Isostructural Compounds Research Articles

Semiconductor to half-metal transition in magnetic Ce cation incorporated A-site-ordered quadruple perovskite CeMn3Mn4O12

The charge degree of freedom of A-site cation as well as B-site cation plays a significant role in determining the internal charge distribution and gives rise to fascinating physical properties in perovskite oxides. Here, we discuss the magnetic couplings and electronic structures of rare-earth Ce cation incorporated A-site-ordered quadruple perovskite CeMn3Mn4O12 via first-principles calculations. This report demonstrates that the A site Ce is magnetic cation with quantity of 4 f electrons, which is quite different from the nonmagnetic Ce4+ usually found in isostructural compounds. As a result, not only the A′ and B site manganese sublattices but also the A site cerium sublattice is involved in the complex magnetic interactions. In the low-temperature phase, CeMn3Mn4O12 is ferrimagnetic with the Ce(↓)-Mn1(↑)-Mn2(↓)-Mn3(↑)-Mn4(↑)-Mn5(↓) type, in which the effective magnetic couplings are generated from A-site Ce sublattice as well as the antiparallel arrangement within both the A and B site manganese sublattices. The analysis of electronic structure reveals the valence distribution is Ce3+Mn3+3Mn3+4O2-12 where both the oxidation state of Ce and Mn is +3. Nevertheless, ferromagnet is the most favorable in energy with a large saturated magnetic moment at the high-temperature phase. Interestingly, the electronic structure undergoes a semiconducting to half-metallic transition accompanying with the phase transformation. The present results offer a new strategy to realizing the tunable charge distribution via variable valence A site cation in A-site-ordered quadruple perovskites and thus open an avenue to modulate these materials with exotic properties.

Syntheses, Crystal Structure, and Second Harmonic Generation Response of Noncentrosymmetric Layered Selenites and Tellurites of Antimony(V), ASb3X2O12 (A = K, Rb, Cs, Tl; X = Se, Te).

Eight quaternary selenites and tellurites of antimony(V), ASb3X2O12 (A = K, Rb, Cs, Tl; X = Se, Te), have been synthesized by solid state reactions and structurally characterized by single crystal X-ray diffraction. They are isostructural compounds, which crystallize in the polar noncentrosymmetric P63mc space group with hexagonal unit cell parameter values in the ranges of a = 7.1538(1)-7.2429(1) Å and c = 11.8978(4)-12.0478(3) Å. Their noncentrosymmetric layered structure consists of hexagonal-tungsten-oxide-related (Sb3X2O12)- layers interleaved with A+ ions. They have optical band gap values of 2.90-4.46 eV and showed powder second harmonic generation response equivalent to 1.0-37.2 × KDP.

Normal coordinate analysis to study the optical phonons in B-site cation disordered Ruddlesden-Popper Sr3B2O7 (B = V, Cr, Fe, Co) crystals

The Raman and infrared (IR) phonons for the Ruddlesden-Popper Srn+1BnO3n+1 (B = V, Cr, Fe, Co) bilayered tetragonal compounds with n = 2 of symmetry D174h and phase I4/mmm (Z = 2) have been analyzed with Wilson's GF-Matrix Method. Theoretical assignments for the optical wavenumbers have been reported first time for the bilayered tetragonal Sr3V2O7, Sr3Cr2O7, and Sr3Co2O7 compounds by using ten short-range force constants. The appropriate optical vibrational modes have been assigned to the bilayered tetragonal Sr3Fe2O7 compound. The theoretically calculated Raman modes found in the literature are not satisfactorily matched with the experimentally observed frequencies for the bilayered tetragonal Sr3Fe2O7 compound. Using the available data of the isostructural compounds Sr3Ti2O7 and Sr3Mn2O7, we have tried to calculate and report better results for the Raman vibrational modes of the Sr3Fe2O7 compound. Also, we have compared all these three compounds together in terms of frequencies and force constants. The impact of cation-B (B = V, Cr, Fe, Co) exchange on the lattice dynamics of the tetragonal bilayered Sr3B2O7 (B = V, Cr, Fe, Co) isostructural compounds has been analyzed by comparison of the Zone centre vibrational modes, force constants, and bond lengths. For understanding the structure more clearly an attempt is also made to analyze the effect of B-cations (B = V, Cr, Fe, Co) on the affected apical bonds. For each normal mode of the bilayered tetragonal Sr3B2O7 (B = V, Cr, Fe, Co) Ruddlesden-Popper phase, the potential energy distribution (PED) has been analyzed for the significant impact of short-range force constants on different vibrational modes.

Combining MN6 Octahedra and PN5 Trigonal Bipyramids in the Mica‐like Nitridophosphates MP6N11 (M=Al, In)

AbstractLayered silicates are a very versatile class of materials with high importance to humanity. The new nitridophosphates MP6N11 (M=Al, In), synthesized from MCl3, P3N5 and NH4N3 in a high‐pressure high‐temperature reaction at 1100 °C and 8 GPa, show a mica‐like layer setup and feature rare nitrogen coordination motifs. The crystal structure of AlP6N11 was elucidated from synchrotron single‐crystal diffraction data (space group Cm (no. 8), a=4.9354(10), b=8.1608(16), c=9.0401(18) Å, β=98.63(3)°), enabling Rietveld refinement of isotypic InP6N11. It is built up from layers of PN4 tetrahedra, PN5 trigonal bipyramids and MN6 octahedra. PN5 trigonal bipyramids have been reported only once and MN6 octahedra are sparsely found in the literature. AlP6N11 was further characterized by energy‐dispersive X‐ray (EDX), IR and NMR spectroscopy. Despite the vast amount of known layered silicates, there is no isostructural compound to MP6N11 as yet.

Combining MN6 Octahedra and PN5 Trigonal Bipyramids in the Mica-like Nitridophosphates MP6 N11 (M=Al, In).

Layered silicates are a very versatile class of materials with high importance to humanity. The new nitridophosphates MP6 N11 (M=Al, In), synthesized from MCl3 , P3 N5 and NH4 N3 in a high-pressure high-temperature reaction at 1100 °C and 8 GPa, show a mica-like layer setup and feature rare nitrogen coordination motifs. The crystal structure of AlP6 N11 was elucidated from synchrotron single-crystal diffraction data (space group Cm (no. 8), a=4.9354(10), b=8.1608(16), c=9.0401(18) Å, β=98.63(3)°), enabling Rietveld refinement of isotypic InP6 N11 . It is built up from layers of PN4 tetrahedra, PN5 trigonal bipyramids and MN6 octahedra. PN5 trigonal bipyramids have been reported only once and MN6 octahedra are sparsely found in the literature. AlP6 N11 was further characterized by energy-dispersive X-ray (EDX), IR and NMR spectroscopy. Despite the vast amount of known layered silicates, there is no isostructural compound to MP6 N11 as yet.

Thermal behavior of acid phosphate salts Ca2MH7(PO4)4·2H2O (M = K+, NH4+) and CaK3H(PO4)2

New knowledge about various aspects of little-known acid salts is of great scientific and practical importance in view of their potential application in different areas such as proton conductors. For the first time, the thermal behavior of three acid phosphate salts, dicalcium potassium heptahydrogen tetrakis(phosphate) dihydrate (Ca2KH7(PO4)4·2H2O), dicalcium ammonium heptahydrogen tetrakis(phosphate) dihydrate (Ca2(NH4)H7(PO4)4·2H2O) and calcium tripotassium hydrogenbis(phosphate) (CaK3H(PO4)2), has been investigated. By means of simultaneous thermogravimetry, differential thermal and mass spectrometry analyses (TG/DTA/MS) the schemes of their thermal decomposition have been proposed. The two isostructural compounds Ca2KH7(PO4)4·2H2O and Ca2(NH4)H7(PO4)4·2H2O are stable up to 90 – 95 °C and then undergo multiple-steps thermal decomposition process owing to dehydration of the crystallization water and dehydration-condensation. The anhydrous salt CaK3H(PO4)2 exhibits very high thermal stability up to 530 °C. The products of the thermal decomposition have been identified.

Pressure induced insulator to metal transition in quantum spin liquid candidate NaYbS2

Pressure induced insulator to metal transition followed by the appearance of superconductivity has been observed recently in inorganic quantum spin liquid candidate NaYbSe2. In this paper, we study the properties of isostructural compound NaYbS2 under pressure. It is found that the resistance of NaYbS2 single crystal exhibits an insulating state below 82.9 GPa, but with a drop of more than six orders of magnitude at room temperature. Then a minimum of resistance is observed at about 100.1 GPa and it moves to lower temperature with further compression. Finally, a metallic state in the whole temperature range is observed at about 130.3 GPa accompanied by a non-Fermi liquid behavior below 100 K. The insulator to metal transition, non-monotonic resistance feature and non-Fermi liquid behavior of NaYbS2 under pressure are similar to those of NaYbSe2, suggesting that these phenomena might be the universal properties in NaLnCh 2 (Ln = rare earth, Ch = O, S, Se) system.

Phonon anharmonicity and equation of state parameters of orthovanadate Mg3(VO4)2: Raman Spectroscopy and X-ray diffraction investigation

Isothermal compression effect is investigated on structure and vibrational properties of orthovanadate Mg3(VO4)2 using Raman spectroscopy and X-ray powder diffraction up to pressures 20.2 and 25.7 GPa respectively. Isobaric temperature effect on the vibrational properties of Mg3(VO4)2 have also been investigated using Raman spectroscopy up to 1273 K. The present investigation indicates stable orthorhombic (Cmca) structure up to the highest pressure achieved and up to near its melting temperature. The high pressure structural behavior is similar to the isostructural compounds Zn3(VO4)2 and Ni3(VO4)2 unlike another isostructural compound Mn3(VO4)2 which is reported to show irreversible structural phase transformation. Experimental equation of state parameters are compared with those reported on the similar compounds and the obtained bulk modulus (141 GPa) of Mg3(VO4)2 matches very well with the empirically calculated value reported earlier. The anharmonicities estimated after combining both studies suggest dominant contribution of three phonon decay process.

Self-Assembly Heterometallic Cu-Ln Complexes: Synthesis, Crystal Structures and Magnetic Characterization

Using N2O4 donor symmetric ligand H2L and dca co-ligand, two new isostructural dinuclear CuII–LnIII complexes [Cu(Cl)(L)Ln(NO3)(CH3OH)(H2O)(dca)] [Ln=Ho (1CuHo), Gd (2CuGd)] [H2L = 6,6′-((1E,1′E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(2-methoxyphenol); dca=dicyanamide] were designed, synthesized and studied. In the two isostructural compounds, the geometric environment around the nine-coordinated Ln(III) ions is muffin, whereas the geometry of the penta-coordinated Cu(II) ions is square pyramid. The magnetic properties of both complexes were also studied. Direct current magnetic susceptibility measurements indicate ferromagnetic interactions between the Cu(II) ion and Gd(III) ion in complex 2CuGd. Alternating current (ac) magnetic measurements indicate that complex 1CuHo displays slow magnetic relaxation behaviour.

μSR Study of Unconventional Pairing Symmetry in the Quasi-1D Na2Cr3As3 Superconductor

We report the finding of a novel pairing state in a newly discovered superconductor Na2Cr3As3. This material has a non-centrosymmetric quasi-one-dimensional crystal structure and is superconducting at TC∼ 8.0 K. We find that the magnetic penetration depth data suggests the presence of a nodal line pz-wave pairing state with zero magnetic moment using transverse-field muon-spin rotation (TF-μSR) measurements. The nodal gap observed in Na2Cr3As3 compound is consistent with that observed in isostructural (K,Cs)2Cr3As3 compounds using TF-μSR measurements. The observed pairing state is consistent with a three-band model spin-fluctuation calculation, which reveals the Sz=0 spin-triplet pairing state with the sinkz pairing symmetry. The long-sought search for chiral superconductivity with topological applications could be aided by such a novel triplet Sz=0p-wave pairing state.

Flat Band and ℤ2 Topology of Kagome Metal CsTi3Bi5

The simple kagome-lattice band structure possesses Dirac cones, flat band, and saddle point with van Hove singularities in the electronic density of states, facilitating the emergence of various electronic orders. Here we report a titanium-based kagome metal CsTi3Bi5 where titanium atoms form a kagome network, resembling its isostructural compound CsV3Sb5. Thermodynamic properties including the magnetization, resistance, and heat capacity reveal the conventional Fermi liquid behavior in the kagome metal CsTi3Bi5 and no signature of superconducting or charge density wave (CDW) transition anomaly down to 85 mK. Systematic angle-resolved photoemission spectroscopy measurements reveal multiple bands crossing the Fermi level, consistent with the first-principles calculations. The flat band formed by the destructive interference of hopping in the kagome lattice is observed directly. Compared to CsV3Sb5, the van Hove singularities are pushed far away above the Fermi level in CsTi3Bi5, in line with the absence of CDW. Furthermore, the first-principles calculations identify the nontrivial ℤ2 topological properties for those bands crossing the Fermi level, accompanied by several local band inversions. Our results suppose CsTi3Bi5 as a complementary platform to explore the superconductivity and nontrivial band topology.

Narrow Band Gap Compounds with β‐Pyrochlore Structure in the A2O‐V2O5‐2TeO3 (A=Rb, Cs) System

AbstractTwo new isostructural compounds with composition of Rb+V3+0.125V5+0.625Te6+1.25O6 and Cs+V3+0.125V5+0.625Te6+1.25O6 have been synthesized by solid‐state reaction. The crystal structure has been determined by X‐ray diffraction analysis using Rietveld refinement. Both compounds possess β‐pyrochlore structure‐type with cubic space group Fd‐3 m (Z=8); the unit cell parameters: a=10.04120(27) Å for RbV0.75Te1.25O6 Å and a=10.09119(23) Å for CsV0.75Te1.25O6. The oxidation states of vanadium and tellurium have been confirmed by X‐ray photoelectron spectroscopy. The compounds contain vanadium in mixed valence state (3+ and 5+). The compounds possess the unusual narrow band gap for oxide compounds – in the infrared (IR) range (∼0.6 eV). The schematic electronic structure of the compounds has been estimated using XPS, UPS and electronic conductivity data; however, the shifts of the top of the valence edge and the bottom of the conduction band in the water conditions have been calculated using theoretical approximation. The thermal behavior of obtained compounds has been studied by differential thermal analysis. RbV0.75Te1.25O6 and CsV0.75Te1.25O6 melts at low temperatures (∼500 °C) with decomposition and weight loss. The RbV0.75Te1.25O6 powder decomposes to amorphous phase, whereas CsV0.75Te1.25O6 transform into new β‐pyrochlore compound with another composition.

Polyoxometalate-Viologen Thermochromic Hybrids for Organic Amine Detectors and Memristors with Temperature-Regulating Resistance Switching Characteristics.

There are relatively few reports on the combination of viologen and polyoxometalates (POMs). Herein, we successfully synthesized three viologen-POM-based compounds by in situ transformation of ligands under hydrothermal conditions, namely, {MII(1,4-cby)2[H2(γ-Mo8O26)]}·nH2O (1: M = Ni, n = 4; 2: M = Co, n = 6), and [NiII(1,3-cby)(H2O)4(β-Mo8O26)0.5]·2H2O (3) (1,4-cby·Cl = 1-(4-carboxy-benzyl)-[4,4']bipyridinyl-1-ium, 1,3-cby·Cl = 1-(3-carboxy-benzyl)-[4,4']bipyridinyl-1-ium). Isostructural compounds 1 and 2 exhibit two-dimensional (2D) layer structures with POMs as linking nodes, while compound 3 shows a one-dimensional (1D) metal-organic chain with dissociative POM anions. When the temperature increases, compounds 1-3 show good reversible thermochromism properties and also have a fluorescence quenching effect. Moreover, compounds 1-3 can also be used as detectors for organic amines, especially in the atmosphere of ammonia, ethylenediamine, and diethylamine with an obvious discoloration effect. In addition, compound 1 was used as a material for the preparation of memristors with superior properties (distinct temperature-adjusted resistive switching properties). It shows bipolar resistive switching (RS) behavior at different temperatures of 20, 50, and 100 °C. The results show that the 1-based memristor has good thermal stability, which is important for high-temperature environment applications. It also shows that crystalline viologen-POM-based compounds are ideal candidates for making memristors.

Lattice vibrational modes in changchengite from Raman spectroscopy and first principles electronic structure

AbstractWe measured room‐temperature phonon Raman spectra of changchengite (IrBiS) and compared the experimental phonon wavenumbers to the theoretical ones obtained by means of the ab initio density‐functional‐theory calculations in the presence and absence of the spin‐orbit coupling effects. Combining two different excitation photon energies all the symmetry predicted Raman modes are experimentally observed. The electronic properties of IrBiS are found to be similar to the recently studied isostructural compound IrBiSe showing a large Dresselhaus spin‐orbit valence band splitting. A good agreement between the experimental and theoretically predicted Raman phonon wavenumbers is found only when the lattice parameter is constrained to the experimental value. The inclusion of the spin orbit coupling does not significantly affect the phonon wavenumbers.

Enhanced CO2 sorption properties in a polarizable [WO2F4]2--pillared physisorbent under direct air capture conditions.

We report the CO2 capture properties of an ultramicroporous physisorbent [Ni(WO2F4)(pyrazine)2]n, WO2F4-1-Ni, which crystallizes in I4/mcm (a = 9.91785(6) Å, c = 15.71516(9) Å) and its structure is solved using laboratory X-ray powder diffraction. The WO2F4 anion is acentric with polarizable WO bonds offering unique potential properties within a porous structure. Despite isostructural compounds being previously reported, the effect of this distorted anion on CO2 capture properties has not been studied. In this context, at a 400 ppm partial pressure of CO2 (applicable for direct air capture), this primitive cubic (pcu) network captures 0.934 mmolCO2 gsorbent-1 under dry conditions and 0.685 mmolCO2 gsorbent-1 at 75%RH, the highest capacity for a physisorbent reported to date.

Particle size-dependent flexibility in DUT-8(Cu) pillared layer metal-organic framework.

The nature of metal in the isomorphous flexible metal-organic frameworks is often reported to influence flexibility and responsivity. A prominent example of such behaviour is the DUT-8(M) family ([M2(2,6-ndc)2(dabco)]n, 2,6-ndc = 2,6-naphthalene dicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane), where the isostructural compounds with Ni, Zn, Co, and Cu in the paddle wheel cluster are known. The macro-sized crystals of Ni, Co, and Zn based compounds transform to the closed pore (cp) phase under desolvation and show typical gate opening behaviour upon adsorption. The choice of metal, in this case, allows the adjustment of switching kinetics, selectivity in adsorption, and gate-opening pressures. The submicron-sized crystals of of Ni, Co, and Zn based compounds remain in the open pore (op) phase after desolvation. In this contribution, we demonstrate that the presence of Cu in the paddle wheel leads to fundamentally different flexible behaviour. The DUT-8(Cu) desolvation does not lead to the formation of the cp phase, independent of the particle size regime. However, according to in situ powder diffraction analysis, the desolvated, macro-sized crystals of DUT-8(Cu)_op show breathing upon adsorption of CO2 at 195 K. The submicron-sized particles show rigid, nonresponsive behaviour.

Magnetic coupling between Fe(NO) spin probe ligands through diamagnetic NiII, PdII and PtII tetrathiolate bridges.

Reaction of the nitrosylated-iron metallodithiolate ligand, paramagnetic (NO)Fe(N2S2), with [M(CH3CN)n][BF4]2 salts (M = NiII, PdII, and PtII; n = 4 or 6) affords di-radical tri-metallic complexes in a stairstep type arrangement ([FeMFe]2+, M = Ni, Pd, and Pt), with the central group 10 metal held in a MS4 square plane. These isostructural compounds have nearly identical ν(NO) stretching values, isomer shifts, and electrochemical properties, but vary in their magnetic properties. Despite the intramolecular Fe⋯Fe distances of ca. 6 Å, antiferromagnetic coupling is observed between {Fe(NO)}7 units as established by magnetic susceptibility, EPR, and DFT studies. The superexchange interaction through the thiolate sulfur and central metal atoms is on the order of NiII < PdII ≪ PtII with exchange coupling constants (J) of -3, -23, and -124 cm-1, consistent with increased covalency of the M-S bonds (3d < 4d < 5d). This trend is reproduced by DFT calculations with molecular orbital analysis providing insight into the origin of the enhancement in the exchange interaction. Specifically, the magnitude of the exchange interaction correlates surprisingly well with the energy difference between the HOMO and HOMO-1 orbitals of the triplet states, which is reflected in the central metal's contribution to these orbitals. These results demonstrate the ability of sulfur-dense metallodithiolate ligands to engender strong magnetic communication by virtue of their enhanced covalency and polarizability.

Straight and twisted open nodal-line phonon states in the CaI2 family of materials.

Based on first-principles calculations and symmetry analysis, we propose that trigonal CaI2 with the space group P3̄m1 possesses straight and twisted open nodal-line phonon states with linear dispersion. The symmetry analysis indicates that joint symmetry PT and rotational symmetry C3z protect the straight nodal lines along Γ-A and K-H while PT and mirror symmetry M010 (M110) maintain the twisted nodal lines that traverse Γ-M (Γ-K) and A-L (A-H). The calculated π Berry phase suggests that all the nodal lines are nontrivial and the corresponding drumhead-like surface states are clearly visible in the observation window, which is less than 6 THz, suggesting a significant chance for them to be measured using meV-resolution inelastic X-ray scattering. The distribution of the nodal lines in the Brillouin zone is also confirmed by the phononic tight-binding model. Furthermore, the isostructural compounds MgBr2 and MgI2 show similar phonon spectra and topological nontrivial surface states. This work provides promising candidates for investigating straight and twisted open nodal-line phonon states in a single material, which will facilitate future experimental observation.

The Thermal Behavior of Two Magnetic States in Smart Anticorrosion Coatings

Compounds of nitrilotrimethylenephosphonic acid (NTP) with transition metals are often used as corrosion inhibitors for steels. An FeNTP anticorrosion coating is formed on the steel surface. Doping with certain metals (for example, Zn or Cd) greatly improves anticorrosion properties. Despite the fact that FeNTP, FeZnNTP, and FeCdNTP are completely isostructural compounds, substantial changes in their properties occur upon doping: (i) according to the X-ray electron spectra, Fe atoms in FeNTP are in a high-spin (HS) state, while FeZnNTP and FeCdNTP contain Fe atoms with zero spin (LS); (ii) the difference in the quadrupole splitting of the Mössbauer spectra is specific to the ratio between the HS and LS states. Quan-tum mechanical calculations of the FeNTP system showed two solutions with the properties coincideing with the experimentally found LS and HS states for these systems. In this study, we tested the hypothesis about the coexistence of two states. To study possible thermal redistribution between two magnetic states, the Möss-bauer spectra of FeNTP, FeZnNTP, and FeCdNTP were recorded at various temperatures (77, 300, and 373 K). The Mössbauer data indicate that, with an increase in the temperature, a second component occurs in FeNTP (the ground state is HS; LS occurs already at room temperature and its fraction increases with an increase in the temperature) and FeZnNTP (the ground state is LS; HS occurs at 373 K). At all investigated temperatures, FeCdNTP has only one LS component.

Spin-wave dynamics in the KCeS2 delafossite: A theoretical description of powder inelastic neutron-scattering data

Layered rare-earth delafossites $ARX_2$ with $R$ = Yb(III) or Ce(III) have received a lot of interest as potential hosts for a quantum spin-liquid ground state. Some systems of this family that show no long-range order down to the lowest measured temperatures, such as NaYbO$_2$, NaYbS$_2$, and NaYbSe$_2$, are presumed to be in a quantum spin-liquid state. However, other isostructural compounds are known to order antiferromagnetically at subkelvin temperatures. Among them, KCeS$_2$ exhibits stripe-$yz$ magnetic order in the triangular-lattice planes that sets in below 400 mK. Here we investigate the spin-wave spectrum of this ordered phase with powder inelastic neutron scattering and describe it using a model Hamiltonian obtained from first-principles calculations based on the complete $|J,m_J\rangle$ multiplet description of the Ce sites with an anisotropic nearest-neighbor exchange interaction. Combing the current understanding of the exchange interaction in the systems with the effects of texturing in the powder, we have been able to model the inelastic neutron scattering spectrum with high fidelity.