow conditions in 0.1 M HClO4. The shape and height of titanium oxide nanosheet were retained after the reduction treatment at 600ºC. However, its two-dimensional size shrank a little. Additionally, its crystallinity decreased drastically by the reduction treatment. A diffraction peak of 220 phase attributed to the in-plane structure of titanium oxide nanosheet was slightly sifted by the reduction treatments. This meant that the distortion site was introduced to the titanium oxide nanosheet. The ORR activity improved by the reduction treatments at 600ºC. Thus, the distortion site probably affects to ORR and acts as the active site. On the other hand, the ORR activity of titanium oxide nanosheet decreased when the calcination temperature of reduction treatment elevated until 700ºC. From the above results, the distortion of crystal structure in titanium oxide is expected to take an optimal value.

(High-Temperature Energy, Materials, & Processes Division J. Bruce Wagner, Jr. Award) Impact of Structural Disorder on Opto-electro-chemo-mechanical Interactions in Mixed Conducting Perovskite Oxides

Multifunctional mixed ionic and electronic conducting (MIEC) perovskite oxides – which chemo-mechanically interact with their environment, catalyze reactions, and selectively transport charged species – serve important functions in electrochemical energy conversion and storage devices, gas separation membranes, sensors, actuators, and reactors for chemical fuel production. Ideally these materials should exhibit rapid surface exchange kinetics and transport, for efficiency and fast responses, and tailorable chemical expansion during stoichiometry changes, for controlled dimensional changes and stresses. Therefore, key materials property metrics relating to performance include the ionic and electronic conductivities, surface exchange coefficients (k), and coefficients of chemical expansion (CCE). It is important to understand at a fundamental level how the structure of MIEC perovskite oxides at various scales impacts these key metrics so that design principles for more efficient and durable MIECs can be established. To this end, we have synthesized and characterized in situ bulk and thin film titanate, gallate, zirconate, and cerate perovskites, with aliovalent substitution, as model systems to understand how systematically varied microstructure, crystallinity, crystal symmetry, and defect chemistry impact the opto-electro-chemo-mechanically coupled behavior. In this talk, I would like to highlight in particular two recent results investigating the role of structural disorder. First, we have been developing in situ optical transmission relaxation for the study of defect equilibria and dynamics in perovskite and perovskite-related thin film mixed conductors. We have demonstrated the origins of optical absorption in a non-dilute model system, Sr(Ti,Fe)O3-x, and shown that in the conditions of our studies, the absorption at key wavelengths is proportional to the oxygen concentration. This relationship allows the fitting of in situ thin film optical relaxation curves, that result from oxygen partial pressure changes, to determine k without any current collectors and continuously. The optical absorption is also sensitive to structural changes in the films, so the technique enables simultaneous monitoring of, e.g., crystallization and k. Through this method, and in combination with X-ray absorption studies, we have observed for several compositions how atomic scale order impacts k and how k is enhanced orders of magnitude through in situ crystallization. Second, we have been investigating disorder at the crystal structure length scale to determine how distortions away from the perfect cubic perovskite structure impact the CCEs. We have seen that CCEs monotonically decrease as crystal structure distortions increase (i.e., tolerance factor deviates more from the ideal value of 1). Both microstructural and crystal chemical mechanisms for the reduced expansion for a given stoichiometry change will be presented. This work complements our earlier studies into atomistic factors that impact perovskite CCEs, including electronic charge localization and size of oxygen vacancies. Practical implications of these recent results demonstrating optical measurement and structure-based tailoring of k and CCEs will be discussed.

Symmetry breaking of in-plane anisotropic magnetoresistance with temperature in La-doped Sr2IrO4 films

Electron-doped $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ has been the subject of much recent attention because of its similarities with hole-doped $\mathrm{L}{\mathrm{a}}_{2}\mathrm{Cu}{\mathrm{O}}_{4}$. However, direct evidence of its superconductivity has not yet been observed, which has led to various unresolved issues related to this material. In this study, a 14-nm-thick La-doped $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ film was grown on a (001) $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrate. We found that the fourfold component of the in-plane anisotropic magnetoresistance disappears and is replaced by a twofold symmetry as the temperature increases. Variable-temperature x-ray diffraction and spatially resolved optical second-harmonic generation experiments eliminate the possibility of crystal structural distortion. The temperature dependence of direct current magnetization measurements indicates that a change in the spin structure may account for the symmetry breaking, similar to the nematic ordering of iron-based and other superconductors. Remarkably, the transition temperature of the symmetry breaking is well consistent with the previously reported onset (50 K) of the low-energy gap in K-doped $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ observed by scanning tunneling spectroscopy. Our results provide a perspective on these materials that helps elucidate the nature of magnetic interactions and explores the expected superconductivity of iridates.

Plastically deformed ultramafites of the Ergaksky chromite-bearing massif (Western Sayan)

Dunites and harzburgites of Ergaksky massif constantly show signs of plastic deformation of olivine and enstatite as inhomogeneous extinction, bands of plastic fracture and sintectonic recrystallization. At level of the upper mantle dunites and harzburgites have undergone plastic deformation by translational sliding in olivine at high temperature and low speed. As a result, ultramafic with medium-grained, meso-granular texture formed. In the process of movement in the Earth’s crust plastic deformation occurs mostly as sintectonic recrystallization at subordinate role of translational sliding in conditions of decreasing temperatures and growing speed of plastic flow. This has contributed to the formation of porphyroclastic textures, while translational sliding promoted the distortion of crystal structure and the emergence of non-homogeneous extinction and bands of plastic fracture. Olivinites appeared as a result of secondary recrystallization of annealing under influence of high-temperature fluids on ultramafites.

Regulation of the Crystal Structure Leading to the Bandgap Widening and Phonon Scattering Increasing in Cu3SnS4‐Cu3SbSe3 Chalcogenides

AbstractCu3SnS4 chalcogenide as a low‐cost, earth abundant thermoelectric material has recently attracted much attention. However, its Seebeck coefficient is rather low due to its metallic‐like behavior; therefore, substantial work is required to enhance its thermoelectric (TE) properties. In this work, an alternative method is proposed, that is, a regulation of the crystal structure through alloying with Cu3SbSe3. This regulation is realized by the incorporation of Sb and Se in the Cu3SnS4 host frame with an addition of Cu3SbSe3, thus altering the bond lengths (CuS and SnS) and bond angles (SCuS and SSnS), and leading to widening of the bandgap and the convergence of top valence bands. At the same time, the lattice thermal conductivity reduces by ≈50% at high temperatures, mainly triggered by the crystal structure distortion and introduced point defects. The approach of crystal structure regulation may help design the properties of other ternary CuSn(Sb)S(Se) compounds for TE applications.

Influence of co-modification with tungsten and tantalum on the crystal structure and electrical properties of bismuth titanate ceramics

Bismuth titanate Bi4Ti3O12 (BIT) based lead-free piezoelectric ceramics with the formula Bi4Ti3-2xWxTaxO12 (abbreviated as BITWT-x, x = 0, 0.015, 0.03, 0.04, 0.045, 0.05) were fabricated by the conventional solid-state sintering method. The effect of W and Ta doping on the crystal structure and electrical properties of BITWT-x ceramics were investigated. BITWT-x ceramics had an orthogonal phase, and crystal structural distortion of W/Ta co-doped BITWT-x based ceramics was higher than that of BITWT-0 ceramics, which improved the ferroelectricity and the piezoelectric property. The ferroelectricity (Pr = 7.78 μC/cm2) of BITWT-0.03 ceramics was better than that (Pr = 0.84 μC/cm2) of BITWT-0 ceramics. The piezoelectric property (d33) was enhanced, and the highest d33 of BITWT-0.04 ceramics was 21.4 pC/N. Moreover, the d33 of the BITWT-x ceramics at 600 °C still kept 80% of its original d33 when the value of x was in the range of 0.03–0.045. Donor ions W6+ and Ta5+ reduced ionic conductivity (oxygen vacancies) and electron conductivity (holes), then increased the resistivity of BITWT-x ceramics (ρ400 °C = 1.82 × 108 Ω cm, x = 0.03). However, the enhanced effect reached a saturated state when x was 0.03. Thus, the BITWT-x ceramics were suitable for the high-temperature application.