Transition Metal Thiophosphates Research Articles

Visible-Light Self-Powered Photodetector with High Sensitivity Based on the Type-II Heterostructure of CdPSe3/MoS2.

Transition metal thiophosphates (MTPs) are a group of emerging van der Waals materials with widely tunable band gaps. In the MTP family, CdPSe3 is demonstrated to possess a wide energy band gap and high carrier mobility, making it a potential candidate in optoelectronic applications. Here, we reported photoelectric response behaviors of both CdPSe3- and CdPSe3/MoS2-based photodetectors (noted as CPS and CM, respectively); these showed prominent photoelectric performances, and the latter proved to be significantly superior to the former. These devices exhibited ultralow dark current at a magnitude order of 10-12 A and fine cycle and air stabilities. Compared with CPS, CM demonstrated the highest responsivity (91.12 mA/W) and detectivity (1.74 × 1011 Jones) at 5 V under 425 nm light illumination. Besides, CM showed self-powered photoelectric responses at zero bias, which was attributed to the improved separation efficiency of photogenerated carriers by the built-in electric field at the interface of the p-n junction. This work proves a prospect for the CM device in portable, self-powered optoelectronic device applications.

Electronic Band Structure and Optical Properties of HgPS3 Crystal and Layers.

Transition metal thiophosphates (MPS3) are of great interest due to their layered structure and magnetic properties. Although HgPS3 may not exhibit magnetic properties, its uniqueness lies in its triclinic crystal structure and in the substantial mass of mercury, rendering it a compelling subject for exploration in terms of fundamental properties. In this work, we present comprehensive experimental and theoretical studies of the electronic band structure and optical properties for the HgPS3 crystal and mechanically exfoliated layers from a solid crystal. Based on absorption, reflectance and photoluminescence measurements supported by theoretical calculations, it is shown that the HgPS3 crystal has an indirect gap of 2.68 eV at room temperature. The direct gap is identified at the Γ point of the Brillouin zone (BZ) ≈ 50 meV above the indirect gap. The optical transition at the Γ point is forbidden due to selection rules, but the oscillator strength near the Γ point increases rapidly and therefore the direct optical transitions are visible in the reflectance spectra approximately at 60-120 meV above the absorption edge, across the temperature range of 40 to 300 K. The indirect nature of the bandgap and the selection rules for Γ point contribute to the absence of near-bandgap emission in HgPS3. Consequently, the photoluminescence spectrum is primarily governed by defect-related emission. The electronic band structure of HgPS3 undergoes significant changes when the crystal thickness is reduced to tri- and bilayers, resulting in a direct bandgap. Interestingly, in the monolayer regime, the fundamental transition is again indirect. The layered structure of the HgPS3 crystal was confirmed by scanning electron microscopy (SEM) and by mechanical exfoliation.

Interfacial Engineering of Cobalt Thiophosphate with Strain Effect and Modulated Electron Structure for Boosting Electrocatalytic Hydrogen Evolution Reaction

AbstractThe fabrication of heterojunctions is an intriguing approach to boost the reactivity of catalysts. However, facile preparation of desirable heterojunction materials remains a challenge. Here, novel CoPS3/CoS2 heterojunctions are created by an intuitive phosphatization process on the basis of structurally flexible cobalt sulfide precursors. Significant stress effect exists at these heterogeneous interfaces, resulting in lattice distortions and the exposure of more active sites. The interface interaction also modifies the catalyst's electronic structure to improve its electrical conductivity and hydrogen adsorption capabilities. Notably, the overpotential of the CoPS3/CoS2 heterojunction for electrocatalytic hydrogen evolution reaction is just 36.3 mV, which is far superior to those of single‐component catalysts and competitive with comparable catalysts reported. This work not only offers an innovative electrocatalyst but also a strategy that can be used to create heterojunctions based on related transition metal thiophosphates.

Ionothermal synthesis and characterization of transition-metal thiophosphates: ideas versus reality

Ionothermal synthesis and characterization of transition-metal thiophosphates: ideas versus reality

Nanoscale Control of Polar Surface Phases in Layered van der Waals CuInP2S6.

Antiferroelectric (AFE) materials, in which alternating dipole moments cancel out to a zero net macroscopic polarization, can be used for high-density energy storage and memory applications. The AFE phase can exist in bulk CuInP2Se6, CuBiP2S6, and a few other transition-metal thiophosphates below 200 K. The required low temperature poses challenges for practical applications. In this work, we report the coexistence of ferrielectric (FE) states and a stable surface phase that does not show piezoelectric response ("zero-response phase") in bulk CuInP2S6 at room temperature. Using piezoresponse force microscopy (PFM) tomographic imaging together with density functional theory, we find that direct and alternating voltages can locally and stably convert FE to zero-response phases and vice versa. While PFM loops show pinched hystereses reminiscent of antiferroelectricity, PFM tomography reveals that the zero-response areas form only on top of the FE phase in which the polarization vector is pointing up. Theoretical calculations suggest that the zero-response phase may correspond to AFE ordering where stacked CuInP2S6 layers have alternating polarization orientations thereby leading to a net-zero polarization. Consistent with experimental findings, theory predicts that the FE polarization pointing down is robust up to the top surface, whereas FE polarization pointing up energetically favors the formation of an AFE surface layer, whose thickness is likely to be sensitive to local strains. AFE order is likely to be more robust against detrimental size effects than polar order, therefore providing additional opportunities to create multifunctional heterostructures with 2D electronic materials.

Phase engineering two-dimensional nanostructures for electrocatalytic hydrogen evolution reaction

Hydrogen (H 2 ) is considered to be a promising substitute for fossil fuels. Two-dimensional (2D) nanomaterials have exhibited an efficient electrocatalytic capacity to catalyze hydrogen evolution reaction (HER). Particularly, phase engineering of 2D nanomaterials is opening a novel research direction to endow 2D nanostructures with fascinating properties for deep applications in catalyzing HER. In this review, we briefly summarize the research progress and present the current challenges on phase engineering of 2D nanomaterials for their applications in electrocatalytic HER. Our summary will be of significance to provide fundamental understanding for designing novel 2D nanomaterials with unconventional phases to electrochemically catalyze HER. This review briefly summarizes the advances on the phase engineering of 2D nanomaterials (transition metal dichalcogenides, metal thiophosphates, and 2D noble metal nanomaterials) and their applications in electrocatalytic hydrogen evolution reaction.

Orbital Contribution to Paramagnetism and Noninnocent Thiophosphate Anions in Layered Li2MP2S6 Where M = Fe and Co.

Transition-metal thiophosphates and selenophosphates are layered systems with the potential for displaying two-dimensional (2D) magnetic phenomena. We present the crystal structures and magnetic properties of two lithium transition-metal thiophosphates, Li1.56Co0.71P2S6 and Li2.26Fe0.94P2S6. The previously unreported Li1.56Co0.71P2S6 crystallizes in the trigonal space group P31m with lattice parameters a = 6.0193(6) Å and c = 6.5675(9) Å. The CoS6 octahedra are arranged in a honeycomb lattice and form 2D layers separated by lithium cations. The previously solved Li2.26Fe0.94P2S6 is isostructural to Li1.56Co0.71P2S6 but displays site mixing between the Li+ and Fe2+ cations within the thiophosphate layer. Unusually, Li1.56Co0.71P2S6 appears to have P2S63- and not P2S64- anions. We therefore term it a "noninnocent" anion because of the ambiguous nature of its oxidation state. Combined neutron diffraction and magnetization measurements reveal that both Li1.56Co0.71P2S6 and Li2.26Fe0.94P2S6 display magnetic anisotropy as well as no long-range magnetic order down to 5 K. In the iron thiophosphate, susceptibility indicates an effective moment of 5.44(3) μB, which may be best described by an S + L model, where S = 2 and L = 2, or close to the free ion limit. In the cobalt thiophosphate, we found the effective moment to be 4.35(2) μB, which would point to an S = 3/2 and L = 1 model due to octahedral crystal-field splitting.

Transition metal thiophosphates Nb4P2S21: New kind of 2D materials for multi-functional sensors

A new of 2D transition metal thiophosphates, Nb4P2S21, was synthesized through a vapor transport reaction. High purity and centimeter-scale large Nb4P2S21 crystals were obtained by controlling the growth temperature and stoichiometric ratio between niobium, phosphorus, and sulfur (using excess sulfur condition, Nb: P: S = 4: 2: 23). It was confirmed that large Nb4P2S21 crystals could be separated to a nanometer scale through mechanical exfoliation, and the exfoliated Nb4P2S21 layer exhibits semiconducting characteristics by measuring the change in electrical conductivity with temperature (increased conductivity with temperature in the range of 93–333 K). Furthermore, the device characteristics for detecting visible ray laser (635 nm) and NO2 gas molecules were verified. Based on these characteristics, the synthesized 2D material is expected to be a potential candidate for additional 2D materials and in multi-functional sensor devices, including optoelectronics and gas sensing applications.

DFT investigation on highly selective NO2 sensing properties of MnPS3

Among transition metal thiophosphates (MPX3), p-type semiconductor MnPS3 is considered to be a promising sensor material due to high selectivity and sensitivity to NO2. To explore gas sensing mechanism of MnPS3 at atomic scale, the electronic properties of NO2, NH3, H2, CO, CO2, C2H2, H2S and CH4 gases in MnPS3 monolayer are analyzed by density functional theory. The calculated charge transfer, adsorption energy, density of state and band gap change suggest that MnPS3 exhibits an intense sensing performance to NO2 than other gases. Upon the adsorption of NO2, one of the NO bond in NO2 breaks and a PO bond forms between NO2 and MnPS3. Further, a significant increasing on DOS occurs near Fermi level, suggesting an obvious change in electric conductivity of MnPS3. The energy barrier and diffusion coefficient shows that the gases are easier to diffuse between adjacent vacancies on the surface of MnPS3, and NO2 is relatively difficult to diffuse than other gases due to chemical adsorption. This work provides a theoretical basis for designing MnPS3-based NO2 sensor.

Tunable magnetism in layered CoPS3 by pressure and carrier doping

Despite extensive research on recently discovered layered ferromagnetic (FM) materials, their further development is hampered by the limited number of candidate materials with desired properties. As a much bigger family, layered antiferromagnetic (AFM) materials represent excellent platforms to not only deepen our understanding of fundamental physics but also push forward high-performance spintronics applications. Here, by systematic first-principles calculations, we demonstrate pressure and carrier doping control of magnetic properties in layered AFM CoPS3, a representative of transition metal phosphorus trichalcogenides. In particular, pressure can drive isostructural Mott transition, in sharp contrast to other transition metal thiophosphates. Intriguingly, both pressure and carrier doping can realize the long-sought FM half-metallic states with 100% spin polarization percentage, which is good for improving the injection and detection efficiency of spin currents among others. Moreover, the Mott transition is accompanied by instantaneous spin-crossover (SCO) in CoPS3, and such cooperative SCO facilitates the implementation of fast-response reversible devices, such as data storage devices, optical displays and sensors. We further provide an in-depth analysis for the mechanisms of FM half-metallicity and SCO. Tunable magnetism in layered AFM materials opens vast opportunities for purposeful device design with various functionalities.

Giant negative electrostriction and dielectric tunability in a van der Waals layered ferroelectric

The interest in ferroelectric van der Waals crystals arises from the potential to realize ultrathin ferroic systems owing to the reduced surface energy of these materials and the layered structure that allows for exfoliation. Here, we quantitatively unravel giant negative electrostriction of van der Waals layered copper indium thiophosphate (CIPS), which exhibits an electrostrictive coefficient Q33 as high as -3.2 m4/C2 and a resulting bulk piezoelectric coefficient d33 up to -85 pm/V. As a result, the electromechanical response of CIPS is comparable in magnitude to established perovskite ferroelectrics despite possessing a much smaller spontaneous polarization of only a few uC/cm2. In the paraelectric state, readily accessible owing to low transition temperatures, CIPS exhibits large dielectric tunability, similar to widely-used barium strontium titanate, and as a result both giant and continuously tunable electromechanical response. The persistence of electrostrictive and tunable responses in the paraelectric state indicates that even few layer films or nanoparticles will sustain significant electromechanical functionality, offsetting the inevitable suppression of ferroelectric properties in the nanoscale limit. These findings can likely be extended to other ferroelectric transition metal thiophosphates and (quasi-) two-dimensional materials and might facilitate the quest towards novel ultrathin functional devices incorporating electromechanical response.

Locally Controlled Cu-Ion Transport in Layered Ferroelectric CuInP2S6

Metal thiophosphates are attracting growing attention in the context of quasi-two-dimensional van der Waals functional materials. Alkali thiophosphates are investigated as ion conductors for solid electrolytes, and transition-metal thiophosphates are explored as a new class of ferroelectric materials. For the latter, a representative copper indium thiophosphate is ferrielectric at room temperature and, despite low polarization, exhibits giant negative electrostrictive coefficients. Here, we reveal that ionic conductivity in this material enables localized extraction of Cu ions from the lattice with a biased scanning probe microscopy tip, which is surprisingly reversible. The ionic conduction is tracked through local volume changes with a scanning probe microscopy tip providing a current-free probing technique, which can be explored for other thiophosphates of interest. Nearly 90 nm-tall crystallites can be formed and erased reversibly on the surface of this material as a result of ionic motion, the size of which can be sensitively controlled by both magnitude and frequency of the electric field, as well as the ambient temperature. These experimental results and density functional theory calculations point to a remarkable resilience of CuInP2S6 to large-scale ionic displacement and Cu vacancies, in part enabled by the metastability of Cu-deficient phases. Furthermore, we have found that the piezoelectric response of CuInP2S6 is enhanced by about 45% when a slight ionic modification is carried out with applied field. This new mode of modifying the lattice of CuInP2S6, and more generally ionically conducting thiophosphates, posits new prospects for their applications in van der Waals heterostructures, possibly in the context of catalytic or electronic functionalities.

Chemical Changes in Layered Ferroelectric Semiconductors Induced by Helium Ion Beam

Multi-material systems interfaced with 2D materials, or entirely new 3D heterostructures can lead to the next generation multi-functional device architectures. Physical and chemical control at the nanoscale is also necessary tailor these materials as functional structures approach physical limit. 2D transition metal thiophosphates (TPS), with a general formulae Cu1−xIn1+x/3P2S6, have shown ferroelectric polarization behavior with a Tc above the room temperature, making them attractive candidates for designing both: chemical and physical properties. Our previous studies have demonstrated that ferroic order persists on the surface, and that spinoidal decomposition of ferroelectric and paraelectric phases occurs in non-stoichiometric Cu/In ratio formulations. Here, we discuss the chemical changes induced by helium ion irradiation. We explore the TPS compound library with varying Cu/In ratio, using Helium Ion Microscopy, Atomic Force Microscopy (AFM), and Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS). We correlate physical nano- and micro- structures to the helium ion dose, as well as chemical signatures of copper, oxygen and sulfur. Our ToF-SIMS results show that He ion irradiation leads to oxygen penetration into the irradiated areas, and diffuses along the Cu-rich domains to the extent of the stopping distance of the helium ions.

High-Tc Layered Ferrielectric Crystals by Coherent Spinodal Decomposition.

Research in the rapidly developing field of 2D electronic materials has thus far been focused on metallic and semiconducting materials. However, complementary dielectric materials such as nonlinear dielectrics are needed to enable realistic device architectures. Candidate materials require tunable dielectric properties and pathways for heterostructure assembly. Here we report on a family of cation-deficient transition metal thiophosphates whose unique chemistry makes them a viable prospect for these applications. In these materials, naturally occurring ferrielectric heterostructures composed of centrosymmetric In4/3P2S6 and ferrielectrically active CuInP2S6 are realized by controllable chemical phase separation in van der Waals bonded single crystals. CuInP2S6 by itself is a layered ferrielectric with a ferrielectric transition temperature (Tc) just over room temperature, which rapidly decreases with homogeneous doping. Surprisingly, in our composite materials, the ferrielectric Tc of the polar CuInP2S6 phase increases. This effect is enabled by unique spinodal decomposition that retains the overall van der Waals layered morphology of the crystal, but chemically separates CuInP2S6 and In4/3P2S6 within each layer. The average spatial periodicity of the distinct chemical phases can be finely controlled by altering the composition and/or synthesis conditions. One intriguing prospect for such layered spinodal alloys is large volume synthesis of 2D in-plane heterostructures with periodically alternating polar and nonpolar phases.

Structural diversity of rare earth and transition metal thiophosphates

Technological interest in the design of solid state materials has stimulated recent research into the development of mild molten polychalcophosphate salt fluxes for the synthesis of complex, multinary rare earth and transition metal thiophosphate compounds. The reaction pathways from elemental or metal sulfide sources can be influenced by a variety of often interdependent factors of which counter cation sizes and charges, basicity, and temperature are of paramount importance. In rare earth and transition metal containing thiophosphates the dominating structural building units are tetrahedral [PS4]3− or ethane-like [P2S6]4− anions. Hierarchical topological relations between individual members of structural families of the type AmMnPySz (A = alkali metal, M = rare earth or transition metal) can be established that provide a detailed insight into probable mechanisms of formation. The findings enable the development of guidelines for the employment of suitable counter cations in controlling the condensation of small species into chains, layers or frameworks.

Contrasting antiferromagnetic order between FePS 3 and MnPS 3

Transition-metal thiophosphates, MPS3 (M = Fe, Mn, etc.), make up a class of antiferromagnetic materials with quasi-two-dimensional magnetic behaviour. The metal atoms occupy a honeycomb lattice. In MnPS3, the first-neighbour interaction is 400 times stronger than the exchange between the planes and the Mn moments show little anisotropy. The antiferromagnetic order is not well established perpendicular to the planes. Here we present the first powder neutron diffraction patterns of FePS3. The absence of trailing edges on the magnetic Bragg peaks, such as have been observed in MnPS3, indicates that the magnetic order is three-dimensional in FePS3.

ChemInform Abstract: New Cluster Condensation Modes in Early Transition Metal Thiophosphates: Synthesis, Structure and Properties of CsTa4P3S19, a Novel Layered Material.

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New cluster condensation modes in early transition metal thiophosphates: synthesis, structure and properties of CsTa4P3S19, a novel layered material

The new layer compound CsTa4S5(S2)(PS4)3 was synthesized by the reaction of Ta metal in polythiophosphate melts. Its structure is based on Ta4S5(S2) clusters which are condensed by PS43– groups.

Resonant2p→3dPhotoemission Measurement of MPS3(M=Mn, Fe, Ni)

Resonant 2 p →3 d photoemission (RPE) spectra in the valence band region of the transition-metal thiophosphates MPS 3 ( M=Mn, Fe, Ni) have been measured by using synchrotron radiation. These spectra show largely enhanced resonated profiles and spread over in the wide range (∼15 eV) at the incident photon energy of the transition-metal 2 p 3/2 absorption peak. Comparing the obtained spectra with the result of the cluster calculation of RPE spectra for transition-metal monoxides carried out by Tanaka and Jo, we argued the differences of the two parameters, charge transfer energy Δ and d - d Coulomb interaction energy U d d of these materials. It is suggested that MnPS 3 and FePS 3 are Mott-Hubbard type insulator with Δ > U d d , while NiPS 3 is a charge transfer type insulator with Δ < U d d .

The S K and P K polarized absorption spectra of layered thiophosphates MPS 3 ( M=Mn, Fe, Ni, Zn, Mg)

The S K and P K polarized absorption spectra were measured on the layered thiophosphates MPS 3 ( M=Mn, Fe, Ni, Zn, Mg) single crystals with linearly polarized synchrotron radiation light source. The S K polarization spectra indicate large polarization dependency especially on NiPS 3. MnPS 3 and FePS 3 show the similar feature, while NiPS 3 shows different feature. No polarization dependency is observed in the spectra of MgPS 3. The P K polarized absorption spectra also exhibit a small polarization dependency. From these spectra, the information about the p x,y and p z unoccupied states is obtained. Metal dependency is observed especially in the S p z spectra. It is revealed that the S p z state is largely mixed with the d orbitals of transition metal ion. Furthermore, we supposed that the P p states and the S p states are overlapped each other in the transition-metal thio-phosphates.