Laser power and high-temperature dependent Raman studies of layered bismuth and copper-based oxytellurides for optoelectronic applications

Layered metal oxychalcogenide materials have gained significant attention in recent years due to their numerous applications in various emerging fields. The bismuth (Bi) based ternary and quaternary oxychalcogenide materials have become popular due to their excellent potential in optoelectronic, thermoelectric, and semiconducting applications. Adding copper (Cu) to these building matrices has enhanced their usefulness in various ways. In this work, Bi and Cu-based ternary and quaternary layered oxytellurides are synthesized using a unique, rarely used "microwave (MW) assisted method," and their temperature and laser power-dependent Raman measurements are carried out. All the samples are prepared at the same MW power and at a fixed irradiation time. Crystallographic studies show that the good crystallinity of the synthesized materials matches well with the phases reported previously. Nanosheet-like morphology was observed for all the prepared samples. The optical properties and band gap energies of these materials were obtained using the diffuse reflectance spectroscopy technique, which are in the range of 1.15-2.52 eV. The photoluminescence spectrum shows broad peaks around orange-red regions, indicating the potential applicability of these materials in various optoelectronic applications. The effect of high temperature and laser power on the Raman spectra of the oxytellurides is demonstrated, where the appearance of different vibrational modes along with a redshift in peak positions with the increase in temperature and power is observed.

Two Purely Inorganic Cationic Tellurite Materials Based on Group IB Metal Tetrafluoroborates with Similar Lamellar Cationic Layers: [Cu2F(Te2O5)](BF4) and [Ag18O2(Te4O9)4(Te3O8)(BF4)2]·2HBF4

Two new purely inorganic cationic tellurite networks of Group IB metal-based tetrafluoroborates, namely, [Cu₂F(Te₂O₅)](BF₄), 1, and [Ag₁₈O₂(Te₄O₉)₄(Te₃O₈)(BF₄)₂]·2HBF₄, 2, have been hydrothermally synthesized under mild conditions. The prepared materials have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, IR and Raman spectroscopy, SEM-energy-dispersive spectroscopy, UV-vis-NIR diffuse reflectance, magnetic study, and TG analyses. Single-crystal diffraction studies show that both materials have similar cationic Cu/Ag tellurite layers with tetrafluoroborates as interlamellar charge-balancing anions. Magnetic results indicate that [Cu₂F(Te₂O₅)](BF₄), 1, exhibits a mainly short-range antiferromagnetic ordering within the 2D layer, and further detailed analysis of magnetic susceptibility analysis confirms a spin-singlet ground state with an energy gap of 85 K.

Unveiling the correlation between structural and magnetic ordering in nano Co1-xNixTeO4

Nanomaterials with unique structures and exotic magnetic phenomena are always intriguing; however, the direct correlation of structural and magnetic ordering up to a few nanometers remains critical. We report structural and magnetic properties of sol-gel grown Co_1-xNi_xTeO₄ (x = 0, 0.5 and 1) nanoparticles. An increase in the calcination temperature leads to the enhancement of the particle size and structural ordering. This is accompanied by changes in the magnetic interactions as well. Calcination at lower temperatures retains the short-range non-crystalline structure and superparamagnetic behavior, while calcination at higher temperatures results in long-range ordering in both the crystal and magnetic structures. Superparamagnetic to antiferromagnetic ordering observed from temperature- and field-dependent magnetization is attributed to the changes in structural ordering. This study presents a new family of nanomaterials displaying stable magnetic order up to ∼6 nm, where the magnetic properties can be uniquely controlled by changing the structural ordering.

Effect of the Ni3TeO6 phase in a Ni2Te3O8/expanded graphite composite on the electrochemical monitoring of metribuzin residue in soil and water samples

Growing food demand and climate change have led to the development of various pest control agents to increase crop yields. Although pesticides help meet the food demand, they cause harm to human health and the environment. Metribuzin (MTBZ) is one of the common herbicides used for controlling weeds. Therefore, monitoring MTBZ residues in soil and water bodies is essential for decreasing risk to the environment and human health. This paper reports a highly selective and sensitive electrochemical sensor electrode based on a Ni₃TeO₆-phase-integrated Ni₂Te₃O₈/expanded graphite (referred to here as NTO-eGR) composite for the detection of MTBZ. The NTO-eGR composite was prepared by a one-step low-temperature hydrothermal method and characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and electron microscopy techniques. The Ni₃TeO₆ phase was found to be an active component in the NTO/eGR composite, which exhibited satisfactory analytical performance in MTBZ detection with a sensitivity of 1.454 µA µM^-1 cm^-2. Moreover, the NTO-eGR electrode exhibited high selectivity to MTBZ even in the presence of a five-fold excess of interfering species in water and soil samples. The studies on practical applicability revealed that NTO-eGR exhibits good reproducibility with a relative standard deviation of 2.67% (n = 5). Moreover, good recoveries of greater than 90% were achieved in the determination of MTBZ in soil and water samples. Hence, the NTO-eGR sensor electrode is highly suitable for the rapid on-site determination of MTBZ.

Synthesis, structure and magnetic properties of two new spin-chain compounds Ca2Ni(HSeO3)2(SeO3)2 and Na2Cu(SeO3)2·2H2O

Two new selenite compounds Ca₂Ni(HSeO₃)₂(SeO₃)₂ (CaNi) and Na₂Cu(SeO₃)₂·2H₂O (NaCu) were obtained by a hydrothermal method. Both compounds crystallize in the triclinic system of space group P1̄, featuring a selenite-bridged one-dimensional (1D) spin-chain structure running along the a-axis. Magnetic measurements indicate that CaNi undergoes a long-range antiferromagnetic order (LRO) at T_N = ∼3.8 K, while NaCu does not exhibit a LRO down to 2 K but the onset of a short-range correlation at T_M = ∼30 K. The intrachain exchange coupling J/k_B = -2.59 K for CaNi and J/k_B = -47.13 K for NaCu can be estimated by a fit using the 1D spin-chain model. The thermogravimetric analyses show that both compounds are stable below 130 °C. The UV-vis diffuse reflectance spectra indicate that the band gaps of CaNi and NaCu are 4.38 eV and 3.18 eV, respectively.

Antiferromagnetic Order and Spin-Canting Transition in the Corrugated Square Net Compound Cu3(TeO4)(SO4)·H2O

Strongly correlated electrons in layered perovskite structures have been the birthplace of high-temperature superconductivity, spin liquids, and quantum criticality. Specifically, the cuprate materials with layered structures made of corner-sharing square-planar CuO4 units have been intensely studied due to their Mott insulating ground state, which leads to high-temperature superconductivity upon doping. Identifying new compounds with similar lattice and electronic structures has become a challenge in solid-state chemistry. Here, we report the hydrothermal crystal growth of a new copper tellurite sulfate, Cu3(TeO4)(SO4)·H2O, a promising alternative to layered perovskites. The orthorhombic phase (space group Pnma) is made of corrugated layers of corner-sharing CuO4 square-planar units that are edge-shared with TeO4 units. The layers are linked by slabs of corner-sharing CuO4 and SO4. Using both the bond valence sum analysis and magnetization data, we find purely Cu2+ ions within the layers but a mixed valence of Cu2+/Cu+ between the layers. Cu3(TeO4)(SO4)·H2O undergoes an antiferromagnetic transition at TN = 67 K marked by a peak in the magnetic susceptibility. Upon further cooling, a spin-canting transition occurs at T* = 12 K, evidenced by a kink in the heat capacity. The spin-canting transition is explained on the basis of a J1-J2 model of magnetic interactions, which is consistent with the slightly different in-plane superexchange paths. We present Cu3(TeO4)(SO4)·H2O as a promising platform for the future doping and strain experiments that could tune the Mott insulating ground state into superconducting or spin liquid states.

Crystal-to-crystal transformation of a new selenite compound CaNi2(SeO3)3·2H2O induced by dehydration

A new zemannite-like compound CaNi₂(SeO₃)₃·2H₂O (1) is found to exhibit crystal-to-crystal transformations upon heating, resulting in a dehydrated form of CaNi₂(SeO₃)₃·1.5H₂O (2) and an anhydrous form of CaNi₂(SeO₃)₃ (3).

Synthesis and characterization of a series of transition metal oxychlorides: MBi(SeO3)2(H2O)Cl (M = Co, Ni, Cu)

Three new transition metal oxychlorides MBi(SeO3)2(H2O)Cl (M = Co, Ni, Cu) have been firstly synthesized through a hydrothermal reaction method at 200 °C. They were structurally determined to be isostructural with the Pbca space group of the orthorhombic system. They feature a 3D framework topology with two-dimensional tunnels intersected and filled with Cl anions parallel to the crystallographic bc-plane. Two neighboring MO5Cl octahedra are connected by a sharing edge into a M2O8Cl2 dimer which serves as the structural knots to knit the 2D [Bi(SeO3)2]∞ layers in the ab-plane together into the total 3D crystal architecture. The optical band gaps of CoBi(SeO3)2(H2O)Cl (1), NiBi(SeO3)2(H2O)Cl (2) and CuBi(SeO3)2(H2O)Cl (3) were evaluated to be 3.7 eV, 3.5 eV and 3.2 eV, respectively, through extrapolating the UV-vis-NIR optical absorption spectra. Besides, the spin-allowed d-d transition absorption spectra of the transition ion centers are observed in three compounds exhibiting different colors. Compounds 1, 2 and 3 can stay thermally stable below 370 °C, 400 °C and 300 °C, respectively, as found from the results of thermal analysis based on the simultaneous thermogravimetry and differential scanning calorimetry techniques. 1, 2 and 3 exhibit antiferromagnetic properties below Néel temperatures 6 K, 18 K and 52 K, respectively. Above the Néel temperatures, Curie-Weiss behavior dominates in the M-T process for the three compounds. The cell parameters are listed: a = 14.056 Å, b = 7.582 Å, c = 14.996 Å, and Z = 8 for 1, a = 14.083 Å, b = 7.575 Å, c = 14.860 Å, and Z = 8 for 2, and a = 14.576 Å, b = 7.371 Å, c = 14.656 Å, and Z = 8 for 3.

Li3Co1.06(1)TeO6: synthesis, single-crystal structure and physical properties of a new tellurate compound with CoII/CoIII mixed valence and orthogonally oriented Li-ion channels

A tellurate compound with Co^II/Co^III mixed valence states and lithium ions within orthogonally oriented channels was realized in Li₃Co_1.06(1)TeO₆. The single-crystal structure determination revealed two independent and interpenetrating Li/O and (Co,Te)/O substructures with octahedral oxygen coordination of the metal atoms. In contrast to other mixed oxides, a honeycomb-like ordering of CoO₆ and TeO₆ octahedra was not observed. Li₃Co_1.06(1)TeO₆ crystallizes orthorhombically with the following unit cell parameters and refinement results: Fddd, a = 588.6(2), b = 856.7(2), c = 1781.5(4) pm, R₁ = 0.0174, wR₂ = 0.0462, 608 F² values, and 33 variables. Additional electron density in tetrahedral voids in combination with neighboring face-linked and under-occupied octahedral lithium sites offers an excellent possible diffusion pathway for lithium ions. According to the symmetry of the crystal structure the diffusion pathways in Li₃Co_1.06(1)TeO₆ were found in two orthogonal orientations. The Co^II/Co^III mixed valence was investigated via X-ray photoelectron spectroscopy (XPS), revealing a composition comparable to that derived from single-crystal X-ray diffractometry. Magnetic susceptibility measurements underlined the coexistence of Co^II and Co^III, the title compound, however, showed no magnetic ordering down to low temperatures. The ionic conductivity of Li₃Co_1.06(1)TeO₆ was determined via alternating current (AC) electrochemical impedance spectroscopy and was found to be in the range of 1.6 × 10^-6 S cm^-1 at 573 K.

Sb-Based antiferromagnetic oxychlorides: MSb2O3(OH)Cl (M = Mn, Fe, Co) with 2D spin-dimer structures

Three new Sb-based antiferromagnetic oxychlorides: MnSb₂O₃(OH)Cl (1), FeSb₂O₃(OH)Cl (2), and CoSb₂O₃(OH)Cl (3) have been synthesized by using hydrothermal reaction methods. Their crystal structures are isostructural and incorporate two types of structural units: sphenoid SbO₄ polyhedra and M₂O₈Cl₂ (M = Mn, Fe, Co) dimers, that share edges forming a two dimensional (2D) MSb₂O₃(OH)Cl network. The neutral MSb₂O₃(OH)Cl 2D layers are arranged from ABAB-type for compounds 1 and 2 to AA'B'B-type for 3 with smaller cation radii. Magnetic measurements show that 1 belongs to an antiferromagnetic material, while 2 and 3 have weak ferromagnetic properties with unsaturated ferromagnetism originating from spin-canting below the transition temperature. In addition, the optical absorption band gaps were determined to be 3.8, 2.4, and 3.6 eV for 1, 2, and 3, respectively. This work demonstrates that utilizing both halide ions and lone-pair elements simultaneously in one structure is a feasible and practical route to reduce framework connectivity in order to synthesize new low-dimensional oxyhalides.

YCu(TeO3)2(NO3)(H2O)3: a novel layered tellurite

A new hydrated yttrium copper tellurite nitrate, yttrium(III) copper(II) bis-[trioxidotellurate(IV)] nitrate trihydrate, has been synthesized hydro-thermally in a Teflon-lined autoclave and structurally determined using synchrotron radiation. The new phase is the first example containing yttrium, copper and tellurium in one structure. Its crystal structure is unique, with relatively strongly bound layers extending parallel to (020), defined by YO8, CuO4 and TeO3 polyhedra, while the NO3 (-) anions and one third of the water mol-ecules lie between those layers. The structural unit consists of [Cu2(TeO3)4](4-) loop-branched chains of {Cu⋯Te⋯Cu⋯Te} squares running parallel to [001], which are linked further into layers only through Y(O,H2O)8 polyhedra. Weak 'secondary' Te bonds and O-H⋯O hydrogen-bonding inter-actions, involving water mol-ecules and layer O atoms, link the layers and inter-layer species. IR spectroscopic data are also presented.

Crystal structure of ammonium divanadium(IV,V) tellurium(IV) heptaoxide

The polyhedral building blocks of the layered inorganic network in the mixed-valence title compound, (NH4)(VIVO2)(VVO2)(TeO3), are vertex-sharing VVO4tetrahedra, distorted VIVO6octahedra and TeO3pyramids, which are linked by V—O—V and V—O—Te bonds, forming double layers lying parallel to (100). The presumed TeIVlone-pairs of electrons appear to be directed inwards into cavities in the double layers. The charge-balancing ammonium cations lie between the layers and probably interact with themviaN—H...O hydrogen bonds.

Effect of lone-pair stereoactivity on polyhedral volume and structural flexibility: application to Te(IV)O6 octahedra

The Distortion Theorem implies that the irregularity of bond distances in a distorted coordination polyhedron causes an increase of mean bond distance. Examination of 40 polyhedra containing the lone-pair cation Te(IV) shows that this does not imply an increase in polyhedral volume. Volumes of these polyhedra are 10.3-23.7 Å(3), compared with the 12.83 Å(3) expected for a hypothetical regular octahedron. There is little correlation between volume and measures of polyhedral distortion such as quadratic elongation, bond-angle variance or vector bond valence. However, the oxygens of our polyhedra lie very close to a sphere of best fit, centred at ~ 1 Å from the Te(IV) atom. The Te(IV)-centre distance is an index of lone-pair stereoactivity and is linearly related to the radius Rsph of the sphere; this is explained by a more localized lone pair repelling the anions more strongly, leading to a longer non-bonded distance between the lone pair and anions. Polyhedral volume still varies considerably for a given Rsph, because the oxygen ligands may be distributed over the whole sphere surface, or confined to a small portion of it. The uniformity of this distribution can be estimated from the distance between the sphere centre and the centroid of the O6 polyhedron. Te(IV)-centre and centroid-centre distances alone then account for 95% of the variation observed in volume for polyhedra which are topologically octahedral. Six of the polyhedra studied that are outliers are closer in shape to pentagonal pyramids than octahedra. These have short distances from the central Te(IV) cation to other Te(IV) and/or to large, polarizable cations, suggesting additional weak bonding interactions between these species and the central lone pair. The flexibility of lone-pair polyhedra is further enhanced by the ability of a single polyhedron to accommodate different cations with different degrees of lone-pair activity, which facilitates more diverse solid solution behaviour than would otherwise be the case.

New large volume hydrothermal reaction cell for studying chemical processes under supercritical hydrothermal conditions using time-resolved in situ neutron diffraction

The design and testing of a new large volume Inconel pressure cell for the in situ study of supercritical hydrothermal syntheses using time-resolved neutron diffraction is introduced for the first time. The commissioning of this new cell is demonstrated by the measurement of the time-of-flight neutron diffraction pattern for TiO(2) (Anatase) in supercritical D(2)O on the POLARIS diffractometer at the United Kingdom's pulsed spallation neutron source, ISIS, Rutherford Appleton Laboratory. The sample can be studied over a wide range of temperatures (25-450 °C) and pressures (1-355 bar). This novel apparatus will now enable us to study the kinetics and mechanisms of chemical syntheses under extreme environments such as supercritical water, and in particular to study the crystallization of a variety of technologically important inorganic materials.

Synthesis and characterization of two novel mixed metal tellurates: KGaTeO5·H2O and K3GaTe2O8(OH)2·H2O

Single crystals of KGaTeO5 x H2O and K3GaTe2O8(OH)2 x H2O have been synthesized by supercritical hydrothermal techniques using Te(OH)6, Ga2O3 and KOH as reagents, and characterized by single crystal X-ray diffraction, thermal analysis, IR and Raman spectroscopy. Ion-exchange studies revealed KGaTeO5 x H2O, with its open-framework structure, is capable of exchanging both smaller (Na+) and larger (Rb+) ions. In addition, higher thermal stability and reversible hydration properties were observed for KGaTeO5 x H2O.

Hydrothermal preparation, structures, and NLO properties of the rare earth molybdenyl iodates, RE(MoO2)(IO3)4(OH) [RE = Nd, Sm, Eu]

The reactions of RE(IO3)3 [RE = Nd, Sm, Eu] with I2O5 and MoO3 in a 1:2:2 molar ratio at 200 degrees C in aqueous media provide access to RE(MoO2)(IO3)4(OH) [RE = Nd (1), Sm (2), Eu (3)] as pure phases as determined from powder X-ray diffraction data. Single crystal X-ray diffraction experiments demonstrate that these compounds are isostructural and crystallize in the chiral and polar space group P2(1). The structures are composed of three-dimensional networks formed from eight-coordinate, square antiprismatic RE3+ cations and MoO2(OH)+ moieties that are bound by bridging iodate anions. The Mo(VI) centers are present in distorted octahedral environments composed of two cis-oxo atoms, a hydroxo group, and three bridging iodate anions arranged in a fac geometry. There are four crystallographically unique iodate anions in the structures of 1-3, one of these is actually present in the form of a IO3+1 polyhedron where a short interaction of 2.285(4) A is formed between the iodate anion and the hydroxo group bound to the Mo(VI) center. This interaction results in significant distortions of the iodate anion similar to those found in tellurites with TeO3+1 units. Two of the four iodate anions are aligned along the polar b-axis, imparting the required polarity to these compounds. Second-harmonic generation (SHG) measurements on sieved powders of 1 show a response of 350 x alpha-quartz. Crystallographic data: 1, monoclinic, space group P2(1), a = 6.9383(5) A, b = 14.0279(9) A, c = 7.0397(5) A, beta = 114.890(1) degrees, Z = 2; 2, monoclinic, space group P2(1), a = 6.9243(6) A, b = 13.963(1) A, c = 7.0229(6) A, beta = 114.681(1) degrees, Z = 2; 3, monoclinic, space group P2(1), a = 6.9169(6) A, b = 13.943(1) A, c = 7.0170(6) A, beta = 114.542(1) degrees, Z = 2.

Lone-pair self-containment in tellurite tubes: hydrothermal syntheses and structures of BaTe(3)O(7) and BaTe(4)O(9)

The hydrothermal syntheses and single-crystal structures of BaTe3O7 and BaTe4O9 are reported. These closely related new phases, which can be regarded as the n = 3 and 4 members of the BaTenO2n+1 family, are built up from infinite, tubular, columns of Te/O polyhedra (6 ring loops for BaTe3O7 and 8 ring loops for BaTe4O9) with barium cations completing the structures. The tubes represent a novel way to accommodate the lone pair of electrons associated with each TeIV species and suggest the possibility of redox intercalation chemistry for these types of material.

Excision of uranium oxide chains and ribbons in the novel one-dimensional uranyl iodates K(2)[(UO(2))3(IO(3))(4)O(2)] and Ba[(UO(2)2(IO(3))(2)O(2)](H(2)O)

The alkali metal and alkaline-earth metal uranyl iodates K(2)[(UO(2))(3)(IO(3))(4)O(2)] and Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) have been prepared from the hydrothermal reactions of KCl or BaCl(2) with UO(3) and I(2)O(5) at 425 and 180 degrees C, respectively. While K(2)[(UO(2))(3)(IO(3))(4)O(2)] can be synthesized under both mild and supercritical conditions, the yield increases from <5% to 73% as the temperature is raised from 180 to 425 degrees C. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), however, has only been isolated from reactions performed in the mild temperature regime. Thermal measurements (DSC) indicate that K(2)[(UO(2))(3)(IO(3))(4)O(2)] is more stable than Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) and that both compounds decompose through thermal disproportionation at 579 and 575 degrees C, respectively. The difference in the thermal behavior of these compounds provides a basis for the divergence of their preparation temperatures. The structure of K(2)[(UO(2))(3)(IO(3))(4)O(2)] is composed of [(UO(2))(3)(IO(3))(4)O(2)](2)(-) chains built from the edge-sharing UO(7) pentagonal bipyramids and UO(6) octahedra. Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O) consists of one-dimensional [(UO(2))(2)(IO(3))(2)O(2)](2)(-) ribbons formed from the edge sharing of distorted UO(7) pentagonal bipyramids. In both compounds the iodate groups occur in both bridging and monodentate binding modes and further serve to terminate the edges of the uranium oxide chains. The K(+) or Ba(2+) cations separate the chains or ribbons in these compounds forming bonds with terminal oxygen atoms from the iodate ligands. Crystallographic data: K(2)[(UO(2))(3)(IO(3))(4)O(2)], triclinic, space group P_1, a = 7.0372(5) A, b = 7.7727(5) A, c = 8.9851(6) A, alpha = 93.386(1) degrees, beta = 105.668(1) degrees, gamma = 91.339(1) degrees, Z = 1; Ba[(UO(2))(2)(IO(3))(2)O(2)](H(2)O), monoclinic, space group P2(1)/c, a = 8.062(4) A, b = 6.940(3) A, c = 21.67(1), beta= 98.05(1) degrees, Z = 4.