Hexagonal Layers Research Articles

Room temperature ferroelectricity in monolayer graphene sandwiched between hexagonal boron nitride

The ferroelectricity in stacked van der Waals multilayers through interlayer sliding holds great promise for ultrathin high-density memory devices, yet mostly subject to weak polarization and cryogenic operating condition. Here, we demonstrate robust room-temperature ferroelectricity in monolayer graphene sandwiched between hexagonal boron nitride layers with a rhombohedral-like stacking (i.e., ABC-like stacking). The system exhibits an unconventional negative capacitance and record high electric polarization of 1.76 μC/cm2 among reported sliding ferroelectrics to date. The ferroelectricity also exists in similarly sandwiched bilayer and trilayer graphene, yet the polarization is slightly decreased with odd-even parity. Ab initio calculations suggest that the ferroelectricity is associated with a unique switchable co-sliding motion between graphene and adjacent boron nitride layer, in contrast to existing conventional vdW sliding ferroelectrics. As such, the ferroelectricity can sustain up to 325 K and remains intact after 50000 switching cycles in ~300000 s duration at 300 K. These results open a new opportunity to develop ultrathin memory devices based on rhombohedral-like heterostructures.

Probing Surface-Mediated Electronic Coupling in Flat Hexagonal Phosphorus Nanostructures and Monolayer on Au(111).

Due to its diverse allotropes and intriguing properties, 2D phosphorus, also known as phosphorene, is a material of great interest. Here, the successful growth of flat hexagonal 2D phosphorus on Au(111) is reported. Starting from phosphorus linear chains at low coverage, a porous network and finally an extended 2D flat hexagonal (HexP) layer while increasing phosphorus deposition is formed. Using scanning tunneling microscopy/spectroscopy combined with ab initio calculations, the structure and electronic properties of the as-grown phosphorus structures are followed. The progressive formation of a phosphorus electronic band in the conduction band region is followed. More strikingly, a partial flatband that appears only on the HexP phase characterized by a sharp peak in the electronic spectrum is observed. These bands arise from the hybridization of phosphorus and gold atoms. This novel phosphorus-based structure exhibits remarkable electronic properties due to gold mediated phosphorus-phosphorus electronic coupling. This work paves the way for new interface material developments with attractive electronicproperties.

Transformation of Mackinawite to Interlayered Greigite-Pyrrhotite and Pyrite in the Gaoping Submarine Canyon Sediments off Southwestern Taiwan

Iron monosulfides and neoformed pyrite below the sulfate‒methane transition zone (SMTZ) of rapidly accumulating turbiditic sediments from the Gaoping submarine canyon off southwestern Taiwan were examined by SEM-EDS-EBSD, HRTEM, and HAADF STEM to investigate their microstructural characteristics and processes of formation and transformation. Within a few meters below the SMTZ, mackinawite (Mkw) is largely replaced by interlayered greigite-pyrrhotite (Grg-Po) with {111}Grg//{001}Po and Grg//Po, followed by pyrite neoformation in clusters of disseminated matrix grains consisting of coalescing pyrite microcrystals, arrays of polycrystalline interlayer pyrite grains between the cleavage planes of layer silicates, with each grain’s core having inclusions of interlayered Grg-Po locally containing relict Mkw, and amassed pyrite microcrystals on the surface of porous interlayered Grg-Po micronodules. In the deeper sediments, neoformed pyrite is absent and Mkw is largely preserved, with partial replacement by interlayered Grg-Po having an overall topotactic relationship of ⟨110⟩Grg//⟨110 ⟩Po//⟨100⟩Mkw and {111}Grg//(001)Po//~{011}Mkw and a sharp reaction front without transitional profiles. The mineral grain boundaries and structural discontinuities with Mkw resulting from extensive interlayering between Grg {111} cubic close-packed segments and Po {001} hexagonal close-packed layers could serve as conduits for fluid flow and mass transport to drive the replacement reaction. The conversion of Mkw to metastable interlayered Grg-Po is inferred to occur through interface-coupled dissolution‒reprecipitation processes associated with partial oxidation while the partial replacement of interlayered Grg-Po ± minor relict Mkw by pyrite microcrystals with irregular grain boundaries and orientations probably occurred via a dissolution‒precipitation mechanism. Mkw could be initially formed by sulfate reduction driven by anaerobic oxidation of methane in reactive iron-rich sediments in paleo-SMTZs and subsequently transformed into interlayered Grg-Po followed by pyrite neoformation in the sulfidization front below the SMTZ or recent SMTZs in the Gaoping submarine canyon sediments.

Two highly-ordered global structures observed in packed beds of balls inside vibrated cylinder: Experiment and modelling of layers

During the vibration of plastic balls put into a cylinder three basic global orderings of the packed beds of balls were observed. Computed microtomography measurements enabled to determine coordinates of all balls. Internal layers and their structure in crystallized beds were studied and a model was developed to predict the radii of the layers. Structural analysis, based on the Coordination Polyhedron method, was used to identify all regular local structural units present in the bed: face-centred cubic (fcc), hexagonal close-packed (hcp), icosahedral (ico) and decahedral (dec). Two already-observed global structures, namely: random loose packing (RLP) and hexagonal layer (HL) with horizontal rows of balls, were investigated in detail. The third one, called columnar structure here, was found during the experiment and has the HL structure with vertical rows of balls. Its internal structure is highly ordered, composed of regularly-spaced columns of atoms with characteristic linear chains of non-crystalline dec units.

First Principle Investigations of Structural, Electronic and Thermal Properties of Pristine, Metal and Non-Metal Doped Silicene for Thermoelectric Applications

Silicene, a two-dimensional hexagonal silicon layer, exhibits exceptional electronic and thermoelectric properties. However, its application in semiconductors is hindered by its zeroband gap, which could be overcome by modifying its electronic properties through doping. In this paper, Density Functional Theory (DFT) calculations were performed to investigate the band gap opening in silicene by studying the effect of magnesium and sulphur doping on its electronic, structural and thermal properties. Pristine silicene has a lattice constant of 3.86 Å and a zero-band gap. Upon doping with 12.5% S and Mg atoms, the lattice constant modifies to 3.45 Å and 3.93 Å, respectively, resulting in a direct band gap opening. For 25% Mg and S doping, the result shows that Mg and S effectively alter the band structure and the band gap of silicene monolayer at various configurations. The maximum band gap was 0.98 eV and 1.22 eV for Mg and S doping into the meta position to the reference point R, respectively. The power factor significantly increases with doping, reaching 1.20 x 1011 WK-2m-1 and 1.40 x 1011 WK- 2 m-1 for 12.5% Mg and S doping compared to 7.4 x 1010 WK-2m-1 for pristine silicene. This substantial enhancement indicates improved thermoelectric performance, making silicene a promising candidate for thermoelectric applications. Results demonstrate that tuning the band gap through doping can simultaneously enhance the power factor, highlighting the potential of Mg/S-doped silicene for efficient energy harvesting and conversion.

The novel Zn-doped hexagonal perovskite Ba7In6Al2O19: electrical conductivity and hydration

The novel phase Ba7In5.9Zn0.1Al2O18.95 with hexagonal perovskite structure was obtained by solid-state technique. The substitution of In3+ by the Zn2+ leads to the expansion of the lattice parameters and cell volume. It was established that the investigated sample is capable of water incorporation from the gas phase; the degree of hydration reaches 1.42 mol H2O, which is significantly higher than that for the undoped phase (0.41 mol H2O). This is a result of the expansion of the hexagonal layer that facilitates the placement of OH–-groups. The oxide-ion and proton conductivities for the doped Ba7In5.9Zn0.1Al2O18.95 sample were higher than those for the undoped composition, Ba7In6Al2O19, by 0.50 and 0.75 orders of magnitude (500 °C), respectively. The new phase Ba7In5.9Zn0.1Al2O18.95 demonstrates the predominant protonic conductivity at Т ≤ 500 °C and pH2O = 1.93·10−2 atm.

Investigation on the hydrogen storage properties, electronic, elastic, and thermodynamic of Zintl Phase Hydrides XGaSiH (X = sr, ca, ba)

This study presents a comprehensive investigation of the electronic, mechanical, and thermodynamic properties of Zintl phase hydrides XGaSiH (X = Sr, Ca, Ba) using Density Functional Theory (DFT) and the FP-LAPW method within the WIEN2k package. Our analysis covers the structural stability, electronic properties, and hydrogen interaction mechanisms in these compounds. The hydrides exhibit narrow band gaps, with values ranging from 0.1 to 0.5 eV using GGA and LDA functionals, and 0.6–1.0 eV with mBJ-GGA and mBJ-LDA. The hydrogen storage capacities are determined to be 0.34 wt %, 0.47 wt %, and 0.40 wt % for SrGaSiH, CaGaSiH, and BaGaSiH, respectively, highlighting their potential for energy storage applications. Thermodynamic properties, evaluated through the quasi-harmonic Debye model, provide insights into the Grüneisen parameter, heat capacity, and thermal expansion coefficient over a range of pressures (0–50 GPa) and temperatures (up to 1000 K). Elastic constants reveal that these compounds are mechanically stable, with a notable anisotropy in the {100} plane and varying degrees of compressibility among the different hydrides. Our study further highlights the slightly ordered hexagonal Ga and Si layers, which contribute to the enhanced hydrogen storage capabilities of these materials. The compounds demonstrate high structural stability, facilitating effective hydrogen retention and release at practical temperatures, making them promising candidates for hydrogen storage applications. Additionally, the analysis of electronic band structures and density of states suggests significant conductivity potential, with band gaps ranging from 0.1 to 1.0 eV, depending on the computational method used. The unique combination of structural, electronic, thermodynamic, and mechanical properties in XGaSiH compounds positions them as valuable materials for renewable energy applications. These findings lay the groundwork for future research focused on optimizing these materials through structural modifications or doping to enhance performance metrics such as hydrogen storage capacity and electrical conductivity.

Titanium metal-organic frameworks for photocatalytic CO2 conversion through a cycloaddition reaction.

The elevated levels of CO2 in the atmosphere have been a major concern for environmental scientists. Capturing CO2 gas and its subsequent conversion to useful organic compounds is one of the avenues that have been extensively studied in the last decade. The photocatalytic cycloaddition of CO2 is a promising approach for effective CO2 capture and the production of value-added chemicals such as cyclic carbonates. MOF-901, a titanium-based metal-organic framework with hexagonal layers and imine linkages, was successfully oxidized in this study to MOF-997, incorporating amide linkages using Oxone. Both MOFs displayed remarkable photocatalytic activity in CO2 cycloaddition under mild conditions, including moderate temperatures and visible light exposure. Particularly noteworthy is MOF-997, exhibiting superior performance with donor-acceptor active sites, achieving a 99.9% yield in catalyzing CO2 conversion from styrene epoxide to styrene carbonate under solvent conditions.

Excited States of Excitons in MoSe2 and WSe2 Monolayers

Excitons in MoSe2 and WSe2 monolayers encapsulated with hexagonal boron nitride have been studied using optical reflectance spectroscopy. The ground and excited states of A- and B-excitons have been studied at temperatures from liquid helium to room temperature. The lines of excitons A:\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1s$$\\end{document}, B:\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1s$$\\end{document} and their excited states А:\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2s$$\\end{document}, А:\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3s$$\\end{document}, and В:\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2s$$\\end{document} are clearly observed in the reflectance spectrum. The observed line shapes of the reflection spectrum of transition metal dichalcogenide monolayers depend on the thickness of the hexagonal boron nitride layers used in the structure and are in good agreement with the numerical simulation using the transfer matrix method. For the first time, the values of the reduced masses of B-excitons have been obtained from experimental data and the performed calculations of the exciton binding energy.

Large-Gap and Topological Crystalline Insulating Phase in RbZnBi and CsZnBi.

Topological insulators (TIs) are a new class of materials with gapless boundary states inside the bulk insulating gap. This metallic boundary state hosts intriguing phenomena such as helical spin textures and Dirac crossing points. Here, we theoretically propose RbZnBi and CsZnBi as a new family of TIs exhibiting large bulk band gaps and unique gapless surface states. Our first-principles density functional calculations show that two materials can be stabilized in two different structures depending on the stacking order of hexagonal ZnBi layers. While both materials in the AA-stacked structure become TI, the AB-stacked RbZnBi and CsZnBi are topological crystalline insulators with hourglass-shaped Fermion surface states protected by nonsymmorphic glide symmetry. The calculated bulk gap is about 1.5-1.8 times larger than that of Bi2Se3, which makes RbZnBi and CsZnBi promising candidates for future applications.

Synthesis and electrochemical properties of activated lignite carbons-reduced graphene oxide nanocomposites symmetric supercapacitors

Ultra-fast chargeable or rechargeable symmetric carbon-based supercapacitors (SCSs) with high capacity, inexpensive, and non-flammability have attracted much attention for electronics and energy storage devices. However, improving both high redox reaction and ion transport/diffusion processes by enhancing high energy storage performance and rapid ion/electron transport SCSs electrode materials remains challenging. Herein, we presented a successful preparation of activated lignite carbons-reduced graphene oxide (ALC-rGO) nanocomposite (NCp) with the ALC:rGO ratio of 80:20 wt% by a one-pot hydrothermal for high electrochemical performance. Importantly, the matrix of ALC-rGO NCp was primary amorphous carbon with hexagonal graphitic layers and pore structures of plentiful micropores and mesopores. Remarkably, the ALC-rGO NCp electrode exhibited a maximum specific capacitance (Csc) of 152.12 F/g at 0.5 A/g. Interestingly, the SCSs-ACL-rGO device could illustrate a good performance at a potential voltage of 1.8 V with Csc of 50.90 F/g at 1 A/g and capacity retention of 96.0 % at 5 A/g after 2,000 cycles GCD test.

Phase Behavior of Sugar-based Block Co-oligomer Modulated by Molecular Chirality

Sugar-based block co-oligomer (BCO) consisting of saccharide block exhibits high segregation strength that overcomes the limitation of the traditional block copolymers for accessing the ordered nanostructures with ultrasmall feature size. This study explores the influence of molecular chirality on the self-assembly behavior of glucose-block-tocopherol (Glc-b-Toc) BCOs, wherein the Toc blocks were either pure in chirality or being a mixture of the stereoisomers. Both the chiral and racemic BCOs formed a hexagonal perforated layer (HPL) structure with an unusually small aspect ratio (c/a) of the unit cell, attributable to the propensity of the Glc block to enhance hydrogen bonding formation. As the temperature was increased, the dominance of hydrogen bonding interactions diminished, resulting in a gradual increase in the c/a ratio and eventually a transformation of the HPL structure to a double gyroid (DG) phase. The chirality of the Toc block enhanced the effective segregation strength of the BCO, leading to elevated order-order transition temperatures associated with the HPL-to-DG and DG-to-hexagonally packed cylinder (HEX) transitions. Within the HPL phase window, the chiral BCO exhibited significantly slower kinetics during thermally-induced structural reorganization in adjusting the c/a ratio, especially in the cooling process. Consequently, a pronounced hysteresis in the structural reorganization of the chiral BCO was observed. This phenomenon was ascribed to the chiral interaction between the Toc blocks, which limited the diffusion of the BCO molecules for the structural reorganization.

The influence of crystal facet on the catalytic performance of MOFs-derived NiO with different morphologies for the total oxidation of propane: The defect engineering dominated by solvent regulation effect

Crystal facet and defect engineering are crucial for designing heterogeneous catalysts. In this study, different solvents were utilized to generate NiO with distinct shapes (hexagonal layers, rods, and spheres) using nickel-based metal-organic frameworks (MOFs) as precursors. It was shown that the exposed crystal facets of NiO with different morphologies differed from each other. Various characterization techniques and density functional theory (DFT) calculations revealed that hexagonal-layered NiO (NiO-L) possessed excellent low-temperature reducibility and oxygen migration ability. The (111) crystal plane of NiO-L contained more lattice defects and oxygen vacancies, resulting in enhanced propane oxidation due to its highest O2 adsorption energy. Furthermore, the higher the surface active oxygen species and surface oxygen vacancy concentrations, the lower the C−H activation energy of the NiO catalyst and hence the better the catalytic activity for the oxidation of propane. Consequently, NiO-L exhibited remarkable catalytic activity and good stability for propane oxidation. This study provided a simple strategy for controlling NiO crystal facets, and demonstrated that the oxygen defects could be more easily formed on NiO(111) facets, thus would be beneficial for the activation of C−H bonds in propane. In addition, the results of this work can be extended to the other fields, such as propane oxidation to propene, fuel cells, and photocatalysis.

Single-Photon Emitters inside Bubbles Formed at Homointerfaces between Hexagonal Boron Nitride Layers

Single-Photon Emitters inside Bubbles Formed at Homointerfaces between Hexagonal Boron Nitride Layers

Mn2Ga2S5 and Mn2Al2Se5 van der Waals Chalcogenides: A Source of Atomically Thin Nanomaterials.

Layered chalcogenides containing 3d transition metals are promising for the development of two-dimensional nanomaterials with interesting magnetic properties. Both mechanical and solution-based exfoliation of atomically thin layers is possible due to the low-energy van der Waals bonds. In this paper, we present the synthesis and crystal structures of the Mn2Ga2S5 and Mn2Al2Se5 layered chalcogenides. For Mn2Ga2S5, we report magnetic properties, as well as the exfoliation of nanofilms and nanoscrolls. The synthesis of both polycrystalline phases and single crystals is described, and their chemical stability in air is studied. Crystal structures are probed via powder X-ray diffraction and high-resolution transmission electron microscopy. The new compound Mn2Al2Se5 is isomorphous with Mn2Ga2S5 crystallizing in the Mg2Al2Se5 structure type. The crystal structure is built by the ABCBCA sequence of hexagonal close-packing layers of chalcogen atoms, where Mn2+ and Al3+/Ga3+ species preferentially occupy octahedral and tetrahedral voids, respectively. Mn2Ga2S5 exhibits an antiferromagnetic-like transition at 13 K accompanied by the ferromagnetic hysteresis of magnetization. Significant frustration of the magnetic system may yield spin-glass behavior at low temperatures. The exfoliation of Mn2Ga2S5 layers was performed in a non-polar solvent. Nanolayers and nanoscrolls were observed using high-resolution transmission electron microscopy. Fragments of micron-sized crystallites with a thickness of 70-100 nanometers were deposited on a glass surface, as evidenced by atomic force microscopy.

Impact of Layer Stacking Manner on the Lithium-Ion-Battery Performance in Electrically Neutral Tetraoxolene-Bridged Iron(II) Hexagonal Layer Metal–Organic Frameworks

Impact of Layer Stacking Manner on the Lithium-Ion-Battery Performance in Electrically Neutral Tetraoxolene-Bridged Iron(II) Hexagonal Layer Metal–Organic Frameworks

Photo‐Induced Electrical Gating with the Inserting of an Interfacial Carrier Blocking Layer for Organic/Graphene Phototransistors

AbstractAlthough ultrahigh photoconductive gain is achieved in organic semiconductor‐sensitized graphene phototransistors, the response speed is limited by the photo‐induced carrier injection at the organic/graphene interface. In this work, an insulating hexagonal boron nitride layer is inserted between the organic heterostructure and graphene to block the interfacial carrier transport. Above the h‐BN layer, the organic heterostructure is adopted as the light‐absorbing layer, and the photoresponse of graphene is realized through electrical gating of the atop h‐BN dielectric layer, by the accumulated carriers in the organic heterostructure. Under this “photo‐induced electrical gating” mechanism, the recombination of nonequilibrium carriers takes place only within the organic heterostructure. Furthermore, monolayer perylene‐3,4,9,10‐tetracarboxylic dianhydride (PTCDA) is deposited on graphene before transfer of the h‐BN, by which the interfacial encapsulated bubbles are effectively reduced. As a step further, the trap states are pre‐filled with background light illumination, then the carrier recombination follows the band‐to‐band pathway. Finally, the response time of the organic/h‐BN/graphene phototransistor is reduced to 7.15 ms, and a high photoresponsivity is achieved even though the carrier multiplication is sacrificed, which is reconciled by the improvement of the device quantum efficiency.

Surface band structure of the reconstructed Ir(001)-[formula omitted] surface

It is well known that the atomic structure of the Ir(001)-(5 × 1) surface consists of a quasi-hexagonal topmost layer on top of quadratic substrate layers. In the present work, we investigate how the electronic structure of Ir(001)-(1 × 1) is modified by the (5 × 1) reconstruction. For this purpose, we perform a first-principles density functional theory (DFT) calculation for semi-infinite Ir(001)-(1 × 1) and -(5 × 1) surfaces by employing the surface embedded Green’s function technique. It will be shown that surface bands on the (1 × 1) surface are strongly modified upon reconstruction. At the same time, we will demonstrate that one-dimensional (1D) surface bands localized in atomic rows in the [110] direction characterizing the buckled hexagonal layer emerge on the reconstructed surface.

The crystal structures and magnetic properties of YbMg0.75In1.25 and Yb6Mg6.41In5.59

Abstract The quasi-binary system YbMg2-YbIn2 was studied around the equiatomic composition. In contrast to the ordered rare earth (RE) phases REMgIn (ZrNiAl type), ytterbium forms phases with different structures and pronounced Mg/In mixing (M sites). The structures of YbMg0.75In1.25 (CaLiSn type, P3m1, a = 501.95(7), c = 1087.3(2) pm, wR2 = 0.0490, 790 F 2 values, 32 variables) and Yb6Mg6.41In5.59 (Yb6Ir5Ga7 type, P63/mcm, a = 1060.77(14), c = 970.27(16) pm, wR2 = 0.0484, 701 F 2 values, 26 variables) were refined from single-crystal X-ray diffractometer data. YbMg0.75In1.25 is an AlB2 superstructure with a tripling of the subcell. The magnesium and indium atoms form three differently puckered layers of M 6 hexagons. The Yb6Mg6.41In5.59 structure is derived from the hexagonal Laves phase YbMg2 (MgZn2 type, P63/mmc). A klassengleiche symmetry reduction leads to four crystallographically independent M sites for the rows of corner- and face-sharing tetrahedra which allow a composition close to the equiatomic one. The M–M distances in both structures cover the broad range from 289 to 331 pm, comparable to the sums of the covalent radii. Temperature dependent magnetic susceptibility studies of the polycrystalline YbMg0.75In1.25 and Yb12Mg13In11 samples indicate Pauli paramagnetism with room temperature values of 2.8(1) × 10−3 emu mol−1 (YbMg0.75In1.25) and 5.2(1) × 10−3 emu mol−1 (Yb12Mg13In11).

Thermal and magnetoelastic properties of the van der Waals ferromagnet Fe3−δGeTe2 : Anisotropic spontaneous magnetostriction and ferromagnetic magnon excitations

By determining the lattice parameters as a function of temperature of the hexagonal van der Waals ferromagnet Fe2.92(1)Ge1.02(3)Te2 we obtain the temperature dependence of the spontaneous in-plane magnetostriction in the ferromagnetic and the linear thermal expansion coefficients in the paramagnetic state. The spontaneous magnetostriction is clearly seen in the temperature dependence of the in-plane lattice parameter a(T), but less well pronounced perpendicular to the planes along c. Below TC the spontaneous magnetostriction follows a power law M(T)3/2 of the magnetization and leads to an expansion of the hexagonal layers. Extrapolating to T→ 0 K we obtain a spontaneous in-plane saturation magnetostriction of λsp,a(T→0)≈−220×10−6. In the paramagnetic state the linear thermal expansion coefficients amount to 13.9(1)×10−6K−1 and to 23.2(2)×10−6K−1 for the in-plane and out-of-plane direction, respectively, indicating a linear volume thermal expansion coefficient of 50.8(4)×10−6K−1 which we use to estimate the volume thermal expansion contribution to the heat capacity determined at constant pressure. A Sommerfeld-type linear term in the low-temperature heat capacities can be quantitatively ascribed to two-dimensional (2D) ferromagnetic magnon excitations. Published by the American Physical Society 2024