Space Group Cmmm Research Articles

Long-Range Structural Order in a Hidden Phase of Ruddlesden-Popper Bilayer Nickelate La3Ni2O7.

The recent discovery of superconductivity in the Ruddlesden-Popper bilayer nickelate, specifically La3Ni2O7, has generated significant interest in the exploration of high-temperature superconductivity within this material family. In this study, we present the crystallographic and electrical resistivity properties of two distinct Ruddlesden-Popper nickelates: the bilayer La3Ni2O7 (referred to as 2222-phase) and a previously uncharacterized phase, La3Ni2O7 (1313-phase). The 2222-phase is characterized by a pseudo F-centered orthorhombic lattice, featuring bilayer perovskite [LaNiO3] layers interspaced by rock salt [LaO] layers, forming a repeated ...2222... sequence. Intriguingly, the 1313-phase, which displays semiconducting properties, crystallizes in the Cmmm space group and exhibits a pronounced predilection for a C-centered orthorhombic lattice. Within this structure, the perovskite [LaNiO3] layers exhibit a distinctive long-range ordered arrangement, alternating between single- and trilayer configurations, resulting in a ...1313... sequence. This report contributes to novel insights into the crystallography and the structure-property relationship of Ruddlesden-Popper nickelates, paving the way for further investigations into their unique physical properties.

Polymorphism in the Ruddlesden-Popper Nickelate La3Ni2O7: Discovery of a Hidden Phase with Distinctive Layer Stacking.

We report the discovery of a novel form of Ruddlesden-Popper (RP) nickelate that stands as the first example of long-range, coherent polymorphism in this class of inorganic solids. Rather than the well-known, uniform stacking of perovskite blocks ubiquitously found in RP phases, this newly discovered polymorph of the bilayer RP phase La3Ni2O7 adopts a novel stacking sequence in which single-layer and trilayer blocks of NiO6 octahedra alternate in a "1313" sequence. Crystals of this new polymorph are described in space group Cmmm, although we note evidence for a competing Imam variant. Transport measurements at ambient pressure reveal metallic character with evidence of a charge density wave transition with an onset at T ≈ 134 K. The discovery of such polymorphism could reverberate to the expansive range of science and applications that rely on RP materials, particularly the recently reported signatures of superconductivity in bilayer La3Ni2O7 with Tc as high as 80 K above 14 GPa.

Effect of sodium substitution by yttrium on the structural, dielectric and electrical properties of Ba2Na(1-3x)YxNb5O15 ceramics

The effects of Na+ substitution by Y3+ on the structural, microstructural, dielectric and electrical properties of Ba2Na(1-3x)YxNb5O15 compositions with (x = 0, 0.02 and 0.04) have been studied in detail. The solid solutions of different compositions were prepared by the solid state reaction route method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Complex Impedance Spectroscopy (CIS) techniques. The XRD study confirmed that all prepared compositions have a single-phase orthorhombic tungsten bronze structure with space group Cmm2 at room temperature. The microstructural studies revealed a grain shape and size change in response to increasing Y3+ concentration. The dielectric properties of the obtained compositions are evaluated over a temperature range of 40–600 °C. The dielectric properties were improved for the Y2O3-substituted Ba2NaNb5O15 compound compared to the undoped Ba2NaNb5O15 compound. The non-Debye type relaxation mechanism is confirmed by the -Z″ versus Z′ traces. The grain contribution was studied using an equivalent electrical circuit with a Resistor R, a Capacitor C, and a Constant-Phase Element CPE in parallel, in the absence of the grain boundary response and the electrode effect in the frequency range 10 Hz-1MHz. The experimental AC conductivity data were evaluated by using Jonscher's power law. The activation energies obtained from the relaxation and conduction processes, present two different regions as a function of temperature related to the two electrical processes for the prepared ceramics.

Influence of synthesis temperature on oxygen exchange behavior of electrode material PrBaFe2O6−δ

PrBaFe2O6−δ attracts attention as a promising material for electrode development for solid oxide fuel cells. A comparative study of the structure, oxygen non-stoichiometry, and high-temperature defect chemistry in PrBaFe2O6−δ prepared at 1000 °C, hereinafter referred to as LTS (low temperature synthesis) and at 1350 °C, hereinafter referred to as HTS, was carried out. Experimental data were obtained by X-ray and electron diffraction, thermogravimetry, and coulometric titration. The onset temperature of oxygen exchange with the gas phase was found to be 278 °C and 484 °C for the LTS and HTS oxides, respectively. The revealed advantage of the LTS oxide is argued to be conditioned by the structural features. Although X-ray diffraction identified the structure of both oxides as cubic perovskite with Pm3¯m space group, electron diffraction found in the LTS oxide the incomplete formation of an ordered superstructure with a Cmmm space group, in contrast to only the short-range ordering in the HTS oxide. The modeling of defect chemistry at 750–950°С indicates a uniform distribution of oxygen ions over the available anion positions with close thermodynamic parameters of the defect formation reactions for both oxides. These results, however, can reflect only a peculiarity of the LTS oxide state with disordered anion sublattice at high temperature and does not mean unambiguous independence of oxygen exchange behavior on thermodynamic parameters of the oxidation reaction.

Insights into the structures and elastic properties of Mg-Sn compounds with superconductivity

The CALYPSO crystal structural search in combination with first-principles calculations are performed to explore the crystalline structures and elastic properties, and superconductivity of Mg-Sn compounds. A novel stoichiometry of Mg4Sn with space group Cmmm has been predicted for the first time, which is different from the previously reported structures of Mg3Sn and Mg2Sn. Compared with P63/mmc-Mg3Sn and Mg2Sn, the Mg4Sn and Pm-3m-Mg3Sn possess excellent ductility. Calculated elastic anisotropy index, 3D shear and Young's modulus imply that these four Mg-Sn compounds are anisotropic. More importantly, Mg4Sn and Pm-3m-Mg3Sn can be the potential superconductors. The superconducting transition temperature of Mg4Sn is predicted to be 2.49K at 0 GPa, which is similar to other binary compound of SnSb (below 1.50K) [Phys. Rev. Mater. 3 (2019) 084603], and slightly lower than 5.03K of Pm-3m-Mg3Sn. In addition, the favorable adsorption site for Mg2Sn(001) and Mg4Sn(001) surfaces is hollow site, whereas for Pm-3m-Mg3Sn(001) and P63/mmc-Mg3Sn(001) surfaces is top sites (T1).

Salt-flux growth of HoCuMg4 single crystals.

Polycrystalline samples of the magnesium-rich intermetallic compounds RECuMg4 (RE = Dy, Ho, Er, Tm) were synthesized by reaction of the elements in sealed tantalum ampoules heated in a high-frequency induction furnace. Phase purity of the RECuMg4 phases was ascertained by powder X-ray diffraction patterns. Well-shaped single crystals of HoCuMg4 could be grown in a NaCl/KCl salt flux and the crystal structure was refined from single crystal X-ray diffraction data: TbCuMg4 structure-type, space group Cmmm, a = 1361.4(2), b = 2039.3(4), c = 384.62(6) pm. The crystal structure of the RECuMg4 phases can be understood as a complex intergrowth variant of CsCl and AlB2 related slabs. The remarkable crystal chemical motif concerns the orthorhombically distorted bcc-like magnesium cubes with Mg-Mg distances ranging from 306 to 334 pm. At high temperatures DyCuMg4 and ErCuMg4 are Curie-Weiss paramagnets with paramagnetic Curie-Weiss temperatures of -15 K and -2 K for RE = Dy and Er, respectively. The effective magnetic moments, 10.66μB for RE = Dy and 9.65μB for RE = Er prove stable trivalent ground states for the rare earth cations. Magnetic susceptibility and heat capacity measurements reveal long-range antiferromagnetic ordering at low temperatures (<21 K). Whereas DyCuMg4 exhibits two subsequent antiferromagnetic transitions at TN = 21 and 7.9 K which successively remove half of the entropy of a doublet crystal field ground state of Dy, ErCuMg4 shows a single, possibly broadened, antiferromagnetic transition at 8.6 K. The successive antiferromagnetic transitions are discussed with respect to magnetic frustration in the tetrameric units present in the crystal structure.

First-principles investigation of optical properties of AlFe(2-x)MxB2 (x= 0–1), (M= Cr, V) intermetallic compounds

Transition-metal borides have garnered considerable attention due to their remarkable properties such as high melting temperature, hardness, good thermal and electrical conductivity, etc. In the past decade, MAB phase AlFe2B2 based compounds have also been at the center of attention owing to their magnetocaloric effects. In this study, intermetallic compounds with AlFe(2-x)MxB2 (x = 0.25, 0.5 and 1), (M = Cr, V) formula in which AlFe2B2 is the base material crystalize in an orthorhombic structure with space group Cmmm (No.65), and then the effects of a fourth alloying element, at ratios of 12.5%, 25% and 50%, are calculated using first-principles calculations based on DFT. After the calculations, using the GGA-PBE functional, examination of the electronic (e.g. total and partial density of states) and a comprehensive optical properties (e.g. dielectric function, reflectivity, absorption, refractive index, conductivity, as well as loss function) of the base material and its doped alloys, with Cr and V as the photon energy, has been carried out. Finally, the capability and potential role of the above mentioned compounds in photovoltaics and photoconductivity applications in the solar radiation range are evaluated.

Suppression of Kondo spin-fluctuations as the origin of metamagnetic transition in the new ternary intermetallic Ce3Pd2Ge7

The metamagnetic transition in cerium-based intermetallics is a very common intriguing phenomenon that has remained the subject of close study for several decades. We report crystal structure, magnetization and resistivity of a new ternary cerium germanide Ce3Pd2Ge7 with an orthorhombic structure of La3Co2Sn7-type (space group Cmmm, cell dimensions a = 4.3257(3), b = 26.339(2), c = 4.3594(3) Å, V = 496.69(2) Å3). Low-temperature magnetic properties are characterized by a two-step metamagnetic transition, which can be associated with two nonequivalent positions of Ce ions in the lattice. The first metamagnetic transition occurs in weak magnetic fields below T1 ≈ 11 K and then moves to higher fields when the temperature goes down (B ∼ 1.5 T at T = 2 K). The second transition manifests itself below T2 ≈ 8 K as a rapid increase of magnetization, which starts from zero field and reaches saturation at fields B ≈ 0.1 T. The magnitude of each transition increases with decreasing temperature and the polarized magnetization ΔM reaches 0.13 μB/Ce and 0.08 μB/Ce upon the first and second transitions respectively. The interchange of nonmagnetic Pd and Ge ions (≈ 0.8 %) leads to the appearance of a hysteresis of metamagnetic transitions, as well as to the splitting of the field cooled (FC) and zero field cooled (ZFC) magnetization curves in hysteresis area. The dependence of the polarized magnetization ΔM on temperature which persists up to high fields as well as the continuation of the hysteresis well above the metamagnetic transition (at least up to B ∼ 9 T) indicates a new type of spin-glass-like state, which is caused by the suppression of spin fluctuations and the localization of magnetic moments during the metamagnetic transition.

Peculiarities of the electric resistivity behavior of R3(Ce,Nd,Sm)Cu4Sn4, R(Gd,Tb,Ho)NiSn2, DyNiSi, and DyNiSi3 compounds in magnetic fields

The resistance of ternary intermetallic compounds, namely RE(Ce, Nd, Sm)3Cu4Sn4 (space group Immm), RE(Gd, Tb, Ho)NiSn2 and DyNiSi (space group Pnma) and DyNiSi3 (space group Cmmm), has been studied in the temperature range up to 0.3 K and magnetic field up to 12 Tl. The temperature dependencies of electrical resistivity evidently show the anomalies at low temperatures. The anomalies of resistance temperature dependencies observed at the absence of an external magnetic field, agree well with magnetic phase transitions. In the majority of the investigated compounds, an increase of the external magnetic field leads to an erosion of the peculiarities on the temperature dependency of resistivity, right up to complete disappearance. Such effect is caused by the corresponding magnetic order phase transitions. Magnetic field influence on the temperature dependency of resistance is treated as an influence on the magnitude of hybridization between (s-d) conductivity electrons and localized f-electrons including influence on change on the charge caries mobility due to a possible spin-compensated interaction. Electron transport properties expose peculiarities in dependency of different chemical environment vicinity in elementary cell of crystal lattice and of magnetic state of the compound.

SCM-25: A Zeolite with Ordered Meso-cavities Interconnected by 12×12×10-Ring Channels Determined by 3D Electron Diffraction.

Zeolites with large cavities that are accessible via wide pore windows are desirable but very rare. They have been dominantly used as catalysts in industry. Here we report a novel porous germanosilicate SCM-25, the zeolite structure containing ordered meso-cavities (29.9 × 7.6 × 6.0 Å3) interconnected by 10- and 12-ring channels. SCM-25 was synthesized as nanosized crystals by using a simple organic structure-directing agent (OSDA). Three-dimensional (3D) electron diffraction shows that SCM-25 crystallizes in the orthorhombic space group Cmmm with a = 14.62 Å, b = 51.82 Å, c = 13.11 Å, which is one of the zeolites with the largest unit cell dimensions. We demonstrate that 3D electron diffraction is a powerful technique for determining the complex structure of SCM-25, including the disorders and distributions of framework atoms silicon and germanium. SCM-25 has a high surface area (510 m2/g) and high thermal stability (700 °C). Furthermore, we propose a potential postsynthetic strategy for the preparation of zeolites with ordered meso-cavities by applying the ADOR (assembly–disassembly–organization–reassembly) approach.

Forming Platinide Phases under Pressure in the Cs–Pt System

A series of platinide-containing phases were identified as thermodynamically favorable compounds at high pressure (10 GPa) using an unbiased automatic crystal structure searching method. Density functional theory paired with a particle swarm optimization (PSO) algorithm supports the formation of Cs2Pt at ambient pressure, agreeing with experimental observations. The calculations then revealed that applying 10 GPa of pressure should result in three new phases: Cs2Pt with the Fe2P-type structure (space group P6̅2m; No. 189), Cs2Pt3 (space group Cmm2; No. 38), and CsPt3 (space group C2/m; No. 12). Subsequent hybrid electronic structure calculations showed that Cs2Pt is a semiconductor with the Fermi level falling in a band gap of 2.18 eV, whereas the Fermi level for Cs2Pt3 and CsPt3 falls into a pseudogap, suggesting a metallic character. Examining the chemical bonding in the Cs-rich phase (Cs2Pt) indicated that Cs–Pt ionic interactions dominate this structure, while Pt–Pt interactions are primary interactions in Pt-rich phases (Cs2Pt3 and CsPt3). Interestingly, the ambient pressure phase and all three high-pressure phases exhibit unusual oxidation states on transition-metal atoms. The Pt charge is approximated to approach −1 due to charge transfer between Cs and Pt, as illustrated by Bader’s QM-AIM charge analysis and electron localization function (ELF) calculations. These results support the presence of a rare pressure-stabilized platinide anion.

Synthesis and structural characterization of the new Zintl phases Eu10Mn6Bi12 and Yb10Zn6Sb12.

Two new ternary compounds, Eu10Mn6Bi12 and Yb10Zn6Sb12, were synthesized and structurally characterized. The synthesis was achieved either through reactions in sealed niobium tubes or in alumina crucibles by combining the elements in excess molten Sb. Their structures were elucidated using single-crystal X-ray diffraction, and they were determined to crystallize in the orthorhombic space group Cmmm (no. 65) with the Eu10Cd6Bi12 structure type. Akin to the archetype phase, both Mn and Zn sites contain about 25% of vacancies. The anionic substructure of the title phases can be described as [M6Pn12] (M = Zn, Mn; Pn = Sb, Bi) double layers composed of the corner and edge-sharing [MPn4] tetrahedra, linked by [Pn2]4- dumbbells. Eu2+/Yb2+ cations fill the space between the layers, with the valence electron counts adhering closely to the Zintl-Klemm rules, i.e., both Eu10Mn6Bi12 and Yb10Zn6Sb12 are expected to be valence-precise compounds. Analysis of the electronic structure and transport properties of Yb10Zn6Sb12 indicate semimetallic behavior with relatively low Seebeck coefficient and resistivity that slightly decreases as a function of temperature.

Phase equilibrium diagram of the Hf-Fe-Sn system at 1070 K

Experimental studies of the phase equilibrium diagram of the Hf-Fe-Sn ternary system at 1070 K were performed by X-ray powder diffractometry, scanning electron microscopy and electron probe microanalysis techniques in the whole concentration range. At annealing temperature four ternary compounds are realized: Hf6FeSn2 (K2UF6 structure type, space group P-62m), Hf1.8Fe5Sn3.8 (Hf1.82Fe5Sn3.82 structure type, space group Cmmm), Hf3Fe4Sn4 (Zr3Fe4Sn4 structure type, space group Pnma), and Hf9Fe3.7Sn10.3 (Hf9Fe4Sn10 structure type, space group Cmc21). An existence of the Hf1-xFe2+x-ySny solid solution formed by substitution of the iron atoms by tin in the Hf1-xFe2+x (MgZn2-type) binary compound up to 19 at. % Sn was found. Solubility of Fe in the Hf5Sn3 binary (Mn5Si3-type) extends up to 10 at. % (a=0.8363(2)-0.8324(4), c=0.5726(1)-0.5686(4) nm).

A superhard carbon allotrope with cage structure: oS44-carbon

First-principles calculations are applied to investigate a new carbon allotrope, denoted oS44-carbon, with orthorhombic symmetry and Cmmm space group. This fully sp3-hybridized bonded carbon network resembles an orderly stack of hexagonal prisms and two types of cages. The total energy is lower, and the thermodynamic stability is better, for oS44-carbon than synthesized T-carbon and supercubane. The dynamic stability and mechanical stability of oS44-carbon under 0–60 ​GPa of pressure are demonstrated by its calculated elastic constants and phonon spectra. Ab initio molecular dynamics simulations show that oS44-carbon can withstand high temperatures up to 1000 ​K. By adopting Chen's model, the hardness of oS44-carbon is found to be 55.93 ​GPa, indicating that it is superhard. Its multicage structure gives it a notably low density (2.77 ​g/cm3) among sp3-bonded superhard carbon allotropes. Surprisingly, the band structure shows that oS44-carbon is an indirect ultrawide-bandgap semiconductor with a bandgap of 4.81 ​eV. Finally, we find that its indirect semiconducting feature can survive pressures from 0 to 60 ​GPa.

Fantastic n = 4: Ce5Co4+xGe13-ySny of the An+1MnX3n+1 homologous series.

Ce-based intermetallics are of interest due to the potential to study the interplay of localized magnetic moments and conduction electrons. Our work on Ce-based germanides led to the identification of a new homologous series An+1MnX3n+1 (A = rare earth, M = transition metal, X = tetrels, and n = 1-6). This work presents the single-crystal growth, structure determination, and anisotropic magnetic properties of the n = 4 member of the Cen+1ConGe3n+1 homologous series. Ce5Co4+xGe13-ySny consists of three Ce sites, three Co sites, seven Ge sites, and two Sn sites, and the crystal structure is best modeled in the orthorhombic space group Cmmm where a = 4.3031(8) Å, b = 45.608(13) Å, and c = 4.3264(8) Å, which is in close agreement with the previously reported Sn-free analog where a = 4.265(1) Å, b = 45.175(9) Å, and c = 4.293(3) Å. Anisotropic magnetic measurements show Kondo-like behavior and three magnetic transitions at 6, 4.9, and 2.4 K for Ce5Co4+xGe13-ySny.

Above Room Temperature Organic Dielectric Switchable and NLO Co‐crystal: [C4H4O4][C8H19N

AbstractA new pure organic co‐crystal compound 1, [C4H4O4][C8H19N] ([C4H4O4]=maleic acid, [C8H19N]=diisobutylamine/DIBA) was discovered to undergo an above room temperature reversible phase transition at around 353/343 K. The variable‐temperature single‐crystal X‐ray structural measurements reveal that space group of the structural phase transition is from space group Cmm2 to space group Imm2. The phase transition of compound 1 is mainly ascribed to the twisted movement of diisobutylamine molecules. Meanwhile, nonlinear optical (NLO) properties were also observed in compound 1.

BiNb5.4O15: A new Li+-storage material with a tetragonal tungsten bronze crystal structure

Niobates with tungsten bronze crystal structures are regarded as prospective Li[Formula: see text]-storage anode candidates due to the rich chemistry of niobium and structural openness. However, the exploration of this type of materials is still insufficient. Here, BiNb[Formula: see text]O[Formula: see text] with a tetragonal tungsten bronze crystal structure (Cmmm space group) is explored. Abundant large-sized tunnels and a large interlayer spacing of [Formula: see text]3.97 Å are found in this open structure, enabling fast Li[Formula: see text] diffusivity (3.25 × 10[Formula: see text]/1.68 × 10[Formula: see text] cm2 ⋅ s[Formula: see text] during lithiation/delithiation). Additionally, this structure is very stable after the first lithiation process, resulting in excellent cyclability (95.4%/[Formula: see text]100% capacity retention after 100/1000 cycles at 1C/10C). BiNb[Formula: see text]O[Formula: see text] further exhibits a safe Li[Formula: see text]-storage potential ([Formula: see text]1.55 V) and a large reversible capacity (309.7 mAh ⋅ g[Formula: see text]@ 0.1C). Therefore, BiNb[Formula: see text]O[Formula: see text] can be a practical Li[Formula: see text]-stora ge anode compound for large-scale energy-storage applications.

Tilting and Distortion in Rutile-Related Mixed Metal Ternary Uranium Oxides: A Structural, Spectroscopic, and Theoretical Investigation.

A systematic investigation examining the origins of structural distortions in rutile-related ternary uranium AUO4 oxides using a combination of high-resolution structural and spectroscopic measurements supported by ab initio calculations is presented. The structures of β-CdUO4, MnUO4, CoUO4, and MgUO4 are determined at high precision by using a combination of neutron powder diffraction (NPD) and synchrotron X-ray powder diffraction (S-XRD) or single crystal X-ray diffraction. The structure of β-CdUO4 is best described by space group Cmmm whereas MnUO4, CoUO4, and MgUO4 are described by the lower symmetry Ibmm space group and are isostructural with the previously reported β-NiUO4 [Murphy et al. Inorg. Chem. 2018, 57, 13847]. X-ray absorption spectroscopy (XAS) analysis shows all five oxides contain hexavalent uranium. The difference in space group can be understood on the basis of size mismatch between the A2+ and U6+ cations whereby unsatisfactory matching results in structural distortions manifested through tilting of the AO6 polyhedra, leading to a change in symmetry from Cmmm to Ibmm. Such tilts are absent in the Cmmm structure. Heating the Ibmm AUO4 oxides results in reduction of the tilt angle. This is demonstrated for MnUO4 where in situ S-XRD measurements reveal a second-order phase transition to Cmmm near T = 200 °C. Based on the extrapolation of variable temperature in situ S-XRD data, CoUO4 is predicted to undergo a continuous phase transition to Cmmm at ∼1475 °C. Comparison of the measured and computed data highlights inadequacies in the DFT+U approach, and the conducted analysis should guide future improvements in computational methods. The results of this investigation are discussed in the context of the wider AUO4 family of oxides.

Manifestation of dissimilar types of magnetism in iron- and chromium-substituted Mn2SnS4.

Mn2SnS4 belongs to the MII2AIVQ4 (M = transition metal; A = Si, Ge and Sn; Q = S, Se and Te) class of compounds that crystallizes in the orthorhombic space group Cmmm and shows complex magnetic properties. Here we report the synthesis and magnetic properties of Fe- and Cr-substituted Mn2SnS4 quaternary chalcogenides. All these compounds have been synthesized using a high-temperature solid-state route. Room temperature neutron diffraction studies on the specific compositions of chromium- and iron-substituted compounds were performed to obtain the site occupancy of different elements in the unit cell. The neutron diffraction analysis by employing the Rietveld refinement shows that for the Fe-substituted compound, most of the Fe goes to the Mn site with a small amount at the Sn site, while in the Cr-substituted sample, all the Cr occupy the Mn site. However, the Sn site almost remains intact in the case of the Fe-substituted compound, while it is significantly disordered for the Cr-substituted sample as a fraction of Mn occupies the Sn site and an equivalent amount of Sn occupies the Mn site. XPS study shows that both Cr and Fe exist in the +3 oxidation state, while Mn exists in the +2 state and Sn exists in a mixture of +2 and +4 oxidation states. Magnetic property study of these substituted compounds shows different types of magnetism, which is attributed to the variation of d-electrons of the substituent atom. The chromium-doped compounds show ferrimagnetic character along with two transitions: one transition at ∼37 K and another at ∼152 K. However, in Fe-substituted Mn2SnS4 samples, the low-temperature transition disappears and an increase in the high-temperature antiferromagnetic ordering temperature i.e. from 152 K (Mn2SnS4) to 174 K (Mn1.82Fe0.18SnS4) is observed. The increase in the antiferromagnetic ordering temperature in Mn2-xFexSnS4 may be attributed to the increase in the covalence of Mn/Fe-S-Mn/Fe bonds (shorter) with iron substitution.

Crystal structure and magnetic properties of R11Co4In9 (R=Tb, Dy, Ho and Er) compounds

Crystal structure and magnetic properties of the R11Co4In9 compounds (R = Tb–Er) have been investigated by means of X-ray diffraction as well as dc magnetic measurements. The compounds crystallize in the orthorhombic Nd11Pd4In9-type crystal structure (Cmmm space group) in which the rare earth atoms occupy five nonequivalent sublattices. Magnetic properties of the investigated compounds are related mainly to the R3+ ions. The values of effective magnetic moments in the paramagnetic state are close to the free R3+ ion values while the moments in the ordered state at T = 2.0 K (R = Tb, Dy) or T = 1.9 K (R = Ho, Er) and H = 90 kOe are lower than the respective R3+ moments. The compounds show complex magnetic properties below 95 K (Tb), 88 K (Dy), 35 K (Ho) and 5.4 K (Er). With increase of temperature the antiferromagnetic ground state changes to the ferro- or ferrimagnetic one. The critical temperatures of magnetic ordering do not fulfill the de Gennes scaling indicating a strong influence of the crystal electric field (CEF) in stabilizing the magnetic order.