- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Doping effects on mixed-phase crystalline perovskite AxSr1?xFeO3?δ (A?=?Pr, Sm; 0?≤?x??≤?0.8) nanoparticles and their application for photodegradation of rhodamine B
摘要： A series of doped perovskite AxSr1?xFeO3?δ (A = Pr, Sm; 0 ≤ x ≤ 0.8) nanoparticles were synthesized using a solution combustion method. By doping lanthanide elements, the crystal phase of the perovskite SrFeO3?δ (SFO) changed from cubic to orthorhombic system. Phase transitions and mixed-phase components of prepared catalysts can be successfully controlled only by varying the mole ratio of A-site doping at 800 °C for 5 h. Compared with pure SFO, the Pr/Sm-doped SFO samples exhibited enhanced absorption capability especially in the visible light region. The band gap of Pr/Sm-doped SFO samples was gradually decreased and the BET surface area increased with the increase of the Pr and Sm dopant content. The perovskite AxSr1?xFeO3?δ (A = Pr, Sm; x = 0.6, 0.8) included mixed phases of cubic and orthorhombic crystallinity and exhibited better photocatalytic degradation of rhodamine B (RhB) than single cubic phase. The photodegradation efficiency of RhB was increased with an increasing amount of A-site doping.
关键词： Phase transition,Perovskite,Photocatalytic oxidation,Photodegradation,Mixed phases
更新于2025-09-09 09:28:46
-
Correlation between thermal-vibration-induced large displacement of Cu atoms and phase transition in Cu4SnS4: First-principles investigation
摘要： First-principles (FP) calculations and first-principles molecular dynamics (FPMD) simulations for Cu4SnS4 were performed to clarify the origin of the structural phase transition at 232 K between the high-temperature phase (HP) and low-temperature phase (LP), which leads to an experimentally measured drastic change in the transport properties of Cu4SnS4. The results of the FP and PFMD calculations indicated that, rather than being caused by the so-called freezing of soft modes, the key driving force behind the phase transition in Cu4SnS4 is a large-scale displacement of the Cu atoms located at particular sites due to thermal vibration. In fact, tetrahedrally coordinated CuS4 is stabilized by the effect of the thermal vibration of Cu atoms in the HP whereas CuS3, which is in a trigonal planar environment, is stabilized in the LP.
关键词： first-principles calculation,molecular dynamics simulation,thermoelectric property,electronic structure,phase transition
更新于2025-09-09 09:28:46
-
Elastic and thermophysical properties of BAs under high pressure and temperature
摘要： The pseudopotential plane-wave approach in the framework of the density functional theory, and the density functional perturbation theory with the generalized gradient approach for the exchange-correlation functional has been used to calculate the structural phase stability, elastic constants and thermodynamic properties of boron-arsenide (BAs) compound. The BAs compound transforms from the zincblende phase to rock-salt structure; the phase transition pressure was found to be 141.2 GPa with a volume contraction of around 8.2 %. The thermodynamic properties under high pressure and temperature up to 125 GPa and 1200 K respectively were also determined, analyzed and discussed in comparison with other data of the literature. The systematic errors in the static energy were corrected using the bpscal EEC method. Our results agree well with those reported in the literature, where for example, our calculated melting temperature (2116 K) deviates from the theoretical one (2132.83 K) with only 0.8 %, and the deviation between our result (1.86) of the Grüneisen parameter and the theoretical one (1.921) is only around 3.2 %.
关键词： Phase transition,Thermodynamic properties,High-pressure,High-temperature,Boron arsenide
更新于2025-09-09 09:28:46
-
Phase diagram and physical properties of (110) oriented Ba(Zr0.08Ti0.92)O3 thin film
摘要： A phenomenological Landau-Devonshire theory is applied to construct the thermodynamic potential of (110) oriented Ba(Zr0.08Ti0.92)O3 thin film and investigate the phase transition, ferroelectric, dielectric and piezoelectric properties. Three ferroelectric phases, such as tetragonal a1 phase, orthorhombic a2c and triclinic γ phase are stable in “misfit strain-temperature” phase diagram. Two triple points are found in the phase diagram and 90° polarization switching can occur directly between tetragonal a1 phase and orthorhombic a2c phase. Complicated phase transitions are induced by the electric field in triclinic γ phase due to the nonlinear coupling terms appeared in the thermodynamic potential. The longitudinal piezoelectric coefficient of (110) oriented Ba (Zr0.08Ti0.92)O3 thin film is smaller than that of (001) oriented film. Moreover, negative longitudinal piezoelectric coefficient can be obtained in triclinic γ phase.
关键词： A. Ferroelectric thin film,D. Piezoelectric property,D. Phase transition
更新于2025-09-09 09:28:46
-
High–pressure electrical conductivity and Raman spectroscopy of chalcanthite
摘要： The phase transitions and dehydration of chalcanthite were investigated by electrical conductivity and Raman spectroscopy at 1.0–24.0 GPa and 293–673 K in a diamond anvil cell. At ambient temperature, two secondary phase transitions were observed according to discontinuous changes in the slope of Raman shifts, full width at half maximum and electrical conductivities at (cid:1)7.3 and (cid:1)10.3 GPa. The dehydration temperatures were determined by the splitting of Raman peaks and changes in electrical conductivity as (cid:1)350 and (cid:1)500 K at respective (cid:1)3.0 and (cid:1)6.0 GPa. A positive relationship for chalcanthite between dehydration temperature and pressure is established.
关键词： dehydration,chalcanthite,phase transition,Raman spectroscopy,electrical conductivity
更新于2025-09-09 09:28:46
-
by means of high-pressure–high-temperature Raman experiments
摘要： We report here high-pressure–high-temperature Raman experiments performed on BiVO4. We characterized the fergusonite and scheelite phases (powder and single crystal samples) and the zircon polymorph (nanopowder). The experimental results are supported by ab initio calculations, which, in addition, provide the vibrational patterns. The temperature and pressure behavior of the fergusonite lattice modes reflects the distortions associated with the ferroelastic instability. The linear coefficients of the zircon phase are in sharp contrast to the behavior observed in the fergusonite phase. The boundary of the fergusonite-to-scheelite second-order phase transition is given by TF ?Sch(K) = ?166(8)P (GPa) + 528(5). The zircon-to-scheelite, irreversible, first-order phase transition takes place at TZ?Sch(K) = ?107(8)P (GPa) + 690(10). We found evidence of additional structural changes around 15.7 GPa, which in the downstroke were found to be not reversible. We analyzed the anharmonic contribution to the wave-number shift in fergusonite using an order parameter. The introduction of a critical temperature depending both on temperature and pressure allows for a description of the results of all the experiments in a unified way.
关键词： zircon,scheelite,BiVO4,fergusonite,high-temperature,phase transition,high-pressure,ab initio calculations,Raman experiments,vibrational patterns
更新于2025-09-09 09:28:46
-
Phase structure analysis and pyroelectric energy harvesting performance of Ba(Hf <sub/><i>x</i> </sub> Ti <sub/> 1 <i>-x</i> </sub> )O <sub/>3</sub> ceramics
摘要： Ba(Ti1-xHfx)O3 ceramics were synthesized by a solid-state reaction process. The evolution of the phase structure was identified by XRD spectrum, dielectric spectroscopy and temperature-dependent Raman spectroscopy for the Ba(Ti1-xHfx)O3 ceramics. In addition, pyroelectric energy harvesting properties based on the Olsen cycle were investigated for the first time. A maximum pyroelectric energy harvesting density value of ND=491.30 kJ/m3 (ΔT=120 °C, EH=50 kV/cm) was achieved in the Ba(Hf0.05Ti0.95)O3 ceramic. Compared with those of BT, the values of ND more than doubled in the temperature range from ΔT=60 °C to ΔT=100 °C in the Ba(Hf0.05Ti0.95)O3 ceramic and even increased 3.2 times at ΔT=80 °C near the Curie temperature (TC) of the Ba(Hf0.05Ti0.95)O3 sample. In addition, a larger pyroelectric energy harvesting density value of ND=367.10 kJ/m3 (ΔT=120 °C, EH=50 kV/cm) was acquired in the Ba(Hf0.12Ti0.88)O3 ceramic. Values of ND-BHT5/ND-BT and ND-BHT12/ND-BT were analyzed in the Ba(Ti1-xHfx)O3 ceramics. The optimal pyroelectric properties can be obtained in the vicinity of the ferroelectric to paraelectric phase-transition region.
关键词： Phase transition,Lead-free ceramics,Raman spectra,Ferroelectric materials,Energy harvesting
更新于2025-09-09 09:28:46
-
Negative Thermal Expansion Near the Precipice of Structural Stability in Open Perovskites
摘要： Negative thermal expansion (NTE) describes the anomalous propensity of materials to shrink when heated. Since its discovery, the NTE effect has been found in a wide variety of materials with an array of magnetic, electronic and structural properties. In some cases, the NTE originates from phase competition arising from the electronic or magnetic degrees of freedom but we here focus on a particular class of NTE which originates from intrinsic dynamical origins related to the lattice degrees of freedom, a property we term structural negative thermal expansion (SNTE). Here we review some select cases of NTE which strictly arise from anharmonic phonon dynamics, with a focus on open perovskite lattices. We find that NTE is often present close in proximity to competing structural phases, with structural phase transition lines terminating near T=0 K yielding the most prominent displays of the SNTE effect. We further provide a theoretical model to make precise the proposed relationship among the signature behavior of SNTE, the proximity of these systems to structural quantum phase transitions and the effects of phase fluctuations near these unique regions of the structural phase diagram. The effects of compositional disorder on NTE and structural phase stability in perovskites are discussed.
关键词： structural phase transition,negative thermal expansion,perovskite,scandium trifluoride,antiferrodistortive phase transition,quantum phase transition,structural negative thermal expansion
更新于2025-09-04 15:30:14
-
Stable 1T Tungsten Disulfide Monolayer and Its Junctions: Growth and Atomic Structures
摘要： Transition metal dichalcogenides in the 1T phase have been a subject of increasing interest partly due to their fascinating physical properties and partly to their potential applications in the next generation of electronic devices, including supercapacitors, electrocatalytic hydrogen evolution, and phase-transition memories. The primary method for obtaining 1T WS2 or MoS2 has been using ion intercalation in combination with solution-based exfoliation. The resulting flakes are small in size and tend to aggregate upon deposition, forming an intercalant-TMD complex with small 1T and 1T’ patches embedded in the 2H matrix. Existing growth methods have, however, produced WS2 or MoS2 solely in the 2H phase. Here we have refined the growth approach to obtain monolayer 1T WS2 up to 80 μm in size based on chemical vapor deposition. With the aid of synergistic catalysts (iron oxide and sodium chloride), 1T WS2 can nucleate in the infant stage of the growth, forming special butterfly-like single crystals with the 1T phase in one wing and the 2H phase in the other. Distinctive types of phase boundaries are discovered at the 1T/2H interface. The 1T structure thus grown is thermodynamically stable over time and even persists at a high temperature above 800 ?C, allowing for a stepwise edge epitaxy of lateral 1T heterostructures. Atomic images show that the 1T WS2/MoS2 heterojunction features a coherent and defectless interface with a sharp atomic transition. The stable 1T phase represents a missing piece of the puzzle in the research of atomic thin van der Waals crystals, and our growth approach provides an accessible way of filling this gap.
关键词： 1T WS2,phase transition,chemical vapor deposition,transition metal dichalcogenides,heterojunctions
更新于2025-09-04 15:30:14
-
Surface-induced transition of nematic liquid crystals on graphene/SiC substrate
摘要： A nematic liquid-crystal director aligns along the armchair direction of graphene grown on a SiC substrate. The temperature-dependent textural change in the nematic phase is di?erent from the usual texture on the alignment layer. The isotropic-nematic phase transition temperature decreases over time after cell fabrication. Tiny domains occur with the phase transition and appear to be merged from a critical temperature with decreasing temperature in the nematic phase. This is thought to be due to the transition occurring at the interface. On the other hand, the nematic liquid crystal in graphene grown on a Cu foil does not show textural changes, and the phase transition temperature does not decrease even after a long time has elapsed. X-ray ?uorescence measurements indicate that silicon atoms exist in the liquid crystal possibly extracted from the SiC substrate. A model of ?rst-order phase transition on the graphene surface has been proposed. This transition is accompanied by an inhomogeneous distribution of scalar order parameters and the transformation from a small multi-grained structure to a large domain distribution in the director ?eld. This structural transformation takes place at a temperature di?erent from that corresponding to the bulk transition. Such behavior may be explained by the adsorption process of silicon atoms in contact with the SiC-graphene interface.
关键词： surface-induced transition,phase transition,SiC substrate,nematic liquid crystals,graphene
更新于2025-09-04 15:30:14