Semiconductor-like Behavior Research Articles

Crystal Structure and Physical Properties of a Layered Oxyarsenide Sr2VCrAsO3.

We report the synthesis, crystal structure, and physical properties of the mixed transition-metal oxyarsenide Sr2VCrAsO3. The compound has an ordered intergrowth structure with the perovskite-like layers of "Sr3V2O6" and the ThCr2Si2-type layers of "SrCr2As2" stacking alternately along the crystallographic c axis, in which ∼10% mixed occupancy between V and Cr is present for the sample synthesized by solid-state reactions. The electrical resistivity data show semiconducting-like behavior, probably associated with the occupancy disorders in the CrAs layers. The magnetic measurement reveals two anomalies at T1 ≈ 85 and T2 ≈ 335 K, which are attributed to short-range antiferromagnetic (AFM) ordering in the VO2 planes and long-range AFM ordering in the CrAs layers, respectively. The neutron powder diffraction measurements indicate a C-type AFM ordering of Cr spins along the c axis within the CrAs layers. Compared with other CrAs-layer-based compounds, the T2 value is remarkably reduced, probably due to the synergistic effect of the nearest-neighbor magnetic interaction, V doping in the CrAs layers, interlayer charge transfer, and enhanced two dimensionality.

Recent developments in atomically precise metal nanocluster-based photocatalysts for hydrogen production.

Photocatalytic hydrogen production offers a sustainable approach for utilising light energy, providing a promising solution to global energy challenges. The efficiency of this process relies on developing photocatalysts with broad light responsiveness and effective charge carrier separation capabilities. Atomically precise metal nanoclusters (NCs) have emerged as a highly favourable class of materials for this role due to their unique atomic arrangements, ultrasmall size, quantum confinement effects, and plenty of surface-active sites. These exceptional properties endow NCs with semiconductor-like behaviour, allowing for the generation of electrons and holes under light excitation, thus driving the hydrogen production reaction. Moreover, their robust light-absorption properties across the UV to near-IR spectrum, coupled with tuneable optical properties controlled by their composition and structure, promise NCs as next-generation photocatalysts. This review explores recent developments in the application of NCs for photocatalytic hydrogen production, emphasising strategies to enhance charge carrier separation and transfer efficiency, as well as photostability. The discussion also highlights the challenges and future opportunities in using NCs for efficient hydrogen production.

First-principles study of robust half-metallic ferromagnetism and electronic structure of the Heusler compounds Co2-xCrxMnGe

Abstract Half-metallic ferromagnets (HMFs) are among the most promising materials in the field of spintronics because of their distinct band structures, which consist of two characteristic subbands, one with semiconductor-like behaviour and the other with metallic features. Using density functional theory-based calculations, we have carried out in-depth studies to predict the effects of Co replacement by Cr on electronic structure as well as the magnetic properties of Co2-xCrxMnGe with 0 ≤ x ≤ 1. The results demonstrate that the alloys are stable in the ferromagnetic phase with half-metallic nature. The origin of ferromagnetism can be explained by Ruderman-Kittel-Kasuya-Yosida (RKKY), like exchange interaction. Due to their high Curie temperatures, which increase linearly with the total magnetic moment, all alloys are suitable for applications at and above room temperature. Besides, the electronic properties have revealed a transition from half-metallic to semi-metallic character for higher doping concentration (x = 0.75, x = 1.0). The calculated total magnetic moments, however, decrease with increasing doping concentration, consistent with the Slater-Pauling rule. The observed high value of spin polarisation of all the studied compounds suggests their futuristic roadmaps for possible spintronics applications beyond room temperature.

Magnetism and Thermoelectric Properties of the Zintl Semiconductor: Eu21Zn4As18.

Compositional diversity and intriguing structural features have made Zintl phases excellent candidates as thermoelectric materials. Zintl phase with 21-4-18 composition has shown high thermoelectric performance in the mid- to high-temperature ranges. The complex crystal structure and favorable transport properties of these compounds indicate the potential for high thermoelectric efficiency. Arsenic-based Eu21Zn4As18, belonging to the Ca21Mn4Sb18 structure type, exhibits a semiconductor-like p-type transport behavior and has a calculated band gap of 0.49 eV. The compound is paramagnetic at high temperatures, with an antiferromagnetic transition occurring at T N = ∼10 K. The moment obtained from the Curie-Weiss data fit aligns with Eu2+ ions. At the same time, the field-dependent measurement at 2 K indicates complex magnetic ordering with a saturation moment consistent with Eu2+ ions. Pristine Eu21Zn4As18 exhibits an ultralow lattice thermal conductivity of 0.40 W m-1 K-1 at 873 K. Electronic transport properties measurement shows evidence of bipolar conduction across much of the measured temperature range (450-780 K). However, the Seebeck coefficient remains extremely high (>440 μV K-1) across this range, indicating the potential for high zT if an appropriate dopant is found. This work represents the first report on the temperature-dependent thermal conductivity, Seebeck coefficient, and thermoelectric efficiency of the arsenic-containing Zintl phase with 21-4-18 composition, showcasing its promise for further optimization of the thermoelectric performance.

The effect of the oxygen dangling on the thermoelectric properties of organic Thienoisoindigo single-molecule junction.

Theoretical investigation for thermoelectric characteristics of organic Thienoisoindigo single-molecule is carried out using the first-principles calculations based on the density functional theory. It reveals that modifying the position or removing oxygen atoms significantly alters the thermoelectric properties. Transmission coefficient calculations show that the lowest unoccupied molecular orbital (LUMO) dominates across all molecular configurations. Repositioning oxygen atoms increases the bandgap from 1.14 to 1.53 eV, while the complete removal of oxygen further increases to 1.8 eV. This change leads to the disruption of constructive quantum interference, which is replaced by destructive one. The electrical conductance is similarly affected by changes in oxygen atom positioning, with values shifting from 1.06 to 1.63. Molecules without oxygen atoms exhibit lower conductance compared to those with dangling oxygen, resulting in reduced semiconductor-like behavior and enhanced insulating properties. The Seebeck coefficient remains stable at 2.99 V/K when oxygen atoms are repositioned. However, the removal of one oxygen atom changes the coefficient to a positive value (290.14 V/K), causing the molecule to transition from n-type to p-type behavior. The complete absence of oxygen atoms returns the Seebeck coefficient to a negative value ( 256.08 V/K), switching the molecule back to n-type conduction. This investigation was achieved by applying the SIESTA software through density functional theory (DFT) computations. To account for exchange and correlation effects, we use a double-zeta polarized (DZP) basis set in conjunction with the generalized gradient approximation (GGA-PBE) to determine the ideal ground-state atomic locations. By combining the Hamiltonian of each system with the quantum transport code GOLLUM, we can calculate the transmission coefficient, projected density of states, electrical conductance, and Seebeck coefficient to examine the thermoelectric characteristics of the molecular junction.

Semiconductive-like behaviour and negative differential effect observed in self-assembled riboflavin layer on gold electrodes

Semiconductive-like behaviour and negative differential effect observed in self-assembled riboflavin layer on gold electrodes

Influence of the reactive gas mixture on the superconducting properties of nitrogen-doped aluminum thin films

Influence of the reactive gas mixture on the superconducting properties of nitrogen-doped aluminum thin films

Conductive single-phase SrMoO3 epitaxial films synthesized in pure Ar ambience via plasma-assisted radio frequency sputtering

ABSTRACT The cubic perovskite SrMoO3 with a paramagnetic ground state and remarkably low room-temperature resistivity has been considered as a suitable candidate for the new-era oxide-based technology. However, the difficulty of preparing single-phase SrMoO3 thin films by hydrogen-free sputtering has hindered their practical use, especially due to the formation of thermodynamically favorable SrMoO4 impurity. In this work, we developed a radio frequency sputtering technology enabling the reduction reaction and achieved conductive epitaxial SrMoO3 films with pure phase from a SrMoO4 target in a hydrogen-free, pure argon environment. We demonstrated the significance of controlling the target-to-substrate distance (TSD) on the synthesis of SrMoO3; the film resistivity drastically changes from 1.46 × 105 μΩ·cm to 250 μΩ·cm by adjusting the TSD. Cross-sectional microstructural analyses demonstrated that films with the lowest resistivity, deposited for TSD = 2.5 cm, possess a single-phase SrMoO3 with an epitaxial perovskite structure. The formation mechanism of the conductive single-phase SrMoO3 films can be attributed to the plasma-assisted growth process by tuning the TSD. Temperature-dependent resistivity and Hall effect studies revealed metal-like conducting properties for low-resistive SrMoO3 films, while the high-resistive ones displayed semiconductor-like behavior. Our approach makes hydrogen-free, reliable and cost-efficient scalable deposition of SrMoO3 films possible, which may open up promising prospects for a wide range of future applications of oxide materials.

From MAX to MXene: A case study of Sc2TlC MAX phase, Sc2C pristine MXene, and surface-functionalized Sc2CT2 (T=O, F) MXenes

From MAX to MXene: A case study of Sc2TlC MAX phase, Sc2C pristine MXene, and surface-functionalized Sc2CT2 (T=O, F) MXenes

Efficiently high energy storage density in Ba2+ ion modified K0·5Na0·5NbO3 (KNN) ferroelectric ceramics for super capacitors

Efficiently high energy storage density in Ba2+ ion modified K0·5Na0·5NbO3 (KNN) ferroelectric ceramics for super capacitors

Synthesis and characterization of Fe-doped CuO nanoparticles: Catalytic efficiency in crystal violet dye degradation and exploration of electrical properties

In recent times, environmental pollution has become a pressing issue. Different methods have been developed to detach hazardous materials from H2O bodies. Among these techniques, photo-catalysis has emerged as a low-cost and advanced method. However, finding a potent photocatalyst has been a topic of considerable research. Our study prepared CuO from copper acetate using hydrothermal treatment in an autoclave at 170 ºC for 14 hours. We introduced various quantities of Fe by adding FeSO4 mixture to Cu (CH3COO)2, following the identical method for preparing CuO. The resulting precipitate was cleaned with deionized H2O and dried at 100 °C. The prepared substance was then heated at 450 ºC in a muffle furnace for 60 minutes. We characterized the manufacture of photocatalysts utilizing various techniques such as Ultraviolet (UV), FT-IR, SEM, EDX, and XRD. Our Ultraviolet (UV) spectrum analysis helped us recognize the adsorption spectroscopic analysis of un-doped and doped CuO with various ratios of Fe. FTIR spectroscopic analysis helped us identify functional groups in CuO NPs. Our XRD study showed the monoclinic composition of copper oxide nanoparticles. The SEM picture suggested that NPs exist in a spherical shape. We studied the catalytic activity of synthesized NPs concerning crystal violet (CV) colorant degradation below a direct ray of light irradiation. Our results showed that the degradation productiveness, as compared to CV colorant, was about 93.52% in 180 min. This research is of great importance in the quest for effective and sustainable solutions to environmental problems. The examination of electrical properties highlighted the promising aspects of Fe-doped CuO, particularly at 6% doping. This variant demonstrated superior dielectric parameters, lower tangent loss, semiconductor-like impedance behavior, and enhanced electrical conductivity, emphasizing its potential for applications in electrical and energy storage domains.

Study on Water Splitting of the 214-Type Perovskite Oxides LnSrCoO4 (Ln = La, Pr, Sm, Eu, and Ga).

We present a study on the electrocatalysis of 214-type perovskite oxides LnSrCoO4 (Ln = La, Pr, Sm, Eu, and Ga) with semiconducting-like behavior synthesized using the sol-gel method. Among these five catalysts, PrSrCoO4 exhibits the optimal electrochemical performance in both the oxygen evolution reaction and the hydrogen evolution reaction, mainly due to its larger electrical conductivity, mass activity, and turnover frequency. Importantly, the weak dependency of LSV curves in a KOH solution with different pH values, revealing the adsorbate evolving mechanism in PrSrCoO4, and the density functional theory (DFT) calculations indicate that PrSrCoO4 has a smaller Gibbs free energy and a higher density of states near the Fermi level, which accelerates the electrochemical water splitting. The mutual substitution of different rare-earth elements will change the unit-cell parameters, regulate the electronic states of catalytic active site Co ions, and further affect their catalytic performance. Furthermore, the magnetic results indicate strong spin-orbit coupling in the electroactive sites of Co ions in SmSrCoO4 and EuSrCoO4, whereas the magnetic moments of Co ions in the other three catalysts mainly arise from the spin itself. Our experimental results expand the electrochemical applications of 214-type perovskite oxides and provide a good platform for a deeper understanding of their catalytic mechanisms.

High-Tc Ferromagnetic Semiconductor in Thinned 3D Ising Ferromagnetic Metal Fe3GaTe2.

Emergent phenomena in exfoliated layered transition metal compounds have attracted much attention in the past several years. Especially, pursuing a ferromagnetic insulator is one of the exciting goals for stimulating a high-performance magnetoelectrical device. Here, we report the transition from a metallic to high-Tc semiconductor-like ferromagnet in thinned Fe3GaTe2, accompanied with competition among various magnetic interactions. As evidenced by critical exponents, Fe3GaTe2 is the first layered ferromagnet described by a 3D Ising model coupled with long-range interactions. An extra magnetic phase from competition between ferromagnetism and antiferromagnetism emerges at a low field below Tc. Upon reducing thickness, the Curie temperature (Tc) monotonically decreases from 342 K for bulk to 200 K for 1-3 nm flakes, which is the highest Tc reported as far as we know. Furthermore, a semiconductor-like behavior has been observed in such 1-3 nm flakes. Our results highlight the importance of Fe3GaTe2 in searching for ferromagnetic insulators, which may benefit spintronic device fabrication.

Synthesis of a new potassium-substituted lead fluorapatite and its structural characterization.

Prismatic crystals of partially potassium substituted lead fluorapatite Pb5.09Ca3.78K1.13(PO4)6F0.87 were grown through a solid-state reaction. The structural study conducted by single-crystal X-ray diffraction revealed that the compound crystallizes in the hexagonal P63/m space group, with unit cell parameters a = b = 9.7190(5) Å, c = 7.1700(6) Å and V = 587.37(7) Å3(Z = 1), as well as final values amounting to R and wR of 0.0309 and 0.0546, respectively. The structural refinement demonstrated that Pb occupies both the (6h) and (4f) structural sites of hexagonal fluorapatite, K occupies the (6h) site, and Ca is placed on the (4f) site. Powder X-ray diffraction study indicated the absence of additional phases or impurities. Chemical analysis using atomic absorption spectrometry and energy-dispersive X-ray spectroscopy confirmed the expected chemical formula. The electrical conductivity measured over a wide temperature range was found to be governed by the ion mobility mechanism in the tunnel along the c axis (probably attributed to the fluorine ion located there). We, therefore, could infer from the analysis of the complex impedance spectra that the electrical conductivity of our apatite depends essentially on the temperature and frequency, which produces a relaxation phenomenon and semiconductor-like behavior. Moreover, the strong absorption in the UV-Visible region was substantiated through studies of the optical properties of the developed sample. Fluorescence spectra exhibited emissions in the orange regions when excited at 375 nm. The findings of the phenomena resulting from the emission and conduction of the apatite in question suggest its potential for application in various technological fields such as photovoltaic cells, optoelectronics, photonics, LED applications, catalysis and batteries.

A low-temperature thermoelectric transport study of non-stoichiometric AgSbTe2.

In recent times, considerable attention has been given to examining the impact of micro/nanostructure on the thermoelectric characteristics of nonstoichiometric AgSbTe2. The present investigation employed direct melting of elements that produced p-type AgSbTe2 with spontaneous nanostructuring due to cation ordering. The product predominantly features an Ag-deficient Ag0.927Sb1.07Te2.005 phase with monoclinic Ag2Te nanoprecipitates and exhibits a degenerate semiconductor-like behavior with an energy band gap of 0.15 eV. A Seebeck coefficient of 251 μV K-1 and a power factor of 741 μW m-1 K-2 at near ambient temperature are attained with this composition. The variable range hopping (VRH) and linear magnetoresistance (LMR) confirmed that the low-temperature transport followed a VRH between the localized states. The composition also exhibited glass like thermal conductivity of 0.2 W m-1 K-1 arising from phonon scattering at all-scale hierarchical structures that led to a high ZT of 1.1 at room temperature. The direct melted ingots show a high relative density of ∼97%, Vickers hardness Hv of ∼108.5 kgf mm-2, and excellent thermal stability, making them an attractive choice for TEGs.

Tailoring the structural, optical, electrical and multiferroic properties of Sm1-xRxFeO3 (x = 0.0 and 0.5; R = Pr, Nd, and Gd) and their synergistic photocatalytic activity

Tailoring the structural, optical, electrical and multiferroic properties of Sm1-xRxFeO3 (x = 0.0 and 0.5; R = Pr, Nd, and Gd) and their synergistic photocatalytic activity

Investigations of two-dimensional Zirconium carbide/nitride MXenes in the presence of Oxygen/Fluorine functional groups

Investigations of two-dimensional Zirconium carbide/nitride MXenes in the presence of Oxygen/Fluorine functional groups

High-pressure synthesis of half-doped perovskites MnV0.5Nb0.5O3 and MnV0.5Ta0.5O3 with unusual A-site small Mn2+ cations

ABSTRACT We have successfully synthesized two new half-doped perovskites, MnV0.5Nb0.5O3 and MnV0.5Ta0.5O3, with unique small Mn2+ cations at the A site under high-temperature and high-pressure conditions (6 GPa and 900–1300 °C). Synchrotron X-ray structure analysis confirmed their crystal structures to belong to the space group Pnma, and they do not exhibit features of an ordered perovskite (double perovskite) structure. Magnetic property measurements revealed an essentially antiferromagnetic nature below 17 and 18 K for both compounds, respectively, accompanied by a small contribution of thermal and magnetic field hysteresis. Electrical conductivity measurements showed activation energies of 0.13 and 0.31 eV, respectively, suggesting semiconductor-like behavior. These findings underscore the potential of these materials with unusual A-site small Mn2+ cations for electronic and magnetic devices, warranting further studies to explore their unique magnetic and electronic properties.

Emergence of High-Temperature Superconducting Phase in Pressurized La3Ni2O7 Crystals

The recent report of pressure-induced structural transition and signature of superconductivity with T c ≈ 80 K above 14 GPa in La3Ni2O7 crystals has garnered considerable attention. To further elaborate this discovery, we carried out comprehensive resistance measurements on La3Ni2O7 crystals grown in an optical-image floating zone furnace under oxygen pressure (15 bar) using a diamond anvil cell (DAC) and cubic anvil cell (CAC), which employ a solid (KBr) and liquid (glycerol) pressure-transmitting medium, respectively. Sample 1 measured in the DAC exhibits a semiconducting-like behavior with large resistance at low pressures and gradually becomes metallic upon compression. At pressures P ⩾ 13.7 GPa we observed the appearance of a resistance drop of as much as ∼ 50% around 70 K, which evolves into a kink-like anomaly at pressures above 40 GPa and shifts to lower temperatures gradually with increasing magnetic field. These observations are consistent with the recent report mentioned above. On the other hand, sample 2 measured in the CAC retains metallic behavior in the investigated pressure range up to 15 GPa. The hump-like anomaly in resistance around ∼ 130 K at ambient pressure disappears at P ⩾ 2 GPa. In the pressure range of 11–15 GPa we observed the gradual development of a shoulder-like anomaly in resistance at low temperatures, which evolves into a pronounced drop of resistance of 98% below 62 K at 15 GPa, reaching a temperature-independent resistance of 20 μΩ below 20 K. Similarly, this resistance anomaly can be progressively shifted to lower temperatures by applying external magnetic fields, resembling a typical superconducting transition. Measurements on sample 3 in the CAC reproduce the resistance drop at pressures above 10 GPa and realize zero resistance below 10 K at 15 GPa even though an unusual semiconducting-like behavior is retained in the normal state. Based on these results, we constructed a dome-shaped superconducting phase diagram and discuss some issues regarding the sample-dependent behaviors on pressure-induced high-temperature superconductivity in the La3Ni2O7 crystals.

Semiconductor-like optical properties unveiled by dispersion relation modeling of short-period aluminum oxide-copper multi-layered nanocomposites deposited by sputtering atomic layer augmented deposition (SALAD)

In our previous publication, we discussed the optical properties of short-period multi-layered nanocomposites consisting of 300 pairs of an AlOx layer and a Cu layer produced from sputtering atomic layer augmented deposition (SALAD). These samples displayed unusual spectral reflectance that could not be well described via conventional means and could not be explained as an interpolation of the constituent materials, which is most likely due to the fact that the samples optically behave as a homogeneous composite rather than a multi-layered structure. Thus, in the present study, dispersion relation modeling (DRM) is used to extract fundamental optical constants – refractive index – to assess distinctive optical properties of the samples. While the DRM model implemented proved to be imperfect with regard to purely non-holomorphic materials, preliminary results nevertheless predicts that the samples – composed of multiple layers of metal and dielectric – should display semiconductor-like optical behavior, therefore, indicating SALAD can potentially yield materials, by combining metal and dielectric, that virtually behave as semiconductors.